FBAR Protective Layer Structure for Higher Q and Coupling

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Solution Overview

Problem

Current manufacturing methods for film bulk acoustic resonators (FBARs) cause damage to the piezoelectric layer, negatively impacting the Q factor and coupling coefficient.

Innovation Solution

The acoustic resonator design includes a substrate with cavities, piezoelectric units with protective and intermediate metal layers, and a series unit connected in series with a bridge metal layer and electrode lead structure, all covered with passivation layers to prevent damage during manufacturing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If current manufacturing methods are used for depositing piezoelectric layers, then the manufacturing process can be completed, but the surface of the piezoelectric layer is damaged which negatively impacts the Q factor and coupling coefficient

Engineering Contradiction:

ImproveQ factor and coupling coefficientVSAvoidsurface damage to piezoelectric layer

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A protective layer is deposited over the piezoelectric layer before subsequent manufacturing steps. This preliminary protective action prevents surface damage during later etching and processing operations, thereby preserving the Q factor and coupling coefficient without requiring changes to the core manufacturing workflow.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The protective layer acts as a cushioning barrier that absorbs mechanical and chemical stress from subsequent manufacturing processes. This beforehand cushioning protects the fragile piezoelectric layer surface from damage that would otherwise occur during standard fabrication steps.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Reliability

If a protective layer is added to protect the piezoelectric unit, then the Q factor and coupling coefficient are improved, but the device complexity and manufacturing steps increase

Engineering Contradiction:

ImproveQ factor and coupling coefficientVSAvoidnumber of layers and manufacturing steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The protective layer serves multiple functions simultaneously: it protects the piezoelectric layer during manufacturing, provides a surface for subsequent electrode deposition, and maintains structural integrity throughout the device. This multi-functionality justifies the added complexity by eliminating the need for separate protective measures at each stage.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The protective layer acts as an intermediary between the piezoelectric layer and the harsh manufacturing environment. It mediates the interaction by providing a sacrificial barrier that can be processed along with subsequent layers, thereby protecting the sensitive piezoelectric material without requiring isolation or special handling procedures.

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

This design protects the piezoelectric unit from damage, enhancing the Q value and coupling coefficient of the acoustic resonator.

Implementation Method 1

By applying a voltage on the first electrode layer and the second electrode layer, the piezoelectric layer deforms. When an alternating voltage is applied, the piezoelectric element will generate piezoelectric effect and inverse piezoelectric effect, so that the signal is transmitted.

Methodology Applied

Scientific EffectInverse piezoelectric effect: Piezoelectric Effect

Implementation Method 2

When an alternating voltage is applied, the piezoelectric element will generate piezoelectric effect and inverse piezoelectric effect, so that the signal is transmitted.

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 3

a protective layer stacked on the piezoelectric unit

Methodology Applied

Scientific EffectPhysical barrier protection: Physical Containment

Data Source

PatentUS20240372528A1Acoustic resonator and method for manufacturing acoustic resonator

Publication Date: 2024.11.07 AAC TECHNOLOGIES PTE LTD

AI summary

An acoustic resonator and a manufacture method thereof. The acoustic resonator includes: a substrate having cavities; piezoelectric units one by one corresponding to the cavities, the piezoelectric units cover the cavities, and each piezoelectric unit includes a first electrode layer, a piezoelectric layer and a second electrode layer sequentially stacked from bottom to top; a protective layer stacked on the piezoelectric unit; a series unit having one end electrically connected to the first electrode layer of one of the piezoelectric units, and the other end electrically connected to the second electrode layer of another one of the piezoelectric units, so as to connect the two piezoelectric units in series. Compared with the 10 related art, the piezoelectric unit is protected from further risk of damages in subsequent manufacturing processes by providing a protective layer on the piezoelectric unit, so that the acoustic resonator has better Q value and coupling coefficient.