Shared Reflector Layout for Compact Acoustic Wave Ladder Filters

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Solution Overview

Problem

Existing acoustic wave devices face challenges in reducing size while maintaining frequency characteristics, as sharing reflectors between surface acoustic wave resonators can lead to decreased frequency performance.

Innovation Solution

The implementation of a shared reflector between adjacent resonators with different frequency characteristics, where the shared reflector's electrode finger pitch and duty are set to intermediate values between the two resonators, ensuring the reflector functions for both resonators and maintains frequency characteristics, thereby allowing for size reduction without compromising performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If a shared reflector is disposed between interdigital transducer electrodes of adjacent surface acoustic wave resonators, then the overall size of the acoustic wave device is reduced, but the frequency characteristics of the device may decrease

Engineering Contradiction:

Improveoverall size of acoustic wave deviceVSAvoidfrequency characteristics

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The patent combines the reflector functions for two adjacent resonators into a single shared reflector structure. The shared reflector is disposed between the interdigital transducer electrodes of the first and second resonators, eliminating the need for separate reflectors for each resonator and thereby reducing the overall device area.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent optimizes the electrode finger pitch and duty cycle of the shared reflector to intermediate values between those of the two adjacent resonators. Specifically, the electrode finger pitch is set between the first pitch of the first resonator and the second pitch of the second resonator, and the duty cycle is set between the first duty cycle and the second duty cycle. This parameter optimization ensures that the shared reflector maintains appropriate frequency characteristics for both resonators while enabling size reduction.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If reflectors are disposed on both sides of interdigital transducer electrodes to reduce signal leakage, then signal propagation is improved, but the device size increases

Engineering Contradiction:

Improvesignal leakage reductionVSAvoiddevice size

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent merges the reflector structures by having the shared reflector serve dual purposes: it acts as a reflector for the first resonator and simultaneously as a reflector for the second resonator. This consolidation maintains signal leakage reduction functionality while eliminating redundant reflector structures and reducing overall device size.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The shared reflector is designed to perform multiple functions: it reflects surface acoustic waves for the first resonator, reflects surface acoustic waves for the second resonator, and reduces signal leakage for both resonators. This multi-functional design eliminates the need for separate reflectors and reduces device area.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 enables a reduction in the size of the acoustic wave device while preventing negative impacts on frequency characteristics, ensuring effective signal reflection and maintaining the desired filter performance.

Implementation Method 1

a substrate including a piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

reflectors are disposed on both sides of an interdigital transducer (IDT) electrode that is a component of each of the surface acoustic wave resonators

Methodology Applied

Scientific EffectSurface acoustic wave reflection: Surface Acoustic Wave

Data Source

PatentUS12255632B2Acoustic wave device, and ladder filter including the same

Publication Date: 2025.03.18 MURATA MFG CO LTD

AI summary

An acoustic wave device includes a substrate including a piezoelectric layer, first and second resonators on the substrate, and a shared reflector. The second resonator is located on the substrate adjacent to the first resonator and has different frequency characteristics than the first resonator. The shared reflector is located on the substrate between the first resonator and the second resonator and is a reflector for both the first resonator and the second resonator. The first resonator includes a first interdigital transducer electrode with electrode fingers positioned with a first pitch. The second resonator includes a second interdigital transducer electrode with electrode fingers positioned with a second pitch. A lower limit frequency of a stop band of the shared reflector is between a lower limit frequency of a stop band of the first resonator and a lower limit frequency of a stop band of the second resonator. An upper limit frequency of the stop band of the shared reflector is between an upper limit frequency of the stop band of the first resonator and an upper limit frequency of the stop band of the second resonator.