The Suspended Mesh Ion Selective Field Effect Transistor

Abstract

An inherent problem in the use of the ion selective field effect transistor (ISFET) has been the poor adhesion of the ion sensitive membrane to the device. Previous solutions to the problem have produced long‐lived devices for research needs but the procedures are time consuming and are not compatible with mass production requirements. The modification described in this paper consists of a polyimide film suspended above the gate of the ISFET. An array of holes in the film allows the solvent‐cast membrane to flow beneath this suspended mesh as well as over it. Removal of the membrane solvent results in a solid membrane anchored to the ISFET by the suspended mesh. ISFET devices with the suspended mesh modification exhibit greatly increased lifetimes over those without any adhesion promoting modification. The electrical and chemical characteristics of the devices were not altered by the modification. The fabrication procedure, which involves only commonly used IC technologies, is described in detail.