Threshold voltage control of a thin-film transistor using an Al–Zn–O channel prepared using atomic layer deposition by controlling the Al dopant positions

Abstract

We proposed a methodology for controlling the threshold voltage (V_TH) by adjusting the position of the Al dopant layer within an Al-doped-ZnO (AZO) active channel of a thin film transistor (TFT). The position of the Al dopant layer was controlled by inserting the Al cycle sequences at the 13^th, 19^th, 38^th, and 44^th cycles among a total of 50 cycles during the atomic layer deposition process. Each designed position of the Al layers was confirmed by secondary ion mass spectroscopy. The crystallinity and temperature-dependent electrical conductivity of the prepared AZO films were found to show no remarkable differences irrespective of the changes in position of the Al dopant layers. On the other hand, when the AZO films prepared with various Al dopant positions were used for active channels, the V_TH of the TFT was significantly modulated. When the Al source was introduced at the 13^th, 19^th, 38^th, and 44^th cycles from the lower side of the channel, the V_TH of AZO-TFT showed remarkable variations from −5.1 to −13.9 V without any marked change in field-effect carrier mobility. Furthermore, the negative and positive bias-stress stabilities were shown to be almost the same for all the fabricated AZO TFTs with different Al dopant layer positions. The V_TH was effectively modulated for the AZO TFTs without any degradation of carrier mobility or bias stability.