LVBAW Resonator Structure for Tunable High-Frequency Confinement

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Solution Overview

Problem

Existing MEMS resonators, such as bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices, face challenges in frequency tunability, integration with CMOS, and robustness for high-power applications, with SAW devices limited to <1 GHz and requiring costly wafer-level packaging, while contour mode resonators have risks during vibration or shock tests.

Innovation Solution

A laterally vibrating bulk acoustic wave (LVBAW) resonator architecture with a piezoelectric plate sandwiched between metal layers and Bragg mirrors, featuring an interdigital transducer and side reflectors, allowing for full lithographic tunability, CMOS integration, and reduced footprint, with the electrode pitch determining the resonance frequency and the thickness of the piezoelectric and metal layers less than half the pitch.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If SAW devices are used for acoustic wave resonance, then they can operate at lower frequencies, but they are limited to frequencies below 1 GHz and require costly wafer-level packaging

Engineering Contradiction:

Improveoperational reliabilityVSAvoidfrequency range adaptability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the fundamental operating parameters by transitioning from surface acoustic wave (SAW) mode to laterally vibrating bulk acoustic wave (LVBAW) mode. This parameter change enables operation above 1 GHz while eliminating the need for wafer-level packaging, as the LVBAW resonator can be integrated using standard CMOS packaging processes.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the SAW mechanical system with an LVBAW system that uses a piezoelectric plate sandwiched between metal layers with interdigital transducers. This substitution allows the resonator to achieve higher frequencies and simpler packaging requirements while maintaining operational reliability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If contour mode resonators are used to achieve lateral vibration, then they can provide lateral vibration mode operation, but they have risks during vibration or shock tests

Engineering Contradiction:

Improvelateral vibration operationVSAvoidrobustness under vibration and shock

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent uses a composite structure consisting of a piezoelectric plate sandwiched between metal layers with interdigital transducers. This composite design provides mechanical robustness during vibration and shock tests while maintaining lateral vibration mode operation, overcoming the fragility issues of contour mode resonators.

Inventive Principle:

Principle #40Composite materials

3Loss of energy

If the combined thickness of metal layers and piezoelectric layer is made less than the pitch of interlocking fingers, then energy confinement is improved, but the manufacturing precision requirements increase

Engineering Contradiction:

Improveenergy leakageVSAvoidlayer thickness control

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The patent optimizes the thickness parameters of the metal layers and piezoelectric layer to be less than the pitch of the interlocking fingers. This parameter optimization achieves effective energy confinement and reduced energy leakage while maintaining compatibility with standard manufacturing processes through careful parameter selection.

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

LVBAW resonators achieve frequency tunability, improved quality factor, and reduced energy leakage, enabling efficient energy confinement and enhanced performance for applications above 1 GHz with smaller footprints and reduced manufacturing costs, making them suitable for high-power applications.

Implementation Method 1

a piezoelectric plate sandwiched between metal layers

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

laterally vibrating bulk acoustic wave (LVBAW) resonator includes a piezoelectric plate sandwiched between metal layers with an upper metal layer patterned into an interdigital transducer

Methodology Applied

Scientific EffectBulk acoustic wave generation: Acoustic Radiation Pressure

Implementation Method 3

LVBAW resonators achieve frequency tunability, improved quality factor, and reduced energy leakage, enabling efficient energy confinement

Methodology Applied

Scientific EffectBragg reflection: Bragg Diffraction

Data Source

PatentUS20230253951A1Laterally Vibrating Bulk Acoustic Wave Resonator

Publication Date: 2023.08.10 TEXAS INSTRUMENTS INC

AI summary

A laterally vibrating bulk acoustic wave (LVBAW) resonator includes a piezoelectric plate sandwiched between first and second metal layers. The second metal layer is patterned into an interdigital transducer (IDT) with comb-shaped electrodes having interlocking fingers. The width and pitch of the fingers of the electrodes determine the resonant frequency. A combined thickness of the first and second metal layers and the piezoelectric layer is less than the pitch of the interlocking fingers.