Mechanically flexible double gate a-IGZO TFTs

In this paper, the concept of double gate transistors is applied to mechanically flexible amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin film transistors (TFTs) fabricated on free standing plastic foils. Due to the temperature sensitivity of the plastic substrate, a-IGZO is a suitable semiconductor since it provides carrier mobilities of ~ 10 cm²/Vs when deposited at room temperature. Double gate TFTs with connected bottom and top gate are compared to bottom gate reference TFTs fabricated on the same substrate. Double gate a-IGZO TFTs exhibit a by 74% increased gate capacitance, a by 0,7 V higher threshold voltage, and therefore an up to 51% increased transconductance. The subthreshold swing and the on/off current ratios are improved as well, and reach excellent values of 69 mV/dec and 2×10⁹, respectively. The mechanical flexibility is demonstrated by showing device operation while the TFT is exposed to tensile strain of 0.55%, induced by bending to a radius of 5 mm.