Thin-Film Bulk Acoustic Resonator Transfer for Improved TCF

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Solution Overview

Problem

Conventional RF technologies face limitations in manufacturing bulk acoustic wave resonators (BAWR) using polycrystalline piezoelectric thin films, which degrade quickly at thicknesses below 0.5 um, and single crystalline films are challenging to transfer, limiting their performance in high-frequency applications.

Innovation Solution

A method and structure for bulk acoustic wave resonator devices using a sacrificial layer, cavity bond transfer, or solidly mounted transfer processes, combined with energy confinement structures and temperature compensation layers, to enhance the quality factor (Q) and performance of single crystal resonators.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If polycrystalline piezoelectric thin films are used in BAWR, then manufacturing is easier and cost is lower, but film quality degrades quickly at thicknesses below 0.5 um

Engineering Contradiction:

Improveease of manufactureVSAvoidfilm quality

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the material parameter from polycrystalline to single-crystalline piezoelectric thin films, which fundamentally alters the film's structural properties and enables maintaining high quality at reduced thicknesses below 0.5 um, thus resolving the contradiction between ease of manufacture and film quality

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces an intermediary transfer process that enables single-crystalline films to be manufactured on suitable substrates and then transferred to the final BAWR device, bridging the gap between the difficulty of direct single-crystal fabrication and the need for high film quality

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If single crystalline piezoelectric thin films are used, then film quality and piezoelectric performance are improved, but transfer and manufacturing become challenging

Engineering Contradiction:

Improvepiezoelectric performanceVSAvoidtransfer difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent employs an intermediary transfer process where single-crystalline films are first grown on suitable substrates, then transferred to the final device structure. This intermediary step resolves the manufacturing challenge while preserving the high piezoelectric performance

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent performs preliminary actions by pre-growing single-crystalline films on appropriate substrates before transfer, allowing the complex single-crystal formation to occur under optimized conditions separate from the final device assembly, thus easing the overall manufacturing process

Inventive Principle:

Principle #10Preliminary action

3Speed

If piezoelectric thin film thickness is reduced below 0.5 um, then resonator frequency increases to 5 GHz and above, but polycrystalline film quality degrades

Engineering Contradiction:

Improveresonator frequencyVSAvoidfilm quality

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent changes the crystalline structure parameter from polycrystalline to single-crystalline, which enables the thin film to maintain high quality at reduced thicknesses required for 5 GHz and above resonator frequencies

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by using single-crystalline structure specifically in the piezoelectric thin film region where high quality is critical for maintaining performance at reduced thickness, while other parts of the device can use different materials optimized for their specific functions

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

Enables the production of reliable, high-performance single crystal acoustic filters and resonators with improved frequency response and temperature stability, suitable for RF filters and resonator devices.

Implementation Method 1

Bulk acoustic wave resonators (BAWR) using crystalline piezoelectric thin films

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS12573995B2Piezoelectric acoustic resonator with improved TCF manufactured with piezoelectric thin film transfer process

Publication Date: 2026.03.10 AKOUSTIS TECHNOLOGIES CORP

AI summary

A method and structure for a transfer process for an acoustic resonator device. In an example, a bulk acoustic wave resonator (BAWR) with an air reflection cavity is formed. A piezoelectric thin film is grown on a crystalline substrate. Patterned electrodes are deposited on the surface of the piezoelectric film. An etched sacrificial layer is deposited over the electrodes and a planarized support layer is deposited over the sacrificial layer. The device can include temperature compensation layers (TCL) that improve the device TCF. These layers can be thin layers of oxide type materials and can be configured between the top electrode and the piezoelectric layer, between the bottom electrode and the piezoelectric layer, between two or more piezoelectric layers, and any combination thereof. In an example, the TCLs can be configured from thick passivation layers overlying the top electrode and/or underlying the bottom electrode.