Mo-W Electrode Composition in Bulk Acoustic Wave Resonators

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Solution Overview

Problem

Current film bulk acoustic resonators (FBARs) face challenges in achieving optimal electrical resistance, acoustic impedance, and process efficiency due to limitations in electrode materials, particularly with the use of molybdenum-tungsten alloys, where increasing tungsten content complicates deposition and patterning processes while reducing acoustic impedance.

Innovation Solution

The use of a molybdenum-tungsten alloy with a weight ratio of molybdenum to tungsten between 3:1 and 1:3, oriented on a (110) crystal face, as electrodes in FBARs, improves electrical resistance, acoustic impedance, and process efficiency, and includes a seed layer of Ti or TiW to enhance sheet resistance properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If tungsten content in molybdenum-tungsten alloy is increased to reduce acoustic impedance, then acoustic impedance is improved, but deposition and patterning processes become more complicated

Engineering Contradiction:

Improveacoustic impedanceVSAvoiddeposition and patterning process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies parameter changes by optimizing the composition ratio of molybdenum to tungsten in the alloy. Specifically, it defines a weight ratio range of 3:1 to 1:3 between molybdenum and tungsten, which balances the acoustic impedance characteristics with manufacturability. This parameter optimization resolves the contradiction by finding the optimal compositional point that satisfies both acoustic performance and processing ease requirements.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If molybdenum-tungsten alloy is used to improve electrical resistance and acoustic impedance, then electrical and acoustic characteristics are improved, but process efficiency decreases

Engineering Contradiction:

Improveelectrical resistance and acoustic impedanceVSAvoidprocess efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent resolves this contradiction through parameter changes by establishing specific compositional ranges for the molybdenum-tungsten alloy (weight ratio 3:1 to 1:3) and specifying a crystal face orientation of (110). These parameter specifications ensure that the alloy maintains good electrical resistance and acoustic impedance while preserving deposition and patterning efficiency, thus balancing performance improvement with manufacturing productivity.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If electrode material composition is optimized to enhance Kt2 and attenuation characteristics, then resonator performance is improved, but manufacturing complexity increases

Engineering Contradiction:

ImproveKt2 and attenuation characteristicsVSAvoidelectrode material composition

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies parameter changes by defining a specific weight ratio range (3:1 to 1:3) for molybdenum to tungsten and specifying the (110) crystal face orientation. These controlled parameter specifications enable optimization of Kt2 and attenuation characteristics while avoiding excessive manufacturing complexity, as the parameters remain within achievable ranges for standard fabrication processes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite materials by using a molybdenum-tungsten alloy instead of pure metals. This composite approach allows tuning of electrical, acoustic, and mechanical properties through composition control, thereby improving resonator performance (Kt2 and attenuation) while managing the complexity through systematic alloy design rather than complex multi-layer structures.

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 enhances the Kt2 and attenuation characteristics of the resonator, improves temperature coefficient of frequency (TCF) stability, and maintains efficient deposition and patterning processes, leading to improved performance in acoustic impedance and electrical characteristics.

Implementation Method 1

when electric energy is applied to the first and second electrodes to induce an electric field in the piezoelectric layer, the electric field may generate a piezoelectric phenomenon in the piezoelectric layer to allow the resonant portion to vibrate in a predetermined direction. As a resultant, a bulk acoustic wave is generated

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS10439589B2Bulk acoustic wave resonator and filter including the same

Publication Date: 2019.10.08 SAMSUNG ELECTRO MECHANICS CO LTD

AI summary

A bulk acoustic wave resonator includes a substrate, a first electrode and a second electrode formed on the substrate, and a piezoelectric layer provided between the first electrode and the second electrode. Either one or both of the first electrode and the second electrode include a molybdenum-tungsten alloy having a weight ratio of molybdenum to tungsten in a range of 3:1 to 1:3.