Abstract
In the oil logging, automotive and spacecraft industriesthere exists a strong interest in sensing devices which canmeasure a static load with very high resolution at normal andelevated temperatures up to 500 °C. We developed,realized and tested a first- and second-order packaged forcesensor for such requirements. The system consists of a resonantstructure vibrating in its bending mode, which is hermeticallyvacuum packaged in a single-crystal silicon housing together withthe resonance detection sensor. The capacitive detectionelectronics are off-chip, giving a high degree of freedom forthe design and fabrication process. The oscillator operates witha switched lock-in amplifier. The packaged silicon load cellachieved a load sensitivity of 27 Hz N-1, a resolution of2 mN and good repeatability for subsequent load cycles. Theelectronics for the first amplifier stage are mounted togetherwith the silicon load cell in the second level package. Thetemperature limitation caused by the electronics was eliminatedby replacing it with a Fabry-Perot interferometer in thesilicon chip. The optical detection was successfully tested andshowed the resolution of the resonator deflection to be more than tentimes better than the capacitive detector.
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