Inverse Resistance Change Cr₂Ge₂Te₆-Based PCRAM Enabling Ultralow-Energy Amorphization

Abstract

Phase-change random access memory (PCRAM) has attracted much attention for next-generation nonvolatile memory that can replace flash memory and can be used for storage-class memory. Generally, PCRAM relies on the change in the electrical resistance of a phase-change material between high-resistance amorphous (reset) and low-resistance crystalline (set) states. Herein, we present an inverse resistance change PCRAM with CrGeTe (CrGT) that shows a high-resistance crystalline reset state and a low-resistance amorphous set state. The inverse resistance change was found to be due to a drastic decrease in the carrier density upon crystallization, which causes a large increase in contact resistivity between CrGT and the electrode. The CrGT memory cell was demonstrated to show fast reversible resistance switching with a much lower operating energy for amorphization than a GeSbTe memory cell. This low operating energy in CrGT should be due to a small programmed amorphous volume, which can be realized by a high-resistance crystalline matrix and a dominant contact resistance. Simultaneously, CrGT can break the trade-off relationship between the crystallization temperature and operating speed.

Magnetic anisotropy and spin-polarized two-dimensional electron gas in the van der Waals ferromagnet Cr2Ge2Te6

“…layers stack along the crystallographic c axis and are only weakly coupled by van der Waals forces. By virtue of intrinsic magnetic two-dimensionality Cr 2 Ge 2 Te 6 has been proposed, e.g., as magnetic substrate for nanoelectronic devices [12] or as a candidate for next generation memory devices [13]. From the fundamental point of view the observation of intrinsic ferromagnetism in atomically thin films of Cr 2 Ge 2 Te 6 is intriguing [14].…”

Van der Waals 2D Transition Metal Tellurides

“…The I–V curves of Al 2 O 3 /MoTe 2 RRAM devices were shown in Figure a . Koike and co‐workers reported the inverse resistive random access memory (RRAM) based on Cr 2 Ge 2 Te 6 (Figure b) . The faster reversible resistance switch speed and lower operating voltage of Cr 2 Ge 2 Te 6 than Ge 2 Sb 2 Te 5 made it an excellent choice for next‐generation nonvolatile memory application …”

“…b) PCM performance of Cr 2 Ge 2 Te 6 and Ge 2 Sb 2 Te 5 . Reproduced with permission . Copyright 2017, American Chemical Society.…”

Nitrogen doping-induced local structure change in a Cr2Ge2Te6 inverse resistance phase-change material

“…9,10 In contrast to traditional PCMs, a new PCM, Cr 2 Ge 2 Te 6 (CrGT), exhibits inverse electrical property changes upon phase transition and shows an extremely high crystalline resistance. 11 Because of the higher crystalline resistance of CrGT, it was shown to be less heat consuming and to operate at a higher speed, which are preferable performance characteristics over those of the mature GST PCM. [11][12][13][14] Besides, (nitrogen) N-doped CrGT (NCrGT) with a N content of 6.5 at% has also been investigated, and it showed no resistance change during phase transformation.…”

“…11 Because of the higher crystalline resistance of CrGT, it was shown to be less heat consuming and to operate at a higher speed, which are preferable performance characteristics over those of the mature GST PCM. [11][12][13][14] Besides, (nitrogen) N-doped CrGT (NCrGT) with a N content of 6.5 at% has also been investigated, and it showed no resistance change during phase transformation. 15 However, the NCrGT-based PCRAM cell can still achieve a typical threshold switching with a three-orders-of-magnitude resistance contrast, which can be attributed to an interfacial property difference (i.e., contact resistance contrast) between the amorphous NCrGT/electrode contact and crystalline NCrGT/electrode contact.…”