1/f noise in ion selective field effect transistors compared to MOSFETs

pH ISFETs are very interesting sensors for biomedical microsystems including in vivo measurements of pH. The noise phenomena and related resolution of these sensors are still not understood. In this paper measurements of low frequency noise in pH ISFETs are presented and compared to similar measurements performed in MOSFETs. Various bias conditions are used corresponding to the gate voltage changing from subthreshold to saturation, in the frequency range between 1 Hz to 100 kHz ISFET noise measurements were performed in solutions with pH in the range of pH4 to pH10, at room temperature. The measured ISFETs exhibit clearly 1/f noise. The dependence of the drain current noise power spectral density upon average drain current follows the same behavior of 1/f noise that the observed in MOSFETs. The measured noise characteristics shown here indicate that the Si/SiO₂ interface dominates the noise behavior of the ISFET. No pH dependent effects are observed and the interface between the solution and the gate insulator does not contribute measurable noise