Graphene-diamond junctions could aid in the realization of neuromorphic optical computers simulating human visual memory systems

Researchers at Nagoya University in Japan have designed highly efficient computing devices using graphene-diamond junctions that mimic some of the functions of the human brain.

A crucial phenomenon for memory and learning is “synaptic plasticity”, the ability of synapses (neural links) to adapt in response to increased or reduced activity. Scientists have attempted to recreate a similar effect using transistors and “memristors” (electronic memory devices whose resistance can be stored). Newly developed light-controlled memristors, or “photomemristors”, can both sense light and provide non-volatile memory, similar to human visual perception and memory. These excellent properties have opened the door to new materials that can act as artificial optoelectronic synapses.

Building on these advances, the Nagoya University research team designed graphene-diamond junctions that can mimic characteristics of biological synapses and key memory functions, thereby enabling memory devices to detect new generation images. In their recent study, the researchers, led by Dr. Kenji Ueda, demonstrated optoelectronically controlled synaptic functions using junctions between vertically aligned graphene (VG) and diamond. The manufactured junctions mimic biological synaptic functions, such as the production of “excitatory postsynaptic current” (EPSC) – the load induced by neurotransmitters at the synaptic membrane – when stimulated by optical impulses and exhibited further. basic brain functions such as the transition to shorts. long-term memory (STM) to long-term memory (LTM).

Dr Ueda explains: “Our brains are well equipped to sift through the available information and store what is important. We tried something similar with our VG-diamond matrices, which emulate the human brain when exposed to optical stimuli. He adds, “This study was triggered due to a discovery in 2016, when we found a large optically induced change in conductivity in graphene-diamond junctions.” Besides EPSC, STM, and LTM, the junctions also show 300% paired pulse facilitation, an increase in postsynaptic current when closely preceded by an anterior synapse.

VG-diamond matrices have undergone redox reactions induced by fluorescent light and blue LEDs under bias voltage. The researchers attributed this to the presence of hybrid carbons different from graphene and diamond at the junction interface, which led to the migration of ions in response to light and in turn allowed the junctions to perform photo-sensing and photo-controllable functions similar to those performed by the brain and retina. In addition, VG-diamond matrices have exceeded the performance of conventional photosensitive materials based on rare metals in terms of photosensitivity and structural simplicity.

Dr Ueda said: “Our study provides a better understanding of the working mechanism behind artificial optoelectronic synaptic behaviors, paving the way for optically controllable brain-mimicking computers, better information processing capabilities than existing computers.” .

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