Fabrication of Silicon-Based Filiform-Necked Nanometric Oscillators

Abstract

For the purpose of improving the resolution of force and mass detection of a noncontact-mode atomic force microscope (AFM), we are developing a mechanical oscillator of nanometric size which consists of a head mass supported by an elastic neck. A silicon-on-insulator (SOI) wafer with the laminated structure top Si layer/buried SiO₂ layer/base Si is used in the fabrication of the nanometric oscillators. By selective etching of Si and SiO₂, nanometric oscillators are successfully obtained. The top Si layer is etched to form a tetrahedral Si dot, which is the mass of the oscillator, and the buried 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 Si 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 triangle and that the neck is situated at the center of the tetrahedral Si dot. According to calculations, the oscillators we obtained have spring constants around 1 N/m and a resonance frequency from 3 MHz to 300 MHz according to their dimensions.