Parallel extended gate MOSFET pH sensing system

This project presents a pH sensing monitoring system using parallel extended gate structure that capture the sensor response to changes in ionic activities in solutions. The objective of this project is to propose a sensing array of conventional MOSFETs that allows detachable sensing membranes. The main task of the intended application is to find the pH value of an ionic solution that is being tested. The sensing membrane is a layer deposited on a conductive substrate, attached with a wire to form an extended gate. The task of the readout circuit is to detect the threshold voltage changes through Vout of the sensing MOSFET, treating the new threshold voltage as a combined effect of reference electrode/solution/extended membrane/sensing MOSFET. A model is constructed to demonstrate the ability of the extended gate setup to detect three pH states of three parallel solutions. The interfacing circuit biases the sensing MOSFET with a constant drain current of 100μA and 0.5 V drain-source voltage to maintain the MOSFET in isothermal region.