1. Department of Materials Science and State Key Laboratory of ASIC and systemFudan University Shanghai 200433 P. R. China
2. State Key Laboratory of Functional Materials for InformaticsShanghai Institute of Microsystem and Information TechnologyChinese Academy of Sciences Shanghai 200050 P. R. China
3. Department of PhysicsUniversity of Seoul Seoul 02504 Republic of Korea
4. State Key Laboratory of ASIC and SystemSchool of MicroelectronicsFudan University Shanghai 200433 P. R. China