1. Department of Nanoscale Semiconductor Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, South Korea
2. Department of Electrical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, South Korea
3. Plasma Technology Research Center, National Fusion Research Institute, 37 Dongjangsan-ro, Gunsan, Jeonbuk 54004, South Korea