SC0.15Al0.85N-based 4 GHz Coupled Bulk Acoustic Resonators (CBAR) and Filters for the Single-Chip Duplexer Solution

In this work, a design of BAW-like thin film resonator is presented and demonstrated with 15% Sc doped AlN piezoelectric material. Utilizing the thickness mode coupled with laterally propagated mode, the proposed coupled bulk acoustic resonator (CBAR) is able to achieve over 4 GHz resonant frequency with 400MHz lithographic tunability and a high effective coupling coefficient over 20%. Filters consisting of the proposed CBARs with different electrode pitches are fabricated on a single-chip. Measurement results show that two discrete filters can operate at 3.85GHz and 4.15GHz with 155MHz and 197MHz bandwidth, respectively. With the same material stack and adjacent operating frequency, these filters provide a promising single-chip duplexer solution for the high frequency filtering applications.