Composite SAW Substrate Interface Structure for Stable Filter Characteristics
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Surface acoustic wave filters using composite substrates face issues with the intervening layer swelling over time, leading to changes in filter characteristics and the occurrence of spurious noise due to reflection and elastic wave trapping at the bonding interface between the piezoelectric crystal film and the supporting substrate.
Innovation Solution
A composite substrate configuration with a piezoelectric single crystal substrate and a supporting substrate, featuring an intervening layer with low chemisorbed water content and an uneven structure at the bonding interface, where the acoustic velocity of the slow transversal wave in the intervening layer is faster than that of the piezoelectric substrate, and the thickness of the intervening layer is optimized to reduce spurious noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an intervening layer is added between the piezoelectric substrate and supporting substrate to improve bonding, then bonding strength is improved, but the intervening layer swells over time causing filter characteristic changes
Solution Approach 1:
The patent uses an intervening layer as a mediator between the piezoelectric substrate and supporting substrate. This layer is specifically designed with low chemisorbed water content (1×10^20 molecules/cm³ or less) to prevent swelling while maintaining bonding functionality. The intervening layer acts as a buffer that improves bonding strength without causing the characteristic changes that would result from excessive water absorption.
Solution Approach 2:
The patent controls the chemisorbed water content parameter of the intervening layer to be 1×10^20 molecules/cm³ or less. This parameter control prevents the swelling that would otherwise occur over time, thereby maintaining filter characteristic stability while still providing the bonding enhancement benefits of an intervening layer.
2Manufacturing precision
If the bonding interface is made smooth to improve manufacturing, then manufacturing precision is improved, but elastic waves are trapped causing spurious noise
Solution Approach 1:
The patent introduces an uneven structure with curved surfaces at the bonding interface instead of a perfectly smooth planar interface. This curvature/unevenness prevents elastic wave trapping by disrupting the wave propagation paths, thereby reducing spurious noise while remaining compatible with manufacturing processes.
Solution Approach 2:
The patent applies local quality by creating an uneven structure specifically at the bonding interface region rather than throughout the entire substrate. This localized modification addresses the spurious noise problem at the critical bonding interface without affecting other areas of the device, and maintains manufacturing feasibility by limiting the complexity to a specific region.
3Volume of moving object
If the piezoelectric substrate is thinned to improve device miniaturization, then device size is reduced, but temperature stability deteriorates due to high thermal expansion coefficient
Solution Approach 1:
The patent creates a composite substrate structure combining the piezoelectric single crystal substrate with a supporting substrate and an intervening layer. This composite structure allows the piezoelectric layer to be thin (enabling miniaturization) while the supporting substrate provides thermal stability. The combination leverages the complementary properties of different materials to achieve both size reduction and temperature stability.
Solution Approach 2:
The supporting substrate acts as a counterweight to the high thermal expansion coefficient of the thin piezoelectric substrate. By bonding the piezoelectric layer to the supporting substrate with appropriate thermal properties, the overall composite structure achieves frequency stability despite the thin piezoelectric layer that enables miniaturization.
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 solution effectively stabilizes the filter characteristics over time, reduces spurious noise, and improves frequency stability by preventing elastic wave trapping and reflection, thereby enhancing the reliability and performance of the surface acoustic wave device.
Implementation Method 1
the amount of chemisorbed water in the intervening layer is 1×10^20 molecules/cm³ or less
Implementation Method 2
spurious noise occurs due to reflection at the bonding interface between the piezoelectric crystal film and the supporting substrate, and trapping of elastic waves in the intervening layer
Implementation Method 3
a piezoelectric single crystal substrate and a supporting substrate
Implementation Method 4
Piezoelectric materials such as lithium tantalate (LT) and lithium niobate (LN) are widely used as materials for surface acoustic wave (SAW) devices
Data Source
AI summary
Manufacturing methods for a composite substrate for surface acoustic wave devices with improved characteristics is provided. The composite substrate for a surface acoustic wave device is configured to include a piezoelectric single crystal substrate and a supporting substrate. An intervening layer is provided between the piezoelectric single crystal substrate and the supporting substrate, the amount of chemisorbed water in the intervening layer is 1×1020 molecules/cm3 or less. At the bonding interface between the piezoelectric single crystal substrate and the supporting substrate, at least one of the piezoelectric single crystal substrate and the supporting substrate may have an uneven structure. It is preferable that the ratio of the average length RSm of the element in the sectional curve of the uneven structure and the wavelength λ of the surface acoustic wave when used as a surface acoustic wave device is 0.2 or more and 7.0 or less.