Microscopic magnetic and high frequency properties of a stress sensor using FeCoBSi magnetorestrictive thin films

Millimeter sized LC resonant circuits have been fabricated in thin film technology on glass wafers. They consist of a Cu strip inductor sandwiched with 500 nm thick FeCoBSi soft magnetic films. SiO₂ was used as a dielectric to isolate the magnetic layers from the conductor and to realize the capacitor. The resonance frequency of the device was around 350 MHz depending on the inductor layout. Kerr-effect microscopy was used to directly illustrate the effect of stress on the magnetic layer. The high frequency properties of the magnetic layers and the devices are discussed especially in view of increasing its quality factor and its use as remote interrogatable stress sensor.