Development And Application Of Transparent Amorphous InZnSnO Based Thin Film Transistor

Transparent amorphous oxide semiconductor（TAOS）thin-film transistors（TFTs）are gradually becoming the mainstream TFT technology due to their high mobility,large aperture ratio,high uniformity,and low cost.However,the average field-effect mobility(μ_FE)of the commercially available indium gallium zinc oxide（In Ga Zn O or IGZO）TFTs is only around 10 cm²/V·s,which cannot meet the requirements for ultra-high-resolution and high-frame-rate displays（>30 cm²/V·s）.Indium zinc tin oxide（In Zn Sn O or IZTO）TFTs,which have higher mobility,are considered the most promising candidates to replace IGZO TFTs.This thesis proposes an innovative approach of doping the channel layer of IZTO and develops high-performance IZTO-based TFTs by optimizing the fabrication conditions.Furthermore,the thesis elucidates the high-mobility mechanism of IZTO TFTs by studying key parameters such as carrier effective mass,relaxation time,and effective thickness of channnel layer.Finally,the application of IZTO TFTs in transparent thin-film memory devices is investigated.The specific details are as follows:（1）IZTO:Ga TFT,IZTO:Al TFT,and IZTO:P TFT were prepared by radio frequency magnetron sputtering,and the effects of channel layer sputtering and annealing processes on the electrical properties of the devices were studied.The binding energies of the elements in the thin films were analyzed using XPS and SIMS techniques,confirming the incorporation of Ga,Al,and P elements in the IZTO films.The microstructure of the films was characterized using XRD technology.The cross-sectional view of the fabricated devices was observed using TEM.The transmittance of the thin films was characterized using a spectrophotometer.The transfer and output characteristics of the devices were measured using a semiconductor tester.The devices exhibited the best electrical performance when the active layer thickness was 10 nm and annealed at 300°C in a nitrogen atmosphere.The saturation mobility(μ_SAT)of IZTO:Ga TFT reached 39.2 cm²/V·s,μ_SAT of IZTO:Al TFT reached 40.3 cm²/V·s,andμ_SAT of IZTO:P TFT reached 37.7 cm²/V·s.The electrical performance of IZTO-based TFTs was significantly improved by effectively controlling the carrier concentration in the IZTO films through ion doping.（2）The carrier effective mass（m*）,relaxation time（τ）,and effective thickness(t_eff)of the channel layer in IZTO TFT were investigated for the first time using a self-developed electric field thermoelectric modulation method.Key parameters were analyzed to understand the device operation mechanism and the physical mechanisms enabling high mobility.Al O_x-insulated IZTO TFTs were fabricated using atomic layer deposition（ALD）and pulsed laser deposition（PLD）techniques.By measuring the Seebeck coefficient（S）of IZTO thin films with different carrier concentrations(n_3D)and combining it with the functional relationship between n_3D and S,the m*of the IZTO film was estimated.Furthermore,based on the functional relationship between m*,μ_FE,andτ,the relaxation time（τ）of the IZTO TFT was estimated.Finally,the effective thickness(t_eff)of the IZTO TFT with different channel layer thicknesses was calculated using the electric field thermoelectric modulation method.It was observed that teff increases with increasing gate voltage,indicating that the source-drain current is mainly contributed by the bulk film portion far from the channel layer/insulating layer interface.Therefore,the lighter m*（0.11 m₀）and longerτ（3.6 fs）are the reasons for the high mobility of IZTO TFTs.（3）Hf Zr O_x insulating layer IZTO TFT（IZTO-Hf Zr O_x TFT）was prepared using ALD and PLD.The Hf Zr O_x thin film structure,thickness,and surface morphology were investigated using GIXRD,XRR,and AFM techniques.The glass substrate/ITO/Hf Zr O_x/IZTO cross-sectional structure and optical properties were studied using HRTEM and transmission spectroscopy.The electrical characterization of the devices revealed a counterclockwise hysteresis loop in the transfer characteristics curve of IZTO-Hf Zr O_x TFT,with a storage window of approximately 0.3 V and a mobility(μ_FE)above 30 cm²/V·s under forward and reverse gate voltage scanning.Thermal performance testing of the IZTO-Hf Zr O_x TFT confirmed the device’s ability to maintain the on-state or off-state even without applied gate voltage.Therefore,IZTO-Hf Zr O_x TFT holds potential for application in transparent thin-film storage devices.