An analytical technique for counteracting drift in ion-selective field effect transistors (ISFETs)

The instability of the dc operating point in pH-sensitive ion-selective field effect transistors (ISFETs) renders the continuous monitoring of physiological pH using these devices inaccurate. This instability, commonly known as drift, manifests itself as a relatively slow, monotonic change in the measuring output signal in the absence of variations in the pH. In this work, a method for correction of ISFET drift is presented. This method takes advantage of the relatively small instantaneous drift rate in ISFETs to compensate for the drift signal superimposed on the sensor output. The validity of this method is experimentally confirmed by continuous monitoring of pH under in vitro conditions approximating metabolic acidosis using a Si/sub 3/N/sub 4/-gate pH-sensitive ISFET.