Date of Completion

5-3-2018

Embargo Period

5-3-2018

Keywords

Iridium Oxide, MEMS, Radiation

Major Advisor

Dr. Bryan D. Huey

Associate Advisor

Dr. Seok-Woo Lee

Associate Advisor

Dr. S. Pamir Alpay

Associate Advisor

Dr. Ryan Q. Rudy

Associate Advisor

Dr. Ronald G. Polcawich

Field of Study

Materials Science and Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The multifunctional properties of ferroelectric materials make them ideal components for numerous applications including for extreme environments such as space. Iridium oxide (IrO2) electrodes have been demonstrated to improve the lifetime of ferroelectric memory devices, however little is known about its influence on the electromechanical properties important for ferroelectric microelectromechanical systems (MEMS). The performance of thin film lead zirconate titanate (PZT) based MEMS is affected by the processing conditions, composition, device design, electrode materials, and the environment. This work details the development and characterization of iridium oxide electrodes for PZT based microelectromechanical and pyroelectric-harvesting systems, fabrication induced defects, and design of clamped vs unclamped devices. This work also considers the influence of iridium oxide top electrodes on the properties of PZT films and MEMS devices subjected to gamma and heavy ion radiation for applications in space and for evaluating nuclear material where human exposure must be kept to a minimum.

Using single point force measurements with an atomic force microscope, this work presents the first known experimental value of Young’s modulus for thin film IrO2 (𝐸𝐸𝐼𝐼𝐼𝐼𝐼𝐼2 = 262 GPa). It was discovered that iridium oxide films of different morphologies are produced by manipulating the reactive gas flow rate in a sputtering process. Planar IrO2 for piezoelectric applications was optimized at 60 sccm O2 flow rate deposited at 500°C. Nanostructured, 2D platelets are observed for high oxygen flow rates (100 sccm) producing a self-limiting dense columnar film as the base of the plate-like structures. While the plate-like region continues to grow with increased deposition at a rate of ~6 nm/s, the dense film appears to reach a critical thickness of approximately 60 ± 10. Devices with iridium oxide top electrode appear to be more radiation resistant when compared to identically fabricated devices with a platinum (Pt) top electrode, when exposed up to 10 Mrad(Si) of gamma rays from a 60Co source and an equivalent dose with Fe3+ ions.

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