Bonded SAW Resonator Thickness Tuning for Bulk Wave Spurious
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Solution Overview
Problem
Surface acoustic wave (SAW) elements with piezoelectric substrates suffer from spurious signals due to bulk waves, which are not effectively suppressed by existing technologies, affecting their frequency stability and performance.
Innovation Solution
A SAW element design that includes a piezoelectric substrate with a support substrate bonded to its bottom surface and a first IDT electrode on the top surface, where the resonance frequency and anti-resonance frequency are maintained between the lowest and next lowest frequencies of bulk wave spurious signals, and the normalized thickness of the piezoelectric substrate is set between 1 and 3, to minimize bulk wave spurious generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a bonded substrate is used to compensate for temperature changes, then temperature stability is improved, but bulk wave spurious signals are generated
Solution Approach 1:
The patent changes the physical parameter of piezoelectric substrate thickness to a specific range (normalized thickness ts/2p of 1 to 3) to suppress bulk wave spurious signals while maintaining temperature compensation functionality through the bonded substrate structure
2Object-generated harmful factors
If the piezoelectric substrate thickness is increased to suppress spurious, then spurious suppression is improved, but manufacturing precision becomes more difficult
Solution Approach 1:
The patent identifies and specifies an optimal parameter range for piezoelectric substrate thickness (normalized thickness ts/2p of 1 to 3) that effectively suppresses bulk wave spurious signals. By defining this specific range, the patent balances spurious suppression performance with manufacturing feasibility, as the range is wide enough to accommodate normal thickness variations while still achieving the desired suppression effect
3Object-generated harmful factors
If the resonance frequency is positioned between bulk wave frequencies, then spurious reduction is improved, but device complexity increases
Solution Approach 1:
The patent establishes a specific frequency positioning strategy where the resonance frequency and anti-resonance frequency of the SAW resonator are placed between the lowest frequency and next lowest frequency of bulk wave spurious. This frequency arrangement, combined with the specified thickness range, creates a design framework that achieves spurious reduction through parameter optimization rather than complex structural modifications
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 significantly reduces bulk wave spurious signals within a specific frequency band, improving the SAW element's frequency stability and performance by broadening the frequency interval of spurious signals, thereby increasing the tolerance to thickness variations and enhancing temperature compensation.
Implementation Method 1
a piezoelectric substrate, a support substrate attached to a bottom surface of the piezoelectric substrate, and a first IDT electrode on a top surface of the piezoelectric substrate
Implementation Method 2
a bonded substrate formed by bonding together a piezoelectric substrate and a support substrate having a smaller thermal expansion coefficient compared with the piezoelectric substrate is used for the SAW element. By utilizing such a bonded substrate, for example, a change of electrical characteristics of the SAW element due to temperature is compensated for
Implementation Method 3
spurious is generated when using a bonded substrate and that the cause of that spurious is a bulk wave
Data Source
AI summary
A SAW element includes a piezoelectric substrate, a support substrate attached to a bottom surface of the piezoelectric substrate, and an IDT electrode on a top surface of the piezoelectric substrate. A resonance frequency and an anti-resonance frequency of a resonator including the IDT electrode are kept between a frequency of a lowest frequency bulk wave spurious and a frequency of a next lowest frequency bulk wave spurious.