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Electromechanical behavior of PZT thin film composites for RF-MEMS

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Title: Electromechanical behavior of PZT thin film composites for RF-MEMS
Author(s): Yagnamurthy, Sivakumar N.
Advisor(s): Chasiotis, Ioannis
Contributor(s): Chasiotis, Ioannis
Department / Program: Aerospace Engineering
Discipline: Aerospace Engineering
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): PZT Thin Films Mechanical Behavior Piezoelectric Behavior
Abstract: The mechanical and piezoelectric behavior of freestanding Lead Zirconate Titanate (PZT) composite films comprised of SiO2, Pt, PZT and Pt, for MEMS applications was investigated by microscale uniaxial tension experiments. Due to the difficulty in fabricating individual freestanding PZT films, thin film stacks were fabricated in combinations of Silicon Oxide (SiO2), Titanium (Ti), Platinum (Pt) and PZT. The specimens tested were stacks of SiO2-TiPt-PZT-Pt, SiO2-TiPt-PZT, SiO2-TiPt, and individual SiO2 and Pt thin films, with gauge lengths of 1,000 μm and widths of 50-100 μm. Full-field strain measurements were conducted with the aid of a fine speckle pattern (1 μm particle size) generated on the samples and the elastic modulus and Poisson’s ratio were calculated by means of digital image correlation. The composite mechanical properties of the PZT stacks were computed from the stress vs. strain plots, while the mechanical properties of individual PZT films were extracted from those of the PZT stacks and the properties of SiO2 and Pt films. It was found that the mechanical response of the PZT layer is non-linear but non-hysteretic, deviating from linearity at 0.35%. Failure is initiated in the PZT layer while the Pt films delay fracture, especially in SiO2-TiPt-PZT-Pt stacks. In addition to the elastic and failure mechanical properties of PZT, the d31 piezoelectric coefficient and the effect of applied stress on the magnitude of the hysteresis curves were investigated. The d31 coefficient was measured from the out-of-plane deflection of biased PZT specimens with dimensions similar to those tested previously. An analytical solution for the bending of a multilayered piezoelectric beam was used to compute d31 as 385±45 pm/V. An alternating field induced in-plane stress hysteresis loops which were asymmetric at small applied pre-stress, then becoming of equal magnitude as the pre-stress increased to hundreds of MPa. Similarly, the intersection of the hysteresis loops shifted from negative to positive electric field at stresses larger than 150 MPa. The applied pre-stress resulted in reduction of the hysteresis in the field induced in-plane stress loops, due to mechanical constraints imposed on 90° domain switching.
Issue Date: 2010-01-06
URI: http://hdl.handle.net/2142/14719
Rights Information: Copyright 2009 Sivakumar N. Yagnamurthy
Date Available in IDEALS: 2010-01-06
2012-01-07
Date Deposited: December 2
 

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