Micromachined high-aspect-ratio parylene beam and its application to low-frequency seismometer

A new microfabrication technology for high-aspect-ratio Parylene structure is developed for soft spring applications and applied to in-plane seismometer which covers low frequency (<1 Hz) and small acceleration range. Parylene beams having 10-40 μm wide and an aspect ratio of 10-30 were successfully fabricated. Since Parylene has a small Young´s modulus and is non-brittle material, high-aspect-ratio robust beam having spring constant on the order of 1 × 10^-3 N/m was realized. A prototype capacitive seismometer was also made, and its resonant frequency and noise spectral density was respectively measured to be 37 Hz and 45 μg/√Hz Since the Brownian noise is only 25 ng/√Hz, seismometer having much lower noise floor may be feasible using this new technology.