BAW Resonator Bridge Structure for Lateral Mode Suppression
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Solution Overview
Problem
Piezoelectric-based Film Bulk Acoustic Resonators (FBARs) face challenges due to lateral modes, such as Rayleigh-Lamb modes, which degrade the quality factor (Q-factor) by losing energy at interfaces, hindering the miniaturization of electronic devices and affecting the performance of acoustic resonators.
Innovation Solution
The design of a Bulk Acoustic Wave (BAW) resonator with a cantilevered portion and a bridge structure over the acoustic reflector, which decouples lateral modes by creating a high impedance mismatch, reflecting and converting lateral modes into desired longitudinal modes, thereby enhancing the Q-factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If FBAR uses piezoelectric material to achieve small size and GHz frequency resonance, then component size is reduced, but lateral modes are generated that degrade Q-factor
Solution Approach 1:
The patent converts the harmful lateral modes into beneficial longitudinal modes by designing a reflective structure that causes lateral modes to reflect and transform into the desired thickness-extensional modes, thereby improving Q-factor while maintaining the compact FBAR design
Solution Approach 2:
The patent segments the acoustic stack into distinct functional regions including a reflective structure with specific layering (acoustic reflector, piezoelectric layer, electrode) to control wave propagation and prevent energy loss at interfaces
2Volume of moving object
If FBAR operates at GHz frequencies with micron-scale thickness, then miniaturization is achieved, but energy loss at interfaces increases
Solution Approach 1:
The reflective structure captures energy that would otherwise be lost at interfaces and converts it into useful longitudinal modes, turning the harmful interface loss mechanism into a beneficial energy recycling mechanism
Solution Approach 2:
The acoustic reflector is positioned and designed in advance to preemptively reflect lateral modes before they can escape or be lost at interfaces, preventing energy loss before it occurs
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly improves the Q-factor of the BAW resonator by reducing energy loss from lateral modes and increasing the energy in longitudinal modes, leading to better performance and miniaturization potential for electronic devices.
Implementation Method 1
a layer of piezoelectric material disposed between two electrodes. Acoustic waves achieve resonance across the acoustic stack
Implementation Method 2
The design of a Bulk Acoustic Wave (BAW) resonator with a cantilevered portion and a bridge structure over the acoustic reflector, which decouples lateral modes by creating a high impedance mismatch, reflecting and converting lateral modes into desired longitudinal modes
Implementation Method 3
Acoustic waves achieve resonance across the acoustic stack, with the resonant frequency of the waves being determined by the materials in the acoustic stack
Data Source
AI summary
A bulk acoustic wave (BAW) resonator includes: a substrate; an acoustic reflector disposed in the substrate; a first electrode disposed over the acoustic reflector; a second electrode; and a piezoelectric layer between the first and second electrodes. The second electrode is not disposed between the first electrode and the acoustic reflector. The BAW resonator further includes a block disposed over the substrate and beneath the piezoelectric layer. A contacting overlap of the acoustic reflector, the first electrode, the second electrode and the piezoelectric layer defines an active area of the BAW resonator.