31.3: Low Optical Crosstalk Micro‐LED Micro‐Display with Semi‐Sphere Micro‐Lens for Light Collimation

Abstract

A 400×240 monochromic micro‐LED micro‐display based on GaN vertical‐LED structure is presented. The micro‐display has the pixel pitch of 30 μm and the size of micro‐LEDs is only 8 μm. It is realized by bonding the GaN epi with the pre‐defined anode pad array to the specific pixel driver on the IC backplane, followed by laser lift‐off and ICP etch process to form isolated micro‐LED pixel array. The electrical connection of n‐type GaN on micro‐LEDs is done by a layer of metal‐grid which serves as a common cathode. Comparing with conventional lateral micro‐LED structure, the vertical‐LED architecture used in our micro‐LED micro‐display is more advantageous of achieving higher device performance such as better current injection, higher light extraction efficiency, low light crosstalk and is more capable of producing compact micro‐LED arrays. In addition, wafer‐level processed semi‐sphere micro‐lens array is also integrated into the micro‐display with each micro‐lens coupled to a single micro‐LED pixel. The micro‐lenses can effectively collimate divergent light emitted from micro‐LEDs leading to a significant improvement of projection brightness when used in a projection light engine. The self‐emissive micro‐LED micro‐display shows its great potentials for projectors and many other applications.

Highly efficient and ultra‐compact micro‐LED pico‐projector based on a microlens array

“…MLA is a common miniature optical element that can be directly integrated with optical systems to achieve specific optical functions by adjusting its faceted structure. This element can not only meet the requirements of pico‐projection systems for element size and collimation efficiency at the same time, but its size is also far larger than the emission wavelength, in which no obvious wavelength dependence is found for the efficiency improvement of the light source system 15 . In this work, each μLED pixel is encapsulated by a microlens, and the two elements together form a light‐emitting unit.…”

“…This element can not only meet the requirements of pico-projection systems for element size and collimation efficiency at the same time, but its size is also far larger than the emission wavelength, in which no obvious wavelength dependence is found for the efficiency improvement of the light source system. 15 In this work, each μLED pixel is encapsulated by a microlens, and the two elements together form a light-emitting unit. Numerous light-emitting units together constitute the lighting system of the pico- projector.…”

Fully Enclosed Composite Micro/Nano‐Package for High‐Quality Micro‐LED Display Pixels and In Situ Nanoimprint Technology

“…Assembling a micro‐lens array on each luminescent pixel is the most commonly method and has been demonstrated to be effective in controlling the divergence angle. [ 20,21 ] However, the assembled microlens has a certain distance from the chips surface, the sidewall illumination of the chips cannot be fully collected by the limited aperture of the microlens, while it is non‐negligible or even occupies the majority for a small size of light chips. Pixel crosstalk caused by sidewall illumination significantly influences the display quality.…”

Design of micro-LED pico-projection optical engine based on an image fiber

“…The self-illuminating projection optical system only needs an image source, a beam shaper element and a projection lens, which simplifies the traditional projection structure's light source module and relay optical module. At present, self-illuminating projection is still in the development stage, and the relevant research literature mainly focus on reducing volume and improving light utilization efficiency [17][18][19][20][21], while there have been still few studies on the improvement of the overall structure. The optical and electrical modules in this projection optical system cannot be entirely separated, limiting their use in specific environments.…”