Y-Cut Bulk Acoustic Resonators for High-Frequency RF Filtering

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Solution Overview

Problem

Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands, such as those proposed for future wireless networks, as they fail to provide optimal performance in terms of insertion loss, rejection, isolation, power handling, linearity, size, and cost.

Innovation Solution

The development of Y-cut film bulk acoustic resonators (YBARs) and solidly-mounted YBARs with specific piezoelectric material orientations, conductor patterns, and acoustic Bragg reflectors, which allow for improved frequency selectivity and reduced parasitic modes, enabling effective operation at higher frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional acoustic wave resonators are used for higher frequency bands, then existing filter structures can be maintained, but performance in terms of insertion loss, rejection, isolation, power handling, linearity, and frequency selectivity deteriorates

Engineering Contradiction:

Improvefilter performanceVSAvoidadaptability to higher frequency bands

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the crystal orientation parameter from conventional cuts to Y-cut with specific rotation angles (60-80 degrees from Y-axis), and adjusts the thickness parameter of the piezoelectric layer to be between 0.5-5 micrometers. These parameter changes enable the resonator to achieve optimal performance at higher frequency bands (3.3-5.9 GHz and beyond) while maintaining good frequency selectivity and reduced parasitic modes

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material structure by combining Y-cut lithium niobate (LN) with lithium tantalate (LT) layers in a specific configuration. This composite piezoelectric structure leverages the complementary properties of LN (high piezoelectric coefficient) and LT (lower acoustic velocity) to achieve enhanced frequency selectivity and reduced parasitic modes at higher operating frequencies

Inventive Principle:

Principle #40Composite materials

2Adaptability or versatility

If Y-cut film bulk acoustic resonators with specific orientations are used, then frequency selectivity and adaptability to higher frequencies are improved, but device complexity increases

Engineering Contradiction:

Improvefrequency selectivityVSAvoidresonator structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments the piezoelectric structure into distinct functional layers: a Y-cut LN layer with specific rotation angle for frequency selectivity, and an LT layer for acoustic wave confinement. This segmentation allows each layer to be optimized independently for its specific function, achieving high frequency selectivity while managing overall device complexity through clear functional division

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a new dimension of control by using rotated Y-cut orientation (60-80 degrees from Y-axis) rather than conventional crystal cuts. This angular rotation in the crystal orientation space provides an additional degree of freedom for optimizing frequency selectivity and parasitic mode suppression, enabling better performance at higher frequencies without proportionally increasing structural complexity

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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

These resonators achieve enhanced frequency selectivity and reduced parasitic modes, leading to improved RF filter performance, including wider communication channel bandwidths and better adaptability to higher frequency bands.

Implementation Method 1

a piezoelectric material such as lithium niobate (LN), lithium tantalate (LT), lanthanum gallium silicate, or gallium nitride

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

acoustic Bragg reflectors

Methodology Applied

Scientific EffectBragg reflection: Bragg Diffraction

Data Source

PatentUS11736090B2Film bulk acoustic resonators in thin LN-LT layers

Publication Date: 2023.08.22 MURATA MFG CO LTD

AI summary

Acoustic resonator devices, filter devices, and methods of fabrication. A resonator device includes a piezoelectric plate having a front surface and a back surface opposite the front surface, a back-side conductor pattern formed on the back surface, and a first front-side conductor pattern and a second front-side conductor pattern formed on respective portions of the front surface opposite the back-side conductor pattern. A portion of the piezoelectric plate between the first front-side conductor pattern and the back-side conductor pattern forms a first resonator and a portion of the piezoelectric plate between the second front-side conductor pattern and the back-side conductor pattern forms a second resonator.