Performance of 5-nm a-IGZO TFTs With Various Channel Lengths and an Etch Stopper Manufactured by Back UV Exposure

Stable and fast-switching thin-film transistors and circuits incorporating 5-nm-thick amorphous-InGaZnO (a-IGZO) active layers are demonstrated, and their dependence on channel length is studied. Turn-on voltage shifts in the positive gate voltage direction as the channel length increases. A low area density of defects in the bulk a-IGZO, which is ultrathin, results in good stability under positive bias stress, whereas interdiffusion of electrons/electron donors from the highly doped source and drain regions to the channel edges results in the dependence of turn-on voltage on channel length. Stable operation of an 11-stage ring oscillator is achieved with a propagation delay time of ~97 μs/stage due to reduced gate-to-drain overlap capacitance and parasitic resistances.