The complete hardware implementation of an optoelectronic neuromorphic computing system is considered as one of the most promising solutions to realize energy‐efficient artificial intelligence. Here, a fully light‐driven and scalable optoelectronic neuromorphic circuit with metal‐chalcogenide/metal‐oxide heterostructure phototransistor and photovoltaic divider is proposed. To achieve wavelength‐selective neural operation and hardware‐based pattern recognition, multispectral light modulated bidirectional synaptic circuits are utilized as an individual pixel for highly accurate and large‐area neuromorphic computing system. The wavelength selective control of photo‐generated charges at the heterostructure interface enables the bidirectional synaptic modulation behaviors including the excitatory and inhibitory modulations. More importantly, a 7 × 7 neuromorphic pixel circuit array is demonstrated to show the viability of implementing highly accurate hardware‐based pattern training. In both the pixel training and pattern recognition simulation, the neuromorphic circuit array with the bidirectional synaptic modulation exhibits lower training errors and higher recognition rates, respectively.
Artificial photonic synapses are emerging as a promising implementation to emulate the human visual cognitive system by consolidating a series of processes for sensing and memorizing visual information into one system. In particular, mimicking retinal functions such as multispectral color perception and controllable nonvolatility is important for realizing artificial visual systems. However, many studies to date have focused on monochromatic‐light‐based photonic synapses, and thus, the emulation of color discrimination capability remains an important challenge for visual intelligence. Here, an artificial multispectral color recognition system by employing heterojunction photosynaptic transistors consisting of ratio‐controllable mixed quantum dot (M‐QD) photoabsorbers and metal‐oxide semiconducting channels is proposed. The biological photoreceptor inspires M‐QD photoabsorbers with a precisely designed red (R), green (G), and blue (B)‐QD ratio, enabling full‐range visible color recognition with high photo‐to‐electric conversion efficiency. In addition, adjustable synaptic plasticity by modulating gate bias allows multiple nonvolatile‐to‐volatile memory conversion, leading to chromatic control in the artificial photonic synapse. To ensure the viability of the developed proof of concept, a 7 × 7 pixelated photonic synapse array capable of performing outstanding color image recognition based on adjustable wavelength‐dependent volatility conversion is demonstrated.
technologies are attracting considerable attention owing to the increasing demand for multiplexed signal processing of broad band stimulation for accurate recognition. Recently, the development of photode tectors such as photodiodes, [11][12][13] photo conductors, [14,15] phototransistors, [16][17][18][19] and photovoltaics [20][21][22] has promoted research to enhance efficiency and sensitivity with multispectral imaging availability for the UV, [23][24][25] visible, [26,27] and IR [28][29][30][31] wave band analysis. In particular, epitaxial semiconductors such as complementary metaloxidesemiconductors (CMOS) compatible silicon technologies have led to revolutionary improvements in sen sory devices because of reasonable cost, large area, and highresolution imaging applicability. [3,32,33] However, their lim ited sensing and actuation functionalities limit opportunities for the realization of multifunctional and multiplexed stateof theart optoelectronics. Furthermore, the difficulty of integrating silicon and III-V semiconductors with printable and flexible platforms has prevented implementation in mechanically com pliant and conformal systems.As an alternative approach to epitaxially grown semiconduc tors, colloidal quantum dots (QDs) have been widely inves tigated as semiconductor nanocrystals for various optoelec tronic applications such as photodetectors, [34,35] lightemitting Color-selective multifunctional and multiplexed photodetectors have attracted considerable interest with the increasing demand for color filter-free optoelectronics which can simultaneously process multispectral signal via minimized system complexity. The low efficiency of color-filter technology and conventional laterally pixelated photodetector array structures often limit opportunities for widespread realization of high-density photodetectors. Here, low-temperature solution-processed vertically stacked full color quantum dot (QD) phototransistor arrays are developed on plastic substrates for highresolution color-selective photosensor applications. Particularly, the three different-sized/color (RGB) QDs are vertically stacked and pixelated via direct photopatterning using a unique chelating chalcometallate ligand functioning both as solubilizing component and, after photoexposure, a semiconducting cement creating robust, insoluble, and charge-efficient QD layers localized in the a-IGZO transistor region, resulting in efficient wavelength-dependent photo-induced charge transfer. Thus, high-resolution vertically stacked full color QD photodetector arrays are successfully implemented with the density of 5500 devices cm -2 on ultrathin flexible polymeric substrates with highly photosensitive characteristics such as photoresponsivity (1.1 × 10 4 AW -1 ) and photodetectivity (1.1 × 10 18 Jones) as well as wide dynamic ranges (>150 dB).
The latest developments in bio-inspired neuromorphic vision sensors can be summarized in 3 keywords: smaller, faster, and smarter. (1) Smaller: Devices are becoming more compact by integrating previously separated components such as sensors, memory, and processing units. As a prime example, the transition from traditional sensory vision computing to in-sensor vision computing has shown clear benefits, such as simpler circuitry, lower power consumption, and less data redundancy. (2) Swifter: Owing to the nature of physics, smaller and more integrated devices can detect, process, and react to input more quickly. In addition, the methods for sensing and processing optical information using various materials (such as oxide semiconductors) are evolving. (3) Smarter: Owing to these two main research directions, we can expect advanced applications such as adaptive vision sensors, collision sensors, and nociceptive sensors. This review mainly focuses on the recent progress, working mechanisms, image pre-processing techniques, and advanced features of two types of neuromorphic vision sensors based on near-sensor and in-sensor vision computing methodologies. "Image missing"
Quantum dot (QD)-based optoelectronics have received great interest for versatile applications because of their excellent photosensitivity, facile solution processability, and the wide range of band gap tunability. In addition, QD-based hybrid devices, which are combined with various high-mobility semiconductors, have been actively researched to enhance the optoelectronic characteristics and maximize the zero-dimensional structural advantages, such as tunable band gap and high light absorption. However, the difficulty of highly efficient charge transfer between QDs and the semiconductors and the lack of systematic analysis for the interfaces have impeded the fidelity of this platform, resulting in complex device architectures and unsatisfactory device performance. Here, we report ultrahigh detective phototransistors with highly efficient photo-induced charge separation using a Sn2S6 4–-capped CdSe QD/amorphous oxide semiconductor (AOS) hybrid structure. The photo-induced electron transfer characteristics at the interface of the two materials were comprehensively investigated with an array of electrochemical and spectroscopic analyses. In particular, photocurrent imaging microscopy revealed that interface engineering in QD/AOS with chelating chalcometallate ligands causes efficient charge transfer, resulting in photovoltaic-dominated responses over the whole channel area. On the other hand, monodentate ligand-incorporated QD/AOS-based devices typically exhibit limited charge transfer with atomic vibration, showing photo-thermoelectric-dominated responses in the drain electrode area.
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