1. Department of Materials Science Fudan University Shanghai 200433 P. R. China
2. School of Microelectronics Shandong University Jinan 250100 P. R. China
3. State Key Laboratory of Functional Materials for Informatics Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai 200050 P. R. China
4. State Key Laboratory of ASIC and Systems Fudan University Shanghai 200433 P. R. China