Fabrication And Reliability Studies On LED Microdisplays

With the diversified development of flat panel display industry,highly miniaturization and integration have become the development trend of display industry.On this basis,LED microdisplay is considered to be the most promising new display technology direction in the future.LED microdisplay device refers to the pixel density>1000 PPI,pixel size<50μm,effective display area diagonal<1Inch,Compared with LCD and OLED,LED microdisplay has many advantages such as fast response speed,large viewing angle,good color expression,high brightness and long life,and is expected to replace LCD and OLED display in the future.The main research contents of this paper are as follows:1.Four groups of blue light and four groups of green light were designed,totaling eight groups of LED microdisplay devices.Its parameters are as follows:length is 9.6 mm,width is 5.4 mm,pixel pitch is 20μm,diagonal is 0.42 inches,effective light-emitting area is 14μm×14μm,and resolution is 480×270.According to the semiconductor manufacturing process including:cleaning process,photolithography process,etching process,coating process and packaging process,etc.,eight groups of designed LED microdisplay devices are prepared.2.Eight groups of fabricated LED microdisplay devices were characterized by electrical properties,optical properties and brightness.Among them,the turn-on voltage of the blue light in group E is 2.52 V,when the current density is 7.14 A/cm²,the external quantum efficiency reaches a peak value of 8.80%,and when the current is 50 m A,the brightness reaches 5272 cd/m².The turn-on voltage of the green light in group H is 2.28 V,the external quantum efficiency reaches a peak value of 6.7%when the current density is 6.12 A/cm²,and the brightness reaches69415 cd/m² when the current is 50 m A.At the same time,the green LED microdisplay device was characterized by cathodoluminescence.3.Perform surface automatic optical inspection（AOI）defect detection on sapphire substrate epitaxial wafers and process wafers for LED microdisplay devices The main defects on the surface were:hexagonal defect,cylindrical defect,flocculation defect,circular defect and so on.4.Carry out laser bonding experiments on the pixels that are not bright or have low luminous brightness in the MiniLED direct display.The experimental results show that:using a CO₂ laser with a power of 16 W,a spot size of 15μm,a frequency of 60 k Hz,and an action time of 2 s,when the continuous pulse width is used,the pixels that are not normally lit can be lit and the pixels can be lit at the same time.Low brightness becomes brighter.When the infrared power is 2.4 W,the frequency is 1000 k Hz,the spot size is 100μm×125μm,the action time is 2 s,and the pulse is 15 ps,the pixels that are not normally lit can be lit and the pixel brightness can be reduced.becomes brighter.5.Eight groups of LED microdisplay devices were aged for 96 h、500 h and1000 h under the lighting conditions of 150 m A at room temperature.Electrical,optical,and relative light intensity tests were performed on the eight groups of LED microdisplay devices in each time period.The changes of dominant wavelength,turn-on voltage,optical power,light decay curve and external quantum efficiency were compared after aging for 1000 h.The experimental results show that the dominant wavelength of the eight groups of LED microdisplay devices prepared this time does not change with aging,the average decrease rate of optical power is 21%,the light decay curve hardly changes,and the decrease rate of the opening voltage reaches 1.54%in 96 h,but with the aging time increases,the opening voltage tends to be stable,and the external quantum efficiency decreases<1.88%.