Differential ISFET/REFET pairs as a reference system for integrated ISFET-sensor arrays
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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.<<ETX>>
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