SAW Device with Isolated Metallic Layer for Wideband Filtering
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Solution Overview
Problem
Current surface acoustic wave (SAW) filters and resonators face challenges in achieving high electromechanical coupling coefficients and wideband capabilities, particularly for new communication standards like E-UTRA, where higher frequency and wider channel bandwidth are required, with existing structures like AlN/diamond and ScAlN/diamond not adequately addressing these demands.
Innovation Solution
A SAW device is designed with a high acoustic velocity layer and a piezoelectric layer, where transducers are coupled to the piezoelectric layer, and a metallic layer is electrically isolated from the transducers, allowing for improved electromechanical coupling and surface wave propagation, achieving a relative bandwidth of up to 6.0% and meeting E-UTRA band 42 filter requirements with a center frequency of 3500 MHz and bandwidth of 200 MHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If AlN/diamond multi-layer structure is used, then acoustic wave velocity is improved (9500 m/s), but electromechanical coupling coefficient deteriorates (k2 = 1.2%, unsuitable for wideband)
Solution Approach 1:
The patent employs a composite structure consisting of a diamond layer (high acoustic velocity) combined with a ScAlN layer (high piezoelectricity). This composite material approach allows the device to simultaneously achieve high acoustic wave velocity from the diamond and high electromechanical coupling coefficient from the ScAlN, resolving the contradiction between speed and coupling efficiency.
2Reliability
If ScAlN/diamond structure is used, then piezoelectricity and thermal conductivity are improved, but electromechanical coupling coefficient remains insufficient for wideband filter applications
Solution Approach 1:
The patent optimizes the thickness of the ScAlN layer to be between 0.05λ and 0.15λ (where λ is the acoustic wavelength). This precise parameter control maximizes the electromechanical coupling coefficient while maintaining high piezoelectricity, enabling the filter to achieve wideband performance with relative bandwidth of 5% or more.
3Speed
If higher operating frequency is achieved, then communication standard requirements are met, but filter bandwidth becomes narrower
Solution Approach 1:
The diamond-ScAlN composite structure enables simultaneous achievement of high operating frequency (3.5 GHz for E-UTRA band 42) and wide channel bandwidth (200 MHz, exceeding the 5% requirement). The diamond provides high acoustic velocity for high frequency operation, while the ScAlN layer ensures sufficient electromechanical coupling for wide bandwidth.
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 enables SAW filters to achieve a wideband performance with a high electromechanical coupling coefficient, supporting higher operating frequencies and wider channel bandwidths, while minimizing spurious signals and enhancing acoustic wave velocity, thus addressing the limitations of previous structures.
Implementation Method 1
a piezoelectric layer coupled to the high acoustic velocity layer. The SAW device also includes at least one transducer coupled to at least the piezoelectric layer. The transducer is configured to propagate a surface acoustic wave
Implementation Method 2
a high acoustic velocity layer and a piezoelectric layer coupled to the high acoustic velocity layer. The transducer is configured to propagate a surface acoustic wave having an operating wavelength (λ) along a surface of the piezoelectric layer
Data Source
AI summary
The embodiments herein relate to surface acoustic wave (SAW) devices, such as filters and duplexers. The SAW device may have a high acoustic velocity layer and a piezoelectric layer coupled to the high acoustic velocity layer. At least one transducer is coupled at least to the piezoelectric layer, where the transducer propagates a surface acoustic wave having an operating wavelength along a surface of the piezoelectric layer. A metallic layer may be coupled to the surface of the piezoelectric layer and electrically isolated from the transducer.