Abstract
High-Q RF bulk acoustic wave filters are still required for mobile communication applications. However, the in-plane orientation of commercial AlN films is random, despite their excellent out-of-plane c-axis orientation. We proposed combining two different orientation control techniques: self-texture for out-of-plane alignment and ion beam irradiation for in-plane alignment. To demonstrate the effectiveness of this approach, both in-plane a-axis and out-of-plane c-axis aligned AlN and ScAlN films were grown on Ti/silica glass substrates using 0.3–0.5 keV grazing ion-beam-assisted RF sputtering technique without using epitaxial growth. The clear six symmetry in the pole-figure observed in AlN and ScAlN thin films indicates the single-crystal-like in-plane a-axis orientation. The ion beam direction corresponded to the in-plane 〈101̄0〉 axis. In-plane x-ray diffraction ϕ-scan curve and ω-scan curve FWHM were measured to be 25° and 2.2°.
Highlights
As available RF frequency bands become increasingly crowded, the demand for sharp filters is increasing in order to avoid the interference between adjacent frequency bands
The Q-factor of surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters is mainly determined by the Qm of the piezoelectric materials when large electrical and mechanical losses in the electrodes and the lateral losses due to waves leaking and scattered at the edges of a resonator are sufficiently suppressed
The pole figure indicates that the AlN thin films were grown so that in-plane ⟨1010⟩ axis corresponds to the ion beam direction
Summary
As available RF frequency bands become increasingly crowded, the demand for sharp filters is increasing in order to avoid the interference between adjacent frequency bands. Electrical LC (inductance and capacitance) filters have large bandwidths, their low Q (
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