Lamb Wave Resonator With Segmented Electrodes
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Solution Overview
Problem
Existing Lamb wave resonators suffer from low quality factor and high series resistance, and require specific treatment of the piezoelectric layer, limiting their effectiveness in RF filtering applications.
Innovation Solution
A Lamb wave resonator design featuring a piezoelectric layer with a first electrode comprising fingers and a contact arm, where the finger width is calculated based on the acoustic propagation speed and resonance frequency, and the piezoelectric layer is partially etched to create active and inactive zones, reducing series resistance and enhancing energy confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Lamb wave resonator uses a standard electrode design with uniform dimensions, then the structure is simple to manufacture, but the quality factor is low and series resistance is high
Solution Approach 1:
The electrode is segmented into multiple fingers with different widths rather than using a uniform structure. This segmentation allows different regions of the piezoelectric layer to have different acoustic propagation coefficients, creating active zones with high Lamb wave energy confinement and inactive zones for electrical connection, thereby improving quality factor while managing complexity
Solution Approach 2:
Different regions of the electrode are designed with locally optimized properties - the active zones have narrow fingers for high Q-factor, while inactive zones have wider fingers for low series resistance. This local differentiation resolves the contradiction by allowing each region to optimize for its specific function
2Reliability
If the piezoelectric layer is left untreated with uniform properties, then the manufacturing process is simpler, but parasitic resonances occur due to lateral wave propagation
Solution Approach 1:
The piezoelectric layer is selectively etched in active zones to create local variations in acoustic propagation coefficients. This local treatment differentiates active zones from inactive zones, preventing parasitic resonances while maintaining manufacturing feasibility through standard etching processes
3Loss of energy
If the electrode covers the entire piezoelectric layer surface, then the electrical connection is maximized, but Lamb wave energy is lost to inactive zones
Solution Approach 1:
The electrode is segmented into active and inactive zones, with active zones confined to specific regions where Lamb waves are generated and confined. This segmentation reduces energy loss in inactive zones while maintaining adequate electrical connection through the finger structure and contact arms
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 achieves a high quality factor, low series resistance, and efficient energy utilization, enabling low-power, low-noise voltage control oscillators and filters with high selectivity and rejection, without the need for specific layer treatment.
Implementation Method 1
A Lamb wave resonator according to the invention comprises at least one layer (102) based on at least one piezoelectric material
Implementation Method 2
The speed of propagation of the waves in the active zone 8 is different from that in the inactive zone 10. This difference in propagation speed results in parasitic resonances due to the propagation of lateral waves perpendicular to the vertical waves, called Lamb waves
Implementation Method 3
Each of the fingers (108) may comprise a first side in contact with the arm (110), and two other sides parallel to one another and spaced apart from one another by a distance W calculated according to the equation... n: order of the resonance mode of the Lamb waves, and f: resonance frequency of the resonator
Data Source
AI summary
A Lamb wave resonator includes a piezoelectric layer, and a first electrode against a first face of the piezoelectric layer. The first electrode includes fingers and a contact arm, with each finger including a first side in contact with the contact arm and two other sides parallel to one another. Portions of the piezoelectric layer are at least partially etched between the two fingers to form a recess. The fingers are spaced apart from one another by a distance W calculated according to the following equation:W=n·valateralf,withn∈Nwhere,valateral is an acoustic propagation speed of Lamb waves,n is an order of a resonance mode of the Lamb waves,f is a resonance frequency of the Lamb wave resonator.