Analysis of the threshold voltage and its temperature dependence in electrolyte-insulator-semiconductor field-effect transistors (EISFET's)

A first-order theoretical model is developed that allows the temperature dependence of the threshold voltage of an electrolyte-insulator-semiconductor field-effect transistor (EISFET) to be determined. Specifically, a detailed analysis is presented for a representative cell consisting of a Ag/AgCI reference electrode, a simple 1:1 electrolyte, and an ISFET. In addition, an insulator is assumed for which the site-binding model is applicable. All temperature-dependent parameters are identified and quantitatively described. Results are computed for SiO
2
and Al
2
O
3
insulators over a pH range from 1 to 12, and a temperature range from 20 to 80°C. Graphs of the surface-site occupancies versus the pH are shown to provide useful physical insight in interpreting the results. The threshold-voltage temperature coefficient is shown to be highly dependent on the pH; however, for Al
2
O
3
, over a 20-80°C range, the variation is roughly linear.