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

Abstract

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.