1. Department of Materials Science and Engineering and Inter-University Semiconductor Research Center; Seoul National University; Gwanak-ro 1, Daehag-dong Gwanak-gu Seoul 151-744 Republic of Korea
2. SK Hynix Inc.; 2091 Gyeongchung-daero, Bubal-eub Icheon-si Gyeonggi-do 467-734 Republic of Korea