[1] Peking Univ, Microelect Lab, Beijing 100871, Peoples R China
[2] Minist Educ, Key Lab Microelect Devices & Circuits, Beijing 100871, Peoples R China
[3] Semicond Mfg Int Corp, Beijing 100176, Peoples R China
[4] SUNY Albany, Coll Nanoscale Sci & Engn, Albany, NY 12203 USA