Application Of Functional Materials Film In Piezoelectric Printhead

Piezoelectric inkjet technology is the main direction of future development of high-precision printing, as the core of piezoelectric inkjet technology, the piezoelectric print head is more and more widely used in graphic and text printing, printing circuit boards,3D printing and other industrial manufacturing fields. However, due to starting late in reserach, complex process of piezoelectric print head and many other reasons, there still no commercial piezoelectric print head with independent intellectual property rights appears in domestic. In this paper, we studied the application of the functional material films used in an independent research piezoelectric print head manufacture.Firstly, we introduced the structure and working principle of piezoelectric print head, then we described the measurement methods and their theoretical models of films residual stress, we also elaborated the measurement ways and their theoretical of the adhesive strength between film and the substrates, the mothods discussed including cross cut method, scratches and vertical stretching. Depending on the performance requirements of the piezoelectric print head vibration plate, we choosed SiO2/SiNx composite film as the vibration plate, and an optimum thickness ratio of SiO2 layer and SiNx layer was obtained by simulation. Then we measured the residual stress of SiO2 layer and SiNx layer using the method of substrate curvature respectively. By changing the deposition process parameters of preparation SiNx film by PECVD, we could get the SiO2/SiNx composite film vibration plate with the lowest overall stress.Based on the protection requirements of piezoelectric print head, we chosed PZT, SiNx, BN303 photoresist and Parylene to protect piezoelectric print head, and researched on their protective effect by experiments. The experimental results showed that PZT, SiNx and BN303 photoresist could not protect piezoelectric print head effectively. Finally we selected Parylene as the protective layer of piezoelectric print head. And we verified the feasibility of Parylene as the protective layer of piezoelectric print head through a lot of experiments, it found that Parylene had a good step coverage performance, with good corrosion resistance and heat resistance, and we could use oxygen plasma etching method to pattern Parylene, Further the preparation of Parylene protective film has a good compatibility with the piezoelectric print head manufacturing. In order to solve the insufficiency adhesive strength between Parylene and substrates, the substrates were pretreated in different ways, then we used the method of vertical stretching to measure the adhesive strength between Parylene and substrates, and the results showed that the substrates pretreated with silane coupling agent (KH570) could improve the adhesive strength between Parylene and the substrates significantly. To determine the thickness of Parylene deposition, the simulation and experimental method were carried out respectively to optimization the thickness of Parylene C, and the results showed that a thickness between 450 nm to 1 μm for Parylene C protective layer was appropriate. Taking the relative dielectric constant of Parylene C as an indicator of the aging properties of Parylene C protective layer immersed in the ink, and found that the ink had little effect on the performance of Parylene C film in the short term. Finally, we had a droplet ejection experiment with the piezoelectric print head protected by Parylene C, and the experimental results showed that Parylene C film was capable of protecting piezoelectric print head effectively.