High-order mode solid mounted resonators with polarity inverted multilayered GeAlN/AlN films

High frequency bulk acoustic wave (BAW) resonators for beyond 5 G communications have low Q values and electromechanical coupling because of their ultra-thin piezoelectric monolayer films. Polarity inverted multilayered film BAW resonators operating in high-order mode resonance can have thicker piezoelectric layers than monolayer BAW resonators. In this paper, we fabricated and evaluated two- to four-layered polarity inverted GeAlN/AlN film solid mounted resonators (SMRs). They resonated in high-order mode. Their total film thicknesses were approximately two- to four-times thicker than that of a monolayer AlN film SMR. The polarity inverted GeAlN/AlN film SMRs had higher Q values than the monolayer SMR.