Optimized Technologies for Cointegration of MOS Transistor and Glucose Oxidase Enzyme on a Si-Wafer

Abstract

The biosensors that work with field effect transistors as transducers and enzymes as bio-receptors are called ENFET devices. In the actual paper, a traditional MOS-FET transistor is cointegrated with a glucose oxidase enzyme, offering a glucose biosensor. The manufacturing process of the proposed ENFET is optimized in the second iteration. Above the MOS gate oxide, the enzymatic bioreceptor as the glucose oxidase is entrapped onto the nano-structured TiO2 compound. This paper proposes multiple details for cointegration between MOS devices with enzymatic biosensors. The Ti conversion into a nanostructured layer occurs by anodization. Two cross-linkers are experimentally studied for a better enzyme immobilization. The final part of the paper combines experimental data with analytical models and extracts the calibration curve of this ENFET transistor, prescribing at the same time a design methodology.

Generalized Analytical Model for Enzymatic BioFET Transistors

“…It is extracted from the initial condition: [A(t = 0)] = A 0 . Replacing this constant in (7), results the analyte concentration:…”

“…Other values can be estimated from the solid-state physics: μ c = 800 cm 2 /Vs for electrons in channel, V 0 = +0.79 V for Ag gate electrode, t H = 100 nm for micro-molar range of ions concentration [ 24 ], dielectric permittivity of the Helmholtz layer is approximated to that of a vacuum. The thickness of the enzymatic region is given by the immobilization technology, offering possible values of t E = 1 mm [ 7 , 8 , 9 ]. Relative dielectric permittivity of the enzymatic membrane is approximated to that of water ε r,Enzy ≅ 80.…”

“…BioFET transistors consist of biosensors composed of a general biological receptor coupled with a FET transducer [9][10][11]. If the receptor consists of an Ion Sensitive Electrode (ISE), then the BioFET is of the ISFET type [11]; if the biological receptor consists of an enzymatic membrane, then the BioFET is of the ENFET type [7,8]. Recently, for Organic Electro-Chemical Transistors (OECT) biosensors, the change in product concentration was translated into a shift of the threshold voltage [12]; a similar theory was proposed for ISFET Biosensors 2022, 12, 474 2 of 12 biosensors [11].…”

“…The lack of models for integrated biosensors is critical in the design stage, though some primary models have recently been developed for glucose biosensors [ 7 , 8 ]. This paper generalizes the previous biosensor concept and extends the glucose-oxidase receptor [ 8 ] to any enzymatic layer as well as the reaction rate from 1-order to 2-order and to n-order, n > 1.…”

Current Status of Field-Effect Transistors for Biosensing Applications

“…In this Special Issue, Ravariu’s group reported a glucose biosensor [ 26 ] that was optimized in the second iteration, starting from a previous experience [ 9 ]. A standard MOS-FET transistor was co-integrated with an enzymatic membrane made by glucose oxidase enzyme entrapped in nafion.…”