A MEMS capacitive pH sensor for high acidic and basic solutions

We have developed a micro-scale chip-based pH sensing system, which can effectively measure the changes in pH ranging from 1 to 4 and 10 to 12. This method relies on fringing field capacitive measurements. A change in pH of the medium results in a permittivity change for the fringing electric field, which in turn affects the capacitance values. Capacitance changes are then converted to resonant frequency shifts via a readout circuit. This technique provides high sensitivity, low hysteresis, and low noise as well as low fabrication cost. Very importantly, the device and the corresponding measurement circuitry have the potential to be integrated in an electronic pill for continuous non-invasive measurement within the body.