1. Center for Neuromorphic Engineering, Korea Institute of Science and Technology, Seoul 02792, Rep. of Korea
2. Department of Materials Science and Engineering, Korea University, Seoul 02841, Rep. of Korea
3. Materials Science & Engineering, Seoul National University, Seoul 08826, Rep. of Korea
4. Department of Materials Science & Engineering, Seoul National University of Science and Technology, Seoul 01811, Rep. of Korea
5. Division of Nano & Information Technology, Korea University of Science and Technology, Daejon 34316, Rep. of Korea