Abstract Radioastronomical observation development, pushes technology research to develop equipment working up to 100-150 GHz. This trend make heavier the Low noise Amplifiers (LNA) noise contribution. A significantly improvement comes from the Indium Phosphide (InP) Technology, that gives the best noise performances in this range. Moreover radioastronomy moves also towards array receivers configuration, this implies high integration and repeatability. In the frame of the FARADAY PROJECT we were involved in designing several kind of MMIC amplifiers in the 18 to 26 GHz range in order to approach the InP technology and the MMIC design methodology

Alessandro Orfei

Andrea Cremonini

Gianni Tofani

Sergio Mariotti

CiteSeerX

International Conference on Antenna Theory and Techniques, 9-12 September, 2003, Sevastopol, Ukraine pp 628-630 
INP MMIC AMPLIFIERS FOR CRYOGENIC 
RADIOASTRONOMICAL APPLICATIONS 
Andrea Cremonini1, Sergio Mariotti1, Alessandro Orfei1, Gianni Tofani1  
 
1 Istituto di Radioastronomia, Consiglio Nazionale delle Ricerche, Bologna, Italy  
 
Abstract 
Radioastronomical observation development, pushes technology research to 
develop equipment working up to 100-150 GHz. This trend make heavier the Low 
noise Amplifiers (LNA) noise contribution. A significantly improvement comes from 
the Indium Phosphide (InP) Technology, that gives the best noise performances in 
this range. Moreover radioastronomy moves also towards array receivers 
configuration, this implies high integration and repeatability. In the frame of the 
FARADAY PROJECT we were involved in designing several kind of MMIC 
amplifiers in the 18 to 26 GHz range in order to approach the InP technology and the 
MMIC design methodology.   
Keywords: Low Noise Amplifiers, InP, MMIC,  Cryogenic Applications, 
Radioastronomical Applications. 
 
1. INTRODUCTION 
 
In order to extend the observation capabilities, the 
radioastronomy research pushes towards higher and 
higher frequencies. Radioastronomical receivers must 
have excellent sensitivity and gain fluctuation 
stability. 
The most used semiconductor were, and in many 
cases actually are, based on Gallium Arsenide (GaAs) 
technology. For frequency higher than 30 GHz this 
technology, for extreme low noise applications, begin 
to show its final limit. Actually InP technology has 
the best noise performances at higher frequencies [3]. 
Moreover, array receivers require a great amount 
of devices that must have very comparable 
performances. For these reasons MMIC design 
approach allows higher integration and repeatability 
level compared with MIC devices, designed using 
discrete component [4,5]. 
FARADAY PROJECT [8], supported by European 
Community, has as a main goal, to promote research 
and  development of receivers based on array concept. 
In this context is inserted the work described in the 
following. We will present some amplifiers designed 
using InP MMIC technology, their specifications and 
design choices in order to realize this devices.  
 
2. AMLIFIERS SPECIFICATIONS  
 
Amplifiers described have been designed in order to 
satisfy the system requirement for a cryogenic 
multifeed array receiver working in the range 18 to 26 
Ghz frequency range. The receiver channel 
specification requests 2 cryogenic amplifier the first 
one optimized for noise performance, the second one 
for return loss and gain, with about 40 dB of  total 
gain . For this reason two classes of amplifiers have 
been designed. In Table I and II specifications are 
reported. 
 
Gain 26±1.5 dB 
Input Return Loss < -15 dB 
Noise Temp. Best effort 
Working Temp. 20 °K 
Table I -  LNA Specifications 
 
Gain 15±1.5 dB 
I/O Return Loss Primary constraint 
Noise Temp. Moderately Low 
Working Temp. 20 °K 
Table II -  BOA Specifications 
0-7803-7881-4/037$17.00 2003IEEE 
InP MMIC Amplifiers for Cryogenic Radioastronomical Applications 
3. AMPLIFIER FABRICATION 
  
Thanks to the collaboration with CSIRO-ATNF, 
the European Partners of FARADAY consortium 
have had the possibility to approach the TRW 0.1 InP 
process. This technology is the result of an ambitious 
project named CHOP, leaded by JPL and TRW, 
having aim to obtain optimized devices for cryogenic 
environment [1,2]. For our devices which aim is 
working at 20°K this is a fundamental characteristic. 
Actually, TRW library model are supported only 
for EESOF  LIBRA Series IV EDA Software. They 
support only 290°K active device models, and 
electromagnetic simulation, models and S-parameters 
for passive devices in the band 1to 50 GHz. About 
HEMT devices only 60%Idss is noise modeled. A 
more exhaustive beta version of semidistributed 
device models is available, but macro layout 
supported by CSIRO aren’t available for this MMIC. 
In this context we assumed to design “hot” devices, 
where each stage has independent bias pad, useful as 
tuning element.  
 
4. AMPLIFIER DESIGN DESCRIPTION 
The active device used are 4-fingers InP HEMT, 
0.1µm gate length. Gate width is 120µm (4x30). Each 
gate is separately biased to tune the best performances 
at cryogenic temperature. The chip size dimension are 
3.2 x 2.25 mm. 
 
4.1. LNA 
 
A 3-stage cascaded low noise amplifier layout is 
shown in Figure 1: 
 
Figure 1 
All matching circuits, except the first one, have 
been designed using distribute element like microstrip 
line. A one turn spiral inductor has been used in the 
first matching circuit as tradeoff between dimension 
constraints and the optimum noise matching point. 
This amplifier has been designed as a front end 
element, the first active device encountered  by the 
received signal. Moreover an off-chip matching 
network has been designed to prevent possible low 
frequency oscillation that could be primed through 
unwanted positive feedback path along the bias line. 
 
4.2. BACK OFF AMPLIFIER 
 
The layout of 2-stage cascade back off amplifier is 
shown in Figure 2: 
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
G ND:
RFO UT
VG 1 VG 2
VD1 VD2
RFI N
Figure 2 
Matching circuit has been designed to achieve high 
return loss performances over the entire 18 to 26 GHz 
bandwidth.  
Stability and RF isolation bias paths are also 
carefully investigated. Stability approach is 
conservative: every single stage has be designed to be 
unconditionally stable, following the indications 
given by K and B1 parameters. The S-probe stability 
check method has been tested for future applications: 
this method let  the designer to probe the stability in 
every internal section of the amplifier [5]. 
We have considered, where applicable,  twice the 
substrate thickness as minimum distance  between 
two microstrip element as general design rule in order 
to reduce coupling effect of microstrip elements. 
Every critical part of microstrip circuit has also been 
electromagnetically simulated with EMSight, the 
Microwave Office EM-simulator,  powered by 
AWR, and the results have been compared with 
circuital simulation: only minor effect has been noted. 
5. RESULTS OF THE SIMULATED 
AMPLIFIER  
  
Expected results are reported in the following 
tables and graphics: 
|S11| |S21| |S22|
18 -9.5 25.6 -15.4 97
22 -31.7 25.6 -19.4 89
26 -15.2 25.3 -9.5 94
LNA05 S Parameters [dB] Te @ 290 [K°] 
Fr
eq
ue
nc
y 
[G
H
z]
Table III
International Conference on Antenna Theory and Techniques, 9-12 September, 2003, Sevastopol, Ukraine 
Andrea Cremonini, Sergio Mariotti, Alessandro Orfei, Gianni Tofani 
Figure 3 
Figure 4 
Table IV 
Figure 5 
 
 
6. AMPLIFIERS PACKAGING 
 
This is a critical point that could result in a 
irreversibly chip damaging if not carefully 
considered. moreover, operative condition are 
different if compared with on wafer testing conditions 
and a on carrier measurement will be necessary to 
discover possibly instability source coming from the 
carrier design. 
Designed devices will operate in a 20°K 
cryogenical environment: cooling down the device 
also result in a undesirable mechanical deformation, 
depending on material physical propriety [6]. 
Semiconductors inside the carrier are usually attached 
by a conductive epoxy or welded. The different 
deformation between carrier and semiconductor may 
cause destructive mechanical stress.  With InP 
semiconductor using common brass carrier results in a 
chip destruction during  cooling down process. It has 
been investigated which kind of alloy could be the 
best trade off for us and several materials has been 
compared. Selected material must offer high thermal 
and electrical conductivity, because carrier is a 
ground reference and also an heat dissipating element. 
It’s thermal Expansion Coefficient must be equal or a 
little bit higher than InP, because semiconductor chip 
offer better compression than stretching performance. 
A lot of time has been spent to find alloy that met our 
specifications:  
10 15 20 25 30
Frequency (GHz)
LNA05
-20
-10
0
10
20
30
-40
-28
-16
-4
8
20
DB(|S[1,1]|) (R)
LNA05 w EBN 1_40  GHz
DB(|S[2,1]|) (L)
LNA05 w EBN 1_40  GHz
DB(|S[2,2]|) (R)
LNA05 w EBN 1_40  GHz
10 14 18 22 26 30
Frequency (GHz)
LNA 05 - Noise Temperature
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
TE
LNA05
W90 / Cu10 is produced using an High temperature 
sintering and infiltrate process. Ni/Au Metallization is 
possible by Electroplating or Physical Vapor 
Deposition ( Ni metalizzation is necessary to avoid 
Gold contamination by Cu during heating process 
necessary for packaging ). As reported in the table 
below this material has excellent physical and 
mechanical properties. Drawback of this material isn’t  
machinable.  
|S11| |S21| |S22|
18 16,6 15 -10,7
22 -25,1 16,2 -22,9
26 -20,4 14,7 -9,5
BOA07 S Parameters [dB]
Fr
eq
ue
nc
y 
[G
H
z]
Si30 / Al70 has excellent thermal expansion 
coefficient and conductivity but this alloy has poor 
electrical conductivity. This is an specification 
important because carrier is our ground reference, and 
high losses in the carrier could produce mismatch 
from the expected results. The preferred candidate 
seems to be Silvar-K  Alloy: It is easy machinable 
and it has been already cryogenically tested with InP 
devices from CSIRO-ATNF staff. Characteristic are 
specified in table V 
10 15 20 25 30
Frequency (GHz)
BOA07 - S Parameters
-10
-5
0
5
10
15
20
-40
-30
-20
-10
0
10
20
DB(|S[2,1]|) (L)
PA07
DB(|S[1,1]|) (R)
PA07
DB(|S[2,2]|) (R)
PA07
 
 CTE 
[µm/m/°C
] 
Thermal Conductivity 
[W/m K @ 25°C] 
γ 
[%IACS] 
Cu 17.8 398 100 
InP 4.5 68  
Brass >12 >120 4 
Kovar 5.3 17 2.2 
Silvar-K  7 110 18 
W90 / Cu10 6.5 202 42 
Si30 / Al70 6.5 180 1.7 
Table V 
ACKNOWLEDGEMENTS 
 
Authors would like to acknowledge CSIRO-ATNF 
(Australia) for design and measurements support, 
FARADAY European partner designers for the 
intense and synergic collaboration and the TOR 
International Conference on Antenna Theory and Techniques, 9-12 September, 2003, Sevastopol, Ukraine 
Andrea Cremonini, Sergio Mariotti, Alessandro Orfei, Gianni Tofani 
VERGATA UNIVERSITY MICROWAVE GROUP, 
in Rome, that shared EDA Software and skillness  
REFERENCES 
1. M.W. Pospieszalski, S.Weinreb, R.D.Norrod, 
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March 1988. 
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5. R.G.Gough, M.W. Sinclair – Low Noise, InP 
MMIC Amplifiers for Radioastronomy – APMC 
2001, page 668-671. 
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communication, on packaging tecnique and 
facilities. Dec 2002. 
7. K. Wang, M. Jones, S. Nelson – The S-Probe: A 
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Evaluating Multi Stage Amplifier Stability. IEEE 
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Access and Yeld - 1st Annual Report - HPRI-CT-
2001-50031 FP5 RTD CONTRACT 
 
 
 
 
International Conference on Antenna Theory and Techniques, 9-12 September, 2003, Sevastopol, Ukraine 


INP MMIC AMPLIFIERS FOR CRYOGENIC RADIOASTRONOMICAL APPLICATIONS

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INP MMIC AMPLIFIERS FOR CRYOGENIC RADIOASTRONOMICAL APPLICATIONS

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