SAW IDT Gap Structure for Transverse Mode Spurious Suppression
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Solution Overview
Problem
Existing surface acoustic wave (SAW) resonators with tungsten layers in interdigital transducer (IDT) electrodes experience increased transverse mode spurious signals, which interfere with device operation, particularly above the anti-resonance frequency, and are less effectively suppressed compared to those with molybdenum layers.
Innovation Solution
Incorporating high-density material segments within or above the gap and edge regions of the IDT electrodes, and adjusting the thickness and placement of dielectric films to modify acoustic wave velocities, thereby reducing transverse mode spurious signals. This includes using materials like tungsten or other metals with higher densities than the dielectric films, and varying the thickness and position of these segments to optimize acoustic wave confinement within the center region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-density material (tungsten) is used in IDT electrodes, then electrical conductivity is improved, but transverse mode spurious signals increase
Solution Approach 1:
The IDT electrode structure is segmented into multiple layers: a lower tungsten layer for electrical conductivity and an upper molybdenum layer to suppress spurious signals. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between conductivity and spurious signal suppression.
Solution Approach 2:
Different materials are applied to different regions of the IDT electrodes. The lower layer uses high-conductivity tungsten while the upper layer uses low-spurious-signal molybdenum. This local differentiation of material properties optimizes both electrical performance and spurious signal suppression in their respective regions.
2Ease of manufacture
If uniform dielectric film thickness is used, then manufacturing simplicity is maintained, but transverse mode spurious signals are not effectively suppressed
Solution Approach 1:
The dielectric film thickness is varied locally across different regions of the substrate. Thinner dielectric regions are positioned over the IDT electrodes where spurious signals originate, while thicker regions are used in other areas. This local thickness variation optimizes spurious signal suppression while maintaining overall manufacturing feasibility through sequential deposition processes.
Solution Approach 2:
The solution moves from a single-dimensional uniform thickness parameter to a two-dimensional thickness profile. By controlling thickness variations in both lateral and vertical dimensions, the patent achieves superior spurious signal suppression while maintaining manufacturing practicality through established thin-film deposition techniques.
3Object-generated harmful factors
If acoustic wave velocity is increased in gap regions, then transverse mode suppression is improved, but device complexity increases
Solution Approach 1:
The patent changes the acoustic wave velocity parameter in the gap regions by selecting materials with appropriate acoustic properties. The dielectric material and its thickness are specifically chosen to achieve the desired acoustic velocity profile, creating acoustic impedance mismatches that suppress transverse mode propagation without requiring complex mechanical structures.
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 inclusion of high-density material segments above the gap regions and adjustments to IDT electrode widths and dielectric film thicknesses significantly reduce transverse mode spurious signals, improving the frequency response and temperature stability of SAW devices.
Implementation Method 1
surface acoustic wave (SAW) resonators
Implementation Method 2
a material having a density greater than a density of the first dielectric film disposed above the gap regions of the IDT electrodes
Implementation Method 3
substrate including a piezoelectric material, interdigital transducer (IDT) electrodes disposed on a surface of the substrate
Data Source
AI summary
An acoustic wave device comprises a substrate including a piezoelectric material, interdigital transducer (IDT) electrodes disposed on a surface of the substrate, the IDT electrodes having gap regions, edge regions, and center regions, a first dielectric film having a lower surface disposed on the IDT electrodes and the surface of the substrate, and a material having a density greater than a density of the first dielectric film disposed above the gap regions of the IDT electrodes.