Piezoelectric mems
- 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
- 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.