p
-type SnO bilayers Based Nano Crossbar Memristors
M. K. Hota, and H. N. Alshareef
*
Materials Science and Engineering, King Abdullah University of Science & Technology
(KAUST), Thuwal 23955-6900, Saudi Arabia
*
Email:
Keywords:
p-type metal oxide based devices, Memristors, nano crossbar memory
Recently, p-type metal oxides, such as tin monoxide (SnO) have attracted significant
attention due to their potential advantages in many applications such as gas sensing, low-
power transparent complementary logic circuits, thin film transistors,
etc.
On the other hand,
among many candidates to replace the existing memory devices, memristor is assumed to be
one of the promising candidates owing to its simple metal–insulator–metal structure, fast
switching speed, low-power operation, excellent scalability potential, and high density along
with its ability to combine the key features of established flash, static random access memory
and dynamic random access memory performances. There are only a few
p
-type oxide
materials have been reported so far as memristive materials. In contrast, SnO might be useful
for 1T1R cell design in the memristor memory chips. Here we fabricated a bilayer of SnO
x
(oxygen rich) and SnO
y
(oxygen deficient) homojunction-based on
p
-type oxides, used as a
memristive material for the fabrication of nanoscale crossbar (300 × 300 nm
2
) memristor
devices. The SnO layers were deposited by dc reactive sputtering under 17% and 5% Oxygen
partial pressure. The total thickness of the bilayer oxides was used as 20 nm. Al and Ti/Au
were used as bottom and top contact electrodes, respectively. The nanoscale patterning of
different layers was done using a CRESTEC CABL-9520C high-resolution electron beam
lithography system. The chemical composition of the oxide films was characterized by X-ray
photoelectron spectroscopy (XPS) and Raman shift analysis. It was found that SnO
y
is more
conducting as compared to SnO
x
. It may be due to the presence of more metallic Tin in SnO
y
film as evidenced from the XPS study. However, the overall conductivity of the film was
showing as
p
-type (
i.e.
, SnO is major). From TEM cross section and electron energy loss
spectroscopy analysis of the device illustrates the existence of interfacial layers at bottom
electrode/SnO (as AlO
x
layer) and at SnO/top electrode (as TiO
x
layer), which believed to
form due to the redox process at the interfaces during the device fabrication process. The
memory performance of the device was obtained after a high voltage electroforming process.
It was observed that a counter-clockwise memristive behavior with more than 10
3
times
ON/OFF ratio, which was maintained up to 180 dc switching cycles. Also, the retention
stability of the device shows no significant degradation of the memory states over 6000 sec
memory operation. The current conduction process of this memory device follows multiple
conduction mechanisms, such as Ohmic at lower voltage region of ON and OFF states.
However, the higher voltage region of both states is found dominated by the space charge
limited conduction process. Here, SnO
x
layer can be considered as an oxygen ion reservoir
raising the possibility that the oxygen ions could be trapped/detrapped within the SnO
y
layer.
Possible defects that can trap mobile oxygen ions are oxygen vacancies depending on the
external bias on the top electrode. The memristive mechanism is suggested to originate from
the oxygen ion migration and subsequent formation/rupture of the conducting filaments,
which are suggested to form by the proper arrangement of the oxygen vacancies under
appropriate external bias.
PS1 33
-189-
