Acoustic Wave Device Shared Cavity Design for Size Reduction
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Solution Overview
Problem
The manufacturing process of cavity type Film Bulk Acoustic Resonators (FBARs) is hindered by the need for a dead space on the surface for etchant inlet and flow channels, which limits size reduction in ladder type filters composed of multiple FBARs.
Innovation Solution
The solution involves forming a shared cavity space between multiple piezoelectric thin-film resonators, where a through-hole is created outside the membrane region to remove a sacrifice layer, allowing for a more compact design and reducing the number of dead spaces, thereby enabling closer packing and easier downsizing of the acoustic wave device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a through-hole is formed on the surface of the substrate for etchant inlet in cavity type FBAR manufacturing, then the sacrifice layer can be removed to form a cavity, but a dead space is created that prevents size reduction
Solution Approach 1:
The invention moves the etchant inlet from the surface plane to the rear side of the substrate, utilizing the third dimension (depth/thickness) to resolve the contradiction. By forming the through-hole from the rear surface rather than the front surface, the cavity can be formed without occupying valuable surface area, thus enabling device size reduction while maintaining manufacturability.
Solution Approach 2:
Instead of forming the etchant inlet from the conventional front surface side, the invention inverts the approach by forming the inlet from the rear side of the substrate. This inversion allows the etchant flow path to be positioned outside the active device area, eliminating the dead space problem while preserving the cavity formation capability.
2Manufacturing precision
If multiple through-holes are formed for etchant inlet in each resonator, then each cavity can be formed independently, but the number of dead spaces increases reducing productivity
Solution Approach 1:
The invention merges the etchant inlet function into a single shared through-hole on the rear side that serves multiple resonators simultaneously. Instead of forming separate through-holes for each resonator, one common inlet allows etchant to flow and remove sacrifice layers across multiple cavities, thereby reducing the total number of through-holes and eliminating associated dead spaces while maintaining precise cavity formation.
Solution Approach 2:
The single rear-side through-hole is designed to serve multiple functions: it acts as the etchant inlet for multiple different resonators and cavities simultaneously. This multi-functional design eliminates the need for dedicated inlets for each resonator, reducing the overall number of through-holes and improving manufacturing efficiency without sacrificing precision.
3Ease of manufacture
If the cavity is formed on the front surface side, then the manufacturing process is simpler, but the dead space on the surface prevents downsizing of ladder type filters
Solution Approach 1:
The invention relocates the etchant inlet from the front surface (2D plane) to the rear side (3D depth), allowing the cavity formation process to remain simple while eliminating surface dead space. This dimensional shift enables the etchant flow path to be positioned in the thickness direction rather than occupying lateral surface area, thus enabling device downsizing.
Solution Approach 2:
Instead of forming the cavity inlet from the front surface side as in conventional methods, the invention inverts the approach by forming it from the rear side. This inversion maintains process simplicity while eliminating the dead space that would otherwise prevent downsizing of ladder type filters.
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 approach stabilizes the resonator characteristics, reduces the size of the acoustic wave device, and increases productivity by minimizing dead spaces and the number of through-holes, leading to improved yield and cost-effectiveness.
Implementation Method 1
a piezoelectric film provided on the lower electrode
Implementation Method 2
the sacrifice layer is removed by executing etching through the through-hole
Data Source
AI summary
An acoustic wave device includes a substrate and a plurality of piezoelectric thin film resonators formed over the substrate. Each of the plurality of the piezoelectric thin film resonators includes lower electrode provided on the substrate, a piezoelectric film provided on the lower electrode, and an upper electrode provided on the piezoelectric film and opposed to the lower electrode through the piezoelectric film. Each of the piezoelectric thin film resonators is partly supported by the substrate and extends above the substrate to form a cavity between the substrate and each lower electrodes. The cavity continuously extending under the plurality of the piezoelectric thin film resonators.