Memristive-based electro-optical neuromorphic hardware takes advantage of both the high-density of electronic circuits and the high bandwidth of their photonic counterparts, thus showing potential for low-power artificial intelligence applications. In this Perspective paper, we introduce a class of electro-optical memristors that can emulate the key properties of synapses and neurons, which are essential features for the realization of electro-optical neuromorphic functionalities. We then describe the challenges associated with existing technologies and finally give our viewpoint on possible developments toward an energy-efficient neuromorphic platform.

Memristive devices are an emerging new type of devices operating at the scale of a few or even single atoms. They are currently used as storage elements and are investigated for performing in-memory and neuromorphic computing. Amongst these devices, Ag/amorphous-SiOx/Pt memristors are among the most studied systems, with the electrically induced filament growth and dynamics being thoroughly investigated both theoretically and experimentally. In this paper, we report the observation of a novel feature in these devices: The appearance of new photoluminescent centers in SiOx upon memristive switching, and photon emission correlated with the conductance changes. This observation might pave the way towards an intrinsically memristive atomic scale light source with applications in neural networks, optical interconnects, and quantum communication.

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In this article, we present ultralow leakage logic circuits by combining 3-D memristors with CMOS transistors. Significant leakage current reductions of up to 99% are found by experiments and simulation for a memristive hybrid-inverter if compared with a conventional inverter. Likewise, circuit simulations of memristive hybrid ring oscillators, NAND, or full adders show more than 100% gain in energy efficiency per cycle over state-ofthe-art circuits. Importantly, the memristive circuits offer hysteresis-free operation. The hysteresis-free operation is due to properly engineered properties-such as the threshold voltage-of the memristors to match the circuit, as well as the self-adaptive filament diameter of our memristor during operation. Lastly, the memristors feature a 10 8 ON-OFF ratio, enabling both high speed and low leakage (∼10 fA) when integrated with a transistor. They also come with a well-controlled filament formation on a ∼10-nm footprint, making them ideal to integrate with modern CMOS technology transistors.

We integrate memristors in a silicon photonic/plasmonic platform and demonstrate modulators, photodetectors and electronic devices complemented with memory effect. The demonstrated memristors could be the key photonic building blocks in hybrid photonic-electronic neuromorphic chips.