Preparation And Application Of Solution-Processed Metal Oxide And Organic Thin-Film Transistors

Thin-film transistors?TFTs?are not only the core components of backplane technology for flat panel display industry,but also important parts that could improve the display's quality and reduce manufacture costs.At present,TFTs based on silicon semiconductor?amorphous and polycrystalline?are still the most used materials in industry.However,with the developement of flexible,large-area,high-resolution and three-dimensional display technology,the requirement for high-performence backplane is higher and higher.And the amorphous silicon and brittle polycrystalline silicon either exhibits low mobility or poor uniformity,which greatly limit their applications.Owing to good mechanical flexibility,decent mobility and diversity of raw materials,organic semiconductors have attracted extensive attention.Meanwhile,due to the high optical transparency,high mobility(1-100 cm² V?^-1?s^-1),electrical stability and uniformity,metal oxide semiconductors have been standing out since its invention and have been commercialized in recent year.However,the preparation of many organic semiconductors and commercially-available metal oxides films still need vacuum techniques,such as evaporation,magnetron sputtering,resulting in high production cost,slow processing speed and complicated lithography process.Therefore,the thesis is focused on the solution-based preparation of metal oxide and organic films to achieve low-cost,high-efficiency,large-area and bottom-up patterned fabrication.Thus,it would provide fundamental guidelines for the roll-to-roll manufacture in the future.Our work includes the following five parts:First,we use three environmentally friendly carbohydrates?sorbitol,glucose and sucrose?as efficient fuels to promote combustion synthesis of indium gallium zinc oxide?IGZO?film,thus to solves the problem of poor device performance by lowtemperature solution-based methods.The results from thermal analysis show that these carbohydrates can significantly reduce the ignition temperature of the IGZO precursor?about-52 °C?and increase the combustion enthalpy(increases from ²00 J ^g-1 to ⁴70 J ^g-1).Film morphology and structural characterization showed that synergistic combustion process with optimal amount of sugars and acetylacetone does not form pinholes in the film,and the high combustion enthalpy promotes the formation of compact and high-purity metal oxide films.Device test results show that synergistic combustion can significantly improve the electron mobility of IGZO TFTs to as high as 8.0 cm² V?^-1?s^-1 with excellent bias-stress stability.Moreover,the first correlations between precursor combustion enthalpy and metal oxide densification/charge transport are established.Second,we select chemically and compositionally different co-fuels?urea,glycine,sorbitol and L-ascorbic acid?to explore the essence of synergistic combustion reaction.Thermal analysis show a substantial reduction?-67 °C for L-ascorbic acid?in the igniting temperatures of synergistic combustion.Meanwhile,with appropriate amount of co-fuels,the combustion process is significantly enhanced with reduced residual weight?about 10%?.Thus enhance the indium gallium zinc oxide?IGZO?film densification,lattice formation and improve the mobility of IGZO TFT with good biasstress stability.By systematically studying the vacuum-dried IGZO precursor with 1H NMR,X-ray diffraction and other thermal analysis,we conclude that the acidity,combustion enthalpy and thermal stability of the co-fuels are the reliable predictors for high efficient combustion process,which provide a new way for searching better fuels.Third,by combining spraying technology with combustion process?SCS?,we obtain fully patterned high-performance all-oxide transistors with high transparency.The automatic spray coater equipped with ultrasonic nozzle provides continuous production of metal oxide films including dielectrics,semiconductors and conductors.The SCSderived zirconium dioxide or aluminum oxide dielectric films exhibit good morphology?mean square roughness of 0.3 nm?,low leakage current density?10-7 A cm-2 at 2 MV cm-1?,high areal capacitance?600 nF cm-2?and high dielectric strength?9 MV cm-1?.SCS-derived indium tin oxide?ITO?conductor has a high conductivity of ²65 S cm-1,significantly higher than that of spin-coated combustion synthesis of ITO conductor?7 S cm-1?.In addition,the SCS-derived indium zinc oxide?IZO?and IGZO TFTs based on zirconium dioxide dielectric exhibit high electron mobility of 42.5 cm² V?^-1?s^-1 and 32.5 cm² V?^-1?s^-1,respectively.Moreover,the flexible devices based on polyester substrate show highest electron mobility of about 10 cm² V?^-1?s^-1 with good bending characteristics.Finally,we achieved all-SCS-derived all-oxide transparent TFTs on the glass with the electron mobility up to 8 cm² V?^-1?s^-1 and good bias-stress stablity.Fourth,addressable growth of organic semiconductor thin film on hydrophobic substrates were achieved by fast dip-coating technique.After hydrophobic treatment of SiO2/Si substrate with patterned hydrophilic gold electrodes,the liquid film will cover the gold electrodes and the channel regions during dip-coating process.Then,organic thin films are formed in these areas after solvent evaporation.The area-selective growth of the microstrips can be controlled by adjusting surface property of TFTs channels,geometry features of the gold electrodes,pulling speed and evaporation atmosphere etc.In addition,we plot the schematic mechanism digram and believe that the competition between receding of the solution and evaporating of the solvent that tunes the films growth behavior.Interestingly,The patterned bottom-contact transistor arrays exhibit carrier mobility of 2.0×10-3 cm² V?^-1?s^-1,while no field-effect characteristics can be detected for bottom-contact arrays without hydrophobic treatment.Such solutionprocessed reliable,fast,bottom-up patterning method provides a feasible method for low-cost and large-area production.Last,the above patterned OTFTs are used as the ammonia sensor.By comparing the morphology and packing structure of organic films,we find the patterned dip-coating process can tune the the thickness and crystallinity of the film with ease,and achieve field-effect characteristic even with monolayer/bilayer organic films.The low-trap dielectric-semiconductor interfaces,stripe-like morphology and ultrathin film?as low as 2 nm?enable the bottom-contact OFETs-based sensors to exhibit unprecedented sensitivity?¹60?with short response/recovery time.According to the transport mechanism of inorganic TFTs,a detailed description of the sensor mechanism based on polycrystalline organic semiconductor is demonstrated.