XBAR Resonator Metal Layer Layout for Independent Coupling Tuning
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators face challenges in independently tuning resonator coupling without affecting other resonator properties, which is crucial for achieving optimal filter performance in communications applications.
Innovation Solution
The proposed acoustic resonator device includes a piezoelectric layer with an interdigital transducer (IDT) and a metal layer disposed between the IDT fingers and the piezoelectric layer. The metal layer has a specific thickness and width ratio relative to the IDT pitch, allowing for independent tuning of resonator coupling while minimizing changes to other resonator properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If resonator parameters such as crystal cut, dielectric thickness, IDT pitch, or IDT mark are modified to tune resonator coupling, then resonator coupling is adjusted, but other important resonator characteristics such as resonance frequency and spur location and amplitude are also affected
Solution Approach 1:
The patent introduces an independent metal layer structure that segments the control of resonator coupling from other resonator parameters. This metal layer can be independently adjusted to tune coupling without modifying the crystal cut, dielectric thickness, or IDT geometry, thereby resolving the contradiction between adapting coupling and maintaining other resonator characteristics.
Solution Approach 2:
The patent adds a new dimensional parameter for controlling resonator coupling by introducing a metal layer with adjustable thickness and/or permittivity. This creates an additional degree of freedom in the vertical dimension (layer thickness) that allows independent tuning of coupling without affecting the planar dimensions or material properties of existing resonator components.
2Manufacturing precision
If the coupling of a resonator is made smaller than required, then the desired bandwidth of the filter cannot be achieved, but if the coupling is larger than required, then selectivity of the filter will decrease
Solution Approach 1:
The patent enables precise adjustment of resonator coupling by changing the parameters of the metal layer, specifically its thickness and/or permittivity. This provides a continuous range of coupling values that can be precisely tuned to meet filter specifications, resolving the contradiction between achieving required bandwidth and maintaining selectivity.
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 solution enables precise tuning of resonator coupling, thereby improving the performance of XBAR devices and the filters that incorporate them, such as achieving desired bandwidth and selectivity in RF filters for communications systems.
Implementation Method 1
An XBAR resonator comprises an interdigital transducer (IDT) formed on a thin floating layer, or diaphragm, of a single-crystal piezoelectric material. The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Implementation Method 2
a metal layer disposed between a finger of the interleaved IDT fingers and the piezoelectric layer in a thickness direction that is measured in a direction normal to the surface of the piezoelectric layer
Data Source
AI summary
An acoustic resonator device is provided that a piezoelectric layer; an interdigital transducer on a surface of the piezoelectric layer and including interleaved IDT fingers extending from first and second busbars respectively; and a metal layer disposed between a finger of the interleaved IDT fingers and the piezoelectric layer in a thickness direction that is measured in a direction normal to the surface of the piezoelectric layer. In this aspect, a ratio of a width of the metal layer to a pitch of the interleaved IDT fingers is greater than or equal to 0.45, the width of the metal layer being measured in a width direction that is parallel to the surface of the piezoelectric layer. Moreover, a thickness of the metal layer in the thickness direction is less than one third a thickness of the finger in the thickness direction.