Acta Materialia,
Journal Year:
2024,
Volume and Issue:
276, P. 120153 - 120153
Published: July 4, 2024
Superconducting
quantum
circuits
(SQC)
are
one
of
the
most
promising
hardware
platforms
for
computing,
yet
their
performance
is
currently
limited
by
presence
various
structural
defects
inside
circuit's
structure.
Despite
impressive
progress
in
past
decade,
a
precise
understanding
origin
these
from
fabrication
processes
and
impact
on
coherence
still
lacking.
In
this
study,
we
performed
comprehensive
investigation
microstructure,
superconductivity,
resonator
quality
factor
Nb
films
deposited
high-power
impulse
magnetron
sputtering
(HiPIMS)
direct
current
(DC)
sputtering.
A
suite
characterization
techniques,
including
electron
microscopy
with
spectroscopy,
secondary
ion
mass
spectrometry,
magneto-optical
microscopy,
pump-probe
reflectivity
spectroscopy
used.
We
reveal
that
niobium
(Nb)
resonators
fabricated
using
HiPIMS
exhibit
smaller
average
grain
size,
thicker
surface
oxide
larger
thickness
variations
(rougher
surface),
amorphous
Nb/Si
interface
layer
compared
to
samples
DC
identified
oxides
(mainly
located
at
along
boundaries)
Nb-Si
layers
(at
interface)
major
potential
sources
two-level
system
(TLS),
while
off-stochiometric
suboxides
close
surface,
crystalline
(i.e.,
dislocations
boundary,
point
introduced
during
deposition)
main
contributors
non-TLS
sources.
Our
findings
clarify
relationship
between
different
loss
mechanisms,
highlighting
importance
material
microstructure
control
optimization
SQC.
AVS Quantum Science,
Journal Year:
2025,
Volume and Issue:
7(2)
Published: May 14, 2025
The
native
oxide
layer
formed
on
aluminum
(Al)
surfaces
in
superconducting
quantum
circuits
is
a
significant
source
of
two-level
system
defects,
which
couple
with
electric
fields
and
degrade
coherence.
Recent
research
has
explored
etching,
encapsulation,
other
surface
treatments
as
potential
strategies
to
mitigate
the
formation
oxides
at
air
interfaces
these
circuits.
This
study
demonstrates
novel
approach
passivate
Al–air
interface
using
molecular
self-assembled
monolayer
(SAM).
Freshly
prepared
Al
thin
films
were
passivated
SAMs
by
immersing
Al-coated
silicon
substrates
SAM
solutions.
X-ray
photoelectron
spectroscopy
(XPS)
confirms
successful
binding
absence
further
growth.
Moreover,
passivation
remains
stable
after
aging
for
15
days
ambient
conditions,
evidenced
XPS
contact
angle
measurements.
Scanning
electron
microscopy
analyses
support
mitigation
These
findings
suggest
that
SAM-based
offers
promising
method
reducing
microwave
loss
improving
performance
Al-based
Physical Review Applied,
Journal Year:
2023,
Volume and Issue:
20(2)
Published: Aug. 18, 2023
Understanding
the
loss
mechanisms
in
materials
is
crucial
to
improving
coherence
superconducting
quantum
circuits.
The
authors
present
a
technique
based
on
multimode
resonators
that
distinguishes
and
quantifies
all
channels
relevant
materials.
Applying
this
reveals
both
chemical
etching
diamond
turning
reduce
surface
losses
high-purity
aluminum,
while
coating
diamond-turned
surfaces
with
thin-film
aluminum
significantly
improves
joint
quality.
This
method
can
be
used
design
on-chip
devices
characterize
microwave
losses,
as
well
quantify
effects
of
fabrication
processes.
Deleted Journal,
Journal Year:
2024,
Volume and Issue:
1(2)
Published: June 1, 2024
We
systematically
investigate
the
influence
of
fabrication
process
on
dielectric
loss
in
aluminum-on-silicon
superconducting
coplanar
waveguide
resonators
with
internal
quality
factors
(Qi)
about
one
million
at
single-photon
level.
These
devices
are
essential
components
quantum
processors;
they
also
serve
as
proxies
for
understanding
energy
qubits.
By
varying
several
steps,
we
identify
relative
importance
reducing
substrate–metal
and
substrate–air
interfaces.
find
that
it
is
to
clean
silicon
substrate
hydrogen
fluoride
(HF)
prior
aluminum
deposition.
A
post-fabrication
removal
oxides
surface
film
by
immersion
HF
further
improves
Qi.
observe
a
small,
but
noticeable,
adverse
effect
omitting
either
standard
cleaning
(SC1),
pre-deposition
heating
300
°C,
or
situ
post-deposition
oxidation
film’s
top
surface.
no
improvement
due
excessive
pumping
meant
reach
background
pressure
below
6
×
10−8
mbar.
correlate
measured
microscopic
properties
interface
through
characterization
x-ray
photoelectron
spectroscopy,
time-of-flight
secondary
ion
mass
spectrometry,
transmission
electron
microscopy,
energy-dispersive
atomic
force
microscopy.
Acta Materialia,
Journal Year:
2024,
Volume and Issue:
276, P. 120153 - 120153
Published: July 4, 2024
Superconducting
quantum
circuits
(SQC)
are
one
of
the
most
promising
hardware
platforms
for
computing,
yet
their
performance
is
currently
limited
by
presence
various
structural
defects
inside
circuit's
structure.
Despite
impressive
progress
in
past
decade,
a
precise
understanding
origin
these
from
fabrication
processes
and
impact
on
coherence
still
lacking.
In
this
study,
we
performed
comprehensive
investigation
microstructure,
superconductivity,
resonator
quality
factor
Nb
films
deposited
high-power
impulse
magnetron
sputtering
(HiPIMS)
direct
current
(DC)
sputtering.
A
suite
characterization
techniques,
including
electron
microscopy
with
spectroscopy,
secondary
ion
mass
spectrometry,
magneto-optical
microscopy,
pump-probe
reflectivity
spectroscopy
used.
We
reveal
that
niobium
(Nb)
resonators
fabricated
using
HiPIMS
exhibit
smaller
average
grain
size,
thicker
surface
oxide
larger
thickness
variations
(rougher
surface),
amorphous
Nb/Si
interface
layer
compared
to
samples
DC
identified
oxides
(mainly
located
at
along
boundaries)
Nb-Si
layers
(at
interface)
major
potential
sources
two-level
system
(TLS),
while
off-stochiometric
suboxides
close
surface,
crystalline
(i.e.,
dislocations
boundary,
point
introduced
during
deposition)
main
contributors
non-TLS
sources.
Our
findings
clarify
relationship
between
different
loss
mechanisms,
highlighting
importance
material
microstructure
control
optimization
SQC.