Bulk Acoustic Resonator Non-Piezoelectric Layer Mode Confinement

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Solution Overview

Problem

Bulk acoustic wave (BAW) resonators face acoustic losses at the boundaries, which degrade mode confinement in the active region of the resonator, leading to energy loss and reduced performance.

Innovation Solution

A BAW resonator structure is designed with a non-piezoelectric layer adjacent to the piezoelectric layer, where the overlap of the non-piezoelectric layer with the electrode is optimized to be greater than or equal to the inverse of the attenuation constant or an integer multiple of a quarter-wavelength of the propagating eigenmode, enhancing mode confinement and reducing acoustic losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If acoustic resonators use piezoelectric material between conductive plates to generate acoustic waves, then electrical signals can be converted to acoustic waves, but lateral propagation modes and higher order harmonic mixing products are generated that have a deleterious impact on functionality

Engineering Contradiction:

Improveelectrical to acoustic wave conversion efficiencyVSAvoidlateral propagation modes and higher order harmonic mixing products

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

A non-piezoelectric layer is introduced as an intermediary between the piezoelectric layer and the second electrode. This intermediate layer acts as a boundary that suppresses the generation of lateral propagation modes and higher order harmonic mixing products while allowing the primary acoustic wave generation function to continue. The non-piezoelectric layer has specific acoustic impedance properties that create destructive interference for unwanted modes.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The acoustic impedance of the layer adjacent to the piezoelectric layer is modified by using a non-piezoelectric material with different acoustic properties. This parameter change in acoustic impedance creates a boundary condition that suppresses lateral mode propagation and higher order harmonics while maintaining efficient electrical to acoustic wave conversion in the piezoelectric layer.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If the resonator structure is simplified without additional layers, then device complexity is reduced, but acoustic losses at boundaries increase and mode confinement deteriorates

Engineering Contradiction:

Improvenumber of layers in resonator structureVSAvoidacoustic losses at boundaries

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The non-piezoelectric layer serves as a boundary intermediary that reduces acoustic energy loss at the interface between the piezoelectric layer and the second electrode. By providing a transition layer with optimized acoustic impedance, it prevents abrupt boundary reflections that would cause energy loss and mode leakage.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The resonator structure uses a composite arrangement combining piezoelectric and non-piezoelectric materials in specific layers. This composite structure leverages the piezoelectric properties of one material for wave generation while using the acoustic impedance properties of the non-piezoelectric material to reduce boundary losses and improve mode confinement.

Inventive Principle:

Principle #40Composite materials

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 significantly improves the quality factor and parallel impedance of the BAW resonator, reducing energy loss and enhancing performance by effectively confining acoustic modes within the active region.

Implementation Method 1

Acoustic transducers, in particular, convert electrical signals to acoustic waves and acoustic waves to electrical signals using inverse and direct piezoelectric effects

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

an overlap of the non-piezoelectric layer with the second electrode has a width substantially equal to an integer multiple of one-quarter wavelength of a first propagating eigenmode in the non-piezoelectric layer, or greater than or equal to an inverse of an attenuation constant (1/k) of a first evanescent eigenmode in the non-piezoelectric layer

Methodology Applied

Scientific EffectAcoustic mode confinement:

Data Source

PatentUS20120319530A1Bulk acoustic resonator comprising non-piezoelectric layer

Publication Date: 2012.12.20 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

In a representative embodiment, a bulk acoustic wave (BAW) resonator structure comprises: a first electrode disposed over a substrate; a first piezoelectric layer disposed over the first electrode; a second electrode disposed over the first piezoelectric layer, wherein c-axis orientations of crystals of the first piezoelectric layer are substantially aligned with one another; a second piezoelectric layer disposed over the second electrode; a non-piezoelectric layer; and a third electrode disposed over the second piezoelectric layer.