Multi-Layer SAW Filter Bonding Without Q Value Deterioration
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Solution Overview
Problem
Existing surface acoustic wave filters face challenges in achieving high Q values due to the introduction of parasitic conductance and structural deterioration caused by bonding layers, which complicates the fabrication process and affects the filter's performance.
Innovation Solution
A surface acoustic wave filter is designed with a multi-layer structure where the high acoustic velocity layer serves as a bonding surface, eliminating the need for an intervening bonding layer, and using techniques like CMP or ion milling to planarize the surfaces, thereby simplifying the process and preventing Q value deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a bonding layer is introduced to bond substrates, then bonding strength is improved, but Q value deteriorates due to parasitic conductance
Solution Approach 1:
The patent removes the bonding layer from the substrate structure entirely. Instead of using a bonding layer to join substrates, the invention directly bonds the piezoelectric substrate to the support substrate through a low acoustic velocity layer, eliminating the source of parasitic conductance that degrades Q value while maintaining bonding strength through the optimized multi-layer structure.
Solution Approach 2:
The patent introduces a low acoustic velocity layer as an intermediary between the piezoelectric substrate and support substrate. This layer serves as the bonding interface, replacing the traditional bonding layer while providing acoustic impedance matching that prevents parasitic conductance and maintains high Q value performance.
2Manufacturing precision
If CMP process is performed on bonding surfaces, then bonding quality is improved, but manufacturing complexity increases
Solution Approach 1:
The patent performs CMP processing on the bonding surfaces of the piezoelectric substrate and support substrate before assembly, ensuring that the surfaces are pre-planarized to achieve optimal bonding quality. This preliminary action eliminates the need for additional CMP steps on the low acoustic velocity layer after bonding, reducing overall manufacturing complexity.
3Reliability
If multiple deposition processes are used to form high and low acoustic velocity layers, then acoustic performance is improved, but manufacturing time increases
Solution Approach 1:
The patent combines the formation of the low acoustic velocity layer and the bonding interface preparation into a single integrated process step. The low acoustic velocity layer is deposited and simultaneously serves as the bonding interface, eliminating the need for separate deposition and planarization steps while maintaining the required acoustic performance characteristics.
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 results in a surface acoustic wave filter with improved Q value stability and reduced scattering, as there is no parasitic conductance from metal-based bonding layers, and the process is simplified by eliminating the need for additional planarization steps.
Implementation Method 1
a bonding structure having a support substrate and a high acoustic velocity layer, in which a bonding layer is not interposed
Implementation Method 2
using techniques like CMP or ion milling to planarize the surfaces
Data Source
AI summary
A surface acoustic wave filter formed on a substrate with a multi-layer substrate and a method of fabricating the same are provided. The surface acoustic wave filter may include a support substrate; a high acoustic velocity layer formed on the support substrate; a low acoustic velocity layer formed on the high acoustic velocity layer; a piezoelectric layer formed on the low acoustic velocity layer; and a plurality of interdigital (IDT) electrodes formed on the piezoelectric layer, wherein the high acoustic velocity layer includes a first surface in contact with the support substrate and a second surface in contact with the low acoustic velocity layer, the low acoustic velocity layer includes a first surface in contact with the high acoustic velocity layer and a second surface in contact with the piezoelectric layer, and at least either one of the first and second surfaces of the high acoustic velocity layer, and the first and second surfaces of the low acoustic velocity layer is configured as a bonding surface.