SAW Electrode Structure Using Ti Buffer for Power Durability
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Solution Overview
Problem
Existing surface acoustic wave devices face challenges in achieving high power durability and low insertion loss due to stress-migration issues, particularly in RF band applications, where current electrode materials and methods like impurity addition, micro-grain size, multi-layering, segregation, high texture development, and single crystal growth face limitations in reproducibility and manufacturing complexity.
Innovation Solution
A pseudo-single crystal aluminum electrode film is developed using a titanium buffer layer on lithium tantalate or lithium niobate substrates, where the aluminum film consists of two (111) domains tilting within 0 to 10 degrees to the substrate surface, formed through a process that omits wet etching preprocessing, allowing for easy manufacturing and high reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impurity addition method is used to enhance electrode rigidity, then power durability is improved, but insertion loss increases due to increased resistivity
Solution Approach 1:
The invention uses a composite electrode structure consisting of a titanium buffer layer and an aluminum electrode layer. The titanium buffer layer (5-50 nm thick) provides structural support and promotes crystal growth, while the aluminum layer maintains low resistivity. This composite structure achieves both high power durability through the titanium layer's rigidity and low insertion loss through the aluminum layer's electrical conductivity, avoiding the need to add impurities to aluminum which would increase resistivity.
2Reliability
If micro-grain size method is used to enhance electrode rigidity, then power durability is improved, but insertion loss increases due to increased electrode resistance
Solution Approach 1:
The titanium buffer layer promotes the formation of a pseudo-single crystal structure in the aluminum electrode layer with controlled grain orientation ((111) texture). This structured approach provides rigidity through crystallographic orientation rather than grain size reduction, maintaining low resistivity while achieving high power durability.
3Reliability
If multi-layering method is used to enhance electrode film rigidity, then power durability is improved, but electrode resistance becomes large causing increased insertion loss
Solution Approach 1:
The invention employs a specific multi-layer structure with a thin titanium buffer layer (5-50 nm) and an aluminum electrode layer. The titanium layer thickness is optimized to provide sufficient structural support and crystal growth promotion without excessive resistivity, while the aluminum layer provides low resistivity. This optimized multi-layer configuration achieves both high power durability and low insertion loss, unlike conventional multi-layer structures that use thicker high-rigidity layers.
4Manufacturing precision
If wet etching preprocessing is performed on piezoelectric substrate, then single crystal aluminum film growth is promoted, but manufacturing complexity increases and reproducibility decreases
Solution Approach 1:
The invention removes the wet etching preprocessing step from the manufacturing process. Instead, it relies on the titanium buffer layer to promote pseudo-single crystal growth of the aluminum electrode layer directly on the cleaned piezoelectric substrate. This extraction of the wet etching step simplifies the manufacturing process, improves reproducibility, and eliminates the need to control multiple etching parameters while still achieving high-quality crystal growth through the titanium buffer layer's surface properties.
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 pseudo-single crystal aluminum film exhibits excellent power durability and low production costs with high yield, maintaining performance comparable to single crystal structures while simplifying the manufacturing process.
Implementation Method 1
the second film is formed of a crystal film including two (111) domains... formed through a process that omits wet etching preprocessing
Implementation Method 2
surface acoustic wave device includes a single crystal piezoelectric substrate... and a comb electrode (inter digital transducer, hereinafter referred to as an IDT) formed on the piezoelectric substrate
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3
AI summary
In order to provide a surface acoustic wave device provided with a pseudo-single crystal aluminum electrode film, having excellent power durability, easy to manufacture, and possible to grow with good reproducibility, a titanium buffer film 4 and an electrode film composed of an aluminum film or an aluminum alloy film are formed on a piezoelectric substrate 2 composed of lithium tantalate or lithium niobate. The electrode film 5 comprises a pseudo-single crystal film composed of two (111) domains (D1,D2). Each of the <111> directions of two (111) domains tilts in the range of 0 to 10 degrees (α1,α2) to the substrate surface, and the <11 - 2> directions in the respective (111) domain planes are 1 to 15 degrees (β) apart.