Phase-Change Memory from Molecular Tellurides

Phase-change memory (PCM) is an emerging memory technology based on the resistance contrast between the crystalline and amorphous states of a material. Further development and realization of PCM as a mainstream memory technology rely on innovative materials and inexpensive fabrication methods. Here, we propose a generalizable and scalable solution-processing approach to synthesize phase-change telluride inks in order to meet demands for high-throughput material screening, increased energy efficiency, and advanced device architectures. Bulk tellurides, such as Sb2Te3, GeTe, Sc2Te3, and TiTe2, are dissolved and purified to obtain inks of molecular metal telluride complexes. This allowed us to unlock a wide range of solution-processed ternary tellurides by the simple mixing of binary inks. We demonstrate accurate and quantitative composition control, including prototype materials (Ge–Sb–Te) and emerging rare-earth-metal telluride-doped materials (Sc–Sb–Te). Spin-coating and annealing convert ink formulations into high-quality, phase-pure telluride films with preferred orientation along the (00l) direction. Deposition engineering of liquid tellurides enables thickness-tunable films, infilling of nanoscale vias, and film preparation on flexible substrates. Finally, we demonstrate cyclable and non-volatile prototype memory devices, achieving performance indicators such as resistance contrast and low reset energy on par with state-of-the-art sputtered PCM layers.

independent measurements.The threshold voltage lies between 0.9 and 1.9 V.

Figure
Figure S1.a) Thermogravimetric analysis of Sb2Te3, GeTe and GST225 inks at a ramp rate of 5 K min -1 and under N2 flow.b) Temperature-ramp resistance measurements of Sb2Te3, Sc0.2Sb2Te3 and GST147 thin films via a two-probe setup.The heating rate was 5 K/min.Note that during the heating ramp, several processes occur sequentially and at different temperatures, such as evaporation of the ethylenediamine (bp = 116 °C), evaporation of the ethanedithiol (bp = 146 °C), loss of bound organic ligands at higher temperatures, and finally, loss of Te at > 400 °C.

Figure
Figure S2.a) Secondary electron micrograph, b) atomic-force microscopy image and c-f) EDX composition mapping of the thin film with nominal composition of GST225.EDX quantification of the film resulted in 23.6 at% Ge, 25.5 at% Sb, 47.3 at% Te, and 3.6 at% S, showing that elements are homogenously distributed within the film.

Figure S3 .
Figure S3.Energy-dispersive X-ray spectra of GeTe, GST225, Sb2Te3 thin-films indicating the presence or absence of Ge, Sb, and Te elements in PCM layers.The pile-up peak at 3.48 keV originates from simultaneous absorption of two Si Ka x-rays (2 × 1.74 eV = 3.48 keV) due to the strong Si signal from the substrate.

Figure S4 .
Figure S4.Composition of GeTe thin films in relation to the total stirring time of bulk GeTe in the amine-thiol co-solvent mixture.The elemental ratios were determined by EDX spectroscopy.For shorter stirring time (1 h), the films are tellurium-rich despite intense purification protocol with alkylphosphine.Longer stirring (> 4 h) leads to proportionally higher sulfur contents.

Figure S5 .
Figure S5.Zoom-in on the XRD pattern of Sc-Sb-Te from Figure 2g.

Figure S6 .
Figure S6.In-plane pole figures of a) Sb2Te3, b) GST147 and c) GST225 thin films.d) Radial integration yields the multiples of random distribution (m.r.d.) as a function of the tilt angle α.Higher m.r.d.values indicate stronger preferred orientation of thin films.e) The degree of texture (m.r.d.value at the origin) as a function of increasing Ge content in thin films.

Figure S7 .
Figure S7.Deposition of GST225 molecular inks on pre-patterned Si|SiO2 substrates.a) Top-view SEM image of the patterned trench structures before the ink deposition.b) Full cross-sectional SEM image and SEM-EDX maps of the infilled trenches, as shown in Figure 3b.Ge in yellow, Sb in red, Te is blue, Si in green.

Figure S8 .
Figure S8.Top-view SEM image of a PCM device with a gap of 300 nm prior to infilling with telluride ink.

Figure S9 .
Figure S9.Extended I-V characterization of the GST225 device.a) I-V sweep of a melt-quenched device plotted linearly.This demonstrates the exponential increase of current with increased voltage.b) I-V sweep of melt-quenched devices exhibiting the "snapback" behaviour for 9 independent measurements.The threshold voltage lies between 0.9 and 1.9 V.

Figure S10 .
Figure S10.Parameter map of the SET pulse with a trailing edge of 1000 ns.Filled symbols denote conditions with successful crystallization (resistance decrease by at least a factor of 5).Open symbols depict no resistance change.

Figure S11 .
Figure S11.Solid-state synthesis of TiTe2.a) XRD of TiTe2, prepared via solid-state synthesis method, b) Image of the ampoule after synthesis

Figure S13 .
Figure S13.XRD pattern of a GST225 film, dried at 70 °C for 10 min, prior to annealing.The film is nominally amorphous, as only a peak at 44.1 °C originating from the holder can be observed.

Figure S14 .
Figure S14.XRD pattern of Sb2Te3 doped with 29 at% Sc, prepared with different spin-coating conditions.Slower spin speed (1250 rpm) leads to thicker films with less texture, compared to faster speeds (2000 rpm), as evidenced by weaker (00l) and more pronounced (105) reflections.

Table S1 .
Elemental composition of Ge-Sb-Te thin films as quantified by EDX spectroscopy.

Table S2 .
Elemental content of Sc-Sb-Te thin films as quantified by EDX spectroscopy.