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

Abstract

High frequency bulk acoustic wave (BAW) resonators for beyond 5G 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.

Analysis of Sezawa mode Rayleigh-type SAWs on ScAlN film/floated electrode layer/ScAlN film/high velocity substrates

“…21) Experimentally, polarization control of AlN-based films can be achieved by seed layer insertion, 24) ion beam irradiation, 25) and Si or Ge doping. [26][27][28][29] However, the growth of multilayer polarization reversal ScAlN films with high crystal orientation would not be easy.…”

Characteristics of c-axis oriented GeAlN films and applications to higher-order mode BAW resonators

“…In addition, the f r of the standard BAW resonator with a ∼1 μm AlN film is dramatically reduced by the mass loading effects of the top and bottom electrode films. 13,15) The electrode area S of the highfrequency BAW resonator with a ∼1 μm AlN film is very small for 50 Ω impedance matching because the capacitive impedance |Z| of the standard BAW resonators is determined as |Z| = d/(2πfεS), where ε is the dielectric constant of the piezoelectric film. Thus, high-frequency AlN film BAW resonators also require ultra-thin top and bottom electrode films of ∼100 nm and a very small electrode area, which tends to result in low conductivity in the electrodes.…”

“…Thus, ultra-thin electrode films are not required in PI multilayered BAW resonators operating at high frequencies. 15) Therefore, we anticipate that the PI multilayered film will solve the problems associated with film BAW resonators operating at high frequencies, such as degradation of the Q factor, electromechanical coupling factor, and power-handling capability.…”