1. IT Nano Electronic Device Laboratory, Department of Electrical and Electronic Engineering, Yonsei University, Seodaemun-gu, Seoul 120-749, South 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. Department of Smart Electric, Korea Polytechnic, 23, Yeomjeon-ro, 333beon-gil, Nam-gu, Incheon 22121, South Korea
4. College of Information Science and Technology, Donghua University, 2999 North Renmin Road, Songjiang District, Shanghai 201620, China