November 13, 2014 at 8:00 pm

CMSS Colloquium: ‘Piezoelectric Thin Film Research at Oregon State University,’ Nov. 13

Brady Gibbons

Brady Gibbons

The Condensed Matter & Surface Sciences Colloquium Series presents Brady Gibbons on “Piezoelectric Thin Film Research at Oregon State University” on Thursday, Nov. 13, at 4:10 p.m. in Walter Lecture Hall 245.

Abstract: An overview of piezoelectric thin film research in the Gibbons research group will be provided. Our efforts are focused primarily in two areas: 1) Discovery of new piezoelectric thin film materials that do not include lead as a major constituent and, 2) Integration of piezoelectric thin film materials with flexible substrates. Brief summaries of these areas follow:

Worldwide, increased restrictions on the use of lead have resulted in a search for candidates to replace lead-based piezoelectric materials. Promising materials have been discovered based on (Bi0.5Na0.5)TiO3 – (Bi0.5K0.5)TiO3 (BNT-BKT).  Although good properties have been observed in bulk materials, similar results have been elusive for BNT-BKT thin films. Here, BNT – BKT based thin films were synthesized via chemical solution deposition. Well-crystallized, stoichiometric, phase pure materials were grown at varying processing conditions. Dense, smooth, crack-free films were achieved with relative dielectric constants from 390 to 730 and low dielectric loss of 2 – 5% at 1 kHz. Very promising piezoelectric response was observed, with d33,f up to 75 pm/V and strain values up to 0.35%. Finally, Rayleigh analysis was completed on several compositions to extract the intrinsic and extrinsic contributions to the dielectric properties.

Lead zirconate titanate (PZT) thin films on copper foils were produced using RF magnetron sputtering and ex situ annealing in controlled atmospheres. Processing is a challenge, as the PZT should be fully oxidized yet the copper must remain oxide free. Films with low loss tangent (<5%) were produced with dielectric constants of ≈500. No interfacial layer was detected in cross-sectional SEM imaging. The remanent polarization was 20-35 µC/cm2. The Rayleigh behavior, characterizing the sub-switching AC response of the domain walls, was determined. Finally, cantilever energy harvesters were fabricated and tested. The device output as a function of frequency was compared with a model based on the Euler-Bernoulli beam equations. The resonant frequencies of the cantilevers, 20-40 Hz, were found to match the model well. Modeled peak-to-peak voltage was highly dependent on material parameters but typical values gave an expected output of 10-40 mV, which match the observed values well.

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