Physics Letters A 383 (2019) 125877
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Physics Letters A
www.elsevier.com/locate/pla
Understanding the conduction and switching mechanism of
Ti/AlO
x
/TaO
x
/Pt analog memristor
Sen Liu, Yi Sun, Bing Song, Zhiwei Li, Haijun Liu, Qingjiang Li
∗
College of Electronic Science and Technology, National University of Defense Technology, Changsha 410073, China
a r t i c l e i n f o a b s t r a c t
Article history:
Received
3 April 2019
Received
in revised form 28 July 2019
Accepted
2 August 2019
Available
online 7 August 2019
Communicated
by M. Wu
Keywords:
Memristor
Switching
mechanism
Tunneling
barrier
Oxygen
ions migration
In this letter, the conduction and bipolar switching mechanism of the ultrathin AlO
x
(3 nm)/TaO
x
(5 nm)
memristor are investigated through the electrical characterization and elemental analysis. The AlO
x
/TaO
x
memristor exhibits high uniformity and excellent analog property after initial reset process. The following
experiments and analyses demonstrate that the switching behavior could take place over the whole
area of TaO
x
/Pt interface and is dominated by the tunneling barrier modulation induced by oxygen ions
migration.
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
Nanoscale memristors are passive devices which can retain in-
ternal
resistance state according to the history of applied electrical
stimuli [1,2]. The most typical application of memristor is resis-
tive
random access memory (ReRAM). Under this circumstance,
binary state (ON/OFF) of the memristor has been employed to rep-
resent
digital information and the conducting filament mechanism
has been widely utilized to elucidate the binary switching be-
havior
[3–5]. Recently, analog memristors have attracted extensive
attention in the applications of neuromorphic computing, analog
computation and multi-level storage due to the excellent capability
of gradual resistance modulation [6–9]. Numerous structures and
various switching materials, such as Ag/GeSe/TiN [6], Ta/HfO
2
/Pd
[7], W/WO
x
/Pd [8], Pt/AlO
x
/TiO
2
/Pt [9], have been studied for ana-
log
memristor applications. Among them, the bi-layer structure
memristor has shown outstanding analog property and attracted
great attention. Clear understanding of the switching and conduc-
tion
mechanisms of this bi-layer structure memristor is important
for device fabrication, performance optimization and reliability im-
provement.
Zhang et al. studied the conduction and switching
mechanism of the AlO
x
/WO
x
(6 nm/65 nm) bi-layer structure de-
vice
[10]. Wang et al. revealed the switching mechanism of the
TaO
x
/TiO
2
(20 nm/60 nm) bi-layer structure analog device [11].
However, due to the difficulty of nano-structure characterization
*
Corresponding author.
E-mail
address: qingjiangli@nudt.edu.cn (Q. Li).
and elemental analysis, the detailed study on the mechanism of
the ultrathin bi-layer structure memristor in sub 10 nm regime
is still rare. It is still challenging and meaningful to explore the
switching mechanism in ultrathin multilayer structure films. Be-
sides,
the chemical composition in ultrathin metal oxides strongly
depends on the methods employed and the element ration is
generally not stoichiometric [12]. This can propose difficulty for
deeply analyzing the mechanism. As a result, post-deposition an-
nealing
is recommended to form stable stoichiometric dielectric
phase [13].
In
this letter, we have investigated the resistive switching
(RS) behaviors and the underlying switching mechanism of the
Ti/AlO
x
(3 nm)/TaO
x
(5 nm)/Pt memristor without post-deposition
annealing process. Current-induced joule-heating molds the con-
dition
for atoms arrangements like annealing. Firstly, in order to
distinguish between the localization-type and interface-type RS be-
haviors,
the area and temperature dependence of resistance were
studied. Then, the I–V curves of HRS were re-plotted in ln(I/V
2
)
vs 1/V for tunneling fitting and the tunneling parameters were
calculated with Simmons’ equation. In addition, electron energy-
loss
spectroscopy (EELS) measurements were implemented to re-
search
the distribution of oxygen ions in the oxide layers. On the
basis of the experimental results, we describe the possible switch-
ing
and conduction mechanism of our device.
2. Methods
The vertical lines of Pt/Ti (25/5 nm) bottom electrode were de-
posited
on the SiO
2
/Si substrate by e-beam evaporation after the
https://doi.org/10.1016/j.physleta.2019.125877
0375-9601/
© 2019 Elsevier B.V. All rights reserved.