Paper-based transistor mimics human brain

The low voltage (1.5V) device is designed to replicate the junction between two neurons, known as a biological synapse. It is expected to propel the development of artificial neural networks for next generation computer processing and robotics. What's more, becuase paper is not only a cheap and widely used material, but also a natural and recyclable one, the team believes the development could pave the way towards low cost, flexible and environmentally friendly electronics. The device consists of indium zinc oxide (IZO), as both a channel and a gate electrode, separated by a 550nm thick film of nanogranular silicon dioxide electrolyte, which was fabricated using a process known as chemical vapour deposition. The design is specific to that of a biological synapse - a small gap that exists between adjoining neurons over which chemical and electrical signals are passed. It is through these synapses that neurons are able to pass signals and messages around the brain. All neurons are electrically excitable, and can generate a 'spike' when the neuron's voltage changes by large enough amounts. These spikes cause signals to flow through the neurons which cause the first neuron to release chemicals, known as neurotransmitters, across the synapse, which are then received by the second neuron, passing the signal on. Similar to these output spikes, the researchers applied a small voltage to the first electrode in their device which caused protons - acting as a neurotransmitter - from the silicon dioxide films to migrate towards the IZO channel opposite it. As protons are positively charged, this caused negatively charged electrons to be attracted towards them in the IZO channel which subsequently allowed a current to flow through the channel, mimicking the passing on of a signal in a normal neuron. The researchers found that when two short voltages were applied to the device in a short space of time, the second voltage was able to trigger a larger current in the IZO channel compared to the first applied voltage, as if it had 'remembered' the response from the first voltage. Qing Wan, from the School of Electronic Science and Engineering at Nanjing University, said: "A paper-based synapse could be used to build lightweight and biologically friendly artificial neural networks, and, at the same time, with the advantages of flexibility and biocompatibility, could be used to create the perfect organism-machine interface for many biological applications."