Acoustic Wave Element Protective Film for Humidity Stability
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Solution Overview
Problem
Existing protective films in acoustic wave devices, such as silicon nitride films with a stoichiometric ratio of Si3N4, deteriorate in function due to moisture absorption and oxidation, leading to corrosion of electrodes and changes in material constants, which affect the sonic speed and characteristics of the devices.
Innovation Solution
A silicon-rich silicon nitride film with a composition ratio of silicon to nitrogen (Si:N) less than 1.15 is used as a protective film, preventing oxidation and moisture permeation, thereby stabilizing the characteristics of the acoustic wave device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional silicon nitride film with stoichiometric ratio Si3N4 is used as a protective film, then the film provides basic protection against moisture, but the film absorbs moisture and undergoes oxidation, leading to deterioration of protective function and changes in material constants that affect sonic speed and device characteristics
Solution Approach 1:
The patent changes the compositional parameter of the silicon nitride film by controlling the Si:N ratio to be greater than 1.15 (silicon-rich composition), deviating from the conventional stoichiometric Si3N4 ratio. This parameter change reduces the film's tendency to absorb moisture and undergo oxidation, thereby maintaining stable material constants and sonic speed while providing reliable protection.
2Object-affected harmful factors
If a protective film is applied to prevent electrode corrosion, then electrode protection is improved, but the protective film itself undergoes oxidation and moisture absorption, causing changes in sonic speed and deterioration of device characteristics
Solution Approach 1:
By adjusting the Si:N composition ratio to greater than 1.15, the patent modifies the chemical composition parameter of the protective film. This creates a silicon-rich environment that is less susceptible to oxidation and moisture absorption, thereby preventing changes in sonic speed and maintaining stable device characteristics while still protecting the electrode from corrosion.
3Reliability
If a silicon nitride film with high nitrogen content (stoichiometric Si3N4) is used, then the film has good protective properties, but the film is more susceptible to oxidation and moisture absorption, leading to greater changes in material constants
Solution Approach 1:
The patent inverts the conventional approach by increasing the silicon content relative to nitrogen, setting the Si:N ratio greater than 1.15. This parameter change creates a silicon-rich film composition that exhibits reduced oxidation and moisture absorption compared to nitrogen-rich stoichiometric films, while maintaining adequate protective properties.
Solution Approach 2:
The patent employs a composite material approach by creating a silicon-rich silicon nitride film with non-stoichiometric composition. This composite structure, rich in silicon and controlled nitrogen content, combines the protective properties of silicon nitride with the oxidation resistance of excess silicon, reducing overall susceptibility to environmental degradation.
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 silicon-rich silicon nitride film effectively minimizes changes in frequency characteristics and standard deviation with humidity, ensuring stable performance and environmental load resistance, while being easier to form and maintain.
Implementation Method 1
preventing oxidation and moisture permeation
Implementation Method 2
moisture absorption of the protective films
Data Source
AI summary
An acoustic wave device includes an acoustic wave element including an IDT electrode provided on a substrate, and a protective film arranged to cover the acoustic wave element so as to stabilize characteristics. The protective film is a silicon nitride film composed of silicon and nitrogen as main components and when a composition ratio of the silicon to the nitrogen is represented by 1:X, X is about 1.15 or less.