Elastic Wave Element Silicon Nitride Oxide Film Stability
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Solution Overview
Problem
Elastic wave elements with silicon oxide films formed by sputtering methods exhibit significant changes in propagation characteristics due to temperature fluctuations and environmental factors, leading to frequency drift and reduced reliability, especially at high frequencies.
Innovation Solution
Incorporating a silicon nitride oxide film on top of the silicon oxide film, with a thickness ratio of silicon oxide film to wave length greater than or equal to 0.15, to prevent argon discharge and maintain physical characteristics, thereby stabilizing the elastic wave propagation and improving humidity resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a silicon oxide film is formed by the sputtering method to reduce propagation loss for high frequency elastic waves, then propagation loss is reduced, but the propagation characteristic changes due to environmental factors such as temperature change
Solution Approach 1:
The patent uses a composite structure consisting of a silicon oxide film and a silicon nitride oxide film. The silicon oxide film (formed by sputtering) provides low propagation loss for high frequency elastic waves, while the silicon nitride oxide film (formed by CVD) with thermal expansion coefficient similar to the piezoelectric substrate compensates for thermal expansion effects. This composite material approach resolves the contradiction between reducing propagation loss and maintaining propagation characteristic stability under temperature changes.
2Ease of manufacture
If a silicon oxide film is formed by the CVD method to simplify manufacturing, then manufacturing is easier, but propagation loss increases for high frequency elastic waves
Solution Approach 1:
The patent divides the protective film into two separate layers: a silicon oxide film formed by sputtering (optimized for low propagation loss) and a silicon nitride oxide film formed by CVD (optimized for thermal expansion compensation and manufacturing ease). This segmentation allows each layer to be optimized for its specific function, resolving the contradiction between manufacturing ease and propagation loss.
3Stability of the object's composition
If the silicon oxide film thickness is increased to improve thermal expansion compensation, then thermal expansion compensation improves, but propagation loss increases
Solution Approach 1:
The patent uses a composite structure where the silicon nitride oxide film (with thermal expansion coefficient matching the piezoelectric substrate) provides the thermal expansion compensation function, while the silicon oxide film provides the low propagation loss characteristic. This allows thermal expansion compensation without increasing propagation loss, as the compensation function is transferred to the silicon nitride oxide film layer.
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 significantly reduces frequency drift and insertion loss, enhances reliability, and allows for less expensive and more productive manufacturing of high-frequency elastic wave devices.
Implementation Method 1
the silicon oxide film has a smaller thermal expansion coefficient than the piezoelectric substrate, accordingly reducing a thermal expansion of the piezoelectric substrate due to a change of temperature
Implementation Method 2
The silicon oxide film of the elastic wave element allowing such a high frequency elastic wave to propagate is manufactured by the sputtering method
Implementation Method 3
The silicon oxide film is formed on the interdigital electrode by a chemical vapor disposition (CVD) method or by a sputtering method. The silicon oxide film formed by the CVD method has a low density
Data Source
AI summary
An elastic wave element includes a piezoelectric substrate, an interdigital electrode provided on the piezoelectric substrate, a silicon oxide film covering the interdigital electrode, and a silicon nitride oxide film provided on the silicon oxide film. A film thickness H of the silicon oxide film and a wave length λ of an elastic wave propagating through the piezoelectric substrate satisfies a relation of H/λ≧0.15. The elastic wave element reduces fluctuation of propagation characteristics of elastic waves, and has high reliability.