1. Low Energy Electronic Systems IRG (LEES), Singapore-MIT Alliance for Research and Technology, 1 CREATE Way, Singapore 138602
2. National University of Singapore, 21 Lower Kent Ridge Rd, Singapore 119077
3. Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
4. School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore