Study On Printed Zirconium Oxide Insulator And Flexible Thin Film Transistors

Thin film transistors are key devices in mainstream display technology.The gate insulator layer is one of the most important materials to realize low power consumption and high stability in TFT devices.High-k dielectric materials such as Zr O₂,have advantages of high capacitance and wide band gap,which can effectively enhance density and performance of display unit array compared with conventional insulating materials such as Si N_x and Si O_x.Traditional vacuum deposition method has disadvantages of high cost and low efficiency.Instead solution-processed method can achieve patterning without mask.Therefore,solution-processed method is more suitable for large-area film deposition.This paper mainly studies thin film transistors with printed zirconia as gate insulator,and focuses on preparation of new dielectric inks,printing technology as well as low temperature process in order to prepare flexible TFT devices.In this paper,the printability and component changes of zirconia insulating ink during annealing process are analyzed systematically.Spin coating and inkjet printing methods to prepare insulator films are studied,and polyvinylpyrrolidone?PVP?organic insulator is doped in Zr O₂ to improve the bending resistance of Zr O₂dielectric layer.Low temperature printed zirconia insulator is realized through the optimization of precursor materials and UV assisted thermal annealing process.Finally,flexible TFT devices with printed zirconia as insulator is obtained.The main results are shown as follows:?1?Particle zirconia inks and precursor zirconia inks are prepared and analyzed respectively.Precursor zirconia inks suitable for the preparation of printed dielectric layer are obtained.TG/DSC,FTIR and XRD tests are used to study the composition change and densification of zirconia ink during annealing process.It comes out that inks with Zr NO₃ and Zr OCl₂ as precursor are beneficial to low temperature film deposition process.The relationship between viscosity,surface tension and rheological properties of dielectric inks with printability is revealed.The printing stability of inks can be characterized by the viscosity stability at different temperatures and shear rates.?2?The effects of precursor solution physical properties?viscosity,surface tension and precursor concentration?,printing conditions and post annealing temperature on zirconia films and devices are studied for spin coated and inkjet-printed Zr O₂ films.Spin coated Zr O₂ TFT achieves mobility of 10.2cm²/V·s,I_on/I_offratio of 2.0×10⁵with thickness of 66nm.And the mobility and I_on/I_off ratio of 55nm-thick inkjet-printed Zr O₂ TFT is 12.4cm²/V·s and 1.2×10⁶.The bias stability test shows that V_th of inkjet-printed Zr O₂ TFT shifts 1.3V positively while spin coated Zr O₂ TFT shifts 0.4V under+5V bias voltage for 1hour.It proves that solution-processed insulating layer has potential in display application.?3?The modification effect of PVP organic insulating material on zirconia film is studied.TFT devices with PVP,PVP doped Zr O₂ and Zr O₂-PVP laminated structure as gate insulator are fabricated by inkjet printing method.It shows that the molecular structure of PVP can be destroyed by high temperature annealing.The mobility of printed PVP insulator device annealed at 200?is 4.6cm²/V·s with I_on/I_off ratio more than 10⁵.The leakage current of the Zr O₂-PVP laminated structure insulator device is large due to uneven surface and more interface defects,and the I_on/I_off ratio is only 10³.Small amount of PVP doping in Zr O₂ film can reduce interface defects.The mobility of 0.5%PVP doped Zr O₂ insulator device is8.2cm²/V·s,and I_on/I_off ratio is 1.5×10⁵.V_th shift 0.8V under positive bias stress for 0.5%PVP doped Zr O₂ insulator device,but there is almost no decline on mobility and I_on/I_off ratio.The hybrid insulator system improves the bending resistance of zirconia films,which is necessary for the preparation of flexible devices.?4?Low temperature process of printing zirconia is studied.By optimizing precursor materials and UV assisted thermal annealing process,the reliability of printed insulator annealed at low temperature is improved.Micro-PCD testing method is proposed to analyze the defects and uniformity of large-area insulating film.Leakage current density of Zr O₂ films from Zr OCl₂ precursor is less than 5×10^-6A/cm²@10V after 200?annealing process.Finally,flexible TFT with 0.5%PVP doped Zr O₂ as insulator is prepared.The mobility of this device remains 5.5cm²/V·s after 10000 bending times with bending radius of 20 mm,and dielectric in this paper shows good bending resistance and offers a reference in printed flexible device fabrication.