SAW Filter Bonding Structure for Temperature-Stable Lithium Tantalate
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Solution Overview
Problem
Surface acoustic wave devices, particularly those using lithium tantalate substrates, face significant passband shifts due to temperature changes, with existing solutions failing to effectively lower the temperature coefficient of frequency change, leading to inadequate temperature stability.
Innovation Solution
A surface acoustic wave device is designed with a piezoelectric single crystal propagation substrate bonded to a supporting substrate using an organic adhesive layer with a thickness of 0.1 to 1.0 μm, specifically using silicon or borosilicate glass as the supporting substrate to improve thermal matching and reduce stress, thereby enhancing temperature characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If lithium tantalate substrate is used for SAW device, then electromechanical coupling coefficient is high and broad-band filtering characteristics are achieved, but temperature stability deteriorates with frequency variation of -35 ppm/°C
Solution Approach 1:
An organic adhesive layer is introduced as an intermediary between the lithium tantalate propagation substrate and the supporting substrate. This adhesive layer acts as a stress buffer that compensates for thermal expansion differences, thereby improving temperature stability while preserving the high electromechanical coupling coefficient of lithium tantalate
Solution Approach 2:
The invention creates a composite structure combining lithium tantalate propagation substrate, organic adhesive layer, and supporting substrate. This composite material approach allows leveraging the high coupling coefficient of lithium tantalate while using the supporting substrate and adhesive to provide thermal stability
2Reliability
If adhesive layer thickness is increased to prevent peeling and cracks, then bonding reliability is improved, but manufacturing precision deteriorates due to difficulty in making thickness constant
Solution Approach 1:
The invention optimizes the adhesive layer thickness parameter to a specific range (5-20 μm) that balances bonding reliability and manufacturability. This parameter optimization ensures sufficient bonding strength while maintaining feasibility for mass production with acceptable thickness uniformity
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 approach results in a significantly lower temperature coefficient of frequency, improving the device's temperature stability by effectively managing thermal expansion coefficient differences between substrates, while maintaining sufficient adhesive strength to prevent peeling or cracking.
Implementation Method 1
an organic adhesive layer having a thickness of 0.1 to 1.0 μm bonding the supporting substrate and the propagation substrate
Implementation Method 2
effectively managing thermal expansion coefficient differences between substrates to improve temperature stability
Implementation Method 3
a propagation substrate comprising a piezoelectric single crystal
Implementation Method 4
a surface acoustic wave filter or resonator provided on the propagation substrate
Data Source
AI summary
A surface acoustic wave device has a supporting substrate, a propagation substrate made of a piezoelectric single crystal, an organic adhesive layer having a thickness of 0.1 to 1.0 μm and bonding the supporting substrate and the propagation substrate, and a surface acoustic wave filter provided on the propagation substrate.