UV Analysis of bottom gate thin film transistor using VisualTCAD

This paper reports the simulation results of bottom gate Thin-Film Transistor (TFT) having SiO₂ as the insulating layer onto a p-type Si substrate with Zinc Oxide (ZnO) channel, using the modelling tool VisualTCAD by Cogenda. Under dark condition, the TFTs exhibited a saturation currents in the range of 20–120 μA, On/Off current ratio of 10⁴, threshold voltages in the range of 1.18–1.32 V and the sub-threshold swings (S) in the range of 0.4–0.7 V/decade, for the different W/L ratios, under an applied gate bias of 2 V. The device behaviour has been further analyzed for its electrical response under UV light, with different optical intensities and wavelengths, for the optimized result of W/L at 30 μm/9 μm. The UV performance analysis of the TFTs, as a sensor, was done under a wide range of UV optical intensities, from 2.5–10 mW cm⁻² and the wavelengths, from 100–300 nm. TFT for the optimized dimensions shows a photo-current gain of more than 150 μA, under similar gate bias voltage of 2 V. It shows that the photo-current increases with rising UV intensities and wavelengths. (paper)