Threshold Voltage Tuning of Low-Voltage Organic Thin-Film Transistors

There are two critical issues involved in voltages of organic thin-film transistors (OTFTs), i.e., high operating voltages V_op and random distributed threshold voltages V_TH, which lead to high power consumption and unreliable logic function in organic integrated circuits, respectively. This paper demonstrates that both issues can be solved in a single OTFT device by using very thin insulator films. The operating voltages could be reduced to be less than 3 V, without lowering the mobility and the on/off ratio. Using light-enhanced bias stress effect, the threshold voltages can be tuned into the range of -4 to 4 V in OTFTs with SiO₂ or Al₂O₃ as dielectric films, demonstrating that light-enhanced bias stress effect in OTFTs is independent of the dielectric material. The ΔV_TH/V_op ratio is about 3, which is one of the largest threshold-voltage-shifting ratios. It is found that the threshold voltage shifting has a linear relationship with the bias voltage and the light illumination time. This tuning technology is a post fabrication and noninvasive method with negligible influence on the mobility and on/off current ratios.