<s>
Electrochemical	B-General_Concept
Random-Access	I-General_Concept
Memory	I-General_Concept
(	O
ECRAM	B-General_Concept
)	O
is	O
a	O
type	O
of	O
non-volatile	B-General_Concept
memory	I-General_Concept
(	O
NVM	O
)	O
with	O
multiple	O
levels	O
per	O
cell	O
(	O
MLC	O
)	O
designed	O
for	O
deep	B-Algorithm
learning	I-Algorithm
analog	O
acceleration	O
.	O
</s>
<s>
An	O
ECRAM	B-General_Concept
cell	O
is	O
a	O
three-terminal	O
device	O
composed	O
of	O
a	O
conductive	O
channel	O
,	O
an	O
insulating	O
electrolyte	O
,	O
an	O
ionic	O
reservoir	O
,	O
and	O
metal	O
contacts	O
.	O
</s>
<s>
The	O
charge-transfer	O
process	O
allows	O
both	O
for	O
state	O
retention	O
in	O
the	O
absence	O
of	O
applied	O
power	O
,	O
and	O
for	O
programming	O
of	O
multiple	O
distinct	O
levels	O
,	O
both	O
differentiating	O
ECRAM	B-General_Concept
operation	O
from	O
that	O
of	O
a	O
field-effect	O
transistor	O
(	O
FET	O
)	O
.	O
</s>
<s>
The	O
write	O
operation	O
is	O
deterministic	O
and	O
can	O
result	O
in	O
symmetrical	O
potentiation	O
and	O
depression	O
,	O
making	O
ECRAM	B-General_Concept
arrays	O
attractive	O
for	O
acting	O
as	O
artificial	O
synaptic	O
weights	O
in	O
physical	O
implementations	O
of	O
artificial	B-Architecture
neural	I-Architecture
networks	I-Architecture
(	O
ANN	O
)	O
.	O
</s>
<s>
The	O
technological	O
challenges	O
include	O
open	O
circuit	O
potential	O
(	O
OCP	O
)	O
and	O
semiconductor	B-Algorithm
foundry	I-Algorithm
compatibility	O
associated	O
with	O
energy	O
materials	O
.	O
</s>
<s>
Universities	O
,	O
government	O
laboratories	O
,	O
and	O
corporate	O
research	O
teams	O
have	O
contributed	O
to	O
the	O
development	O
of	O
ECRAM	B-General_Concept
for	O
analog	O
computing	O
.	O
</s>
<s>
Notably	O
,	O
Sandia	O
National	O
Laboratories	O
designed	O
a	O
lithium-based	O
cell	O
inspired	O
by	O
solid-state	O
battery	O
materials	O
,	O
Stanford	O
University	O
built	O
an	O
organic	O
proton-based	O
cell	O
,	O
and	O
International	O
Business	O
Machines	O
(	O
IBM	O
)	O
demonstrated	O
in-memory	O
selector-free	O
parallel	O
programming	O
for	O
a	O
logistic	O
regression	O
task	O
in	O
an	O
array	O
of	O
metal-oxide	O
ECRAM	B-General_Concept
designed	O
for	O
insertion	O
in	O
the	O
back	B-Algorithm
end	I-Algorithm
of	I-Algorithm
line	I-Algorithm
(	O
BEOL	B-Algorithm
)	O
.	O
</s>
<s>
Although	O
in	O
ECRAM	B-General_Concept
,	O
the	O
programming	O
of	O
the	O
memory	O
element	O
is	O
defined	O
not	O
as	O
a	O
change	O
in	O
capacity	O
or	O
opacity	O
,	O
but	O
by	O
a	O
change	O
of	O
channel	O
conductivity	O
associated	O
with	O
atomic	O
species	O
being	O
inserted	O
or	O
removed	O
as	O
a	O
result	O
of	O
the	O
stress	O
signal	O
.	O
</s>
<s>
The	O
programming	O
speed	O
of	O
ECRAM	B-General_Concept
cells	O
is	O
not	O
limited	O
by	O
the	O
bulk	O
diffusion	O
of	O
ions	O
.	O
</s>
<s>
ECRAM	B-General_Concept
arrays	O
are	O
integrated	O
in	O
a	O
pseudo-crossbar	O
layout	O
,	O
the	O
gate	O
access	O
line	O
being	O
common	O
to	O
all	O
devices	O
in	O
a	O
row	O
or	O
column	O
.	O
</s>
<s>
Suppressing	O
OCP	O
in	O
the	O
ECRAM	B-General_Concept
design	O
,	O
minimizes	O
the	O
cell	O
size/complexity	O
,	O
allowing	O
for	O
selector-free	O
parallel	O
read/programming	O
of	O
device	O
arrays	O
.	O
</s>
<s>
Non-volatile	B-General_Concept
memory	I-General_Concept
(	O
NVM	O
)	O
can	O
be	O
leveraged	O
for	O
in-memory	B-General_Concept
compute	I-General_Concept
,	O
thereby	O
reducing	O
the	O
frequency	O
of	O
data	O
transfer	O
between	O
storage	O
and	O
processing	O
units	O
.	O
</s>
<s>
Hence	O
,	O
when	O
using	O
multi-level	B-Device
cells	I-Device
(	O
MLC	O
)	O
at	O
the	O
nodes	O
of	O
cross-bar	O
arrays	O
,	O
one	O
can	O
perform	O
analog	O
operations	O
on	O
time	O
or	O
voltage	O
encoded	O
data	O
such	O
as	O
vector	O
(	O
row	O
input	O
signal	O
)	O
×	O
matrix	O
(	O
memory	O
array	O
)	O
multiply	O
.	O
</s>
<s>
For	O
ECRAM	B-General_Concept
cells	O
,	O
an	O
additional	O
line	O
is	O
added	O
at	O
each	O
row	O
to	O
write	O
the	O
cells	O
during	O
programming	O
cycles	O
,	O
thereby	O
yielding	O
a	O
pseudo-crossbar	O
architecture	O
.	O
</s>
<s>
In	O
the	O
field	O
of	O
artificial	B-Application
intelligence	I-Application
(	O
AI	B-Application
)	O
,	O
deep	O
neural	B-Architecture
networks	I-Architecture
(	O
DNN	O
)	O
are	O
used	O
for	O
classification	O
and	O
learning	O
tasks	O
,	O
relying	O
on	O
a	O
large	O
number	O
of	O
matrix-multiply	O
operations	O
.	O
</s>
<s>
ECRAM	B-General_Concept
cells	O
are	O
uniquely	O
positioned	O
for	O
use	O
in	O
analog	O
deep	B-General_Concept
learning	I-General_Concept
accelerators	I-General_Concept
due	O
to	O
their	O
inherent	O
deterministic	O
and	O
symmetric	O
programming	O
nature	O
when	O
compared	O
to	O
other	O
devices	O
such	O
as	O
resistive	B-General_Concept
RAM	I-General_Concept
(	O
ReRAM	B-General_Concept
or	O
RRAM	B-General_Concept
)	O
and	O
phase-change	B-Device
memory	I-Device
(	O
PCM	O
)	O
.	O
</s>
<s>
Physical	O
implementation	O
of	O
artificial	B-Architecture
neural	I-Architecture
networks	I-Architecture
(	O
ANN	O
)	O
must	O
perform	O
at	O
iso-accuracy	O
when	O
benchmarked	O
against	O
floating	B-Algorithm
point	I-Algorithm
precision	I-Algorithm
weights	O
in	O
software	O
.	O
</s>
<s>
This	O
sets	O
the	O
boundary	O
for	O
device	O
properties	O
needed	O
for	O
analog	O
deep	B-General_Concept
learning	I-General_Concept
accelerators	I-General_Concept
.	O
</s>
<s>
During	O
each	O
programming	O
cycle	O
(	O
back-propagation	B-Algorithm
)	O
,	O
weight	O
updates	O
can	O
be	O
negative	O
or	O
positive	O
,	O
and	O
the	O
up/down	O
traces	O
therefore	O
need	O
symmetry	O
to	O
allow	O
learning	O
algorithms	O
to	O
converge	O
.	O
</s>
<s>
ECRAM	B-General_Concept
individual	O
cells	O
can	O
meet	O
such	O
stringent	O
metrics	O
,	O
but	O
also	O
need	O
to	O
demonstrate	O
high-density	O
array	O
yield	O
and	O
stochasticity	O
.	O
</s>
<s>
In	O
particular	O
a	O
2-layer	O
neural	B-Architecture
network	I-Architecture
is	O
mapped	O
to	O
the	O
array	O
by	O
transferring	O
the	O
weights	O
necessary	O
to	O
perform	O
an	O
inference	O
task	O
resulting	O
in	O
a	O
XOR	O
operation	O
on	O
the	O
binary	O
input	O
vector	O
.	O
</s>
<s>
Using	O
metal-oxide	O
ECRAM	B-General_Concept
cells	O
,	O
selector-free	O
,	O
the	O
team	O
demonstrates	O
parallel	O
programming	O
and	O
addressing	O
in	O
2×2	O
arrays	O
.	O
</s>
<s>
Various	O
institutions	O
have	O
demonstrated	O
ECRAM	B-General_Concept
cells	O
with	O
vastly	O
different	O
materials	O
,	O
layouts	O
,	O
and	O
performances	O
.	O
</s>
<s>
Based	O
on	O
lithium	O
ions	O
,	O
Li-ECRAM	O
devices	O
have	O
demonstrated	O
repeatable	O
and	O
controlled	O
switching	O
by	O
applying	O
known	O
materials	O
from	O
battery	O
technology	O
to	O
the	O
memory	O
design	O
.	O
</s>
<s>
Based	O
on	O
hydrogen	O
ions	O
,	O
H-ECRAM	O
devices	O
have	O
proven	O
fast	O
,	O
necessitating	O
small	O
driving	O
forces	O
to	O
induce	O
programming	O
.	O
</s>
<s>
Most	O
H-ECRAM	O
designs	O
use	O
liquid	O
and/or	O
organic	O
electrolytes	O
.	O
</s>
<s>
The	O
same	O
year	O
researchers	O
at	O
the	O
Royal	O
Institute	O
of	O
Technology	O
KTH	O
showed	O
ECRAMS	B-General_Concept
based	O
on	O
hydrogen	O
intercalation	O
into	O
the	O
2D	O
material	O
MXene	O
,	O
marking	O
the	O
first	O
demonstration	O
of	O
high	O
speed	O
2D	O
ECRAMs	B-General_Concept
.	O
</s>
<s>
Metal-oxide	O
based	O
ECRAM	B-General_Concept
,	O
are	O
inspired	O
from	O
OxRam	B-General_Concept
materials	O
and	O
high-k/metal	B-Algorithm
gate	I-Algorithm
technology	O
used	O
in	O
commercial	O
semiconductor	O
offerings	O
.	O
</s>
<s>
MO-ECRAM	O
do	O
enable	O
negligible	O
OCP	O
and	O
sub-μs	O
write	O
operations	O
.	O
</s>
<s>
The	O
implications	O
for	O
ECRAM	B-General_Concept
are	O
described	O
here	O
.	O
</s>
<s>
A	O
semiconductor	B-Algorithm
foundry	I-Algorithm
can	O
handle	O
several	O
technologies	O
and	O
has	O
strict	O
rules	O
when	O
it	O
comes	O
to	O
materials	O
being	O
introduced	O
in	O
its	O
expensive	O
toolset	O
to	O
avoid	O
cross-contamination	O
and	O
loss	O
of	O
device	O
yield	O
.	O
</s>
<s>
There	O
are	O
several	O
other	O
considerations	O
for	O
the	O
foundries	B-Algorithm
;	O
including	O
safety	O
,	O
cost	O
,	O
volume	O
,	O
etc	O
.	O
</s>
<s>
Hence	O
,	O
lithium	O
ion-based	O
Li-ECRAM	O
faces	O
unique	O
challenges	O
beyond	O
the	O
presence	O
of	O
OCP	O
.	O
</s>
<s>
Such	O
periphery	O
is	O
based	O
on	O
field-effect	O
transistors	O
(	O
FETs	O
)	O
built	O
on	O
the	O
surface	O
of	O
silicon	B-Architecture
wafer	I-Architecture
substrates	B-Architecture
with	O
a	O
high	O
thermal	O
budget	O
at	O
the	O
front	B-Algorithm
end	I-Algorithm
of	I-Algorithm
line	I-Algorithm
(	O
FEOL	B-Algorithm
)	O
.	O
</s>
<s>
Memory	O
cells	O
can	O
be	O
inserted	O
between	O
upper	O
metal	O
levels	O
at	O
back	B-Algorithm
end	I-Algorithm
of	I-Algorithm
line	I-Algorithm
(	O
BEOL	B-Algorithm
)	O
but	O
will	O
still	O
need	O
to	O
remain	O
unaffected	O
by	O
temperatures	O
up	O
to	O
~	O
400°C	O
used	O
in	O
subsequent	O
steps	O
.	O
</s>
<s>
The	O
ECRAMs	B-General_Concept
based	O
on	O
2D	O
MXene	O
materials	O
have	O
shown	O
the	O
potential	O
to	O
be	O
unaffected	O
by	O
400	O
°C	O
heating	O
,	O
but	O
additional	O
development	O
is	O
needed	O
for	O
the	O
integration	O
of	O
ion	O
conductors	O
.	O
</s>
<s>
One	O
way	O
to	O
introduce	O
novel	O
memory	O
materials	O
can	O
be	O
to	O
use	O
heterogeneous	B-Algorithm
integration	I-Algorithm
(	O
HI	O
)	O
where	O
the	O
device	O
array	O
is	O
fabricated	O
independently	O
from	O
the	O
logic	O
controls	O
and	O
then	O
bonded	O
to	O
the	O
FET-containing	O
chip	O
to	O
enable	O
its	O
use	O
as	O
high	O
bandwidth	O
memory	O
(	O
HBM	O
)	O
.	O
</s>
