Tunable Film Bulk Acoustic Wave Resonator Based on Magnetostrictive Fe65Co35 Thin Films

We have developed a Tunable Film Bulk Acoustic Wave Resonator (TFBAR) based on magnetostrictive Fe
₆₅
Co
₃₅
thin films. The resonator layer stack consists of Pt/ZnO/Fe
₆₅
Co
₃₅
layers for tuning of devices. When resonator is subject to magnetic field there is expansion in Fe
₆₅
Co
₃₅
layer due to magnetostrictive effect. This expansion in Fe
₆₅
Co
₃₅
layer induces strain, which alters the Young's modulus of magnetostrictive layer and this behavior is denoted as AE effect. In an unbiased condition, series (f
_s
) and parallel (f
_p
) resonance frequency are detected at 1.14 GHz and 1.187 GHz, respectively. When resonator was placed in magnetic field series and parallels both resonance frequencies are lower shifted by ~7MHz. Electromechanical coupling coefficient (k
_t
²
) was found 9.69% when there is no magnetic field and reduced to 9.53% with magnetic field. This reduction in k
_t
²
is due to magnetic field induced strain in magnetostrictive Fe
₆₅
Co
₃₅
layer. The proposed resonator is very promising and can be utilized for various reconfigurable microwave resonators, frequencies agile devices and magnetic sensors.