Articles | Volume 3, issue 2
J. Sens. Sens. Syst., 3, 167–175, 2014
J. Sens. Sens. Syst., 3, 167–175, 2014

Regular research article 08 Aug 2014

Regular research article | 08 Aug 2014

Fabrication and characterization of a piezoresistive humidity sensor with a stress-free package

T. Waber1, M. Sax1, W. Pahl2, S. Stufler2, A. Leidl2, M. Günther3, and G. Feiertag1 T. Waber et al.
  • 1Munich University of Applied Sciences, Lothstraße 64, 80335 Munich, Germany
  • 2EPCOS AG, a member of TDK-EPC Corporation, Anzingerstraße 13, 81617 Munich, Germany
  • 3Technical University of Dresden, Helmholtzstraße 18, 01062 Dresden, Germany

Abstract. A highly miniaturized piezoresistive humidity sensor has been developed. The starting point of the development was a 1 × 1 mm2 piezoresistive pressure sensor chip. As sensing material, a polyimide was used that swells with increasing adsorption of water molecules. To convert the swelling into an electrical signal, a thin layer of the polyimide was deposited onto the bending plate of the pressure sensor. The humidity sensor was characterized in a climate chamber. The measurements show a sensitivity of 0.25 mV per percent relative humidity (%RH) and a non-linearity of 3.1% full scale (FS) in the range of 30–80% RH. A high cross-sensitivity to temperature of around 0.5 mV °C−1 was measured, so temperature compensation is necessary. For stress-free packaging of the sensor chip, a novel packaging technology was developed.