1. Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 30010, Taiwan
2. Intelligent Semiconductor Nano-system Technology Research Center, National Yang Ming Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 30010, Taiwan
3. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, USA
4. Taiwan Semiconductor Research Institute, 26 Prosperity Road I, Hsinchu 30010, Taiwan