Method of Fabricating Multiple-Frequency Film Bulk Acoustic Resonators in a Single Chip

We report experimental results of a novel approach to integrate multiple-frequency film bulk acoustic resonators (FBAR) in a single chip. An additional tuning layer was deposited and patterned on a conventional Metal/AlN/Metal FBAR film stack. By controlling in-plane dimensions of the periodic tuning patterns, resonance frequencies are modulated according to the corresponding loading percentages. To obtain a desirable frequency response of the modulated resonance peaks (a pure frequency shift), the pitch of the tuning patterns needs to be smaller than the membrane thickness. Three thicknesses of the tuning layers are fabricated to demonstrate different tuning ranges and sensitivities. This approach provides a potential solution to integrate multiple-frequency FBAR filters of adjacent bands by only one additional lithographic patterning step