High Overtone Bulk Acoustic Resonator with improved effective coupling coefficient

A High Overtone Bulk Acoustic Wave Resonator (HBAR) is fabricated with the active material being Ba
0.5
Sr
0.5
TiO
3
(BST). Owing to its strong electrostrictive property, the BST needs an external dc voltage to yield an electromechanical coupling. The variations in resonances with respect to varying dc fields are noted and analyzed with the aid of an Resonant Spectrum Method (RSM) model. Effective coupling coefficient $(\mathrm{K}_{\mathrm{e}\mathrm{f}\mathrm{f}}^{2}(\%))$ in the case of employed MIM based structure is observed and the comparisons are drawn with the corresponding values of the CPC structures. An improvement of 70% in the value of $\mathrm{K}_{\mathrm{e}\mathrm{f}\mathrm{f}}^{2}$(%)at 1.34 GHz is witnessed in MIM structures because of direct access to the bottom electrode of the structure.