1. Microsystem Research Center, KIST, , 39-1 Haweolgog-dong, Seongbuk-gu, Seoul, 136-791, Korea
2. Department of Ceramic Eng., Hanyang University , 17 Hangdang-Dong, Seongdong-Gu, Seoul, 133-791, Korea
3. Department of Mater. Sci. and Eng., KAERI, , 150 Duckjin-dong, Yuseong-gu, Daejeon, 305-353, Korea