BAW Sandwich Electrodes for Higher Resonant Frequency
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Solution Overview
Problem
Conventional bulk acoustic wave (BAW) devices face challenges in achieving higher resonant frequencies due to difficulties in manufacturing thinner electrode layers and piezoelectric layers, which increase electrical resistance and reduce power handling capability, while thinner layers also lead to poor heat conduction and lower breakdown voltages.
Innovation Solution
The introduction of sandwich electrodes, comprising an outer layer with higher acoustic impedance and an inner layer with lower acoustic impedance, disposed between the piezoelectric layer, allows for higher resonant frequencies without the need for thinning the piezoelectric and electrode layers, with the acoustic cavity length corresponding to half or one and a half times the resonant frequency wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the thickness of electrode layers and piezoelectric layer is reduced to achieve higher resonant frequencies, then the resonant frequency increases, but the electrical resistance increases and manufacturing difficulty increases
Solution Approach 1:
The electrode layer is segmented into multiple sub-layers (first electrode layer, second electrode layer, third electrode layer) with different thicknesses and materials. This segmentation allows each sub-layer to contribute differently to the overall electrical and acoustic properties, reducing total resistance while maintaining manufacturability of individual layers
Solution Approach 2:
The patent employs composite electrode structures combining different materials (e.g., tungsten, molybdenum, copper, aluminum) with different acoustic impedances. The first electrode layer uses high-acoustic-impedance materials, while subsequent layers use lower acoustic impedance materials, creating a composite structure that optimizes both electrical conductivity and acoustic wave propagation
2Speed
If the thickness of electrode layers and piezoelectric layer is reduced to achieve higher resonant frequencies, then the resonant frequency increases, but the power handling capability decreases
Solution Approach 1:
The electrode is divided into multiple segments (first, second, and third electrode layers) where the first layer provides acoustic isolation and the second and third layers provide electrical conductivity. This segmentation allows the device to handle higher power by distributing current across multiple conductive paths while maintaining the thin profile needed for high frequency operation
Solution Approach 2:
The first electrode layer acts as an intermediary between the piezoelectric layer and the second electrode layer. It provides acoustic isolation to prevent spurious modes while the second and third layers provide electrical conduction paths, enabling power handling capability without requiring thick individual layers
3Speed
If the thickness of electrode layers and piezoelectric layer is reduced to achieve higher resonant frequencies, then the resonant frequency increases, but the heat conduction capability decreases
Solution Approach 1:
The composite electrode structure uses materials with different thermal and acoustic properties. The first electrode layer uses high acoustic impedance materials for acoustic isolation, while subsequent layers use materials optimized for thermal conduction, creating a composite structure that simultaneously addresses heat dissipation and acoustic performance in thin layers
4Speed
If the thickness of electrode layers and piezoelectric layer is reduced to achieve higher resonant frequencies, then the resonant frequency increases, but the breakdown voltage decreases
Solution Approach 1:
The electrode structure is segmented into multiple layers with progressively lower acoustic impedances. This segmentation distributes the electrical stress across multiple interfaces and layers, preventing breakdown at any single point while maintaining the overall thin profile required for high resonant frequency operation
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 enables BAW devices to operate at higher frequencies with improved electrical properties and thermal conductivity, reducing manufacturing complexity and maintaining power handling capabilities.
Implementation Method 1
BAW devices receive an electrical signal that produces a varying (RF) electric field between two electrodes in a BAW device, causing the piezo layer positioned between the electrodes to expand and contract to produce acoustic waves having a resonant frequency
Implementation Method 2
A sandwich electrode includes an outer layer with a higher acoustic impedance and an inner layer with a lower acoustic impedance, with the inner layer disposed between the outer layer and the piezoelectric layer
Data Source
AI summary
A bulk acoustic wave (BAW) device comprises a piezoelectric layer disposed between a first electrode layer and a sandwich electrode. The sandwich electrode includes a first layer of a first material having a first acoustic impedance and a second layer of a second material having a second acoustic impedance that is less than the first acoustic impedance of the first layer. The second layer of the sandwich electrode having the lower acoustic impedance is disposed between the first layer and the piezoelectric layer. The sandwich electrode combined with the piezoelectric layer and first electrode can cause the BAW device to resonate at a frequency whose wavelength corresponds to an acoustic cavity length of the BAW device, depending on an acoustic mirror included on one side of the BAW device. In one example, the acoustic cavity length is about 1.5 times of the resonant frequency wavelength.