Heterostructure Optoelectronic Neuromorphic Devices with Multi-Spectral Light Modulated Synaptic Behaviors

Recently, the hardware-based neuromorphic chip is considered as the promising solution to realize the synaptic behaviors for complete intelligent process. In particular, neuromorphic photonics has been researched for promising solutions capable of high bandwidth, low crosstalk, high density and low power consumption compared to the neuromorphic device with an electrical domain, such as complementary metal-oxide-semiconductor (CMOS) integrated circuit. The recent research for neuromorphic photonics mainly underlies the persistent photoconductivity behavior (PPC) effect by using the various methodologies such as Schottky barrier, charge trapping, electrochemical doping, film reflectivity change and point defect ionization. By using these approach, photonic and optoelectronic neuromorphic devices with biological synaptic functions can be achieved. Particularly, two-connected indium-gallium-zinc-oxide (IGZO) devices, one of the amorphous metal oxide semiconductors, showed photonic synaptic behaviors using ionization of oxygen vacancies and PPC effect. However, since the light has only positive power, the optoelectronic neuromorphic device with an optical domain barely demonstrated the complete neuromorphic behaviors. In this regard, optoelectronic neuromorphic device capable of bidirectional synaptic modulation by all-photonic stimulation, high-density scalability, wavelength fidelity and the CMOS process compatibility are considered as the key factors to obtain the viability and efficacy of optoelectronic neuromorphic systems.<br/>Here, we propose a large-area pixelized optoelectronic neuromorphic system realized by multispectral light-stimulated bidirectional optoelectronic neuromorphic pixel circuits and demonstrated the hardware-based pattern training capability in an array level. In particular, the bidirectional synaptic modulation is achieved by the optoelectronic neuromorphic pixel circuit comprising metal-oxide (MO) and metal-chalcogenide (MC)-based synaptic transistor and photovoltaic divider. It is performed by adjusting electron trapping or de-trapping in the MC/MO hetero-interface of the photo transistor with the assistance of a photovoltaic divider. This optoelectronic neuromorphic pixel circuit successfully emulated the biological synaptic functions such as short-term plasticity, long-term potentiation, long-term depression and paired pulse facilitation/depression via multi-spectral light selectivity. To confirm the viability of hardware-based optoelectronic neuromorphic computing in an array level, pattern training in pixelized device array was demonstrated using multi-spectral light pattern irradiation. In both the empirical pixel training in the optoelectronic neuromorphic array and the pattern recognition simulation, the optoelectronic neuromorphic array operated with bidirectional synaptic modulation exhibited higher recognition rates (up to 97%), lower mismatched pixel along with fast speed (less epochs) than those with unidirectional synaptic modulation. Furthermore, optoelectronic neuromorphic device based on the combination of two different transition metal dichalcogenide (TMDC) also implemented bidirectional synaptic modulation.