1. Key Laboratory of Advanced Materials (MOE) School of Materials Science and Engineering Tsinghua University Beijing 100084 P. R. China
2. Center for Brain Inspired Computing Research (CBICR) Tsinghua University Beijing 100084 P. R. China
3. Microelectronics Institute Tsinghua University Beijing 100084 P. R. China
4. School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100082 P. R. China