Artificial neuron made from VO2

PATEL: Our brains conduct information through electrical signals. Little voltage spikes that neurons pass around. And the frequency of those little spikes encodes information. But disorders like depression or ADHD can weaken these signals or alter their frequency. Here’s Shriram Ramanathan at Purdue University, with a materials engineer’s take.

SHRIRAM RAMANATHAN: Basically you can think of the neuron as a material that integrates charge. So imagine the neuron is collecting charge as it receives charge. And then at some critical charge level it fires a signal. So this can be referred to as a leaky integrate fire function. So the neuron is integrating charge but it’s not a perfect insulator so it leaks a little bit of charge as it’s collecting.

PATEL: A failing neuron just leaks all its charge and is unable to collect enough to trigger a signal. And now Ramanathan and his colleagues have made an artificial neuron that can precisely mimic this behavior of normal and faulty neurons in the brain. This could have important implications for neuroscience.

SR: We introduce a quantum material, vanadium dioxide, as a powerful analog of neurons that can be found in the animal brain. We can control the electrical properties of these materials in an exceptionally careful manner. We can, you know, very rigorously grow these materials and also pattern them into devices with very precise geometries. So what we are proposing is we can build these very well defined structures with well defined electrical characteristics and we can emulate the propagation and transmission of signals in these structures which mimic the natural neurons. And so we are hoping that these types of studies will allow neuroscientists to understand, for example, thresholds for resistances or capacitances or electrical leakage across wires and so forth to look at the very, very early stages of breakdown of normal functioning in neural circuits.

PATEL: Why vanadium dioxide? It can undergo a phase transition at room temperature. The material is a semiconductor. But pass enough current through it and at some critical current level it becomes a metal. This property is key for making a simple artificial neuron. 

SR: The beauty of this class of materials is that you can couple this type of a phase transition material to a capacitor and you can build an artificial neuron. So it’s really remarkably simple. It just contains this material, the phase transition material, which happens to be a quantum material that’s connected to a capacitor. That’s all it is to build and emulate an individual neuron! It can integrate charge, it can basically collect charge in an insulated state when it’s coupled to this capacitor. And when there is a critical level of charge accumulated or when it hits a certain temperature the material becomes metallic. And so suddenly there is a burst of electrical current through this material because it’s now no longer an insulator; it becomes a metal. So this mimics the integrate-and-fire capability. 

PATEL: Then the material returns to its original state and the cycle starts again. Tweaking the material’s oxygen composition ever so slightly changes its conductivity. So the researchers can emulate different types of neurons found in animal brains. And if they make the material really conductive, it cannot integrate charge so it behaves like a faulty neuron. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin.