Guest Editors’ Introduction: A Promising Alternative to Conventional Silicon

FLEXIBLE ELECTRONICS ARE emerging as an alternative to conventional silicon electronics for large-area, low-cost applications such as rollable displays and TVs, e-papers, smart sensors, and disposable RFID tags. Through inexpensive manufacturing methods (e.g., ink-jet printing and roll-to-roll imprinting), flexible electronics can be printed on low-cost plastics. This advantage makes flexible electronics attractive for next-generation consumer products that require lightweight, bendable, portable, and low-cost electronics. Device performance and reliability have impeded the widespread adoption of flexible electronics. Thinfilm transistors (TFTs), the key elements of flexible electronics, operate much more slowly and are less reliable than their silicon counterparts. Furthermore, depending on the material properties, TFTs are usually monotype (either por n-type) devices; manufacturing air-stable complementary TFT circuits is challenging and infeasible for most TFT technologies. Existing design and test technologies, therefore, cannot be directly applied to flexible electronics. This special issue of IEEE Design & Test provides an overview on the challenges, the current practice, and the future research directions of design and test of flexible electronics for various applications. In ‘‘Robust Circuit Design for Flexible Electronics,’’ Tsung-Ching Huang et al. review key TFT technologies materials, devices, and the implementation process. The authors present digital and analog design practices for TFT-based circuits and explain that more circuit and system research is needed to circumvent performance constraints and reliability issues. Flexible devices are indispensable for large-area sensor arrays. In ‘‘Materials, Processing, and Testing of Flexible Image Sensor Arrays,’’ William S. Wong et al. review the requirements for flexible image sensor arrays, including materials, mechanical considerations, and implementation. The authors then address sensor array implementation and mechanical strain issues. Whereas mechanical strain can significantly impact the performance of TFT devices, in ‘‘Placement Optimization of Flexible TFT Digital Circuits’’ Chester Liu et al. present a strain-aware placement optimization technique to cope with strain-induced timing failures. The proposed solution suggests several placement modes, including even-distribution, keep-in, and keep-out, for different kinds of bending. Finally, in ‘‘Powering the Future: Organic Solar Cells with Polymer Energy Storage,’’ Yindar Chuo et al. illustrate a flexible self-sustainable energy storage solution of long-lasting solar cells and polymer energy storage films. This research addresses the needs for better energy storage solutions for several exciting applications in surveillance, remote sensing, and mobile computing.