1. School of Optoelectronic Science and Engineering University of Electronic Science and Technology of China Chengdu 610054 P. R. China
2. School of Materials Science and Engineering The Pennsylvania State University University Park PA 16802 USA
3. School of Computer Science and Engineering University of Electronic Science and Technology of China Chengdu 610054 P. R. China
4. Lab of Dielectric Materials School of Materials Science and Engineering Zhejiang University Hangzhou 310027 P. R. China