Stabilizing High-Frequency Magnetic Properties of Stretchable CoFeB Films by Ribbon-Patterned Periodic Wrinkles.

The intrinsic nonstretchable feature of magnetic films has significantly limited its applications on wearable high-frequency devices. Recent studies have proved that the wrinkling surface structure based on the growth on polydimethylsiloxane (PDMS) is an effective route to obtain stretchable magnetic films. However, it is still a great challenge to simultaneously achieve a desired stretchability and stretching-insensitive high-frequency properties of magnetic films. Herein, we reported a convenient method to stabilize the high-frequency properties of stretchable magnetic films by depositing magnetic ribbon-patterned films on prestrain PDMS membranes. The ribbon-patterned wrinkling CoFeB films have far fewer cracks than the continuous film, which indicates a nice strain-relief effect and thus confers the stability of high-frequency properties for the films under stretching. However, the wrinkle bifurcation and the uneven thickness at the ribbon edge could adversely affect the stability of its high-frequency properties. The 200 μm wide ribbon-patterned film shows the best stretching-insensitive behaviors and maintains a constant resonance frequency of 3.17 GHz at strain from 10% to 25%. Moreover, a good repeatability has been demonstrated by performing thousands of stretch-release cycles, which did not significantly deteriorate its performances. The ribbon-patterned wrinkling CoFeB films with excellent stretching-insensitive high-frequency properties are promising for application in flexible microwave devices.