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|Wafer Level Encapsulation of Micromachined Pressure Sensors to Realize a Liquid Flow Sensor|
|Keywords: Glass frit bonding, Pressure sensor, Flow sensor|
|A differential pressure flow sensor capable of measuring low flow rates 0.1 ml/hr to 100 ml/hr has been developed, using wafer level bonding technology. Surface micromachined MEMS pressure sensors were utilized to create a flow sensor. A cap wafer with etched flow channel and sensor cavity was bonded to a pressure sensor wafer. Glass frit was used to bond the wafers. The flow channel was created by combination of seal glass bonding material and etch step carried out earlier in the cap wafer fabrication process. Differential pressure sensing principle measures the pressure drop across a restriction channel. The differential pressure measured is related to the volumetric flow of the fluid. Literature review reveals differential pressure sensing based MEMS flow sensors have been developed. Records indicate various wafer bonding technologies like direct wafer bonding, anodic wafer bonding has been used to demonstrate a differential pressure flow sensor. Research published so far identifies glass frit bonding as one of the successful bonding technology for MEMS sensors. Glass frit bonding could also be applied to create a flow sensor and has not yet been recorded. Glass frit bonding also helps us overcome the limitations that exist in other bonding technologies listed earlier. The limitations in a broader perspective include maximum temperature the device could handle, surface topography due to metal lines and other fabrication process steps etc. This research summarizes the fabrication and assembly work behind developing a flow sensor by wafer level encapsulation. Results and conclusions arrived from testing these flow sensors with different fluids and flow rates will also be listed.|
|Ali Shakir, Student