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PiezoelectricPiezoelectric MEMS MEMS EnergyEnergy HarvestersHarvesters
Danick Briand, D. Isarakorn, J. Pattanaphong, N.F. de Rooij
Team leader EnviroMEMS
Sensors, Actuators and Microsystems LabInstitute of MicroengineeringEPFL STI IMT-NENeuchâtel, Switzerland
http://samlab.epfl.chdanick.briand@epfl.ch
2Energy Harvesting Workshop | Biel - CH27.10.10| D.Briand
Sources of energy and harvesting approaches
From Dr. C Van Hoof, IMEC - Holst Center
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Towards miniaturization
From Dr. C Van Hoof, IMEC - Holst Center
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Vibration sources
S. Roundy et al., Computer Communications 26 (2003) 1131–1144
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Electrical parameters of energy harvesters
POWER
VOLTAGE
CURRENTLOAD
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Three ways to convert vibrationsPiezoelectric
Strain in piezoelectricmaterial causes a charge separation (voltage acrosscapacitor)
Capacitive
Change in capacitance causes either voltageor charge increase.
Inductive
Coil moves through magnetic field causing current in wire.
LoadVs
C RsPiezoelectric generator
Amirtharajah et. al., 1998
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Piezoelectric scavengers on silicon
Resonant type and impact type harvesters d31 or d33
Thick PZT sheet - Thick PZT films - Thin films (AlN, PZT)
F33 Mode (longitudinal)
V-
+
3
12
F33 Mode (longitudinal)
V-
+
3
12
V-
+V
-
+
-
+
-
+
3
12
3
12
31 Mode (transverse)
FV+-
3
12
31 Mode (transverse)
FV+-
3
12
FV+-
3
12
FV+-
3
12
3
12
30 µm
80-130 µm
LAAS-FR
InSensor
IMEC
1-10 µm
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Piezoelectric micro energy harvesters
1. Impact generators2. Resonant generators
- d31 mode (transverse) - d33 mode (longitudinal)- AlN- Epitaxial films
AlN
Impact
d31
d33
Epi-PZT
Auburn Univ.IMEC
IMTEK
SAMLAB
National Taiwan Univ.
9Energy Harvesting Workshop | Biel - CH27.10.10| D.Briand
MEMS power generator
Objective
Design and fabricate a MEMS-basedpiezoelectric power generator for the vibrational energy harvesting
Project description•Optimize the structure and load impedance to maximizethe efficiency of the vibration-to-electricity conversion
•Develop microfabrication processes
•Study the effect of viscous air damping on the power generation
•Design a piezoelectric converter circuit
•Develop an experiment set-up for power generating test
Pow
er N
eeds
Pow
er O
utpu
t
TimePresent
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Resonant type harvesterStructure design requirementsLow resonant frequency
The frequency range of the ambient vibrations 60-200 Hz
High power generationLarge stress in the PZT film Large deflection
Cantilever with a proof mass
- Heavy proof mass: low resonant frequency and high power generation- Low damping effect- Compactness
Modelling of PZT cantilever with a proof mass(1000um x 2000um) at 1g
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Analytical power model (Roundy)
( )
( )( ) ( ) 2231
2231
2
22
2312
2 444
5.1
21
ζωζωζε
ω +++
⎟⎟⎠
⎞⎜⎜⎝
⎛ +
=bb
inb
sppPb
RCkRCk
Al
tttdERC
P
Measured parameters-Frequency-Damping ratio-Coupling factor-Dielectric constant-Piezo coefficient d31
P: output power (bimorph)R: resistive loadCb: PZT capacitanceEp: PZT Young’s modulusd31: piezoelectric coeff.ε: dielectric constanttp: PZT thicknessts: silicon thicknesslb: cantilever lengthAin: accelerationζ: damping ratiok: coupling coeff.ω: angular frequency
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Piezoelectric films for energy harvesters
18.20.1823.3110018.2Epi-PZT (20/80)**
120.0130.1690012Poly-PZT (53/47)*
1.050.1000.1110.51.05AlN*
IFVFPFεr-e31 (Cm-2)Piezo material
*S. Trolier-McKinstry and P. Muralt, J. Electroceram. 12, 7 (2004)**Measured data
High piezoelectric coefficientLow dielectric permittivity
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Si substrateSTOSRO bottom electrodeSingle crystalline piezoelectric film
SrTiO3: Strontium Titanate Oxide (STO)SrRuO3: Strontium Ruthenate Oxide (SRO)
Uniform control of the piezoelectric response over nanometer length scales
Atomically smooth and exhibit microstructural homogeneities
Very large piezoelectric coefficients
Limited to maximum thickness of 0.5 µm
Epi Piezo MEMS Harvester
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Technology platform
Piezo SRO STO Silicon
a)
b)
c)
d)
e)
f)
Au/Cr
Before
After
D. Isarakorn et al. JMM, 2010
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Epitaxial PZT cantilevers
Cantilever: 1000×2500×40 μm3
PZT thickness: ~100 nm
d31: ~130-140 pm/V
( )31 2
13 s p s s p
KdVs s h h h Lδ
= −+
3 3 2 4 2 4 2 24 4 6p s s p p s s p p s s p p s s pK s s h h s s h h s h s h s s h h= + + + +
ss : the compliance of the Si layer (7.7 × 10-12 m2/N) sp : the compliance of the PZT film (12.4 × 10-12 m2/N) hs : the thickness of Si layer hp : the thickness of the PZT film
Sensitivity: ~ 5 um/VQ factor: 230 in air
D. Isarakorn et al. JMM, 2010
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Experimental setup
Multimeter(Agilent 34411A)
Power AmplifierType 2712
Exciter ControlType 1050
Resistor
High g shakerType 4811
Accelerometer Type 4374
Metallic box
Bruel & Kjaer vibration exciter system- Max acceleration 210g - Maximum displacement 12.7 mm- Frequency 1 Hz – 10kHz - Frequency resolution 1.19 mHz
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Experimental results
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Epitaxial PZT cantilever with mass: ~500 nm PZT
0 5 10 15 20 25
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Out
put p
ower
(μW
)
Load resistance (kΩ)
0.1 g 0.3 g 0.5 g
23 nW @ 1 kΩ
160 nW @ 2.2 kΩ
370 nW @ 2.2 kΩ
f=2.3 kHz
Front
Back
Epi PZT MEMS energy harvester
D. Isarakorn et al. Proc. PowerMEMS, 2010
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Epi Piezo MEMS Harvester - comparison
SAMLAB
SAMLAB
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Epi Piezo MEMS Harvester - Optimisation
3.63.71795370.1578Typ
C (nF)RL (kΩ)f (Hz)Vac (mV)Iac (mA)P (µW)
Simulation results @ 0.5g of acceleration
Base Mass
STOSi PZTSROSiO2
Simulation parametersd31: 130 pC/NDielectric constant: 100PZT thickness: 500 nmk31: 0.23Damping: 0.0004Acceleration: 0.2 and 0.5g
L
W
Length of the beam: 1500 µm
Width of the beam: 750 µm
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Thick PZT sheet harvesters
Base
WH
Cantilever: W × L × H µm3
L
Glue
• Cantilever size: 3000 x 5000 x 50 (100 and 150) µm3
• Thickness of PZT sheet : 135 µm• Adhesive bonding• Gap of interdigitated electrodes : 150 - 200 µm
Si PZT Au
1 mm
Thick PZT cantilever
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Ouput power measurement on impact mode
Impact type harvester
0.111.5250
0.061.2240
0.030.8530
0.0120.6220
0.0060.410
Max. I @ 10Ω (µA)Max. Vo (Volts)Amplitude (µm)
0 80000 160000 2400000.0
0.8
1.6
2.4
3.2
Out
put p
ower
(nW
)
Load resistance (Ω)
Output power (nW) @ 10 um Output power (nW) @ 20 um Output power (nW) @ 30 um Output power (nW) @ 40 um Output power (nW) @ 50 um
-Max. output power :
3.2 nW @ 267 kΩ
- Optimisation: cantilevers with different stiffness and differentgaps of IDEs on piezo
Open circuit voltage and current measurement
Open circuit voltage waveform
0.0 0.2 0.4 0.6 0.8 1.0 1.2-0.3
0.0
0.3
0.6
0.9
1.2
1.5
Ope
n ci
rcui
t vol
tage
(V)
Time (S)
Vo (V)
0.00 0.05 0.10 0.15 0.20 0.25 0.30-0.3
0.0
0.3
0.6
0.9
1.2
1.5
Ope
n ci
rcui
t vol
tage
(V)
Time (S)
Vo (V)
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Conclusions
MEMS based energy scavengers- Resonant and impact types- Modelling, technology platforms, characterisation tools- Variety of materials and characteristics
Potential for:- Compactness, multi-elements: Cost ???- CMOS integration on chip- Autonomous smart systems : no battery !
Application first, solution second !!!
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Acknowledgements
Research work
University of Geneva, CH
HES Geneva, CH
University of Yale, USA
Funding:
SNF-NCCR MaNEP program: Materials with Novel Electronic Properties
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http://samlab.epfl.ch
Danick Briand : danick.briand@epfl.ch
Sensors, Actuators and Microsystems LabInstitute of MicroengineeringEPFL STI IMT-NENeuchâtel, Switzerland
Contact detailsContact details
THANK YOU !
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