Study on the electroforming and resistive switching behaviour of nickel oxide thin films for non-volatile memory applications
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Beschreibung
Over the past decade, the resistance switching eect has drawn attention within
the scientic community as a potential candidate for non-volatile random access
memories (RAM) and crossbar logic concepts. The resistance switching memory
cells are based on (at least) two well-dened non-volatile resistance states, e.g.,
high resistance state (HRS) and low resistance state (LRS), that dene two (or
more) logic memory states, e.g., 1 or 0. Often these cells have a simple capacitor
structure and are therefore easy to fabricate. However, the market launch of
RRAMs is hindered by several serious obstacles. For example, the underlying
microscopical physical and chemical switching mechanism of RRAM devices
is still under debate although various models have been proposed to explain
the observed phenomena. By missing a deep understanding of the resistive
switching eect on an atomistic scale, a reliable fabrication of predictable and
well performing Gbit memory seems to be questionable.
This thesis is an attempt to develop and physically understand the nickel oxide
(NiO) based resistive switching non-volatile memory devices. Although the
underlying microscopical switching mechanism is still under debate, the macroscopic
switching mechanism of this material system is often described by the
creation and rupture of well-conducting nickel laments embedded within an
insulating NiO matrix, the so called fuse-antifuse mechanism. The resistive
switching characteristics, essentials for future non-volatile memories, such as
low voltage and current operation with high resistance ratio between HRS and
LRS, fast switching speed, high retention and endurance are presented.
Additionally, the emphasis is layed on the understanding of the so called forming
process. It describes the rst resistance transition of the resistive switching
device in which the proposed nickel lament is formed. Therefore, it is the key
process for understanding the resistive switching phenomena. The statistical distribution
of the observed forming process is studied under accelerated constant
voltage stress conditions and at varying temperatures within the framework of
the Weibull statistics.
To understand the physical and chemical nature of the lamentary structure,
the in
uence of dierent ambient atmospheres and temperatures on the forming
process is analyzed electrically as well as chemically by XPS analysis. Combining
these results with the results of the potentiostatic breakdown studies, a model
for the forming process in Pt/NiO/Pt non-volatile resistive switching memory
devices is proposed.
Autor*in
Robert Weng