1. R&D Division; SK Hynix, Inc.; 2091, Gyeongchung-daero, Bubal-eub Icheon-si Gyeonggi-Do 167-701 Korea
2. Division of Materials Science and Engineering; Hanyang University; Seoul 133-791 Korea
3. Department of Nanoscale Semiconductor Engineering; Hanyang University; Seoul 133-791 Korea