MINIATURIZED REFERENCE ELECTRODE BASED ON A PERCHLORATE-SELECTIVE FIELD-EFFECT TRANSISTOR

A new type of reference held effect transistor (REFET) based on a perc hlorate-selective held effect transistor has been developed. The top o f the ion-selective layer is coated with another layer containing soli d potassium perchlorate. Potassium perchlorate is not readily soluble in aqueous solutions; therefore, the perchlorate activity in the aqueo us surface layer is equal to that of a saturated solution. The constan t activity leads to a constant potential of the REFET. The stability o f this REFET potential was examined in solutions of different salt con centrations and different pH values. The influence of the pH value on the REFET potential was compared to that of a commercially available A g/AgCl electrode. According to this comparision, the perchlorate refer ence electrode proved to be very well suited for an integration on an ISFET chip.