Flexible electronics has recently attracted much attention because of their potential in providing cost-efficient solutions to large-area applications such as rollable displays and TVs, e-paper, smart sensors and transparent RFIDs. The key advantages of flexible electronics, compared with current silicon technologies, are low-cost manufacturing (e.g. ink-jet printing and roll-to-roll imprinting) and inexpensive flexible substrates (e.g. plastics). These advantages make flexible electronics an attractive candidate for next-generation consumer products which require lightweight, bendable, portable, and low-cost electronics.