Super-Nernstian Floating-Extended Gate Ion Sensitive Field Effect Transistor for pH sensing

The exceptional sensing characteristics of ion-sensitive field-effect transistors (ISFETs) have received wide recognition in the biosensors research community to create miniaturized, cost-effective, label-free Point-of-care (PoC) biosensing devices for remote diagnostics. Various architectures have been investigated to achieve enhanced detection sensitivity beyond the theoretical Nernst limit of 59 mV/pH, but they are limited by non-idealities like instabilities, durability, and non-reproducible performance from being successfully commercialized. This work introduces and demonstrates a multi-gated, floating-extended gate super-Nernstian ISFET with MoS₂ as the channel material. The device incorporates nanometer-scale SiO₂ and AhO₃ layers as bottom, top, and sensing oxides. High sensitivity is achieved by engineering capacitive mismatch in the dielectric stack. The proposed device gives a linear response and a maximum sensitivity of 1884.94 mV/pH, beyond the Nernst limit, when measured against the back-gate. Further technology computer-aided (TCAD) simulations predict an even higher sensitivity of 3922 m V/pH with scaled top gate electrodes. The experimental results validate the potential of these pH sensors for developing next-generation label-free biosensors for minute molecular detection and Point-of-care remote diagnostics.