Highly Tunable Film Bulk Acoustic Wave Resonator Based on Pt/ZnO/Fe₆₅Co₃₅ Thin Films

We have developed a highly tunable film bulk acoustic wave resonator (TFBAR) using magnetostrictive (MS) Fe₆₅Co₃₅ thin films in acoustic layer stack. The resonator acoustic layer stack consists of Pt/ZnO/Fe₆₅Co₃₅ layers to tune the devices. Due to ∆E effect, TFBAR resonance frequency was up-shifted ~106.9 MHz (4.91%) in the presence of 2-kOe magnetic field. From experimental measurement, ∆E enhancement was estimated to be ~35 GPa. Further, it is observed that return loss ( S₁₁ ), phase response, and quality factor were improved in the presence of magnetic field. This improvement is due to the field-induced stiffness in the magnetic layer. Equivalent-modified Butterworth-Van Dyke (mBVD) circuit model was developed and fit with the experimental data, and circuit parameters were extracted. The proposed resonator is compact, low loss, power efficient, and highly tunable. This method also facilitates a new method of tuning FBAR devices using MS thin films.