Solution-Processed Oxide Thin Film Transistors And Applications In Logic Devices

Solution-based method to prepare thin film transistors?TFTs?features with low cost,simple process,controllable component proportion and convenient mass production.It is especially suitable for the exploration of new materials and the determination of optimal technological conditions,and plays an important role in the preparation of transparent display devices and the construction of logic gate devices.In recent years,the preparation technology and electrical performance of TFTs have made great progress.TFTs represented by indium gallium zinc oxide?IGZO?have been industrialized.However,the use of indium as a scarce element limits the cost reduction and wider application of devices,so the development of the indium-free TFTs has urgent market demand and strategic significance.In this dissertation,the application of new metal oxides as dielectric layer is deeply investigated,and the aging stability,light stability and bias interface stability of the TFTs device are studied.In addition,the inexpensive indium-free channel layers have been integrated with the gate dielectric layers to build a series of TFTs,and the application of inverter in logic circuits have been explored.The main results are as follows:1.Solution-derived dysprosium oxide thin films have been prepared to act as the dielectric layer of high-performance indium zinc oxide?IZO?TFTs.IZO TFTs with 10 days aging treatment have demonstrated improved electrical performance,including high current on/off ratio of 1×10⁹,large saturation mobility value of 12.6 cm²·V^-1·s^-1and negligible hysteresis,which can be attributed to the diffused water molecule from the air into film to act as the electron donors.The inverter with operating voltage of 3 V based on IZO TFTs has displayed superior performance,including large gain of 10.1 and good dynamic response behavior.The light stability measurements for TFTs have indicated the white light illuminating TFTs behaves the excellent bias stability with the tiny threshold voltage shift of0.25 V among various lights,which is ascribed that the weaker stimulating photoelectron energy only can activate the electrons to the conduction band without introducing new defects in the interface.The different stabilities for various illuminations show the potential application in photoelectric detectors.2.Solution-derived dysprosium oxide thin films have been prepared to act as the dielectric layer of zinc tin oxide?ZTO?with low cost.Microstructure characterization has shown that the ternary spinel Zn₂SnO₄phase has peaked at the zinc tin proportion of 1:1.After10 days aging treatments,the fabricated TFTs have indicated the dramatic improvement on electrical performance,containing the increased saturation mobility value from 0.57 to 2.5cm²V^-1s^-1,the lifted current on/off ratio from 7.8×10⁴to 2.4×10⁶.The integrated inverter demonstrates a gain of 7.3 and good dynamic response behavior at a operating voltage of 2.5V.The electron transport model in crystal state has displayed that incoherent interfaces tend to form more stable semi-coherent interfaces and liberate the captured electrons.Besides,the exponential model between aging days and hysteresis variation has been proposed for the first time,and the detected aging stability is not only related to the annealing temperature,but also relevant to interface compatibility factors.3.Solution-driven ytterbium oxide films have been prepared to act as the dielectric layer of ZTO TFTs with low operating voltage.The annealed TFTs behave the large saturation mobility value of 9.1 cm²V^-1s^-1and the high current on/off ratio of 2.15×10⁷,which even surpass that of the reported indium-based TFTs.The built inverter displays a gain of 5.6 and good dynamic response behavior at the operating voltage of 2 V.The energy band diagrams have been modeled to explain the hump phenomenon and the interfacial changes under different biases,and it is pointed out that the electric field delay effect will also lead to the improvement of bias stability.At the same time,it is found that the integrated TFT still conforms to the exponential model of aging days and hysteresis variation proposed above,and the interface matching degree factor is determined by the material of the interface layer rather than the annealing temperature.4.To build low-cost and environment-friendly TFTs,dysprosium oxide,ytterbium oxide and gadolinium oxide have been added into zirconia aqueous solution to prepare the dielectric layers.It has been found that the gadolinium oxide doping zirconia behaves the optimum surface quality.By using the variable range-hopping?VRH?model to compare and analyze the electrical performance of building devices,it is found that the water-based zirconia gadolinium film contributes to a clean interface.The low leakage current density of?6×10^-10A cm^-2and high break electric field of 7.32 MV/cm have been obtained.As a result,the optimal channel layer annealing temperature can reduce to 430 ? from 500 ?,and the saturation mobility of 3.10 cm²V^-1s^-1is available at low operating voltage of 2 V.What's more,the high current on/off ratio of 8×10⁷and small threshold voltage shift of?0.25 V can be notable after1.5 V bias for 5400s.The resistor-loaded unipolar inverters show the maximum gain of 7.3 at operating voltage of 2.5 V.This is an important step in the development of flexible electronic devices with low power consumption and large area.