Microstructured Multilayered Surface-Acoustic-Wave Device for Multifunctional Sensing

Abstract

A multifunctional sensor based on a surface-acoustic-wave (SAW) device is fabricated. It allows independent measurements of temperature and applied magnetic field. Optimization of the multilayered device structure leads to a temperature-coefficient frequency of the Love-wave resonance reduced to zero. The sensitivity to an applied magnetic field is obtained through magnetostriction of a $\mathrm{Co}$-$\mathrm{Fe}$-$\mathrm{B}$ layer. By use of shape anisotropy, the variation of intrinsic magnetic anisotropy with temperature is strongly reduced. On one hand, interrogating the device at the Love-wave-resonance frequency allows us to extract the applied magnetic field independently of the temperature in a [130--370 K] range. On the other hand, the Rayleigh or Leaky waves are less or not sensitive to applied fields but have a high temperature coefficient of frequency. So interrogating the device at the Rayleigh resonance frequency allows us to extract the temperature independently of the magnetic field. In addition, the used resonator geometry offers the possibility for future batteryless and wireless interrogation.