Acoustic Wave Filter Dielectric Film for Moisture-Stable Frequency
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Solution Overview
Problem
Acoustic wave devices with a multilayer body, including a high-acoustic-velocity supporting substrate and a piezoelectric film, face instability in frequency due to moisture absorption by the dielectric film covering the IDT electrode, leading to variations in acoustic wave velocity and frequency.
Innovation Solution
An acoustic wave device with a high-acoustic-velocity material layer, a piezoelectric layer, and an IDT electrode, where the dielectric film is made of a material including hydrogen atoms, such as silicon oxide, to reduce moisture absorption and stabilize the frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric film is provided on the piezoelectric film to cover the IDT electrode, then the IDT electrode is protected, but the dielectric film absorbs moisture causing frequency variations
Solution Approach 1:
The patent changes the material parameters of the dielectric film by incorporating hydrogen atoms (e.g., using silicon oxide with hydrogen content). This parameter change reduces moisture absorption while maintaining the protective function, thus resolving the contradiction between electrode protection and frequency stability
Solution Approach 2:
The patent uses composite material structure by combining dielectric material with hydrogen-containing compounds (such as silicon oxide and hydrogen). This composite approach creates a dielectric film that provides both protection and moisture resistance, simultaneously achieving electrode protection and frequency stability
2Stability of the object's composition
If the dielectric film weight varies due to moisture absorption, then the acoustic velocity varies, but this causes frequency variations
Solution Approach 1:
The patent changes the compositional parameters of the dielectric film by adding hydrogen atoms, which reduces moisture absorption capability. This prevents weight variations in the dielectric film, thereby maintaining stable acoustic velocity and frequency
3Loss of energy
If energy of acoustic waves is concentrated on the piezoelectric film side, then the Q value is high, but frequency variations occur due to dielectric film moisture absorption
Solution Approach 1:
The patent modifies the dielectric film's material parameters by incorporating hydrogen, which reduces moisture absorption. This allows the acoustic wave device to maintain high Q value through energy concentration while preventing frequency variations caused by moisture-induced weight changes
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 prevents damage to the IDT electrode, increases the Q value, and significantly reduces frequency variations, even in humid environments, thereby enhancing the stability and filter characteristics of the acoustic wave device.
Implementation Method 1
the dielectric film absorbs moisture, which may cause the weight of the dielectric film to vary
Implementation Method 2
a piezoelectric layer provided directly or indirectly on the high-acoustic-velocity material layer, an interdigital transducer (IDT) electrode provided on the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a high-acoustic-velocity film, a piezoelectric layer provided directly or indirectly on the high-acoustic-velocity film, an IDT electrode provided on the piezoelectric layer, and a dielectric film provided on the piezoelectric layer to cover the IDT electrode. An acoustic velocity of bulk waves propagating through the high-acoustic-velocity film is higher than an acoustic velocity of acoustic waves propagating through the piezoelectric layer. The dielectric film includes a material including hydrogen atoms.