Single-wafer-processed trench-sidewall integration and its application in a micro resonant detector for vacuum monitoring

Abstract

A trench-sidewall technology is developed for single-wafer-based integration of micro sensors and actuators with in-plane lateral configuration. Piezoresistive sensing and electrostatic actuating elements can be integrated together onto the deep-trench sidewalls of in-plane microelectromechanical structures by sidewall boron diffusion. Adjacent sidewall elements are electrically isolated by previously formed SiO2-refilled trenches. Electric transference from the sidewall to wafer surface is performed via the overlaps between the sidewall-diffusion and previously doped p+ at wafer surface. As a versatile micro-fabrication process, the technology promises to be widely used. As a typical application, a cantilever-shaped micro resonant vacuum detector was formed with both sidewall piezoresistive sensing and electrostatic resonance-driving elements integrated. In addition to satisfactory electric principles measured to verify the trench-sidewall technology, the resonant sensor was used to detect vacuum by measuring the value change of quality factor in terms of vacuum pressure. The detector was successfully embedded into a glass-frit vacuum package to evaluate the vacuum-package performance. The packaged vacuum of near 20 mbar with satisfactory stability of two months was measured.