Integration of Spiking Neurons with Electrochemical Transistors Using a Photopatternable Solid Electrolyte

Organic electrochemical transistors (OECTs) emerged as promising building blocks for brain-inspired hardware thanks to the interplay of electronic and ionic species in their operation. Several studies demonstrated OECTs with synaptic properties, e.g., short- and long-term plasticity and spike-time-dependent plasticity. However, to go beyond academic demonstrations, the design and fabrication of neuromorphic circuits require high-density integration of OECTs, hardly possible due to the conductive nature of the electrolyte.<br/>Here, we present a photopatternable solid electrolyte that we use to produce high-density OECT integrated circuits with a resolution of 10 µm. We use the patternability of the electrolyte to decouple adjacent devices and minimize the gate current. At the single-device level, the electrolyte offers strong gate-channel coupling, resulting in outstanding performance: the OECT exhibit an on-off ratio of 10⁶ and a subthreshold swing of 61 mv/dec close to the thermodynamic minimum.<br/>This allows us to integrate OECTs into traditional and neuromorphic circuits without crosstalk between devices as well as adjust the heterosynaptic plasticity in OECT circuits. Therefore, we discuss the influence of the channel material and device dimensions on the device properties. We then tune the threshold voltage, switching speed, hysteresis, and retention time to our needs. As such, we control the device synaptic properties such as short- and long-term plasticity of single devices in a circuit. Finally, we use the device as building blocks in a Morris-Lecar spiking neuron circuit. We discuss the influence of tunable device properties on the behavior of the neuron’s subcircuits.