On the influence of vacuum on the design and characterization of MEMS
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文摘
The article will be focused on the influence of vacuum on resonant micro electromechanical sensor and actuator systems (MEMS). The system¡¯s encapsulation with a pressure below atmospheric pressure plays a key role in the sensor performance especially in the field of vibration sensors. These sensors are becoming increasingly important for structural health or wear state monitoring in many engineering applications. Structural health, wear states and damage levels can be recognized by means of the vibration spectrum generated by propagating sound waves in solid materials known as ¡®acoustic emission? Commonly the vibration spectrum is measured by wide band accelerometers and subsequent Fourier transformation. Alternatively mechanical vibrations can be detected by resonant sensor systems. In particular these can be arrays of tiny cantilevers with multiple fixed Eigenfrequencies or single resonators with tunable Eigenfrequencies. Advantages of resonant pick-up compared to wide band sensors are the inherent spectral filtering and signal amplification in the mechanical domain due to the high quality factor at resonance. Therefore, an important design parameter is viscous damping of moving silicon cantilevers in the surrounding gas (e.g. air). The theoretical background of fluid-structural interactions and methods for experimental characterization of damping properties at atmospheric pressure and in evacuated environment will be presented. Measurements using a vacuum wafer prober for electrostatic actuation and optical motion sensing were conducted.
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