Thick $LiNbO3$ layers on diamond-coated silicon for surface acoustic wave filters

Surface acoustic wave (SAW) technology based on lithium niobate/diamond/silicon multilayered structures has been investigated due to the large demand of frequency filters for communication systems, particularly for cellular phones. Thick $LiNbO3$ layers (∼1 μm) with a good morphology, i.e., surface roughness lower than 10 nm have been grown at 490 °C on diamond-coated silicon substrates by multistep rf magnetron sputtering. A SAW devices operating at 300 MHz was designed and fabricated in order to validate the proposed structure; in particular, our main objective was to verify the high velocity in the layered structure. Preliminary filter responses were very promising: the SAW velocity was estimated to 8200 m/s and the coupling factor was $K2∼0.93%.$ The film growth, the technology, and the electrical measurements are described in this letter.