title: Enhanced nanoscale resistive switching memory characteristics and switching mechanism using high-Ge-content Ge0.5Se0.5 solid electrolyte.
abstract: We demonstrate enhanced repeatable nanoscale bipolar resistive switching memory characteristics in Al/Cu/Ge0.5Se0.5/W, as compared with Al/Cu/Ge0.2Se0.8/W structures, including stable AC endurance (>105 cycles), larger average SET voltage (approximately 0.6 V), excellent data retention (>105 s) at 85°C, and a high resistance ratio (>104) with a current compliance of 8 μA and a small operation voltage of ±1.5 V. A small device size of 150 × 150 nm2 and a Cu nanofilament with a small diameter of 30 nm are both observed by high-resolution transmission electron microscope in the SET state. The GexSe1 - x solid electrolyte compositions are confirmed by both energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The switching mechanism relies on the smaller barrier heights for holes rather than for electrons; the positively charged Cuz+ ions (i.e., holes) migrate through the defects in the GexSe1 - x solid electrolytes during SET/RESET operations. Hence, the Cu nanofilament starts to grow at the Ge0.5Se0.5/W interface, and starts to dissolve at the Cu/Ge0.5Se0.5 interface, as illustrated in the energy band diagrams. Owing to both the higher barrier for hole injection at the Cu/Ge0.5Se0.5 interface than at the Cu/Ge0.2Se0.8 interface and greater thermal stability, the resistive switching memory characteristics of the Al/Cu/Ge0.5Se0.5/W are improved relative to the Al/Cu/Ge0.2Se0.8/W devices. The Al/Cu/Ge0.5Se0.5/W memory device can also be operated with a low current compliance of 1 nA, and hence, a low SET/RESET power of 0.61 nW/6.4 pW is achieved. In addition, a large memory size of 1,300 Pbit/in2 is achieved with a small nanofilament diameter of  0.25 Å for a small current compliance of 1 nA.
authors.affiliation: Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan, 333, Taiwan. sidhu@mail.cgu.edu.tw.
authors.forename: Sheikh Ziaur
authors.initials: SZ
authors.lastname: Rahaman
authors.forename: Siddheswar
authors.initials: S
authors.lastname: Maikap
authors.forename: Atanu
authors.initials: A
authors.lastname: Das
authors.forename: Amit
authors.initials: A
authors.lastname: Prakash
authors.forename: Ya Hsuan
authors.initials: YH
authors.lastname: Wu
authors.forename: Chao-Sung
authors.initials: CS
authors.lastname: Lai
authors.forename: Ta-Chang
authors.initials: TC
authors.lastname: Tien
authors.forename: Wei-Su
authors.initials: WS
authors.lastname: Chen
authors.forename: Heng-Yuan
authors.initials: HY
authors.lastname: Lee
authors.forename: Frederick T
authors.initials: FT
authors.lastname: Chen
authors.forename: Ming-Jinn
authors.initials: MJ
authors.lastname: Tsai
authors.forename: Liann-Be
authors.initials: LB
authors.lastname: Chang