1. Key Laboratory of Microelectronic Devices and Integrated Technology Institute of Microelectronics Chinese Academy of Sciences Beijing 100029 China
2. School of Integrated Circuits University of Chinese Academy of Sciences Beijing 100049 China
3. Department of Electrical Engineering and Computer Sciences University of California Berkeley CA 94720 USA
4. School of Microelectronics University of Science and Technology of China Hefei 230026 China
5. School of Microelectronics Northwestern Polytechnical University Xi'an 710072 China
6. Department of Physics Xiamen University Xiamen 361005 China