Light Emitting Diode Microdisplay Design And Its Optoelectronic Properties

Light Emitting Diode(LED)is widely used as general lighting products.Micron sized LED(in terms of MicroLED,typically less than 100 ?m)as core element of display technology,has merits of high brightness,low power consumption,fast response,and can be combined with large scale integrated circuit,which can meet the needs of smart wearable products.In this thesis,various microdisplay technologies were introduced.The compensation pixel circuit with pitch of 50?m was designed and simulated.The LED microdisplay device with active area of 9.6 mm × 5.4 mm,diagonal size of 0.42 inch;resolution of 480 × 270(1/16 HD);pixel density of 1310 PPI(Pixel Per Inch);pixel pitch of 20 ?m was fabricated on 6 inch sapphire substrate blue GaInN epitaxial wafer based on 3 photomasks process,and effective number of chips on a wafer is 100.Optoelectronic properties of blue LED microdisplay device was characterized.Research content includes:In view of the existence of threshold voltage dispersion and drift phenomenon of LTPS TFT(Low Temperature Poly Silicon Thin Film Transistor),the feasibility of using LTPS TFT to drive MicroLED pixel array was verified.In this thesis,we used the 5T1C(5 Thin Film Transistors and 1 Capacitor)compensation pixel circuit to drive the MicroLED pixel array,and Spice software was used for simulating.The simulation result showed that the output current change ratio of the driving circuit is 7.7%when the threshold voltage of the driving TFT is 0.9 V and the threshold voltage variation is within ?V=±0.3V(33%).This result indicates that the 5T1C compensation pixel circuit has good compensation characteristics,which can effectively eliminate the problem of threshold voltage dispersion and the drift of driving transistor.The stress,resistivity of P and N layers,surface defects of 6 inch sapphire substrate GaInN epitaxial wafers were characterized,and the influence of these factors on the manufacturing process and display characteristics of LED microdisplay device were analyzed?The major optoelectronic properties of the LED microdisplay device were characterized,and its brightness reached more than 7000 nits at a driving voltage of 2.65 V and a current density of 1 A/cm2;the peak wavelength was 454 nm,the full width at half maximum was 20 nm;the CIE1931 color coordinate was(0.1468,0.0312);the external quantum efficiency was 10.05%;the current efficiency was 0.73cd/A;the display brightness uniformity was 90%,and the measured optoelectronic properties of the device have reached the advanced level.