Research Of AMOLED Pixel Circuit Based On A-InGaZnO Thin Film Transistor

Currently,Active Matrix Organic Light Emitting Diode(AMOLED)is considered to be a new display technology because of its high contrast,fast response and low power consumption.AMOLED display is composed of multiple pixels,and the emitting of each pixel depends on the pixel circuit.Thin Film Transistor(TFT)is the basis and core device of the AMOLED pixel circuit,which acts as a switch transistor and a driver tube in the circuit.Among them,amorphous-InGaZnO Thin Film Transistor(a-IGZO TFT)has the advantages of high mobility,good uniformity and low preparation temperature,which stands out among various TFT devices.However,a-IGZO TFT will undergo performance drift such as threshold voltage after long-term operation,resulting in changes in the current flowing through the OLED,which in turn affects the stability and uniformity of the display screen.Therefore,pixel circuits need to have corresponding compensation functions,and existing pixel circuits lack compensation for mobility drift,and can not compensate for both negative threshold voltage and mobility drift.To overcome these deficiencies,AMOLED pixel circuits should have a more comprehensive compensation function.Fisrt of all,preparation and performance study of single-gate and double-gate a-IGZO TFT devices with bottom-gate top contact structures were finished.The test results showed that the threshold voltage,mobility and sub-threshold slope of the single-gate a-IGZO TFT is 3.61 V,0.19 V/dec and 7.58 cm~2/V.s respectively,and the threshold voltage,mobility and sub-threshold slope of the dual-gate a-IGZO TFT is 2.58 V,17.4 cm~2/V.s and 0.25 V/dec respectively.Next,based on the state density theory,the numerical device model of a-IGZO TFT was established,and the state density parameters of a-IGZO was extracted through the fitting of the model and experimental data,so an accurate a-IGZO TFT device model was as to constructed.Finally,in view of the shortcomings of the current AMOLED pixel circuit lacking mobility compensation function,above single-gate a-IGZO TFT was used to design an AMOLED pixel circuit with both threshold voltage and mobility compensation,and the circuit has a 5T2C structure.Simulation results show that when the threshold voltage of the drive tube changed 3.6V±2 V,the OLED current change rate was less than 15.1%,and when the drive tube mobility was drifted by 30%,the OLED current change rate was less than 9.6%.In order to solve the problem that the circuit cannot compensate for the insufficient negative threshold voltage of the drive transistor futherly,another AMOLED pixel circuit using the dual-gate a-IGZO TFT was proposed.The circuit also has a 5T2C structure,which can compensate for the positive and negative threshold voltage and mobility drift of the drive transistor at the same time.After simulation optimization,the threshold voltage compensation effect of the pixel circuit was improved:when the threshold voltage of the drive tube drifted from 0 V to-2 V,the OLED current change rate did not exceed 10.8%.The AMOLED pixel circuit proposed has both positive and negative threshold voltage and mobility compensation,and has a more comprehensive compensation function,which can further improve the stability and uniformity of the display screen and expand the application scenarios of AMOLED display products.