Studies On Inkjet-printed Oxide Thin-film Transistors

With the rapid development of the flat panel display field towards the direction of low cost,large size and green processing,the requirements for thin film transistor(TFT)backboard technology are getting higher and higher.Compared with the traditional vacuum manufacturing process and lithography process,inkjet printing,as a non-contact micro-nano scale net forming processing technology,is environmentally friendly in the processing process and suitable for large-area processing.It can save the materials and the cost of equipment and time,so that TFT can be used as a cheap electronic device in a large area.In this paper,the oxide TFT for inkjet printing was studied.Progress has been made in the printing graphic process based on the coffee ring,the printability and spreadability of the ink,the oxide TFT with double electrode and the alumina dielectric layer based on the glycol solvent.Some explorative work has been done for the large-scale application of the oxide TFT in the future.The main research results are as follows:(1)Inkjet etching based on the effect of coffee ring was studied,and the influences of droplet spacing,number of printing layers and time interval on the morphology were discussed.Based on this,hydrophobic coffee rings with different morphologies were prepared,which were used as the limiting stripes of ink spreading,and the problem of graphic control of ink was solved.Secondly,the printability of several common solvent inks is studied,and the effects of ink parameters and nozzle temperature on printability are discussed.On this basis,the ink was printed in the coffee ring,and the effects of substrate treatment and different solvents on the spreading property of the ink were discussed.The related research on improving the printability and spreading of ink has a certain guiding effect on the preparation of ink.Finally,using the above ink-jet etching technology,a short channel electrode was prepared,which provides a method for realizing high-precision inkjet printing.The above results are expected to provide some references for the realization of higher resolution inkjet printing.(2)The interfacial contact characteristics between inkjet-printed Ag electrode and semiconductor layer were studied.It is found that the serious diffusion of Ag nanoparticles,the erosion of the semiconductor layer by Ag ink solvent,the residual organic matter at the interface and the formation of Ag₂O are the main factors leading to the deterioration of the performance of oxide TFT based on silver electrode.By inserting inkjet-printed indium tin oxide(ITO)buffer layer between the Ag electrode and the semiconductor layer,the diffusion of Ag nanoparticles in the semiconductor layer can be blocked.In addition,the ITO buffer layer can form good contact characteristics with Ag and semiconductor,greatly reducing the contact resistance.The performance of TFT based on Ag/ITO double-layer electrode is significantly improved compared with that based on single-layer silver electrode:a mobility of 16.0 cm²V^-1s^-1,a switching ratio of 6.2×10⁷,a subthreshold swing of 174m V/Decade,and a threshold voltage of-2.0V.The results demonstrate the application potential of printed Ag electrode in oxide TFT,and contribute to the establishment of a composite conductive film system of stacked structure of metallic conductive nanomaterials and conductive oxide film,realizing complementary advantages.(3)The large capacitance effect and diode effect of printed alumina dielectric layer based on ethylene glycol(EG)solvent were studied.By analyzing the Electrical characteristics of the dielectric layer based on different solvents,it is found that the quasi-static capacitance of the device prepared with the dielectric layer containing EG solvent is very large,and the leakage current has the single-guide ability.Further analysis showed that the carbon residue in the solvent layer containing EG,the incomplete decomposition of NO^3-and more oxygen vacancies in the film led to the strong frequency dependence of the capacitor.The leakage current is single-guide because of the diode effect between the dielectric layer and the inkjet printed ITO electrode.In order to realize the application of aluminum oxide based on EG solvent in TFT,a full inkjet printed TFT was prepared to suppress the leakage current.The principle is to form two reverse interface diodes in the structure to make the circuit open.This provides a new idea for restraining leakage current.The breakdown field intensity of the prepared device is greater than 10m V/cm,and the leakage current density is only 3.4×10^-7 A/cm² when the electric field intensity is 10m V/cm.Finally,the corresponding circuit model is established to analyze the abnormal phenomenon of leakage current.