Acoustic Wave Filter Dielectric Layers for Balanced Temperature Coefficients
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Solution Overview
Problem
Existing acoustic wave devices face challenges in simultaneously improving temperature characteristics at resonance and anti-resonance frequencies, leading to significant differences in temperature coefficients.
Innovation Solution
The implementation of a piezoelectric substrate with a first dielectric film, such as silicon oxide, and a second dielectric film, like silicon oxide or aluminum oxide, which is thicker than the electrodes, to reduce the temperature coefficient difference between resonance and anti-resonance frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single dielectric film structure is used to improve temperature characteristics, then the temperature coefficient at one frequency can be improved, but the temperature characteristics at resonance and anti-resonance frequencies cannot be simultaneously improved
Solution Approach 1:
The patent divides the dielectric film into two separate layers: a first dielectric film (SiO2) directly on the piezoelectric substrate and a second dielectric film (Al2O3) covering the electrodes. Each layer has different thickness and material properties, allowing independent optimization for resonance and anti-resonance frequency temperature characteristics. This segmentation enables simultaneous improvement of temperature stability across both frequency bands.
Solution Approach 2:
The patent uses a composite dielectric structure combining two different materials: silicon oxide (SiO2) for the first dielectric film and aluminum oxide (Al2O3) for the second dielectric film. These materials have different temperature coefficients and acoustic properties, allowing the composite structure to achieve balanced temperature compensation across resonance and anti-resonance frequencies that a single material cannot provide.
2Reliability
If foreign particles are present at the interface between media, then frequency variation increases and electrical loss increases
Solution Approach 1:
The first dielectric film (SiO2) acts as an intermediary layer between the piezoelectric substrate and the second dielectric film (Al2O3), creating a clean, controlled interface that prevents foreign particle contamination. This intermediary layer eliminates direct contact between potentially contaminating materials and maintains acoustic wave propagation quality, preventing frequency variation and electrical loss increase.
3Ease of manufacture
If the second dielectric film is made thinner to reduce device complexity, then manufacturing is easier, but etching resistance decreases
Solution Approach 1:
The patent uses aluminum oxide (Al2O3) for the second dielectric film, which has superior etching resistance compared to other dielectric materials. This allows the film to be made thinner for device simplification while maintaining adequate etching resistance. The composite material structure with Al2O3 provides the necessary mechanical and chemical strength even at reduced thickness.
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 configuration allows for improved temperature characteristics across both the low- and high-frequency sides of the pass band, reducing frequency variation and maintaining low electrical loss.
Implementation Method 1
A SAW (Surface Acoustic Wave) device is well known in which comb-like electrodes formed by an IDT (InterDigital Transducer) and reflection electrodes are formed in a surface of a piezoelectric substrate. An acoustic wave is excited by the comb-like electrodes and is propagated on the surface of the piezoelectric substrate.
Implementation Method 2
Another acoustic wave device (hereinafter referred to as second prior art) has been developed. As shown in FIG. 2, the second prior art is based on the first prior art and is configured by forming an aluminum oxide (Al2O3) film 20 on the silicon oxide film 18. Energy of acoustic wave is confined between the piezoelectric substrate 12 and the silicon oxide film 18 and is propagated through the interface therebetween.
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate, a first dielectric film provided on the piezoelectric substrate, electrodes that are provided on the first dielectric film and excite an acoustic wave, and a second dielectric film that is provided so as to cover the electrodes and is thicker than the electrodes.