Single-Crystal BAW Structure With Acoustic Reflector for High Q

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Solution Overview

Problem

The existing bulk acoustic wave (BAW) structures face challenges in achieving high Q values due to the difficulty in growing single crystal piezoelectric material layers, which affects the reliability of BAW filters, especially in portable electronic products where strict frequency specifications are required.

Innovation Solution

A BAW structure is designed with a single crystal piezoelectric material layer, where the second electrode covers the entire surface of the layer and an acoustic reflector is disposed on one or both surfaces of the electrodes, enhancing the Q value by eliminating substrate constraints and allowing for miniaturization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional piezoelectric material layer growth methods are used, then manufacturing is easier, but the Q value of the BAW filter decreases

Engineering Contradiction:

ImproveQ valueVSAvoidmanufacturing difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent extracts the substrate from the final BAW structure by growing the piezoelectric material layer on a sacrificial substrate and then removing the substrate. This extraction eliminates the substrate's negative impact on the Q value while maintaining the benefits of controlled material growth during manufacturing.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the physical state and properties of the piezoelectric material layer by growing it as a single crystal on a sacrificial substrate, then removing the substrate to achieve single-crystal-like properties in the final structure. This parameter change transforms the material from polycrystalline to single-crystal equivalent, significantly improving the Q value.

Inventive Principle:

Principle #35Parameter changes

2Volume of moving object

If the BAW structure is miniaturized for portable devices, then it becomes suitable for portable electronics, but the frequency specification requirements become stricter

Engineering Contradiction:

Improvedevice sizeVSAvoidfrequency specification

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The patent uses a sacrificial substrate that is removed after serving its purpose during the growth process. This disposable substrate enables precise control of the piezoelectric material layer during manufacturing, allowing for miniaturized devices with strict frequency specifications to be achieved.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of manufacture

If the piezoelectric material layer is grown on a substrate, then growth control is easier, but the Q value is reduced due to substrate constraints

Engineering Contradiction:

Improvegrowth controlVSAvoidQ value

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent segments the manufacturing process into two distinct phases: growth phase where the piezoelectric material layer is grown on a substrate for easy control, and final phase where the substrate is removed to eliminate constraints. This segmentation allows both easy manufacturing control and high Q value to be achieved.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The sacrificial substrate acts as an intermediary during the manufacturing process, enabling controlled growth of the piezoelectric material layer. After serving its mediating function, the substrate is removed, leaving the high-Q piezoelectric layer without substrate constraints.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 improves the Q value of the BAW structure, enabling it to meet the size requirements for miniaturized products and provide reliable filtering performance across various frequency ranges.

Implementation Method 1

When an electric field is applied to the metal electrodes, the piezoelectric material layer generates an acoustic wave due to vibration

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

the acoustic wave oscillates in the piezoelectric material layer to form a standing wave, so as to reduce energy loss

Methodology Applied

Scientific EffectAcoustic resonance: Resonance

Implementation Method 3

an acoustic reflector is disposed on one or both surfaces of the electrodes, enhancing the Q value

Methodology Applied

Scientific EffectAcoustic reflection: Reflection

Data Source

PatentUS11646712B2Bulk acoustic wave structure and bulk acoustic wave device

Publication Date: 2023.05.09 RICHWAVE TECH CORP

AI summary

A bulk acoustic wave (BAW) structure includes a single crystal piezoelectric material layer, a first electrode, a second electrode and an acoustic reflector. The first and second electrodes are respectively located on a first surface and a second surface of the single crystal piezoelectric material layer. The area of the second electrode is greater than or equal to that of the second surface of the single crystal piezoelectric material layer, and the contact area of the single crystal piezoelectric material layer with the second electrode is equal to the area of the second surface of the single crystal piezoelectric material layer. The acoustic reflector is disposed on a surface of the first electrode.