Bulk Accumulation a-IGZO TFT for High Current and Turn-On Voltage Uniformity

We present here an amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) in which the accumulation layer is not only confined to the a-IGZO/gate-insulator interface, but extends the entire depth of the a-IGZO. This bulk accumulation TFT is achieved by the use of top- and bottom-gate, that are electrically tied together, resulting in drain current that is over seven times higher than that of a single-gate device, for an a-IGZO thickness of 10 nm. Thus, high drive current is achieved for a relatively small channel width due to bulk accumulation. Furthermore, being independent of carrier scattering at the interface and owing to the bulk accumulation/depletion, the subthreshold swing is always small and turn-on voltage around zero volts with device-to-device uniformity that is much better than that of single-gate TFTs.