Fabrication of microstructure array directly on β-phase poly(vinylidene fluoride) thin film by O₂ reactive ion etching

The ability to pattern a thin film of poly(vinylidene fluoride) (PVDF), a piezoelectric, pyroelectric and ferroelectric polymer, has potential applications in the fields of microelectromechanical systems (MEMS), nonlinear optics and nonvolatile ferroelectric random access memory technology. Low pressure O₂ reactive ion etching (RIE) was employed to realize fine pitch microstructures on a β-phase PVDF (β-PVDF) film for the first time; a line and space (70/130 μm) microstructure array with a height of over 30 μm was fabricated. Different to the traditional method of PDMS molding, the proposed technology did not result in significant loss of piezoelectricity. Furthermore, unlike the x-ray photo-etching method, there was no etching saturation limit with the proposed method. Here, we introduce the fabrication process technology in detail and report on the etching properties of the β-PVDF film under different process conditions. The effect of process variables, such as supplied gas flow, applied RF power and etch time, on the PVDF etching characteristics were investigated in detail. The RF power and etch time showed a more predominant influence on PVDF etching progress than the gas flow. The etched depth was linearly increased with the etch time and the amount of RF power. Etching rates over 10 μm h⁻¹ were achieved and increased linearly with the applied RF power. By means of a responding photomask design and control of process conditions, much finer and higher microstructure arrays are also possible. (paper)