A 6.1 GHz Wideband Solidly-Mounted Acoustic Filter on Heterogeneous Substrate for 5G Front-Ends

This paper reports a 6.1 GHz wideband solidly-mounted acoustic filter based on the novel LiNbO
3
-on-SiC (LNOSiC) substrate for the first time. The well-confined S0 mode waves with high phase velocity and large electromechanical coupling (k
²
t
) in LNOSiC were theoretically and experimentally investigated. Compared with conventional surface acoustic wave (SAW) resonators, the resonators using the S0 mode in the transferred single crystal LiNbO
3
thin film offer 1.5- to 1.8-fold higher frequencies and 2- to 3-fold larger k
²
t
, thus enabling 6-GHz filters with a fractional bandwidth of more than 7%. The newly proposed S0 mode devices on the LNOSiC substrate break the frequency limitation (~ 3 GHz) of conventional SAW devices, which are promising for compact, high frequency and large bandwidth 5G RF front-ends.