1. Institute of Microelectronics, Department of Electrical Engineering, National Cheng-Kung University, Tainan 701, Taiwan
2. Institute of Electronics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
3. Department of Electrical Engineering and Computer Science, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
4. Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan
5. Department of Physics, Konkuk University, Seoul 05029, Korea