1. IT Nano Electronic Device Laboratory, Department of Electrical and Electronic Engineering, Yonsei University, 134 Shinchon-Dong, Seodaemun-gu, Seoul 120-749, Republic of Korea
2. National Center for Nanoprocess and Equipment, Korea Institute of Industrial Technology, 6 Cheomdangwagi-ro 208beon-gil, Buk-gu, Gwangju 500-480, South Korea
3. Electrical Engineering, Changwon National University, 20 changwondaehak-ro, Unichang-gu, Changwon, Gyeonnam, 51140, Korea