Improved Performance of Passive-Matrix Micro-LED Displays Using a Multi-Function Passivation Structure

Abstract

The enhanced light output efficiency of passive-matrix micro light-emitting-diode (LED) display was achieved by employing the tapered sidewalls and distributed-Braggreflector (DBR) passivation structure. The oblique angles at the bottom of multi-quantum wall and n-GaN are 48.9°and 21.8°, which can favor the planarization structure of pixel interconnection. As increasing the number of DBR (SiO 2 /TiO 2 ) stacking from 3.5 to 5.5 pairs, the reflectance increased obviously from 81.4% to 98.0% at the wavelength of 450 nm. As the micro-LED display with a multi-function DBR structure, the output power of 1.07 mW under 1 mA, the external-quantum efficiency of 42% under 0.2 mA, and the luminance of 435 nits were obtained.

Processing and Characterization of Monolithic Passive-Matrix GaN-Based MicroLED Arrays With Pixel Sizes From 5 to 50 µm

“…The approach we present here uses a filling procedure based on benzocyclobuthene (BCB), which is planarized after spin-on by mechanical polishing to directly access the p-GaN surface. We demonstrate that this design enables the fabrication of small pixels down to the size of 5 µm, i.e., resolutions of up to 2540 ppi, which is smaller than what has previously been reported for the passive-matrix approach [16], [17]. Current transport in the cathodes is realized without additional metallization.…”

“…These values could be enhanced by using p-GaN spreading layers with a higher optical transparency, e.g., ITO [16]. Alternatively, a flipchip approach with backside emission through the sapphire substrate would increase the extraction efficiency [17]. The impact of sidewall defects at the plasma-etched fins, especially affecting the IQE in case of smaller pixels, could be reduced by additional passivation measures [38], [39].…”

“…Due to required space for wiring, this architecture only allows a limited number of pixels, but can be brought to a very high level of miniaturization with pixel sizes as low as 200 nm [14]. Still monolithic, but with enhanced scaling capabilities concerning the pixel number, passive-matrix approaches have been developed as an alternative [1], [15]- [17]. In this architecture, pixels are defined by orthogonal cathode and anode lines, which both need to be set to the according potential to activate the pixel located at the crossover of the two electrode lines.…”

“…So far, different strategies to address this issue have been presented, e.g. a multi-step or tapered etching profile of the fins to avoid high vertical steps [15], [17]. In other designs, the gaps in between the fins are filled, e.g., with SiO2 or a polymer [1], [16], [18], [19].…”

Detailed Successive Layer Modeling and Design Factor Analysis for Single Micro-LED Pixel

“…Thus, the need arises for a detailed analysis procedure for pixel-based intensity distribution (apodization), light extraction, and uniformity predictions. Among various reports, few studies have discussed the optical modeling of the construction and design of micro-LED devices [6]- [8]. However, there is a lack of simulation details and a proper protocol for further investigation.…”