Energy-Efficient Nonvolatile SRAM Design Based on Resistive Switching Multi-Level Cells. - Sun, Yanan; Gu, Jiawei; He, Weifeng; Wang, Qin; Jing, Naifeng; Mao, Zhigang; Qian, Weikang; Jiang, Li (IEEE Transactions on Circuits & Systems. Part II: Express Briefs, 2019)