R&D: Importance of Contacts in Cu2GeTe3 Phase Change Memory Devices

Journal of Applied Physics has published an article written by Satoshi Shindo, Yi Shuang, Shogo Hatayama, epartment of Materials Science, Graduate School of Engineering, Tohoku University, 6-6-11 Aoba-yama, Sendai, Miyagi 980-8579, Japan, Yuta Saito, Device Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, Higashi 1-1-1, Tsukuba, Ibaraki 305-8565, Japan, Paul Fons, Device Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, Higashi 1-1-1, Tsukuba, Ibaraki 305-8565, Japan, and Department of Electronics and Information Engineering, Faculty of Science and Technology, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan, Alexander V. Kolobov, Device Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, Higashi 1-1-1, Tsukuba, Ibaraki 305-8565, Japan, and Department of Physical Electronics, Faculty of Physics, Herzen State Pedagogical University of Russia, 48 Moika Embankment, St. Petersburg 191186, Russia, Keisuke Kobayashi, Research Institute of Kochi University of Technology, Tosa yamada, Kami City, Kochi 782-8502, Japan, and Institute of Materials and Systems for Sustainability, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan, and Yuji Sutou, Department of Materials Science, Graduate School of Engineering, Tohoku University, 6-6-11 Aoba-yama, Sendai, Miyagi 980-8579, Japan.

Abstract: “Cu₂GeTe₃ (CGT) is a promising phase change material for phase change random access memory (PCRAM) applications because of its high thermal stability in the amorphous phase and its capability to undergo rapid phase change. In this paper, the electrical conduction mechanism of a CGT memory device fabricated using W electrodes (W/CGT) was investigated using current–voltage (I–V) measurements and angle resolved hard x-ray photoelectron spectroscopy (AR-HAXPES). The I–V characteristics of the W/CGT memory device were found to display non-linear behavior in the RESET (amorphous) state, while linear behavior was observed in the SET (crystalline) state, indicating that the W/CGT memory device exhibited Schottky conduction in the RESET state, but Ohmic conduction in the SET state. The effective Schottky barrier height was found to increase linearly as the ideality factor decreased to unity with the ideal W/CGT Schottky barrier height in the RESET state estimated to be 0.33 eV, a value in good agreement with the directly measured Schottky barrier height of 0.35 eV between W and amorphous CGT by AR-HAXPES measurements. These results suggest that the interface between the metal electrode and the phase change material plays an important role in PCRAM devices, and its comprehensive understanding is necessary for future application development.“

ACKNOWLEDGMENTS
This work was supported by the JSPS KAKENHI (Grant Nos. 15H04113, 17J03876, and 18H02053). A.V.K. acknowledges financial support from the Ministry of Education of the Russian Federation (project No. FSZN-2020-0026). The authors acknowledge Professor Junichi Koike for valuable discussions and comments. The synchrotron radiation experiments were performed at beamline BL47XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2015B1204).