Characterization of a Nozzle-Integrated Capacitive Sensor for Microfluidic Jet Systems

This paper presents the modeling and characterization of a novel nozzle-integrated capacitive sensor for microfluidic jet systems. The integration of a sensor in the nozzle for closed loop control is a promising way to increase the accuracy and reliability of the droplet formation. With the electrodes fabricated on slanted nozzle walls, as presented in previous work (van der Velden et al., 2007), the small and fast changing sensor signals cannot be measured properly. In this paper, a novel integrated sensor with a more ideal configuration of vertical electrodes and substrate isolation is presented and characterized. The sensor behaves similar to a MOS capacitor with capacitances ranging from 20-60 fF. Parasitic components were identified and analyzed using an equivalent circuit model of the device. Extrapolation of the circuit shows 4 frequency regions in the Bode diagram, which can be used to optimize the design and determine the measurement strategy.