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.

High-Resolution Pixel LED Headlamps: Functional Requirement Analysis and Research Progress

“…12 of 18 meaning that they can draw the driver's attention to danger without dazzling people or animals in front of the vehicle. [54]. The array uses a photosensitive polyimide core dielectric layer to form multi-level metallization.…”

“…Reiss et al clarified that, for highly clear glare-free and road marking functions, a highly pixelated automotive headlight system should be adopted [55]. Among spatial light [54]. The array uses a photosensitive polyimide core dielectric layer to form multi-level metallization.…”

Improving Emission Uniformity of InGaN/GaN-Based Vertical LEDs by Using Reflective ITO/Ag n-Contact

“…Thus, the region beneath and surrounding the n-contact becomes dimmer than the areas away from the contact. This emission non-uniformity can act as a serious technological issue in micro-LED display and vehicle headlamp applications, where absence of dark space between LED pixels is essentially required [20,21]. For instance, Kim et al [20] investigated the light output performance of 16 × 16 pixelated micro-LEDs for headlights by enhancing the reflectivity and coverage of the p-electrode.…”

“…This emission non-uniformity can act as a serious technological issue in micro-LED display and vehicle headlamp applications, where absence of dark space between LED pixels is essentially required [20,21]. For instance, Kim et al [20] investigated the light output performance of 16 × 16 pixelated micro-LEDs for headlights by enhancing the reflectivity and coverage of the p-electrode. The array was fabricated by multi-level metallization using a photosensitive polyimide inter-metal dielectric (IMD) layer.…”

“…The variation of dark spaces in emission images was examined as a function of the pixel pitch for the controlled micro-LED array at 20 mA. It was shown that the dark space between pixels almost disappeared at a pixel pitch of 125 µm [20]. Thus, in this study, in order to improve the emission uniformity and light output of LEDs for vertical LED-based vehicle headlamp application, via-hole-type thin film vertical-geometry LEDs with buried reflective ITO/Ag n-contact were fabricated and their electrical and optical properties and reliability were characterized.…”