Study On Flexible Indium Tin Zinc Oxide Thin Film Transistor Based On Molecular Self-assembled Passivation Layer

Active matrix organic light-emitting diode display?AMOLED?is known as the next generation display technology.Compared with traditional liquid crystal displays used in most mobile phones,AMOLED has a wider viewing angle,higher refresh rate and thinner size.At the same time,AMOLED is gradually developing towards flexible display.Flexible display technology requires that thin film transistors?TFTs?can not only be prepared on glass substrates,but also be fabricated on flexible substrates such as plastics,and can still work normally when bent.At present,the most promising TFT in AMOLED is metal oxide thin film transistor?MO TFT?.The MO TFT has much higher mobility than the amorphous silicon thin film transistor?a-Si:H TFT?,and it has the characteristics of low processing temperature and high transparency in the visible light band.Therefore,the MO TFT is widely used.However,the stability of MO TFT is poor,especially for MO TFTs based on flexible substrates.Therefore,in the fabrication of flexible TFTs,a passivation layer is generally deposited to protect the device.Based on this,this thesis proposes a self-assembled monomolecular film prepared by molecular self-assembly technology as a passivation layer.The thickness of this passivation layer is only 2.2 nm,and at the same time it can achieve a good passivation effect.In this thesis,the RF magnetron sputtering process is used to deposit indium tin zinc oxide?ITZO?thin film as the active layer of TFT device,and the self-assembled monolayer was adopted as a passivation layer to improve the electrical performance and stability of the ITZO TFT device.At the same time,the fabrication process has a relatively low temperature and is suitable for preparation on a flexible substrate to obtain a flexible MO TFT device.The main research work of this thesis includes the following contents:Firstly,the flexible ITZO TFT was fabricated by RF magnetron sputtering,and the fabrication process was studied to achieve good performance and high repeatability.The annealing temperature was under 350?,which made it possible to fabricate the TFT on the flexible substrate.The field-effect mobility of the flexible ITZO TFT is 15.05 cm²V^-1s^-1,the threshold voltage is-1.4V,the switching current ratio is 1.01×10⁷,and the sub-threshold swing is 0.50 V/dec.Self-assembled monolayer of octadecylphosphonic acid was prepared by solution method as a passivation layer to improve the performance and electrical stability of flexible ITZO TFT.The field-effect mobility of flexible ITZO TFT with octadecylphosphonic acid monolayer as a passivation layer is 18.60 cm²V^-1s^-1,the threshold voltage is-0.6V,the switching current ratio is 4.32×10⁷,and the sub-threshold swing is only 0.19 V/dec.Secondly,the low frequency noise test and the stability test under positive and negative bias stress are carried out for the flexible ITZO TFT without passivation and the flexible ITZO TFT with passivation respectively.The results of low frequency noise analysis show that after passivation,the low frequency noise of the flexible ITZO TFT is reduced to a certain extent.The PBS test results of the flexible ITZO TFT without passivation were compared with those of the flexible ITZO TFT with passivation.The results show that the stability of the TFT with passivation is improved obviously in PBS.The results show that the molecular self-assembly passivation has a certain effect on the stability of the device.Thirdly,the contact resistance of the unpassivated flexible ITZO TFT and the passivated flexible ITZO TFT was extracted from the transfer characteristic curve under linear region by Y function method,respectively.The source-drain contact resistance of the flexible ITZO device with ODPA self-assembled passivation layer is smaller,as compared to that without passivation.The research results show that the flexible ITZO TFT based on molecular self-assembly passivation layer designed in this thesis has relatively good and stable device performance.For application in the next generation of flexible displays and other fields,its superior device performance will bring broad development prospects.