High-Quality Factor Electrolyte Insulator Silicon Capacitor for Wireless Chemical Sensing

This letter reports on the design, fabrication, and characterization of a high Q electrolyte insulator silicon (EIS) capacitive structure and its application to LC wireless chemical sensors. LC sensors are based on the variation of inductance or capacitance in response to changes in the magnitude of interest. In this new type of LC sensor, the EIS structure is used as a pH-to-capacitance transductor. A double electrode scheme, one for stable dc potential and another for low ac series resistance, has been adopted in order to obtain sufficient Q at the resonator. An almost linear response and a sensitivity of 1% frequency change per pH unit have been achieved