Process Integration and Interconnection Design of Passive-Matrix LED Micro-Displays With 256 Pixel-Per-Inch Resolution

Abstract

A 0.28-inch InGaN-based blue micro-LED display with 256 pixel-per-inch resolution and a pitch of 100 μm was successfully fabricated in this study. A thick Ti/Al/Ti/Au interconnection metal was deposited on the n-type gallium nitride (n-GaN) region to reduce the interconnection resistance. The micro-LED array with interconnection metal exhibits better electrical property consistency as compared with that of the traditional one. The output power, forward voltage, and external quantum efficiency of micro-LED, which measured under 1-mA current injection with the full lighting mode, are 0.8 mW, 3.0 V, and 10%, respectively. This technique has the potential to integrate InGaN-based LEDs with quantum dots for full-color applications.

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.…”

“…As a consequence, the design of the leads, especially on the cathode side, has a massive impact on the obtained IV behaviour and also dominates the variation of the series resistances across the array. As shown in a similar approach for an array of 50 µm pixels, the homogeneity of the IV curves improves noticeably when applying a buried metallization along the cathodes [16]. However, due to the intention to scale the pixel pitch down to the low micrometer regime, this additional fabrication step was not pursued in the approach presented here.…”

“…This is rather low when compared to conventional high-power LEDs and presumably due to a limited light extraction efficiency (LEE), caused by the metallic spreading layer for the top-emitting devices. The LEE could be increased by applying a p-contact with higher transparency, e.g., based on indium tin oxide (ITO) [16]. The obtained data points enable the calculation of absolute EQE values in the following manner:…”

“…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]. Electrical access to the p-GaN is then provided by chemical mechanical polishing (CMP) or subsequent etching of openings into the dielectric layer.…”

59‐3: Ultra‐Precise Printing of Micrometer‐Size Interconnectors for High‐Resolution MicroLED Displays

“…In this contribution we introduce an ultra-precise deposition (UPD) technology [4], [5] to print micrometric conductive structures and make arbitrarily-shaped interconnectors on steps that are much larger than then the feature size of the printed structure. Since the quality of interconnections in µLED arrays significantly influences the performance of a display [6], we will argue that UPD is a suitable technology for making mechanically robust and high-conductivity interconnectors in µLED displays.…”