High-Density Micro-OLEDs on Shank-Shaped CMOS Chips for Optogenetic Implants

Optogenetics allows the manipulation and detection of neuronal activity through the use of genetically targeted light-sensitive ion channels and voltage- or ion-sensitive fluorescent reporters, and thus offers a highly specific and selective tool for neuroscience research, with a number of promising clinical applications now emerging. However, achieving simultaneous delivery and collection of light with sufficient spatial and temporal resolution remains highly challenging, especially when working in freely behaving animal models and/or deep in tissue that is outside the direct reach of microscopes.<br/>Organic light-emitting diodes (OLEDs) have allowed the realization of high-resolution, portable and low power-consumption displays for mobile phones and TVs. Integrating top-emitting OLEDs on silicon-based complementary metal–oxide–semiconductor (CMOS) chips enables the production of micro-displays with high fill-factor and micrometer-sized, direct emissive-element pixels.<br/>Here, we demonstrate the monolithic integration of OLED technology on CMOS chips to realize implants with an unprecedented number of simultaneously addressable light-sources, thus bridging a current technology gap for controlled and specific optical excitation at the cellular level. Our hybrid device unites the direct deposition of organic semiconductor materials on dense arrays of pixel-electrodes with active addressing of these pixels through a CMOS backplane. As a proof-of-concept, OLEDs were integrated on a CMOS device with four shanks, each with a length of 3 mm, a width of 150 μm, and with a total of 1024 pixel-electrodes each 15x15 µm² in size.<br/>Due to the molecular nature of the materials used in OLEDs, their emission wavelength can be readily adjusted to the activation spectrum of different channelrhodopsins. We demonstrate integration of both red and blue top-emitting OLEDs on CMOS chips, and employ doped charge transport layers that prove particularly useful in providing maximum brightness at the limited driving voltage provided by CMOS chips [1]. We further show systematic optimization of device brightness and pixel yield to 50 µW/mm² and &gt;90%, respectively, using plasma-based surface treatment of the aluminum pixel electrodes on the CMOS chips. In combination, these parameters are more than sufficient to achieve reliable neuronal stimulation with state-of-the-art light-sensitive channelrhodopsins [2]. Our devices are encapsulated by our latest chemical vapor based thin-film deposition methods in order to render them biocompatible and stable for implantation [3].<br/>The integration of high-brightness OLEDs with microscopic dimensions on CMOS devices paves the way for stimulation and detection of neuronal activity on the cellular level, thus opening multiple opportunities to further our understanding of neural circuits and brain disorders.<br/><br/>1. Deng, Y. <i>et al.</i> Development of Very High Luminance p-i-n Junction-Based Blue Fluorescent Organic Light-Emitting Diodes. <i>Advanced Optical Materials</i> <b>8</b>, 1901721 (2020).<br/>2. Murawski, C. <i>et al. </i>Segment-specific optogenetic stimulation in Drosophila melanogaster with linear arrays of organic light-emitting diodes. <i>Nat Commun</i> <b>11</b>, 6248 (2020).<br/>3. Keum, C. <i>et al.</i> A substrateless, flexible, and water-resistant organic light-emitting diode. <i>Nat Commun</i> <b>11</b>, 6250 (2020).