Acoustic Wave Reflector Layout to Cut Capacitive Loss
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Solution Overview
Problem
Acoustic wave devices with metal reflectors suffer from unintentional capacitive components that degrade high-frequency propagation characteristics, leading to increased acoustic wave propagation loss.
Innovation Solution
The acoustic wave device incorporates a layered structure with a metal layer and dielectric layers of varying acoustic impedances, where the metal layer encompasses the IDT electrode and not the wiring electrode, reducing unwanted capacitive components and confining the main mode of acoustic waves above the metal layer, thereby minimizing propagation loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a metal film is used as the acoustic reflector, then the acoustic wave confinement is improved, but an unintentional capacitive component is generated that degrades high frequency propagation characteristics
Solution Approach 1:
The acoustic reflector is segmented into multiple functional layers: a first dielectric layer, a metal layer, and a second dielectric layer. This segmentation allows the metal layer to provide acoustic reflection while the dielectric layers isolate it from capacitive coupling with electrodes, thus reducing unwanted capacitive components while maintaining acoustic wave confinement.
Solution Approach 2:
Dielectric layers are introduced as intermediary materials between the metal layer and the electrodes (IDT and busbar). These dielectric intermediaries prevent direct capacitive coupling between the metal reflector and electrodes, eliminating the harmful capacitive effect while preserving the acoustic reflection function.
2Object-affected harmful factors
If the metal layer area is reduced to minimize capacitive components, then the capacitive effect is reduced, but the acoustic wave confinement may be weakened
Solution Approach 1:
The acoustic reflector structure implements local quality differentiation: the metal layer is positioned and sized to provide adequate acoustic reflection in critical regions, while dielectric layers are strategically placed to minimize capacitive coupling in electrode proximity regions. This local optimization allows simultaneous achievement of good acoustic confinement and minimal capacitive effect.
Solution Approach 2:
The acoustic reflector uses a composite structure combining metal and dielectric materials. The metal provides high acoustic impedance for wave confinement, while the dielectric materials provide electrical isolation. This composite approach allows the reflector to simultaneously achieve acoustic wave confinement and electrical isolation, resolving the contradiction between confinement effectiveness and capacitive effect minimization.
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 effectively reduces unwanted capacitive components and propagation loss, improving the confinement efficiency of acoustic waves and maintaining high-frequency propagation characteristics.
Implementation Method 1
the second dielectric layer... has an acoustic impedance higher than that of the first dielectric layer; the metal layer... has an acoustic impedance higher than that of the first dielectric layer
Implementation Method 2
a piezoelectric layer that is laminated directly or indirectly on the acoustic reflection layer; one or more IDT electrodes that are provided directly or indirectly on the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes in order a substrate, an acoustic reflection layer, a piezoelectric layer, an IDT electrode including a pair of comb electrodes, and wiring electrodes. The acoustic reflection layer includes a low Z dielectric layer, a high Z dielectric layer below the low Z dielectric layer and having an acoustic impedance higher than that of the low Z dielectric layer, and a metal layer above the low Z dielectric layer and having an acoustic impedance higher than that of the low Z dielectric layer. When the acoustic reflection layer is viewed in plan, in a region encompassing the IDT electrode and the wiring electrodes but no IDT electrodes other than the IDT electrode, an area including the metal layer is smaller than an area including the high Z dielectric layer.