Multilayer IDT Structure for Sezawa-Spurious Rayleigh Wave Filters
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Solution Overview
Problem
Elastic wave devices using lithium niobate substrates face challenges in reducing spurious responses due to Sezawa waves and improving frequency-temperature characteristics, as silicon oxide films either exacerbate spurious responses when too thick or fail to reduce temperature coefficient of frequency when too thin.
Innovation Solution
Incorporating an interdigital transducer electrode with multiple main electrode layers, where at least one layer is made of a metal with a C112/C12 ratio greater than silicon oxide, and the sum of these layers' thickness is 55% or more of the total electrode thickness, covered by a silicon oxide dielectric film, to reduce Sezawa wave spurious responses and enhance frequency-temperature characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the silicon oxide film has a large thickness, then frequency-temperature characteristics are improved, but spurious response due to Sezawa wave increases
Solution Approach 1:
The interdigital transducer electrode is divided into multiple main electrode layers with different metal materials having different C112/C12 ratios. This segmentation allows each layer to contribute differently to wave suppression, enabling the thick silicon oxide film to improve frequency-temperature characteristics while the specific electrode structure suppresses Sezawa wave spurious responses.
Solution Approach 2:
The invention changes the elastic constant ratio parameter (C112/C12) by selecting specific metal materials for the electrode layers. Metals with C112/C12 ratios greater than silicon oxide are used to alter the acoustic impedance and suppress Sezawa wave propagation, thereby resolving the contradiction between film thickness benefits and spurious response suppression.
2Object-generated harmful factors
If the silicon oxide film has a small thickness, then spurious response due to Sezawa wave is reduced, but frequency-temperature characteristics deteriorate
Solution Approach 1:
The interdigital transducer electrode uses composite metal layer structures combining different materials (e.g., Mo, W, Cu, Pt, Ta, Al, Ag, Au) with specific C112/C12 ratios. This composite structure enables effective Sezawa wave suppression even with thinner silicon oxide films, while maintaining good frequency-temperature characteristics through the combined properties of the metal layers.
3Device complexity
If the interdigital transducer electrode uses thin metal layers, then device complexity is reduced, but ohmic loss increases
Solution Approach 1:
Different metal layers in the interdigital transducer electrode are assigned different local qualities based on their C112/C12 ratios and electrical properties. High-conductivity metals are used in specific layers to minimize ohmic loss, while other layers focus on acoustic wave suppression, optimizing both electrical performance and wave control without excessive complexity.
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 responses and improves frequency-temperature characteristics while minimizing ohmic loss in the interdigital transducer electrode.
Implementation Method 1
an elastic wave device includes a piezoelectric substrate mainly including lithium niobate; an interdigital transducer electrode provided on the piezoelectric substrate
Implementation Method 2
a dielectric film, provided on the piezoelectric substrate so as to cover the interdigital transducer electrode, and mainly including silicon oxide
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate mainly including lithium niobate, an interdigital transducer electrode provided on the piezoelectric substrate, and a dielectric film, provided on the piezoelectric substrate and covering the interdigital transducer electrode, and mainly including silicon oxide. The elastic wave device uses a Rayleigh wave. The interdigital transducer electrode includes main electrode layers that include one or more first main electrode layer made of a metal with a C112/C12 ratio greater than the C112/C12 ratio of the silicon oxide with regard to the elastic constants C11 and C12. The sum of the thicknesses of the one or more first main electrode layers is about 55% or more based on the thickness of the whole interdigital transducer electrode is about 100%.