Energy Harvesting using piezoelectric thin-film cantilever MEMS

8/16/2019 Energy Harvesting using piezoelectric thin-film cantilever MEMS

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ENERGY HARVESTING USING

PIEZOELECTRIC THIN-FILM CANTILEVER

MEMS

Emanuel Antunes (53759), Manuel Nascimento (52294)

Nanotecnologias e Nanoelectrónica – IST - 1ºSem 2009/2010



Energy Harvesting



Energy Harvesting

Scavenging power from ambient “free” sources:

Top part: fixed power output

Bottom part: fixed storage energy



Energy Harvesting

Scavenging power from ambient “free” sources:

Comparison of power from vibrations, solar, and various battery chemistries.



Sources of vibration




Two key

characteristics: Large peak in magnitude

somewhere below 200Hz –

fundamental mode

Displacement spectrum falls

of as 1/ω2

Fig: Displacement and acceleration specter for a

typical microwave casing.






Piezoelectricity

What is it?

Piezoelectric Materials

Mechanism

A particular case - PZT



Piezoelectricity – What is it?

Ability of some materials to generate an E-field in

response to an applied mechanical stress.

The reverse effect is also present in some materials



Piezoelectricity - Materials

Crystals

Quartz

Apatite

Lithium Tantalate Ceramics

Barium Titanate (BaTiO3)

Lead Zirconate Titanate (PZT) (Pb[Zr xTi1- x]O3 - 0< x<1)

Aluminum Nitride (AlN)

Polymers

Crystallized polymers such as PVDF



Piezoelectricity – Mechanism

Closely related to the occurrence of electric dipole

moments in solids – Weiss domains.

Relevant factor – Change in Polarization when

applying mechanical stress.

Depends on:

Orientation of dipole density Crystal Symmetry

The applied mechanical stress




It’s a combined effect of:

The electrical behaviour of the material

The mechanical properties of the material

E D

sT S




These can be combined in the following coupled

equations:

The following piezoelectric coefficients are defined

for the direct piezoelectrical effect:




Essential to increase the piezoelectric coeficients are

three factors:

Density

Orientation control

Compositional uniformity



Piezoelectricity – PZT (Pb[Zr xTi1- x]O3)

Existing techniquesallow PZT deposition

and alignment bypoling, furtherincreasing piezoelectriccoefficients.

It has a perovskitecrystaline structure





Vibration conversion



Vib. Conversion - General model

Linear system theory based model

independent of actual mechanism

Idea: oscillating mass acts as a damper

to the mass-spring system

System’s Newton equation:

be – electrical damping coefficient

bm – mechanical damping coefficient

k – spring constant



General model - power

Derivation from equation

allows to obtain:

ζe – electrical damping ratio; ζm – mechanical ratio;ζt – total ratio: ζt = ζe + ζm ;

ω – vibration frequency; ωn – natural frequency;

Y – Young’s module; m – mass; A – acceleration of

input vibrations

If ω=ωn :



Vibration conversion mechanisms

Electrostatic: two conductors separated by a dielectric (capacitor)

moving relative to one another, change in electrical energy stored.

Electromagnetic: relative motion between a coil and a magnetic field

causes a current to flow in the coil.

Piezoelectric: mechanical strain causes charge separation and thusvoltage.



Piezoelectric conversion



Piezoelectric conversion - cantilever

Why cantilever devices:

• Different lengths allow different resonance freqs.

• Compatibility with MEMS manufacturing process.

• Different vibration modes possible.

Fig: Cantilever

Fig: Common vibration modes

Piezoelectric coefficients:



Piezoelectric conversion – d33 vs d31

Typical usage mode

Greater coupling coefficient

(approx 2-2.5x)

Greater open-circuit voltage

(20x)

Greater flexibility allows greater

strain with same forces

Lower natural frequencies



Piezoelectric conversion - setups

Fig: Unimorph d33 Fig: Bimorph d33

Fig: Interdigitated d31



Experiment – Bimorph setup



Bimorph setup – equivalent circuit

Combining system equation with

piezoelectric equations for this system:

Where:



Bimorph setup – derivations

From the previous equations it’s

possible to derive:

With ω=ωn

, the resistance that

optimizes power load is:

The resulting electrical damping

ratio is:





Bimorph setup – prototype results

Assembly of cm sized prototype and

testing.



Experiment – Unimorph setup



Unimorph setup – considerations

Ambient vibrations cannot be fully

predicted and vary over time

A single cantilever has a single natural

frequency

Possible solution: array of cantilevers withclose but different lengths!



Unimorph setup – fabrication

Topology and fabrication steps

done with usual techniques



Unimorph setup – testing

Testing the system with various associated electronics





Unimorph setup – optimal results

Due to phase shift between

different cantilevers, direct

coupling causes smaller AC output:

3.06V vs 2.01+1.64+1.606 =5.256V

Possible solution: full AC-DC

rectification of each cantilever

Result is like serial connection of

batteries:

DC voltage: 3.93 V DC power output: 3.98 μW





Interdigitated setup – Topology

d31 mode allows greater strains



Interdigitated setup – Results

With parameter optimizations, very good results can be

obtained:



Interdigitated setup – Future

More complex configurations yield even better results

With the thickness of the PZT 1.2 μm, the predicted

powerout put is 0.207mW for the input vibration of 5ms-2



Further Applications

Atomic force microscopes (AFMs)

Micro-actuators for millimiter-scale

robotics

RF Switches and Resonators

Wearable sensor/ energy

harvesting units units

Smart Floor – Biometric matching

and and energy harvesting

And many more…



[1] P. Muralt, R.G. Polcawich, and S. Trolier-McKinstry, Piezoelectric Thin Films for Sensors,

Actuators, and Energy Harvesting, MRS Bulletin vol. 34, September 2009: 658-664

[2] S. Roundy, P. K. Wright, J. Rabaey, A study of low level vibrations as a power source for

wireless sensor nodes, Comput. Commun. 26 (2003) 1131 – 1144;

[3] B. Xu, Y. Ye , L.E. Cross, J. Bernstein, R.Miller, Dielectric hysteresis from transverse electric

fields in lead zirconate titanate thin films, Applied Physics Letters, 74, 3549 – 3551(1999);

[4] J.Q. Liu, H.B. Fang, Z.Y. Xu, Xin-Hui Mao, Xiu-Cheng Shen, D. Chen, Hang Liao, B.C. Cai, A

MEMS-based piezoelectric power generator array for vibration energy harvesting,

Microelectronics Journal 39 (2008): 802 – 806;

[5] H.B. Fang, J.Q. Liu, Z.Y. Xu, D. Chen, B.C. Cai, Fabrication and performance of a MEMS-based

piezoelectric power generator for vibration energy harvesting, Microelectron. J. 37 (2006):

1280 – 1284 [6] W.J. Choi, Y. Jeon, J.H. Jeon, S.G. Kim, Energy harvesting MEMS device based on thin film

piezoelectric cantilevers, J. Electroceram (2006)

[7] Y.B. Jeon, R. Sood, J.H. Jeong, S.G. Kim, MEMS power generator with transverse mode thin

film PZT , Sensors Actuators A122 (2005) 16 – 22

References



[8] Y. C. Shu and I. C. Lien, Analysis of power output for piezoelectric energy harvesting systems,

IOP Smart Mater. Struct. 15 (2006): 1499-1512

[9] P. Muralt, Recent Progress in Materials Issues for Piezoelectric MEMS , J. Am. Ceram. Soc. 91,

1385-96 (2008)

[10] J. Bronson, J.S. Pulskamp, R.G. Polcawich, C. Kronigner, E. Wetzel., Bio-Mimetic Millimeter-

Scale Flapping Wings for Micro Air Vehicles, Proc. IEEE MEMS 1047 (2009)

[11] P.D. Mitchelson, E.M Yeatman, G.K. Rao, A.S. Holmes, T.C. Gren, Energy Harvesting From

Human and Machine Motion for Wireless Electronic Devices, Proc. IEEE 96 (2008), 1457

Wikipedia articles

Reference usage:

References

Global review of energy harvesting and

MEMS-based piezoelectric devices – 1

Energy harvesting and ambient

vibrations – 2

Vibration energy conversion – 2, 8, 11

PZT – 3, 7, 9, 10

MEMS and PZT device – 1, 4, 6, 10

Device fabrication – 5, 7, 10

Further applications – 10, 11

Documents

Energy Harvesting using piezoelectric thin-film cantilever MEMS