BAW Resonator Layer Stack Tuning for Frequency and Q Control

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Solution Overview

Problem

Existing bulk acoustic wave (BAW) devices face challenges in energy efficiency due to losses in acoustic wave energy and irregularities in the crystalline structure of piezoelectric layers, which affect the quality factor (Q) and resonant frequency tuning, particularly in handheld wireless devices where energy efficiency is critical.

Innovation Solution

The BAW device incorporates a piezoelectric layer with varying thicknesses in different regions to create resonators with distinct resonance frequencies, coupled with an acoustic mirror to reduce energy loss and lateral acoustic features to suppress spurious modes, while ensuring a regular crystalline structure for enhanced energy conversion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a uniform piezoelectric layer is used in BAW devices, then manufacturing is simplified, but resonant frequency tuning and energy efficiency are compromised

Engineering Contradiction:

Improveresonant frequency tuningVSAvoidpiezoelectric layer structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent implements a piezoelectric layer with non-uniform thickness, where different regions have different thicknesses to achieve distinct resonant frequencies. This local variation in thickness allows each region to be optimized for specific frequency requirements while maintaining overall device functionality, directly resolving the contradiction between manufacturing simplicity and resonant frequency tuning precision.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If acoustic energy is contained in the piezoelectric material, then resonant frequency tuning improves, but energy loss increases

Engineering Contradiction:

Improveresonant frequency tuningVSAvoidacoustic wave energy

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

The patent converts the potentially harmful acoustic energy loss into a beneficial feature by using the contained acoustic energy to enhance resonant frequency tuning. The piezoelectric layer's structure is designed to contain acoustic energy in specific regions, which initially appears to cause energy loss but actually improves the quality factor and frequency selectivity by reinforcing the resonant modes.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Use of energy by moving object

If mode suppression is enhanced in BAW resonators, then energy efficiency improves, but device complexity increases

Engineering Contradiction:

Improveenergy efficiencyVSAvoidresonator structure

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The patent achieves mode suppression by carefully controlling the thickness parameter of the piezoelectric layer in different regions. By adjusting the thickness to specific values, the device suppresses unwanted acoustic modes while maintaining the desired resonant frequencies. This parameter-based approach to mode suppression improves energy efficiency without requiring additional complex structural elements.

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 configuration enhances the energy efficiency of BAW devices by tuning resonant frequencies, reducing energy loss, and improving the quality factor, thereby meeting the stringent energy requirements of handheld wireless devices.

Implementation Method 1

SAW and BAW resonators convert electromagnetic waves into acoustic waves and back into electromagnetic waves using inter-digitated electrodes on top of a piezoelectric material or layers of piezoelectric material sandwiched between electrodes, respectively.

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

an acoustic mirror on a second side of the piezoelectric layer

Methodology Applied

Scientific EffectAcoustic reflection: Reflection

Data Source

PatentUS20240039510A1Acoustic wave devices with resonance-tuned layer stack and method of manufacture

Publication Date: 2024.02.01 RF360 SINGAPORE PTE LTD

AI summary

A bulk acoustic wave (BAW) device with resonance-tuned layer stack is disclosed. The BAW device includes two acoustic resonators with top electrodes in different regions on a top side of a piezoelectric layer. The BAW device includes an acoustic mirror on a bottom side of the piezoelectric layer and a bottom electrode between the acoustic mirror and the piezoelectric layer. The piezoelectric layer includes a recess in a second region on the bottom side of the piezoelectric layer. The bottom electrode is disposed in the recess on the bottom side of the piezoelectric layer. A distance between a first top electrode in a first region and the bottom electrode may be greater than a distance between a second top electrode in the second region and the bottom electrode.