Elastic Wave Resonator Structure for Temperature Stability and Spur Control
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Solution Overview
Problem
Elastic wave devices with surface acoustic wave elements, commonly used in high-frequency communication systems, face challenges in maintaining good temperature characteristics and suppressing spurious responses, especially at the high-frequency end.
Innovation Solution
The proposed elastic wave device incorporates a supporting substrate with a high Young's modulus and low coefficient of linear expansion, along with a dielectric layer featuring alternating strip-shaped acoustic impedance regions. This configuration ensures that the total thickness of the insulating layer, piezoelectric layer, and dielectric layer is 1.0λ or less, where λ is the wavelength determined by the IDT electrode spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a supporting substrate with high Young's modulus and low coefficient of linear expansion is used to improve temperature characteristics, then temperature stability is improved, but spurious response increases at high frequency
Solution Approach 1:
The device is divided into functionally distinct layers: a supporting substrate for mechanical stability and temperature compensation, and a separate piezoelectric layer for acoustic wave generation. This segmentation allows each layer to be optimized for its specific function without compromising the other, resolving the contradiction between temperature stability and spurious response suppression.
Solution Approach 2:
Different regions of the device are assigned different material properties: the supporting substrate provides high mechanical strength and low thermal expansion, while the piezoelectric layer provides acoustic wave generation capability. This local differentiation of material qualities enables simultaneous achievement of temperature stability and spurious response reduction.
2Reliability
If the thickness of the piezoelectric layer is increased to improve acoustic wave generation, then acoustic coupling is improved, but spurious response is enhanced
Solution Approach 1:
The thickness of the piezoelectric layer is precisely controlled within the range of 0.05λ to 0.45λ, where λ is the acoustic wavelength. This parameter optimization ensures sufficient acoustic wave generation while suppressing spurious responses by avoiding thickness values that would resonate at unwanted frequencies.
Solution Approach 2:
Instead of using a thick piezoelectric layer that would guarantee strong acoustic coupling but cause spurious response, the invention uses a partially sufficient thickness (0.05λ to 0.45λ) that achieves the necessary acoustic coupling while avoiding the harmful effects of excessive thickness.
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 design effectively improves the temperature characteristics of the elastic wave device while significantly reducing spurious responses, leading to enhanced filtering performance.
Implementation Method 1
a piezoelectric layer formed on the insulating layer; a resonator including IDT electrodes formed on the piezoelectric layer
Implementation Method 2
elastic surface wave device using SH waves
Implementation Method 3
a piezoelectric layer that transmits elastic waves is bonded to a supporting substrate with a smaller coefficient of thermal expansion than the piezoelectric layer
Data Source
AI summary
The present application relates to an elastic wave device and a module using the elastic wave device. The elastic wave device comprises a supporting substrate; a dielectric layer formed on the supporting substrate; an insulating layer formed on the dielectric layer; a piezoelectric layer formed on the insulating layer; and a resonator including IDT electrodes formed on the piezoelectric layer. The dielectric layer includes a first strip-shaped acoustic impedance region with a long side direction and a short side direction; and a second strip-shaped acoustic impedance region arranged alternately with the first acoustic impedance region and having a different acoustic impedance from that of the first acoustic impedance region. The elastic wave device of this application provides good temperature characteristics and effectively suppresses spurious response.