An ISFET Pixel with Integrated Trapped Charge Compensation using Temperature Feedback

摘要

This paper introduces the use of a diode-connected MOSFET as a temperature controlled switch for trapped charge cancellation of ISFET sensors. The current flowing through the reverse-biased diodes of 2.7 aA is negligible at low temperature but reaches 23 fA when heated to 100^{°C, which allows for low temperature readout and high temperature compensation of trapped charge. The diode-connected device is tied to the floating gate of the ISFET which is integrated as part of a source-follower readout. The in-pixel feedback loop uses a comparator to turn off the polysilicon heaters once the offset has been cancelled, triggering the readout by switching the op amp into a buffer configuration. Simulations show that the system is calibrated in 35s and the output sensitivity reaches 27.74 mV/pH. The pixel output then tracks any ionic change at its surface without sensor offset.}