1. School of Electronic Science and Engineering (National Exemplary School of Microelectronics), University of Electronic Science and Technology of China, Chengdu 610054, China
2. Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
3. School of Electronic Information and Electrical Engineering, Chengdu University, Chengdu 610106, China
4. Department of Mechanical Engineering, University of Houston, Houston, Texas 77204, USA