Super-Nernstian pH detection using out-of-equilibrium body potential in silicon on insulator ISFET sensors: Proof-of-concept and optimization paths

• Published in: Sensors and actuators. A. Physical. Vol. 373; p. 115439
• Main Authors: Alepidis, Miltiadis, Delacour, Cecile, Bawedin, Maryline, Ionica, Irina
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-08-2024; Elsevier
• Subjects: Body potential; Engineering Sciences; Metal contacts; Out-of-equilibrium; PH sensor; Silicon-on-insulator; TCAD simulations; Metal contacts; TCAD simulations; Body potential; PH sensor; Silicon-on-insulator; Out-of-equilibrium
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2024.115439

In this work, we demonstrate pH sensing using the out-of-equilibrium body potential (VB) monitored in silicon-on-insulator (SOI) double-gate “ISFET-like” devices with deposited metal contacts. Similar to the behavior of a dual-gate ISFET, in this study, the conductive channel induced by the back-gate voltage at the silicon/buried oxide (Si/BOX) interface is modulated by the charges to-be-sensed that are intentionally placed on the top silicon oxide layer SiO2 covering the Si film. The detection of the surface charge modulation was evidenced by monitoring in real-time the out-of-equilibrium body potential, while the classic shift in the drain current served as control experiment and for benchmarking. These first experiments demonstrate the successful implementation of this new pH detection paradigm, with super-Nernstian sensitivity. To provide optimization options for the body-potential sensing, TCAD simulations of the pH sensors were performed in a 2D structure and illustrated the possibility to further enhance the device sensitivity with an optimized architecture. Moreover, the pH-induced shift occurs at very high applied gate biases for the drain current, contrary to the body potential, which implies a sensor with lower power consumption when VB is used as reading method. Thus, body potential monitoring provides a promising reading method to reach the required low-power consumption regime of the tomorrow’s sensing devices.
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•Out-of-equilibrium body potential, a new dynamic reading method with ISFET-like devices.•Super-Nernstian response in Silicon-On-Insulator sensors with deposited metal contacts.•Fabrication of ISFETs for "in-liquid" detection based on the out-of-equilibrium body potential.•Sensitivity investigation of ISFET sensors through TCAD simulations.•Benchmark of sensing: out-of-equilibrium body potential versus drain current method.