1. Graduate Institute of Electronic Engineering, National Taiwan University, Taipei 10617, Taiwan
2. Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
3. Taiwan Semiconductor Research Institute, Hsinchu 30078, Taiwan
4. Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
5. Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87123, USA