Dynamic response of a Ta2O5-gate pH-sensitive field-effect transistor

The dynamic response of a Ta2O5-gate pH-sensitive field-effect transistor (pH-ISFET) has been investigated using an activity step method. The measurement set-up can produce the activity step of pH within time-frames of several tens of milliseconds. The response time, t(95%), is found to be 0.25-0.30 s, which is almost independent of various factors including the flow rate and the direction of the pH change. The measured response times are slower than those previously reported. The applicability of the existing theories to interpret the dynamic response curves is discussed.