Acoustic Wave Device with Differentiated Low-Velocity Films
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Solution Overview
Problem
Conventional acoustic wave devices face issues with spurious responses of higher-order modes, which affect their performance across a wide band.
Innovation Solution
The acoustic wave device incorporates a silicon substrate with specific layering of high- and low-acoustic-velocity films and a piezoelectric film, where the materials and thicknesses of the low-acoustic-velocity films differ, along with a carefully designed IDT electrode structure to reduce or prevent unwanted higher-order modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multilayer structure with high-acoustic-velocity films and low-acoustic-velocity films is used, then the Q value is increased, but spurious responses of higher-order modes occur
Solution Approach 1:
The patent applies local quality by using different materials for the first and second low-acoustic-velocity films (SiO2 and Si3N4 respectively) rather than uniform materials throughout. This localized differentiation in material properties at specific positions within the multilayer structure suppresses higher-order modes while preserving the high Q value characteristic of the multilayer configuration.
Solution Approach 2:
The patent employs composite materials by combining multiple film types with different acoustic velocity characteristics (high-acoustic-velocity films of SiN and low-acoustic-velocity films of SiO2 and Si3N4) in a multilayer structure. This composite approach enables simultaneous achievement of high Q value and suppression of spurious responses through the complementary properties of different materials.
2Reliability
If conventional multilayer structures are used, then device performance is improved, but unwanted waves of higher-order modes affect performance over wide band
Solution Approach 1:
The patent addresses wide-band performance by implementing local quality differentiation in the low-acoustic-velocity films. By positioning SiO2 and Si3N4 films at different locations within the multilayer structure, the device achieves suppression of higher-order modes across a broader frequency range, enhancing adaptability over wide band while maintaining overall device performance.
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 effectively suppresses higher-order modes and unwanted waves over a wide frequency range, improving the device's frequency-temperature characteristics and reducing the temperature coefficient of frequency.
Implementation Method 1
a piezoelectric film on the second high-acoustic-velocity film, and an IDT electrode on the piezoelectric film
Implementation Method 2
an acoustic velocity of a bulk wave propagating through the first high-acoustic-velocity film and an acoustic velocity of a bulk wave propagating through the second high-acoustic-velocity film are higher than an acoustic velocity of a bulk wave propagating through the piezoelectric film, an acoustic velocity of a bulk wave propagating through the first low-acoustic-velocity film and an acoustic velocity of a bulk wave propagating through the second low-acoustic-velocity film are lower than an acoustic velocity of a bulk wave propagating through the piezoelectric film
Data Source
AI summary
An acoustic wave device includes a silicon substrate, a first high-acoustic-velocity film on the silicon substrate, a first low-acoustic-velocity film on the first high-acoustic-velocity film, a second low-acoustic-velocity film on the first low-acoustic-velocity film, a second high-acoustic-velocity film on the second low-acoustic-velocity film, a piezoelectric film on the second high-acoustic-velocity film, and an IDT electrode on the piezoelectric film. Acoustic velocities of bulk waves propagating through the first and second high-acoustic-velocity films are higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric film. Acoustic velocities of bulk waves propagating through the first and second low-acoustic-velocity films are lower than an acoustic velocity of a bulk wave propagating through the piezoelectric film. Materials of the first and second low-acoustic-velocity films are different from each other.