Lateral bulk acoustic wave filter devices are disclosed. A device (600) includes an intermediary layer (606, 616) providing or on a topmost layer of an acoustic reflector (608, 618). The intermediary layer has a first region (606) and a second region (616). The first region has a first layer thickness and the second region has a second layer thickness different from the first layer thickness. The device includes a first multilayer stack (604, 602, 610) on the first region and a second multilayer stack (614, 612, 620) on the second region of the intermediary layer. Each of the first (100a) and the second stacks (100b) includes a piezoelectric layer (602, 612) on a counter electrode (604, 614) that is located on the respective region, an input (150, 150a; 670, 670a) and an output electrode (170, 170a; 650, 650a). The output electrode of the first stack being connected to the input electrode of the second stack. Application of a radio frequency voltage between the input electrode and the counter electrode layer of the first stack creates acoustic resonance modes in the piezoelectric layer between the input and output electrodes of the first and the second stack. The frequency of spurious modes in the the two stacks is offset with respect to each other through the differing thickness of the intermediary layer. Thereby the spurious modes in the resulting device are reduced.
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