Fabrication of silicon-based filiform-necked nanometric oscillators

For the purpose of improving the resolution of force and mass detection of a noncontact-mode atomic force microscope (AFM), we are developing a mechan ical oscillator of nanometric size which consists of a head mass supported by an elastic neck. A silicon-on-insulator (SOI) wafer with the laminated s tructure top Si layer/buried SiO2 layer/base Si is used in the fabrication of the nanometric oscillators. By selective etching of Si and SiO2, nanomet ric oscillators are successfully obtained. The top Si layer is etched to fo rm a tetrahedral Si dot, which is the mass of the oscillator, and the burie d SiO2 layer is etched to form the elastic neck resting on the base Si. The size of the tetrahedral Si dot is determined by the thickness of the top S i layer without depending on the precision of the Lithography technique. We found that the cross-sectional shape of the SiO2 neck is a right-angled tr iangle and that the neck is situated at the center of the tetrahedral Si do t. According to calculations, the oscillators we obtained have spring const ants around 1 N/m and a resonance frequency from 3 MHz to 300MHz according to their dimensions.