composite beam structure formed by masked-maskless etch of silicon

A novel micromachined composite beam structure has been designed and fabricated using the maskless anisotropic etching technology for {100} steps. The composite beam consists of two beam sections, a horizontal beam and a vertical beam, linked in series along the {100} direction. The composite beam is compliant in two orthogonal directions: the direction normal to the wafer due to the horizontal beam and the direction parallel with the wafer surface and perpendicular to the beam direction due to the vertical beam. The geometries of the two beam sections can be independently optimized through the process control. By attaching a mass to the end of the beam and integrating piezoresistive bridges on both beam sections, a composite beam-mass structure sensitive to two acceleration components can be formed. This structure can work as a rate gyroscope if the mass is electrostatically driven into vibration in the vertical direction and the Coliois force in the lateral direction is detected by a piezoresistive bridge. The principle, mask design and the process of the {100} masked-maskless etching for the composite beam structure are described and the experimental results on acceleration sensitivities and angular rate are presented.