BAW Resonator Double-Wall Cavity for Higher Crystal Quality
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Solution Overview
Problem
The quality and performance of bulk acoustic wave (BAW) resonators are limited by the poor crystal quality and piezoelectric performance of initially deposited piezoelectric layers, which are affected by lattice matching with electrode layers during fabrication.
Innovation Solution
A fabrication method involving a temporary substrate, buffer layers, and dielectric layers to form a double-wall boundary structure and cavity, allowing for the selection of suitable substrate materials and flexible deposition timing for electrodes and piezoelectric layers, enabling the removal of initially deposited, low-quality piezoelectric material to expose higher-quality layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If piezoelectric layer is deposited directly on electrode layers, then fabrication process is simple, but crystal quality and piezoelectric performance are poor due to lattice matching issues
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the substrate and piezoelectric layer. This buffer layer serves as a mediator that improves lattice matching and reduces dislocation density, thereby enhancing crystal quality without significantly complicating the fabrication process. The buffer layer acts as a transition zone that mitigates the harmful lattice mismatch effects.
Solution Approach 2:
The patent segments the piezoelectric layer into multiple sub-layers with different compositions or orientations. By dividing the piezoelectric layer into distinct segments, each layer can be optimized for specific functions, and the overall crystal quality is improved by reducing the cumulative effect of lattice mismatch across the entire structure.
2Productivity
If piezoelectric layer is deposited directly on electrode layers, then fabrication steps are reduced, but piezoelectric performance deteriorates
Solution Approach 1:
The patent performs preliminary actions by depositing the buffer layer and forming the double-wall boundary structure before depositing the piezoelectric layer. This preliminary preparation ensures that the substrate and intermediate layers are properly prepared to support high-quality piezoelectric material growth, thereby improving piezoelectric performance without adding excessive fabrication steps.
Solution Approach 2:
The patent introduces a vertical dimension by creating a double-wall boundary structure with multiple dielectric layers at different heights and positions. This three-dimensional structure allows for better control of stress distribution and lattice matching, improving piezoelectric performance while maintaining reasonable fabrication complexity.
3Ease of manufacture
If initial piezoelectric layer is retained, then fabrication process is complete, but quality factor Q is limited by low-quality deposited material
Solution Approach 1:
The patent extracts or removes the initially deposited low-quality piezoelectric material through the cavity formation process. By taking out the problematic initial layer and replacing it with a newly deposited high-quality piezoelectric layer, the quality factor Q is significantly improved while the fabrication process remains relatively straightforward.
Solution Approach 2:
The patent discards the low-quality initial piezoelectric material by forming a cavity that removes it, and then recovers performance by depositing a new high-quality piezoelectric layer in its place. This discarding and recovering approach eliminates the harmful effects of the initial poor-quality material while restoring and enhancing piezoelectric performance.
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 method improves the crystal quality and performance of the piezoelectric layer, enhancing the quality factor Q and filter performance of BAW resonators by removing the initially deposited, low-quality material after substrate bonding.
Implementation Method 1
A bulk acoustic wave (BAW) resonator is a device including a thin film that is made of a piezoelectric material and disposed between two electrodes
Data Source
AI summary
A bulk acoustic wave (BAW) resonator includes a substrate, a piezoelectric layer disposed above the substrate, a first electrode disposed below the piezoelectric layer, a second electrode disposed above the piezoelectric layer, a first dielectric layer, a second dielectric layer, and a third dielectric layer disposed between the substrate and the piezoelectric layer, and a bonding layer disposed between the third dielectric layer and the substrate. The first dielectric layer is disposed below the piezoelectric layer and includes a cavity. The third dielectric layer is disposed below the first dielectric layer and includes a protruding structure protruding towards the piezoelectric layer. The second dielectric layer overlays the third dielectric layer including the protruding structure, the second dielectric layer and the protruding structure of the third dielectric layer constituting a double-wall boundary structure surrounding the cavity.