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. Department of Electrical and Electronic Engineering, Jeonju University, 303 Cheonjam-ro, Wansan-gu, Jeonju-si, Jeollabuk-do 55069, Republic of Korea
3. College of Information Science and Technology, Donghua University, 2999 North Renmin Road, Songjiang District, Shanghai 201620, China