XBAR Resonator Structure With Thermal Etch-Stop for High-Frequency RF Filters

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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, due to limitations in performance parameters like insertion loss, rejection, and power handling.

Innovation Solution

The development of a transversely-excited film bulk acoustic resonator (XBAR) with an etch-stop layer and bonding layer, which enhances the resonator's performance by protecting the piezoelectric plate during etching and improving mechanical support, allowing for effective operation in higher frequency bands.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If existing acoustic wave resonators (SAW, BAW, FBAR) are used in current RF filters, then the filters can operate in present communication bands, but they are not well-suited for higher frequency bands above 3 GHz

Engineering Contradiction:

Improvefrequency band adaptabilityVSAvoidperformance at higher frequencies

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the physical parameters of the resonator structure by introducing a thermally conductive etch-stop layer with specific thickness (50-200 nm) and thermal conductivity properties. This parameter modification enables the resonator to operate effectively at higher frequencies above 3 GHz while maintaining structural integrity and acoustic wave propagation characteristics.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite structure combining piezoelectric material (e.g., aluminum nitride) with a thermally conductive etch-stop layer (e.g., aluminum oxide). This composite material approach provides both the piezoelectric properties needed for acoustic wave generation and the thermal management capabilities required for high-frequency operation, resolving the limitation of conventional single-material resonators.

Inventive Principle:

Principle #40Composite materials

2Reliability

If a thermally conductive etch-stop layer is added to the XBAR structure, then thermal management and mechanical support are enhanced, but the device complexity increases

Engineering Contradiction:

Improvethermal management capabilityVSAvoidnumber of layers

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The etch-stop layer serves multiple functions simultaneously: it acts as a thermal conduction path for heat dissipation, provides mechanical support to the piezoelectric plate, and serves as an etch-stop barrier during fabrication. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity while achieving improved thermal management.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The thermally conductive etch-stop layer acts as an intermediary between the piezoelectric plate and the substrate, mediating thermal transfer and mechanical stress. This intermediary layer enables effective thermal management without requiring direct modification of the piezoelectric material or substrate, thus adding minimal complexity to the overall device structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The XBAR design improves the performance of RF filters by enabling wider communication channel bandwidths, specifically in frequencies above 3 GHz, with enhanced power handling and reduced insertion loss, making it suitable for future wireless communication systems.

Implementation Method 1

an etch-stop layer and bonding layer, which enhances the resonator's performance by protecting the piezoelectric plate during etching

Methodology Applied

Scientific EffectEtch-stop layer protection:

Implementation Method 2

an etch-stop layer and bonding layer, which enhances the resonator's performance by protecting the piezoelectric plate during etching and improving mechanical support

Methodology Applied

Scientific EffectBonding layer adhesion: Adhesive

Implementation Method 3

Transversely-excited film bulk acoustic resonator with thermally conductive etch-stop layer

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS11996826B2Transversely-excited film bulk acoustic resonator with thermally conductive etch-stop layer

Publication Date: 2024.05.28 MURATA MFG CO LTD

AI summary

Acoustic resonator devices and methods are disclosed. An acoustic resonator device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces. An etch-stop layer is sandwiched between the surface of the substrate and the back surface of the piezoelectric plate, a portion of the piezoelectric plate and the etch-stop layer forming a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm. The etch-stop layer is impervious to an etch process used to form the cavity. The etch-stop layer is a high thermal conductivity material selected from aluminum nitride, boron nitride, and diamond.