Acoustic Resonator Air-Ring and Frame Structure for Energy Confinement
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Solution Overview
Problem
Conventional acoustic resonators face performance degradation due to lateral modes, which are not effectively suppressed by existing ancillary structural features, leading to energy scattering and increased costs without significant improvements in stability and efficiency.
Innovation Solution
The implementation of composite or add-on frames and air-rings around the acoustic resonator's main membrane region, which create acoustic impedance mismatches and cutoff frequency mismatches to suppress propagating eigenmodes and enhance energy confinement, thereby improving the resonator's Q-factor and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic resonators are used without additional structural features, then the device complexity is low, but lateral modes are not suppressed leading to energy scattering and performance degradation
Solution Approach 1:
The resonator structure is segmented into distinct functional regions by introducing frames and air-rings. The frame divides the resonator into an active region (inside the frame) and a frame region (between the frame and air-ring), with each region having different acoustic properties. This segmentation allows the active region to support desired piston modes while the frame region suppresses unwanted lateral modes through acoustic impedance mismatch.
Solution Approach 2:
The frame acts as an intermediary structure between the active region and the peripheral regions. It provides acoustic impedance mismatch that suppresses propagating eigenmodes while allowing the desired piston mode to continue in the active region. The frame mediates the transition between regions with different acoustic characteristics, preventing energy scattering into lateral modes.
2Loss of energy
If frames and air-rings are added to suppress lateral modes, then energy confinement is enhanced and Q-factor increases, but device complexity and manufacturing cost increase
Solution Approach 1:
Different regions of the resonator are given different acoustic properties through the selective placement of frames and air-rings. The active region maintains properties suitable for piston mode operation, while the frame region is designed with acoustic impedance mismatch to suppress lateral modes. This local differentiation of acoustic properties allows energy confinement in the active region without uniformly complicating the entire structure.
Solution Approach 2:
The acoustic impedance parameters are changed by introducing frames and air-rings with specific geometric and material properties. The frame's thickness, material composition, and positioning are optimized to create the desired acoustic impedance mismatch. By adjusting these parameters, the structure suppresses propagating eigenmodes while maintaining the desired resonant behavior in the active region.
3Reliability
If multiple frames are used (first frame below bottom electrode, second frame above piezoelectric layer), then suppression of propagating eigenmodes is improved, but manufacturing complexity increases
Solution Approach 1:
The acoustic impedance mismatch is achieved in multiple dimensions by placing frames at different locations: one frame below the bottom electrode and another frame above the piezoelectric layer. This multi-dimensional approach to impedance mismatch provides more comprehensive suppression of propagating eigenmodes throughout the resonator structure, addressing the limitation of single-frame designs.
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 lateral modes, enhances energy confinement, and increases the Q-factor and parallel resistance of the acoustic resonator, leading to improved performance and reduced energy loss.
Implementation Method 1
Where an input electrical signal is applied between the electrodes, reciprocal or inverse piezoelectric effect causes the acoustic stack to mechanically expand or contract depending on the polarization of the piezoelectric material. As the input electrical signal varies over time, expansion and contraction of the acoustic stack produces acoustic waves that propagate through the acoustic resonator in various directions and are converted into an output electrical signal by the piezoelectric effect.
Implementation Method 2
Some of the acoustic waves achieve resonance across the acoustic stack, with the resonant frequency being determined by factors such as the materials, dimensions, and operating conditions of the acoustic stack.
Implementation Method 3
The implementation of composite or add-on frames and air-rings around the acoustic resonator's main membrane region, which create acoustic impedance mismatches and cutoff frequency mismatches to suppress propagating eigenmodes and enhance energy confinement
Data Source
AI summary
An acoustic resonator device includes a bottom electrode disposed on a substrate over an air cavity, a piezoelectric layer disposed on the bottom electrode, and a top electrode disposed on the piezoelectric layer, where an overlap between the top electrode, the piezoelectric layer and the bottom electrode over the air cavity defines a main membrane region. The acoustic resonator device further includes at least one air-ring defining a boundary of the main membrane region, and at least one first frame formed between the bottom electrode and the piezoelectric layer or formed between the substrate and the bottom electrode, and a second frame formed between the piezoelectric layer and the top electrode.