Single-Crystal BAW Resonator Structure for Thin-Film 5 GHz RF Filters

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Solution Overview

Problem

Current bulk acoustic wave resonators using polycrystalline piezoelectric thin films face degradation at frequencies above 5 GHz due to poor quality at thin thicknesses, limiting their performance in high-frequency applications.

Innovation Solution

The use of single crystalline or epitaxial piezoelectric thin films grown on compatible substrates, combined with advanced manufacturing processes, to create high-quality bulk acoustic wave resonators with enhanced performance and efficiency for RF filters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If polycrystalline piezoelectric thin films are used in bulk acoustic wave resonators, then manufacturing is simpler and cost-effective, but quality factor and electro-mechanical coupling degrade at frequencies above 5 GHz due to poor quality at thin thicknesses

Engineering Contradiction:

Improvequality factorVSAvoidfilm quality at thin thicknesses

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent changes the fundamental parameter of crystal structure from polycrystalline to single crystal, enabling the material to maintain high quality factor and electro-mechanical coupling at frequencies above 5 GHz while being manufacturable at thin thicknesses required for high-frequency operation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite structure combining single crystal piezoelectric material with compatible crystalline substrates, leveraging the superior properties of single crystal materials for high-frequency performance while using substrate integration techniques to maintain manufacturing feasibility

Inventive Principle:

Principle #40Composite materials

2Reliability

If single crystalline piezoelectric thin films are used, then quality factor and electro-mechanical coupling improve for high-frequency operation, but manufacturing complexity and difficulty increase

Engineering Contradiction:

Improvequality factorVSAvoidmanufacturing process complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent uses compatible crystalline substrates as intermediaries to grow single crystal piezoelectric thin films, enabling the complex single crystal structure to be manufactured through controlled growth processes on suitable substrate materials rather than direct fabrication

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent makes single crystal piezoelectric films universally applicable to high-frequency resonator manufacturing by developing growth techniques on compatible substrates that can be integrated into existing manufacturing workflows, making the complex material accessible for practical device fabrication

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Speed

If thin film thickness is reduced to achieve higher frequencies, then resonator frequency increases, but polycrystalline film quality degrades quickly below 0.5 um thickness

Engineering Contradiction:

Improveresonator frequencyVSAvoidfilm quality

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The patent changes the crystal structure parameter from polycrystalline to single crystal, which fundamentally alters how the material maintains quality at reduced thicknesses, enabling thin films to support higher frequencies without the rapid quality degradation that plagues polycrystalline materials below 0.5 micrometer thickness

Inventive Principle:

Principle #35Parameter changes

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 approach enables high-performance RF filters with improved quality factor and electro-mechanical coupling, capable of operating effectively at frequencies up to 5 GHz and beyond, while maintaining cost-effectiveness and simplicity in manufacturing.

Implementation Method 1

single crystal piezoelectric material formed overlying the air cavity and a portion of the enhancement layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

bulk acoustic wave resonator devices

Methodology Applied

Scientific EffectAcoustic resonance: Resonance

Data Source

PatentUS11316496B2Method and structure for high performance resonance circuit with single crystal piezoelectric capacitor dielectric material

Publication Date: 2022.04.26 AKOUSTIS TECHNOLOGIES CORP

AI summary

A method and structure for a single crystal acoustic electronic device. The device includes a substrate having an enhancement layer formed overlying its surface region, a support layer formed overlying the enhancement layer, and an air cavity formed through a portion of the support layer. A single crystal piezoelectric material is formed overlying the air cavity and a portion of the enhancement layer. Also, a first electrode material coupled to the backside surface region of the crystal piezoelectric material and spatially configured within the cavity. A second electrode material is formed overlying the topside of the piezoelectric material, and a dielectric layer formed overlying the second electrode material. Further, one or more shunt layers can be formed around the perimeter of a resonator region of the device to connect the piezoelectric material to the enhancement layer.