Acoustic Wave Resonator Reflector Pitch for Lower-Frequency Return Loss

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Solution Overview

Problem

Acoustic wave resonators in mobile phone front-end circuits face issues with high return loss at frequencies lower than the resonant frequency due to spurious waves, degrading bandpass characteristics.

Innovation Solution

The acoustic wave element incorporates a piezoelectric layer with IDT electrodes on both surfaces and reflectors, where the IDT-reflector gap is smaller than the reflector wave length, and the reflector wave length is greater than the IDT wave length, to generate a spurious wave that cancels out the return loss at lower frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional IDT electrodes and reflectors are used in acoustic wave resonators, then the basic resonant function is achieved, but return loss increases at frequencies lower than the resonant frequency due to spurious waves

Engineering Contradiction:

Improvebandpass characteristicsVSAvoidspurious waves causing return loss increase

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The invention converts the harmful spurious waves into beneficial cancellation waves by carefully designing the reflector array pitch to be larger than the IDT array pitch. This configuration generates spurious waves from the reflectors that are out of phase with the unwanted reflections, causing them to cancel each other out and reduce return loss at frequencies below the resonant frequency.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The invention changes the critical parameter of array pitch relationship between IDT and reflector elements. By setting the reflector array pitch (Pr) to be larger than the IDT array pitch (Pi), the phase characteristics of reflected waves are modified, enabling destructive interference of spurious waves and constructive interference at the desired resonant frequency.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If multiple filter devices are arranged in mobile phone front-end circuits for multi-band systems, then data transfer speed is increased, but isolation between adjacent bands and loss characteristics become critical requirements that are difficult to meet

Engineering Contradiction:

Improvedata transfer speedVSAvoidisolation between bands and loss characteristics

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention converts the harmful effect of spurious wave reflections into a beneficial cancellation mechanism. By designing the reflector array with a larger pitch than the IDT array, the reflected spurious waves are transformed into cancellation waves that reduce return loss, thereby improving isolation characteristics and enabling better bandpass performance in multi-band filter systems.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The invention modifies the array pitch parameter relationship to optimize both resonant frequency performance and lower frequency rejection. By setting Pr > Pi, the system achieves improved return loss characteristics across the frequency spectrum, enabling multiple filters to operate with better isolation and lower loss in multi-band mobile phone systems.

Inventive Principle:

Principle #35Parameter changes

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 configuration reduces or prevents the increase of return loss at frequencies lower than the resonant frequency, improving the bandpass characteristics and reducing higher-order mode generation.

Implementation Method 1

an acoustic wave element includes a piezoelectric layer, interdigital transducer (IDT) electrodes that are provided on two main surfaces of the piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a plurality of reflectors that are provided on both of the two main surfaces... each include a plurality of reflection electrode fingers... G is smaller than Pr

Methodology Applied

Scientific EffectAcoustic wave reflection: Reflection

Data Source

PatentUS20240364301A1Acoustic wave element, acoustic wave filter device, and multiplexer

Publication Date: 2024.10.31 MURATA MFG CO LTD

AI summary

An acoustic wave element includes IDT electrodes on two main surfaces of a piezoelectric layer, and reflectors on both of the two main surfaces. The IDT electrodes each include electrode fingers extending in a second direction that intersects a first direction. The reflectors each include reflection electrode fingers extending in the second direction. An array pitch of the electrode fingers along the first direction is Pi, an array pitch of the reflection electrode fingers is Pr, and an IDT-reflector gap in the first direction d1 between a center of an electrode finger and a center of a reflection electrode finger that is closest to the IDT electrode among the plurality of reflection electrode fingers is G, a thickness of the piezoelectric layer is smaller than or equal to twice Pi, G is smaller than Pr, and Pr is greater than Pi.