Fabrication And Characterizations Of Red LED Micro-Display

Flat panel display is an important component of supporting information technology.Light emitting diode(LED)has many advantages,such as small size,high brightness,low power consumption,long life and so on.With the development of mobile computing technology,people pursue smaller devices to replace the currently widely used smart phones,such as wearing smart glasses,so they need to use the micro-display technology with higher integration.Micro-display refers to devices with display diagonal size less than 1 inch and resolution greater than 1000 PPI(pixels per inch).The typical size of high-power LED devices used in lighting is 1mm ×1mm,while that of micro-display devices is about 10 ?m × 10?m,which requires that the quality and manufacturing equipment of LED epitaxial chips are different from that of LED lighting industry.Micro-display technology has become a research focus of mobile computing technology.Micro-display not only inherits the advantages of LED lighting,but also has the advantages of high resolution and high color saturation,which is called the ultimate display technology.At present,the blue and green LED micro-displays are mainly made of GaInN,while the red LED micro-displays are mainly made of AlGaInP.According to the proportion of Al component,the forbidden band width of AlGaInP is different,ranging from 1.9 ev to 2.3 ev.When AlGaInP is used to grow epitaxial wafers,the GaAs monomorph matched with its lattice is generally selected as the substrate,which is limited by the visible light absorption and poor thermal conductivity of GaAs substrate.Therefore,in the fabrication process of AlGaInP light-emitting devices,the appropriate process will be selected to remove the GaAs substrate.It has been reported that the AlGaInP epitaxial material is transferred to the sapphire substrate to remove the GaAs substrate,and then the AlGaInP light-emitting pixel mesa is etched to form an N-type electrode,and then the N-type light-emitting pixel electrode is bonded with the n-type electrode of the active driving circuit,which is a typical device structure of the reverse polarity red light-emitting diode device.These devices are not compatible with the pixel circuit structure of P-type electrode bonding used in the active driving circuit of GaInN blue and green light devices.The main research content of this paper is to adopt a new device manufacturing method,which can be compatible with the blue and green light active driving circuit.The method of removing GaAs substrate first and then making light-emitting pixels is adopted.Red LED micro-display device with flip-chip structure was developed,and the basic fabrication process of the device and their photoelectric characteristics were reported.The active display size is 9.6 mm×5.4 mm(0.42" diagonal),the resolution of device is 480×270,the pixel pitch is 20 ?m×20?m,the pixel mesa size is 14?m×?m,and the pixel density is 1300 PPI(pixels per inch).The device turns on at a forward driving voltage 1.4 V.When the driving voltage is 4.0 V,the current density is 82 A/cm2.the peak wavelength is 624 nm at 30 mA driving current,the peak wavelength of electroluminescent spectrum is 624 nm,the color coordinates CIE 1931 are(0.699,0.301),the luminous flux is 0.018 1m,and the efficiency is 0.1 lm/W.