BAW Filters (Bulk Acoustic Wave Filters)

Definition: BAW filters are high-performance RF filters using acoustic waves in a piezoelectric material to provide frequency selectivity.

Structure:

• Piezoelectric layer (e.g., AlN or ZnO)
• Top and bottom electrodes
• Acoustic reflector (in FBAR) or air cavity (in SMR)

Types:

• FBAR: Film Bulk Acoustic Resonator – uses Bragg reflector
• SMR: Solidly Mounted Resonator – dielectric mirror stack

Advantages:

• High Q factor
• Excellent temperature stability
• Suitable for high frequencies (1.5–10 GHz)
• Low insertion loss

Applications:

• 5G/4G smartphones
• Wi-Fi modules
• Base station front-end modules

Comparison vs. SAW: