Performance and system-on-chip integration of an unmodified CMOS ISFET

An ISFET fabricated by an unmodified, commercial CMOS process displays significant threshold voltage drift, which is attributed to the diffusion of hydrogen ions into the passivation layer. A ‘stretched-exponential’ model can compensate for the drift and produce a useful device with a sensitivity of 48 mV/pH. The CMOS ISFET has been used to create a complete ‘system-on-chip’ digital pH meter, capable of real-time drift compensation.