UHF/VHF resonators using lamb waves co-integrated with bulk acoustic wave resonators

Abstract

Bulk Acoustic Wave (BAW) resonators exhibit attractive properties in terms of power handling capacity and on- chip integration to realize filters in the GHz range. A current problem in the design of BAW resonators is the existence of spurious resonances due to Lamb waves propagation. This work demonstrates that Lamb wave resonances can be used to realize resonators with high quality factor in the Ultra-High Frequency/Very High Frequency (UHF/VHF) ranges. Design of lateral resonators are performed using finite element modelling. Influence of electrode geometry and type of excitation (one- or two-phase) upon coupling of fundamental or higher order resonances is discussed. Lamb wave and Film Bulk Acoustic Resonators (FBAR) are simultaneously manufactured using surface micro-machining process compatible with Above IC integration. S0 Lamb wave resonances from 20 to 277 MHz are measured showing good agreement with simulation. High quality factors (Qs and Qp) of 2000 and k 2 ~0.8% (k coupling coefficient) are obtained at 92 MHz for 3 rd order resonator. For co- integrated BAW resonators, thickness extensional resonance is measured at 2.5 GHz.