We have investigated the time and temperature dependence of a threshold voltage shift and also investigated charge detrapping effects. The temperature strongly influences the threshold voltage shift. We have found that the detrapping effect of the charge is larger when the negative bias and illumination are applied simultaneously than when the negative bias only is applied. Specially the former mostly recovers the annealed state at 75c. Illumination with the negative bias has no effect on off current change (Staebler-Wronski effect) because of depletion layer at interface by the negative bias. Charge trapping and detrapping effects are mostly the conduction in the silicon nitride by hopping. This is a principle instability in a-Si:H TFTs. We have found that the positive bias and illumination has larger effect on threshold voltage shift than the positive bias only. We also have investigated the effects of a-Si:H thicknesses.
We also investigated the effects of a-Si:H thicknesses, measuring source-drain current. We have obtained the following results. At first, the thickness of a-Si:H have effects on off current. Secondly, that of a-Si:H is related with charge trapping.
