Schottky-contact gated-four-probe a-Si:H TFT structure: a new structure to investigate the electrical instability of a-Si:H TFT

In this letter, we describe a new device structure, the Schottky-contact (SC) gated-four-probe (GFP) hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) structure, that can be used to study the electrical instability of a-Si:H TFTs induced by bias-temperature-stress (BTS). In this SC-GFP TFT structure, the evolution of both electron and hole conduction characteristics can he studied before and after BTS without the influence of source-drain contacts. We observed that low-bias negative stress induces a reduction in the deep-gap state density, while high-bias negative stress mainly causes trapping of holes in the gate-insulator. On the other hand, positive BTS induces mainly the trapping of electrons in the gate-insulator, which causes positive shifts of both electron and hole conduction characteristics.