1. Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi’an Jiaotong University, 710049 Xi’an, China
2. School of Electronic Science and Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China
3. School of Information Science and Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China
4. Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131-0001, USA
5. Beijing Vacuum Electronics Research Institute, Beijing 100015, China
6. Extreme Energy-Density Research Institute Nagaoka, University of Technology, Nagaoka, 940-2188 Niigata, Japan
7. School of Electronics Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China