Study of SiNx films used as protective layer on Ni film flow sensors

In this study, silicon nitride (SiNx) protective films were deposited on flexible Ni film flow sensors using ion beam assisted deposition (IBAD). Microstructures of the Ni films with and without SiNx protective layer were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD). The effect of SiNx protective layer on the performance stability of flexible Ni film flow sensor on polyimide substrate was investigated. The results showed that the SiNx film was composed of the stoichiometric nitride Si3N4, Si3N2 and oxynitride SiO1.6N0.3, and that the SiNx protective layer presented amorphous structure. The resistivity of the Ni film without SiNx protective layer increased and the temperature coefficient of resistivity (TCR) decreased after exposure in the air for 102 days, while the electrical properties of Ni film with SiNx protective layer changed negligibly, highlighting the importance of the SiNx protective layer in improving the performance stability of Ni film flow sensors. The flexible sensor subjected to different flow velocities has been tested, and the results show that the output voltage decreased with increasing flow velocity within the flow velocity of 0 to 6 m/s, and the fabricated sensors had a good linearity. The comparison of the results obtained with the two sensors showed that the SiNx protective layer increased the response sensitivity of Ni film flow sensor.