1. National Key Laboratory of Science and Technology on Vacuum Electronics, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
2. Institute of Electronic Engineering, Chinese Academy of Engineering Physics, Mianyang, 621900, China
3. State Key Laboratory of Electronic Thin Films and Integrated Devices Zhongshan Lab, Department of Electronic Engineering, University of Electronic Science and Technology of China Zhongshan Institute, Zhongshan 528402, China