EUMC 1998
An NLTL based Integrated Circuit for a
70-200 GHz VNA System
O. Wohlgemuth, B.Agarwal*, R. Pullela*, D. Mensa*,
Q. Lee*, J. Guthrie*, M. J. W. Rodwell*, R. Reuter,
J. Braunstein, M. Schlechtweg, T. Krems, K. Köhler
Fraunhofer Institute for Applied Solid State Physics (IAF),
Tullastr. 72, D-79108 Freiburg - Germany
*Department of Electrical and Computer Engineering,
University of California, Santa Barbara, CA 93106
Archivierungsangabe
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Outline
• Motivation
• Conventional S-parameter measurement set-up
and integration on a chip
• Design and fabrication
• Performance of the
– integrated components
– full chip
• Summary
page 2
Archivierungsangabe
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Motivation
•Advancement in III-V technology especially in InP based devices
– HEMTs and HBTs with fmax > 500 GHz
•ICs, operating above 120 GHz
•Presently no commercial broadband on-wafer S-parameter
measurement system above 120 GHz available
page 3
Archivierungsangabe
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Measurement System
M ult iplier
Sampler/
harmonic
mixer
Chip
RF source
LO source
Chip
Sampler/
harmonic
mixer
IF
Sampler/
harmonic
mixer
HP
8510
DUT
Sampler/
harmonic
mixer
M ult iplier
page 4
Archivierungsangabe
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Block Diagram of the Chip
Chip
Bias
St imulus signal
33-50 GHz,
12 dBm
St robe signal
16.5-25 GHz -f ,
20 dBm
Low pass
f ilt er
Coupler
NLTL
RF
Coupler
Coupler
DUT
Sampler
NLTL
IF
(t o HP8510)
page 5
Archivierungsangabe
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
NLTL
Zl
Zl
Zl
V
Zl
t
Limiting faktors:
f per  1/  LCl  Cd 
–
Bragg Frequency
–
Skin-effect loss and diode loss
page 6
MD, 26th EuMC 1996
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Technology
• Planar Schottky diode
process
• N- layer exponential
doped
• Further process steps:
– Interconnect metal,
– Si3N4
– Air bridges
Semi-insulat ing GaAs
N+ layer
N- layer
Ohmic met al
Isolat ion implant
Schot t ky met al
page 7
MD, 26th EuMC 1996
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Problems with High Drive Frequency
• High skin-effect losses
• DC walk of because of the high loss
– Doides are driven through a minor capacitance variation
• Only low power available
– Long lines neccassary, to reach enough compression
page 8
MD, 26th EuMC 1996
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Design of the Multiplier NLTL
• Bragg frequency increases exponential
• Air bridge line combines wide center conductor with high Bragg
frequency
Exponent ial
t apered CPW
ZLS=40
Air bridge
line
ZLS=50
Line length: 4.2 mm
page 9
MD, 26th EuMC 1996
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Waveform at the Output of the Multiplier NLTL
0,0
• Input:
-0,2
– 36 GHz sine wave
with 12 dBm power
-0,4
Volatge [V]
-0,6
• Measured output:
– ~4.1 ps fall time
-0,8
-1,0
-1,2
-1,4
-1,6
-1,8
-15
-10
-5
0
5
10
15
Time [ps]
page 10
Archivierungsangabe
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Directional Coupler Designed for 180 GHz
25
•Coupler designed for
10 dB coupling
•Zeven, Zodd, geven and godd are
calculated with a 3D simulator
(HFSS)
Directivity [dB]
20
15
10
5
0
0
50
100
150
200
250
300
Frequency [GHz]
Measured directivity of the coupler
using on-wafer sampling circuits
page 11
MD, 26th EuMC 1996
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Low Pass Filter
Low pass filter neccassary with low reflection over the entire bandwidth
0
ZL
ZL
ZL
S21
-5
R
R
R
C
C
C
S-parameter [dB]
-10
-15
-20
S11
-25
-30
-35
ZL=75
C choosen for Zeff=50
-40
0
20
40
60
80
100
120
Frequency [GHz]
page 12
MD, 26th EuMC 1996
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Nonlinearity of the Sampling Circuits
Input Power [dBm]
-25
-20
-15
-10
-5
0
5
0
1. H
•Harmonic generation is negligible
for input powers below 0 dBm
-20
Output Voltage [dBV]
•Sampling circuit was driven with a
input frequency of 36 GHz
3. H
-40
5. H
-60
2. H
4. H
-80
-100
-40
-35
-30
-25
-20
-15
-10
-5
Input Voltage [dBV]
page 13
MD, 26th EuMC 1996
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Power at the DUT
0
•Not in the simulation included
are:
simulated
-10
– Attenuation of the
sampling circuit
– Skin-effect losses of the
coupler
Power [dBm]
1.H
2.H
3.H
-20
4.H
-30
measured
5.H
-40
•-35 dBm @ 200 GHz is
sufficient for measuring
-50
0
50
100
150
200
250
Frequency [GHz]
page 14
Archivierungsangabe
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Measured Directivity of the Full Chip
30
Measurement of 2 Chips
25
– open test port
20
Directivity [dB]
– 50  (44 +/-1.5 ) chip
resistor
15
10
5
0
50
100
150
200
250
Frequenz [GHz]
page 15
MD, 26th EuMC 1996
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
Summary
• The first IC, which can be used as a S-parameter
test set within 70-200 GHz
• Design and fabrication
• Performance of the single components and the full
chip
• Packaging these chips into active probes will
permit convenient on-wafer S-parameter
measurements
This work was supported by the German Ministry BMBF in the frame work of 01BM620 (555339)
Archivierungsangabe
IAF
Fraunhofer Insti tut
Angew andte
Festkörp erph ysik
page 16