Ph.D. Presentation

MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion

Piezoelectric MEMS Accelerometer - PiMEMS

Christian Gammeltoft Hindrichsen

Supervisor: Professor, Erik V. Thomsen

Piezoelectric Accelerometer

Motivation

Design

Fabrication

Characterization

Conclusion

Piezoelectric Accelerometer

What is piezoelectricity and how does an accelerometer work?

MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionPiezoelectric AccelerometerPiezoelectric Accelerometer

http://electronicdesign.com/

Piezoelectric effect

MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionPiezoelectric AccelerometerPiezoelectric Accelerometer

Cantilever

Bridge

MEMS springs:

Membrane

Fixed frame

Piezoelectric

SpringMass

acceleration

F = m·a

Accelerometer operating in bending mode

Motivation

Why use MEMS and what is state-of-the-art?

MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionMotivationMotivation

Applications

Bulk PZT Thick Film PZT Thin Film Nanotech1 mm 100 μm 10 μm 1 μm 100 nm

1 10 100 1000Price [$]

MEMS Capacitive(surface micromachined)

Movement monitoringand event detection

Piezoelectric

Measurement and control

MEMS Capacitive(bulk micromachined)

MEMSPiezoelectric

Special applications:PiezoresistiveOpticalServo

MotivationMotivation

Accelerometer market

Smaller

Lower fabrication costs

Higher integration

Comparable performance

Beeby et al. (2000)

Kunz et al. (2001) Yu et al. (2003)

12 x 1216-7.6Beeby et al.

7 x 722-0.5Kunz et al.

4 x 40.190.4722Yu et al.

Chipsize[mm]

ChargeSensitivity[pC/g]

Voltagesensitivity[mV/g]

Resonancefrequency[kHz]

State-of-the-art

The Toolbox The MEMS Accelerometer

Integrate PZT thick film and MEMS

Design process flow

Optimize cleanroom processes

Design, model, fabricate, characterizean accelerometer:

• Resonance frequency > 20 kHz

• Chip size in the mm-range

• Sensitivity as high as possible

MotivationMotivation

Design

What is special about this accelerometer?

MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionDesignDesign

Hindrichsen et al., Triaxial MEMS Accelerometer with PZT Thick Film, Journal of Electroceramics (2010)

Hindrichsen et al., Analytical Model of a PZT Thick Film Triaxial Accelerometer for Optimum Design, IEEE Sensors Journal (2009)

10 x 100.040.3612.5

Chipsize[mm]

Square Design

Dimensions:

Membrane radius: 1.8 mm

Seismic mass: 6 mg

Silicon membrane: 20 μm

PZT thickness: 9 – 27 μmMass

Membrane Membrane

Electrodes

Circular Design

Resonance frequency > 20 kHz

Chip size in the mm-range

Sensitivity as high as possible

Membrane < 10 μm: thin filmMembrane > 30 μm: thick film

DesignDesign

Hindrichsen et al., Advantages of PZT Thick Film for MEMS Sensors , Sensors and Actuators A (in review)

Sensitivity-Resonance Balance

FEM model

Proposal for Triaxial Design

Fabrication

How can we integrate PZT thick film and MEMS?

MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionFabricationFabrication

Oxidation

UV lithografy

Plasma etch

Metal evaporation

Screen printing

Lou-Møller et al., Screen-printed piezoceramic thick films for miniturised devices, Journal of Electroceramics (2007)

Silicon substrate

PZT thick filmBottom electrode

Silicon oxide

Top electrode

Process Flow

Fragile substrate

High temperature sintering

Diffusion barrier layer

Adhesion

Thin film electrodes

Wafer scale production

Reproducibility

Diffusion barrier layer (DBL)

31-mode

33-mode

Stylus Profiler Atomic Force Microscopy

Silicon

Hindrichsen et al., Investigation of Top/Bottom Electrode and Diffusion Barrier Layer for PZT Thick Film MEMS Sensors , Ferroelectrics (2009)

Top electrode

Lift-off process

20 μm thick photo resist

No sonication

58 accelerometers

4 mask fabrication process

Price estimation:

70 DKK per accelerometer

FabricationFabrication

Hindrichsen et al., Circular Piezoelectric Accelerometer for High Band Width Application, IEEE Sensor Conference (2009)

LTCC on front side

Pyrex wafer on backside

Packaging

Characterization

How is the accelerometer performing?

MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization

Capacitance [pF]

Couplings coefficient [%]

Resonance frequency [kHz]

Sensitivity [pC/g]

Quality factor

Range [g]

Impedance analyzer

Shaker setup

Accelerometer Specifications

PZT thickness: 9 μm – 27 μm

Dielectric, mechanical & piezoelectric properties

Impedance Sweep (dielectric, mechanical, piezoelectric)

Coupling Coefficient (dielectric, mechanical, piezoelectric)

Shaker

Accelerometer

Wave Generator

Charge Amplifier

LabView

Shaker Setup

Frequency Sweep (mechanical)

Quality factor: 150 - 250

Resonance Frequency (mechanical)

Charge Sensitivity (mechanical, piezoelectric)

Range and Linearity (dielectric, mechanical, piezoelectric)

MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionConclusionConclusion

Screen printed PZT on membranes with thicknesses down to 10 μm

Designed process flow

Diffusion barrier layer & thin film top electrode

Detailed analytical and FEM model

Square and circular design for triaxial sensing presented

Accelerometers are fabricated with high yield

Performance:

1.60.940.5732.5Model1.60.460.2825.8Measured2

Capacitance[nF]

0.190.4722Yu et al.

Thank you for your attention

Acknowledgement

Erik Thomsen, Thomas Pedersen, Christian Hansen, Jesper Olsen, Tobias, Jack Larsen, Johan Nagstrup, Ninia, Simon, Louise, Gustav, MEMS Applied Sensor Group, Rasmus Lou-Moller,

Karsten Hansen, Ferroperm, Ole Hansen, Lars Kofoed , Danchip people, Kristian Hvass, Anne, ...

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