A Design Approach for High-Q FBARs With a Dual-Step Frame

Area of Science:

• Acoustic Resonators
• Materials Science
• Electrical Engineering

Background:

• Film bulk acoustic resonators (FBARs) are crucial components in modern electronics.
• Energy loss due to Lamb waves at the antiresonant frequency (f_a) degrades the quality factor (Q_a) of FBARs.
• Existing FBAR designs struggle to mitigate Lamb wave propagation effectively.

Purpose of the Study:

• To develop a novel design approach for FBARs to improve the quality factor (Q_a) at antiresonant frequency (f_a).
• To specifically address and alleviate energy loss caused by Lamb waves.
• To optimize a dual-step frame structure for enhanced FBAR performance.

Main Methods:

• An optimization process was employed for a dual-step frame structure.
• The frame design utilizes differing acoustic impedances to reflect dominant Lamb modes.
• Lamb wave dispersion curves and power flows were calculated using the global matrix method and acoustic Poynting's Theorem, with dimensions determined via the diffraction grating method.

Main Results:

• A significant enhancement in the quality factor (Q_a) of nearly 82% was achieved for an FBAR with the dual-step frame compared to a non-framed FBAR.
• The optimized FBAR exhibited a smoother electrical response.
• A moderate increase in spurious resonances was observed at frequencies between f_a and the resonant frequency (f_r).

Conclusions:

• The dual-step frame structure is an effective method for mitigating Lamb wave losses in FBARs.
• This design approach leads to substantial improvements in FBAR quality factor (Q_a) and electrical performance.
• The findings offer a pathway for designing higher-performance FBARs for various applications.