A micromachined silicon vibrating-beam angular rate sensor : a design and implementation study

Design and Implementation of a Silicon-Beam Angular Rate Sensor is studied. The sensing device is designed based on a micromachined single crystal silicon beam. Electromagnetic actuation supplies the reference vibration, and the Coriolis-induced vibration is sensed by a capacitor plate in close proximity to the vibrating beam. Beams with precise dimensions, and vertical side walls are fabricated using wet anisotropic etching of Si100 wafers in TMAH 25%. Several issues essential for a successful design are discussed. The required circuitry for actuation of the beam and detection of the Coriolis induced vibrations are discussed. A complete model for the mechanical and electrical components of the sensor is built in HSPICE and used to simulate the basic operation of the sensor. To improve the mismatch between beam resonant frequencies, a scheme of novel Concave Corner Compensation Patterns is devised to substantially reduce the size of the residual 111 flanges at both ends of the beams. The design principles are explained in detail and a numerical simulation program is developed to track the etch progress of the corner compensation patterns. The etch progress in patterns is simulated using a graphical simulation tool and tested experimentally. Experimental results are matched with simulation results. Several test beam structures have been fabricated and tested. Some critical mechanical characteristics of the beam structures are measured and satisfactorily compared with the results from theory and Finite Element Model simulation. Functional sensor structures are fabricated and characterized. The effect of concave corner compensation on mismatch is shown both using the Finite Element Model simulation and experiment