1. School of Electrical Engineering, Kookmin University, Seoul 02707, Korea
2. Mechatronics R&D Center, Samsung Electronics, Gyeonggi-do 18448, Korea
3. Department of Nano-process, National Nanofab Center (NNFC), Daejeon 34141, Korea
4. Department of Electrical Engineering, Sejong University, Seoul 05006, Korea