Acoustic wave devices on stacked die

An acoustic wave device assembly comprising:

• a first die including a first boundary acoustic wave device, the first boundary acoustic wave device including a piezoelectric layer, an interdigital transducer electrode on the piezoelectric layer, first and second high velocity layers on opposing sides of the piezoelectric layer, and a low velocity layer positioned between the piezoelectric layer and the first high velocity layer, the low velocity layer having a lower acoustic velocity than the first high velocity layer, and the first high velocity layer having a thickness sufficient to maintain mechanical durability of the first boundary acoustic wave device;
• and
• a second die stacked with the first die, the second die including a second boundary acoustic wave device.

An acoustic wave filter comprising:

• a boundary acoustic wave device including a piezoelectric layer, an interdigital transducer electrode on the piezoelectric layer, first and second high velocity layers on opposing sides of the piezoelectric layer, and a low velocity layer positioned between the piezoelectric layer and the first high velocity layer, the low velocity layer having a lower acoustic velocity than the first high velocity layer, and the first high velocity layer having a thickness sufficient to maintain mechanical durability of the first boundary acoustic wave device;
• and
• a plurality of acoustic wave resonators, the plurality of acoustic wave resonators and the boundary acoustic wave device together configured to filter a radio frequency signal.