Bulk-Accumulation Oxide Thin-Film Transistor Circuits With Zero Gate-to-Drain Overlap Capacitance for High Speed

The overlap between gate and source/drain electrodes gives rise to parasitic capacitance (C-gd), which causes RC signal delay in thin-film transistor (TFT) circuits. Here, we show that in amorphous-indium-gallium-zinc-oxide TFTs, offsets as large as 0.5 mu m, result in only slight reductions in drain-current, such that (compared with single-gate TFTs with 2.5-mu m gate-to-source/drain overlaps) an overall three times increase in switching speed can be achieved in dual-gate TFTs with offset top-gates shorted to offset bottom-gates. The high switching speed (similar to 18 ns/stage delay), which is a combined effect of the bulk-accumulation achieved by shorting the two gates and zero C-gd, results in high-speed amorphous oxide TFT-based circuits.