Abstract
In this paper we present and discuss two innovative liquid-free SOI sensors for pressure measurements in harsh environments. The sensors are capable of measuring pressures at high temperatures. In both concepts media separation is realized using a steel membrane. The two concepts represent two different strategies for packaging of devices for use in harsh environments and at high temperatures. The first one is a “one-sensor-one-packaging_technology” concept. The second one uses a standard flip-chip bonding technique. The first sensor is a “floating-concept”, capable of measuring pressures at temperatures up to 400 °C (constant load) with an accuracy of 0.25% Full Scale Output (FSO). A push rod (mounted onto the steel membrane) transfers the applied pressure directly to the center-boss membrane of the SOI-chip, which is placed on a ceramic carrier. The chip membrane is realized by Deep Reactive Ion Etching (DRIE or Bosch Process). A novel propertied chip housing employing a sliding sensor chip that is fixed during packaging by mechanical preloading via the push rod is used, thereby avoiding chip movement, and ensuring optimal push rod load transmission. The second sensor can be used up to 350 °C. The SOI chips consists of a beam with an integrated centre-boss with was realized using KOH structuring and DRIE. The SOI chip is not “floating” but bonded by using flip-chip technology. The fabricated SOI sensor chip has a bridge resistance of 3250 Ω. The realized sensor chip has a sensitivity of 18 mV/µm measured using a bridge current of 1 mA.
Highlights
The realized sensor chip has a sensitivity of 18 mV/μm measured using a bridge current of 1 mA
The steel membrane has a center-boss connected with the SOI chip in the middle
The measured pressure acts on a robust steel membrane
Summary
High accuracy pressure control is a key feature in many industrial processes (e.g., the plastic, ceramic, chemical, aerospace, or pharmaceutical industry) [1,2,3]. These processes often require measurements at elevated temperatures (>150 °C). The usage of mercury or oil as a coupling medium (not allowed in the food industry and the EU), the complicated filling technology, contamination of products by the liquids used, and the fact that the steel membrane for media separation is prone to rupture are additional drawbacks. Sensors capable of direct measurement at high temperatures would permit fast, accurate, and simple process control. Deep silicon etching using a Bosch-process allows small chip size and arbitrary membrane geometry
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