1. Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan
2. Department of Mathematics and Physical Sciences, General Education, R.O.C. Air Force Academy, Kaohsiung 820, Taiwan
3. Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 701, Taiwan
4. Department of Electronic Engineering, National Kaohsiung Normal University, Kaohsiung 802, Taiwan