  We present a physics-based circuit-compatible model for pH-sensitive
field-effect transistors based on two-dimensional (2D) materials. The
electrostatics along the electrolyte-gated 2D-semiconductor stack is treated by
solving the Poisson equation including the Site-Binding model and the
Gouy-Chapman-Stern approach, while the carrier transport is described by the
drift-diffusion theory. The proposed model is provided in an analytical form
and then implemented in Verilog-A, making it compatible with standard
technology computer-aided design tools employed for circuit simulation. The
model is benchmarked against two experimental transition-metal-dichalcogenide
(MoS2 and ReS2) based ion sensors, showing excellent agreement when predicting
the drain current, threshold voltage shift, and current/voltage sensitivity
measurements for different pH concentrations.
