Advances in Organic Thin-Film Transistor Technology for Flexible Analog Front Ends in Wearable Electronics

Recent development in health monitoring applications have heightened the need for wearable devices to acquire human bio-electrical and bio-chemical signals. To realize sampling of these signals, it is urgent to develop highly customizable analog front-ends that meet diverse processing and performance requirements such as low cost manufacturing, unique form factor for flexibility, and accurate acquisition of signal under strict power constraint. Organic thin-film transistor (OTFT), owning superior mechanical flexibility and feasibility of being manufactured on arbitrary plastics, is regarded as a promising technology platform for developing such customized front-ends. This paper gives a brief overview of the recent development of OTFT-based analog front-ends applied in wearable electronics. The key performance indicators of state-of-the-art OTFTs, including sub-60 mV/dec switching, high transconductance efficiency of 38.7 S/A, and operation at 1 volt, are presented, highlighting their potential for application in flexible and wearable electronics. The commonly used device structures, material stacks and manufacturing strategies for flexible low voltage device technology are firstly discussed. Efforts devoted to OTFT-based analog front-end circuits and systems, including amplifier, analog-to-digital converter and power management circuit, are then introduced. Finally, the remaining challenges to address for future development of advanced OTFT front-ends are clarified. This review will provide guidelines for processing and design of flexible OTFT analog front-end for wearable electronics.