Artificial semiconductor synapses

So far we are still trying to figure out specific functions of a brain. Our best conventional technology looks nothing like the biological system. The reason for that is because computer processors are built on 2D planar silicon, which are connect via controller hubs, and what is most important they use binary system for determining whether or not a given transistor is on or off.

 Researchers and scientist have discovered that the neurons connect to each other in 3D and are decidedly non-binary. The release of neurotransmitters in the brain is governed by the movement of the calcium ions across cell membranes. Larger influxes of calcium into the synapse produce larger downstream effects.

IBM researchers have detailed a new discovery that brings us one step closer to bridging the gap between synapses and silicon. The research team has detailed a method for transforming an insulative layer into a conductive material by exposing it to a charged fluid. VO2 (vanadium (IV) oxide) is a compound with a particularly odd (and interesting) habit. It transforms from an insulator to a conductor depending on its temperature. That’s the sort of capability that makes scientists giddy, but it’s just the starting point for what the IBM team found.

By exposing the VO2 thin film to an ionic fluid, the scientists were able to stabilize the metallic phase of VO2 down to five degrees Kelvin. Normally, VO2 is an insulator below 340K (68C) and metallic/conductive at 68C or above. The previous explanation for this dramatic change in behavior is called electrolyte gating. This theory posited that the dramatic change in VO2′s transition capabilities was caused by the introduction of the ionic liquid into the gate structure.

The research team tested this by cleaning the heck out of their test substrate. The VO2 thin film was examined using X-ray photoelectron spectroscopy (XPS) — no fluid was found. The treated VO2 film, meanwhile, could still be flipped between low and high conductance by a sufficient voltage change. The team confirmed its findings on VO2 thin films over different substrates, to make certain that particular properties of the underlying material weren’t the cause of the results.

For the IBM team the next step is to create larger fluidic circuits that flip on or off depending on local fluid concentrations. This way we coud form or disrupt connections just the same way a synaptic connection in the brain could be remade, or the strength of that connection could be adjusted.

What is interesting about this research is long-term goals. Generally it is very difficult to model or simulate behavior and function of a system if you can’t build a representative model of it. The Blue Brain project is one of the world’s leading efforts to simulate neuronal structure. The last major project milestone was the simulation of a cellular mesocircuit with 100 neocortical columns and a million cells in total. Doing so required the use of an IBM Blue Gene/P, one of the most power-efficient supercomputers in existence. At present, simulating one simplified component of a rat brain requires multiple orders of magnitude more power than an organic brain uses.

And that’s why advances like this matter. The ability to modify a material’s insulative properties without applying electricity could be critical to future attempts to scale brain modeling downward. Creating circuits that model synapse functions (even if they do so imperfectly and very simply) can help us understand how their biological counterparts function. It could dramatically reduce the power consumption (and waste heat) generated by such attempts, just as the advent of modern semiconductor manufacturing reduced computers from structures that fit into warehouses to pockets.

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