The fabrication and characterisation of ion-sensitive field-effect transistors with a silicon dioxide gate

Abstract

The ion-sensitive field-effect transistor (ISFET) is a new type of miniaturised semiconductor chemical sensor. It is based on the structure of the metal-insulator-semi-conductor field-effect transistor (MISFET) in which a metal gate is replaced by an ion selective membrane, an electrolyte and a reference electrode. In this paper, an ISFET is fabricated with silicon dioxide as a gate for a pH selective membrane. The measurement of pH sensitivity, selectivity and long-term characteristics of this device have been made. A pH sensitivity can be reached of 40 mV per pH. The oxide gate ISFET device has a significant response to K+ and Na+ ions even at the low concentration of 0.01 mol 1-1. The response to K+ ion is much higher than Na+ ion. The long-term stability of the silicon dioxide gate ISFET is also studied. The long-term drift is about 1 mV per hour after a ten hour immersion.

Investigation of tin oxides as sensing layers in conductimetric interdigitated pH sensors

“…Although a novel method, ISFETs suffer from degradation of response over time. In the work by Chen et al [11], a good linear response to pH was observed (40 mV/pH), however, a drift of up to 1 mV/h was recorded. A review on the subject by Miao et al [12] showed that the gate oxide material is important in the sensitivity of the device to pH.…”

“…Many publications have appeared in the literature referring to other approaches, such as the ion sensitive field effect transistor (ISFET) [9][10][11][12]. Although a novel method, ISFETs suffer from degradation of response over time.…”

Functionalized Carbon Nanotube Thin Films as the pH Sensing Membranes of Extended-Gate Field-Effect Transistors on the Flexible Substrates

“…In other words, our experimental results of 55.7 mV/pH for the oxygen-plasmatreated CNTFs present a much better response with respect to the as-sprayed CNTFs. Moreover, as compared to other pH sensing platforms, such as Si 3 N 4 -gated ISFET [7] and SiO 2 -gated ISFET [8], the oxygen-plasma-treated CNTFs demonstrate the higher pH voltage sensitivity and larger linearity which can accurately respond to the ions of interest in different pH levels.…”

“…Since the ionselective field-effect transistors (ISFETs) was first proposed by Bergveld in 1970 [5], there have been many researches invested in the improvement of sensing characteristics due to the low current sensitivity and instability of ISFETs [6]- [8]. In contrast, extended-gate field-effect transistor (EGFET) was considered as an alternative for the conventional ISFET owing to the lower cost, simpler to package, more insensitive to environment, and better long-term stability [9], [10].…”

Analytical modelling of monolayer graphene-based ion-sensitive FET to pH changes

“…Their short and consistent response times are very favorable to the electronics industry [8,9]. ISFETs introduce new features such as the integration of data processing and compensation circuits in the similar circuit for this type of sensors [10-12]. By altering the gate material, depositing layers of selective membrane or a bio-recognition element onto the gate, variance of selectivity can be achieved [13,14].…”