Dual-mechanism model to describe the slow response of ISFETs

It has been known that the slow response of ion-sensitive field-effect-transistors (ISFETs), with tremendous challenges on meeting the requirements of the accuracy and long-term stability, handicaps extensive application of ISFET sensors. In this paper, dual-mechanism slow site-response (DSSR) model, combining enriched buried sites theory and the mechanism of specific adsorption activity (SAA) of effective sites, is proposed to systematically understand the slow response characteristics of ISFETs during a test of pH variation. The SAA variation occurs during the whole slow response process, while the effects of buried sites dominate only at the short-term slow response stage. Experiments based on extended-gate ion-sensitive field-effect-transistors using both aluminum oxide and silicon nitride as sensing layer were carried out. It is found that the DSSR model can excellently explain the slow response characteristics of the measured ISFETs. Furthermore, the slow response characteristics of ISFETs with silicon nitride are revealed to be superior to that of ISFETs with aluminum oxide in the slow response performance.