Evaluation of layered structures for micromachines by means of ultrasonic micro-spectroscopy

Elastic properties of Si-B-O glass layers fabricated on (100) Si substrates by the flame hydrolysis deposition method were measured. Thicknesses of the layers were about 20 μm. The longitudinal velocity of the layers was measured by ultrasonic spectroscopy of normal incidence covering the frequency range from 100 MHz to 300 MHz. Frequency dispersion of the Rayleigh wave velocity was also measured by means of an ultrasonic microspectrometer. It was found that the Young´s modulus decreased with the boron dopant concentration, while the Poisson´s ratio was about 0.26 regardless of the boron dopant concentration. The measured elastic properties will be used in the design of micromachines fabricated with Si substrates and glass layers