Appl Phys A (2011) 102: 997–1001
DOI 10.1007/s00339-011-6312-5
Enhanced bipolar resistive switching of HfO
2
with a Ti interlayer
DooSung Lee · YongHun Sung · InGun Lee ·
JongGi Kim · Hyunchul Sohn · Dae-Hong Ko
Received: 18 October 2010 / Accepted: 22 December 2010 / Published online: 22 February 2011
© Springer-Verlag 2011
Abstract The characteristics of resistive switching of
TiN/HfO
2
/Ti/HfO
2
/Pt/Ti stacks on SiO
2
/Si substrates were
investigated and compared to TiN/HfO
2
/Pt/Ti stacks in or-
der to study Ti interlayer effects on resistive switching. The
Ti interlayers were deposited in situ during the reactive sput-
tering of HfO
2
films. The current–voltage measurements
showed that the Ti interlayers enhanced the memory win-
dow but reduced the endurance of SET/RESET operations.
The energy filtered images by TEM showed asymmetric
oxygen accumulation at the Ti/HfO
x
interfaces. Subsequent
heat treatment improved the endurance of SET/RESET op-
eration of TiN/HfO
2
/Ti/HfO
2
/Pt/Ti stacks.
1 Introduction
With the scaling down of conventional memory devices,
the demand for high performance nonvolatile memory de-
vices is increasing. Among new memory devices, resistance
random access memory (ReRAM) devices are regarded as
promising candidates for next generation memory devices
because of their fast switching speeds, low power con-
sumption, non-destructive readout, nonvolatility, and sim-
ple metal-insulator-metal (MIM) structures. However, re-
search efforts related to ReRAM are still focused on find-
ing appropriate materials and improving switching charac-
teristics [1–3]. Specifically, several transition metal oxides
(TMOs) such as TiO
2
[4], NiO [5], Al
2
O
3
[6], ZrO
2
[7],
D.S. Lee · Y.H. Sung · I.G. Lee · J.G. Kim · H. Sohn ( ) ·
D.-H. Ko
Department of Materials Science and Engineering, Yonsei
University, Seoul 120-749, Korea
e-mail: hyunchul.sohn@yonsei.ac.kr
and MnO
2
[8], have been widely investigated as potential
materials for ReRAM applications.
Among TMO materials, hafnium oxide is a favorite
dielectric material because of its compatibility with ad-
vanced metal–oxide–semiconductor devices. However, rel-
atively few studies have been performed regarding its ap-
plication to ReRAM. Various metal layers, including Ti [9],
Zr [10], Au [11], and Cu [12] in the metal oxide have been
shown to improve resistive switching properties of HfO
2
films when used as dopants. In particular, Ti metal is known
for its ability to absorb oxygen atoms from metal oxide high-
k layers. Since Hf and Ti are in the same group of the peri-
odic table, Ti can be employed as an interlayer for the mod-
ification of material properties [13].
In this study, we investigated the effects of a Ti inter-
layer in HfO
2
on the resistive switching properties of HfO
2
thin film for ReRAM applications. The microstructures of
TiN/HfO
2
/Ti/HfO
2
/Pt devices were also studied using TEM
after resistive switching with heat treatment in conjunction
with the resistive switching properties of the stacks.
2 Experimental
Using a dc magnetron sputtering method, Ti (10 nm) and
Pt (150 nm) films were deposited as an adhesive layer and
bottom electrode on a thermally grown SiO
2
layer on a p-
type Si(100) wafer. Subsequently, a HfO
2
thin film was de-
posited on the Pt/Ti/SiO
2
/Si substrates by a reactive sput-
tering method using a single Hf target at room temperature
and an Ar + O
2
mixture ambient (Ar : O
2
= 40 : 7). In or-
der to investigate the effects of the metallic interlayer on the
resistive switching characteristics of HfO
2
films, additional
Ti interlayers were deposited in situ in the middle of the
HfO
2
films. Then the structure was annealed at 300°C for