A differential p-ISFET based on-chip pH sensor with substrate based drift reset capability

Abstract

This paper presents a monolithic, inexpensive, label free, robust pH sensor that can be fabricated in an unmodified CMOS process. The sensor uses a differential p-ISFET architecture which substantially reduces non-ideal common mode effects which corrupt readout in ISFET based pH sensors and occupy only a small footprint. Additionally, the design offers the capability to correct for drift through control of the n-well voltage, which has not been demonstrated previously. We present results obtained from testing the sensor that is fabricated in the AMS 0.35μm process, including a demonstration of the drift correction. We demonstrate a differential sensitivity of 15 mV/pH over the entire pH range, with the ability to remove the already small drift of 0.1 mV/min using the bulk-source voltage adjustment.