Increase of mobility in dual gate amorphous-InGaZnO₄ thin-film transistors by pseudo-doping

Dual gate amorphous-InGaZnO₄ (a-IGZO) thin-film transistors (TFTs) with a bottom gate that covers the whole channel and a top gate that covers only a small portion of the channel are investigated. It is shown that if the larger gate (bottom gate) is held at constant positive bias, while the smaller gate (top gate) drives the TFT, not only does the V_TH shift negatively but the on-current also increases, resulting in dramatic increase in field-effect mobility (μ_FE). The μ_FE reaches ∼70 cm²/V·s with a bottom gate potential of 15 V - confirming that the carrier mobility of a-IGZO TFTs can be significantly increased by electron doping in the channel. In such a configuration, the larger bottom gate acts as an electron supplier - effectively raising the conductivity of the a-IGZO layer (pseudo-doping). The smaller one works in the usual way, which is to either deplete of or accumulate the channel with carriers.