1. a Research and Development Division , Hynix Semiconductor Inc. , San 136-1, Ami-ri, Bubal-eub, Ichon-si, Kyoungki-do, 467-701, Korea
2. b Research Center for Sustainable Device & ECo-Materials (ReSEM) , Chungju National University , 123 Gumdan-ri, Iryu-myeon, Chungju-si, Chungbuk, 380-702, Korea