High-density Integration of Ultrabright OLEDs on a Miniaturized Needle-shaped CMOS backplane.

Direct deposition of organic light-emitting diodes (OLEDs) on silicon-based complementary metal-oxide-semiconductor (CMOS) chips has enabled self-emissive microdisplays with high resolution and fill-factor. Emerging applications of OLEDs in augmented and virtual reality (AR/VRss) displays and in biomedical applications, e.g. as brain implants for cell-specific light delivery in optogenetics, require light intensities orders of magnitude above those found in traditional displays. Further requirements often include a microscopic device footprint, a specific shape and an ultrastable passivation, e.g. to ensure biocompatibility and minimal invasiveness of OLED-based implants. Here, up to 1024 ultrabright, microscopic OLEDs were deposited directly on needle-shaped CMOS chips. Transmission electron microscopy and energy-dispersive X-ray spectroscopy were performed on the foundry-provided aluminum contact pads of the CMOS chips to guide a systematic optimization of the contacts. Plasma treatment and implementation of silver interlayers led to ohmic contact conditions and thus facilitated direct vacuum deposition of orange and blue-emitting OLED stacks leading to micrometer-sized pixels on the chips. The electronics in each needle allowed to switch each pixel individually. OLED pixels generated a mean optical power density of 0.25 mW/mm 2 , corresponding to >40,000 cd/m 2 , well above the requirement for daylight AR applications and optogenetic single-unit activation in the brain. This article is protected by copyright. All rights reserved.