Buried Temperature Compensating Layer in Resonator Electrodes

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Solution Overview

Problem

Resonator filters in cellular devices face issues with passband frequency shifts due to temperature and power fluctuations, leading to increased power absorption and battery drain, as conventional temperature compensation methods compromise acoustic coupling coefficients and contaminate piezoelectric materials.

Innovation Solution

Incorporating a buried temperature compensating layer with a positive temperature coefficient, such as boron silicate glass, within composite electrodes, which is isolated from the piezoelectric layer by a conductive interposer layer to offset negative temperature coefficients and prevent contamination, thereby enhancing the acoustic coupling coefficient and stability of resonator devices.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If oxide material is added to the piezoelectric layer for temperature compensation, then temperature stability is improved, but acoustic coupling coefficient is greatly compromised

Engineering Contradiction:

Improvetemperature stabilityVSAvoidacoustic coupling coefficient

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The electrode structure is segmented into multiple functional layers: a base electrode layer providing electrical connection, a temperature compensating layer for thermal stability, and a conductive interposer layer for acoustic coupling. This segmentation allows each layer to perform its specific function without compromising the others.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A conductive interposer layer is introduced as an intermediary between the temperature compensating layer and the piezoelectric layer. This interposer prevents oxygen diffusion from the oxide material into the piezoelectric material while maintaining electrical and acoustic connectivity, thus preventing contamination that would degrade the acoustic coupling coefficient.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If passband frequency is stabilized against temperature changes, then filter performance is improved, but device complexity increases

Engineering Contradiction:

Improvepassband frequency stabilityVSAvoidelectrode structure complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

Multiple functions are merged into a single integrated electrode structure: the base electrode layer provides electrical connection, the temperature compensating layer provides thermal stability, and the conductive interposer layer provides acoustic coupling and contamination prevention. This merging achieves passband stabilization without requiring separate components for each function.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The electrode is constructed as a composite structure with distinct material layers optimized for different functions: conductive materials for electrical connection, oxide materials for temperature compensation, and conductive interposer materials for acoustic coupling. This composite approach enables multifunctionality while managing complexity through material science rather than mechanical complexity.

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

This solution effectively stabilizes the passband frequency, reduces power absorption, and minimizes battery drain by maintaining the acoustic coupling coefficient while preventing contamination of the piezoelectric material, thus improving the operational efficiency and longevity of cellular device filters.

Implementation Method 1

The first electrode includes a buried temperature compensating layer having a positive temperature coefficient, and the piezoelectric layer has a negative temperature coefficient. The positive temperature coefficient of the temperature compensating layer offsets at least a portion of the negative temperature coefficient of the piezoelectric layer.

Methodology Applied

Scientific EffectTemperature coefficient compensation: Thermal Expansion

Implementation Method 2

A BAW resonator, for example, is an acoustic stack that generally includes a layer of piezoelectric material between two electrodes. Acoustic waves achieve resonance across the acoustic stack

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 3

the conductive interposer layer prevents oxygen contamination and enhances acoustic coupling

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Data Source

PatentUS8436516B2Resonator device including electrode with buried temperature compensating layer

Publication Date: 2013.05.07 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

An acoustic resonator device includes a composite first electrode on a substrate, a piezoelectric layer on the composite electrode, and a second electrode on the piezoelectric layer. The first electrode includes a buried temperature compensating layer having a positive temperature coefficient. The piezoelectric layer has a negative temperature coefficient, and thus the positive temperature coefficient of the temperature compensating layer offsets at least a portion of the negative temperature coefficient of the piezoelectric layer.