Neuromorphic memristor operates at biological voltages
Such a device, say the researchers, runs extremely efficiently on very low power, as brains do, to carry signals between neurons, addressing one of the biggest hurdles to neuromorphic computing – being able to operate at neurological voltages. While most conventional computers operate at over 1 volt, the brain sends signals – called action potentials – between neurons at around 80 millivolts,
The researchers demonstrated that their bioinspired bio-voltage memristors function at the biological voltages of 40 – 100 mV.
“This is the first time that a device can function at the same voltage level as the brain,” says electrical and computer engineering researcher Jun Yao, a co-author of a paper on the research. “People probably didn’t even dare to hope that we could create a device that is as power-efficient as the biological counterparts in a brain, but now we have realistic evidence of ultra-low power computing capabilities. It’s a concept breakthrough and we think it’s going to cause a lot of exploration in electronics that work in the biological voltage regime.”
The protein nanowires used in the research were harvested from the bacterium Geobacter. Geobacter‘s electrically conductive protein nanowires, say the researchers, offer many advantages over expensive silicon nanowires, which require toxic chemicals and high-energy processes to produce. Protein nanowires also are more stable in water or bodily fluids, an important feature for biomedical applications.
The researchers sheared nanowires off the bacteria so only the conductive protein was used and then “put the purified nanowires through their paces” to see what they are capable of at different voltages. They experimented with a pulsing on-off pattern of positive-negative charge sent through a tiny metal thread in a memristor, which creates an electrical switch.
They used a metal thread because protein nanowires facilitate metal reduction, changing metal ion reactivity and electron transfer properties. This microbial ability is not surprising, say the researchers, because wild bacterial nanowires breathe and chemically reduce metals to get their energy the way we breathe oxygen.
As the on-off pulses create changes in the metal filaments, new branching and connections are created in the tiny device, which is 100 times smaller than the diameter of a human hair, creating an effect similar to learning – new connections – in a real brain.
“You can modulate the conductivity, or the plasticity of the nanowire-memristor synapse so it can emulate biological components for brain-inspired computing,” says Yao. “Compared to a conventional computer, this device has a learning capability that is not software-based.”
The researchers say they plan to follow up this discovery with more research on mechanisms, and to “fully explore the chemistry, biology and electronics” of protein nanowires in memristors. In addition, they plan to explore possible applications, which might, for example, include a device to monitor heart rate.
“This,” says Yao, “offers hope in the feasibility that one day this device can talk to actual neurons in biological systems.”
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