High contact resistivity enabling low-energy operation in Cr${}_2$Ge${}_2$Te${}_6$-based phase-change random access memory

A phase-change material (PCM) exhibiting a significant difference in resistance between the amorphous and crystalline phases can be used for phase-change random access memory (PCRAM). Reduction of the energy to operate is one of the major challenges in PCRAM technology. One strategy for energy reduction is to increase the resistance of the memory device in the crystalline state of the PCM. Cr${}_2$Ge${}_2$Te${}_6$ (CrGT) shows p-type semiconductor characteristics in both the amorphous and crystalline phases. A CrGT-based memory device shows a contact resistance-dominant behavior, suggesting that the resistance of a CrGT-based memory device can be increased by changing the electrode material. The contact resistivity (ρ${}_c$) of a CrGT/electrode increases with a decrease in the work function of the electrode material in both amorphous and crystalline phases, as with general p-type semiconductor materials. The highest ρ${}_c$ is observed for a LaB${}_6$ electrode. The resistance of the CrGT-based device with a LaB${}_6$ electrode (LaB${}_6$ device) is three or four orders of magnitude greater than that of a device with a W electrode (W device). The LaB${}_6$ device is indicated to require much smaller operation energy than the W device. (© 2020 Wiley‐VCH GmbH)