Positive stretching dependence of resonance frequency in CoFeB films modulated by lateral growth pre-strain

We demonstrated a method via applying a lateral pre-strain to achieve a positive stretching dependence of resonance frequency in CoFeB films. An artificial wrinkling surface structure by adhering CoFeB films to biaxially pre-strained elastomeric polydimethylsiloxane (PDMS) supports was employed to fabricate stretchable magnetic films. The lateral growth pre-strain was used to adjust the longitudinal stretching dependence of resonance frequency of CoFeB films. For the sample fabricated on an elastomeric support that can freely contract in the lateral direction, the resonance frequency f_r monotonously decreases with applying a tensile strain ε_app. For the sample fabricated on an elastomeric support that can partially contract in the lateral direction, the f_r first decreases and then increases as the ε_app increases. The sample fabricated on an elastomeric support in which the lateral contraction is strictly limited display a positive stretching dependence of f_r in the whole range of ε_app. Thousands of fatigue tests show that the stretching dependence of microwave properties have a good repeatability.