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Functional Inorganic Materials and Devices

Radiofrequency Schottky Diodes Based on p-Doped Copper(I) Thiocyanate (CuSCN)
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  • Dimitra G. Georgiadou*
    Dimitra G. Georgiadou
    Electronics and Computer Science, University of Southampton, Highfield Campus, Southampton SO17 1BJ, United Kingdom
    Department of Physics, Imperial College London, Prince Consort Road, South Kensington, London SW7 2AZ, United Kingdom
    *Email: [email protected]
    More by Dimitra G. Georgiadou
    Orcidhttps://orcid.org/0000-0002-2620-3346
  • Nilushi Wijeyasinghe
    Nilushi Wijeyasinghe
    Department of Physics, Imperial College London, Prince Consort Road, South Kensington, London SW7 2AZ, United Kingdom
    More by Nilushi Wijeyasinghe
  • Olga Solomeshch
    Olga Solomeshch
    The Sarah and Moshe Zisapel Nano-Electronic Center, Department of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 3200, Israel
    More by Olga Solomeshch
  • Nir Tessler
    Nir Tessler
    The Sarah and Moshe Zisapel Nano-Electronic Center, Department of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 3200, Israel
    More by Nir Tessler
    Orcidhttps://orcid.org/0000-0002-5354-3231
  • Thomas D. Anthopoulos*
    Thomas D. Anthopoulos
    Department of Physics, Imperial College London, Prince Consort Road, South Kensington, London SW7 2AZ, United Kingdom
    King Abdullah University of Science and Technology (KAUST), Division of Physical Sciences and Engineering, Thuwal 23955-6900, Saudi Arabia
    *Email: [email protected]
    More by Thomas D. Anthopoulos
    Orcidhttps://orcid.org/0000-0002-0978-8813
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ACS Applied Materials & Interfaces

Cite this: ACS Appl. Mater. Interfaces 2022, 14, 26, 29993–29999
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https://doi.org/10.1021/acsami.1c22856
Published June 1, 2022

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Abstract

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Schottky diodes based on inexpensive materials that can be processed using simple manufacturing methods are of particular importance for the next generation of flexible electronics. Although a number of high-frequency n-type diodes and rectifiers have been demonstrated, the progress with p-type diodes is lagging behind, mainly due to the intrinsically low conductivities of existing p-type semiconducting materials that are compatible with low-temperature, flexible, substrate-friendly processes. Herein, we report on CuSCN Schottky diodes, where the semiconductor is processed from solution, featuring coplanar Al–Au nanogap electrodes (<15 nm), patterned via adhesion lithography. The abundant CuSCN material is doped with the molecular p-type dopant fluorofullerene C60F48 to improve the diode’s operating characteristics. Rectifier circuits fabricated with the doped CuSCN/C60F48 diodes exhibit a 30-fold increase in the cutoff frequency as compared to pristine CuSCN diodes (from 140 kHz to 4 MHz), while they are able to deliver output voltages of >100 mV for a VIN = ±5 V at the commercially relevant frequency of 13.56 MHz. The enhanced diode and circuit performance is attributed to the improved charge transport across CuSCN induced by C60F48. The ensuing diode technology can be used in flexible complementary circuits targeting low-energy-budget applications for the emerging internet of things device ecosystem.

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This paper was published ASAP on June 1 2022, with an incorrect graphic for Figure 2. The corrected version was reposted on June 22, 2022.

Introduction

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Over the last decade, there has been a growing interest in delivering electronics that are flexible, lightweight, disposable, low-power, and inexpensive to be used in wearable devices and as integral part of the internet of things ecosystem. (1) A number of electronic devices, such as light-emitting diodes, solar cells, (2) sensors, microprocessors, (3) and supercapacitors, have been demonstrated on flexible substrates. (4) All these components need to be integrated with hardware that provides wireless connectivity and/or radiofrequency (RF) energy harvesting capabilities to render them truly energy-autonomous and connected. To this end, significant progress has been made toward scalable manufacturing of flexible diodes and rectifiers that can harvest RF signals from ambient sources or from a reader and convert them to usable direct current (DC) signals, which can then be used to power the microelectronic components. (5) Of particular relevance to commercial applications are RF identification (RFID) and near-field communication (NFC) technologies that operate at low (125 and 135 kHz) and high (13.56 MHz) frequencies to enable object identification and peer-to-peer data transfer usually via mobile phones. (6)
The operational frequency of the rectifier is dictated by the diode performance, which depends both on the semiconductor material’s electronic (transport) properties as well as on the device geometry and architecture. In general, large-area processable n-type diodes outperform their p-type counterparts as the electrical performance of the latter is limited by the intrinsically lower (hole) mobility, which is in turn set out by the scarcity of suitable materials. Furthermore, the materials used must comply with the low temperature processing (<200 °C) constraints posed by the inexpensive flexible substrate. This further narrows the gamut of materials that can be employed. (5) Organic materials, such as small molecules and polymers, have been the materials of choice for RF diodes due to their ease of processing using solution-based and printing methods, (7) although higher (>GHz) cutoff frequencies have been reported with vacuum-deposited small organic molecules, (8) metal oxides, (9) Si microparticles, (10) and low-dimensional (2D) transition metal dichalcogenide materials. (11) The main drawback of all these materials, however, is the very high cost, associated with either their synthesis and purification (organics) or their integration with high device yield in large-area manufacturing processes (e.g., 2D materials).
Herein, we propose a route toward improving the performance of Schottky diodes based on the inexpensive inorganic molecular p-type semiconductor copper(I) thiocyanate (CuSCN), which is processed from solution at very low temperatures (80–100 °C), thus compatible with the majority of targeted flexible and biodegradable substrates (e.g., plastic and paper). (12) We apply a two-pronged optimization approach that includes both material and device engineering. More specifically, we increase the mobility of CuSCN via molecular doping using the molecular p-type dopant C60F48 and employ a coplanar high-aspect-ratio nanogap device architecture, fabricated using the high-throughput adhesion lithography (a-Lith) technique. (13) We demonstrate p-doped CuSCN/C60F48 diodes and rectifiers that operate at frequencies up to 13.56 MHz and deliver hundreds of millivolts of output voltage, capable of powering the internet of tiny things, which includes microelectronic devices with minimal power budget (e.g., an RF-based wakeup receiver). (14)

Experimental Methods

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Fabrication of Nanogap Electrodes

Coplanar nanogap separated Al–Au electrodes were patterned using a-Lith following previously reported procedures. (15) In brief, an aluminum (Al) electrode with a thickness of 40 nm was thermally evaporated in high vacuum (10–6 mbar) on 2 × 2 cm Borofloat glass substrates and patterned to the desired design using photolithography, followed by wet etching. The patterned substrates were soaked in 1 mg mL–1 solution of octadecylphosphonic acid (Sigma Aldrich) in isopropanol to form a self-assembled monolayer (SAM) on the Al surface. Next, a global gold (Au) electrode (35 nm) with a 5 nm Al adhesion layer was sequentially deposited via thermal evaporation. An adhesive film (First Contact, Photonic Cleaning Technologies) was applied on the top of Au and left to dry in air. Then, the adhesive glue was peeled off, removing the Au metal from the top of the SAM-functionalized Al. The SAM and any remaining photoresist were cleaned via 10 min ultraviolet (UV)–ozone treatment to reveal an empty nanogap typically on the order of 10–15 nm.

CuSCN and C60F48-Doped CuSCN Formulations and Film Deposition

Cu(I)SCN powder (Merck, 99%) was dissolved in diethyl sulfide (DES) (Merck, 98%) at concentrations of 5 mg mL–1 and stirred for 1 h at room temperature. C60F48 was synthesized, as described in refs (16) and (29) at the Jozef Stefan Institute (Slovenia), and the purity was estimated to be 96%. C60F48 powder was dissolved in DES at room temperature, and then, calculated volumetric quantities of C60F48/DES (μL) were added to the CuSCN/DES solutions to create dopant concentrations of 0.05–1 mol %. Next, the C60F48-doped CuSCN precursor solutions were spin-cast at 800 rpm for 60 s in a N2-filled glovebox, and the films were annealed at 100 °C for 15 min.

Thin Film Surface Characterization

Optical microscopy images were captured using a Nikon Eclipse E600 POL optical microscope. The scanning electron microscopy (SEM) topology images of Al/Au nanogap electrodes were acquired using an ultra-high-resolution field emission Magellan scanning electron microscope equipped with a two-mode final lens (immersion and field-free).

Electrical Characterization

Current–voltage (I–V) characterization of the diodes was carried out on an Agilent B2902A parameter analyzer at room temperature inside a N2-filled glovebox. The measurement resolution of this source measure unit is 100 fA. High-frequency measurements were performed by applying an alternating current signal to the circuit shown in Figure 5a using an Agilent 33220A function generator. This was achieved by mounting a 1 nF capacitor directly onto the measurement micromanipulator, while the output voltage was measured across a load resistor RL = 1 MΩ. A photograph of the experimental setup is shown elsewhere. (17) The output and input signals were monitored using an Agilent DSO6014A oscilloscope. The setup was controlled using LabView program.

Results and Discussion

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The coplanar Schottky diodes were fabricated with circular patterns of asymmetric Al–Au electrodes (Figure 1a,b). The width of the diodes (W) was defined by the circumference of the circles bearing a diameter of 300 μm (diode width: 942 μm), as shown in the schematic in Figure 1b, while the two metals were separated by a 10 nm nanogap channel length (L). The high-resolution SEM image in Figure 1c shows the ultrashort and homogeneous gap that is formed along the two metals. a-Lith has been proven to yield consistent nanogaps in the range of 10–15 nm. (15) Given these geometrical values, the aspect ratio of the diodes (W/L) is around 105. This geometry is advantageous to commonly employed vertical structures when it comes to high-frequency applications. A high-aspect-ratio coplanar structure allows for considerable resistance and capacitance reduction by confining the active material to the nanogap channel length, while the device width remains on the macroscale, thus overcoming film deposition challenges (e.g., pinholes) often encountered with ultra-thin films. Using such coplanar nanogap device structures, we have demonstrated high-frequency (13.56 MHz) diodes based on n-type semiconductor zinc oxide (ZnO) processed from aqueous solution and vacuum-deposited C60. (17) Recently, we showed that solution-processed coplanar Al-doped ZnO diodes fabricated with nanogap electrodes can operate at micro- and millimeter wave frequency bands (intrinsic fcut-off > 100 GHz), expanding the application range to 5G and 6G communications. (15) Furthermore, using the wide-band-gap semiconductor CuSCN as a photoactive material deposited on coplanar nanogap electrodes, we have demonstrated deep UV photodetectors with high responsivity and photosensitivity. (18)

Figure 1

Figure 1. (a) Schematic of the electrode cross-section, depicting the 10 nm nanogap separating the two metals, formed via a-Lith. (b) Optical micrograph of the coplanar Al–Au electrodes with a diameter of 300 μm, where the circular shape was patterned via photolithography. (c) Top view of the nanogap along the metal electrode interface imaged using SEM.

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CuSCN is a semiconductor of quasi-molecular nature, belonging to the pseudohalide materials class, and is known to exhibit p-type conductivity, mostly owing to Cu vacancies created during material synthesis. (19) Notwithstanding its attractive optoelectronic properties, (20) these are very much dependent on the solution processing parameters (e.g., solvent, concentration, spin speed, and thermal annealing), which have been shown to have a direct impact on the film crystallinity, surface roughness, and thickness. (21,22) An optimized deposition protocol that rendered nanocrystalline films with a thickness comparable to the coplanar electrodes thickness (30–40 nm) resulted in the representative current–voltage (I–V) characteristic shown in Figure 2a. Current rectification was observed in the negative voltage regime when the Au electrode was biased positive and the Al electrode negative (see insets in Figure 2a), with a rectification ratio at ±4 V equal to 103 and no hysteresis between forward (i.e., biasing toward negative voltage) and reverse scans (Figure S1a). Note that the measured current in the reverse bias is at the same range (∼200 pA) as that of the current we measured for an empty electrode before depositing the CuSCN semiconductor (Figure S1b), indicating that the actual rectification ratio may be even higher. Analysis of the log–log plot of the forward biasing regime of the diode’s I–V curve reveals three distinct areas (Figure 2b): (23) (I) an Ohmic region at low voltages (−0.86 to −0.1 V, close to turn-on), where current is proportional to voltage, (II) a thermionic emission region, showing an exponential dependence, indicating the prevalence of thermionic emission of carriers over the barrier, as would be expected in a Schottky diode, and (III) a trap-assisted space-charge-limited current (SCLC) region (>−1.6 V), which obeys a power law relationship (J–Vm), where m = 3.4. SCLC is commonly encountered as the dominant charge transport mechanism in materials with low free carrier density such as dielectrics or semiconductors with wide band gaps or low doping levels. (24) Pattanasattayavong et al. calculated the unintentional hole doping concentration in CuSCN films (NA = 7.2 × 1017 cm–3), which they attributed to the acceptor-like states, most likely due to the presence of unintentional structural defects and/or chemical impurities derived from solution processing, and proposed the multiple trapping and release model as the dominant mechanism for CuSCN hole transport. (25) Further analysis of the exponential regime (II) and fitting it to the Shockley diode equation (26) yield an ideality factor of n = 11, a large deviation from the ideal diode (n = 1). This can be explained by considering the modified thermionic emission over the inhomogeneous barrier model, which accounts for Schottky barrier inhomogeneities due to spatially distributed fluctuations in the valence band (VB) energy levels or metal work function. (27) These fluctuations may be due to interface roughness between the Schottky electrode and semiconductor or at metal grain boundaries or due to tunneling currents through interface states or insulating layers (e.g., AlOx) at the interface, (28) all of which are likely to coexist given the coplanar nature and the low dimensionality of the Al–Au nanogap electrodes (see the SEM image in Figure 1c).

Figure 2

Figure 2. Current–Voltage (I–V) characteristic of the pristine CuSCN film spin-coated on the top of the prepatterned Al–Au coplanar electrodes in (a) semi-log plot double scans and (b) log–log plot depicting the different transport regimes of the diode under forward bias. The thermionic emission regime is zoomed-in and plotted as ln I–V to allow calculation of the ideality factor (n) and saturation current (I0) of the p-type diode. Inset: Schematic of the forward and reverse biasing of the diode under test.

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The chemical structures of CuSCN and the p-type dopant C60F48 are shown in Figure 3a. In the pristine Al/CuSCN/Au diode, Au acts as the Ohmic contact as the energy difference between the Au Fermi level (5.2 eV) and the VB edge of CuSCN (5.4 eV) is relatively small. At the Al/CuSCN interface, however, a Schottky contact is formed due to the work function of Al (4.3 eV) creating a ∼1.1 eV Schottky barrier for holes with the VB edge of CuSCN (Figures 3b and S2). This is contributing to the high rectification ratio and low reverse currents observed with the CuSCN diodes. Doping CuSCN with the molecular p-type fluorofullerene dopant C60F48 has been previously found to result in the creation of free holes in CuSCN owing to the transfer of electrons from the VB of CuSCN to the lowest unoccupied molecular orbital (LUMO) energy level of C60F48 (5.3 eV), which lies only 0.1 eV above the VB edge of CuSCN. (29) The energetics of the Schottky and Ohmic interfaces including the dopant LUMO energy levels are illustrated in Figure 3b, while the injection of majority carriers (holes) under forward and reverse biasing of the diode is depicted in Figure S2.

Figure 3

Figure 3. (a) Molecular structures of Cu(I) thiocyanate and of the fluorofullerene dopant C60F48. (b) Energy band diagram of the Al/CuSCN/Au diode in a flat band configuration, depicting also the acceptor levels introduced by the p-type C60F48 dopant. The values are derived from ref (29). (c) I–V characteristics of the undoped (0 mol %) CuSCN film and the CuSCN film doped with 0.05–1 mol % doping of C60F48. The inset shows a magnified area close to the turn-on voltage of the diodes.

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The I–V characteristics of pristine and C60F48-doped CuSCN diodes are shown in Figure 3c and are characterized by high asymmetry. The doping concentrations ranged from 0 (undoped) to 1 mol %. The diode properties are initially improved as the doping concentration increases up to 0.2–0.5 mol % and the turn-on voltage of the diode shifts toward lower (less negative) values. This is better illustrated in the inset of Figure 3c. Further analysis of the I–V characteristics is presented in Figure 4a, which depicts the linear fit of the forward biasing region of the I–V curves at the thermionic emission regime of the undoped, low doped (0.05, 0.1, and 0.2%), and highly doped (0.5 and 1%) diodes in a ln I–V plot. The results of the fitting to the Shockley diode equation are shown in the Supporting Information Table S1 and summarized in Figure 4b. It is evident that the diode ideality factor is reduced for low doping concentrations (up to 0.1 mol %), whereas it begins to increase again when the doping increases further up to 1 mol %, and the results obtained for doping levels >0.2 mol % do not follow a monotonic increase. On the other hand, the reverse current generally increases with the doping concentration. A plausible explanation for these observations can be proposed by considering the effect of doping on both the film morphology and the energetics of the Schottky diode device. An atomic force microscopy study that has been previously published by our group (29) showed that the addition of even small amounts of C60F48 forms ellipsoidal (platelet-like) grains with a typical diameter of ≈20 nm, a value which is comparable to the nanogap channel length. Increased dopant concentration results in the formation of larger crystallites that may obstruct the material from filling the nanogap, negatively affecting the charge transport between the coplanar electrodes. This is manifested in the lower forward current and deterioration of the diode characteristics upon a higher level of doping. However, in the low-doped devices where this effect is not prominent, the increased forward current and the shift in the I–V toward lower voltages that were observed in Figure 3c are an indication of the increased conductivity due to the passivation of existing traps in CuSCN by C60F48. On the other hand, the formation of acceptor levels close to the CuSCN VB edge reduces the barrier height, and this may be the reason of the small increase in reverse current as the dopant concentration increases. It should be noted that the diodes showed good stability after storage in air for 60 min with minimal reduction in the forward current and no increase in the reverse current (Figure S3). Similar stability was observed in flexible undoped CuSCN thin film transistors, (12) while C60F48 is expected to further contribute to ambient stability (especially toward water uptake in the film) due to its inherent hydrophobicity owing to its high fluorine content, as compared, for example, to pure C60 fullerenes. (30)

Figure 4

Figure 4. (a) ln I–V plots of the forward biasing regime of 0–0.2 mol % (low) and 0.5–1 mol % (high) doping levels of CuSCN films and linear fits to the thermionic emission regions (depicted with dashed horizontal lines) used for the extraction of the ideality factor (n) and saturation (reverse) currents (I0), summarized in Supporting Information Table S1 and in (b) for both low and highly doped films.

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What renders Schottky diodes particularly attractive for high-frequency applications is their fast response time due to the presence of majority carriers (unipolar devices). To explore the high-frequency response of the pristine and C60F48-doped CuSCN diodes, we constructed a half-wave rectifier circuit as shown in Figure 5a. The circuit consists of a 1 nF load capacitor and a 1 MΩ load resistor to obtain a stable DC output voltage (VOUT) following the rectification of the AC input signal (VIN) by the CuSCN diode. Figure 5b shows the dependence of VOUT as a function of VIN frequency in a decibel scale. The cutoff frequency (fcutoff) is defined as the frequency at −3 dB, namely, the frequency at which the output voltage of the diode drops to 1/√2 of its peak value at low frequency. It can be seen that fcutoff increases gradually from 0.14 to 4 MHz as the doping level increases up to 0.2 mol % and then starts to decrease (2 MHz for 0.5 mol % doping), which is in accordance with the DC characterization results. Figure 5c shows the VOUT and fcutoff as a function of the doping level for an AC peak-to-peak voltage (VPP) of 10 V (±5 V). The highest fcutoff of 4 MHz is obtained for the 0.2 mol % C60F48-doped CuSCN diode and is shown in Figure S4, while statistical data of the fcutoff and VOUT measured for six distinct devices at each doping level are given in Figure S5. For the same device, the output voltage at 13.56 MHz was plotted as a function of the input root mean square voltage (VRMS = 1/2√2 × VPP), and a square law fit was obtained, showcasing the good rectifying properties of these diodes (Figure 5d). The low-frequency (10 kHz) VOUT was 310 mV for this diode, whereas at the commercially relevant frequency of 13.56 MHz, the diode still outputs 162 mV, proving that it can be of use in high-frequency RFID tags and, more specifically, in targeted applications with low power demands. This corresponds to an efficiency of about 10–5% (POUT/PIN, where POUT is calculated from the VOUT over the 1 MΩ load resistor). The very low energy harvesting efficiency could be attributed to the parasitic series resistance of the diode, RS, since the RF energy coupled into RS is lost as heat and does not contribute to the rectified output of the diode. Careful design that minimizes the bond wire and lead frame resistance on the final rectifier circuitry, as compared to that of the bulk experimental setup we used here, could significantly improve this. Interestingly, the output voltage of the 0.5 mol % doped diode is higher despite the lower fcutoff and slightly deteriorated diode characteristics. This is an indication for improved transport at higher frequencies owing possibly to faster kinetics at the trapping sites introduced by the acceptor levels of the dopant.

Figure 5

Figure 5. (a) Half-wave rectifier circuitry comprising a 1 nF load capacitor (CL) and a 1 MΩ load resistor (RL) mounted directly onto the measurement micromanipulator for measuring the DC output voltage from the coplanar CuSCN diodes. (b) VOUT amplitude (in dB) as a function of frequency depicting the fcutoff for the undoped and C60F48-doped CuSCN diodes at −3 dB for VIN = ±5 V (corresponding to VRMS = 3.53 V). (c) VOUT calculated at 10 kHz and 13.56 MHz and fcutoff values as a function of the doping concentration. (d) VOUT at the commercially relevant RFID frequency of 13.56 MHz vs varying input VRMS signals.

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An example of the input AC waveform and the rectified VOUT is shown in Figure S6. The ripple that can be seen in the output voltage is probably due to the mismatch of the load capacitor with the capacitance of the RF diode. We can minimize this ripple by keeping the period of the input signal below the load RC time constant, τRC, something which holds for relatively high frequencies but can be problematic at kilohertz frequencies. Additionally, the load capacitance should generally be much larger than the capacitance of the diode (typically, for these diodes, capacitance is <1 pF); however, this depends on the diode area and should be taken into account when different diode widths are implemented. The load resistor over which the output voltage is measured could also be modified to control the magnitude of the output voltage. (31) Moreover, parasitic junction capacitance of the diode, CJ, could be minimized by controlling the geometrical characteristics of the diode. We have showed in our previous publication how increasing the diode width can increase the output voltage at the expense of a lower cutoff frequency. (15) In this paper, we show how to decrease the high resistivity of the semiconductor material by doping; however, it should be noted that the voltage drop can be further reduced by improving the currently nonideal metal–semiconductor contacts, for example, via applying specific treatments or SAMs to the electrodes. (13,32) Finally, the design of the rectifier topology is of critical importance, as integration of single diodes in full-wave or bridge rectifiers or even voltage multiplier circuits can tune the performance accordingly to fit the requirements of the targeted applications. (33)

Conclusions

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We demonstrated Schottky diodes based on the abundant nontoxic p-type semiconductor CuSCN, processed from solution at low temperature, and nanogap coplanar electrodes fabricated using a-Lith. A molecular doping strategy was adopted using the p-type dopant C60F48 at an optimized ratio to the CuSCN solution. The fabricated Schottky diodes showed a high rectification ratio (>1000) and a low reverse current (200 pA) in DC, and the effect of the dopant concentration in the current–voltage characteristics was analyzed and discussed. It was found that relatively low doping levels (<0.2 mol %) improve the diode properties owing to the C60F48 providing electrons close to the CuSCN VB (acceptor levels), thus reducing the barrier height and improving injection and transport without inducing a major increase in the leakage current. The high-frequency rectifiers fabricated with these diodes showed cutoff frequencies in the megahertz regime and output voltages in the order of hundreds of millivolts (Vin = ±5 V). These results compare well with that of recently published nanoscale rectifiers based on copper phthalocyanine (CuPc) molecular diodes with thickness of 4.5–15 nm, showing a rectification ratio of up to 500 and fcutoff ≈ 10 MHz, which, however, were fabricated using more complicated and less prone to industrial upscale methods. (34) Thus, with this work, we show that p-type rectifiers can be fabricated with inexpensive materials and using high-throughput patterning techniques compatible with flexible electronics and implemented in low-cost disposable RFID tags or NFC devices for smart packaging, medical devices and patches, and the internet of things.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.1c22856.

  • Characteristics of diodes upon doping, additional I–V curves of the empty and CuSCN-filled nanogap electrodes, energy level diagrams depicting injection at forward and reverse biasing, diode stability in air, and high-frequency supplementary and statistical performance data (PDF)

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Author Information

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  • Corresponding Authors
    • Dimitra G. Georgiadou - Electronics and Computer Science, University of Southampton, Highfield Campus, Southampton SO17 1BJ, United Kingdom;  Department of Physics, Imperial College London, Prince Consort Road, South Kensington, London SW7 2AZ, United Kingdom;  Orcidhttps://orcid.org/0000-0002-2620-3346;  Email: [email protected]
    • Thomas D. Anthopoulos - Department of Physics, Imperial College London, Prince Consort Road, South Kensington, London SW7 2AZ, United Kingdom;  King Abdullah University of Science and Technology (KAUST), Division of Physical Sciences and Engineering, Thuwal 23955-6900, Saudi Arabia;  Orcidhttps://orcid.org/0000-0002-0978-8813;  Email: [email protected]
  • Authors
    • Nilushi Wijeyasinghe - Department of Physics, Imperial College London, Prince Consort Road, South Kensington, London SW7 2AZ, United Kingdom
    • Olga Solomeshch - The Sarah and Moshe Zisapel Nano-Electronic Center, Department of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 3200, Israel
    • Nir Tessler - The Sarah and Moshe Zisapel Nano-Electronic Center, Department of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 3200, Israel;  Orcidhttps://orcid.org/0000-0002-5354-3231
  • Author Contributions

    T.D.A. and D.G.G. conceived the project. T.D.A. guided and supervised the project. D.G.G. fabricated the devices, performed electrical measurements, and analyzed the data. N.W. provided the C60F48-doped CuSCN formulations. N.T. and O.S. provided the C60F48 dopant, which was synthesized at the Jozef Stefan Institute (Slovenia). D.G.G. wrote the first draft of the manuscript. All authors discussed the results and contributed to the final version of the paper.

  • Funding

    T.D.A. acknowledges the support from the King Abdullah University of Science and Technology (KAUST) Sponsored Research (OSR) under Award No: OSR-2018-CARF/CCF-3079 and No: OSR-2019-CRG8-4095.3 and from the European Research Council (ERC) AMPRO (Grant No. 280221). D.G.G. acknowledges the financial support from the European Union Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement 706707.

  • Notes
    The authors declare no competing financial interest.

References

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This article references 34 other publications.

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    A review. Bio-integrated wearable systems can measure a broad range of biophys., biochem., and environmental signals to provide crit. insights into overall health status and to quantify human performance. Recent advances in material science, chem. anal. techniques, device designs, and assembly methods form the foundations for a uniquely differentiated type of wearable technol., characterized by noninvasive, intimate integration with the soft, curved, time-dynamic surfaces of the body. This review summarizes the latest advances in this emerging field of "bio-integrated" technologies in a comprehensive manner that connects fundamental developments in chem., material science, and engineering with sensing technologies that have the potential for widespread deployment and societal benefit in human health care. An introduction to the chemistries and materials for the active components of these systems contextualizes essential design considerations for sensors and assocd. platforms that appear in following sections. The subsequent content highlights the most advanced biosensors, classified according to their ability to capture biophys., biochem., and environmental information. Addnl. sections feature schemes for elec. powering these sensors and strategies for achieving fully integrated, wireless systems. The review concludes with an overview of key remaining challenges and a summary of opportunities where advances in materials chem. will be critically important for continued progress.
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  2. 2
    Dauzon, E.; Sallenave, X.; Plesse, C.; Goubard, F.; Amassian, A.; Anthopoulos, T. D. Pushing the Limits of Flexibility and Stretchability of Solar Cells: A Review. Adv. Mater. 2021, 33, 2101469,  DOI: 10.1002/adma.202101469
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    2
    Pushing the Limits of Flexibility and Stretchability of Solar Cells: A Review
    Dauzon, Emilie; Sallenave, Xavier; Plesse, Cedric; Goubard, Fabrice; Amassian, Aram; Anthopoulos, Thomas D.
    Advanced Materials (Weinheim, Germany) (2021), 33 (36), 2101469CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Emerging forms of soft, flexible, and stretchable electronics promise to revolutionize the electronics industries of the future offering radically new products that combine multiple functionalities, including power generation, with arbitrary form factor. For example, skin-like electronics promise to transform the human-machine-interface, but the softness of the skin is incompatible with traditional electronic components. To address this issue, new strategies toward soft and wearable electronic systems are currently being pursued, which also include stretchable photovoltaics as self-powering systems for use in autonomous and stretchable electronics of the future. Here recent developments in the field of stretchable photovoltaics are ed and their potential for various emerging applications are examd. Emphasis is placed on the different strategies to induce stretchability including extrinsic and intrinsic approaches. In the former case, engineering and patterning of the materials and devices are key elements while intrinsically stretchable systems rely on mech. compliant materials such as elastomers and org. conjugated polymers. The result is a article that provides a comprehensive summary of the progress to date in the field of stretchable solar cells from the nanoscale to macroscopic functional devices. The article is concluded by discussing the emerging trends and future developments.
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  3. 3
    Biggs, J.; Myers, J.; Kufel, J.; Ozer, E.; Craske, S.; Sou, A.; Ramsdale, C.; Williamson, K.; Price, R.; White, S. A Natively Flexible 32-bit Arm Microprocessor. Nature 2021, 595, 532– 536,  DOI: 10.1038/s41586-021-03625-w
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    3
    A natively flexible 32-bit Arm microprocessor
    Biggs, John; Myers, James; Kufel, Jedrzej; Ozer, Emre; Craske, Simon; Sou, Antony; Ramsdale, Catherine; Williamson, Ken; Price, Richard; White, Scott
    Nature (London, United Kingdom) (2021), 595 (7868), 532-536CODEN: NATUAS; ISSN:0028-0836. (Nature Portfolio)
    Abstr.: Nearly 50 years ago, Intel created the world's first com. produced microprocessor-the 4004 (ref. 1), a modest 4-bit CPU (central processing unit) with 2,300 transistors fabricated using 10 μm process technol. in silicon and capable only of simple arithmetic calcns. Since this ground-breaking achievement, there has been continuous technol. development with increasing sophistication to the stage where state-of-the-art silicon 64-bit microprocessors now have 30 billion transistors (for example, the AWS Graviton2 (ref. 2) microprocessor, fabricated using 7 nm process technol.). The microprocessor is now so embedded within our culture that it has become a meta-invention-i.e., it is a tool that allows other inventions to be realized, most recently enabling the big data anal. needed for a COVID-19 vaccine to be developed in record time. Here we report a 32-bit Arm (a reduced instruction set computing (RISC) architecture) microprocessor developed with metal-oxide thin-film transistor technol. on a flexible substrate (which we call the PlasticARM). Sep. from the mainstream semiconductor industry, flexible electronics operate within a domain that seamlessly integrates with everyday objects through a combination of ultrathin form factor, conformability, extreme low cost and potential for mass-scale prodn. PlasticARM pioneers the embedding of billions of low-cost, ultrathin microprocessors into everyday objects.
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  4. 4
    Corzo, D.; Alejandro, D.; Blazquez, G. T.; Baran, D. Flexible Electronics: Status, Challenges and Opportunities. Front. Electron. 2020, 1, 594003,  DOI: 10.3389/felec.2020.594003
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    There is no corresponding record for this reference.
  5. 5
    Semple, J.; Georgiadou, D. G.; Wyatt-Moon, G.; Gelinck, G.; Anthopoulos, T. D. Flexible Diodes for Radio Frequency (RF) Electronics: A Materials Perspective. Semicond. Sci. Technol. 2017, 32, 123002,  DOI: 10.1088/1361-6641/aa89ce
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    5
    Flexible diodes for radio frequency (RF) electronics: a materials perspective
    Semple, James; Georgiadou, Dimitra G.; Wyatt-Moon, Gwenhivir; Gelinck, Gerwin; Anthopoulos, Thomas D.
    Semiconductor Science and Technology (2017), 32 (12), 123002/1-123002/45CODEN: SSTEET; ISSN:0268-1242. (IOP Publishing Ltd.)
    A review. Over the last decade, there has been increasing interest in transferring the research advances in radiofrequency (RF) rectifiers, the quintessential element of the chip in the RF identification (RFID) tags, obtained on rigid substrates onto plastic (flexible) substrates. The growing demand for flexible RFID tags, wireless communications applications and wireless energy harvesting systems that can be produced at a low-cost is a key driver for this technol. push. In this topical review, we summarise recent progress and status of flexible RF diodes and rectifying circuits, with specific focus on materials and device processing aspects. To this end, different families of materials (e.g. flexible silicon, metal oxides, org and carbon nanomaterials), manufg processes (e.g. vacuum and soln. processing) and device architectures (diodes and transistors) are compared. Although emphasis is placed on performance, functionality, mech. flexibility and operating stability, the various bottlenecks assocd. with each technol. are also addressed. Finally, we present our outlook on the commercialisation potential and on the positioning of each material class in the RF electronics landscape based on the findings summarised herein. It is beyond doubt that the field of flexible high and ultra-high frequency rectifiers and electronics as a whole will continue to be an active area of research over the coming years.
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  6. 6
    Finkenzeller, K. RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication; Wiley, 2010.
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    There is no corresponding record for this reference.
  7. 7
    Viola, F. A.; Brigante, B.; Colpani, P.; Dell’Erba, G.; Mattoli, V.; Natali, D.; Caironi, M. A 13.56 MHz Rectifier Based on Fully Inkjet Printed Organic Diodes. Adv. Mater. 2020, 32, 2002329,  DOI: 10.1002/adma.202002329
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    7
    A 13.56 MHz rectifier based on fully inkjet printed organic diodes
    Viola, Fabrizio A.; Brigante, Biagio; Colpani, Paolo; Dell'Erba, Giorgio; Mattoli, Virgilio; Natali, Dario; Caironi, Mario
    Advanced Materials (Weinheim, Germany) (2020), 32 (33), 2002329CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The increasing diffusion of portable and wearable technologies results in a growing interest in electronic devices having features such as flexibility, lightness-in-wt., transparency, and wireless operation. Org. electronics is proposed as a potential candidate to fulfill such needs, in particular targeting pervasive radio-frequency (RF) applications. Still, limitations in terms of device performances at RF, particularly severe when large-area and scalable fabrication techniques are employed, have largely precluded the achievement of such an appealing scenario. In this work, the rectification of an electromagnetic wave at 13.56 MHz with a fully inkjet printed polymer diode is demonstrated. The rectifier, a key enabling component of future pervasive wireless systems, is fabricated through scalable large-area methods on plastic. To provide a proof-of-principle demonstration of its future applicability, its adoption in powering a printed integrated polymer circuit is presented. The possibility of harvesting elec. power from RF waves and delivering it to a cheap flexible substrate through a simple printed circuitry paves the way to a plethora of appealing distributed electronic applications.
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  8. 8
    Kang, C.-M.; Wade, J.; Yun, S.; Lim, J.; Cho, H.; Roh, J.; Lee, H.; Nam, S.; Bradley, D. D. C.; Kim, J.-S.; Lee, C. 1 GHz Pentacene Diode Rectifiers Enabled by Controlled Film Deposition on SAM-Treated Au Anodes. Adv. Electron. Mater. 2016, 2, 1500282,  DOI: 10.1002/aelm.201500282
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  9. 9
    Li, M.; Honkanen, M.; Liu, X.; Rokaya, C.; Schramm, A.; Fahlman, M.; Berger, P. R.; Lupo, D. 0.7-GHz Solution-Processed Indium Oxide Rectifying Diodes. IEEE Trans. Electron Devices 2020, 67, 360– 364,  DOI: 10.1109/ted.2019.2954167
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    9
    Solution-processed indium oxide rectifying diodes at 0.7-GHz
    Li, Miao; Honkanen, Mari; Liu, Xianjie; Rokaya, Chakra; Schramm, Andreas; Fahlman, Mats; Berger, Paul R.; Lupo, Donald
    IEEE Transactions on Electron Devices (2020), 67 (1), 360-364CODEN: IETDAI; ISSN:1557-9646. (Institute of Electrical and Electronics Engineers)
    Soln.-based deposition, with its simplicity and possibility for upscaling through printing, is a promising process for low-cost electronics. Metal oxide semiconductor devices, esp. indium oxide with its excellent elec. properties, offer high performance compared to amorphous Si-based rivals, and with a form factor conducive to flexible and wearable electronics. Here, rectifying diodes based on an amorphous spin-coated indium oxide are fabricated for high-speed applications. We report a soln.-processed diode approaching the UHF range, based on indium oxide, with aluminum and gold as the electrodes. The device was spin-coated from a precursor material and configured into a half-wave rectifier. The J-V and frequency behavior of the diodes were studied, and the material compn. of the diode was investigated by X-ray photoemission spectroscopy (XPS). The 3-dB point was found to be over 700 MHz. The results are promising for the development of autonomously powered wireless Internetof-Things systems based on scalable, low-cost processes.
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  10. 10
    Sani, N.; Robertsson, M.; Cooper, P.; Wang, X.; Svensson, M.; Andersson Ersman, P.; Norberg, P.; Nilsson, M.; Nilsson, D.; Liu, X.; Hesselbom, H.; Akesso, L.; Fahlman, M.; Crispin, X.; Engquist, I.; Berggren, M.; Gustafsson, G. All-Printed Diode Operating at 1.6 GHz. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 11943– 11948,  DOI: 10.1073/pnas.1401676111
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    10
    All-printed diode operating at 1.6 GHz
    Sani, Negar; Robertsson, Mats; Cooper, Philip; Wang, Xin; Svensson, Magnus; Ersman, Peter Andersson; Norberg, Petronella; Nilsson, Marie; Nilsson, David; Liu, Xianjie; Hesselbom, Hjalmar; Akesso, Laurent; Fahlman, Mats; Crispin, Xavier; Engquist, Isak; Berggren, Magnus; Gustafsson, Goeran
    Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (33), 11943-11948CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    Printed electronics are considered for wireless electronic tags and sensors within the future internet-of-things (IoT) concept. As a consequence of the low charge carrier mobility of present printable org. and inorg. semiconductors, the operational frequency of printed rectifiers is not high enough to enable direct communication and powering between mobile phones and printed e-tags. Here, we report an all-printed diode operating ≤1.6 GHz. The device, based on 2 stacked layers of Si and NbSi2 particles, is manufd. on a flexible substrate at low temp. and in ambient atm. The high charge carrier mobility of the Si microparticles allows device operation to occur in the charge injection-limited regime. The asymmetry of the oxide layers in the resulting device stack leads to rectification of tunneling current. Printed diodes were combined with antennas and electrochromic displays to form an all-printed e-tag. The harvested signal from a global system for mobile communications mobile phone was used to update the display. Our findings demonstrate a new communication pathway for printed electronics within IoT applications.
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  11. 11
    Yang, S. J.; Park, K.-T.; Im, J.; Hong, S.; Lee, Y.; Min, B.-W.; Kim, K.; Im, S. Ultrafast 27 GHz Cutoff Frequency in Vertical WSe2 Schottky Diodes with Extremely Low Contact Resistance. Nat. Commun. 2020, 11, 1574,  DOI: 10.1038/s41467-020-15419-1
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    11
    Ultrafast 27 GHz cutoff frequency in vertical WSe2 Schottky diodes with extremely low contact resistance
    Yang, Sung Jin; Park, Kyu-Tae; Im, Jaeho; Hong, Sungjae; Lee, Yangjin; Min, Byung-Wook; Kim, Kwanpyo; Im, Seongil
    Nature Communications (2020), 11 (1), 1574CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
    Abstr.: Ultra-thin two-dimensional semiconducting crystals in their monolayer and few-layer forms show promising aspects in nanoelectronic applications. However, the ultra-thin nature of two-dimensional crystals inevitably results in high contact resistance from limited channel/contact vol. as well as device-to-device variability, which seriously limit reliable applications using two-dimensional semiconductors. Here, we incorporate rather thick two-dimensional layered semiconducting crystals for reliable vertical diodes showing excellent Ohmic and Schottky contacts. Using the vertical transport of WSe2, we demonstrate devices which are functional at various frequency ranges from megahertz AM demodulation of audio signals, to gigahertz rectification for fifth-generation wireless electronics, to UV-visible photodetection. The WSe2 exhibits an excellent Ohmic contact to bottom platinum electrode with record-low contact resistance (∼50 Ω ) and an exemplary Schottky junction to top transparent conducting oxide electrode. Our semitransparent vertical WSe2 Schottky diodes could be a key component of future high frequency electronics in the era of fifth-generation wireless communication.
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  12. 12
    Petti, L.; Pattanasattayavong, P.; Lin, Y.-H.; Münzenrieder, N.; Cantarella, G.; Yaacobi-Gross, N.; Yan, F.; Tröster, G.; Anthopoulos, T. D. Solution-Processed pType Copper(I) Thiocyanate (CuSCN) for Low-Voltage Flexible Thin-Film Transistors and Integrated Inverter Circuits. Appl. Phys. Lett. 2017, 110, 113504,  DOI: 10.1063/1.4978531
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    12
    Solution-processed p-type copper(I) thiocyanate (CuSCN) for low-voltage flexible thin-film transistors and integrated inverter circuits
    Petti, Luisa; Pattanasattayavong, Pichaya; Lin, Yen-Hung; Munzenrieder, Niko; Cantarella, Giuseppe; Yaacobi-Gross, Nir; Yan, Feng; Troster, Gerhard; Anthopoulos, Thomas D.
    Applied Physics Letters (2017), 110 (11), 113504/1-113504/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    The authors report on low operating voltage thin-film transistors (TFTs) and integrated inverters based on copper(I) thiocyanate (CuSCN) layers processed from soln. at low temp. on free-standing plastic foils. As-fabricated coplanar bottom-gate and staggered top-gate TFTs exhibit hole-transporting characteristics with av. mobility values of 0.0016 cm2 V-1 s-1 and 0.013 cm2 V-1 s-1, resp., current on/off ratio in the range 102-104, and max. operating voltages between -3.5 and -10 V, depending on the gate dielec. employed. The promising TFT characteristics enable fabrication of unipolar NOT gates on flexible free-standing plastic substrates with voltage gain of 3.4 at voltages ≥-3.5 V. Importantly, discrete CuSCN transistors and integrated logic inverters remain fully functional even when mech. bent to a tensile radius of 4 mm, demonstrating the potential of the technol. for flexible electronics. (c) 2017 American Institute of Physics.
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  13. 13
    Semple, J.; Georgiadou, D. G.; Wyatt-Moon, G.; Yoon, M.; Seitkhan, A.; Yengel, E.; Rossbauer, S.; Bottacchi, F.; McLachlan, M. A.; Bradley, D. D. C.; Anthopoulos, T. D. Large-Area Plastic Nanogap Electronics Enabled by Adhesion Lithography. npj Flexible Electron. 2018, 2, 18,  DOI: 10.1038/s41528-018-0031-3
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    There is no corresponding record for this reference.
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    Oh, S.; Blaauw, D.; Sylvester, D. The Internet of Tiny Things: Recent Advances of Millimeter-Scale Computing. IEEE Des. Test 2019, 36, 65– 72,  DOI: 10.1109/mdat.2019.2898187
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    Georgiadou, D. G.; Semple, J.; Sagade, A. A.; Forstén, H.; Rantakari, P.; Lin, Y.-H.; Alkhalil, F.; Seitkhan, A.; Loganathan, K.; Faber, H.; Anthopoulos, T. D. 100 GHz Zinc Oxide Schottky Diodes Processed from Solution on a Wafer Scale. Nat. Electron. 2020, 3, 718– 725,  DOI: 10.1038/s41928-020-00484-7
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    15
    Hundred GHz zinc oxide Schottky diodes processed from solution on a wafer scale
    Georgiadou, Dimitra G.; Semple, James; Sagade, Abhay A.; Forsten, Henrik; Rantakari, Pekka; Lin, Yen-Hung; Alkhalil, Feras; Seitkhan, Akmaral; Loganathan, Kalaivanan; Faber, Hendrik; Anthopoulos, Thomas D.
    Nature Electronics (2020), 3 (11), 718-725CODEN: NEALB3; ISSN:2520-1131. (Nature Research)
    Abstr.: Inexpensive radio-frequency devices that can meet the ultrahigh-frequency needs of fifth- and sixth-generation wireless telecommunication networks are required. However, combining high performance with cost-effective scalable manufg. has proved challenging. Here, we report the fabrication of soln.-processed zinc oxide Schottky diodes that can operate in microwave and millimetre-wave frequency bands. The fully coplanar diodes are prepd. using wafer-scale adhesion lithog. to pattern two asym. metal electrodes sepd. by a gap of around 15 nm, and are completed with the deposition of a zinc oxide or aluminum-doped ZnO layer from soln. The Schottky diodes exhibit a max. intrinsic cutoff frequency in excess of 100 GHz, and when integrated with other passive components yield radio-frequency energy-harvesting circuits that are capable of delivering output voltages of 600 mV and 260 mV at 2.45 GHz and 10 GHz, resp.
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  16. 16
    Kepman, A. V.; Sukhoverkhov, V. F.; Tressaud, A.; Labrugere, C.; Durand, E.; Chilingarov, N. S.; Sidorov, L. N. Novel Method of Synthesis of C60F48 with Improved Yield and Selectivity. J. Fluorine Chem. 2006, 127, 832– 836,  DOI: 10.1016/j.jfluchem.2006.02.019
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    16
    Novel method of synthesis of C60F48 with improved yield and selectivity
    Kepman, A. V.; Sukhoverkhov, V. F.; Tressaud, A.; Labrugere, C.; Durand, E.; Chilingarov, N. S.; Sidorov, L. N.
    Journal of Fluorine Chemistry (2006), 127 (7), 832-836CODEN: JFLCAR; ISSN:0022-1139. (Elsevier B.V.)
    A novel two-stage method of prepn. of C60F48 with 96% purity and 80% yield is reported. A C60 embedded into a MnF2 matrix is reacted with mol. fluorine under dynamic conditions, i.e. in flow of fluorine gas and with sublimation of volatile products, which gave C60F34-C60F38 mixts. with >90% yield. Subsequent fluorination of the mixt. thus obtained in the closed reactor at elevated pressure directly leads to the final product. C60F48 thus synthesized was characterized by EI-MS, MALDI-MS, IR-spectroscopy and XPS. The problems of fullerene burning and degrdn. in the fluorine atm. are discussed.
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  17. 17
    Semple, J.; Rossbauer, S.; Burgess, C. H.; Zhao, K.; Jagadamma, L. K.; Amassian, A.; McLachlan, M. A.; Anthopoulos, T. D. Radio Frequency Coplanar ZnO Schottky Nanodiodes Processed from Solution on Plastic Substrates. Small 2016, 12, 1993– 2000,  DOI: 10.1002/smll.201503110
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    17
    Radio Frequency Coplanar ZnO Schottky Nanodiodes Processed from Solution on Plastic Substrates
    Semple, James; Rossbauer, Stephan; Burgess, Claire H.; Zhao, Kui; Jagadamma, Lethy Krishnan; Amassian, Aram; McLachlan, Martyn A.; Anthopoulos, Thomas D.
    Small (2016), 12 (15), 1993-2000CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Radio frequency coplanar ZnO Schottky nanodiodes were prepd. and characterized. Thermally evapd. Al films were patterned using conventional photolithog. and wet chem. etching for nanogap electrode fabrication.
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  18. 18
    Wyatt-Moon, G.; Georgiadou, D. G.; Semple, J.; Anthopoulos, T. D. Deep Ultraviolet Copper(I) Thiocyanate (CuSCN) Photodetectors Based on Coplanar Nanogap Electrodes Fabricated via Adhesion Lithography. ACS Appl. Mater. Interfaces 2017, 9, 41965– 41972,  DOI: 10.1021/acsami.7b12942
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    18
    Deep Ultraviolet Copper(I) Thiocyanate (CuSCN) Photodetectors Based on Coplanar Nanogap Electrodes Fabricated via Adhesion Lithography
    Wyatt-Moon, Gwenhivir; Georgiadou, Dimitra G.; Semple, James; Anthopoulos, Thomas D.
    ACS Applied Materials & Interfaces (2017), 9 (48), 41965-41972CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Adhesion lithog. (a-Lith) is a versatile fabrication technique used to produce asym. coplanar electrodes sepd. by a <15 nm nanogap. A-Lith was used to fabricate deep UV (DUV) detectors by combining coplanar asym. nanogap electrode architectures (Au/Al) with soln.-processable wide-band-gap (3.5-3.9 eV) p-type semiconductor Cu(I) thiocyanate (CuSCN). Because of the device's unique architecture, the detectors exhibit high responsivity (≈79 A W-1) and photosensitivity (≈720) when illuminated with a DUV-range (λpeak = 280 nm) light-emitting diode at 220 μW cm-2. The photosensitivity of the photodetectors remains fairly high (≈7) even at illuminating intensities down to 0.2 μW cm-2. The scalability of the a-Lith process combined with the unique properties of CuSCN paves the way to new forms of inexpensive, yet high-performance, photodetectors that can be manufd. on arbitrary substrate materials including plastic.
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  19. 19
    Tennakone, K.; Jayatissa, A. H.; Fernando, C. A. N.; Wickramanayake, S.; Punchihewa, S.; Weerasena, L. K.; Premasiri, W. D. R. Semiconducting and Photoelectrochemical Properties of n- and p-Type β-CuCNS. Phys. Status Solidi A 1987, 103, 491– 497,  DOI: 10.1002/pssa.2211030220
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    19
    Semiconducting and photoelectrochemical properties of n- and p-type β-copper(I) thiocyanate
    Tennakone, K.; Jayatissa, A. H.; Fernando, C. A. N.; Wickramanayake, S.; Punchihewa, S.; Weerasena, L. K.; Premasiri, W. D. R.
    Physica Status Solidi A: Applied Research (1987), 103 (2), 491-7CODEN: PSSABA; ISSN:0031-8965.
    β-CuCNS, a three-dimensional polymeric solid with interbonded layers is found to have unusual photoelectrochem. and solid state properties. The material becomes p- or n type depending on whether CNS or Cu is in stoichiometric excess. The n-type is found to be sensitive to the visible spectrum. The methods of prepn. of p- and n-type films of β-CuCNS and their photoelectrochem. and solid state properties are discussed.
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  20. 20
    Pattanasattayavong, P.; Promarak, V.; Anthopoulos, T. D. Electronic Properties of Copper(I) Thiocyanate (CuSCN). Adv. Electron. Mater. 2017, 3, 1600378,  DOI: 10.1002/aelm.201600378
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    Elucidating the Coordination of Diethyl Sulfide Molecules in Copper(I) Thiocyanate (CuSCN) Thin Films and Improving Hole Transport by Antisolvent Treatment
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  1. Songyu Li, Penghui Ren, Di Zhao, Dan Liu, Jianqiao Wang, Hang Zhou, Wei Liu, Yuheng Zeng, Xuegong Yu, Can Cui, Peng Wang. Vacancy defect regulation in Copper(I) thiocyanate hole selective layer for efficient and stable crystalline silicon solar cells. Materials Today Energy 2025, 48 , 101782. https://doi.org/10.1016/j.mtener.2024.101782
  2. Samyuktha Noola, Gyanendra Shankar, Francesca De Rossi, Emanuele Calabrò, Matteo Bonomo, Claudia Barolo, Francesca Brunetti. Cuprous thiocyanate as an inorganic hole transport material for carbon-based flexible perovskite solar cells. Sustainable Energy & Fuels 2025, 1 https://doi.org/10.1039/D4SE01222D
  3. Jetnipat Songkerdthong, Thanasee Thanasarnsurapong, Adisak Boonchun, David J. Harding, Pichaya Pattanasattayavong. Band gap engineering in pyridyl-functionalized two-dimensional (2D) CuSCN coordination polymers. Molecular Systems Design & Engineering 2024, 9 (8) , 814-825. https://doi.org/10.1039/D4ME00022F
  4. Pengjie Hang, Chenxia Kan, Ge Li, Jiangsheng Xie, Biao Li, Yuxin Yao, Degong Ding, Zechen Hu, Deren Yang, Xuegong Yu. Unveiling and overcoming the interfacial degradation between CuSCN and metal electrodes in perovskite solar cells. Journal of Materials Chemistry A 2023, 11 (37) , 20225-20233. https://doi.org/10.1039/D3TA02895J
  5. Rajesh Deb, Manjula G. Nair, Ujjal Das, Saumya R. Mohapatra. Contrasting analog and digital resistive switching memory characteristics in solution-processed copper( i ) thiocyanate and its polymer electrolyte-based memristive devices. Journal of Materials Chemistry C 2023, 11 (23) , 7629-7640. https://doi.org/10.1039/D3TC00090G
  6. Jianjun Zhang, Bicheng Zhu, Liuyang Zhang, Jiaguo Yu. Femtosecond transient absorption spectroscopy investigation into the electron transfer mechanism in photocatalysis. Chemical Communications 2023, 59 (6) , 688-699. https://doi.org/10.1039/D2CC06300J
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  • Abstract

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    Figure 1

    Figure 1. (a) Schematic of the electrode cross-section, depicting the 10 nm nanogap separating the two metals, formed via a-Lith. (b) Optical micrograph of the coplanar Al–Au electrodes with a diameter of 300 μm, where the circular shape was patterned via photolithography. (c) Top view of the nanogap along the metal electrode interface imaged using SEM.

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    Figure 2

    Figure 2. Current–Voltage (I–V) characteristic of the pristine CuSCN film spin-coated on the top of the prepatterned Al–Au coplanar electrodes in (a) semi-log plot double scans and (b) log–log plot depicting the different transport regimes of the diode under forward bias. The thermionic emission regime is zoomed-in and plotted as ln I–V to allow calculation of the ideality factor (n) and saturation current (I0) of the p-type diode. Inset: Schematic of the forward and reverse biasing of the diode under test.

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    Figure 3

    Figure 3. (a) Molecular structures of Cu(I) thiocyanate and of the fluorofullerene dopant C60F48. (b) Energy band diagram of the Al/CuSCN/Au diode in a flat band configuration, depicting also the acceptor levels introduced by the p-type C60F48 dopant. The values are derived from ref (29). (c) I–V characteristics of the undoped (0 mol %) CuSCN film and the CuSCN film doped with 0.05–1 mol % doping of C60F48. The inset shows a magnified area close to the turn-on voltage of the diodes.

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    Figure 4

    Figure 4. (a) ln I–V plots of the forward biasing regime of 0–0.2 mol % (low) and 0.5–1 mol % (high) doping levels of CuSCN films and linear fits to the thermionic emission regions (depicted with dashed horizontal lines) used for the extraction of the ideality factor (n) and saturation (reverse) currents (I0), summarized in Supporting Information Table S1 and in (b) for both low and highly doped films.

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    Figure 5

    Figure 5. (a) Half-wave rectifier circuitry comprising a 1 nF load capacitor (CL) and a 1 MΩ load resistor (RL) mounted directly onto the measurement micromanipulator for measuring the DC output voltage from the coplanar CuSCN diodes. (b) VOUT amplitude (in dB) as a function of frequency depicting the fcutoff for the undoped and C60F48-doped CuSCN diodes at −3 dB for VIN = ±5 V (corresponding to VRMS = 3.53 V). (c) VOUT calculated at 10 kHz and 13.56 MHz and fcutoff values as a function of the doping concentration. (d) VOUT at the commercially relevant RFID frequency of 13.56 MHz vs varying input VRMS signals.

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      Nature (London, United Kingdom) (2021), 595 (7868), 532-536CODEN: NATUAS; ISSN:0028-0836. (Nature Portfolio)
      Abstr.: Nearly 50 years ago, Intel created the world's first com. produced microprocessor-the 4004 (ref. 1), a modest 4-bit CPU (central processing unit) with 2,300 transistors fabricated using 10 μm process technol. in silicon and capable only of simple arithmetic calcns. Since this ground-breaking achievement, there has been continuous technol. development with increasing sophistication to the stage where state-of-the-art silicon 64-bit microprocessors now have 30 billion transistors (for example, the AWS Graviton2 (ref. 2) microprocessor, fabricated using 7 nm process technol.). The microprocessor is now so embedded within our culture that it has become a meta-invention-i.e., it is a tool that allows other inventions to be realized, most recently enabling the big data anal. needed for a COVID-19 vaccine to be developed in record time. Here we report a 32-bit Arm (a reduced instruction set computing (RISC) architecture) microprocessor developed with metal-oxide thin-film transistor technol. on a flexible substrate (which we call the PlasticARM). Sep. from the mainstream semiconductor industry, flexible electronics operate within a domain that seamlessly integrates with everyday objects through a combination of ultrathin form factor, conformability, extreme low cost and potential for mass-scale prodn. PlasticARM pioneers the embedding of billions of low-cost, ultrathin microprocessors into everyday objects.
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      Semple, James; Georgiadou, Dimitra G.; Wyatt-Moon, Gwenhivir; Gelinck, Gerwin; Anthopoulos, Thomas D.
      Semiconductor Science and Technology (2017), 32 (12), 123002/1-123002/45CODEN: SSTEET; ISSN:0268-1242. (IOP Publishing Ltd.)
      A review. Over the last decade, there has been increasing interest in transferring the research advances in radiofrequency (RF) rectifiers, the quintessential element of the chip in the RF identification (RFID) tags, obtained on rigid substrates onto plastic (flexible) substrates. The growing demand for flexible RFID tags, wireless communications applications and wireless energy harvesting systems that can be produced at a low-cost is a key driver for this technol. push. In this topical review, we summarise recent progress and status of flexible RF diodes and rectifying circuits, with specific focus on materials and device processing aspects. To this end, different families of materials (e.g. flexible silicon, metal oxides, org and carbon nanomaterials), manufg processes (e.g. vacuum and soln. processing) and device architectures (diodes and transistors) are compared. Although emphasis is placed on performance, functionality, mech. flexibility and operating stability, the various bottlenecks assocd. with each technol. are also addressed. Finally, we present our outlook on the commercialisation potential and on the positioning of each material class in the RF electronics landscape based on the findings summarised herein. It is beyond doubt that the field of flexible high and ultra-high frequency rectifiers and electronics as a whole will continue to be an active area of research over the coming years.
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    6. 6
      Finkenzeller, K. RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication; Wiley, 2010.
      There is no corresponding record for this reference.
    7. 7
      Viola, F. A.; Brigante, B.; Colpani, P.; Dell’Erba, G.; Mattoli, V.; Natali, D.; Caironi, M. A 13.56 MHz Rectifier Based on Fully Inkjet Printed Organic Diodes. Adv. Mater. 2020, 32, 2002329,  DOI: 10.1002/adma.202002329
      7
      A 13.56 MHz rectifier based on fully inkjet printed organic diodes
      Viola, Fabrizio A.; Brigante, Biagio; Colpani, Paolo; Dell'Erba, Giorgio; Mattoli, Virgilio; Natali, Dario; Caironi, Mario
      Advanced Materials (Weinheim, Germany) (2020), 32 (33), 2002329CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The increasing diffusion of portable and wearable technologies results in a growing interest in electronic devices having features such as flexibility, lightness-in-wt., transparency, and wireless operation. Org. electronics is proposed as a potential candidate to fulfill such needs, in particular targeting pervasive radio-frequency (RF) applications. Still, limitations in terms of device performances at RF, particularly severe when large-area and scalable fabrication techniques are employed, have largely precluded the achievement of such an appealing scenario. In this work, the rectification of an electromagnetic wave at 13.56 MHz with a fully inkjet printed polymer diode is demonstrated. The rectifier, a key enabling component of future pervasive wireless systems, is fabricated through scalable large-area methods on plastic. To provide a proof-of-principle demonstration of its future applicability, its adoption in powering a printed integrated polymer circuit is presented. The possibility of harvesting elec. power from RF waves and delivering it to a cheap flexible substrate through a simple printed circuitry paves the way to a plethora of appealing distributed electronic applications.
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    8. 8
      Kang, C.-M.; Wade, J.; Yun, S.; Lim, J.; Cho, H.; Roh, J.; Lee, H.; Nam, S.; Bradley, D. D. C.; Kim, J.-S.; Lee, C. 1 GHz Pentacene Diode Rectifiers Enabled by Controlled Film Deposition on SAM-Treated Au Anodes. Adv. Electron. Mater. 2016, 2, 1500282,  DOI: 10.1002/aelm.201500282
      There is no corresponding record for this reference.
    9. 9
      Li, M.; Honkanen, M.; Liu, X.; Rokaya, C.; Schramm, A.; Fahlman, M.; Berger, P. R.; Lupo, D. 0.7-GHz Solution-Processed Indium Oxide Rectifying Diodes. IEEE Trans. Electron Devices 2020, 67, 360– 364,  DOI: 10.1109/ted.2019.2954167
      9
      Solution-processed indium oxide rectifying diodes at 0.7-GHz
      Li, Miao; Honkanen, Mari; Liu, Xianjie; Rokaya, Chakra; Schramm, Andreas; Fahlman, Mats; Berger, Paul R.; Lupo, Donald
      IEEE Transactions on Electron Devices (2020), 67 (1), 360-364CODEN: IETDAI; ISSN:1557-9646. (Institute of Electrical and Electronics Engineers)
      Soln.-based deposition, with its simplicity and possibility for upscaling through printing, is a promising process for low-cost electronics. Metal oxide semiconductor devices, esp. indium oxide with its excellent elec. properties, offer high performance compared to amorphous Si-based rivals, and with a form factor conducive to flexible and wearable electronics. Here, rectifying diodes based on an amorphous spin-coated indium oxide are fabricated for high-speed applications. We report a soln.-processed diode approaching the UHF range, based on indium oxide, with aluminum and gold as the electrodes. The device was spin-coated from a precursor material and configured into a half-wave rectifier. The J-V and frequency behavior of the diodes were studied, and the material compn. of the diode was investigated by X-ray photoemission spectroscopy (XPS). The 3-dB point was found to be over 700 MHz. The results are promising for the development of autonomously powered wireless Internetof-Things systems based on scalable, low-cost processes.
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    10. 10
      Sani, N.; Robertsson, M.; Cooper, P.; Wang, X.; Svensson, M.; Andersson Ersman, P.; Norberg, P.; Nilsson, M.; Nilsson, D.; Liu, X.; Hesselbom, H.; Akesso, L.; Fahlman, M.; Crispin, X.; Engquist, I.; Berggren, M.; Gustafsson, G. All-Printed Diode Operating at 1.6 GHz. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 11943– 11948,  DOI: 10.1073/pnas.1401676111
      10
      All-printed diode operating at 1.6 GHz
      Sani, Negar; Robertsson, Mats; Cooper, Philip; Wang, Xin; Svensson, Magnus; Ersman, Peter Andersson; Norberg, Petronella; Nilsson, Marie; Nilsson, David; Liu, Xianjie; Hesselbom, Hjalmar; Akesso, Laurent; Fahlman, Mats; Crispin, Xavier; Engquist, Isak; Berggren, Magnus; Gustafsson, Goeran
      Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (33), 11943-11948CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      Printed electronics are considered for wireless electronic tags and sensors within the future internet-of-things (IoT) concept. As a consequence of the low charge carrier mobility of present printable org. and inorg. semiconductors, the operational frequency of printed rectifiers is not high enough to enable direct communication and powering between mobile phones and printed e-tags. Here, we report an all-printed diode operating ≤1.6 GHz. The device, based on 2 stacked layers of Si and NbSi2 particles, is manufd. on a flexible substrate at low temp. and in ambient atm. The high charge carrier mobility of the Si microparticles allows device operation to occur in the charge injection-limited regime. The asymmetry of the oxide layers in the resulting device stack leads to rectification of tunneling current. Printed diodes were combined with antennas and electrochromic displays to form an all-printed e-tag. The harvested signal from a global system for mobile communications mobile phone was used to update the display. Our findings demonstrate a new communication pathway for printed electronics within IoT applications.
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    11. 11
      Yang, S. J.; Park, K.-T.; Im, J.; Hong, S.; Lee, Y.; Min, B.-W.; Kim, K.; Im, S. Ultrafast 27 GHz Cutoff Frequency in Vertical WSe2 Schottky Diodes with Extremely Low Contact Resistance. Nat. Commun. 2020, 11, 1574,  DOI: 10.1038/s41467-020-15419-1
      11
      Ultrafast 27 GHz cutoff frequency in vertical WSe2 Schottky diodes with extremely low contact resistance
      Yang, Sung Jin; Park, Kyu-Tae; Im, Jaeho; Hong, Sungjae; Lee, Yangjin; Min, Byung-Wook; Kim, Kwanpyo; Im, Seongil
      Nature Communications (2020), 11 (1), 1574CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
      Abstr.: Ultra-thin two-dimensional semiconducting crystals in their monolayer and few-layer forms show promising aspects in nanoelectronic applications. However, the ultra-thin nature of two-dimensional crystals inevitably results in high contact resistance from limited channel/contact vol. as well as device-to-device variability, which seriously limit reliable applications using two-dimensional semiconductors. Here, we incorporate rather thick two-dimensional layered semiconducting crystals for reliable vertical diodes showing excellent Ohmic and Schottky contacts. Using the vertical transport of WSe2, we demonstrate devices which are functional at various frequency ranges from megahertz AM demodulation of audio signals, to gigahertz rectification for fifth-generation wireless electronics, to UV-visible photodetection. The WSe2 exhibits an excellent Ohmic contact to bottom platinum electrode with record-low contact resistance (∼50 Ω ) and an exemplary Schottky junction to top transparent conducting oxide electrode. Our semitransparent vertical WSe2 Schottky diodes could be a key component of future high frequency electronics in the era of fifth-generation wireless communication.
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    12. 12
      Petti, L.; Pattanasattayavong, P.; Lin, Y.-H.; Münzenrieder, N.; Cantarella, G.; Yaacobi-Gross, N.; Yan, F.; Tröster, G.; Anthopoulos, T. D. Solution-Processed pType Copper(I) Thiocyanate (CuSCN) for Low-Voltage Flexible Thin-Film Transistors and Integrated Inverter Circuits. Appl. Phys. Lett. 2017, 110, 113504,  DOI: 10.1063/1.4978531
      12
      Solution-processed p-type copper(I) thiocyanate (CuSCN) for low-voltage flexible thin-film transistors and integrated inverter circuits
      Petti, Luisa; Pattanasattayavong, Pichaya; Lin, Yen-Hung; Munzenrieder, Niko; Cantarella, Giuseppe; Yaacobi-Gross, Nir; Yan, Feng; Troster, Gerhard; Anthopoulos, Thomas D.
      Applied Physics Letters (2017), 110 (11), 113504/1-113504/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      The authors report on low operating voltage thin-film transistors (TFTs) and integrated inverters based on copper(I) thiocyanate (CuSCN) layers processed from soln. at low temp. on free-standing plastic foils. As-fabricated coplanar bottom-gate and staggered top-gate TFTs exhibit hole-transporting characteristics with av. mobility values of 0.0016 cm2 V-1 s-1 and 0.013 cm2 V-1 s-1, resp., current on/off ratio in the range 102-104, and max. operating voltages between -3.5 and -10 V, depending on the gate dielec. employed. The promising TFT characteristics enable fabrication of unipolar NOT gates on flexible free-standing plastic substrates with voltage gain of 3.4 at voltages ≥-3.5 V. Importantly, discrete CuSCN transistors and integrated logic inverters remain fully functional even when mech. bent to a tensile radius of 4 mm, demonstrating the potential of the technol. for flexible electronics. (c) 2017 American Institute of Physics.
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    13. 13
      Semple, J.; Georgiadou, D. G.; Wyatt-Moon, G.; Yoon, M.; Seitkhan, A.; Yengel, E.; Rossbauer, S.; Bottacchi, F.; McLachlan, M. A.; Bradley, D. D. C.; Anthopoulos, T. D. Large-Area Plastic Nanogap Electronics Enabled by Adhesion Lithography. npj Flexible Electron. 2018, 2, 18,  DOI: 10.1038/s41528-018-0031-3
      There is no corresponding record for this reference.
    14. 14
      Oh, S.; Blaauw, D.; Sylvester, D. The Internet of Tiny Things: Recent Advances of Millimeter-Scale Computing. IEEE Des. Test 2019, 36, 65– 72,  DOI: 10.1109/mdat.2019.2898187
      There is no corresponding record for this reference.
    15. 15
      Georgiadou, D. G.; Semple, J.; Sagade, A. A.; Forstén, H.; Rantakari, P.; Lin, Y.-H.; Alkhalil, F.; Seitkhan, A.; Loganathan, K.; Faber, H.; Anthopoulos, T. D. 100 GHz Zinc Oxide Schottky Diodes Processed from Solution on a Wafer Scale. Nat. Electron. 2020, 3, 718– 725,  DOI: 10.1038/s41928-020-00484-7
      15
      Hundred GHz zinc oxide Schottky diodes processed from solution on a wafer scale
      Georgiadou, Dimitra G.; Semple, James; Sagade, Abhay A.; Forsten, Henrik; Rantakari, Pekka; Lin, Yen-Hung; Alkhalil, Feras; Seitkhan, Akmaral; Loganathan, Kalaivanan; Faber, Hendrik; Anthopoulos, Thomas D.
      Nature Electronics (2020), 3 (11), 718-725CODEN: NEALB3; ISSN:2520-1131. (Nature Research)
      Abstr.: Inexpensive radio-frequency devices that can meet the ultrahigh-frequency needs of fifth- and sixth-generation wireless telecommunication networks are required. However, combining high performance with cost-effective scalable manufg. has proved challenging. Here, we report the fabrication of soln.-processed zinc oxide Schottky diodes that can operate in microwave and millimetre-wave frequency bands. The fully coplanar diodes are prepd. using wafer-scale adhesion lithog. to pattern two asym. metal electrodes sepd. by a gap of around 15 nm, and are completed with the deposition of a zinc oxide or aluminum-doped ZnO layer from soln. The Schottky diodes exhibit a max. intrinsic cutoff frequency in excess of 100 GHz, and when integrated with other passive components yield radio-frequency energy-harvesting circuits that are capable of delivering output voltages of 600 mV and 260 mV at 2.45 GHz and 10 GHz, resp.
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    16. 16
      Kepman, A. V.; Sukhoverkhov, V. F.; Tressaud, A.; Labrugere, C.; Durand, E.; Chilingarov, N. S.; Sidorov, L. N. Novel Method of Synthesis of C60F48 with Improved Yield and Selectivity. J. Fluorine Chem. 2006, 127, 832– 836,  DOI: 10.1016/j.jfluchem.2006.02.019
      16
      Novel method of synthesis of C60F48 with improved yield and selectivity
      Kepman, A. V.; Sukhoverkhov, V. F.; Tressaud, A.; Labrugere, C.; Durand, E.; Chilingarov, N. S.; Sidorov, L. N.
      Journal of Fluorine Chemistry (2006), 127 (7), 832-836CODEN: JFLCAR; ISSN:0022-1139. (Elsevier B.V.)
      A novel two-stage method of prepn. of C60F48 with 96% purity and 80% yield is reported. A C60 embedded into a MnF2 matrix is reacted with mol. fluorine under dynamic conditions, i.e. in flow of fluorine gas and with sublimation of volatile products, which gave C60F34-C60F38 mixts. with >90% yield. Subsequent fluorination of the mixt. thus obtained in the closed reactor at elevated pressure directly leads to the final product. C60F48 thus synthesized was characterized by EI-MS, MALDI-MS, IR-spectroscopy and XPS. The problems of fullerene burning and degrdn. in the fluorine atm. are discussed.
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    17. 17
      Semple, J.; Rossbauer, S.; Burgess, C. H.; Zhao, K.; Jagadamma, L. K.; Amassian, A.; McLachlan, M. A.; Anthopoulos, T. D. Radio Frequency Coplanar ZnO Schottky Nanodiodes Processed from Solution on Plastic Substrates. Small 2016, 12, 1993– 2000,  DOI: 10.1002/smll.201503110
      17
      Radio Frequency Coplanar ZnO Schottky Nanodiodes Processed from Solution on Plastic Substrates
      Semple, James; Rossbauer, Stephan; Burgess, Claire H.; Zhao, Kui; Jagadamma, Lethy Krishnan; Amassian, Aram; McLachlan, Martyn A.; Anthopoulos, Thomas D.
      Small (2016), 12 (15), 1993-2000CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Radio frequency coplanar ZnO Schottky nanodiodes were prepd. and characterized. Thermally evapd. Al films were patterned using conventional photolithog. and wet chem. etching for nanogap electrode fabrication.
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    18. 18
      Wyatt-Moon, G.; Georgiadou, D. G.; Semple, J.; Anthopoulos, T. D. Deep Ultraviolet Copper(I) Thiocyanate (CuSCN) Photodetectors Based on Coplanar Nanogap Electrodes Fabricated via Adhesion Lithography. ACS Appl. Mater. Interfaces 2017, 9, 41965– 41972,  DOI: 10.1021/acsami.7b12942
      18
      Deep Ultraviolet Copper(I) Thiocyanate (CuSCN) Photodetectors Based on Coplanar Nanogap Electrodes Fabricated via Adhesion Lithography
      Wyatt-Moon, Gwenhivir; Georgiadou, Dimitra G.; Semple, James; Anthopoulos, Thomas D.
      ACS Applied Materials & Interfaces (2017), 9 (48), 41965-41972CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Adhesion lithog. (a-Lith) is a versatile fabrication technique used to produce asym. coplanar electrodes sepd. by a <15 nm nanogap. A-Lith was used to fabricate deep UV (DUV) detectors by combining coplanar asym. nanogap electrode architectures (Au/Al) with soln.-processable wide-band-gap (3.5-3.9 eV) p-type semiconductor Cu(I) thiocyanate (CuSCN). Because of the device's unique architecture, the detectors exhibit high responsivity (≈79 A W-1) and photosensitivity (≈720) when illuminated with a DUV-range (λpeak = 280 nm) light-emitting diode at 220 μW cm-2. The photosensitivity of the photodetectors remains fairly high (≈7) even at illuminating intensities down to 0.2 μW cm-2. The scalability of the a-Lith process combined with the unique properties of CuSCN paves the way to new forms of inexpensive, yet high-performance, photodetectors that can be manufd. on arbitrary substrate materials including plastic.
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    19. 19
      Tennakone, K.; Jayatissa, A. H.; Fernando, C. A. N.; Wickramanayake, S.; Punchihewa, S.; Weerasena, L. K.; Premasiri, W. D. R. Semiconducting and Photoelectrochemical Properties of n- and p-Type β-CuCNS. Phys. Status Solidi A 1987, 103, 491– 497,  DOI: 10.1002/pssa.2211030220
      19
      Semiconducting and photoelectrochemical properties of n- and p-type β-copper(I) thiocyanate
      Tennakone, K.; Jayatissa, A. H.; Fernando, C. A. N.; Wickramanayake, S.; Punchihewa, S.; Weerasena, L. K.; Premasiri, W. D. R.
      Physica Status Solidi A: Applied Research (1987), 103 (2), 491-7CODEN: PSSABA; ISSN:0031-8965.
      β-CuCNS, a three-dimensional polymeric solid with interbonded layers is found to have unusual photoelectrochem. and solid state properties. The material becomes p- or n type depending on whether CNS or Cu is in stoichiometric excess. The n-type is found to be sensitive to the visible spectrum. The methods of prepn. of p- and n-type films of β-CuCNS and their photoelectrochem. and solid state properties are discussed.
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    20. 20
      Pattanasattayavong, P.; Promarak, V.; Anthopoulos, T. D. Electronic Properties of Copper(I) Thiocyanate (CuSCN). Adv. Electron. Mater. 2017, 3, 1600378,  DOI: 10.1002/aelm.201600378
      There is no corresponding record for this reference.
    21. 21
      Worakajit, P.; Hamada, F.; Sahu, D.; Kidkhunthod, P.; Sudyoadsuk, T.; Promarak, V.; Harding, D. J.; Packwood, D. M.; Saeki, A.; Pattanasattayavong, P. Elucidating the Coordination of Diethyl Sulfide Molecules in Copper(I) Thiocyanate (CuSCN) Thin Films and Improving Hole Transport by Antisolvent Treatment. Adv. Funct. Mater. 2020, 30, 2002355,  DOI: 10.1002/adfm.202002355
      21
      Elucidating the Coordination of Diethyl Sulfide Molecules in Copper(I) Thiocyanate (CuSCN) Thin Films and Improving Hole Transport by Antisolvent Treatment
      Worakajit, Pimpisut; Hamada, Fumiya; Sahu, Debashis; Kidkhunthod, Pinit; Sudyoadsuk, Taweesak; Promarak, Vinich; Harding, David J.; Packwood, Daniel M.; Saeki, Akinori; Pattanasattayavong, Pichaya
      Advanced Functional Materials (2020), 30 (36), 2002355CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Copper(I) thiocyanate (CuSCN) is rising to prominence as a hole-transporting semiconductor in various opto/electronic applications. Its unique combination of good hole mobility, high optical transparency, and soln.-processability renders it a promising hole-transport layer for solar cells and p-type channel in thin-film transistors. CuSCN is typically deposited from sulfide-based solns. with di-Et sulfide (DES) being the most widely used. However, little is known regarding the effects of DES on CuSCN films despite the fact that DES can coordinate with Cu(I) and result in a different coordination polymer having a distinct crystal structure when fully coordinated. Herein, the coordination of DES in CuSCN films is thoroughly investigated with a suite of characterization techniques as well as d. functional theory. This study reveals that DES directly affects the microstructure of CuSCN by stabilizing the polar cryst. surfaces via the formation of strong coordination bonds. Furthermore, a simple antisolvent treatment is demonstrated to be effective at modifying the microstructure and morphol. of CuSCN films. The treatment with THF or acetone leads to uniform films consisting of CuSCN crystallites with high crystallinity and their surfaces passivated by DES mols., resulting in an increase in the hole mobility from 0.01 to 0.05 cm2 V-1 s-1.
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    22. 22
      Wijeyasinghe, N.; Regoutz, A.; Eisner, F.; Du, T.; Tsetseris, L.; Lin, Y.-H.; Faber, H.; Pattanasattayavong, P.; Li, J.; Yan, F.; McLachlan, M. A.; Payne, D. J.; Heeney, M.; Anthopoulos, T. D. Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers Processed from Aqueous Precursor Solutions and Their Application in Thin-Film Transistors and Highly Efficient Organic and Organometal Halide Perovskite Solar Cells. Adv. Funct. Mater. 2017, 27, 1701818,  DOI: 10.1002/adfm.201701818
      There is no corresponding record for this reference.
    23. 23
      Chiu, F.-C. A Review on Conduction Mechanisms in Dielectric Films. Adv. Mater. Sci. Eng. 2014, 2014, 578168,  DOI: 10.1155/2014/578168
      There is no corresponding record for this reference.
    24. 24
      Son, Y.; Peterson, R. L. The Effects of Localized Tail States on Charge Transport Mechanisms in Amorphous Zinc Tin Oxide Schottky Diodes. Semicond. Sci. Technol. 2017, 32, 12LT02,  DOI: 10.1088/1361-6641/aa95d2
      There is no corresponding record for this reference.
    25. 25
      Pattanasattayavong, P.; Mottram, A. D.; Yan, F.; Anthopoulos, T. D. Study of the Hole Transport Processes in Solution-Processed Layers of the Wide Bandgap Semiconductor Copper(I) Thiocyanate (CuSCN). Adv. Funct. Mater. 2015, 25, 6802– 6813,  DOI: 10.1002/adfm.201502953
      25
      Study of the Hole Transport Processes in Solution-Processed Layers of the Wide Bandgap Semiconductor Copper(I) Thiocyanate (CuSCN)
      Pattanasattayavong, Pichaya; Mottram, Alexander D.; Yan, Feng; Anthopoulos, Thomas D.
      Advanced Functional Materials (2015), 25 (43), 6802-6813CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Wide bandgap hole-transporting semiconductor copper(I) thiocyanate (CuSCN) has recently shown promise both as a transparent p-type channel material for thin-film transistors and as a hole-transporting layer in org. light-emitting diodes and org. photovoltaics. Herein, the hole-transport properties of soln.-processed CuSCN layers were studied. Metal-insulator-semiconductor capacitors are employed to det. key material parameters including: dielec. const. [5.1 (±1.0)], flat-band voltage [-0.7 (±0.1) V], and unintentional hole doping concn. [7.2 (±1.4) × 1017 cm-3]. The d. of localized hole states in the mobility gap is analyzed using elec. field-effect measurements; the distribution can be approximated invoking an exponential function with a characteristic energy of 42.4 (±0.1) meV. Further study using temp.-dependent mobility measurements in the range 78-318 K reveals the existence of three transport regimes. The 1st two regimes obsd. at high (303-228 K) and intermediate (228-123 K) temps. are described with multiple trapping and release and variable range hopping processes, resp. The 3rd regime obsd. at low temps. (123-78 K) exhibits weak temp. dependence and is attributed to a field-assisted hopping process. The transitions between the mechanisms are discussed based on the temp. dependence of the transport energy.
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    26. 26
      Sze, S. M.; Ng, K. K. Metal-Semiconductor Contacts. Physics of Semiconductor Devices, 3rd ed.; John Wiley & Sons, Inc., 2007; Chapter 3, pp 134– 196.
      There is no corresponding record for this reference.
    27. 27
      Werner, J. H.; Güttler, H. H. Barrier Inhomogeneities at Schottky Contacts. J. Appl. Phys. 1991, 69, 1522– 1533,  DOI: 10.1063/1.347243
      27
      Barrier inhomogeneities at Schottky contacts
      Werner, Juergen H.; Guettler, Herbert H.
      Journal of Applied Physics (1991), 69 (3), 1522-33CODEN: JAPIAU; ISSN:0021-8979.
      A new anal. potential fluctuation model is presented for the interpretation of current/voltage and capacitance/voltage measurements on spatially inhomogeneous Schottky contacts. A new evaluation scheme of current and capacitance barriers permits a quant. anal. of spatially distributed Schottky barriers. The ideality coeff. n of abrupt Schottky contacts reflects the deformation of the barrier distribution under applied bias; a general temp. dependence for the ideality n is predicted. The model offers a soln. for the so-called TO problem. Not only author's measurements on PtSi/Si diodes, but also previously published ideality data for Schottky diodes on Si, GaAs, and InP with the theory.
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    28. 28
      Bacaksiz, E.; Aksu, S.; Çankaya, G.; Yılmaz, S.; Polat, İ.; Küçükömeroğlu, T.; Varilci, A. Fabrication of p-Type CuSCN/n-Type Micro-Structured ZnO Heterojunction Structures. Thin Solid Films 2011, 519, 3679– 3685,  DOI: 10.1016/j.tsf.2011.01.254
      28
      Fabrication of p-type CuSCN/n-type micro-structured ZnO heterojunction structures
      Bacaksiz, E.; Aksu, S.; Cankaya, G.; Yilmaz, S.; Polat, I.; Kuecuekoemeroglu, T.; Varilci, A.
      Thin Solid Films (2011), 519 (11), 3679-3685CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)
      Micro-sized ZnO rods on a SnO2 coated glass substrate were obtained by the spray pyrolysis method. Then a p-type CuSCN layer was deposited on this micro-sized n-ZnO to produce a p-n heterojunction. Temp. dependent current-voltage characteristics were measured in the temp. range 150-300 K with a step of 25 K The current-voltage characteristics exhibit elec. rectification behavior. The zero bias barrier height Φb0 increases and the ideality factor n decreases with an increase in temp. The apparent Richardson const. and mean barrier height are 0.0028 Acm-2K-2 and 0.228 eV resp. in the range 150-300 K. After a barrier height inhomogeneity correction, the Richardson const. and the mean barrier height were obtained as 65.20 Acm-2K-2 and 0.840 eV, resp.
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    29. 29
      Wijeyasinghe, N.; Eisner, F.; Tsetseris, L.; Lin, Y.-H.; Seitkhan, A.; Li, J.; Yan, F.; Solomeshch, O.; Tessler, N.; Patsalas, P.; Anthopoulos, T. D. p-Doping of Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers for High-Performance Transistors and Organic Solar Cells. Adv. Funct. Mater. 2018, 28, 1802055,  DOI: 10.1002/adfm.201802055
      There is no corresponding record for this reference.
    30. 30
      Babuji, A.; Temiño, I.; Pérez-Rodríguez, A.; Solomeshch, O.; Tessler, N.; Vila, M.; Li, J.; Mas-Torrent, M.; Ocal, C.; Barrena, E. Double Beneficial Role of Fluorinated Fullerene Dopants on Organic Thin-Film Transistors: Structural Stability and Improved Performance. ACS Appl. Mater. Interfaces 2020, 12, 28416– 28425,  DOI: 10.1021/acsami.0c06418
      30
      Double Beneficial Role of Fluorinated Fullerene Dopants on Organic Thin-Film Transistors: Structural Stability and Improved Performance
      Babuji, Adara; Temino, Ines; Perez-Rodriguez, Ana; Solomeshch, Olga; Tessler, Nir; Vila, Maria; Li, Jinghai; Mas-Torrent, Marta; Ocal, Carmen; Barrena, Esther
      ACS Applied Materials & Interfaces (2020), 12 (25), 28416-28425CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The present work assesses improved carrier injection in org. field-effect transistors by contact doping and provides fundamental insight into the multiple impacts that the dopant/semiconductor interface details have on the long-term and thermal stability of devices. We investigate donor [1]benzothieno[3,2-b]-[1]benzothiophene (BTBT) derivs. with one and two octyl side chains attached to the core, therefore constituting asym. (BTBT-C8) and sym. (C8-BTBT-C8) mols., resp. Our results reveal that films formed out of the asym. BTBT-C8 expose the same alkyl-terminated surface as the C8-BTBT-C8 films do. In both cases, the consequence of depositing fluorinated fullerene (C60F48) as a mol. p-dopant is the formation of C60F48 cryst. islands decorating the step edges of the underlying semiconductor film surface. We demonstrate that local work function changes along with a peculiar nanomorphol. lead to the double beneficial effect of lowering the contact resistance and providing long-term and enhanced thermal stability of the devices.
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    31. 31
      Heljo, P. S.; Li, M.; Lilja, K. E.; Majumdar, H. S.; Lupo, D. Printed Half-Wave and Full-Wave Rectifier Circuits Based on Organic Diodes. IEEE Trans. Electron Devices 2013, 60, 870– 874,  DOI: 10.1109/ted.2012.2233741
      There is no corresponding record for this reference.
    32. 32
      Ferchichi, K.; Pecqueur, S.; Guerin, D.; Bourguiga, R.; Lmimouni, K. High Rectification Ratio in Polymer Diode Rectifier through Interface Engineering with Self-Assembled Monolayer. Electron. Mater. 2021, 2, 445– 453,  DOI: 10.3390/electronicmat2040030
      There is no corresponding record for this reference.
    33. 33
      Tran, L.-G.; Cha, H.-K.; Park, W.-T. RF Power Harvesting: a Review on Designing Methodologies and Applications. Micro Nano Syst. Lett. 2017, 5, 14,  DOI: 10.1186/s40486-017-0051-0
      There is no corresponding record for this reference.
    34. 34
      Li, T.; Bandari, V. K.; Hantusch, M.; Xin, J.; Kuhrt, R.; Ravishankar, R.; Xu, L.; Zhang, J.; Knupfer, M.; Zhu, F.; Yan, D.; Schmidt, O. G. Integrated Molecular Diode as 10 MHz Half-Wave Rectifier Based on an Organic Nanostructure Heterojunction. Nat. Commun. 2020, 11, 3592,  DOI: 10.1038/s41467-020-17352-9
      34
      Integrated molecular diode as 10 MHz half-wave rectifier based on an organic nanostructure heterojunction
      Li Tianming; Bandari Vineeth Kumar; Ravishankar Rachappa; Xu Longqian; Zhu Feng; Schmidt Oliver G; Li Tianming; Bandari Vineeth Kumar; Ravishankar Rachappa; Xu Longqian; Zhu Feng; Schmidt Oliver G; Li Tianming; Bandari Vineeth Kumar; Zhu Feng; Schmidt Oliver G; Hantusch Martin; Kuhrt Robert; Knupfer Martin; Xin Jianhui; Zhang Jidong; Zhu Feng; Yan Donghang
      Nature communications (2020), 11 (1), 3592 ISSN:.
      Considerable efforts have been made to realize nanoscale diodes based on single molecules or molecular ensembles for implementing the concept of molecular electronics. However, so far, functional molecular diodes have only been demonstrated in the very low alternating current frequency regime, which is partially due to their extremely low conductance and the poor degree of device integration. Here, we report about fully integrated rectifiers with microtubular soft-contacts, which are based on a molecularly thin organic heterojunction and are able to convert alternating current with a frequency of up to 10 MHz. The unidirectional current behavior of our devices originates mainly from the intrinsically different surfaces of the bottom planar and top microtubular Au electrodes while the excellent high frequency response benefits from the charge accumulation in the phthalocyanine molecular heterojunction, which not only improves the charge injection but also increases the carrier density.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.1c22856.

    • Characteristics of diodes upon doping, additional I–V curves of the empty and CuSCN-filled nanogap electrodes, energy level diagrams depicting injection at forward and reverse biasing, diode stability in air, and high-frequency supplementary and statistical performance data (PDF)


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