BAW Resonator Step Piezoelectric Layer for Lateral Wave Reflection

Solution Overview

Problem

Bulk acoustic wave (BAW) resonators face challenges in improving quality coefficient (Q performance) due to frame resonance and noise in wide band regions, which degrades performance and increases insertion loss, especially when frames are formed thicker than the active area using the same material as the upper electrode.

Innovation Solution

A bulk acoustic wave resonator design featuring a piezoelectric layer with a step portion and inclined surfaces, where the step portion's width satisfies specific wavelength conditions, and an upper electrode with a support member and connecting part, reduces lateral wave leakage and enhances reflection efficiency without a separate frame, thereby improving Q performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a frame is formed to be thicker than the active area using the same material as the upper electrode, then lateral wave reflection is improved, but the active area is reduced and noise occurs in wide band region

Engineering Contradiction:

Improvelateral wave reflectionVSAvoidactive area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The piezoelectric layer is segmented into different thickness regions: a first thickness in the active area and a second thickness (step portion) at the side, extending onto the lower electrode. This segmentation allows the side region to reflect lateral waves while the active area maintains full thickness for optimal performance, resolving the contradiction between reflection efficiency and active area preservation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The piezoelectric layer is designed with non-uniform thickness: the first thickness in the active area provides strong piezoelectric effect for resonance, while the second thickness (step portion) at the side provides lateral wave reflection. This local quality variation allows each region to perform its specific function optimally without compromising the other.

Inventive Principle:

Principle #3Local quality

2Reliability

If a frame is formed to be thicker than the active area using the same material as the upper electrode, then lateral wave reflection is improved, but noise occurs in wide band region

Engineering Contradiction:

Improvelateral wave reflectionVSAvoidnoise in wide band region

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The piezoelectric layer is segmented into different thickness regions: a first thickness in the active area and a second thickness (step portion) at the side, extending onto the lower electrode. This segmentation allows the side region to reflect lateral waves while the active area maintains full thickness for optimal performance, resolving the contradiction between reflection efficiency and active area preservation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The piezoelectric layer is designed with non-uniform thickness: the first thickness in the active area provides strong piezoelectric effect for resonance, while the second thickness (step portion) at the side provides lateral wave reflection. This local quality variation allows each region to perform its specific function optimally without compromising the other.

Inventive Principle:

Principle #3Local quality

3Loss of energy

If the piezoelectric layer includes a step portion extended from the side, then lateral wave leakage is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improvelateral wave leakageVSAvoidpiezoelectric layer structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The step portion is formed during the piezoelectric layer deposition process by controlling the deposition pattern, before the resonator is assembled. This preliminary formation of the reflection structure eliminates the need for separate frame components and reduces manufacturing complexity while effectively preventing lateral wave leakage.

Inventive Principle:

Principle #10Preliminary action

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 design effectively increases the quality factor (Q performance) by optimizing lateral wave reflection and reducing leakage, improving the resonator's ability to select desired frequency bands while minimizing noise and insertion loss.

Implementation Method 1

a piezoelectric layer disposed on a flat surface of the lower electrode

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

resonance energy should be confined in an active area of the BAW resonator by forming a frame around the resonator and reflecting lateral waves generated at the time of a resonance occurring in the resonator

Methodology Applied

Scientific EffectAcoustic wave reflection: Reflection

Data Source

PatentUS11476826B2Bulk acoustic wave resonator

Publication Date: 2022.10.18 SAMSUNG ELECTRO MECHANICS CO LTD

AI summary

A bulk acoustic wave resonator includes: a substrate; a membrane layer forming a cavity together with the substrate; a lower electrode disposed on the membrane layer; a piezoelectric layer disposed on a flat surface of the lower electrode; and an upper electrode covering a portion of the piezoelectric layer and exposing a side of the piezoelectric layer to air, wherein the piezoelectric layer includes a step portion extended from the side of the piezoelectric layer and disposed on the flat surface of the lower electrode.