Study On Improvement Of Self-assembled Passivation Layer Of Flexible InSnZnO Thin Film Transistors

The next generation of flexible displays has proposed high mobility,high stability,and good flexibility performance goals for thin film transistors(TFT).Metal oxides have the advantages of medium mobility and low process temperature,and are considered to be one of the most potential active layer materials for TFT.In Sn Zn O(ITZO)TFT,as a metal oxide thin film transistor(MO TFT)that has attracted much attention,can maintain high switching current ratio and low subthreshold swing while ensuring high mobility.However,in the actual working environment,the back channel is susceptible to the influence of atmospheric atmosphere and water vapor resulting in poor bias stability.Therefore,in this paper,the ITZO-TFT was prepared on the polyimide(PI)substrates,and the effects of SAMs on the electrical properties and stability of TFT devices were systematically investigated using self-assembled single molecule layers(SAMs)deposited in different ways as passivation layers.The ITZO-TFT devices with excellent electrical properties and good stability were obtained.The main research results of this paper are as follows:(1)To solve the problem of poor bias stability of flexible ITZO-TFT,the passivation layer of 1-octadecanthiol(ODT)was deposited on the prepared flexible ITZO-TFT by liquid-phase method.After optimizing the solution concentration and immersion time,the prepared device has a threshold voltage drift of 0.8V under PBS in 1 hour.The research results show that the ODT is adsorbed on the surface of the back channel through a chemical reaction,modifying and passivating the ITZO film to prevent the adsorption/desorption process of water and oxygen.The device can maintain good electrical properties under bending stress with a minimum radius of curvature of 10mm,which is attributed to the natural flexibility of SAMs.After extracting the device contact resistance,it was found that the contact resistance of some devices deteriorated,which may be caused by uncontrollable impurities entering the active layer/source-drain electrode interface during the immersion process.(2)To solve the problem of difficult curing and low yield of the solution-treated film,the ODT passivation layer was deposited by vapor-phase method.The vapor phase method is a vapor treatment process that can deposit ODT directly onto the substrate,avoiding the contact between the ODT solution and the substrate.The performance of the prepared device is that the mobility is as high as 22.5cm²V^-1s^-1,the threshold voltage is 0.2V,the threshold swing is as low as 0.091V/dec,the switching current ratio is as high as 1.92×10⁹,the threshold voltage drifts only 0.5V/0.9V under PBS/NBS in 1 hour,and there is basically no hysteresis.The electrical performance has been comprehensively improved.The thin film characterization results show that the improvement of device performance is related to the hydrophobic and smooth back-channel interface obtained using vapor-phase deposition of ODT.(3)The head group(-Si-O-CH₃)of trimethoxy(3,3,3-trifluoropropyl)silane(TFP)can react with hydroxyl group(-OH),and its terminal group(-CF₃)is a hydrophobic group,which is used to modify the back channel in favor of flexible ITZO-TFT stability improvement.Using the vapor-phase deposition of TFP passivation layer,the prepared device shows a threshold voltage drift of 1.4 V/-1.7 V under PBS/NBS in 1 hour.The performance of the flexible ITZO-TFT treated by TFP is not satisfactory,probably because of the short TFP carbon chain length and weak molecular cohesion,which can be used as a reference for the selection of high-quality self-assembled passivation layers.