Embedded IDT Structure in SAW Substrates for Higher Coupling
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Solution Overview
Problem
Current lithium tantalate (LT) based multilayer piezoelectric substrate (MPS) surface acoustic wave (SAW) filter packages have a limited coupling coefficient (keff2) of around 12%, which is insufficient for achieving sufficient passband and good insertion loss, and the use of a thick silicon dioxide layer to compensate for temperature coefficient of frequency (TCF) in lithium niobate (LN) based MPS SAW filter packages leads to mechanical loss, reducing Q performance.
Innovation Solution
The proposal involves forming an interdigital transducer (IDT) structure at least partially in a piezoelectric layer with high permittivity, such as lithium tantalate, to enhance coupling coefficient and maintain high Q performance without the need for a thick silicon dioxide layer, by embedding the IDT electrode within the piezoelectric layer and using materials like tungsten and aluminum with varying thicknesses and orientations to optimize acoustic and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a thick silicon dioxide layer is used to compensate for temperature coefficient of frequency in lithium niobate based MPS SAW filter packages, then temperature stability is improved, but mechanical loss increases and Q performance deteriorates
Solution Approach 1:
The patent changes the material parameter from silicon dioxide to silicon nitride, which has different mechanical and acoustic properties. Silicon nitride provides the necessary temperature compensation while introducing lower mechanical loss, thereby maintaining high Q performance. This material substitution resolves the contradiction by finding a material that satisfies both temperature stability and low mechanical loss requirements.
2Ease of manufacture
If the IDT electrode is formed only on the surface of the piezoelectric layer, then manufacturing simplicity is maintained, but coupling coefficient remains limited at around 12%
Solution Approach 1:
The patent transitions from a two-dimensional surface-mounted IDT electrode to a three-dimensional structure by embedding the IDT electrode partially or fully within the piezoelectric layer. This dimensional change increases the interaction volume between the electrode and the piezoelectric material, thereby enhancing the coupling coefficient beyond the limited 12% achieved with surface-only configurations.
Solution Approach 2:
The IDT electrode is nested within the piezoelectric layer, with the electrode structure embedded inside the host piezoelectric material. This nesting arrangement maximizes the coupling between the electrode and piezoelectric material while maintaining a compact structure, resolving the contradiction between manufacturing simplicity and coupling coefficient.
3Reliability
If the IDT electrode is embedded deeper in the piezoelectric layer, then coupling coefficient is enhanced, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs partial embedding of the IDT electrode, where only a portion of the electrode is embedded within the piezoelectric layer while the remainder extends to or beyond the surface. This partial action approach achieves enhanced coupling coefficient without requiring precise full-depth embedding, thereby reducing manufacturing precision requirements while still obtaining the benefits of increased coupling.
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 beyond 12%, improves insertion loss, and maintains high Q performance, enabling a wider passband and reduced size of the SAW device while avoiding the mechanical losses associated with thick silicon dioxide layers.
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 surface acoustic wave (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 surface acoustic wave device is disclosed. The surface acoustic wave device can include a multilayer piezoelectric substrate having a support substrate and a piezoelectric layer over the support substrate and an interdigital transducer electrode formed at least partially in the piezoelectric layer. The interdigital transducer electrode has a first layer and a second layer including different materials. The first layer includes a material that has a mass density greater than or equal to a mass density of molybdenum.