Differential ISFET/REFET pairs as a reference system for integrated ISFET-sensor arrays

In order to make use of all the advantages over conventional glass electrodes which an ISFET sensor system provides, an integrated reference electrode has to be developed. The concept of using a noble metal as a pseudo-reference electrode requires a different ISFET/REFET (ion-sensitive FET/reference FET) pair. Two types of reference system are compared. The first system is a pair of ISFETs, one with the pH sensitivity of a bare Si/sub 3/N/sub 4/ gate insulator (ca. 50 mV/pH) and a second with a reduced sensitivity in the range of 25 mV/pH. This pseudo-reference-FET was realized by depositing an extremely thin polymeric film on the gate insulator. An enzyme FET was studied as the second system to examine the application of a pseudo-reference electrode to biosensors. Both systems show similar behavior with regard to the influence of the pseudo-reference electrode. The results have led to the design of an ISFET sensor array which is optimized for using an integrated noble metal electrode as a solution contact.<>