Interdigital Transducer Finger Tapering for Cleaner Acoustic Wave Filtering
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Solution Overview
Problem
Existing acoustic wave devices suffer from the generation of unwanted waves due to the interdigital transducer electrode design, leading to degradation of frequency characteristics.
Innovation Solution
The acoustic wave device incorporates a support with a space on one principal surface, a piezoelectric layer on top, and a functional electrode that overlaps this space. The electrode is an interdigital transducer with electrode fingers having a width that linearly changes, specifically with a ratio of 1+σ:1−σ, where σ is between 0.01 and 0.054.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an interdigital transducer electrode is used in an acoustic wave device, then the device can function as intended, but unwanted waves are generated leading to degradation of frequency characteristics
Solution Approach 1:
The electrode fingers are designed with non-uniform width, where the width varies along the propagation direction. Specifically, the width at one end is greater than the width at the other end, creating local variations in the electrode structure. This local quality change modifies the acoustic wave generation characteristics and reduces the generation of unwanted waves while maintaining the desired frequency characteristics.
Solution Approach 2:
The interdigital transducer electrode employs asymmetric electrode finger widths, where adjacent electrode fingers have different widths. This asymmetry breaks the symmetry of the acoustic wave generation, thereby suppressing the formation of unwanted symmetric wave modes and improving the overall frequency characteristics of the acoustic wave device.
2Ease of manufacture
If the electrode finger width is made uniform, then the manufacturing is simpler, but unwanted waves are generated degrading performance
Solution Approach 1:
Instead of uniform electrode fingers, the invention introduces local variations in electrode finger width. The width changes progressively along the propagation direction, creating a gradient structure that is relatively simple to manufacture using standard photolithography techniques while effectively reducing unwanted wave generation and improving frequency characteristics.
3Object-generated harmful factors
If the electrode finger width varies significantly, then unwanted waves are reduced, but the device complexity increases
Solution Approach 1:
The electrode finger width varies in a controlled and gradual manner rather than through complex geometric shapes. This moderate variation achieves effective suppression of unwanted waves while keeping the structure relatively simple and compatible with standard manufacturing processes, thus avoiding excessive device complexity.
Solution Approach 2:
The invention modifies the width parameter of the electrode fingers along the propagation direction. By systematically varying this single geometric parameter in a controlled way, the device achieves reduced unwanted wave generation without introducing complex structural elements, thereby maintaining manufacturing simplicity.
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 design effectively reduces or prevents the generation of unwanted waves while maintaining good resonance characteristics and a high figure of merit, thus improving the overall performance of the acoustic wave device.
Implementation Method 1
a piezoelectric layer on the one principal surface of the support
Implementation Method 2
a functional electrode on at least one principal surface of the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a support including a space in a surface thereof, a piezoelectric layer on the surface of the support, and a functional electrode on at least one surface of the piezoelectric layer to at least partially overlap the space as viewed in a first direction. The functional electrode is an interdigital transducer electrode including first and second busbars, and first and second electrode fingers. At least one electrode finger of the first and second electrode fingers includes a portion with a width that linearly changes in a second direction. In the at least one electrode finger, when a ratio of a width at a proximal end to a minimum width between the proximal end and a distal end is 1+σ:1−σ, σ is greater than or equal to about 0.01 and less than or equal to about 0.054.