A large memory window and low power consumption self-rectifying
memristor for electronic synapse
Qingjiang Li1, Shihao Yu1, Peng
Yang1, Qin Wang1, and Sen
Liu1
1 College of Electronic Science and Technology,
National University of Defense Technology, Changsha, 410073, China
Email: liusen@nudt.edu.cn
Self-rectifying memristor has no need for selector devices, but possess
the one-way transmission behavior and multi-level non-volatile memory
characteristics, which makes it promising candidate for electronic
synapse. In this letter, we propose a novel self-rectifying memristor
based on
Pt/Hf0.5Zr0.5O2/TiN
structure. The devices show large memory window (104)
and high rectifying ratio (104), which can block the
sneak current in passive crossbar array without any additional hardware
overhead. Moreover, the devices demonstrate excellent multi-level states
modulation capability, low power consumption, high endurance and long
retention. The final benchmark demonstrates that the proposed
Pt/Hf0.5Zr0.5O2/TiN
self-rectifying memristor is a promising candidate for electronic
synapse application.
Introduction: Due to the simple structure, multi-level operation
and non-volatile memory capacity, memristor has been considered as a
potential synapse device for constructing brain-inspired computing
systems, which is expected to break the von Neumann bottleneck in
traditional computing system [1,2]. Nonetheless, the sneak current,
flowing through unselected cells in passive crossbar array, will lead to
read-out errors and failure of program operations. Though additional
selectors (i.e. transistors or diodes) in serial can solve the sneak
path issues, they will lower the integration density due to their larger
size. The self-rectifying memristor cell, whose nonlinear and asymmetric
current-voltage characteristics can greatly suppress the sneak current
flowing through the unselected cells, is attracting significant
attention because of their simple two-terminal structure and 3D
integration ability [3,4]. However, most current type
self-rectifying memristors suffer from relatively small memory window
and high-power consumption. Thus, new self-rectifying memristor is
needed for being a promising candidate in electronic synapse
applications.
In this letter, by using the amorphous high-k Zr-doped hafnium
oxide as resistive switching material, we propose a novel
self-rectifying memristor based on
Pt/Hf0.5Zr0.5O2/TiN
structure. Experimental results demonstrate the as-fabricated device has
high rectifying ration (104) and large memory window
(104), which is sufficient to suppress sneak path
issue in Mb-level passive crossbar array. Moreover, the devices possess
excellent multi-level states, endurance (106) and
non-volatility (103 s) capability. The excellent
resistive switching performance can be ascribed to the trap-controlled
space charge limited current (SCLC) effect in
Hf0.5Zr0.5O2 films. The
final benchmark demonstrates the outstanding self-rectifying performance
with previous reported devices.
Devices and experiments: The proposed self-rectifying memristors
were fabricated with a 10-nm-thick
Hf0.5Zr0.5O2 (HZO) layer
sandwiched between TiN top electrode and Pt bottom electrode, as shown
in Fig. 1a . The vertical lines of Pt/Ti (25/5 nm) were deposited
on the SiO2/Si substrate as bottom electrode by e-beam
evaporation after the first lithography process. Then a 10-nm-thick HZO
layer was deposited on the Pt bottom electrode at a stage temperature of
280 °C. The
Hf[N(C2H5)CH3]4,
Zr[N(C2H5)CH3]4and H2O were used as hafnium precursor, Zr precursor and
oxygen source, respectively. The hafnium/zirconium ratio was controlled
by alternate deposition of one HfO2 cycle and one
ZrO2 cycles. Finally, the horizontal lines of TiN (30
nm) were deposited by magnetron sputtering. The cell areas of the
devices range from 9 μm2 (3 µm×3 µm) to 2500
µm2 (50 µm×50 µm). During the electrical measurement,
the voltage was applied to the Pt bottom electrode and the TiN top
electrodes were grounded.