Thermomechanical rigidity of a wireless pressure senosr node for high-temperature applications

• Aimed for here, are microsensorequippednodes for environments too harsh for conventionalMEMS devices, especially with respect totemperature. Therefore, a prototype pressure sensorhas been made from micromachined, laminated andfired High-Temperature Co-fired Ceramic (HTCC)aluminium oxide green tapes. The Sensor is readwirelessly using LC resonating circuits made ofplatinum screen-printed on the tapes. In the specificwork package reported on here, the focus is on thethermomechanical characterization of the stackforming the device, since the bimorphic behavior dueto CTE mismatch of its constituents was believed toaffect the sensor performance. This part was conductedboth by optical profilometry of samples,ranging from 410 to 890 μm in thickness, heated to400°C, and by monitoring the frequency shift whenthe samples were subjected to three-point bending atroom temperature. With only negligible deformationsobserved for temperatures up to 400°C, a highthermomechanical rigidity was demonstrated.Furthermore, only when deformations larger thanthe thermomechanically induced ones were imposedon the thinnest samples, a shift in resonance frequencywas observed, indicating that the LC circuitrywill not be affected by the thermomechanicaldeformation of the sensor node. The sensor element,being a capacitor formed by a membrane sealing acavity and deflecting with changes in the ambientpressure, integrated in one of the samples, exhibiteda clear pressure-induced frequency shift of6785 ppm at 1.5 bar and room temperature. Inconclusion, the sensor node concept has been verifiedto have high thermal robustness.

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