Multilayer SAW Substrate With Dense IDTs for Near-Zero TCF
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Solution Overview
Problem
Existing acoustic wave devices face challenges in achieving high bandwidth operations with low temperature coefficients of frequency, as the temperature coefficient of frequency (TCF) often exceeds desirable limits, affecting the performance and size of surface acoustic wave (SAW) resonators.
Innovation Solution
A multilayer piezoelectric substrate structure is introduced, incorporating a trap-rich layer, a first functional layer with a positive temperature coefficient of frequency, and a second functional layer with a negative temperature coefficient, along with high-density interdigital transducer electrodes, to balance and reduce the TCF while maintaining or enhancing electromechanical coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional single-layer piezoelectric substrate is used, then device structure is simple, but temperature coefficient of frequency exceeds desirable limits
Solution Approach 1:
The patent applies composite materials by creating a multilayer piezoelectric substrate structure comprising a first piezoelectric layer with positive temperature coefficient and a second piezoelectric layer with negative temperature coefficient. This composite structure enables temperature compensation where the opposing TCF characteristics of the layers balance each other, achieving near-zero overall TCF while maintaining device reliability.
Solution Approach 2:
The patent segments the piezoelectric substrate into multiple functional layers with distinct temperature coefficient characteristics. The first piezoelectric layer and second piezoelectric layer are separated into discrete segments that can be independently designed and optimized, allowing each layer to contribute differently to the overall temperature compensation mechanism.
2Ease of manufacture
If traditional aluminum electrodes are used, then manufacturing is easier, but electromechanical coupling coefficient is insufficient for high bandwidth operations
Solution Approach 1:
The patent changes the material parameter of the electrode from traditional aluminum to high-density metals such as molybdenum, tungsten, or platinum. This parameter change increases the electrode density, which enhances the electromechanical coupling coefficient and enables high bandwidth operations, while still maintaining compatibility with standard fabrication processes.
3Reliability
If high-density metal electrodes are used, then electromechanical coupling improves, but electrode fabrication complexity increases
Solution Approach 1:
The patent modifies the density parameter of the electrode material to achieve higher electromechanical coupling. By selecting high-density metals and optimizing their thickness parameters (first metal layer: 0.025λ-0.075λ, second metal layer: 0.0065λ-0.08λ), the design enhances coupling coefficients while managing fabrication complexity through parameter optimization.
4Reliability
If thicker functional layers are used, then temperature compensation is improved, but device size increases
Solution Approach 1:
The patent optimizes the thickness parameters of the functional layers to achieve effective temperature compensation without excessive size increase. By carefully controlling the thickness of the first functional layer, second functional layer, and piezoelectric material layer, the design balances temperature compensation performance with compact device dimensions.
Solution Approach 2:
The patent uses composite material layers with complementary properties to achieve temperature compensation in a compact configuration. The combination of layers with different TCF characteristics allows for effective compensation while maintaining reasonable device size through synergistic material interactions.
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 achieves a temperature coefficient of frequency near zero, improves electromechanical coupling, and reduces resonator size, enabling efficient high-bandwidth operations in radio frequency filters.
Implementation Method 1
a layer of piezoelectric material disposed on an upper surface of the second functional layer, and interdigital transducer (IDT) electrodes including interdigitated electrode fingers disposed on a surface of the piezoelectric material layer
Implementation Method 2
surface acoustic wave device comprises a support substrate, a first functional layer having a positive temperature coefficient of frequency disposed above an upper surface of the support substrate
Implementation Method 3
a second functional layer having a negative temperature coefficient of frequency disposed on an upper surface of the first functional layer
Data Source
AI summary
Aspects and embodiments disclosed herein include a surface acoustic wave device comprising a support substrate, a first functional layer having a positive temperature coefficient of frequency disposed above an upper surface of the support substrate, a second functional layer having a negative temperature coefficient of frequency disposed on an upper surface of the first functional layer, a layer of piezoelectric material disposed on an upper surface of the second functional layer, and interdigital transducer (IDT) electrodes including interdigitated electrode fingers disposed on a surface of the piezoelectric material layer, the IDT electrodes including a metal with a density greater than aluminum.