Tsurumaki-Fukuchi Atsushi, Tsubaki Keiji, Katase Takayoshi, Kamiya Toshio, Arita Masashi, Takahashi Yasuo
Graduate School of Information Science and Technology, Hokkaido University, Kita-14, Nishi-9, Kita-ku, Sapporo 060-0814, Japan.
Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan.
ACS Appl Mater Interfaces. 2020 Jun 24;12(25):28368-28374. doi: 10.1021/acsami.0c05181. Epub 2020 Jun 9.
Owing to the recent discovery of the current-induced metal-insulator transition and unprecedented electronic properties of the concomitant phases of calcium ruthenate CaRuO, it is emerging as an important material. To further explore the properties, the growth of epitaxial thin films of CaRuO is receiving more attention, as high current densities can be applied to thin-film samples and the amount can be precisely controlled in an experimental environment. However, it is difficult to grow high-quality thin films of CaRuO due to the easy formation of the crystal defects originating from the sublimation of RuO; therefore, the metal-insulator transition of CaRuO is typically not observed in the thin films. Herein, a stable current-induced metal-insulator transition is achieved in the high-quality thin films of CaRuO grown by solid-phase epitaxy under high growth temperatures and pressures. In the CaRuO thin films grown by ex situ annealing at >1200 °C and 1.0 atm, continuous changes in the resistance of over 2 orders of magnitude are induced by currents with a precise dependence of the resistance on the current amplitude. A hysteretic, abrupt resistive transition is also observed in the thin films from the resistance-temperature measurements conducted under constant-voltage (variable-current) conditions with controllability of the transition temperature. A clear resistive switching by the current-induced transition is demonstrated in the current-electric-field characteristics, and the switching currents and fields are shown to be very stable. These results represent a significant step toward understanding the high-current-density properties of CaRuO and the future development of Mott-electronic devices based on electricity-driven transitions.
由于最近发现了电流诱导的金属-绝缘体转变以及钙钌酸盐CaRuO伴随相前所未有的电子特性，它正成为一种重要的材料。为了进一步探索其性质，CaRuO外延薄膜的生长受到了更多关注，因为可以对薄膜样品施加高电流密度，并且在实验环境中量可以精确控制。然而，由于容易形成源于RuO升华的晶体缺陷，很难生长出高质量的CaRuO薄膜；因此，在薄膜中通常观察不到CaRuO的金属-绝缘体转变。在此，通过在高生长温度和压力下进行固相外延生长，在高质量的CaRuO薄膜中实现了稳定的电流诱导金属-绝缘体转变。在通过高于1200°C和1.0 atm的异位退火生长的CaRuO薄膜中，超过2个数量级的电阻连续变化是由电流引起的，电阻对电流幅度有精确的依赖性。在恒压（变电流）条件下进行的电阻-温度测量中，薄膜中还观察到滞后的、突然的电阻转变，且转变温度具有可控性。在电流-电场特性中证明了由电流诱导转变引起的明显电阻开关，并且开关电流和电场显示出非常稳定。这些结果代表了在理解CaRuO的高电流密度特性以及基于电驱动转变的莫特电子器件未来发展方面迈出的重要一步。
