Paper EM-WeM11
Effects of Different Organic Passivation Layers on the Electrical Stabilities of Flexible Organic Thin Film Transistors under Cyclic Bendin

Wednesday, November 11, 2009, 11:20 am, Room B1

One of the critical issues for applications of flexible organic thin film transistors (OTFTs) for flexible electronic systems is the electrical stabilities of the OTFT devices, including variation of the current on/off ratio (I_on/I_off), leakage current, threshold voltage, and hysteresis, under repetitive mechanical deformation. In particular, repetitive mechanical deformation accelerates the degradation of device performance at the ambient environment. In this work, electrical stabilities of the pentacene organic thin film transistors (OTFTs) employing various passivation layers were investigated under mechanical cyclic bending. Flexible bottom-gated pentacene-based OTFTs fabricated on flexible polyimide substrate with poly-4-vinyl phenol (PVP) dielectric as a gate dielectric were passivated by the solution-processed, evaporated, and plasma-deposited organic layers. For cyclic bending experiment of flexible OTFTs, the devices were cyclically bent up to 10⁵ times with 5 mm bending radius. In the most of the devices after 10⁵ times of bending cycles, the off-current of the OTFT with no passivation layers was quickly increased due to increases in the conductivity of the pentacene caused by doping effects from O₂ and H₂O in the atmosphere, which leads to decrease in the I_on/I_off and increase in the hysteresis. With passivation layers, however, the electrical stabilities of the OTFTs were improved significantly. In particular, the OTFTs with plasma-deposited organic layers showed the best electrical stabilities up to the bending cycles of 10⁵ times compared to the devices with the solution-processed or thermal-evaporated organic layer. Changes in electrical properties of cyclically bent OTFTs with different organic passivation layers will be compared and discussed in detail.