1. Department of Materials Science and State Key Laboratory of ASIC and Systems; Fudan University; Shanghai 200433 P. R. China
2. Center for Bio-Integrated Electronics; Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana Champaign; Northwestern University; Evanston IL 60208 USA
3. Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology; School of Physics Science and Engineering; Tongji University; Shanghai 200092 P. R. China
4. Shanghai Institute of Microsystem and Information Technology; Chinese Academy of Sciences; Shanghai 200050 P. R. China