Letter
HfO
2
-based resistive switching memory with CNTs electrode for high
density storage
W.K. Cheng, F. Wang
⇑
, Y.M. Han, Z.C. Zhang, J.S. Zhao, K.L. Zhang
⇑
School of Electronics Information Engineering, Tianjin Key Laboratory of Film Electronic & Communication Devices, Tianjin University of Technology, Tianjin 300384, China
article info
Article history:
Received 5 December 2016
Received in revised form 17 January 2017
Accepted 3 March 2017
Available online 6 March 2017
The review of this paper was arranged by
Prof. S. Cristoloveanu
Keywords:
RRAM
HfO
2
Carbon nanotube
High density storage
abstract
In this paper, the HfO
2
-based resistive switching memory (RRAM) using carbon nanotubes (CNTs) as con-
tact electrodes for high density integration is demonstrated. The Al/HfO
2
/CNTs devices show self-
compliance, forming-free and low resistive state (LRS) nonlinearity with less than 130 nA reset current
(I
reset
). By contrast with the Al/HfO
2
/Ti devices, resistive switching behavior has been enhanced signifi-
cantly by using CNTs electrode. For the Al/HfO
2
/CNTs devices, current–voltage (I-V) characteristics
demonstrate that the current conduction in high resistive state (HRS) and low resistive state (LRS) is con-
trolled by space-charge-limited current (SCLC) and trap-controlled SCLC mechanism, respectively.
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
The superior memory performances and excellent scalability
have made resistive random access memory (RRAM) devices
become a potential candidate to the current main memory [1–3].
Usually, the traditional RRAM devices require a high voltage to
trigger its resistive switching ability [4]. Moreover, there is compli-
ance current (I
cc
) applied on the device to avoid the permanent
breakdown during the set process [5]. For the RRAM devices, the
properties of self-compliance, forming-free and LRS nonlinearity
indicate that extrinsic current limiting device and selection device
are not required in crossbar arrays, which is beneficial to high-
density integration.
Carbon nanotubes (CNTs) are attractive as emerging electrode
materials to improve the devices performance [6–12]. Nevertheless,
the research about CNTs electrode-based RRAM is restricted to AlO
x
[6,7], amorphous carbon (a-C) [8] and SiO
x
[11,12] up till now. As for
a superior RRAM material [13–16], there is scarcely any correla-
tional research of HfO
2
-based memory with CNTs electrode.
This paper demonstrates the Al/HfO
2
/CNTs device, the I
reset
has
been reduced to 130 nA successfully by the employment of CNTs
electrode, self-compliance, forming-free and LRS nonlinearity are
also obtained. The resistive switching mechanism of this device
is discussed as well.
2. Experiment
Fig. 1(a) depicts the process flow of Al/HfO
2
/CNTs devices. The
CNTs bottom electrode (BE) were grown on ST-cut quartz substrate
with 500 sccm CH
4
and 60 sccm H
2
at 864 °C for 40 min. Fig. 1(b)
shows a SEM image of the 10
l
m-wide stripes of CNTs separated
by distances of 50
l
m. Fig. 1(c) displays the SEM image of the sin-
gle stripe. Fig. 1(d) gives the SEM image of single CNT with 20 nm
diameter. 200-nm Ti was e-beam evaporated on the ends of the
stripes as the electrical contact to CNTs. 30-nm HfO
2
film was sput-
tered on CNTs by radio frequency (RF) magnetron sputtering with
36sccm Ar. Then the devices were patterned by lift-off. At last, 200-
nm Al was deposited by e-beam evaporation (EBE) as top electrode
(TE), which was patterned by the metal mask (
U
= 400
l
m).
After the RRAM devices were fabricated, the electrical proper-
ties of devices were tested by the Agilent B1500A Semiconductor
Parameter Analyzer. During the measurement, BE was grounded
while TE was applied with voltage.
3. Result and discussions
As shown in Fig. 2(a), Al/HfO
2
/CNTs devices displayed the typi-
cal bipolar resistive switching (BRS) characteristics. The set process
http://dx.doi.org/10.1016/j.sse.2017.03.004
0038-1101/Ó 2017 Elsevier Ltd. All rights reserved.
⇑
Corresponding author.
E-mail addresses: fwang75@163.com (F. Wang), kailiang_zhang@163.com
(K.L. Zhang).
Solid-State Electronics 132 (2017) 19–23
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