Special Session: Calibrating mismatch in an ISFET with a Floating-Gate

CMOS-based Ion-Sensitive Field Effect Transistors (ISFETs) are used to measure a given media's pH. CMOS-based ISFETs, in contrast to traditional glass electrode-based pH meters, are compact and consume lower power. However, ISFETs suffer from a mismatch in their output current due to the variations in CMOS fabrication and post-fabrication insulation steps. This mismatch can significantly impact the accuracy of the pH measurements. This work presents a Floating-Gate (FG) to reduce the mismatch in the ISFETs. By employing FG-based ISFET, the study effectively tunes its threshold voltage to calibrate against the mismatch. Fowler-Nordheim tunneling removes the charge from the floating node, which effectively increases the threshold voltage. In contrast, hot-electron injection is used to program the charge onto the FG node, decreasing the threshold voltage. The work experimentally demonstrates the programming of FG-based ISFETs by fabricating them in 0.5μm CMOS process. Moreover, the work characterizes different biasing schemes to program the FG-based ISFETs efficiently.