Multilayer SAW Resonator Structure for Thermal Stability and Reflection

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Solution Overview

Problem

Conventional surface acoustic wave (SAW) resonators with low thermal conductivity piezoelectric layers, such as lithium tantalate and lithium niobate, experience heat dissipation issues and frequency shifts due to thermal expansion, leading to high-frequency spurious signals and poor reflection characteristics.

Innovation Solution

A multilayer piezoelectric substrate (MPS) structure is implemented, featuring a silicon substrate bonded to a piezoelectric layer with optimized cut angles and propagation directions, along with an adhesive layer, to enhance thermal dissipation and suppress spurious signals, thereby improving reflection characteristics across a broader frequency range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a piezoelectric layer with low thermal conductivity (lithium tantalate or lithium niobate) is used in a conventional SAW resonator, then the piezoelectric properties are maintained, but heat dissipation is insufficient causing thermal expansion and frequency shifts

Engineering Contradiction:

Improvethermal dissipationVSAvoidfrequency stability

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent applies composite materials by bonding a piezoelectric layer (lithium tantalate or lithium niobate) to a silicon substrate. The silicon substrate provides high thermal conductivity for heat dissipation, while the piezoelectric layer maintains the necessary piezoelectric properties. This composite structure resolves the contradiction by combining materials with complementary thermal and piezoelectric characteristics.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent segments the resonator structure into distinct functional layers: a piezoelectric layer for generating acoustic waves and a silicon substrate for thermal management. This segmentation allows each layer to optimize its specific function without compromising the other, enabling effective heat dissipation while maintaining piezoelectric performance.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If a silicon substrate with conventional cut angle and propagation direction is used in the MPS structure, then the structure is simple, but large amounts of high-frequency spurious signals occur

Engineering Contradiction:

Improvesubstrate configurationVSAvoidspurious signals

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the parameters of the silicon substrate by using non-conventional cut angles (such as 35° or 45° off-cut from <100> plane) and specific propagation directions relative to the crystal axes. This parameter optimization suppresses spurious signals at high frequencies while maintaining the structural simplicity of the MPS design.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by optimizing specific regions of the silicon substrate (cut angle and propagation direction) to suppress spurious signals in particular frequency ranges. This targeted optimization addresses the spurious signal issue without requiring complete redesign of the entire device structure.

Inventive Principle:

Principle #3Local quality

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 MPS structure effectively reduces thermal-induced frequency shifts and spurious signals, achieving better thermal dissipation and reflection characteristics, particularly at high frequencies, by utilizing silicon substrates with specific cut angles and propagation directions.

Implementation Method 1

A silicon substrate can be bonded to the lower surface of the piezoelectric substrate of the SAW resonators opposite the upper surface of the wafer of the piezoelectric material defining a multilayer piezoelectric substrate (MPS) structure... the silicon having a cut direction and/or acoustic wave propagation direction which is different from those of a silicon substrate

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

Embodiments of the present disclosure relate to surface acoustic wave (SAW) resonators comprising a multilayer piezoelectric substrate (MPS) for enhanced reflection characteristics of the SAW resonators

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Implementation Method 3

A surface acoustic wave (SAW) device includes a piezoelectric layer such as lithium tantalate or lithium niobate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20230104405A1Acoustic wave device with multilayer piezoelectric substrate for reduced spurious signals

Publication Date: 2023.04.06 SKYWORKS SOLUTIONS INC

AI summary

An acoustic wave resonator is disclosed. The acoustic wave resonator can include a plurality of interdigital transducer electrodes and a multilayer piezoelectric substrate (MPS) adjacent the plurality of interdigital transducer electrodes. The MPS includes a first substrate layer of a piezoelectric material, and a second substrate layer of silicon that is bonded to the first layer. The silicon has a cut direction and/or acoustic wave propagation direction that is different from those of a silicon substrate. The silicon substrate has a cut direction and a propagation direction property defined by the silicon cut angle of {100} and the propagation direction <110>.