Research On The Fabrication And Photoelectric Characterization Of Micro-LEDs

As a high-efficiency solid-state light-emitting device,LEDs are widely used in many fields such as lighting,outdoor display,conference projection,and military communications.With the development of micro-displays,various research has focused on the miniaturization of LEDs to satisfy the new display technologies.In recent years,reducing large LEDs to fabricate high-density Micro-LED arrays has gradually become a research hotspot.Micro-light-emitting-diode(Micro-LED)is an array of high-density LEDs of several microns.Micro-LEDs have excellent application potential and good value in the high-resolution display,optical neural interface,maskless lithography,and visible light communication due to their advantages of high resolution,high brightness,low energy consumption,fast response,high contrast ratio,and long lifetime.Due to the enormous application demand,Micro-LEDs are developing in smaller sizes and higher densities.However,when the Micro-LED chip's pixel size is less than 100 ?m,the device gradually encounters difficulties such as current crowding and sidewall effects.And the transfer printing of RGB chips also faces low yield and slow speed,limiting the Micro-LED applications in related fields.Because of the above problems,this thesis has studied the fabrication and optoelectronic characteristics of Micro-LEDs array display devices.The specific work of this thesis can be divided into the following parts:1.The fabrication process and optoelectronic properties of flip-chip GaN-based blue Micro-LEDs were studied.By improving the ICP dry etching mask and recipe,a flip-chip GaN-based blue Micro-LED array with a pixel size of 10 ?m×10 ?m was designed and fabricated,and the pixel density of the Micro-LED array was 1500 PPI.Micro-LEDs with sizes of 80 ?m,40 ?m,20 ?m,and 10 ?m were also compared and analyzed.The results show that smaller Micro-LEDs have a higher current density on the same voltage.And smaller Micro-LEDs also have a higher series resistance,which will affect the spectrum stability of the device.2.The fabrication process and optoelectronic properties of vertical AlGaInP red Micro-LEDs were studied.The GaAs substrate was removed using wafer bonding and substrate lift-off technology,which solved the GaAs substrate's light absorption and heat dissipation difficulty.By fabricating an Ag-based mirror on the p-GaP layer and using Cr/Pt as the protective layer,an Ag-based mirror with a reflectivity of more than90% was obtained.A vertical red Micro-LED array device with a pixel size of 8 ?m and a pixel density of 2100 PPI was fabricated with dry etching,trench filling,and electrode fabrication techniques.The test results show that the light output power density of the Micro-LEDs prepared by this method is improved,and the peak wavelength and color gamut are stable.Subsequently,the optoelectronic properties of different sizes of vertical Micro-LEDs were studied and analyzed.The results show that the device's peak EQE and light output power decreased when the chip size was reduced,but smaller Micro-LEDs obtained a more stable luminescence spectrum.3.The fabrication process and optoelectronic properties of vertical GaN-based blue Micro-LED were studied.The stress was relieved by patterned In-Ag bonding,and the effects of the planarized sapphire substrate and patterned sapphire substrate were analyzed.The methods of removing u-GaN by dry etching and wet etching are also compared.Vertical GaN-based blue Micro-LED array with a pixel size of 32 ?m was prepared successfully.4.The fabrication process and optoelectronic properties of full-color Micro-LED display were studied.Flip-chip red,green,and blue Micro-LED chips were designed and fabricated;a silicon passive driver backplane was also designed and fabricated;then,RGB Micro-LED chips were transferred print into the silicon drive backplane by using solder and PDMS,and a 48×48 full-color Micro-LED display was prepared.Subsequently,the full-color microdisplay was tested,and the optoelectronic properties were analyzed.Finally,after optimizing the current of RGB Micro-LED chips,a color gamut of 112.88% NTSC is obtained.