Fine frequency selection techniques for aluminum nitride Lamb wave resonators

This paper reports fine frequency selection techniques for aluminum nitride (AlN) Lamb wave mode resonators (LWR) to control the relative frequency of resonators in an array to 0.1%. The technique that works the best is by adjusting the so-called 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. Experimental results suggest the center frequency can be linearly adjusted by up to ±2.5% with no significant effect on other resonator parameters including Q, R_m, C₀, and k²_t. Preliminary results of filter banks at 735 MHz utilizing this technique demonstrate that the relative center frequency of each channel can be evenly spaced by 0.05% without post-process trimming.