Multi-Layer SAW Substrate for Heat Dissipation and Frequency Stability
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Solution Overview
Problem
Surface acoustic wave devices experience self-heating due to the thermal conductivity mismatch between quartz and lithium tantalate piezoelectric layers, leading to high surface temperatures and potential degradation of electrical performance.
Innovation Solution
Incorporating a thermally conductive layer between the quartz substrate and lithium tantalate piezoelectric layer, with a thermal conductivity at least 10 times higher than the piezoelectric layer, to dissipate heat effectively, and optionally adding a temperature compensating layer to stabilize frequency coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a quartz substrate is used as the support substrate, then the acoustic wave device can be manufactured with standard materials and processes, but the thermal conductivity is insufficient leading to heat accumulation and high surface temperatures
Solution Approach 1:
The patent applies composite materials by creating a multi-layer structure combining quartz substrate, buffer layer, and lithium tantalate piezoelectric layer. This composite structure leverages the manufacturing advantages of quartz while incorporating high thermal conductivity materials to dissipate heat effectively, resolving the contradiction between ease of manufacture and temperature control.
Solution Approach 2:
The patent introduces a buffer layer as an intermediary between the quartz substrate and lithium tantalate piezoelectric layer. This buffer layer serves as a thermal conduit to improve heat dissipation from the piezoelectric layer to the substrate, while also providing a transition zone that maintains manufacturing feasibility with standard materials and processes.
2Temperature
If the thermally conductive layer thickness is increased, then heat dissipation performance improves, but the acoustic wave performance deteriorates due to interference with the acoustic wave
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness of the thermally conductive layer and piezoelectric layer within specific ranges (thermally conductive layer: 10nm to 0.03λ, piezoelectric layer: 0.05λ to 0.2λ). These parameter optimizations ensure sufficient heat dissipation while maintaining acoustic wave performance by preventing excessive thermal conductivity layer thickness from interfering with acoustic wave propagation.
3Reliability
If a temperature compensating layer is added, then frequency stability is improved, but the device complexity increases
Solution Approach 1:
The patent applies parameter changes by selecting specific materials with appropriate thermal expansion coefficients and elastic properties for the temperature compensating layer. By carefully choosing material parameters and layer thickness, the patent achieves frequency stability compensation without excessive complexity, as the compensating layer integrates seamlessly into the existing multi-layer structure.
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
Reduces surface temperatures to below 60°C, maintains electrical performance, and stabilizes frequency coefficients, enhancing the durability and reliability of the acoustic wave devices.
Implementation Method 1
a thermally conductive layer configured to dissipate heat associated with the acoustic wave device. The thermally conductive layer has a higher thermal conductivity than the support substrate
Implementation Method 2
Each resonator can include a surface acoustic wave device. A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer
Implementation Method 3
The acoustic wave device can further include a temperature compensating layer having a positive temperature coefficient of frequency
Data Source
AI summary
Aspects of this disclosure relate to a filter that includes an acoustic wave device with a multi-layer substrate with heat dissipation. The multi-layer substrate includes a support substrate (e.g., a quartz substrate), a piezoelectric layer, an interdigital transducer electrode on the piezoelectric layer, and a thermally conductive layer configured to dissipate heat associated with the acoustic wave device. The thermally conductive layer is disposed between the support substrate and the piezoelectric layer. The thermally conductive layer has a thickness that is greater than 10 nanometers and less than a thickness of the piezoelectric layer.