Composite Bragg Mirror Structure for Temperature-Stable BAW Resonators

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Solution Overview

Problem

Conventional Bragg mirrors in SMR-BAW resonators face challenges with temperature compensation and spurious resonances, especially at higher signal levels, leading to performance degradation and increased energy loss.

Innovation Solution

A Bragg mirror design with alternating layers of metals and materials with specific acoustic impedance and velocity ratios, where one material is radially embedded within the other, enhancing temperature compensation and suppressing spurious resonances by hindering lateral wave propagation and improving heat transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If conventional Bragg mirror with alternating SiO2 and W layers is used, then acoustic isolation is provided, but temperature compensation is insufficient at high signal levels

Engineering Contradiction:

Improvetemperature compensationVSAvoidperformance stability

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent changes the material parameters of the Bragg mirror by replacing part of the SiO2 layers with a composite structure consisting of a metal layer (Al, Cu, Ag, or Au) and a dielectric layer (SiO2, Si3N4, or TiO2). This parameter change in material composition and acoustic impedance enables effective temperature compensation at high signal levels while maintaining acoustic isolation performance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a composite material structure where a metal layer is combined with a dielectric layer to form a new Bragg mirror layer. This composite structure provides both the acoustic isolation properties of traditional Bragg mirrors and the temperature compensation capabilities needed for high-power applications, resolving the contradiction between temperature stability and performance reliability.

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If conventional Bragg mirror structure is used, then manufacturing is simple, but spurious resonances occur that suppress bandwidth and increase insertion loss

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidinsertion loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent modifies the acoustic impedance parameters of the Bragg mirror by introducing metal-dielectric composite layers with specifically controlled thickness ratios. The metal layer thickness is set between 10-90% of the total composite layer thickness, which changes the acoustic wave propagation characteristics and effectively suppresses spurious resonances while maintaining manufacturability through standard thin-film deposition processes.

Inventive Principle:

Principle #35Parameter changes

3Power

If signal level is increased for new applications, then power handling is improved, but temperature increase worsens temperature compensation

Engineering Contradiction:

Improvesignal levelVSAvoidtemperature variation

Core Design Contradiction:

PowerVSTemperature

Solution Approach 1:

The patent replaces the traditional mechanical/structural temperature compensation approach with a material-property-based solution. By using metal-dielectric composite layers with specific acoustic impedance ratios, the system passively compensates for temperature effects through the inherent thermal and acoustic properties of the materials, enabling high-power operation without degrading temperature compensation performance.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 solution provides simultaneous temperature compensation and spurious resonance suppression, improving acoustic isolation and reducing energy loss, thereby enhancing the performance and longevity of SMR-BAW resonators.

Implementation Method 1

Layers of materials with high and low acoustic impedance alternate in the Bragg mirror creating a layer stack which reflects acoustic waves back to the active part

Methodology Applied

Scientific EffectAcoustic impedance mismatch: Reflection

Implementation Method 2

SiO2 has a positive temperature coefficient of frequency (TCF) near room temperature, which means that SiO2 stiffens with increased temperature

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

The active part of the SMR-BAW resonator consists of a top electrode, a piezo layer, and a bottom electrode

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 4

improving heat transfer

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS11233498B2Bragg mirror, resonator and filter device

Publication Date: 2022.01.25 HUAWEI TECH CO LTD

AI summary

Disclosed is a Bragg mirror, a resonator and a filter device comprised thereof. The Bragg mirror comprises a stack of plurality of layers arranged in an axial direction, wherein the plurality of layers comprises at least one first layer comprising, in a radial direction, a first material and a second material, wherein the first material is a first metal and the second material is a different material with respect to the first material, and wherein the first material is radially embedded by the second material in the first layer, or vice versa. The resonator comprises a top electrode, a bottom electrode, a piezo electric layer arranged between the top electrode and the bottom electrode, a substrate, and a Bragg mirror arranged between the bottom electrode and the substrate.