1. Piezoelectric MEMS with Giant
Piezo Actuation

2. MEMS on Si – 1. Capacitive with metallic electrodes
2. Piezoelectric with active piezo-materials (like PZT)
 MEMS with piezoelectric materials - Integrated Actuation
‘’ Sensing
‘’ Transduction
 Applications - Ultrasound Medical Imaging
Microfludic Control
Mechanical Sensing
Energy Harvesting

3. Piezoelectricity
 “Piezo” – Pressure; Piezo-electricity - pressure electricity
 Direct and Converse piezoelectric effect
Important Piezoelectric Parameters
Piezoelectric Figure of Merit
Piezoelectric Strain Constant (d) – Magnitude of the induced strain (x) by an external
electric field. x= d.E
Piezoelectric Voltage constant (g) – field per unit strain.
g =d/(εε0) ; ε= permittivity
Electromechanical Coupling Factor (k) – Conversion rate between elec. & mech. energy.
= (stored elec. Energy)/(Input mech. Energy)
= d2/ (εε0).s
Energy Transmission Coefficient (λ) – Maximum k in actual device
= ʃ E.dp = (εε0E + d.x)E
Efficiency (Ƞ) - (output mech. Energy)/(Consumed elec. Energy)

4. Displacement and Stress/Strain relation (at low fields)
Clamping to the Substrate changes it all !!
31 and 33 modes of piezoresponse

5. Piezoelectric Properties of representative materials

6. MEMS Based on PbZr(1-x)Tix03
Interesting Properties at MPB –
2.High Dielectric Susceptibility
3.High Remnant Polarization
4.High Piezoelectric Coefficient
Pertinent issues encountered while integrating on Si –
1. Suitable buffer layer owing to higher lattice mismatch.
2. Suitable bottom electrode maintaining epitaxial nature .
3. Suitable growth condition leading to defect-minimal interface.

7. MEMS Based on PZT
Earlier Works Appl. Phys. Lett., Vol. 74, No. 23, 7

8. Appl. Phys. Lett. 68 (10)

9. Appl. Phys. Lett. 63 (26),
LSCO
PZT
LSCO
YSZ
SiO2
(001) Si

10. Appl. Phys. Lett. 63 , 189

11. Appl. Phys. Lett., Vol. 76, No. 11, 13
Electron Diffraction Patterns
PZT/YBCO YBCO/MgO STO/MgO TiN/Si

13. J. Micromech. Microeng. 20 (2010) 055008
Process Flow for MEMS Micro-fabrication
Hysteresis Loop

14. PZT Membrane PZT Cantilever

15. MEMS with Giant Piezo Coefficients
Problem with Giant Piezo MEMS – Relaxor materials are difficult
to integrate in Si matrix for device fabrication

17. PMN:25%PT
PMN:33%PT
PYN:46%PT
PZT

18. Giant Piezoelectricity for Hyperactive MEMS
Material: PMN:33%PT
Orientation : (001) {according to S. E. Park, T. R. Shrout, J. Appl. Phys. 82, 1804 (1997)}
Problem : Growth of Pyrochlore Phase.
Approaches : 1) The use of SrTiO3 buffer layer.
2) a high miscut in Si substrate.
(To incormorate volatile components in the film like PbO suppressing
formation of pyrochlore)
Zero Miscut 4o miscut

19. HRTEM at the Interface
 Atomically sharp interfaces.
Dielectric and Ferroelectric Measurement
 Existence of a built-in-bias – advantages and drawbacks.

20. Piezoresponse
Possible reason of higher piezo-activity- 1. Substantial self-polarization
2. Built in bias
Highest e31,f measured after poling = -27 +/- 3 c/m2

21. How far the properties hold w.r.t. microfabrication ?
Fabrication

22. Cantilever deflection with external bias

23. Conclusions
 Epitaxial growth of PMN-PT on (001)Si using STO buffer.
 Improved growth through introduction of a high miscut in Si.
 Manifestation of giant piezoelectric properties.
 Higher figure of merit suitable for device integration.
 Preserved properties after microfabrocation.
Coda and Future Challenges
 High piezo-actuation through use of relaxors may enhance device sensitivity
 Denser device integration in IC – actuator arrays through easing downscaling.
 Low power consumption owing to reduction in actuation charge density.
 Smaller electromechanical devices with better performances.
 Exploitation of higher 33 mode response of PMN-PT rather 31 mode.
 Tuning the elastic properties of passive layers (SiO2, electrode, STO)to
enhance in figure of merit further.
 Using SOI for complex device structures with desired passive layer thickness.
 Beyond EMS devices – tune and modulate multifunctional properties with
giant electrostriction and dynamic strain control.