Synthesis of narrowband AlN Lamb wave ladder-type filters based on overhang adjustment

By adjusting the aluminum nitride (AlN) "overhang" dimension, OH, measured from the center of the outermost electrode to the edge of AlN plate, independently of the interdigital transducer (IDT) pitch, AlN Lamb wave mode resonators (LWRs) with 0.25% relative frequency control were demonstrated. Unlike adjusting electrode number, NE, device length, L, and electrode coverage, η, all of which affect device parameters such as Q, R_m, C₀, and k_t², overhang frequency selection technique can linearly shift the center frequency up to 2.5% with no influence on other resonator parameters. Preliminary results of narrowband ladder filters using these finely spaced AlN LWRs as building blocks were fabricated and measured. Fine tuning of bandwidth and center frequency were studied.