<s>
Resistive	B-General_Concept
random-access	I-General_Concept
memory	I-General_Concept
(	O
ReRAM	B-General_Concept
or	O
RRAM	B-General_Concept
)	O
is	O
a	O
type	O
of	O
non-volatile	B-General_Concept
(	O
NV	O
)	O
random-access	B-Architecture
(	O
RAM	B-Architecture
)	O
computer	O
memory	O
that	O
works	O
by	O
changing	O
the	O
resistance	O
across	O
a	O
dielectric	O
solid-state	O
material	O
,	O
often	O
referred	O
to	O
as	O
a	O
memristor	O
.	O
</s>
<s>
ReRAM	B-General_Concept
bears	O
some	O
similarities	O
to	O
conductive-bridging	B-General_Concept
RAM	I-General_Concept
(	O
CBRAM	B-General_Concept
)	O
and	O
phase-change	B-Device
memory	I-Device
(	O
PCM	B-Device
)	O
.	O
</s>
<s>
CBRAM	B-General_Concept
involves	O
one	O
electrode	O
providing	O
ions	O
that	O
dissolve	O
readily	O
in	O
an	O
electrolyte	O
material	O
,	O
while	O
PCM	B-Device
involves	O
generating	O
sufficient	O
Joule	O
heating	O
to	O
effect	O
amorphous-to-crystalline	O
or	O
crystalline-to-amorphous	O
phase	O
changes	O
.	O
</s>
<s>
By	O
contrast	O
,	O
ReRAM	B-General_Concept
involves	O
generating	O
defects	O
in	O
a	O
thin	O
oxide	O
layer	O
,	O
known	O
as	O
oxygen	O
vacancies	O
(	O
oxide	O
bond	O
locations	O
where	O
the	O
oxygen	O
has	O
been	O
removed	O
)	O
,	O
which	O
can	O
subsequently	O
charge	O
and	O
drift	O
under	O
an	O
electric	O
field	O
.	O
</s>
<s>
Although	O
ReRAM	B-General_Concept
was	O
initially	O
seen	O
as	O
a	O
replacement	O
technology	O
for	O
flash	B-Device
memory	I-Device
,	O
the	O
cost	O
and	O
performance	O
benefits	O
of	O
ReRAM	B-General_Concept
have	O
not	O
been	O
enough	O
for	O
companies	O
to	O
proceed	O
with	O
the	O
replacement	O
.	O
</s>
<s>
Apparently	O
,	O
a	O
broad	O
range	O
of	O
materials	O
can	O
be	O
used	O
for	O
ReRAM	B-General_Concept
.	O
</s>
<s>
However	O
,	O
the	O
discovery	O
that	O
the	O
popular	O
high-κ	B-Algorithm
gate	O
dielectric	O
HfO2	O
can	O
be	O
used	O
as	O
a	O
low-voltage	O
ReRAM	B-General_Concept
has	O
encouraged	O
researchers	O
to	O
investigate	O
more	O
possibilities	O
.	O
</s>
<s>
RRAM	B-General_Concept
is	O
the	O
registered	O
trademark	O
name	O
of	O
Sharp	O
Corporation	O
,	O
a	O
Japanese	O
electronic	O
components	O
manufacturer	O
,	O
in	O
some	O
countries	O
,	O
including	O
members	O
of	O
the	O
European	O
Union	O
.	O
</s>
<s>
An	O
energy-efficient	O
chip	O
called	O
NeuRRAM	O
fixes	O
an	O
old	O
design	O
flaw	O
to	O
run	O
large-scale	O
AI	B-Application
algorithms	O
on	O
smaller	O
devices	O
,	O
reaching	O
the	O
same	O
accuracy	O
as	O
wasteful	O
digital	O
computers	O
,	O
at	O
least	O
for	O
applications	O
needing	O
only	O
a	O
few	O
million	O
bits	O
of	O
neural	O
state	O
.	O
</s>
<s>
In	O
the	O
early	O
2000s	O
,	O
ReRAMs	B-General_Concept
were	O
under	O
development	O
by	O
a	O
number	O
of	O
companies	O
,	O
some	O
of	O
which	O
filed	O
patent	O
applications	O
claiming	O
various	O
implementations	O
of	O
this	O
technology	O
.	O
</s>
<s>
ReRAM	B-General_Concept
has	O
entered	O
commercialization	O
on	O
an	O
initially	O
limited	O
KB-capacity	O
scale	O
.	O
</s>
<s>
In	O
February	O
2012	O
,	O
Rambus	O
bought	O
a	O
ReRAM	B-General_Concept
company	O
called	O
Unity	O
Semiconductor	O
for	O
$35	O
million	O
.	O
</s>
<s>
Panasonic	O
launched	O
an	O
ReRAM	B-General_Concept
evaluation	O
kit	O
in	O
May	O
2012	O
,	O
based	O
on	O
a	O
tantalum	O
oxide	O
1T1R	O
(	O
1	O
transistor	O
–	O
1	O
resistor	O
)	O
memory	O
cell	O
architecture	O
.	O
</s>
<s>
In	O
2013	O
,	O
Crossbar	O
introduced	O
an	O
ReRAM	B-General_Concept
prototype	O
as	O
a	O
chip	O
about	O
the	O
size	O
of	O
a	O
postage	O
stamp	O
that	O
could	O
store	O
1TB	O
of	O
data	O
.	O
</s>
<s>
In	O
August	O
2013	O
,	O
the	O
company	O
claimed	O
that	O
large-scale	O
production	O
of	O
their	O
ReRAM	B-General_Concept
chips	O
was	O
scheduled	O
for	O
2015	O
.	O
</s>
<s>
The	O
memory	O
structure	O
(	O
Ag/a-Si/Si	O
)	O
closely	O
resembles	O
a	O
silver-based	O
CBRAM	B-General_Concept
.	O
</s>
<s>
Also	O
in	O
2013	O
,	O
Hewlett-Packard	O
demonstrated	O
a	O
memristor-based	O
ReRAM	B-General_Concept
wafer	B-Architecture
,	O
and	O
predicted	O
that	O
100	O
TB	O
SSDs	O
based	O
on	O
the	O
technology	O
could	O
be	O
available	O
in	O
2018	O
with	O
1.5	O
PB	O
capacities	O
available	O
in	O
2020	O
,	O
just	O
in	O
time	O
for	O
the	O
stop	O
in	O
growth	O
of	O
NAND	O
flash	O
capacities	O
.	O
</s>
<s>
Different	O
forms	O
of	O
ReRAM	B-General_Concept
have	O
been	O
disclosed	O
,	O
based	O
on	O
different	O
dielectric	O
materials	O
,	O
spanning	O
from	O
perovskites	O
to	O
transition	O
metal	O
oxides	O
to	O
chalcogenides	O
.	O
</s>
<s>
Leon	O
Chua	O
argued	O
that	O
all	O
two-terminal	O
non-volatile	B-General_Concept
memory	I-General_Concept
devices	O
including	O
ReRAM	B-General_Concept
should	O
be	O
considered	O
memristors	O
.	O
</s>
<s>
Stan	O
Williams	O
of	O
HP	O
Labs	O
also	O
argued	O
that	O
ReRAM	B-General_Concept
was	O
a	O
memristor	O
.	O
</s>
<s>
Whether	O
redox-based	O
resistively	O
switching	O
elements	O
(	O
ReRAM	B-General_Concept
)	O
are	O
covered	O
by	O
the	O
current	O
memristor	O
theory	O
is	O
disputed	O
.	O
</s>
<s>
CBRAM	B-General_Concept
cells	O
generally	O
would	O
not	O
require	O
forming	O
if	O
Cu	O
ions	O
are	O
already	O
present	O
in	O
the	O
electrolyte	O
,	O
having	O
already	O
been	O
driven-in	O
by	O
a	O
designed	O
photo-diffusion	O
or	O
annealing	O
process	O
;	O
such	O
cells	O
may	O
also	O
readily	O
return	O
to	O
their	O
initial	O
state	O
.	O
</s>
<s>
For	O
random-access	B-Architecture
type	O
memories	O
,	O
a	O
1T1R	O
(	O
one	O
transistor	O
,	O
one	O
resistor	O
)	O
architecture	O
is	O
preferred	O
because	O
the	O
transistor	O
isolates	O
current	O
to	O
cells	O
that	O
are	O
selected	O
from	O
cells	O
that	O
are	O
not	O
.	O
</s>
<s>
Thin	O
film	O
based	O
threshold	O
switch	O
can	O
work	O
as	O
a	O
selector	O
for	O
bipolar	O
and	O
unipolar	O
ReRAM	B-General_Concept
.	O
</s>
<s>
The	O
cross-point	O
architecture	O
requires	O
BEOL	B-Algorithm
compatible	O
two	O
terminal	O
selectors	O
like	O
punch-through	O
diode	O
for	O
bipolar	O
ReRAM	B-General_Concept
or	O
PIN	O
diode	O
for	O
unipolar	O
ReRAM	B-General_Concept
.	O
</s>
<s>
In	O
these	O
structures	O
,	O
A	B-Application
is	I-Application
a	O
monovalent	O
organic	O
or	O
inorganic	O
(	O
MA:CH3NH3	O
+	O
,	O
FA	O
:	O
CH(NH2 )	O
2+	O
,	O
Cs+	O
,	O
Rb+	O
)	O
,	O
B	O
is	O
a	O
divalent	O
metal	O
cation	O
(	O
Pb2+	O
,	O
Sn2+	O
)	O
,	O
and	O
X	O
is	O
a	O
halide	O
anion	O
(	O
Cl	O
,	O
Br	O
,	O
I	O
)	O
.	O
</s>
<s>
Given	O
the	O
fact	O
that	O
resistance	O
switching	O
in	O
halide	O
perovskite-based	O
RRAM	B-General_Concept
is	O
caused	O
by	O
migrations	O
of	O
halide	O
atoms	O
through	O
vacancies	O
,	O
the	O
migration	O
characteristics	O
of	O
a	O
vacancy	O
within	O
the	O
RRAM	B-General_Concept
are	O
one	O
of	O
the	O
most	O
important	O
material	O
properties	O
of	O
the	O
RRAM	B-General_Concept
determining	O
the	O
key	O
features	O
of	O
it	O
.	O
</s>
<s>
However	O
,	O
despite	O
its	O
importance	O
,	O
the	O
activation	O
energy	O
of	O
halide	O
vacancy	O
in	O
RRAMs	B-General_Concept
has	O
been	O
no	O
serious	O
study	O
topic	O
at	O
all	O
.	O
</s>
<s>
Obviously	O
,	O
a	O
small	O
activation	O
barrier	O
of	O
halide	O
vacancy	O
expected	O
in	O
halide	O
perovskite-based	O
RRAMs	B-General_Concept
plays	O
a	O
central	O
role	O
in	O
allowing	O
this	O
RRAM	B-General_Concept
to	O
operate	O
at	O
low	O
voltages	O
and	O
thus	O
at	O
low	O
power	O
consumption	O
mode	O
.	O
</s>
<s>
Papers	O
at	O
the	O
IEDM	O
Conference	O
in	O
2007	O
suggested	O
for	O
the	O
first	O
time	O
that	O
ReRAM	B-General_Concept
exhibits	O
lower	O
programming	O
currents	O
than	O
PRAM	B-Device
or	O
MRAM	B-General_Concept
without	O
sacrificing	O
programming	O
performance	O
,	O
retention	O
or	O
endurance	O
.	O
</s>
<s>
Some	O
commonly	O
cited	O
ReRAM	B-General_Concept
systems	O
are	O
described	O
further	O
below	O
.	O
</s>
<s>
At	O
IEDM	O
2008	O
,	O
the	O
highest-performance	O
ReRAM	B-General_Concept
technology	O
to	O
date	O
was	O
demonstrated	O
by	O
ITRI	O
using	O
HfO2	O
with	O
a	O
Ti	O
buffer	O
layer	O
,	O
showing	O
switching	O
times	O
less	O
than	O
10ns	O
and	O
currents	O
less	O
than	O
30μA	O
.	O
</s>
<s>
IMEC	O
presented	O
updates	O
of	O
their	O
ReRAM	B-General_Concept
program	O
at	O
the	O
2012	O
Symposia	O
on	O
VLSI	O
Technology	O
and	O
Circuits	O
,	O
including	O
a	O
solution	O
with	O
a	O
500	O
nA	O
operating	O
current	O
.	O
</s>
<s>
Winbond	O
had	O
done	O
more	O
recent	O
work	O
toward	O
advancing	O
and	O
commercializing	O
the	O
HfO2-based	O
ReRAM	B-General_Concept
.	O
</s>
<s>
Panasonic	O
revealed	O
its	O
TaOx-based	O
ReRAM	B-General_Concept
at	O
IEDM	O
2008	O
.	O
</s>
<s>
On	O
8	O
July	O
they	O
announced	O
they	O
would	O
begin	O
prototyping	O
ReRAM	B-General_Concept
using	O
their	O
memristors	O
.	O
</s>
<s>
The	O
TaOx-based	O
device	O
has	O
some	O
material	O
similarity	O
to	O
Panasonic	O
's	O
ReRAM	B-General_Concept
,	O
but	O
the	O
operation	O
characteristics	O
are	O
different	O
.	O
</s>
<s>
The	O
Adesto	O
Technologies	O
ReRAM	B-General_Concept
is	O
based	O
on	O
filaments	O
generated	O
from	O
the	O
electrode	O
metal	O
rather	O
than	O
oxygen	O
vacancies	O
.	O
</s>
<s>
Weebit	O
Nano	O
has	O
been	O
working	O
with	O
CEA-Leti	O
,	O
one	O
of	O
the	O
largest	O
nanotechnology	O
research	O
institutes	O
in	O
Europe	O
to	O
further	O
ReRAM	B-General_Concept
technology	O
.	O
</s>
<s>
Beginning	O
in	O
November	O
,	O
2017	O
,	O
the	O
company	O
has	O
demonstrated	O
the	O
manufacturability	O
in	O
40nm	O
SiOx	O
ReRAM	B-General_Concept
cells	O
,	O
followed	O
by	O
demonstrations	O
of	O
working	O
arrays	O
in	O
2018	O
and	O
discrete	O
components	O
in	O
2020	O
.	O
</s>
<s>
In	O
July	O
2021	O
,	O
the	O
company	O
taped	O
out	O
its	O
first	O
embedded	O
ReRAM	B-General_Concept
modules	O
.	O
</s>
<s>
In	O
September	O
2021	O
,	O
Weebit	O
,	O
together	O
with	O
Leti	O
,	O
produced	O
,	O
tested	O
and	O
characterized	O
a	O
1	O
Mb	O
ReRAM	B-General_Concept
array	O
,	O
using	O
a	O
28nm	O
FDSOI	O
process	O
on	O
300mm	O
wafers	B-Architecture
.	O
</s>
<s>
Crossbar	O
implements	O
an	O
Ag	O
filament	O
in	O
amorphous	O
Si	O
along	O
with	O
a	O
threshold	O
switching	O
system	O
to	O
achieve	O
a	O
diode+ReRAM	O
.	O
</s>
<s>
Infineon	O
Technologies	O
calls	O
it	O
conductive-bridging	O
RAM(CBRAM )	O
,	O
NEC	O
has	O
a	O
variant	O
called	O
"	O
Nanobridge	O
"	O
and	O
Sony	O
calls	O
their	O
version	O
"	O
electrolytic	O
memory	O
"	O
.	O
</s>
<s>
New	O
research	O
suggests	O
CBRAM	B-General_Concept
can	O
be	O
3D	O
printed	O
.	O
</s>
<s>
Quantum	O
dot	O
based	O
non-volatile	B-General_Concept
resistive	O
memory	O
device	O
with	O
a	O
switching	O
speed	O
of	O
10	O
ns	O
and	O
ON/OFF	O
ratio	O
of	O
10	O
000	O
.	O
</s>
<s>
Compared	O
to	O
PRAM	B-Device
,	O
ReRAM	B-General_Concept
operates	O
at	O
a	O
faster	O
timescale	O
(	O
switching	O
time	O
can	O
be	O
less	O
than	O
10ns	O
)	O
,	O
while	O
compared	O
to	O
MRAM	B-General_Concept
,	O
it	O
has	O
a	O
simpler	O
,	O
smaller	O
cell	O
structure	O
(	O
less	O
than	O
8F²	O
MIM	O
stack	O
)	O
.	O
</s>
<s>
Compared	O
to	O
flash	B-Device
memory	I-Device
and	O
racetrack	O
memory	O
,	O
a	O
lower	O
voltage	O
is	O
sufficient	O
,	O
and	O
hence	O
it	O
can	O
be	O
used	O
in	O
low-power	O
applications	O
.	O
</s>
<s>
ITRI	O
has	O
shown	O
that	O
ReRAM	B-General_Concept
is	O
scalable	O
below	O
30nm	O
.	O
</s>
<s>
The	O
motion	O
of	O
oxygen	O
atoms	O
is	O
a	O
key	O
phenomenon	O
for	O
oxide-based	O
ReRAM	B-General_Concept
;	O
one	O
study	O
indicated	O
that	O
oxygen	O
motion	O
may	O
take	O
place	O
in	O
regions	O
as	O
small	O
as	O
2nm	O
.	O
</s>
<s>
A	O
significant	O
hurdle	O
to	O
realizing	O
the	O
potential	O
of	O
ReRAM	B-General_Concept
is	O
the	O
sneak	O
path	O
problem	O
that	O
occurs	O
in	O
larger	O
passive	O
arrays	O
.	O
</s>
<s>
Another	O
bi-layer	O
structure	O
was	O
introduced	O
for	O
bipolar	O
ReRAM	B-General_Concept
to	O
improve	O
the	O
HRS	O
and	O
stability	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
for	O
a	O
3D-ReRAM	O
1TNR	O
array	O
,	O
with	O
a	O
column	O
of	O
N	O
ReRAM	B-General_Concept
cells	O
situated	O
above	O
a	O
select	O
transistor	O
,	O
only	O
the	O
intrinsic	O
nonlinearity	O
of	O
the	O
HRS	O
is	O
required	O
to	O
be	O
sufficiently	O
large	O
,	O
since	O
the	O
number	O
of	O
vertical	O
levels	O
N	O
is	O
limited	O
(	O
e.g.	O
,	O
N	O
=	O
8	O
–	O
32	O
)	O
,	O
and	O
this	O
has	O
been	O
shown	O
possible	O
for	O
a	O
low-current	O
ReRAM	B-General_Concept
system	O
.	O
</s>
<s>
Modeling	O
of	O
2D	O
and	O
3D	O
caches	O
designed	O
with	O
ReRAM	B-General_Concept
and	O
other	O
non-volatile	B-General_Concept
random	B-Architecture
access	I-Architecture
memories	I-Architecture
such	O
as	O
MRAM	B-General_Concept
and	O
PCM	B-Device
can	O
be	O
done	O
using	O
DESTINY	O
tool	O
.	O
</s>
<s>
The	O
increasing	O
computational	O
demands	O
necessary	O
for	O
many	O
improvements	O
in	O
artificial	B-Application
intelligence	I-Application
have	O
led	O
many	O
to	O
speculate	O
that	O
ReRAM	B-General_Concept
implementations	O
could	O
be	O
extremely	O
useful	O
hardware	O
for	O
running	O
artificial	B-Application
intelligence	I-Application
and	O
machine	O
learning	O
applications	O
.	O
</s>
<s>
Researchers	O
at	O
School	O
of	O
Engineering	O
of	O
Stanford	O
University	O
Havel	O
built	O
up	O
a	O
RRAM	B-General_Concept
that	O
"	O
does	O
the	O
AI	B-Application
processing	O
within	O
the	O
memory	O
itself	O
,	O
thereby	O
eliminating	O
the	O
separation	O
between	O
the	O
compute	O
and	O
memory	O
units.	O
"	O
</s>
