Low-voltage organic thin-film transistors with π-σ-phosphonic acid molecular dielectric monolayers

Pentacene-based organic thin-film transistors (OTFTs) have been fabricated using pi-sigma-phosphonic acid self-assembled monolayers (SAMs) on top of aluminum oxide as the gate dielectrics. With ultrathin dielectrics, high capacitances up to 760 nF/cm(2) and low leakage current densities of 10(-8) A/cm(2) at 2 V could be obtained, allowing operation of OTFTs within -3 V. Vast improvements in the gate leakage current (similar to 2 orders), on/off current ratio (1 order), and subthreshold slope down to 85 mV/decade are achieved compared to control devices without SAMs. The OTFTs with pentacene vapor deposited at room temperature on SAM dielectrics-modified substrates exhibit mobilities of 0.14-0.30 cm(2)/V s, on/off current ratios of 10(5), and threshold voltages of -(1.3-1.5) V. (C) 2008 American Institute of Physics.