Solid-state ion sensors. Theoretical and practical issues

Abstract

Integrated ion-sensor devices may be constructed using the methods of microcircuit fabrication. The suitabilities of the silicon integrated circuit and thick-film hybrid circuit processes for this purpose are compared and it is argued that the hybrid approach will offer advantages in many cases. Theoretical questions about the operation of both the hybrid and ISFET (ion-sensitive field-effect transistor) types of device are discussed and possible origins are suggested for the output drift that is commonly observed in ISFET. Practical issues which might affect the commercial development of integrated ion-sensor devices are noted.