FBAR Electrode Perforation Layout for Spurious Resonance Suppression
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Solution Overview
Problem
Film bulk acoustic resonators (FBARs) face performance issues due to spurious resonances and lateral wave propagation, which affect filter performance by causing impedance ripples and energy leakage.
Innovation Solution
The implementation of perforations and posts around the perimeter of the active region in the FBAR stack, including staggered and non-uniform perforation slots, and an annular air gap or trench, to reflect and impede lateral waves, thereby reducing spurious resonances and enhancing filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FBAR operates with longitudinal bulk acoustic waves, then fundamental resonance is achieved, but spurious resonances occur due to lateral wave reflections
Solution Approach 1:
The patent extracts and removes the harmful lateral wave components from the system by introducing perforations that selectively eliminate spurious resonances while preserving the fundamental longitudinal bulk acoustic wave resonance, thereby resolving the contradiction between achieving precise fundamental resonance and eliminating harmful spurious resonances
Solution Approach 2:
The patent applies local quality by creating non-uniform perforation patterns in specific regions of the FBAR structure. The perforations are strategically positioned and varied in density to locally suppress lateral wave reflections at edges while maintaining the overall resonance characteristics, thus addressing spurious resonances without compromising fundamental frequency precision
2Reliability
If perforations are added to suppress spurious waves, then filter performance improves, but device complexity increases
Solution Approach 1:
The patent segments the FBAR structure by introducing periodic perforations that divide the continuous piezoelectric layer into multiple sections. This segmentation approach suppresses spurious resonances through destructive interference of lateral waves while maintaining a relatively simple overall structure that can be manufactured using standard fabrication processes
Solution Approach 2:
The patent modifies structural parameters by varying the perforation size, spacing, and distribution patterns to optimize spurious resonance suppression. By adjusting these parameters, the patent achieves improved filter performance while controlling device complexity through systematic parameter optimization rather than complex structural design
3Object-generated harmful factors
If staggered and non-uniform perforation slots are implemented, then lateral wave propagation is impeded, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs asymmetric and non-uniform perforation patterns where perforation slots are intentionally placed at varying positions and orientations. This asymmetry effectively disrupts lateral wave propagation paths and suppresses spurious resonances while the patterns are designed to be manufacturable with standard precision capabilities through systematic design approaches
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 effectively suppresses spurious waves and impedes lateral wave propagation, leading to improved filter performance and reduced energy leakage, resulting in more precise frequency resonance and enhanced operational stability of the FBAR.
Implementation Method 1
When an electrical signal is applied to the top and bottom electrodes, the piezoelectric thin film layer converts the electrical energy of the signal into mechanical energy. An oscillating electrical signal applied to the piezoelectric thin film layer causes pressure and/or shear waves to propagate through the bulk of the FBAR stack.
Implementation Method 2
The bulk waves reflect from the free surfaces at the top and the bottom of the stack, yielding sharply defined fundamental resonant frequencies
Implementation Method 3
the arrangement of perforations, posts, and/or beams suppress resonance of spurious waves and/or impede propagation of lateral waves by, for example, reflecting lateral waves in the FBAR
Data Source
AI summary
Devices and processes for preparing devices are described for reducing resonance of spurious waves in a bulk acoustic resonator and/or for obstructing propagation of lateral waves out of an active region of the bulk acoustic resonator. A first electrode is coupled to a first side of a piezoelectric layer and a second electrode is coupled to a second side of the piezoelectric layer to form a stack having the active region. The piezoelectric layer in the active region is configured to resonate in response to an electrical signal applied between the first electrode and the second electrode. One or more perforations in the first electrode, the piezoelectric layer and/or the second electrode, and/or one or more posts or beams supporting the stack, reduce resonance of spurious waves and obstruct propagation of lateral acoustic waves out of the active region.