A resonant accelerometer is a sensor that responds to an acceleration force by producing a frequency shifted output signal. Quartz-based resonant accelerometers have been used in many commercial applications, including navigation-grade precision accelerometers.
Micromachined resonant sensors have been developed. The acceleration force amplification provided by these early devices has been limited by the leverage systems for the proof masses of the devices. Thus, to improve the response of micromachined resonant sensors, it is important to improve upon prior art proof mass leverage systems.
Some recent work has focused on micromachined resonant sensors in bulk silicon processes, but this class of sensor has not yet been pursued in a surface-micromachining technology. Surface-micromachining technology embeds a micromechanical device in an anisotropically etched trench below the surface of a wafer. Prior to microelectronic device fabrication, this trench is refilled with oxide, chemical-mechanically polished, and sealed with a nitride cap in order to embed the micromechanical devices below the surface of the planarized wafer. The wafer is then used as the starting material for integrated circuit fabrication in a conventional process, such as CMOS or BiCMOS. Thus, surface-micromachining technology allows a micromachined device to be combined with integrated circuitry in a single wafer.
In view of the foregoing, it would be highly desirable to provide a resonant accelerometer with an improved leverage system for enhanced force amplification. In addition, it would be highly desirable to provide a resonant accelerometer design that is compatible with surface-micromachining technologies.