1. Department of Materials Science and EngineeringNational Chiao Tung University University Rd. 1001 Hsinchu 30010 Taiwan
2. IMEC Kapeldreef 75 Leuven B-3001 Belgium
3. Division of Applied PhysicsFaculty of Pure and Applied ScienceUniversity of Tsukuba Tsukuba Ibaraki 305-8573 Japan
4. Department of Electrical EngineeringKatholieke Universiteit Leuven Kasteelpark 10 B-3001 Leuven Belgium