Flexible electronics based on polysilicon TFTs on steel foil: Fabrication and characterization under strain

Flexible electronics is an emerging technology that offers many advantages compared to the conventional rigid electronic circuits. Flexible electronics has unique features, such as low profile, light weight and good flexibility that enable many new applications, such as flexible displays. Poly-Si TFT on Steel Foil Technology has been successfully demonstrated as a platform for high performance flexible electronics because of its high device mobility, reliability and compatibility with conventional CMOS processes. Depending on the application, flexible electronics will be subjected to different levels of strain. Failure of materials may occur and the characteristics of thin film devices/circuits might change under strain thus, it is important to understand the effects if strain on the flexible electronics system.;In this dissertation, we present the development of flexible electronics with poly-Si TFT technology on steel foils. This discussion includes the fabrication and characterization of poly-Si TFT devices/circuits and displays on steel foils. The results show the average mobility of n- and p-channel poly-Si TFTs are 328 cm2/V˙s and 152 cm2/V·s respectively, and the propagation delay per stage of ring oscillators can reach 1ns or less, which demonstrates the potential of the poly-Si technology on steel foils, for high performance flexible digital circuits. In the second part of the dissertation, we present the effects of mechanical strain on materials of flexible electronics. In particular, the failure mechanisms and failure strain of thin film materials including isolation layers and metal interconnects on steel foil are analyzed. A finite element method is used to simulate the strain distribution on a poly-Si TFT under bending to predict. Finally, the effects of strain on the electrical response of poly-Si TFT devices and circuits are investigated. The results show that electrical characteristics of poly-Si TFT are a function of strain and the response of circuit (ring oscillator) under strain is attributed to the change of TFT characteristics. Poly-Si TFTs on steel foil failed at a tensile strain of 1.2% due to cracking of the channel material.;In conclusion, the work performed in this dissertation validates the compatibility of poly-Si technology on steel foil substrate for large-area microelectronics application and provides a guideline for the design of flexible electronics based on this technology.