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This article presents a study of ladder-lattice bulk acoustic wave (BAW) filters. First, a review of BAW technology and filters topologies is addressed. Next, a mixed ladderlattice BAW filter for application on W-CDMA reception front-ends (2.11-2.17 GHz) is presented. An improved solidly mounted resonators (SMR) technology was used for the filter implementation. The filter synthesis methodology is briefly described. Layout guidelines are discussed enabling an optimized filter design. The filter on-wafer measurement results are as follows: 23.55 dB of insertion loss, 28.7 dB of return loss, an isolation higher than 247 dB at the transmission band (1.92-1.98 GHz) and an improved selectivity (230 dB at 2.14 GHz 6 60 MHz). Therefore, we can observe that the mixed topology combines the advantages of ladder and lattice networks, having very steep responses and an improved isolation at undesired bands.

Coupled resonator filters designed using a single-layer coupler require coupling materials with an acoustic impedance less than 5.0 MRayl. Carbon-doped oxide, with an acoustic impedance of 4.8 MRayl and an acoustic attenuation of 200 to 600 dB/cm at 1 GHz, can be used as a single-layer coupler to produce a competitive 2-stage coupled resonator filter for cellular handset applications in the gigahertz frequency range. The electrical response of our filter is superior to that of coupled resonator filters using a traditional acoustic mirror as the coupling element. We present an ultra-miniature 0.58 mm x 0.38 mm coupled resonator filter operating at a frequency of 2.15 GHz.

This article presents a study about the design of film bulk acoustic wave resonator (FBAR) filters at higher frequency bands. FBAR filters are expected to replace traditional filter technologies (SAW and ceramic). This is mainly due to their compatibility with silicon low-cost process, enabling mass production and filter integration on above-IC processes. Nonetheless, increasing the operation frequency of FBAR filters, new acoustical and electromagnetic constraints are introduced to the filter design. These new constraints of designing of FBAR filters are presented. Further, a design technique using higher harmonic modes is addressed. This technique enables the realization of FBAR filters for operation at higher frequency bands (X, Ku, K, and Ka) using the same fabrication conditions of FBAR filters in L, S, and C bands.

A theoretical approach of the frequency trimming of BAW filters is presented. We discuss the way to integrate this step already in the design stage by considering the frequency adjustment of worst cases. In particular, we show that the frequency trimming puts some requirements on the acoustical design of resonators. We also discuss the limits of this adjustment, and evaluate on an example the minimum dispersion that cannot be suppressed.