SAW Filter Electrode Thickness Tuning for Spurious Emission
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Solution Overview
Problem
SAW elements with bonded substrates often experience spurious emission issues not present in solo piezoelectric substrates, which affect their electrical characteristics.
Innovation Solution
An acoustic wave device featuring a piezoelectric substrate bonded to a support substrate with filters of differing passbands and IDT electrode thicknesses to minimize spurious emission, where the thickness of the IDT electrodes in the first and second filters are differentiated to control bulk wave spurious emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a bonded substrate is used to compensate for temperature change, then temperature stability is improved, but spurious emission is generated
Solution Approach 1:
The patent applies local quality by making the IDT electrode thicknesses different in different regions (first IDT electrode vs second IDT electrode). This local variation in thickness creates different acoustic wave propagation characteristics that suppress spurious emissions while maintaining the temperature compensation benefit of the bonded substrate structure.
Solution Approach 2:
The patent changes the physical parameter of IDT electrode thickness to resolve the contradiction. By setting the first IDT electrode thickness to be different from the second IDT electrode thickness, the acoustic wave characteristics are modified to suppress spurious emissions generated by the bonded substrate, while the bonded substrate continues to provide temperature stability.
2Object-generated harmful factors
If IDT electrode thickness is differentiated to reduce spurious emission, then spurious emission is reduced, but device complexity increases
Solution Approach 1:
The patent implements local quality by varying the thickness of IDT electrodes at specific locations on the piezoelectric substrate. This targeted approach reduces spurious emissions without requiring complex modifications throughout the entire device structure, thereby limiting the increase in device complexity to only the necessary electrode thickness variations.
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 effectively reduces spurious emission in SAW devices by adjusting the thickness of IDT electrodes, allowing for improved frequency characteristics and temperature compensation, thereby enhancing the device's performance.
Implementation Method 1
a piezoelectric substrate including a first surface and a second surface
Implementation Method 2
a bonded substrate comprised of a piezoelectric substrate and a support substrate having a smaller thermal expansion coefficient compared with the piezoelectric substrate bonded to each other in a SAW element. By utilizing such a bonded substrate, for example, a temperature change of electrical characteristics of the SAW element is compensated for
Data Source
AI summary
An acoustic wave device 1 includes a piezoelectric substrate 2 including a first surface 2A and a second surface 2B, a support substrate 6 bonded to the second surface 2B of the piezoelectric substrate 2, and a first filter 10a and a second filter 10b a passband of which is higher than that of the first filter, both being on the first surface 2A of the piezoelectric substrate 2. The first filter 10a and the second filter 10b each includes an IDT electrode 3. A thickness of the IDT electrode 3 of the first filter 10a and a thickness of the IDT electrode 3 of second filter 10b are different.