High‐Density Integration of Ultrabright OLEDs on a Miniaturized Needle‐Shaped CMOS Backplane

Abstract

AbstractDirect 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/VR) 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 ultrastable passivation, e.g., to ensure biocompatibility and minimal invasiveness of OLED‐based implants. In this work, up to 1024 ultrabright, microscopic OLEDs are deposited directly on needle‐shaped CMOS chips. Transmission electron microscopy and energy‐dispersive X‐ray spectroscopy are 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 lead to ohmic contact conditions and thus facilitate direct vacuum deposition of orange‐ and blue‐emitting OLED stacks leading to micrometer‐sized pixels on the chips. The electronics in each needle allow each pixel to switch individually. The OLED pixels generate 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.