In situ modification of low-cost Cu electrodes for high-performance low-voltage pentacene thin film transistors (TFTs)

We demonstrate low-voltage pentacene thin film transistors (TFTs) using in situ modified low-cost Cu (M-Cu) as source-drain (S/D) electrodes and solution-processed high capacitance (200 nF/cm(2)) gate dielectrics. Under a gate voltage of -3 V, the device with M-Cu electrodes shows a much higher apparent mobility (1.0 cm(2)/V s), a positively shifted threshold voltage (-0.62 V), a lower contact resistance (0.11 M Omega) and a larger transconductance (12 mu S) as compared to the device with conventional Au electrodes (corresponding parameters are 0.71 cm(2)/V s, -1.44 V, 0.41 M Omega, and 5.7 mu S, respectively). The enhancement in the device performance is attributed to the optimized interface properties between S/D electrodes and pentacene. Moreover, after encapsulation the M-Cu electrodes with a thin layer of Au in the aim of suppressing unfavorable surface oxidation, the electronic characteristics of the device are further improved, and highly enhanced apparent mobility (2.3 cm(2)/V s) and transconductance (19 mu S) can be achieved arising from the increased conductivity of the electrode itself. Our study provides a simple and feasible approach to achieve high performance low-voltage OTFTs with low-cost S/D electrodes, which is desirable for large area applications. (C) 2012 Elsevier B.V. All rights reserved.