1. College of Information Science and Technology, Jinan University, Guangzhou 510632, PR China
2. State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science & Technology of China, Chengdu, Sichuan 610054, PR China
3. Zhongshan Branch of State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Zhongshan Institute, Zhongshan, Guangdong 528402, PR China