A Facile FBAR Design for Air Gap Replacement

This study proposes an asymmetry electrode-cavity design for film bulk acoustic resonators (FBAR), which reduces fabrication complexity and enhances mechanical stability. The fabricated FBARs exhibit series (fs) and parallel (fp) resonance frequencies at approximately 5.0 GHz and 5.5 GHz, respectively, with effective electromechanical coupling coefficient (${k_{eff}}^2$) ranging from 18% to 22%. Experimental results show that the FBAR resonators with the asymmetric design achieves Bode quality factors comparable to those with the air-gap, along with the increased ${k_{eff}}^2$. Statistical analysis of the quality factors across various active areas (400~2000 μm²) confirms the scalability of the asymmetric design. The proposed design offers a practical and robust solution for high-performance FBARs, enabling simplified manufacturing without sacrificing acoustic quality or resonance purity, and is well-suited for next-generation radio-frequency (RF) front-end applications.