Micro-scale light emitting diode (micro-LED) is a potentially disruptive display technology because of its outstanding features such as high dynamic range, good sunlight readability, long lifetime, low power consumption, and wide color gamut. To achieve full-color displays, three approaches are commonly used: 1) to assemble individual RGB micro-LED pixels from semiconductor wafers to the same driving backplane through pick-and-place approach, which is referred to as mass transfer process; 2) to utilize monochromatic blue micro-LED with a color conversion film to obtain a white source first, and then employ color filters to form RGB pixels, and 3) to use blue or ultraviolet (UV) micro-LEDs to pump pixelated quantum dots (QDs). This dissertation is devoted to investigating and improving optical performance of these three types of micro-LED displays from device design viewpoints. For RGB micro-LED display, angular color shift may become visually noticeable due to mismatched angular distributions between AlGaInP-based red micro-LED and InGaN-based blue/green counterparts. Based on our simulations and experiments, we find that the mismatched angular distributions are caused by sidewall emission from RGB micro-LEDs. To address this issue, we propose a device structure with top black matrix and taper angle in micro-LEDs, which greatly suppresses the color shift while keeping a reasonably high light extraction efficiency. These findings will shed new light to guide future micro-LED display designs. For white micro-LEDs, the color filters would absorb 2/3 of the outgoing light, which increases power consumption. In addition, color crosstalk would occur due to scattering of the color conversion layer. With funnel-tube array and reflective coating on its inner surface, the crosstalk is eliminated and the optical efficiency is enhanced by ~3X. For quantum dot-converted micro-LED display, its ambient contrast ratio degrades because the top QD converter can be excited by the ambient light. To solve this issue, we build a verified simulation model to quantitatively analyze the ambient reflection of quantum dot-converted micro-LED system and improve its ambient contrast ratio with a top color filter layer.
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Doctor of Philosophy (Ph.D.)
College of Optics and Photonics
Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Gou, Fangwang, "High Performance Micro-scale Light Emitting Diode Display" (2020). Electronic Theses and Dissertations, 2020-. 222.