FLEXIBLE ELECTRONICS ARE emerging as an alternative to conventional silicon electronics for applications such as large-area sensors, flexible displays, foldable solar cells, and disposable RFID tags. Flexible displays on low-cost plastic substrates are as much as 95percent thinner and 90percent lighter in weight than conventional LCD displays on glass substrates. Mechanically, flexible displays withstand bending and folding--even crushing--many thousands of times beyond what is possible with conventional displays. In addition, flexible electronics and displays can be made by "printing," a process as simple as the printing of newspapers and magazines. The manufacturing cost and time-to-market of flexible electronics, therefore, can offer significant savings over silicon electronics that require a sophisticated manufacturing process and high nonrecurring expense. In this review article, we compare thin-film transistors (TFTs) with their silicon CMOS counterparts and introduce key TFT technologies for implementing flexible circuits and display backplanes. We also discuss design advances and techniques for digital circuits such as zero-V_(GS) and pseudo-CMOS, as well as gain-enhancement and variation-cancelation methods for analog circuits. Finally, we highlight implementation practices for applications in sensing, display, and RFID tags based on printed TFT technologies.
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