Horizontal Harmonics Mitigation in Thickness Shear $\mathrm{A}_{1}$ Mode Resonators

Spurious free ultra-wideband acoustic wave resonators are becoming the key foundation of the new 5G radio bands. Here we explore thickness shear
$\mathbf{A}_{\mathbf{1}}$
mode resonator with lateral field excitation offering large electromechanical coupling coefficient exceeding 35%. The higher order horizontal harmonic
$\mathbf{A}_{1}$
modes
$(\mathbf{A}_{\mathbf{1}-\mathbf{n}})$
have been big challenges to implement ripple free filters using these devices. An effective mechanism of mitigation is proposed by using SiO
2
sided IDTs. The proposed mechanism not only mitigates the higher order ‘horizontal’ harmonic
$\mathbf{A}_{\mathbf{1}}$
modes but also improves the bandwidth from 20% to 20.8%.