Flexible double gate a-IGZO TFT fabricated on free standing polyimide foil

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 foil. Due to the temperature sensitivity of the plastic substrate, a-IGZO is a suitable semiconductor because it provides carrier mobilities around 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 78% increased gate capacitance, a by 700 mV higher threshold voltage, and therefore an up to 92% increased transconductance when characterized at the same gate voltage above threshold (over-bias voltage). 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 of double gate TFTs compared to bottom gate TTFs is investigated, and device operation is shown while the double gate TFT is exposed to tensile strain of 0.55%, induced by bending to a radius of 5 mm.

► Fabrication of flexible double gate TFTs using a 10 nm thick Al2O3 gate oxide.
► Double gate TFTs exhibit a by 92% increased gm when compared to single gate TFTs.
► Subthreshold swing of 69 mV/dec and on/off current ratio of 2 × 109.
► Device operation under mechanical stain induced by bending to a radius of 5 mm.