Threshold voltage shifts in top-gate Al-doped ZnO TFTs by adjusting the position of Al dopant layer during the atomic-layer deposition process

We investigated the effects of controlling the relative positions of Al dopant layers on the device characteristics of the thin-film transistors using Al-doped ZnO (AZO) active channels for the first time. The position control was accomplished by the cycle designs of atomic-layer deposition process for the AZO channels. When the Al dopant layer was positioned at relative bottom sides of the channel, the turn-on operations were performed at smaller negative gate voltages in their transfer characteristics. Other device properties including the positive bias stability did not show any marked variations among the devices. The distance between the incorporated Al dopant layers had also impacts on the TFT characteristics. Concentrated positioning of two cycles of Al doping layers was found to severely degrade the current drivability due to the decrease in carrier mobility. Further optimization of this technique would be very helpful to enhance the device performance of the AZO TFTs for practical transparent electronics applications.