A Wireless Potentiometric Chemical Sensor Based on a Low Resistance ENOS Capacitive Structure

This paper reports on the concept, fabrication and experimental results of a new LC wireless sensor for pH measurements. LC sensors are based on the variation of inductance or capacitance in response to changes in the magnitude of interest. In the sensor presented here an Electrolyte-Nitride-Oxide-Silicon structure is used as an electrochemical potential-to-capacitance transductor. The electrochemical potential at the Electrolyte-Nitride interface is linearly dependent on the electrolyte pH. Therefore, the resonant frequency of the LC resonator will follow the electrolyte pH variations. A double electrode scheme, one for stable DC potential and another for low AC impedance, has been adopted in order to obtain sufficient Q at the resonator. A sensitivity of 1.2% frequency change per pH unit has been achieved.