Acoustic Wave Resonator Polycrystalline Substrate Spurious Signal Reduction
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Solution Overview
Problem
Existing surface acoustic wave resonators face challenges in reducing spurious signals, particularly at frequencies higher than the passband, due to bulk waves, despite optimizing the thickness of the piezoelectric substrate to be equal to or less than the wavelength of the acoustic wave.
Innovation Solution
Incorporating a polycrystalline substrate with an average particle size equal to or less than 66 times the average pitch of the electrode fingers, and bonding it with a piezoelectric substrate using an amorphous layer to reduce thermal stress and improve temperature characteristics, while using comb-shaped electrodes to excite and confine acoustic waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the thickness of the piezoelectric substrate is reduced to equal to or less than the wavelength of the acoustic wave, then spurious signals are reduced, but the temperature characteristics deteriorate due to thermal stress
Solution Approach 1:
An amorphous layer is introduced as an intermediary between the piezoelectric substrate and the support substrate. This amorphous layer acts as a stress buffer that decouples the thermal stress transmission, allowing the piezoelectric substrate to be thin (reducing spurious signals) while the support substrate provides thermal stability without directly transmitting stress to the piezoelectric layer.
2Strength
If a monocrystalline support substrate is used, then mechanical strength is improved, but spurious signals increase due to bulk wave resonance
Solution Approach 1:
The crystal structure parameter of the support substrate is changed from monocrystalline to polycrystalline. This parameter change eliminates the bulk wave resonance that causes spurious signals, while the polycrystalline structure maintains sufficient mechanical strength for the device.
3Object-generated harmful factors
If the particle size of the polycrystalline substrate is reduced, then spurious signals are reduced, but manufacturing precision becomes more difficult to control
Solution Approach 1:
A specific parameter range for particle size is established (equal to or less than 66 times the average pitch of electrode fingers). This quantified parameter provides a clear manufacturing target that balances spurious signal reduction with manufacturability, transforming an abstract quality requirement into a measurable specification.
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 reduces spurious signals at frequencies higher than the passband and improves the temperature coefficient of the resonant frequency, enhancing the performance of acoustic wave resonators and filters.
Implementation Method 1
a piezoelectric substrate; a pair of comb-shaped electrodes that is located on the piezoelectric substrate and excites an acoustic wave
Implementation Method 2
a polycrystalline substrate that is located at an opposite side of the piezoelectric substrate from a surface on which the pair of comb-shaped electrodes is located, an average particle size of the polycrystalline substrate being equal to or less than 66 times an average pitch of the plurality of electrode fingers
Data Source
AI summary
An acoustic wave resonator includes: a piezoelectric substrate; a pair of comb-shaped electrodes that is located on the piezoelectric substrate and excites an acoustic wave, each of the pair of comb-shaped electrodes including a plurality of electrode fingers; and a polycrystalline substrate that is located at an opposite side of the piezoelectric substrate from a surface on which the pair of comb-shaped electrodes is located, an average particle size of the polycrystalline substrate being equal to or less than 66 times an average pitch of the plurality of electrode fingers.