Flexible and solution-processed organic thin film transistors for high voltage applications

Abstract

6,13-Bis(triisopropylsilylethynyl)pentacene and pentacene high-voltage organic thin film transistors (HVOTFTs) were fabricated on solid and flexible substrates via a low temperature (< 120 °C) solution-processed and vacuum-deposited fabrication methods, achieving breakdown voltages and on/off current ratios beyond -550 V and 10⁶ A/A, respectively, a first of its kind. The HVOTFT design was based on a dual channel architecture, where a gated region enabled FET capabilities and an offset region accommodated the high-voltage. An HVOTFT capable of driving high-voltages ([V[lower case DS]] > 100 V) while being controlled by a relatively low gate-to-source voltage ([V[lower case GS]] < 50 V) will enable new applications on arbitrary and flexible substrates, such as large electrostatic MEMS actuators, electroactive polymers, novel displays, field-emitter arrays for digital x-ray imaging as well as photovoltaic systems on glass. A high-k dielectric Bi₁.₅Zn₁Nb₁.₅O₇ and a low-k organic dielectric parylene-C were incorporated into the HVOTFT process to improve threshold voltage and mobility. Field plate designs and self-assembled monolayers were also explored to enhance the HVOTFT's electrical characteristics by directly controlling the charge carrier distribution within the channel or by improving the charge carrier injection into the organic semiconductor. Moreover, a self-shearing drop cast deposition method has been employed for the HVOTFT for the first time, growing large and highly oriented organic semiconductor grains. Solution-processing will enable room-temperature, air ambient and large-area depositions techniques, reducing fabrication overhead. Furthermore, a self-aligned solution-processing method based on surface energy engineering was developed with self-assembled monolayers to create pre-patterned organic semiconductor channels without the need for etching.