A generalized theory of an Ag+-sensitive electrolyte—insulator—semiconductor field-effect transistor with silica surface modified by chemical grafting
✍ Scribed by H. Perrot; N. Jaffrezic-Renault; P. Clechet; W.B. Wlodarski; N.F. de Rooij; H.H. van den Vlekkert
- Publisher
- Elsevier Science
- Year
- 1990
- Tongue
- English
- Weight
- 494 KB
- Volume
- 1
- Category
- Article
- ISSN
- 0925-4005
No coin nor oath required. For personal study only.
✦ Synopsis
The feasibility of an Ag+-sensitive electrolyteinsulator-semiconductor field-effect transistor (EISFET) with silica surface modified by chemical grafting has been previously proved. Fabricated EISFET sensors feature a long lifetime and a fast response.
The main purpose of this paper is to provide further insight into the chemical processes that govern the chemical sensitivity of an Ag+-sensitive EISFET sensor. A first order theoretical model is developed that allows the potential at the insulator-electrolyte interface, the threshold voltage potential and the gate voltage of an Ag+sensitive EISFET sensor, with silica surface modified by chemical grafting, to be determined.
The site-binding model has been applied to the modified silica/electrolyte interface. The model successfully explains the Ag' sensitivity as well as the H+ ion interference effect on the EISFET as an Ag+ sensor. Some discussion of the parameters influencing the Ag+ sensitivity has been presented. From this model, it is concluded that the cyanografted site density, NsCN, and the complexation constant, pKcN , are the main controlling factors for the EISFET as an Ag+ sensor. For high sensitivity, large NsCN and pKcN values are required. This provides guideline for selecting a proper chemical grafting process to achieve improved Ag+ performance.
In this study, a one-dimensional model with the insulator surface potential, Y,, assumed to be constant along the direction of the channel is used. The current-voltage (terminal) characteristic of the EISFET is then derived in a manner similar to the derivation of MISFET characteristics, in which 'I',, is obtained by solving the system of equations for the EIS structure. The overall model is used to predict the manner 09254005/90/$3.50 in which the gate voltage varies with the Ag+ concentration.
The presented model can be adapted to other ion-sensitive EISFET sensors.