Monitoring of meniscus motion at nozzle orifice with capacitive sensor for inkjet applications

This paper reports a capacitive sensor system to monitor the meniscus motion during the droplet generation at a nozzle orifice for inkjet applications. As the nominal capacitance value of the sensor is at only fF-level with an expected resolution of about 10 aF, suppression of the parasitic components and reduction of the electrical noise are extremely relevant. The sensor is fabricated with a bulk micromachining process and a CMOS readout chip is designed to achieve a compact system. The sensor and the readout are assembled on a piezoelectric inkjet nozzle, and a dedicated measurement setup has been built. The meniscus motion during the generation of water droplets from an inkjet nozzle is successfully recorded as an output waveform for a time period of 900 μs. The amplitude and time of the maximum sensor output (500mV) is captured, and the oscillatory motion of the meniscus after the jetting is recorded as well. The recorded sensor output is consistent with the optical observation of the droplet formation. The detected motion can be used for in-situ diagnosis and feedback control of jetting system for better accuracy and reliability.