Retina‐Inspired Color‐Cognitive Learning via Chromatically Controllable Mixed Quantum Dot Synaptic Transistor Arrays

Abstract

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.

A brief review on device operations and working mechanisms of organic transistor photomemories

“…On the other hand, the holes are effectively confined in quantum dots because of an unfavorably high potential barrier. 115 This mechanism is kind of similar to the photo-writing phenomenon for a transistor photomemory elaborated in the fourth section.…”

“…13a). 91,115–126 The so-called “photosynaptic transistor” resembles that of a biological synapse construction wherein the source/drain terminals can be associated with the pre-/postsynapses, and the external light stimuli/gate bias corresponds to the action potentials exerted in the presynapse (see Fig. 13b).…”

“…13c, the respective band energies are drawn schematically based on the mixed quantum dot photoabsorbers and metal-oxide semiconducting layer that built-up a photosynaptic transistor in a recent report. 115 Upon the incident light signal pulse to the device (an action potential exerted presynapse), the photogenerated electron–hole pairs in quantum dots (photoactive materials, in general) are readily separated, and subsequently, the electrons transfer to the most favorable energy level which is in the metal-oxide part. On the other hand, the holes are effectively confined in quantum dots because of an unfavorably high potential barrier.…”

“…In the latter paragraph, the progress of photosynaptic transistors will be elaborated on the latest reports found in the literature which are not limited to the use of photoactive organics/polymers, 97,130,131 but also hybrid-inorganics and other potential photoactive materials. 115,118,119,121,132…”

Progress of Materials and Devices for Neuromorphic Vision Sensors

“…An all-in-one neuromorphic vision sensor should be able to simultaneously perform image sensing and neuromorphic in-memory computing during the vision computing of image data. Therefore, it must include functional areas for photosensing, conductance switching, and analog update functions [ 51 – 56 ]. When visual information arrives in the OS array, each OS with a light-absorbing site experiences a change in the channel conductance.…”