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

Abstract

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 fr monotonously decreases with applying a tensile strain εapp. For the sample fabricated on an elastomeric support that can partially contract in the lateral direction, the fr first decreases and then increases as the εapp increases. The sample fabricated on an elastomeric support in which the lateral contraction is strictly limited display a positive stretching dependence of fr in the whole range of εapp. Thousands of fatigue tests show that the stretching dependence of microwave properties have a good repeatability.