1. State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China
2. Engineering Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20878, USA
3. Department of Electrical and Computer Engineering, George Mason University, Fairfax, Virginia 22030, USA
4. Institute for Advanced Materials, South China Normal University, Guangzhou 510006, China