Improved Light Output Power of 16 × 16 Pixelated Micro-LEDs for Headlights by Enhancing the Reflectivity and Coverage of the p-Electrode

A pixel array of micro-light emitting diodes (µ-LEDs) based on a flip-chip structure and driven by a passive matrix is fabricated. The array is fabricated through multi-level metallization using a photosensitive polyimide (PSPI) inter-metal dielectric (IMD) layer. The device consisted of 256 pixels in a 2 × 2 mm² array (the individual pixel area is 115 × 115 µm²). This device facilitates the control of individual µ-LEDs in the array. To investigate the effect of reflectivity and coverage to p-GaN on mesa area of p-type electrode, controlled and uncontrolled µ-LED arrays is fabricated with different reflectivity and coverage of the p-type electrode. The results show that the devices has similar electrical properties. The light output power and maximum electroluminescence intensity of the controlled µ-LED array is improved by 3.7 and 5.1 times at injection currents of 100 and 60 mA compared to the uncontrolled µ-LED array, respectively. The variation of dark spaces in several emission images (total 9 pixels) is investigated as a function of the pixel pitch for the controlled µ-LED array at an injection current of 20 mA. The results shows that the dark space between pixels almost disappears at a pixel pitch of 125 µm.