A Miniaturized Acoustic Dual-Band Bandpass Filter using Thin-Film Lithium Niobate

This work presents a new design of an acoustic-only dual-band bandpass filter operating beyond 6 GHz. The operating frequencies are achieved by resorting to the third-order antisymmetric Lamb wave mode (A3) in an 800 nm thick Z-cut lithium niobate thin film. The dual-band operation utilizes a fine-controlled regional thinning technique on lithium niobate thin film. Due to the spurious-free and high-Q performance of the A3 dual-resonance lithium niobate resonators, the fabricated dual-band bandpass filter has been demonstrated with small in-band ripples and sharp roll-offs. The two transmission bands are contiguous and located at 6.75 GHz and 7.35 GHz, respectively, with a fractional bandwidth of 2.5%. These two passbands share the same static capacitance leading to a miniaturized footprint of 0.6 mm2, which shows the strong potential of this dual-band design for front-end applications.