Composite SAW Filter Substrate for Piezoelectric Thickness Uniformity

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Solution Overview

Problem

Conventional surface acoustic wave (SAW) filters face challenges in achieving high frequency stability and uniformity due to temperature variations, leading to significant thickness variations in the piezoelectric layer, which result in poor performance and high frequency drift in 5G communication systems.

Innovation Solution

A method involving the formation of a composite substrate with a centrally protruding structure on the base substrate, followed by bonding and thinning of the piezoelectric layer, which reduces thickness variation to less than 10%, using a combination of grinding and polishing techniques to achieve uniformity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the piezoelectric layer is thinned to achieve high frequency performance, then the frequency response improves, but the thickness uniformity deteriorates significantly

Engineering Contradiction:

Improvefrequency responseVSAvoidthickness uniformity

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The base substrate is pre-processed to form a centrally protruding structure before bonding the piezoelectric layer. This preliminary action creates a controlled thickness distribution that compensates for the thinning process, ensuring uniform final thickness despite the reduction to less than 5 μm for high frequency performance

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The base substrate is given non-uniform local quality through the centrally protruding structure, which has different heights in different regions. This local variation in substrate thickness compensates for the piezoelectric layer thinning, maintaining overall thickness uniformity while enabling the piezoelectric layer to be sufficiently thin for high frequency operation

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If conventional thinning and polishing techniques are used, then the processing is simple, but the thickness variation ranges from 20% to 40%

Engineering Contradiction:

Improveprocessing simplicityVSAvoidthickness variation

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The centrally protruding structure is formed on the base substrate before bonding and thinning operations. This preliminary structuring enables subsequent simple thinning and polishing to achieve much better thickness uniformity (less than 10%) compared to conventional methods, without adding significant process complexity

Inventive Principle:

Principle #10Preliminary action

3Speed

If the piezoelectric layer thickness is reduced for high frequency applications, then the frequency performance improves, but the frequency drift increases due to thickness variation

Engineering Contradiction:

Improvefrequency performanceVSAvoidfrequency drift

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The centrally protruding structure creates controlled local thickness variations in the base substrate that compensate for the thin piezoelectric layer. This ensures that even when the piezoelectric layer is thinned to less than 5 μm for high frequency performance, the overall composite structure maintains sufficient thickness uniformity to limit frequency drift to acceptable levels

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention uses a composite structure combining the base substrate with the centrally protruding structure and the piezoelectric layer. This composite design allows the substrate's thickness profile to compensate for the thin piezoelectric layer, achieving both high frequency performance and acceptable frequency stability

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 method significantly reduces thickness variation of the piezoelectric layer, improving frequency stability and yield, with frequency drift controlled to less than 500 ppm at 900 MHz and 1000 ppm at 1800 MHz, enhancing the performance of temperature-compensated SAW filters.

Implementation Method 1

connecting a first side of the base substrate having the centrally protruding structure to a piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

using a combination of grinding and polishing techniques to achieve uniformity

Methodology Applied

Scientific EffectAbrasion: Abrasion

Data Source

PatentUS20230188112A1Composite substrate of filter, method for making composite substrate of filter, and temperature compensated surface acoustic wave filter

Publication Date: 2023.06.15 FUJIAN JING AN OPTOELECTRONICS CO LTD

AI summary

A method for making a composite substrate of a filter includes: processing a base substrate to form a centrally protruding structure having a height that decreases in a radially outward direction from a center of the base substrate to an outer periphery of the base substrate; connecting a first side of the base substrate having the centrally protruding structure to a piezoelectric layer so as to obtain a multilayer substrate; and thinning the piezoelectric layer of the multilayer substrate followed by polishing a surface of the piezoelectric layer.