SAW Multi-Layer Substrate Using Spinel to Suppress Spurious Modes

Solution Overview

Problem

Surface acoustic wave (SAW) devices with piezoelectric layers on high impedance support substrates experience spurious responses due to back reflections, degrading frequency response, and high temperature issues due to low thermal conductivity of ceramic substrates like polycrystalline spinel.

Innovation Solution

Incorporating a support substrate with higher thermal conductivity than the ceramic layer, such as silicon, and using a polycrystalline spinel layer that scatters back reflections to suppress spurious modes, while directly bonding the ceramic and piezoelectric layers for improved thermal dissipation and structural integrity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a ceramic layer (polycrystalline spinel) is used as the support substrate for piezoelectric layers, then the device structure is simplified and manufacturing is easier, but the thermal conductivity is low causing high chip temperature

Engineering Contradiction:

Improveease of manufactureVSAvoidchip temperature

Core Design Contradiction:

Ease of manufactureVSTemperature

Solution Approach 1:

The support substrate is segmented into two distinct layers: a ceramic layer (polycrystalline spinel) providing mechanical support and ease of manufacture, and a separate heat dissipation layer (silicon or other high thermal conductivity material) positioned adjacent to the piezoelectric layer to conduct heat away from the active device region. This segmentation allows each layer to optimize its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The support substrate structure is designed as a composite of two different materials: the ceramic layer maintains the benefits of polycrystalline spinel (mechanical strength, ease of manufacturing), while the heat dissipation layer contributes high thermal conductivity. This composite approach combines the advantageous properties of different materials to simultaneously achieve ease of manufacture and effective heat dissipation.

Inventive Principle:

Principle #40Composite materials

2Device complexity

If a high impedance support substrate is used with piezoelectric layers, then the device structure is simplified, but spurious responses occur due to back reflections degrading frequency response

Engineering Contradiction:

Improvedevice complexityVSAvoidfrequency response

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The ceramic layer (polycrystalline spinel) serves as an intermediary layer between the piezoelectric layer and the high impedance support substrate. This intermediate ceramic layer disrupts the direct acoustic path that causes back reflections, thereby suppressing spurious responses while maintaining the simplified device structure provided by the high impedance substrate.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Strength

If ceramic layers with low thermal conductivity are used, then manufacturing is easier and structural integrity is maintained, but thermal dissipation is poor leading to high operating temperatures

Engineering Contradiction:

Improvestructural integrityVSAvoidthermal dissipation

Core Design Contradiction:

StrengthVSLoss of energy

Solution Approach 1:

The support substrate is segmented into two distinct layers: a ceramic layer (polycrystalline spinel) providing mechanical support and ease of manufacture, and a separate heat dissipation layer (silicon or other high thermal conductivity material) positioned adjacent to the piezoelectric layer to conduct heat away from the active device region. This segmentation allows each layer to optimize its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The support substrate structure is designed as a composite of two different materials: the ceramic layer maintains the benefits of polycrystalline spinel (mechanical strength, ease of manufacturing), while the heat dissipation layer contributes high thermal conductivity. This composite approach combines the advantageous properties of different materials to simultaneously achieve ease of manufacture and effective heat dissipation.

Inventive Principle:

Principle #40Composite materials

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 effectively reduces chip temperature and suppresses spurious modes, enhancing the thermal dissipation and frequency response of SAW devices by using a high thermal conductivity support substrate and a polycrystalline spinel layer that scatters back reflections.

Implementation Method 1

The support substrate has a higher thermal conductivity than the ceramic layer

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

using a polycrystalline spinel layer that scatters back reflections

Methodology Applied

Scientific EffectAcoustic wave scattering: Scattering

Implementation Method 3

A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11876501B2Acoustic wave device with multi-layer substrate including ceramic

Publication Date: 2024.01.16 SKYWORKS SOLUTIONS INC

AI summary

An acoustic wave device is disclosed. The acoustic wave device includes a support layer, a ceramic layer positioned over the support layer, a piezoelectric layer positioned over the ceramic layer, and an interdigital transducer electrode positioned over the piezoelectric layer. The support layer has a higher thermal conductivity than the ceramic layer. The ceramic layer can be a polycrystalline spinel layer. The acoustic wave device can be a surface acoustic wave device configured to generate a surface acoustic wave.