Optically Transparent Flexible IGZO TFTs Fabricated with a Selective Wet-Etch Process

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Given the relatively poor selectivity to common semiconductor etchants, IGZO (InGaZnO) thin film transistors (TFTs) are typically fabricated using lift-off processes to define the electrical contacts. However, the success of the emerging transition-metal oxide materials system for flexible electronics requires compatibility with conventional TFT fabrication processes. In this research, flexible IGZO TFTs having 85% optical transparency in the visible regime were fabricated on polyethylene napthalate (PEN) substrates using a selective wet etching process to eliminate the need for lift-off processing. The devices were processed directly onto the plastic platform at the maximum temperature of 150°C. The fabricated TFTs exhibited a field-effect mobility of ~12.5 cm2/V.sec, threshold voltage of ~5.0 V, and an Ion/Ioff ratio of <106. No current crowding behavior was observed for the TFTs at the low drain-source voltage (VD) regime. The highly selective etching process provides a means to fabricate IGZO based circuits with low processing complexity that will enable system-on-“plastic” integration of flexible transparent flexible displays.