AeroMEMS Wall Hot-Wire Anemometer on Polyimide Substrate Featuring Top Side or Bottom Side Bondpads

• Published in: IEEE sensors journal Vol. 7; no. 8; pp. 1095 - 1101
• Main Authors: Buder, U., Berns, A., Petz, R., Nitsche, W., Obermeier, E.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2007; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aerodynamics; Bonding; Curvature; Design; Flexible manufacturing systems; Fluid flow measurement; Metallization; Metallizing; Microelectromechanical systems; Microelectromechanical systems (MEMS); Micromechanical devices; polyimide; Polyimide resins; Polyimides; Sensor phenomena and characterization; Sensors; Substrates; Thermal conductivity; via; wall hot-wire; Walls
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2007.897933

Design, manufacturing, calibration, and basic characterization of a microelectromechanical systems (MEMS) wall hot wire sensor on a flexible polyimide substrate are presented. A configuration exhibiting bond pads on the top side of the foil, as well as an improved setup featuring a through-foil metallization and bottom side bond pads were established. Both sensor designs make use of a highly sensitive nickel thin-film resistor spanning a reactive ion etched cavity in a polyimide substrate. The polyimide base material enables the sensor to be adapted to curved aerodynamic surfaces, e.g., airfoils and turbine blades. A mismatch of curvature of aerodynamic surface and silicon sensor surface, as observed with previously presented MEMS hot-wire anemometers is avoided. The combination of polyimide's low thermal conductivity and a cavity featuring FEM-optimized dimensions accounts for a very low-power consumption (<25 mW). Fluctuations in wall shear stress up to 85 kHz can be resolved in constant-temperature mode. An average sensitivity of 0.166 V/(N/m 2 ) is achieved in a wall shear stress range from 0 to 0.72 N/m 2 . The specifically designed through-foil metallization process allows for electrical contacts to be positioned on the backside of the substrate, thus effectively minimizing aerodynamic disturbances.