1. Department of Digital Game and Animation Design, Tung Fang Design Institute, Kaohsiung 829, Taiwan
2. Department of Electrical Engineering, National Cheng Kung University, Tainan 701, 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