Embedded IDT Acoustic Filter Structure for Higher keff2 and Q
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Solution Overview
Problem
Current multilayer piezoelectric substrate (MPS) devices for acoustic wave filters face limitations in achieving high coupling coefficient (keff2) and quality factor (Q) performance while maintaining small temperature coefficient of frequency (TCF) and power durability, particularly in lithium tantalate (LiTaO3) based SAW filter packages.
Innovation Solution
The implementation of an embedded interdigital transducer (IDT) structure within a high permittivity piezoelectric substrate, utilizing layers of materials like molybdenum (Mo), aluminum (Al), and lithium tantalate (LiTaO3) with specific cut angles and embedment depths, along with capping layers, to enhance static coupling and resonance frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional IDT structures are used on piezoelectric substrates, then manufacturing is simpler, but coupling coefficient and quality factor performance are limited
Solution Approach 1:
The IDT structure is embedded within the piezoelectric substrate, nesting the transducer elements inside the substrate volume rather than placing them on the surface. This nesting approach increases the interaction between the IDT electrodes and the piezoelectric material, thereby enhancing the coupling coefficient and quality factor while managing the complexity through integrated fabrication processes.
Solution Approach 2:
The invention transitions from a surface-mounted IDT configuration to an embedded three-dimensional structure within the substrate. By utilizing the vertical dimension and embedding the IDT fingers throughout the substrate thickness, the patent achieves enhanced coupling performance through increased electrode-piezoelectric material interaction volume, effectively adding a dimensional aspect to the traditional planar IDT design.
2Reliability
If IDT embedment depth is increased to improve coupling, then coupling coefficient increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent systematically varies the embedment depth parameter of the IDT structure within the piezoelectric substrate to optimize coupling coefficient performance. By establishing specific embedment depth ranges and relationships between different layer thicknesses, the invention identifies optimal parameter zones that achieve high coupling while remaining manufacturable, thus managing the trade-off between performance and manufacturing precision.
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 approach increases the coupling coefficient (keff2) and quality factor (Q) performance, allowing for size reduction and improved frequency velocity, while maintaining temperature stability and power handling capabilities.
Implementation Method 1
An acoustic wave device can include a plurality of resonators arranged to filter a radio frequency signal. Example acoustic wave resonators include SAW resonators and bulk acoustic wave (BAW) resonators. A surface acoustic wave resonator can include an interdigital transducer (IDT) electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transducer electrode is disposed.
Data Source
AI summary
A radio frequency acoustic filter includes a plurality of resonators arranged to filter a signal. At least one resonator of the plurality of resonators includes a support substrate, a functional layer, and a piezoelectric layer. Both the piezoelectric layer and the functional layer are supported by the support substrate. An interdigital transducer structure is at least partially formed in the piezoelectric layer.