Acoustic Wave Device Reflectors with Gradient Electrode Finger Widths
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Solution Overview
Problem
Acoustic wave devices with interdigital transducer (IDT) electrodes and reflectors on a single-layer piezoelectric substrate suffer from excessive stop band responses, leading to degraded attenuation characteristics and insertion loss when connected in composite filter devices.
Innovation Solution
The acoustic wave device incorporates a piezoelectric substrate with a laminated structure of high-acoustic-velocity and low-acoustic-velocity layers, featuring IDT electrodes and reflectors with varying electrode finger widths and orientations to reduce or prevent stop band responses, and a composite filter device design that includes an acoustic wave resonator to minimize spurious modes and confine energy effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If reflectors with uniform electrode finger width are used, then the device structure is simple and easy to manufacture, but stop band response is excessive and attenuation characteristics are degraded
Solution Approach 1:
The electrode fingers of the reflectors are designed with non-uniform widths, where the width varies along the propagation direction of the acoustic wave. Specifically, the electrode finger width is smaller at the input end and larger at the output end, creating a gradient structure. This local variation in geometry suppresses the stop band response by reducing the periodicity effect that causes spurious reflections, while maintaining manufacturability through standard photolithography processes.
Solution Approach 2:
The reflector structure employs asymmetric electrode finger widths where adjacent fingers have different widths. This asymmetry breaks the periodic symmetry of the traditional uniform reflector design, thereby suppressing the formation of stop bands. The asymmetric pattern is achieved by designing electrode fingers with widths that alternate or gradiently change, preventing coherent spurious wave generation while maintaining effective acoustic wave reflection.
2Object-generated harmful factors
If reflectors with varying electrode finger widths are used, then stop band response is reduced and attenuation characteristics are improved, but device complexity increases
Solution Approach 1:
The complexity is localized only to the reflector electrode finger widths, while the rest of the device structure (IDT electrodes, substrate, encapsulation) remains conventional. The varying widths are implemented within the existing manufacturing framework, requiring only modified photolithography patterns. This localized approach minimizes overall device complexity while achieving the desired suppression of stop band response.
3Adaptability or versatility
If filter devices are connected in composite filter devices, then filtering functionality is enhanced, but insertion loss increases due to stop band response
Solution Approach 1:
The non-uniform electrode finger width structure creates an effective 'acoustic porosity' by introducing controlled variations in the reflector geometry. This variation acts as an acoustic impedance gradient that allows pass-band signals to transmit while suppressing stop band frequencies. The gradient structure effectively filters out spurious frequencies without causing excessive insertion loss, enabling efficient composite filter device operation.
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
Significantly reduces or prevents stop band responses, enhancing attenuation characteristics and insertion loss performance in composite filter devices by efficiently confining acoustic wave energy and reducing spurious modes.
Implementation Method 1
an acoustic wave device according to a preferred embodiment of the present invention includes a piezoelectric substrate, an interdigital transducer (IDT) electrode provided on or above the piezoelectric substrate
Implementation Method 2
a propagation direction of an acoustic wave on a piezoelectric substrate
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate, an interdigital transducer (IDT) electrode provided on the piezoelectric substrate, and a pair of reflectors provided on both sides of the IDT electrode in a first direction on the piezoelectric substrate, the first direction being a propagation direction of an acoustic wave. The pair of reflectors include a plurality of electrode fingers and a plurality of electrode fingers, respectively, which extend in a second direction, the second direction being perpendicular to the first direction. The electrode finger widths of second end portions are greater than the electrode finger widths of first end portions. The electrode finger width at any given position in the electrode fingers is equal to or greater than the electrode finger width at a position closer than the given position to the first end portions.