Improved Negative Bias Illumination Stability and Thermal Stability of HfZnSnO/ZnSnO Thin-Film Transistor Using Double-Channel Structure by Cosputtering

Double-channel structure HfZnSnO/ZnSnO thin-film transistors (HZTO/ZTO TFTs) with a high electrical property and a superior stability under negative bias illumination stress (NBIS) or temperature stress (TS) is fabricated by cosputtering. Double-channel structure HZTO/ZTO TFT only suffers from 1.4 V negative threshold voltage shift (ΔVT) under the same NBIS and 6.3 V negative ΔVTunder the same TS, but its mobility can also stay appropriately 8 cm2/Vs. The high performance, superior NBIS stability, and superior TS stability of HZTO/ZTO TFT are due to the effect of Hf doping on suppression of oxygen vacancies in HZTO top channel layer and high carrier concentration in a ZTO bottom channel layer, which can be confirmed by X-ray photoelectron spectroscopy (XPS) measurement and Hall effect measurement. In addition, based on the measurement of IDS-VGunder various temperatures, the density of states (DOS) can be extracted from thermally excited drain current. The HZTO/ZTO TFT shows fewer DOSs than that of single ZTO TFT, and it is comparable with that of single HZTO TFT. This result can be well matched with the TS stability, NBIS stability, and XPS measurement.