Analyzing Few-Layer and Heterostructure pH-Sensitive 2D-Material Field-Effect Transistors Using a Physics-Based SPICE Compact Model

In this work, we introduce a surface-potential (SP)-based compact model designed for two-dimensional (2D)-material-based pH-sensitive field-effect transistors (FETs). To address device electrostatics toward the electrolyte side, we employ Poisson’s equation, site-binding theory, and the Gouy–Chapman–Stern approach. Simultaneously, electrostatics in the channel are handled by integrating 2D density of states and Fermi–Dirac statistics. Our model builds upon our previous work, where we extensively demonstrated a Verilog-A implementation of a physics-based 2D-material FET model, which yielded explicit SP expressions achieved through the Lambert-W function and Halley’s correction method. Additionally, the model computes the drain current by using the drift-diffusion transport model. The explicit nature of our model renders it suitable for SPICE-circuit simulation. Validation of our model is conducted using experimental data from ion-sensitive field-effect transistors (ISFETs) based on various transition-metal dichalcogenide (TMD) materials. The model is also extended to capture the behavior of heterostructure ISFETs wherein a vertical heterostructure is established between different TMD materials. The results demonstrate a high level of agreement between the experimental data and our model predictions, underscoring the model’s accuracy. This model holds promise for practical applications, particularly in the realm of pH sensing using 2D-nanomaterial FETs.