Picosecond
electrical
spectroscopy
using
monolithic
GaAs
circuits
Y.
KonishLa)
M.
Kamegawa,
a)
M.
Case,
FL
Yu,
M.
J.
W.
Rodwell,
and
R.
A.
York
Department
of
Electrical
and
Computer
Engineering,
University
of
Cal$ornia,
Santa
Barbara,
California
93106
D.
8.
Rutledge
Division
of
Engineering
and
Applied
Science,
California
Institute
of
Technology,
Pasadena,
California
91125
(Received
24
April
1992;
accepted
for
publication
29
September
1992)
This
article
describes
an
experimental
apparatus
for
free-space
mm-wave
transmission
measurements
(spectroscopy).
GaAs
nonlinear
transmission
lines
and
sampling-circuits
are
used
as
picosecond
pulse
generators
and
detectors,
with
planar
monolithic
bowtie
antennas
with
associated
substrate
lenses
used
as
the
radiating
and
receiving
elements.
The
received
pulse
is
270
mV
amplitude
and
2.4
ps
rise
time.
Through
Fourier
transformation
of
the
received
pulse,
30-250
GHz
measurements
are
demonstrated
with
~0.3
dB
(rms)
accuracy.
Broadband
terahertz
(THz)
spectroscopy
using
fem-
tosecond
lasers
has
been
demonstrated
by
several
groups.
Iv3
In
these
systems,
antenna-coupled
photoconduc-
tors
illuminated
by
the
pulsed
laser
generate
and
detect
subpicosecond
electromagnetic
transients.
Through
Fou-
rier
analysis
of
the
received
signal,
material
amplitude
and
phase
transfer
functions
can
be
measured
at
frequencies
as
high
as
2
THz.
Nonlinear
transmission
lines
(
NLTLs)
and
NLTL-gated
sampling
circuits
are
an
alternative
solid-
state
technology
for
generation
and
detection
of
picosec-
ond
transients.4’5
Combining
NLTLs
with
broadband
an-
tennas,
picosecond
transients
can
be
radiated
and
detected
for
spectroscopic
measurements.6
The
resulting
apparatus
is
very
compact,
and
the
transmitters
and
receivers
are
inexpensive
components
fabricated
on
GaAs
with
a
5
mask
process
at
3
pm
device
geometries.
The
large
signal
ampli-
tude
permits
rapid
data
acquisition
and
direct
display
of
the
received
signal
on
an
oscilloscope.
The
system
attains
go.3
dB
accuracy
(standard
deviation)
from
30
to
250
GHz.
A
key
system
attribute
is
frequency
resolution,
dem-
onstrated
through
measurements
at
100
MHz
intervals
of
a
mm-wave
Bragg
filter.
the
120
“C
(52
a)
antenna,
through
a
coplanar
waveguide
(CPW)
feed
[Fig.
l(a)].
Two
100
R
resistances
at
the
antenna
perimeter
terminate
the
antenna
at
low
frequen-
cies.
The
receiver
is
a
bowtie
antenna
interfaced
to
an
NLTL-gated
sampling
circuit
[Fig.
1
(b)].
The
0.9
mm
ra-
dial
lengths
of
the
transmitter
and
receiver
antennas
sets
a
35
GHz
antenna
low-frequency
cutoff.
To
couple
the
radiated
power
from
the
GaAs
substrate
(
er=
13),
the
transmitter
and
receivers
are
placed
on
sili-
con
(Ed=
11.8)
hyperhemispherical
substrate
1enses”a
(Fig.
2).
The
lenses
also
partially
collimate
the
antenna
radiation.
The
radiated
beam
is
collimated
with
off-axis
parabolic
mirrors,
and
is
focused
on
the
receiver
through
similar
optics.
Above
the
low-frequency
cutoff,
the
antenna
system
loss
is
20
dB
as
determined
by
45
MHz-40
GHz
network
analysis4
on
larger
(3
mm)
antennas.
Imaging
the
The
NLTL
is
a
transmission
line
periodically
loaded
with
reversed-biased
diodes
serving
as
voltage-variable
ca-
pacitors
which
introduce
a
voltage-variable
propagation
velocity.4
The
negative-going
transitions
of
a
sinusoidal
in-
put
are
compressed
into
shock
waves,
and
the
output
is
a
sawtooth
wave
form.
In
on-wafer
measurements,
less
than
1.8
ps
fall
time
and
4.5
V
amplitude
wave
fronts
have
been
attained4
NLTL-gated
sampling
circuits
attained
similar
rise
times.4
The
NLTL
output
is
coupled
to
a
broadband
bowtie
antenna
having
a
frequency-independent
far-field
radiation
pattern
and
antenna
impedance.
This
antenna
permits
close
integration
of
the
antenna
and
NLTL,
but
has
a
mul-
tilobed
radiation
pattern,
resulting
in
nonuniformity
in
the
collimated
beam.
The
transmitter
NLTL
(50
fi
output
impedance),
fabricated
within
one
electrode
plane,
drives
“On
leave
from
Shimadzu
Corporation,
1,
Nishinokyo-Kuwabaracho,
FIG.
1.
Simplified
integrated
circuit
layouts
of
(a)
picosecond
transmit-
Nakagyo-ku,
Kyoto
604,
Japan.
ter
and
(b)
picosecond
receiver.
2829
Appl.
Phys.
Lett.
61
(23),
7
December
1992
0003-6951/92/482829-03$03.00
@
1992
American
Institute
of
Physics
2829
Downloaded 04 Apr 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp
synthesizer
(RF)
phase
reference
synth_esizer
(LO)
er
IC
off-
paraboloidal
mirror
material
under
test
is
2.
cnz
vi
3
s
E
4
0
-1
-2
-3
-4
-5
:
”
first
measurement
x
second
measurement
+
third
measurement
-...-
theory
0
50
100
150
Frequency
(GHz)
200
250
FIG.
4.
Vector
transmission
measurement
of
a
254
pm
thickness
alumina
test
sample.
FIG.
2.
Measurement
system
schematic
diagram
(left:
transmitter,
right:
receiver).
A
mixer
is
used
to
generate
a
stable
phase
reference
signal.
transmitter
antenna
onto
the
receiver
produces
a
resonant
cavity
because
of
reflections
at
the
air-lens
and
iens-
antenna
interfaces.
This
cavity
is
resonant
at
the
frequen-
cies
fN=Nc/21,
where
I
is
the
transmitter-receiver
separa-
tion
(1=25
cm).
These
resonances
are
suppressed
by
placing
5
dB
attenuators
at
oblique
incidence
on
both
sides
of
the
sample
under
test.
The
effect
of
cavity
resonances
on
transmission
measurements
can
also
be
suppressed’
by
lim-
iting
the
duration
of
observation
of
the
received
signal.
With
proper
adjustment
of
the
transmitter-receiver
spac-
ing,
secondary
signals
arising
from
multiple
transits
of
the
resonant
cavity
will
arrive
at
the
receiver
outside
the
period
of
observation,
and
are
not
measured.
Restricting
the
pe-
riod
of
observation
of
the
received
signal
to
duration
AT
restricts
the
frequency
resolution
of
the
measurement
to
Af
=
l/AT,2
if
AT
is
less
than
the
repetition
period
of
the
stimulus
signal.
The
transmitter
NLTL
is
driven
between
7
and
14
GHz,
while
the
sampling
circuit
is
driven
at
a
frequency
100
Hz
below
the
transmitter
frequency.
The
resulting
sampled
100
Hz
signal
is
observed
directly
on
an
oscillo-
scope.
Without
the
attenuators,
the
received
signal
at
the
sampling
circuit
output
(Fig.
3)
is
a
270
mV
peak-peak
pulse
train
with
2.4
ps
rise
time
(
lo%-90%)
and
a
decay
time
set
by
the
antenna
35
GHz
low-frequency
cutoff.
Res-
50
t
3
I
!
I
I
I
I
I
I
I
1
I
I
1
I
to
VI
I
I,
I
L
.
.
..I
TL
LyLL.-&
270
L
1
4
4
2.4~
-100
-
-100
mV
-300
~~
-400
-500
0
50
100
150
ml
jI;..~~~
‘;r.
/
risetime,
1
O-90%
-L--l
40
45
50
55
60
65
70
Time
(ps)
FIG.
3.
Received
wave
form
at
the
sampling
circuit
output.
In
the
inset
the
full
period
of
the
signal
is
shown.
onances
observed
after
the
pulse
may
be
arising
from
re-
flections
within
the
lens
system,
the
antennas,
or
the
NLTL
and
sampling
circuit.
Attenuation-frequency
and
phase-frequency
measure-
ments
are
obtained
by
taking
the
ratio
of
the
received
Fou-
rier
spectrum
with
the
device
under
test
in
place
with
the
spectrum
of
a
reference
measurement
taken
with
the
device
under
test
removed.
Figure
4
shows
the
measured.
trans-
missivity
of
a
254~pm-thickness
A&O3
substrate,
which
has
minima
when
C/2/4
+
n;1/2)/
,&=254
,um.
With
three
measurements,
the
accuracy
is
~0.3
dB
in
amplitude
and
5”
in
phase
(standard
deviations).
Figure
5
shows
measured
transmission
of
a
Bragg
filter
consisting
of
alternating
lay-
ers
of
alumina
(
10
pieces,
257
pm
thickness)
and
Teflon
(9
pieces,
523
,um
thickness).
Data
was
taken
at
100
NLTL
drive
frequencies
between
10
and
11
GHz,
yielding
mea-
surement
at
the
frequencies
n(
10
GHz+m
x
10
MHz)
where
n
and
O<m<99
are
integers,
corresponding
to
100
MHz
separation
at
100
GHz.
The
filter
shows
10
dB/GHz
slope
at
118
GHz.
We
have
demonstrated
a
simple
apparatus
for
accu-
rate,
high
resolution
broadband
mm-wave
electromagnetic
gain-frequency
measurements.
The
current
system
will
al-
low
convenient
and
accurate
measurement
of
mm-wave
materials
and
components.
0
-25
-30
100
150
200
250
GHz
.,---r-T--r
-7
r71-R
-7-r
130
140
Frequency
(GHz)
150
160
FIG.
5.
Transmission
measurement
of
a
Bragg
filter
consisting
of
alter-
nating
layers
of
10
pieces
of
alumina
and
9
pieces
of
TeRon.
The
inset
shows
transmission
over
an
expanded
frequency
range.
2830
Appl.
Phys.
Lett.,
Vol.
61,
No.
23,
7
December
1992
Konishi
et
a/.
2830
Downloaded 04 Apr 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp
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work
was
supported
by
the
Air
Force
Office
of
Scientific
Research
under
Grant
No.
( AFSOR-89-0394).
‘P.
R.
Smith,
D.
H.
Auston,
and
hl.
C.
Nuss,
IEEE
J.
Quantum
Elec-
tron.
QE-24,
255
(1988).
“G.
Arjavalingam,
Y.
Pastrol,
J.
M.
Halbout,
and
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V.
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IEEE
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38,
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Van
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and
D.
R.
Grischkowsky,
IEEE
Trans.
MTT
38,
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r199n1
~
____,.
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J.
W.
Rodwell,
M.
Kamegawa,
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M.
Case,
E.
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and
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23,
7
December
1992
Konishi
et
a/.
2831
Downloaded 04 Apr 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp