Computer-Aided Modeling and Tuning of RF Acoustic Wave Filters

Abstract

Mobile radios must operate across many frequency bands while sharing antennas and supporting closely spaced transmit and receive paths. Achieving this requires high-performance RF filtering that suppresses interference, limits unwanted emissions, and provides strong isolation. In smartphones, these functions are predominantly realized using acoustic-wave devices, particularly SAW- and BAW-based resonator filters implemented as duplexers and multiplexers. Their high selectivity, low insertion loss, and compact size have displaced conventional solutions as systems expanded from limited third-generation band sets to much larger fifth-generation portfolios. This growth in band count has increased both the number and diversity of filters within a single platform, making acoustic filters a dominant contributor to RF front-end cost and area. This dissertation addresses key challenges in the dynamic tuning of acoustic filters and in late-stage band targeting under process-induced detuning. Several bandwidth-reconfigurable architectures are introduced that integrate switches with resonators to enable bandwidth reconfiguration. In addition, the dissertation demonstrates that strategic modification of interdigital transducer configurations in ladder acoustic filters enables discrete control of the resonator electromechanical coupling coefficient. By adjusting the ratio of positive to negative IDT fingers, coupling can be set to selected levels to improve selectivity and asymmetry and to meet diverse specifications. VO₂-based RF switches are integrated directly with SAW resonators to select discrete IDT states, enabling ladder bandwidth tuning while maintaining low insertion loss. The dissertation further demonstrates a computer-aided tuning framework for late-stage band targeting in acoustic filters. A resonator-level extraction method reconstructs ladder element parameters directly from measured filter responses using stable rational approximation of the driving-point function, pole-zero identification via partial and continued fraction expansions, topology-aligned element matching, and sequential decomposition of series and shunt resonators. In addition, an on-wafer tuning strategy is demonstrated that prescribes minimal, physically realizable corrections without embedded tuning components or manual intervention. The approach spatially programs mass loading through patterned dielectric overlays for additive shifts and electrode thinning or ion milling for subtractive shifts, enabling heterogeneous per-resonator trims simultaneously. Experimental results demonstrate recovery of target passband characteristics, with improved return loss and insertion loss, establishing a practical framework for acoustic-filter correction under manufacturing-induced non-idealities.