An Oxynitride ISFET Modified for Working in a Differential Mode for pH Detection

Abstract

In this study, we have shown that it is possible to deposit a silicon oxynitride membrane on silica ISFETs by plasma enhanced chemical vapor deposition (PECVD) and to develop a solid‐state device for pH detection which works in a differential mode. Silicon technology using a new encapsulation technique and a new geometry of the ISFETs is described. The PECVD oxynitride membrane is deposited without damaging the structure. A nernstian stable pH response is obtained: between pH 2 and 8.3 and it is only slightly affected by the concentration of Na⁺ ions. Moreover, this silicon oxynitride membrane can be grafted with a long alkyl chain silane in order to make a REFET with a sensitivity of between pH 3.3 and 8.1. The pH response of the solid‐state device obtained is from pH 2 to 8.