Negative Capacitance Dual-Gated ISFETs as Ultra-Sensitive pH Sensors

Ion-sensitive field-effect transistors (ISFETs) are promising candidates for next-generation pH sensors, enabling highly sensitive and label-free biomolecular and chemical detection. Emerging FETs based on the negative capacitance (NC) effect offer steep-subthreshold switching and higher drive current simply by integrating a ferroelectric (FE) material into the gate stack. Here, we propose a novel NC dual-gated ISFET (NC-DG-ISFET)-based pH sensor, with FE layers integrated into both the top and the bottom gate stacks. The current and voltage sensitivities of the proposed device are extracted from its transfer characteristics, obtained by combining the numerical solutions of the one-dimensional (1D) Landau-Khalatnikov (L-K) equation with three-dimensional (3D) technology computer-aided design (TCAD) simulations. Results show that the NC-DG-ISFET can surpass the sensitivity of some of the state-of-the-art DG-ISFET pH sensors. The inclusion of the FE layers into the gate stacks of a baseline DG-ISFET leads to 51% reduction in subthreshold swing (SS), causing a 5× increase in current sensitivity (S_I) in the subthreshold region of operation and a 2× increase in voltage sensitivity (S_V). The influence of channel thickness and channel length on the sensor performance is also invesitgated. The findings presented here provide a new pathway to leverage the steep-switching behavior of NCFETs for the next generation of highly sensitive and label-free DG-ISFET pH sensors.