4.5 GHz Lithium Niobate MEMS Filters With 10% Fractional Bandwidth for 5G Front-Ends

This paper presents a new class of micro-electro-mechanical system (MEMS) C-band filters for 5G front-ends. The filter is comprised of resonators based on the first-order asymmetric Lamb wave (A1) mode in thin-film lithium niobate. Two filters have been demonstrated at 4.5 GHz with sharp roll-off, flat in-band group delay, and spurious-free response over a wide frequency range. The first design shows a 3-dB fractional bandwidth (FBW) of 10%, an insertion loss (IL) of 1.7 dB, an out-of-band (OoB) rejection of -13 dB, and a compact footprint of 0.36 mm
²
, while the second design shows a 3-dB FBW of 8.5%, an IL of 2.7 dB, an OoB rejection of -25 dB, and a footprint of 0.9 mm
²
. The demonstrations herein mark the largest FBW achieved for acoustic-only filters at 5G frequencies.