1. Department of System Semiconductor Engineering, Yonsei University, Seoul 03722, South Korea
2. Department of Materials Science and Engineering, Yonsei University, Seoul 03722, South Korea
3. Center for Neuromorphic Engineering, Korea Institute of Science and Technology (KIST), Seoul 02792, South Korea
4. Department of Electrical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, South Korea