Telluride-Based Multilayered Heterostructures for Thermally Stable Phase Change Materials

Chalcogenide phase change memory (PCM) alloys are extensively used in non-volatile electronic memory devices due to their ability to alternate between two distinct solid-state structural phases, crystalline and amorphous, triggered by electrical stimuli.<br/>While the standard Ge₂Sb₂Te₅ (GST-225) alloy is prevalent in phase change memory technology, its application in the automotive sector is hindered by its low thermal stability, with a crystallization onset temperature of approximately 140 °C. Conversely, automotive memory systems require data retention at temperatures up to 155°C for 2x10³cycles. Compounds with a higher Ge content in the GST-x25 (x &gt; 0.22) composition have already been shown to demonstrate enhanced thermal stability over GST-225, however, the challenge of Ge segregation, especially when the Ge content surpasses 40%, limits their adoption [1,2].<br/>In this study, combining different chalcogenide films of the system Ge/Sb₂Te₃/GST-225/Ge-rich Ge-Sb-Te, multilayered heterostructures will be shown to exhibit adjustable physical properties compared to their individual film components, thanks to the pairing of thermally stable layers (such as Ge-rich Ge_5.5Sb₂Te₅ and Ge) with films that have rapid switching capabilities (such as Sb₂Te₃). The heterostructures were deposited onto Si(100) substrates using radio frequency sputtering and then heated to 400 °C. Both the pristine and heat-treated samples underwent analysis through X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy. The studied multilayers not only exhibited higher temperatures for the onset of crystallization compared to the conventional GST-225 alloy but also showed little to no segregation of Ge. Such heterostructures turned out to be promising in view of their integration into automotive PCM applications.<br/><br/><b>REFERENCES</b><br/>[1] A. Díaz Fattorini <i>et al.</i>, “Growth, Electronic and Electrical Characterization of Ge-Rich Ge–Sb–Te Alloy”, <i>Nanomaterials</i>, 12, 1340,2 022, doi: 10.3390/nano12081340.<br/>[2] S. Cecchi <i>et al.</i>, “Crystallization and Electrical Properties of Ge-Rich GeSbTe Alloys”, <i>Nanomaterials</i>, 12, 631, 2022, doi: 10.3390/nano12040631.