Abstract
In this thesis, the major goal is to develop an individually addressable 960×540 Gallium Nitride (GaN) based micro-light emitting diode array in assistant of mature LED processing technique: On top of patterned sapphire grows a thin GaN epitaxy layer, and using inductively-coupled plasma reactive ion etching (ICP-RIE) system, a MESA of epitaxy layer is then formed, after n-metal and p-metal is deposited [1][2], using plasma-enhanced chemical vapor deposition system (PECVD) to deposit dielectric layer, and via hole for indium bump is etched by RIE system, last, flip chip bonding is performed, the micro-LED array is now ready to display with the help of SDK controller. Light emitting diode has many advantages such as long life time, high luminous efficiency, low power consumption, high brightness, and operates at harsh condition, traditional applications of LED mostly focus on illumination purpose, but we hope to make good use of LED’s tremendous advantages, and here comes the idea of micro-LED array. To develop a high brightness, high power efficiency, low power consumption, good uniformity micro-LED array and integrated into pico-projectors or mask-free lithography, first, we design an Indium Tin Oxide (ITO) current spreading layer for higher brightness and better power efficiency, next, the epitaxial wafer with ten quantum wells for active layer is used to increase the chance of electron-hole pair recombination. By the way, LED MESA is etched with gentle recipe, and passivation layer is adopted to reduce side wall damage and restrain leakage currant. For better optical output uniformity, we design a grid-shaped n-metal to lowering series resistance for each pixel to be similar, at the same time, flip-chip bonding technique is adopt for shorter current path and smaller series resistance. In order to increase light output from backside of micro-LED array, a specially designed passivation layer is deposited for total reflection at front side, and sapphire substrate is polished with decreased thickness to avoid light crosstalk when displaying. In this thesis, we use various structure of epitaxial grown wafer, including wafer emits blue light, green light, and UV light, the pitch of 960×540 micro-LED array is 12.8μm, the diameter of each pixel is 7.8μm, the length of 960×540 micro-LED array is 12.288 mm, width is 6.912 mm, and diagonal length is 0.55 inch (14.098 mm). As for the single pixel characteristics of micro-LED array, the reverse leakage current at -5 volts for blue LED is 0.1 pA, for green LED is 0.25 pA, for UV LED is 3.26 pA. At open circuit voltage, the open circuit current for blue LED is 1 fA, for green LED is 0.02 fA, for UV LED is 5 fA. At forward bias, the turn on voltage for blue LED is 2.75 V, for green LED is 2.55 V, for UV LED is 3.15 V. The power efficiency of micro-LED array for blue LED is 2.329%, for green LED is 1.3%, for UV LED is 2.1%. At last, we successfully demonstrate a working sample of micro-LED display with blue light, with an operability of 99.674%