N AN O E X P R E S S Open Access
High-performance HfO
x
/AlO
y
-based resistive
switching memory cross-point array fabricated by
atomic layer deposition
Zhe Chen, Feifei Zhang, Bing Chen, Yang Zheng, Bin Gao, Lifeng Liu, Xiaoyan Liu and Jinfeng Kang
*
Abstract
Resistive switching memory cross-point arrays with TiN/HfO
x
/AlO
y
/Pt structure were fabricated. The bi-layered resistive
switching films of 5-nm HfO
x
and 3-nm AlO
y
were deposited by atomic layer deposition (ALD). Excellent device
performances such as low switching voltage, large resistance ratio, good cycle-to-cycle and device-to-device uniformity,
and high yield were demonstrated in the fabricated 24 by 24 arrays. In addition, multi-level data storage capability
and robust reliability characteristics were also presented. The achievements demonstrated the great potential of
ALD-fabricated HfO
x
/AlO
y
bi-layers for the application of next-generation nonvolatile memory.
Keywords: RRAM; Cross-point array; Atomic layer deposition (ALD)
Background
Metal oxide-based resistive random access memory
(RR A M) has been extensively studied a s one of the
most promising candidates for next-generation nonvol-
atile memory due to the great performances such as
fast switching speed, low operating voltage, 3D integra-
tion, and good compatibility with CMOS fabrication
processes [1-5]. For high-density integration of RR A M
array, a cross-point structure with the smallest cell
area of 4 F
2
is needed [6,7]. However, the metal oxide-
based RRA M devices usually have a large variability
[8-10], which hinders application in i ndustries. Thus, it
is imperative to seek an effectively te chnical solution
to minimize the variability of RR A M devices.
Various transitional metal oxides such as HfO
x
[11-13],
TaO
x
[14-16], TiO
x
[17-19], and ZrO
x
[20-22] have been
reported as resistive switching materials. Among them,
HfO
x
is a superior resistive switching material, which has
stable electrical properties, good process repeatability, and
small leakage current [23,24]. Based on a previous work
[25], an additional buffer oxide layer of AlO
y
which has
a larger oxygen ion migration barrier (E
m
)willconfine
the switching in the active oxide, which can improve
the uniformity in HfO
x
-based RRAM de vices. Both
physical vapor deposition (PV D) and atomic layer de-
position (ALD) have b een a pplied to fabricate resistive
switching layers. Compared to P VD, the ALD te chnique
has more advantages at constructing uniform, conformal,
and ultrathin films, which is a central component for
high-density and 3D integration.
In this paper, the bi-layered HfO
x
/AlO
y
films are de-
posited by ALD as the resistive switching layer of cross-
point RRA M array, which shows the p re cise control of
the resistive switc hing layer in thickness, uniformity,
and conformity. The fabricated TiN/HfO
x
/AlO
y
/Pt RRAM
devices in the cross-point array show excellent perfor-
mances including low operation voltage (+2/−2 V), suf-
ficient resistance ratio (>10), smaller cycle-to-cycle and
device-to-device variations, and high yield (>95%). Mean-
while, multi-level data storage capability, good direct
current (DC) endurance (>1,000 cycles), and retention
(>10
4
s at 85°C) properties are demonstrated in the devices.
Methods
The fabrication flow of the HfO
x
/AlO
y
-based cross-point
RRA M array is schematically shown in Figure 1. Firstly,
both the 20-nm Ti adhesion layer and 100-nm Pt bot-
tom electrode (BE) layers were deposited on a SiO
2
/Si
substrate by physical vapor deposition (PVD). Then, the
Pt bottom electrode bars were formed by photolitho-
graphy and lift-off. After that, the 20-nm SiO
2
film was
* Correspondence: kangjf@pku.edu.cn
Institute of Microelectronics, Peking University, #5 Yiheyuan Road, Beijing
100871, China
© 2015 Chen et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction
in any medium, provided the original work is properly credited.
Chen et al. Nanoscale Research Letters (2015) 10:70
DOI 10.1186/s11671-015-0738-1