Ph.D. Presentation
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Transcript of Ph.D. Presentation
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
Piezoelectric MEMS Accelerometer - PiMEMS
Christian Gammeltoft Hindrichsen
Supervisor: Professor, Erik V. Thomsen
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
Piezoelectric Accelerometer
Motivation
Design
Fabrication
Characterization
Conclusion
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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:
Plate
Membrane
Fixed frame
Piezoelectric
SpringMass
acceleration
F = m·a
Accelerometer operating in bending mode
V
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
1 10 100 1000Price [$]
Per
form
ance
MEMS Capacitive(surface micromachined)
Movement monitoringand event detection
Piezoelectric
Measurement and control
MEMS Capacitive(bulk micromachined)
MEMSPiezoelectric
Special applications:PiezoresistiveOpticalServo
MotivationMotivation
Accelerometer market
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionMotivationMotivation
Smaller
Lower fabrication costs
Higher integration
Comparable performance
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionMotivationMotivation
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
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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
Goal
MotivationMotivation
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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]
ChargeSensitivity[pC/g]
Voltagesensitivity[mV/g]
Resonancefrequency[kHz]
Square Design
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionDesignDesign
x
y
x
z
Dimensions:
Membrane radius: 1.8 mm
Seismic mass: 6 mg
Silicon membrane: 20 μm
PZT thickness: 9 – 27 μmMass
Membrane Membrane
PZT
Electrodes
Circular Design
x
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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
>1 mm
10 mm
Hindrichsen et al., Advantages of PZT Thick Film for MEMS Sensors , Sensors and Actuators A (in review)
Sensitivity-Resonance Balance
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionDesignDesign
xy
z
FEM model
Proposal for Triaxial Design
x
y
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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)
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionFabricationFabrication
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
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionFabricationFabrication
Diffusion barrier layer (DBL)
DBL
PZT
Si
31-mode
33-mode
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionFabricationFabrication
Stylus Profiler Atomic Force Microscopy
PZT
Silicon
Hindrichsen et al., Investigation of Top/Bottom Electrode and Diffusion Barrier Layer for PZT Thick Film MEMS Sensors , Ferroelectrics (2009)
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionFabricationFabrication
Top electrode
Lift-off process
20 μm thick photo resist
No sonication
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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)
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionFabricationFabrication
LTCC on front side
Pyrex wafer on backside
Packaging
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization
Impedance Sweep (dielectric, mechanical, piezoelectric)
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization
Impedance Sweep (dielectric, mechanical, piezoelectric)
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization
Coupling Coefficient (dielectric, mechanical, piezoelectric)
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization
Shaker
Accelerometer
Wave Generator
Charge Amplifier
LabView
Shaker Setup
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization
Frequency Sweep (mechanical)
Quality factor: 150 - 250
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization
Resonance Frequency (mechanical)
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization
Charge Sensitivity (mechanical, piezoelectric)
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusionCharacterizationCharacterization
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.
ChargeSensitivity[pC/g]
Voltagesensitivity[mV/g]
Resonancefrequency[kHz]
MotivationMotivationPiezoelectric AccelerometerPiezoelectric Accelerometer DesignDesign FabricationFabrication CharacterizationCharacterization ConclusionConclusion
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, ...