Simultaneous summation and recognition effects for a dual-emitter light-induced neuromorphic device

📝 Abstract

We propose and fabricate a dual-emitter light-induced neuromorphic device composed of two light-induced devices with a common collector and base. Two InGaN multiple quantum well diodes (MQW-diodes) are used as the emitters to generate light, and one InGaN MQW-diode is used as the common collector to absorb the emitted light. When the presynaptic voltages are synchronously applied to the two emitters, the collector demonstrates an adding together of the excitatory post synaptic voltage (EPSV). The width and period of the two input signals constitute the code to generate spatial summation and recognition effects at the same time. Experimental results confirm that temporal summation caused by the repetitive-pulse facilitation could significantly strengthen the spatial summation effect due to the adding together behavior when the repetitive stimulations are applied to the two emitters in rapid succession. Particularly, the resonant summation effect occurs at the co-summation region when the two repetitive-pulse signals have a resonant period, which offers a more sophisticated spatiotemporal EPSV summation function for the dual-emitter neuromorphic device.

💡 Analysis

We propose and fabricate a dual-emitter light-induced neuromorphic device composed of two light-induced devices with a common collector and base. Two InGaN multiple quantum well diodes (MQW-diodes) are used as the emitters to generate light, and one InGaN MQW-diode is used as the common collector to absorb the emitted light. When the presynaptic voltages are synchronously applied to the two emitters, the collector demonstrates an adding together of the excitatory post synaptic voltage (EPSV). The width and period of the two input signals constitute the code to generate spatial summation and recognition effects at the same time. Experimental results confirm that temporal summation caused by the repetitive-pulse facilitation could significantly strengthen the spatial summation effect due to the adding together behavior when the repetitive stimulations are applied to the two emitters in rapid succession. Particularly, the resonant summation effect occurs at the co-summation region when the two repetitive-pulse signals have a resonant period, which offers a more sophisticated spatiotemporal EPSV summation function for the dual-emitter neuromorphic device.

📄 Content

1  Abstract-We propose and fabricate a dual-emitter light-induced neuromorphic device composed of two light-induced devices with a common collector and base. Two InGaN multiple quantum well diodes (MQW-diodes) are used as the emitters to generate light, and one InGaN MQW-diode is used as the common collector to absorb the emitted light. When the presynaptic voltages are synchronously applied to the two emitters, the collector demonstrates an adding together of the excitatory post synaptic voltage (EPSV). The width and period of the two input signals constitute the code to generate spatial summation and recognition effects at the same time. Experimental results confirm that temporal summation caused by the repetitive-pulse facilitation could significantly strengthen the spatial summation effect due to the adding together behavior when the repetitive stimulations are applied to the two emitters in rapid succession. Particularly, the resonant summation effect occurs at the co-summation region when the two repetitive-pulse signals have a resonant period, which offers a more sophisticated spatiotemporal EPSV summation function for the dual-emitter neuromorphic device. Index Terms-InGaN multiple quantum well diode, dual-emitter light-induced neuromorphic device, excitatory postsynaptic voltage, resonant summation effect, adding together behavior. I. INTRODUCTION The artificial synaptic device is a hot topic for brain-inspired neuromorphic systems [1-5], and synaptic electronics have gained considerable attention in recent years, including two-terminal memristors and three-terminal ionic/electronic hybrid devices. Based on phase change materials, nanoelectronic programmable synapses have been developed for brain-inspired computing [6]. Dynamic logic and learning have been presented using a carbon nanotube synapse [7]. An Ag2S inorganic synapse has been reported to emulate the synaptic functions of both short-term plasticity and long-term potentiation characteristics [8]. Flexible metal oxide/grapheme oxide hybrid neuromorphic devices have demonstrated the realization of spatiotemporal correlated logics [9]. Proton-conducting grapheme oxide-coupled neuron devices have been proposed for brain-inspired cognitive systems [10]. Compared with other synaptic devices, the light-induced synaptic device uses photons rather than electrons or protons to induce excitatory postsynaptic voltage (EPSV) behavior for artificial synapse applications [11].
Here, we propose and fabricate a dual-emitter light-induced neuromorphic device on an III-nitride-on-silicon platform. Figure 1(a) shows a schematic illustration of the proposed dual-emitter light-induced neuromorphic device, which has a common base (B). The collector (C) absorbs the pulse light

generated by the emitter (E) to achieve a photon-electron conversion, leading to an EPSV for the mimicking of synaptic activity with different signal sources. The period, shape and width of pulses constitute the code to transfer information in the biological nervous system, which is characterized by the EPSV summation [12]. When the two emitters are synchronously biased, the EPSVs happen at the same time and are added together, leading to a spatial summation. The adding together of EPSVs generated at the same emitter forms a temporal summation if they occur in a rapid succession. The spatial summation can be significantly reinforced by the temporal summation, which is investigated for emulating the complicated memory effect during the learning process.

Fig. 1. (a) Schematic diagram of a dual-emitter neuromorphic device; (b) SEM image of fabricated dual-emitter neuromorphic device. II. EXPERIMENTAL RESULTS AND DISCUSSION

The proposed dual-emitter neuromorphic device is fabricated on a 2-inch III-nitride-on-silicon wafer. The 1500-μm-thick starting wafer is firstly thinned to approximately 200 μm by chemical mechanical polishing. The emitter, collector and probing pad are patterned by photolithography and formed by induced coupled plasma reactive ion etching (ICP-RIE) of III-nitride epitaxial films with Cl2 and BCl3 hybrid gases at the flow rates of 10 sccm and 25 sccm, respectively. The Ni/Au (20nm/180nm) metal stacks are used as p- and n-type contacts. Then, waveguide structures are defined and etched by ICP-RIE. After protecting the top device structure with thick photoresist, silicon removal is conducted by deep reactive ion etching with alternating steps of SF6 etching and C4F8/O2 passivation. Subsequently, III-nitride backside thinning is carried out by ICP-RIE to obtain ultrathin membrane-type device architecture. Figure 1(b) shows a scanning electron microscope (SEM) image of the fabricated dual-emitter neuromorphic device. The suspended device architecture can form a highly-confined waveguide structure for the in-plane light coupling between the emitter and the c

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