1. Department of Electronic Engineering, National Changhua University of Education, No. 2, Shi-Da Rd., Changhua 500, Taiwan
2. Department of Electronic Engineering, Ming Chi University of Technology, No. 84, Gongzhuan Rd., Taishan Dist., New Taipei City 243, Taiwan
3. Department of Electrical Engineering, National Dong Hwa University, No. 1, Sec. 2, Da Hsueh Rd., Shoufeng, Hualien 974, Taiwan
4. Department of Physics, National Changhua University of Education, No. 1, Jin-De Rd., Changhua 500, Taiwan
5. Department of Materials Science and Engineering, National Chung Hsing University, No. 145, Xingda Rd., South Dist., Taichung 402, Taiwan