1. Recent Progress in Materials Issues
for Piezoelectric MEMS
A feature journal by American Ceramic Society (2008).
AUTHOR: Paul Muralt.
PRESENTED BY: Niranjan Ramakrishnegowda.
3. INTRODUCTION
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What is Piezoelectric Effect and it’s Inverse?
http://upload.wikimedia.org/wikipedia/commons/c/c4/SchemaPiezo.gif
4. Continues…
Advantages of Piezoelectric Bulk Materials
strong forces.
low voltage.
high efficiency in energy conversion.
high-speed and high-frequency operation possible.
high acoustic quality.
For thin film Piezoelectric Materials?
For thin-film applications, the same principles remain valid.
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5. Continues…
Main concern is on Miniaturization.
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http://www.docstoc.com/docs/83516847/What-are-MEMS
6. Continues…
What are Piezo MEMS?
Deposition of a piezo layer (nm) on to the substrate (si,pt),
incorporating electronics results in Piezo MEMS.
It is expected that the Piezoelectric materials with their
intrinsic electro-mechanical coupling should and will play an
important role in MEMS.
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Journal of the American ceramic society-Muralt, Page 1386
D=e31,f (S1+S2)
7. Continues…
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The history of the transverse piezoelectric coefficient e31,f as an indicator of the advancement in the
field. The small numbers aside of the points are the filmthickness in micrometers.
9. Experimentation
Processing of Lead-Based Ferroelectric Thin Films
The force champion among piezoelectric thin film materials, Pb(Zr,Ti)O3
(PZT).
PbZrxTi1-xO3 or PZT exhibits outstanding properties at the morphotropic
phase boundary at x=0.53
PZT and related materials can be deposited by the major standard methods
applied in wafer processing, i.e., metal–organic chemical vapor
deposition(MOCVD), sputtering, and chemical solution deposition(CSD).
Texture control-Starting a layer of PbTiO3 with TiO2 leads rather to (111)
orientation, starting with PbO leads rather to (100)-orientation.
Gradients in Zr/Ti ratio- Lead excess.
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10. Continues…
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Epitaxial Pt film ((SrTiO3(111)substra
2nm thick TiO2
2-nm-PZT(Nuclei density is 60 times
larger than on bare Pt(111))
150nmx150nm(Single grains of PZT(100)
PZT nanoislands
11. Continues…
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Dark field TEM images of 2-mm-thick PZT53/47 films deposited
by a sol–gel technique in eight steps.
The schematic depicts the formation of the
concentration gradient during crystallization
anneal per one single annealed layer of 250 nm.
Gradient free(By installing
counter gradient-Spin of
different orientation per
crystallization anneal)
Well visible tetragonal/
rhombohedral phase mixture.
12. Continues…
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Zr content within 2 m thick PZT thin films measured as a function of the distance to the
bottom electrode. Open squares: standard film with 53/47 solutions; filled circles: film with
optimized Zr/Ti ratio as described in the text.
Grad: Fluctuation-43-62%
Grad free: 50-55%
•Gradient removal results in increase of
dielectric constant from 1300-1700
13. Continues…
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Improved peaking of the transverse e31,f coefficient at the morphotropic
phase boundary by increased film thickness and improved homogeneity of
film composition.
14. Continues…
Microstructure—Piezoelectric Coefficients—Operation
Principles
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Electrode systems for driving piezoelectric films: (a) Planar capacitor structure with top and bottom
electrode. (b) Electric fieldwith interdigitated electrodes. (c) Case of polar film with uniform
perpendicular polarization. (d) Schematic drawing of strains induced by d15 between the electrodes,
and d33, d31 below the electrodes for situation in (c).
x5 =d15 E1
To work with shear strain
15. Applications
Bulk Acoustic Wave (BAW) Devices
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• Efficient transformation of electrical power into mechanical power and vice versa.
• fa = Vs/(2tp).
• This is the improvement over SAW.
• This principle is very successfully applied in ultrasound probes for medical
imaging and nondestructive testing at a few MHz.
Trapped ultra sound wave
16. Continues…
Piezoelectric Micro machined Structures in Deflective
Mode.
piezoelectric laminated structures in the bending mode using beam and
plate structures.
At the upper frequency range (0.1–15 MHz) we find piezoelectric micro
machined ultrasonic transducers (pMUT).
Potential applications are ultrasonic imaging, nondestructive testing,
droplet ejection, sensors using ultrasound and ultrasonic micromotors.
Also used in ink jet printing heads and for analog signal processing in
mobile communication.
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18. Conclusion
Considerable Progress in the last 10 years.
Thin film material property approaches or even surpasses the bulk material
properties.
A promising new material in the game is electrostrictive SrTiO3 enabling
ultrasonic valve and tuning devices.
There are many other applications under investigation like energy
scavenging, active damping, mirror arrays and scanners, and further more.
Now the question is with the Domain Engineering of Piezoelectric Thin
Films, and how they can be established by suitable growth conditions,
electrode geometries, and electrical treatments.
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19. References
N. Malouf, An introduction to Microelectromechanical Systems
Engineering, p. 265. Artech House, Boston, London, 2000.
F. Calame and P. Muralt, ‘‘Growth and Properties of Gradient Free
Sol–Gel Lead Zirconate Titanate Thin Films,’’ Appl. Phys. Lett., 90,
062907 (2007).
S. Buhlmann, P. Muralt, and S. VonAllmen, ‘‘Site Controlled
Nucleation and Growth of Small Ferroelectric PZT Single Crystals,’’
Appl. Phys. Lett., 84, 2614–6 (2004).
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