Open-Gate Junction Field Effect Transistor (OG-JFET) for Life Science Applications: Design, Implementation, and Characterization

Abstract

This article introduces a new foundry-based ion-sensitive field-effect transistor named open-gate junction field-effect transistor (OG-JFET), which is intended to be used for chemical and biological sensing applications. OG-JFET can be realized by removing the n-type gate in a p-type JFET to open the space for electrolyte gating. The new configuration enables applying a bias voltage via back-gate that results in more efficient channel current control. Accordingly, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6 ~{\mu }\text{m}$ </tex-math></inline-formula> thick p-type conductive layer has been epitaxially grown on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$450 ~{\mu }\text{m}$ </tex-math></inline-formula> thick n-type silicon layer based on a standard foundry process. The design promotes a large sensing area including seven p-type conduction channels with dimensions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1000\,\, {\mu }\text{m}\,\,{\times }\,\,100\,\, {\mu }\text{m}$ </tex-math></inline-formula> (W <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\times }$ </tex-math></inline-formula> L) and depth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6 ~{\mu }\text{m}$ </tex-math></inline-formula> . All the necessary transfer characteristics required for biosensing/ion-sensing of OG-JFET have been derived. Furthermore, we have conducted a COMSOL Multiphysics simulation on OG-JFET to verify the operation of the sensor, which helps to comprehend the functionality of the sensor in different biasing conditions. The COMSOL semiconductor simulation results showed good consistency with experimental results that make the simulations a reliable reference for optimization and customizing the chip for specific applications. OG-JFET showed a sensitivity of 55.29 mV/pH, a hysteresis of 16 mV, and drift of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3 ~{\mu }\text{A}$ </tex-math></inline-formula> /hours which are in the order of standard ISFET sensors in the literature. The simulation and experimental results in this paper, for the first time, put forward the OG-JFET as a new foundry-process-based, mass-producible ion-sensitive FET sensor for chemical and biological applications.