1. Department of Electrical and Computer Engineering University of Virginia Charlottesville VA 22904 USA
2. School of Electronic Engineering Soongsil University 06938 Seoul South Korea
3. Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge MA 02139 USA
4. Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA
5. Department of Intelligent Semiconductors Soongsil University Seoul 06938 South Korea
6. Department of Material Science and Engineering University of Virginia Charlottesville VA 22904 USA