Research On Key Circuit Of OLED-on-silicon Microdisplay

Organic Light-Emitting Diodes-on-Silicon Microdisplay is an emerging display technology which integrates organic light emitting diodes on single crystal silicon wafers.It has many advantages,such as self-luminescence,all-solid state,fast response,wide viewing angle and easy integration.It attracts many researchers' interests.In this paper,the pixel circuits of OLED-on-Silicon microdisplay are studied and a corresponding driving circuit is proposed.The highlight works of this paper are shown as following:(1)An OLED equivalent circuit model consists of three resistors,two capacitors and one diode which based on Trapped-Charge-Limited Current(TCLC)theory is proposed to ensure the accuracy of the simulation results of the pixel driving circuit in this paper.By HSPICE software simulation,the maximum error between simulation current and experimental measurement current is 6.7%,which reduced 17.8% compared to the empirical model.The simulation results show that the OLED equivalent circuit model is in good agreement with experimental measurement results and accurately match with the V-I characteristics of OLED.(2)A novel pixel circuit comprising six NMOS transistors and one capacitor(6T1C)is proposed to compensate for the decrease of emission current caused by threshold voltage drift and OLED degradation.The deviation in emission current of the proposed pixel circuit ranges from-0.144 LSB to 0.416 LSB,when the threshold voltage variation ranges from-7.25 mV to 7.12 mV.The deviation in emission current of the proposed pixel circuit ranges from-0.48 LSB to 0.6LSB,when the internal resistor of organic light emitting diode increases from 0M? to 8M?.The layout area of the proposed pixel circuit is 5.5?m×16.5?m.Meanwhile,another pixel circuit consists of four transistors and one capacitor(4T1C)is proposed to improve current stability of OLED-on-Silicon microdisplay and reduce the area of pixels and driving complexity.The deviation in emission current of the proposed pixel circuit ranges from-0.16LSB~0.24 LSB,when the threshold voltage variation ranges from-7.25 mV to 7.12 mV.The deviation in emission current of the proposed pixel circuit ranges from-0.72LSB~0.024 LSB,when the internal resistor of organic light emitting diode increases from 0M? to 8M?.The layout area of the proposed pixel circuit is 5?m×15?m which reduced 17.36% compared to 6T1 C pixel circuit.(3)A corresponding driving circuit of OLED-on-Silicon microdisplay is proposed,which includes row driving circuit,pixel matrix and column driving circuit.The designed microdisplay is a 256-level gray-scale display with a resolution of 800×600 and a frame frequency of 60 Hz.The power consumption of the microdisplay is reduced by using 3.3V/5V dual power supply voltage.Each module of the driving system is simulated by Cadencesoftware.The simulation results show that the proposed driving circuit could meet the design specifications of the OLED-on-Silicon microdisplay.