An in situ study of resistance degradation and switching of bulk yttria-stabilized zirconia and strontium titanate single crystals / Ana Alvarez.

Format:

Book

Thesis/Dissertation

Author/Creator:

Alvarez, Ana María (Editor), author.

Contributor:

Chen, I-Wei, degree supervisor.

University of Pennsylvania. Department of Materials Science and Engineering, degree granting institution.

Language:

English

Subjects (All):

Engineering.

Materials science.

Materials science and engineering--Penn dissertations.

Penn dissertations--Materials science and engineering.

Local Subjects:

Engineering.

Materials science.

Materials science and engineering--Penn dissertations.

Penn dissertations--Materials science and engineering.

Physical Description:

1 online resource (354 pages)

Contained In:

Dissertations Abstracts International 83-08B.

Place of Publication:

[Philadelphia, Pennsylvania] : University of Pennsylvania ; Ann Arbor : ProQuest Dissertations & Theses, 2021.

Language Note:

English

System Details:

Mode of access: World Wide Web.

Summary:

Understanding resistance changes under a constant or set of bipolar-switching voltage(s) is important for thin-film devices, specifically multilayer capacitors and resistance-switching memory. However, identifying critical locations of changes and failures in thin films is difficult, so this work studies the same phenomena in single crystals of yttria-stabilized zirconia (YSZ) and iron-doped strontium titanate (STO) starting with highly accelerated lifetime tests (HALT) at higher temperatures. Although doped STO is a p-type semiconductor and YSZ a fast oxygen-ion conductor with little electronic conductivity, their DC resistance-degradation curves are remarkably indistinguishable. Yet different mechanisms were revealed by in-situ hot-stage photography and thermal imaging in two test environments-air and silicone oil. In YSZ, DC (electro)reduction does not appreciably alter oxygen stoichiometry; nevertheless, above a threshold voltage, it can raise the chemical potential of electrons to the conduction-band level, thereby triggering a metal-insulator (resistance) transition. In contrast, DC-stressed STO undergoes oxygen-vacancy demixing, forming a p-n junction with elevated electronic conductivity, albeit late-stage-demixing can be so sluggish that the steady state is difficult to reach in low-temperature HALT. In both oxides, an inherent instability in the governing field equation dictates degradation follows filament-like paths, which explains the strong field dependence and large variation of lifetimes. Upon further voltage reversals, degraded crystals exhibit different, large resistance changes. In YSZ, a change in DC voltage can already cause a resistance change, which is unipolar switching. But additional resistance degradation after voltage reversal can facilitate filament fragmentation, thus rendering the crystal bipolarly switchable due to a voltage-sensitive metal-insulator transition in a thin layer of barely metallic YSZ adjacent to the original anode. In STO, voltage reversals broaden/narrow a nanolayer of stoichiometric, ionic STO (called i-region) that straddles the p-n junction, by driving electromigration to act in-concert/against back-diffusion of oxygen ions. Thickening/thinning of such region leads to resistance increase/decrease, resulting in the so-called "eightwise" bipolar switching. (Interface-controlled, "counter-eightwise" switching was also observed in more severely degraded STO.) As these phenomena find analogies in thin-film devices, mechanisms revealed above have provided new insight that will help understand and improve the performance and reliability of engineering devices.

Notes:

Source: Dissertations Abstracts International, Volume: 83-08, Section: B.

Advisors: Chen, I-Wei; Committee members: Davies, Peter K.; Feng, Liang; Gorte, Raymond J.

Department: Materials Science and Engineering.

Ph.D. University of Pennsylvania 2021.

Local Notes:

School code: 0175

ISBN:

9798780658207

Access Restriction:

Restricted for use by site license.

This item must not be sold to any third party vendors.