1. Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Korea
2. Department of Mechanical Engineering, Dong-A University, Busan 49315, South Korea
3. Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics, 445-701, South Korea
4. Research Institute of Advanced Materials and Inter-university Semiconductor Research Center, Seoul National University, Seoul 08826, South Korea