1. Plasma Processing and Technology Laboratory and Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
2. Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124, USA
3. Department of Engineering and System Science, National Tsing Hua University, Hsinchu 300, Taiwan
4. Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA