A one-transistor organic electrochemical self-sustained oscillator model for neuromorphic networks.

Organic electrochemical transistors (OECTs) operating in wet biological environments offer new possibilities for neuromorphic biosensors and bioelectronics. This work presents a device physics approach to develop an organic spiking neuron using a single OECT combined with passive RC components. The key condition is that charge carrier mobility decreases with ion concentration in the organic conductor. This leads to a Z-shaped current-voltage response that, when coupled with an external load, produces self-sustained oscillations. We model the system as a nonlinear oscillator described by a set of first-order differential equations, exhibiting a stable limit cycle. Through nonlinear dynamics and bifurcation theory, we construct a two-variable fast/slow model and identify the conditions for a Hopf bifurcation that triggers oscillatory behavior. The system's output can shift between sinusoidal spiking and relaxation oscillations by adjusting the external capacitor. Crucially, this neuron-like behavior is achieved using a single transistor without external amplifiers. This minimalistic design offers a promising pathway toward energy-efficient, low-cost, and biomimetic neuromorphic systems, with strong potential for integration in future bioelectronic devices.