Dimensioning a full color LED microdisplay for augmented reality headset in a very bright environment

This paper focuses on the dimensioning of a very bright full color 10 mu m-pitch light-emitting device (LED) microdisplay for avionics application. Starting from the specifications of head-mounted display to be used in an augmented reality optical system, a theoretical approach is proposed that enables predicting the specifications of the main technology building blocks entering into the microdisplay manufacturing process flow. By taking into account various material and technological parameters, kept as realistic as possible, it is possible to assess the feasibility of a very bright LED microdisplay (1 Mcd/m(2) full white) and to point out the main limitations. The theoretical specifications are then compared with the technical results obtained so far in the framework of the H2020 Clean Sky "HILICO" project. It shows that 350 000 cd/m(2) of white emission may be accessible with the present gallium nitride (GaN)-micro-LED technology provided a color conversion solution with stable external quantum efficiency of 30% is available. Beyond such level of luminance, the inherent limitations of driving circuit (4 V, 15 mu A per pixel) commands working with materials enabling higher external quantum efficiency (EQE). In particular, 10-mu m-pitch micro-LEDs with electroluminescence EQE of 15% and color conversion EQE approaching 60% are needed, opening the way to future challenging material and technology research developments.