Micromachined high-aspect-ratio parylene spring and its application to low-frequency accelerometers

A new microfabrication technology for high-aspect-ratio parylene structure has been developed for soft spring applications. Free-standing parylene beams with widths of 10-40 mu m and aspect ratios of 10-20 have been successfully fabricated. Since parylene has a small Young's modulus, a high-aspect-ratio beam with a spring constant of the order of 1 X 10(-3) N/m has been realized. The large yield strain of parylene enables a test structure to have a large-amplitude oscillation of 600 pimp-p, without any failure of the high-aspect-ratio springs. An early prototype of in-plane capacitive accelerometer was also developed. It was found that its resonant frequency is as low as 37 Hz, and the noise spectral density is 64 mu g/(Hz)(0.5).