Implementation and Characterization of a femto-Farad Capacitive Sensor for pico-Liter Liquid Monitoring

An fF-level capacitive sensor, intended for pL liquid measurements, has been fabricated with MEMS technology and successfully characterized. The sensor measures liquid level variations in a microfluidic channel. The sensor’s capacitance varies from 1.5 fF (channel empty) to 12.8fF (channel filled with 63 pL of water). To reliably detect such small capacitance changes, a low noise measurement system, based on a lock-in amplifier, was implemented. The measured sensitivity of the system is 14.1 mV/fF, and the capacitance detection limit is 0.057 aF/Hz1/2, which corresponds to a volumetric resolution of about 0.22 fL/Hz1/2.