1. Department of Materials Science and Engineering, and Inter-University Semiconductor Research Center, Seoul National University, San 56-1, Shillim-Dong, Kwanak-Gu, Seoul 151-744, Korea
2. Technology Development Team 2, System-LSI Division, Samsung Electronics Co., Ltd., San 24, Nongseo-Dong, Kiheung-Gu, Yongin-City, Kyungki-Do 449-900, Korea