Study On Fabrication And Stability Of ZnO-based Thin-film Transistors Via Atomic Layer Deposition Technique

High-performance oxide TFTs have attracted more and more researchers to investigate due to their excellent electric properties and potential applications in flat panel displays.ALD?Atomic Layer Deposition?technique has a lot of advantages,including the high-controllability for composition and thickness,excellent reproducibility,and low deposition temperatures.This paper studied the preparation process,electrical properties and stability of TFT.Main research contents and innovations are as follows:1.One-volt ZnO thin film transistors with ultrathin ALD-ZrO₂ gate dielectricThe high-performance ZnO thin film transistors?TFTs?were fabricated on ITO glass with high-capacitance ALD-processed ZrO₂ as the gate dielectric.The 5 nm ultrathin ZrO₂ film showed a very high areal capacitance of 820 n F/cm² at 20 Hz,a relatively high breakdown field of 14 MV/cm,and low surface root-mean-square?RMS?roughness of 0.22 nm,making it possible for ZnO/ZrO₂ TFT to not only be operated by an ultra-low operating voltage of 1 V but also present a near theoretical limit subthreshold swing of 69 m V/dec..Furthermore,the ZnO TFT with a 5 nm ZrO₂ gate dielectric exhibited excellent performance,such as a high I_on/I_off of 10⁷,large field effect mobility of 36.8 cm²/Vs.The ultra-low operating voltage TFTs exhibited great potential for low-powered electronics applications.2.Enhanced stability in Zr-Doped ZnO TFTs with minor influence on mobility by ALDWe developed a novel method to fabricate Zr-doped ZnO?Zr ZnO?thin films via low-temperature atomic layer deposition?ALD?technique.Zr ZnO films were deposited by DEZ/TDMAZr/H₂O cycles instead of traditional DEZ/H₂O/TDMAZr/H₂O cycles and applied in thin film transistors?TFTs?.It is found that Zr ZnO-TFTs with a Zn-Zr-O:ZnO atomic ratio of 1:49,i.e.,Zr ZnO?1:49?exhibit excellent properties,such as a minimum subthreshold swing?SS?value of 0.37V/dec.,a maximum I_on/I_off value of 2.4×10⁷,a larger mobility of 12.38 cm²/Vs,and a smaller threshold voltage shift(?V_th)of 0.61 V under temperature-stress from 25 to105?,which are superior compared with TFTs with ZnO channel doped by ZrO₂ layer.The stability of ZnO TFTs was improved greatly by Zr-Zn-O doping.Moreover,the field-effect mobility of Zr ZnO-TFTs was rarely influenced.Temperature-stress test was carried out to build up the correlation model in terms of the defect structures,subgap states,and stability.These results could provide a new access to understand the device instability of Zr ZnO TFTs.3.Nitrogen-doped ZnO film fabricated via ALD for ZnON transistorsHigh-performance nitrogen-doped ZnO?ZnON?based thin film transistors?TFTs?were fabricated by atomic layer deposition?ALD?with a rapid purging time of only 5s at a temperature as low as 150?.It is the first time to report ALD ZnON TFT using NH₃ as N source.It is found that ZnON TFT with a N:Zn atomic ratio of 1:19?ZnON1:19?exhibited excellent properties,such as a lower sub-threshold swing?SS?of 0.47V/decade and a smaller?V_th of 0.71 V under the temperature-stress from 25 to 105?.The Ion and Ioff decreased as N doping concentration increased,and ZnON 1:19 TFT presented a high I_on/I_off ratio of 1.75×10⁷.We built a model to explain the reaction mechanism that the moderate amount of N doping could significantly suppress the creation of oxygen defects.As a result,the low consumption optoelectronics provide great inspiration for researchers to construct the next generation high performance wearable and flexible devices.