Lithium Niobate Rayleigh Wave Electrode Stack for Sezawa Suppression
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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 provide adequate frequency stability when too thin.
Innovation Solution
The elastic wave device incorporates a piezoelectric substrate with a dielectric film of silicon oxide and an interdigital transducer electrode featuring multiple main electrode layers, where the first main electrode layer is made of a metal with a C112/C12 ratio greater than that of silicon oxide, with the sum of these layers' thicknesses being about 55% of the total electrode, to reduce Sezawa wave spurious responses and enhance frequency-temperature characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the silicon oxide film is made thick to improve frequency-temperature characteristics, then frequency stability is improved, but spurious response due to Sezawa wave increases
Solution Approach 1:
The interdigital transducer electrode is divided into multiple electrode layers (first electrode layer, second electrode layer, third electrode layer) with different materials and functions. The first electrode layer (Mo) suppresses Sezawa waves, the second electrode layer (Ag) reduces ohmic loss, and the third electrode layer (Al) provides adhesion, allowing each layer to address specific issues independently
Solution Approach 2:
The patent specifies precise thickness ratios for each electrode layer: the first electrode layer thickness is 40-70% of total electrode thickness, the second is 20-50%, and the third is 5-20%. These parameter optimizations enable simultaneous suppression of Sezawa waves and reduction of ohmic loss while maintaining good frequency-temperature characteristics
2Object-generated harmful factors
If the silicon oxide film is made thin to suppress spurious response due to Sezawa wave, then spurious response is reduced, but frequency-temperature characteristics deteriorate
Solution Approach 1:
The first electrode layer made of Mo serves as an intermediary between the piezoelectric substrate and the dielectric film, actively suppressing Sezawa waves before they can propagate. This mediator layer enables the use of thinner dielectric films without sacrificing frequency-temperature characteristics
3Loss of energy
If the interdigital transducer electrode uses thin metal layers to reduce ohmic loss, then electrical resistance is reduced, but the electrode becomes more susceptible to Sezawa wave spurious responses
Solution Approach 1:
The electrode uses a composite structure of three different metal layers: Mo (high density, C11/C12 ratio > SiO2) for Sezawa wave suppression, Ag (high conductivity) for low ohmic loss, and Al (good adhesion) for bonding. This composite structure achieves 40-70% Mo content to suppress Sezawa waves while maintaining low overall resistance through the Ag layer
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; and a dielectric film, provided on the piezoelectric substrate so as to cover the interdigital transducer electrode, and mainly including silicon oxide, the elastic wave device using a Rayleigh wave
Implementation Method 2
When the silicon oxide film has an excessively large thickness, the spurious response due to a Sezawa wave is large in some cases. When the silicon oxide film has a small thickness, frequency-temperature characteristics are poor.
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%.