XBAR Resonator Diaphragm Geometry for Spurious Mode Suppression

Solution Overview

Problem

Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands above 3 GHz, as they face challenges in achieving optimal performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size, and cost, especially in future wireless communication systems that require wider channel bandwidths.

Innovation Solution

The development of transversely-excited film bulk acoustic resonators (XBARs) with non-rectangular diaphragms and asymmetric shapes, which utilize a thin film conductor pattern on a piezoelectric plate to excite shear-mode acoustic waves, providing higher piezoelectric coupling and improved frequency selectivity by suppressing spurious modes through non-rectangular cavity and diaphragm designs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional acoustic wave resonators are used for RF filters, then existing design methods can be applied, but performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size and cost cannot be optimized for higher frequency bands above 3 GHz

Engineering Contradiction:

Improvefilter performanceVSAvoidfrequency band adaptability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent employs asymmetric diaphragm shapes (non-rectangular geometries including trapezoidal, triangular, and irregular polygons) to suppress spurious acoustic modes and improve filter rejection characteristics. The asymmetric configuration breaks the symmetry of acoustic wave propagation, thereby reducing unwanted resonances and enhancing overall filter performance in high-frequency bands.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The invention changes the geometric parameters of the diaphragm from conventional rectangular shapes to various non-rectangular configurations. This parameter change includes modifying side lengths, angles, and overall geometry to optimize acoustic mode suppression and improve filter performance for frequency bands above 3 GHz, enabling better adaptability to future wireless communication systems.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If rectangular diaphragms are used in XBAR resonators, then manufacturing is simpler, but spurious modes are not sufficiently suppressed and frequency selectivity is reduced

Engineering Contradiction:

Improvediaphragm fabricationVSAvoidfrequency selectivity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent employs asymmetric diaphragm shapes (non-rectangular geometries including trapezoidal, triangular, and irregular polygons) to suppress spurious acoustic modes and improve filter rejection characteristics. The asymmetric configuration breaks the symmetry of acoustic wave propagation, thereby reducing unwanted resonances and enhancing overall filter performance in high-frequency bands.

Inventive Principle:

Principle #4Asymmetry

3Productivity

If higher piezoelectric coupling is achieved through XBAR design, then bandwidth and frequency selectivity improve, but device complexity increases due to non-rectangular cavity and diaphragm designs

Engineering Contradiction:

ImprovebandwidthVSAvoiddiaphragm geometry

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent employs asymmetric diaphragm shapes (non-rectangular geometries including trapezoidal, triangular, and irregular polygons) to suppress spurious acoustic modes and improve filter rejection characteristics. The asymmetric configuration breaks the symmetry of acoustic wave propagation, thereby reducing unwanted resonances and enhancing overall filter performance in high-frequency bands.

Inventive Principle:

Principle #4Asymmetry

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

XBARs effectively enhance RF filter performance by achieving better bandwidth and rejection characteristics, enabling the design of high-frequency filters with improved bandwidth and reduced spurious modes, suitable for future wireless communication systems up to 28 GHz.

Implementation Method 1

utilize a thin film conductor pattern on a piezoelectric plate to excite shear-mode acoustic waves, providing higher piezoelectric coupling

Methodology Applied

Scientific EffectPiezoelectric coupling: Piezoelectric Effect

Implementation Method 2

excite shear-mode acoustic waves... by suppressing spurious modes through non-rectangular cavity and diaphragm designs

Methodology Applied

Scientific EffectAcoustic wave resonance: Resonance

Data Source

PatentUS11929735B2XBAR resonators with non-rectangular diaphragms

Publication Date: 2024.03.12 MURATA MFG CO LTD

AI summary

Acoustic resonator devices, filter devices, and methods of fabrication are disclosed. An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces. The back surface is attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The IDT is configured to excite a primary acoustic mode in the diaphragm in response to a radio frequency signal applied to the IDT. At least a portion of an edge of the diaphragm is at an oblique angle to the fingers.