Abstract 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/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.
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Optogenetic stimulation probes with single-neuron resolution based on organic LEDs monolithically integrated on CMOS
Abstract The use of optogenetic stimulation to evoke neuronal activity in targeted neural populations—enabled by opsins with fast kinetics, high sensitivity and cell-type and subcellular specificity—is a powerful tool in neuroscience. However, to interface with the opsins, deep-brain light delivery systems are required that match the scale of the spatial and temporal control offered by the molecular actuators. Here we show that organic light-emitting diodes can be combined with complementary metal–oxide–semiconductor technology to create bright, actively multiplexed emissive elements. We create implantable shanks in which 1,024 individually addressable organic light-emitting diode pixels with a 24.5 µm pitch are integrated with active complementary metal–oxide–semiconductor drive and control circuitry. This integration is enabled by controlled electrode conditioning, monolithic deposition of the organic light-emitting diodes and optimized thin-film encapsulation. The resulting probes can be used to access brain regions as deep as 5 mm and selectively activate individual neurons with millisecond-level precision in mice.
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- Award ID(s):
- 1706207
- NSF-PAR ID:
- 10462935
- Date Published:
- Journal Name:
- Nature Electronics
- ISSN:
- 2520-1131
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Organic doping is widely used for defining the majority charge carriers of organic thin films, tuning the Fermi level, and improving and stabilizing the performance of organic light‐emitting diodes and organic solar cells. However, in contrast to inorganic semiconductors, the doping concentrations commonly used are quite high (in the wt% range). Such high concentrations not only limit the scope of doping in organic field‐effect transistors (OFETs), but also limit the doping process itself resulting in a low doping efficiency. Here, the mechanism of doping at ultralow doping concentrations is studied. Doped C60metal‐oxide‐semiconductor (MOS) junctions are used to study doping at the 100 ppm level. With the help of a small‐signal drift‐diffusion model, it is possible to disentangle effects of traps at the gate dielectric/organic semiconductor interface from effects of doping and to determine the doping efficiency and activation energy of the doping process. Doped C60OFETs with an ultralow operation voltage of 800 mV and an excellent on/off ratio of up to 107are realized. The devices have low subthreshold swing in the range of 80 mV dec−1and a large transconductance of up to 8 mS mm−1.
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Epitaxial heterostructures based on oxide perovskites and III–V, II–VI and transition metal dichalcogenide semiconductors form the foundation of modern electronics and optoelectronics. Halide perovskites—an emerging family of tunable semiconductors with desirable properties—are attractive for applications such as solution-processed solar cells, light-emitting diodes, detectors and lasers. Their inherently soft crystal lattice allows greater tolerance to lattice mismatch, making them promising for heterostructure formation and semiconductor integration. Atomically sharp epitaxial interfaces are necessary to improve performance and for device miniaturization. However, epitaxial growth of atomically sharp heterostructures of halide perovskites has not yet been achieved, owing to their high intrinsic ion mobility, which leads to interdiffusion and large junction widths, and owing to their poor chemical stability, which leads to decomposition of prior layers during the fabrication of subsequent layers. Therefore, understanding the origins of this instability and identifying effective approaches to suppress ion diffusion are of great importance22–26. Here we report an effective strategy to substantially inhibit in-plane ion diffusion in two-dimensional halide perovskites by incorporating rigid π-conjugated organic ligands. We demonstrate highly stable and tunable lateral epitaxial heterostructures, multiheterostructures and superlattices. Near-atomically sharp interfaces and epitaxial growth are revealed by low-dose aberration-corrected high-resolution transmission electron microscopy. Molecular dynamics simulations confirm the reduced heterostructure disorder and larger vacancy formation energies of the two-dimensional perovskites in the presence of conjugated ligands. These findings provide insights into the immobilization and stabilization of halide perovskite semiconductors and demonstrate a materials platform for complex and molecularly thin superlattices, devices and integrated circuits.more » « less
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Abstract Organized nano‐ and microstructures of molecular semiconductors display interesting optical and photonic properties, and enhanced charge carrier mobilities, as compared to disordered thin films. However, known directed‐growth and self‐organization strategies cannot create structured molecular heterojunctions and cannot be practically incorporated into existing device fabrication routines to create large‐area optoelectronic devices. Here, an ultrathin (
< 2 nm) seed layer of the compound coronene creates 1D nanostructures of an electron‐transporting molecule (IFD) is shown, which possesses an intrinsic proclivity to form disordered thin films in the absence of the seed layer. It is revealed that nanostructured IFD films exhibit enhanced light absorption and emission, and greater electron mobilities, as compared to amorphous counterparts. This seed layer strategy creates uniform IFD nanowires over large areas of up to 18 mm2at low processing temperatures. Notably, the coronene seed layer creates IFD nanowires when applied over either oxide surfaces or predeposited organic layers, meaning that this structuring approach can be integrated into diode manufacturing routines to realize large‐area flexible optoelectronic devices. Flexible organic light‐emitting diodes and fullerene‐free organic solar cells containing IFD nanowires in the photoactive layer to demonstrate that molecular nanostructures can lead to robust, large‐area device arrays on flexible substrates being fabricated. -
The wide bandgap semiconductors SiC and GaN are commercialized for power electronics and for visible to UV light-emitting diodes in the case of the GaN/InGaN/AlGaN materials system. For power electronics applications, SiC MOSFETs (metal–oxide–semiconductor field effect transistors) and rectifiers and GaN/AlGaN HEMTs and vertical rectifiers provide more efficient switching at high-power levels than do Si devices and are now being used in electric vehicles and their charging infrastructure. These devices also have applications in more electric aircraft and space missions where high temperatures and extreme environments are involved. In this review, their inherent radiation hardness, defined as the tolerance to total doses, is compared to Si devices. This is higher for the wide bandgap semiconductors, due in part to their larger threshold energies for creating defects (atomic bond strength) and more importantly due to their high rates of defect recombination. However, it is now increasingly recognized that heavy-ion-induced catastrophic single-event burnout in SiC and GaN power devices commonly occurs at voltages ∼50% of the rated values. The onset of ion-induced leakage occurs above critical power dissipation within the epitaxial regions at high linear energy transfer rates and high applied biases. The amount of power dissipated along the ion track determines the extent of the leakage current degradation. The net result is the carriers produced along the ion track undergo impact ionization and thermal runaway. Light-emitting devices do not suffer from this mechanism since they are forward-biased. Strain has also recently been identified as a parameter that affects radiation susceptibility of the wide bandgap devices.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41928-023-01013-y
