Acoustic Wave Cavity Structure to Prevent Piezoelectric Layer Cracks

The patent applies preliminary action by forming a relief structure (a recessed region) in the piezoelectric layer at the location where the through-hole will be formed, before the through-hole is actually created. This relief structure is formed by selectively removing material in advance, creating a stepped configuration where the piezoelectric layer has a first thickness in the region and a second, greater thickness elsewhere. When the through-hole is subsequently formed to communicate with the cavity, the pre-formed relief structure prevents stress concentration and crack initiation at the hole entrance, thus resolving the contradiction between ease of manufacture and crack prevention.

The patent applies local quality by creating a relief structure with different thickness regions in the piezoelectric layer - a first thickness in the through-hole region and a second, greater thickness in the surrounding region. This local variation in thickness allows the device to maintain smaller overall size with reduced electrodes while the thicker surrounding region preserves the resonant characteristics and quality factor by providing adequate piezoelectric material for effective acoustic wave generation and propagation.