Zinc tin oxide thin film transistor: Effect on channel isolation and channel width

The n-channel field-effect thin-film transistors (TFTs) with amorphous zinc tin oxide as an active layer has been investigated. The transparent ZTO thin films deposited at room temperature using rf magnetron sputtering have an optical bandgap of 3.3 eV. Before the fabrication of TFT postdeposition annealing of the film was carried out 300°C for 1 hour. The channel layer on Si/SiO2 substrate was deposited in two different structures, isolating each device from the neighboring devices and without isolation. The isolation of active material improves TFT performance by reducing the gate leakage current and parasitic bias stress. The on-off ratio and subthreshold swing were significantly changed from 2.3x103 and 0.73 V/dec to 2.55x106 and 0.23 V/dec respectively on isolation. The effect of channel width on the TFT parameters such as saturated mobility, subthreshold swing and threshold voltage are also studied. The threshold voltage decreases with increasing channel width but mobility and subthreshold swing are relatively constant. The threshold voltage decreased from 19 V to 11 V when the channel width increased. It may be due to the increasing parasitic resistance between the source/drain contacts and the ZTO channel layer.