Bulk Acoustic Resonator Layout for Spurious Mode Suppression
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Solution Overview
Problem
Conventional acoustic filters face challenges in improving communication quality due to limitations in frequency band usage and spurious resonance issues, particularly in high-frequency bands like N77 and N79, where current surface acoustic wave, film bulk acoustic resonators, and solidly mounted bulk acoustic resonators fail to meet the required electromechanical coupling coefficient and are restricted by severe spurious modes.
Innovation Solution
A bulk acoustic resonator design incorporating a piezoelectric material layer, an interdigital transducer, and a dielectric layer with fluctuating thicknesses between electrodes, which disrupts the periodicity of sound wave propagation to suppress high-order modes and enhance the electromechanical coupling coefficient, thereby reducing spurious resonance and improving filter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional surface acoustic wave, film bulk acoustic resonators, or solidly mounted bulk acoustic resonators are used, then the device can operate in high-frequency bands, but the electromechanical coupling coefficient is insufficient and spurious modes are severe
Solution Approach 1:
The patent changes the physical parameters of the resonator by using a bulk acoustic wave resonator structure with specific layer configurations (piezoelectric layer on substrate with acoustic reflector) to achieve higher electromechanical coupling coefficient and suppress spurious modes, transitioning from surface acoustic wave or film bulk acoustic resonator parameters to bulk acoustic wave parameters
Solution Approach 2:
The patent converts the harmful spurious modes into beneficial effects by carefully designing the acoustic reflector and piezoelectric layer thickness to suppress unwanted high-order modes while enhancing the fundamental mode, thereby improving filter selectivity and performance
2Productivity
If more frequency bands are used to increase communication speed, then communication performance improves, but acoustic filter performance faces greater challenges due to spurious resonance
Solution Approach 1:
The patent adjusts the physical parameters of the acoustic resonator including layer thicknesses, material compositions, and structural configurations to optimize performance across multiple frequency bands (N77, N79, etc.), enabling the filter to maintain high reliability in wideband operations
Solution Approach 2:
The patent employs composite material structures combining piezoelectric materials with specific acoustic impedance substrates and acoustic reflectors to achieve broad frequency band operation while maintaining high electromechanical coupling and suppressing spurious resonance across different communication bands
3Device complexity
If the dielectric layer thickness is uniform, then the structure is simple, but high-order modes are excited during sound wave propagation
Solution Approach 1:
The patent applies local quality variation by creating a dielectric layer with non-uniform thickness distribution, where the thickness changes locally to disrupt the periodicity of sound wave propagation and suppress high-order mode excitation, while maintaining overall structural simplicity
Solution Approach 2:
The patent introduces thickness variation in the dielectric layer as an additional dimensional parameter to control acoustic wave propagation, transforming the uniform two-dimensional layer into a three-dimensional structure with controlled thickness gradients to suppress spurious modes
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
The design effectively excites the main mode, reduces or avoids spurious resonance, and enhances the electromechanical coupling coefficient, meeting the bandwidth requirements of high-frequency bands like N77, thus improving the acoustic filter's performance and design flexibility.
Implementation Method 1
A bulk acoustic resonator includes a piezoelectric material layer, an interdigital transducer, and a dielectric layer. The interdigital transducer is disposed on the piezoelectric material layer.
Implementation Method 2
thicknesses of a part, of the dielectric layer, located between at least one pair of adjacent first electrode and second electrode fluctuate. The part, of the dielectric layer, whose thicknesses fluctuate is used to suppress excitation of a high-order mode during sound wave propagation.
Data Source
AI summary
Embodiments of this application provide a bulk acoustic resonator, an acoustic filter, and an electronic device, to improve performance of the acoustic filter. The bulk acoustic resonator includes a piezoelectric material layer, an interdigital transducer, and a dielectric layer. The interdigital transducer is disposed on the piezoelectric material layer. The interdigital transducer includes a first busbar and a second busbar that are disposed opposite to each other, a plurality of first electrodes, and a plurality of second electrodes. The plurality of first electrodes sequentially protrude from the first busbar to the second busbar along an extension direction of the first busbar. The plurality of second electrodes sequentially protrude from the second busbar to the first busbar along an extension direction of the second busbar. The plurality of first electrodes and the plurality of second electrodes are sequentially arranged in a staggered manner between the first busbar and the second busbar.