A Bio-Mimicking Synaptic Tactile Sensor Based on SWCNT Transistors

The skin is the largest organ in the human body, with a network of receptors that are essential for our perception of the surrounding environment. Among various receptors, the Merkel cell acts as the mechanoreceptor, and it forms a synapse called Merkel cell-neurite complex with an afferent neuron. With this complex, a tactile stimulus applied on the skin can be sensed, preprocessed, and then transmitted to the brain. To mimic the function of Merkel cell neurites, several devices such as sensors and synaptic transistors usually need to be integrated together. In this work, a synaptic tactile sensor capable of sensing and memorizing the stimulus in one device is demonstrated to imitate the main functions of the Merkel cell neurite. The synaptic sensor is based on a single-walled carbon nanotube (SWCNT) transistor with a surface patterned polymeric ionic gel as the solid electrolyte. We find that ions can be released from the ionic gel into the transistor channel when the ionic gel is compressed. Modulation of the post-synaptic current of the device is realized by electrochemically doping SWCNTs under presynaptic pressure spikes. Due to the unique morphology of SWCNTs and slow ion motion in the ionic gel, long-time conditioning up to 24 hours can be achieved. For sensing performance, the device also shows a high gate sensitivity (~14.24 kPa^-1) in a wide sensing range (~30 kPa). By combining the functions of mechanical sensors and synaptic transistors, the space and energy efficient design in this work can facilitate the development of next-generation electronic skin and artificial neuron systems.