P3I-2 Cavityless Wafer Level Packaging of SAW Devices

Original implementations of the solution to cavityless WLP by means of isolation of waves are discussed. Variants of waveguiding layer acoustic wave (WLAW) (similar to boundary and interface waves) and isolated layer acoustic wave (ILAW) together with Bragg mirror-like additional acoustical isolation are compared in modeling and experimentally. The structures include metal electrode patterns and subsequent layers. The first among these layers is a dielectric layer, usually SiO₂ (or Pyrex) that possesses temperature compensating properties, while the outer layers are formed with either metals or dielectrics. In order for the wave to be confined into the SiO₂ layer the stack of the outer layers may be formed in different ways. For implementation of the WLAW concept, the main feature of subsequent layers is the increased acoustical velocity in comparison to the SiO₂ layer. Thus the wave attenuates exponentially in the structure on both sides of the SiO₂ waveguiding core. The ILAW concept is based on the application of high acoustical impedance materials providing abrupt change in boundary conditions between the layers. Further improvement of acoustical isolation in this approach is effectuated by means of alternating several layers with low and high acoustical impedance.