Nanoscience and Microsystems ETDs

Publication Date

Summer 7-30-2021

Abstract

Thin-film piezoelectric materials are increasing in demand, but most materials are stiff ceramic materials. Polyvinylidene fluoride (PVDF) is a common polymer piezoelectric material, but it has limitations such as it requires post-processing steps to promote appropriate β-phase and it has a low operating and Curie Temperature, which limits its use in traditional microfabrication processing. The toxicity of PZT makes it incompatible with biomedical applications. Therefore, there is a need to develop a new class of polymer piezoelectric films that are compatible with current microfabrication methods. Parylene C (PA-C) is a chemical vapor deposited semi-crystalline polymer material with a nonsymmetric polymer structure, which is extensively used in microfabrication and has relatively high melting temperature (290 C). PA-C is compatible with a wide range of etchants and solvents and can be deposited in thin layers from 200 nm to >50 μm while being pin-hole free. Although PA-C is semi-crystalline it does not have piezoelectric properties upon deposition. This thesis study investigates methods of converting PA-C into a piezoelectric film based on annealing to increase the crystallinity and poling the film. The conformal coating of PA-C and its compatibility with other materials offers significant advantages if it can demonstrate piezoelectric properties. Poling was performed using direct poling using high electric fields of 0-140 MV/m. PA-C films with a thickness of 25 μm were deposited onto silicon substrates and then removed from the substrate for processing and analysis. Conducting ink was applied to the substrate to act as electrical contacts during poling and to measure piezoelectric coefficient d33 using a high-resolution thin film piezometer. Results of annealing the thin film PA-C demonstrate increased crystallinity as temperature is increased resulting in a FWHM XRD 2theta scan of 6.52  at RT to 0.72  at 250 C. A piezoelectric d33 value of 4.5 pC/N was achieved before reaching the breakdown voltage when poled at 150 C for 1 hour at 60 MV/m. Annealing the PA-C resulted in an increased crystallinity which further enhanced the piezoelectric properties. The concept of converting PA-C into a piezoelectric film has been validated and future works propose investigating methods of enhancing the piezoelectric properties.

Keywords

Parylene, Polymer piezoelectric materials, Piezoelectric material, Piezoelectric constant, poling, crystallinity.

Document Type

Thesis

Language

English

Degree Name

Nanoscience and Microsystems

Level of Degree

Masters

Department Name

Nanoscience and Microsystems

First Committee Member (Chair)

Prof. Nathan Jackson

Second Committee Member

Prof. Sakineh Chabi

Third Committee Member

Prof. Matthias Pleil

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