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

Abstract

MicroLED arrays with the capability of switching each pixel separately with high frequency can serve as structured micro-illumination light engines for applications in sensing, optogenetics, microscopy and many others. We describe a scalable chip process chain for the fabrication of passive-matrix microLED arrays, which were integrated with PCB-based driving electronics. The arrays were produced by deep-etching of conventional planar LED structures on sapphire, followed by filling and planarization steps. The pixel resolution lies in the range of 254 to 2540 pixelsper-inch (ppi), the arrays consist of 32 x 32 pixels. Optical output powers up to 50 µW per pixel were measured. In comparison to CMOS-based approaches, the presented technology is a simplified strategy to produce microLED arrays with high pixel counts.

Droop and light extraction of InGaN-based red micro-light-emitting diodes

“…For example, Guo et al [25], investigating interdigitated mesas of LEDs, experimentally found that a narrower mesa that has a relatively longer sidewall dimension resulted in a higher η e . For µLEDs, an increasing EQE with shrinking size could be attributed to the increasing total η e via a higher contribution from sidewall emission [26][27][28]. Considering the impact of sidewall emission on η e , it could be interpreted that a larger peak EQE for a longer periphery (regardless of the device area shown in figure 2) is associated with increasing η e .…”

“…Second, we speculate that the change in η e is related not only to the device area but also to the length of the light propagation and the emission width of the device. It has been demonstrated that η e can increase with shrinking device size due mostly to the reduced light propagation length resulting in an increased EQE [26][27][28]. Assuming the light propagation lengths of 160 × 40 µm 2 and 160 × 10 µm 2 devices to be 40 µm and 10 µm, respectively, it is understood that a shorter light propagation length yields a larger η e , resulting in the ratio of 160 × 10 µm 2 to 160 × 40 µm 2 devices being greater than 1.0 over the whole current regime.…”

Fluorescence Multi-Detection Device Using a Lensless Matrix Addressable microLED Array

“…The fabrication of the matrix-addressed LED arrays ( Figure 1 c) is described in detail in a previous publication [ 51 ]. It consists of 32 × 32 squared LEDs of 50 µm edge length edge length with 100 µm pitch ( Figure 1 c).…”

“…The driver can operate up to 10 V, thus allowing the LED to provide high optical power (~30 µW at 6 V [ 51 ]). The capability of these drivers to generate driving voltages up to 10 V also enables the circuit to be used to drive nanoLEDs [ 54 ], which usually work at a higher voltage bias [ 55 ] because of the high resistance associated with the interconnection of the LED with the CMOS [ 54 ].…”

53.1: Invited Paper: Process optimization of passive matrix GaN Micro‐LED displays

“…Recently, in the work of Bornemann et al, they used etched n-GaN as the cathode line. However, using semiconductor as the electrode line increased the resistance [14] .…”