The cryogenic noise temperature performance of a two-stage and a three-stage 32 GHz High Electron Mobility Transistor (HEMT) amplifier was evaluated. The amplifiers employ 0.25 micrometer conventional AlGaAs/GaAs HEMT devices, hybrid matching input and output microstrip circuits, and a cryogenically stable dc biasing network. The noise temperature measurements were performed in the frequency range of 31 to 33 GHz over a physical temperature range of 300 K down to 12 K. Across the measurement band, the amplifiers displayed a broadband response, and the noise temperature was observed to decrease by a factor of 10 in cooling from 300 K to 15 K. The lowest noise temperature measured for the two-stage amplifier at 32 GHz was 35 K with an associated gain of 16.5 dB, while the three-stage amplifier measured 39 K with an associated gain of 26 dB. It was further observed that both amplifiers were insensitive to light

Ballingall, J. M.

Bautista, J. J.

Chao, P. C.

Duh, K. H. G.

Ho, P.

Kao, M. Y.

Kopp, W. F.

Ortiz, G. G.

Smith, P. M.

English

NASA Technical Reports Server

TDA Progress Report 42-95 July-September 1988 
32-GHz Cryogenically Cooled HEMT Low-Noise Amplifiers 
J. J. Bautista and G. G. Ortiz 
Radio Frequency and Microwave Subsystems Section 
K. H. G. Duh, W. F.  Kopp, P. Ho, P. C. Chao, M. Y .  Kao, 
P. M. Smith, and J. M. Ballingall 
G E  Electronics Laboratory 
The cryogenic noise temperature performance of  a two-stage and a three-stage 32-GHz 
HEMT amplifier has been evaluated. The amplifiers employ 0.25-pm conventionalAIGdsl 
G d s  HEMT devices, hybrid matching input and output microstrip circuits, and a cryo- 
genically stable dc biasing network. The noise temperature measurements were performed 
in the frequency range of31 to 33 GHz over a physical temperature range of 300 K down 
to 12 K. Across the measurement band, the amplifiers displayed a broadband response, 
and the noise temperature was observed to decrease by a factor of  10 in cooling from 
300 K to 15 K. The lowest noise temperature measured for the two-stage amplifier a t  
32 GHz was 35 K with an associated gain of 16.5 dB, while the three-stage amplifier 
measured 39 K with an associatedgain of  26 dB. It was further observed that both ampli- 
fiers were insensitive to light. 
1. Introduction 
Traditionally, the extraordinarily sensitive receiver systems 
operated by the Jet Propulsion Laboratory’s Deep Space Net- 
work (DSN) have employed ruby masers as the low-noise 
front-end amplifiers. The rapid advances recently achieved by 
cryogenically cooled high-electron-mobility transistor (HEMT) 
low-noise amplifiers (LNAs) in the 1- to 10-GHz range are 
approaching maser amplifier performance [ l ]  , [2] . In order to 
address its future spacecraft navigation, telemetry, radar, and 
radio science needs, the DSN is investigating both maser [3] 
and HEMT amplifiers for its 32-GHz downlink capability. 
This report describes the noise temperature performance of 
the 32-GHz HEMT LNAs. 
II. HEMT Device 
Since one of the primary functions of the LNA is to mini- 
mize the receiver system noise temperature, the characteriza- 
tion and selection of HEMT devices is critical to the LNA’s 
performance. The selection of the 0.25-pm gate length con- 
ventional AlGaAs/GaAs HEMTs was based on their previously 
demonstrated reliability and exceptionally high gain and low 
noise characteristics [4] , [5] .  
The devices were fabricated on selectively doped AlGaAs/ 
GaAs heterostructures grown by molecular beam epitaxy 
(MBE) with a Varian GEN I1 system on a 3-inch-diameter 
GaAs substrate. The details of the material growth conditions 
71 
https://ntrs.nasa.gov/search.jsp?R=19890010965 2020-03-20T03:53:42+00:00Z
are discussed elsewhere [6] . Figure 1 schematically illustrates 
the cross section of the HEMT device. The HEMT wafer 
exhibited a sheet carrier density of 8.1 X 1012/cmZ with a 
mobility of more than 75,000 cm2/V*sec at 77 K. All levels 
were defined by electron beam lithography, and the T-shape 
gates were fabricated using the PMMA/P(MMA-MMA)/PMMA 
tri-layer resist technique [7] to achieve a low series gate 
resistance. 
For low-noise performance at cryogenic temperatures, the 
HEMT device must exhibit good pinch-off characteristics and 
high transconductance, gm . Good pinch-off characteristics are 
achieved by strong confinement of the charge carriers to the 
channel region with a sharp interface of high quality and a 
large conduction band discontinuity. An enhanced g, at the 
operating bias is obtained by a judicious choice of doping 
concentration and space layer thickness [8] .  An A1 mole 
fraction of approximately 30% is required for a large conduc- 
tion band discontinuity, while the high g, is achieved with a 
4-nm spacer layer and a doping concentration of approxi- 
mately 2 X 10l8 dopant atoms/cm3. Although these values 
will result in a high-performance room-temperature device, 
at physical temperatures below 150 K the device will suffer 
from I-V collapse [9] and exhibit the persistent photocon- 
ductivity effect associated with the presence of deep donor 
traps (called DX centers). In order to obtain excellent device 
performance at cryogenic temperatures and to eliminate light 
sensitivity, previous work [ l ]  , [8] has demonstrated that the 
A1 composition must not exceed 23% and the doping concen- 
tration must be approximately 101*/cm3. 
The data shown in Table 1 ,  comparing two HEMTs with the 
same Al mole fraction (23%) but different doping concentra- 
tions in the n-AlGaAs layer, serves to illustrate the difference 
between low-temperature and room-temperature device opti- 
mization. Device A has an n-AlGaAs doping concentration of 
1018/cm3, while that of B is twice as high. As expected, 
device B exhibited a higher gm and associated gain than device 
A, with approximately the same noise figure for both devices 
at 300 K. However, at 13 K and 8.5 GHz, device B exhibited 
a minimum noise temperature of 13.1 K ,  while device A 
yielded a value of 5.3 K. 
111. Amplifier Design and Circuit 
Both LNAs were designed to achieve the best room-temper- 
ature low-noise performance based on the measured room- 
temperature device parameters. Following construction and 
room-temperature optimization, the LNAs are then biased for 
lowest noise performance at cryogenic temperatures. 
The device gate width of 75 pm selected for this work was 
determined by the tradeoffs associated with optimum impe- 
dance matching, circuit bandwidth, intermodulation distor- 
tion, power handling capability, and power dissipation. Figure 2 
shows a photograph of the 32-GHz hybrid two-stage HEMT 
LNA package. The input and output ports utilize a broadband 
WR28-to-stepped ridge waveguide-to-microstrip transition. 
Figure 3 shows the insertion loss and return loss of a stepped 
ridge fixture that consists of two stepped-ridge transitions 
connected back-to-back with a microstrip 50-ohm line 0.5 in. 
long. The input and output matching networks were designed 
based on the device equivalent circuit values obtained from 
fitting measured S-parameters at the low-noise bias condition 
to the model from 2 to  20 GHz. Figure 4 shows the topology 
used for the 0.25-pm HEMT equivalent circuit model. Input, 
output, and interstage matching circuits were designed on 
1 0-mil quartz substrate with TaN thin-film resistors and 
TiWAu metallization. A schematic diagram of the two-stage 
hybrid HEMT LNA is shown in Fig. 5 .  The edge-coupled 
symmetric microstrip dc blocking transmission line also served 
as a bandpass filter, improving the out-of-band stability. As 
shown in Fig. 6, the three-stage LNA is constructed from the 
two-stage LNA by the insertion of another interstage match- 
ing circuit. 
The LNA fixture (OFHC copper) and dc bias circuits [ 101 
are designed for operation at cryogenic temperatures. Diode 
protection was included in both the gate and drain bias cir- 
cuits. LEDs were mounted on the cover of the fixture above 
each of the HEMTs for the purpose of examining their light 
sensitivity at cryogenic temperatures. All of the stages use 
devices from the same wafer. 
IV. Measurement Results 
The LNAs were first measured at room temperature with 
the devices biased for lowest noise at room temperature and 
then biased for lowest noise performance at cryogenic tem- 
peratures. The LNA room-temperature broadband noise fig- 
ure and gain for the two- and three-stage LNAs are shown in 
Figs. 7 and 8, respectively. Both LNAs exhibited an average 
noise figure of approximately 2 dB from 28 to 36 GHz. From 
29 to 34 GHz, the gain measured approximately 17 dB and 
24 dB for the two-stage and three-stage LNA, respectively. 
The addition of an external isolator only slightly degraded the 
gain and noise figure by 0.3 dB. 
With the devices biased for lowest noise at cryogenic tem- 
perature (1 2 K), the noise temperature (referenced at the 
room-temperature input waveguide flange) of both LNAs was 
observed to decrease nearly quadratically as a function of 
physical temperature as they cooled from 300 K to 12 K. 
(See Fig. 9 for a diagram of the closed-cycle refrigerator and 
measurement system.) The noise temperature of the two- 
stage LNA decreased from 350 K at ambient to 35 K at 
72 
14.5 K,  while the three-stage LNA decreased from 400 K to 
41 K at 12.5 K (Figs. 10 and 11). Figures 12 and 13 show the 
cryogenic noise temperature and gain response from 3 1 to 
33 GHz, along with bias settings for the two-stage and three- 
stage LNA, respectively. At 32 GHz, the two-stage LNA noise 
temperature measured 35 K,  with an associated gain of 16.5 dB, 
at a physical temperature of 14 K, while the three-stage LNA 
yielded a value of 41 K with a 26.0-dB associated gain. It is 
also noted that the three-stage LNA displayed an almost 
flat noise temperature response across the measurement band, 
with a minimum noise temperature of 39 K at 32 GHz, while 
the two-stage LNA displayed a noise temperature response 
decreasing monotonically from 31 to 33 GHz, with a mini- 
mum noise temperature of 31 K at 33 GHz. 
It was further observed that both amplifiers did not show a 
persistent photoconductivity effect. That is, it was found that 
these devices can be cooled with or without illumination 
and/or dc bias, without any observable effect on the cryogenic 
low-noise performance. 
V. Conclusion 
Cryogenic coolable state-of-the-art 32-GHz HEMT LNAs 
have been demonstrated using 0.25-pm AlGaAs/GaAs HEMTs. 
The results clearly demonstrate their potential to meet the 
future need for extremely low-noise receivers for applications 
such as the DSN. Further advances in HEMT technology 
[12] promise to lead to improved performance at all frequen- 
cies and make possible the development of amplifiers operat- 
ing at frequencies up to 94 GHz. 
Currently, the DSN relies on maser amplifiers in order to 
provide the best possible telemetry support for deep space 
missions. These systems require a complex and expensive 
cryogenic system operating at 4.5 K. Since HEMT LNAs 
require less cooling power and operate at a higher physical 
temperature (12 K), they can be operated at less cost with a 
more reliable refrigeration system. The lower cost of HEMT 
LNAs will lead to greater frequency coverage and the eco- 
nomic realization of multiple-element cryogenic array feed 
systems. 
Acknowledgments 
The authors wish to thank M. Pospieszalski for providing X-band cryogenic HEMT 
data, and J .  Merrill for the waveguide transition design. The authors would also like to 
acknowledge the support of A. A. Jabra, D. Neff, J. Bowen, and D. Norris. GE Elec- 
tronics Laboratory’s 32-GHz cryogenic low-noise HEMT development was supported by 
JPL under Contract No. 957352. 
73 
References 
[ 11 M. W. Pospieszalski, S. Weinreb,P. C. Chao,U. K. Mishra, S. C. Palmateer,P. M. Smith, 
and J. C. M. Hwang, “Noise Parameters and Light Sensitivity of Low-Noise High- 
Electron-Mobility Transistors,” IEEE Trans. Electron Devices, vol. ED-33, pp. 2 18- 
223,1986. 
[2] S. Weinreb, M. W. Pospieszalski, and R. Norrod, “Cryogenic, HEMT, Low-Noise 
Receivers for 1.3 to.43 GHz Range,” IEEEMTT-S Digest, pp. 945-948, 1988. 
[3] J. Shell and D. Neff, “A 32-GHz Reflected Wave Maser Amplifier with Wide In- 
stantaneous Bandwidth,” IEEEMTT-S Digest, pp. 789-792, 1988. 
[4] K. H. G .  Duh, P. C. Chao, P. M. Smith, L. F. Lester, B. R. Lee, J. M. Ballingall, 
and M. Y Kao, “Millimeter-Wave Low-Noise HEMT Amplifiers,” IEEE MTT-S 
Digest, pp. 923-926,1988. 
[SI P. M. Smith, P. C. Chao, K. H. G. Duh, L. F. Lester, B. R. Lee, J. M.  Ballingall, 
and M. Y. Kao, “Advances in HEMT Technology and Applications,” IEEEMTT-S 
Digest, pp. 749-752, 1987. 
[6] S. C. Palmateer,P. A. Maki, W. Katz, A. R. Calawa, J. C. M. Hwang, and L. F. Eastman, 
“The influence of V:III flux ratio on unintentional impurity incorporation during 
molecular beam epitaxial growth,” in Proc. Gallium Arsenide and Related Com- 
pounds 1984 (Inst. Phys. Conf. Series 74), pp. 217-222, 1985. 
[7] P. C. Chao, P. M. Smith, S .  C. Palmateer, and J. C. M. Hwang, “Electron-Beam 
Fabrication of GaAs Low-Noise MESFETs Using a New Tri-Layer Resist Technique,” 
IEEE Trans. Electron Devices, vol. ED-22, pp. 1042-1046, 1985. 
[8] K. H. G. Duh, M.  W. Pospieszalski, W. F. Kopp, P. Ho, A. A. Jabra, P. C. Chao, 
P. M. Smith, L. F.  Lester, J. M. Ballingall, and S. Weinreb, “Ultra-Low-Noise 
Cryogenic High-Electron Mobility Transistors,” IEEE Trans. Electron Devices, 
VOI. ED-35, pp. 249-256, 1988. 
[9] A. Kzstarsky and R. A. Klein, “On the low temperature degradation of AIGaAs/ 
GaAs modulation doped field-effect transistors,” lEEE Trans. Electron Devices, 
V O ~ .  ED-33, pp. 414-423, 1986. 
[IO] S. Weinreb and R. Harris, “A 23-GHz Coolable FET Amplifier,” NRAO Internal 
Report. 
[ I l l  P. C. Chao, P. M. Smith, K. H. G .  Duh, J. M. Ballingall, L. F. Lester, B. R. Lee, 
A. A. Jabra, and R. C. Tiberio, “High Performance 0.1 pm Gate-Length Planar- 
Doped HEMTs,” 1987 International Electron Devices Meeting, Washington, D. C., 
Dec. 1987, Paper 17.1, pp. 410-413. 
[12] P. Ho, P. C. Chao, K. H. G. Duh, A. A. Jabra, J. M. Ballingall, and P. M. Smith, 
“Extremely High Gain, Low Noise InAIAslInCaAs HEMTs Grown by Molecular 
Beam Epitaxy,” to  be published in I988 IEDM Technical Digest. 
74 
Table 1. Performance comparison of two types of conventional AIGaAsdGaAs HEMTs 
Ambient Freq., Performance Type A Type B 
Temp., K GHz parameter (1 0 1 8/,rn 3) (2  x 10181~m3) 
300 gm (mS/mm) 380 450 
300 8 Noise figure (dB) 0.4 - 
300 8 Associated gain (dB) 15.2 - 
300 18 Noise figure (dB) 0.1 0.7 
300 18 Assoc. gain (dB) 11.5 15.0 
300 32 Noise figure (dB) 1.3 1.2 
300 32 Assoc. gain (dB) 7.5 10.0 
13 8.5 Noise temp. (K) 5.3 13.1 
13 8.5 Assoc. gain (dB) 13.9 14.5 
75 
I d e g J  
Fig. 1. Cross section of the 0.25-pm T-gate HEMT. 
Fig. 2. Ka-band two-stage HEMT LNA. 
76 
0 I I I 1 1 1 1 
0 
-4.0 t 
I I I I I I 
1 
-10 I 
-401- I 
I 
i’ 
Fig. 4. Equivalent circuit model of 0.2Cpm AIGaAsIGaAs HEMT. 
26 20 30 32 34 36 38 40 
FREQUENCY, GHr 
Fig. 3. Measured performance of Ka-band stepped ridge fixture. 
VG1 VD1 VG2 VD2 
Fig. 5. Schematic diagram of two-stage hybrid LNA using 0.25~75-pm HEMTs. 
ORIGINAL PAGE IS 
OF POOR QUALtTY 
Fig. 6. Two-stage (a) and three-stage (b) HEMT LNA microstrip 
matching circuits. 
20 - 1 I I 1 1 I I I I I 
18 - 
16 - 
14 - 
12 I I I I I I I I 1 I .  
l 1 26 27 28 29 30 31 32 33 34 35 36 37 
FREQUENCY, GHz 
Fig. 7. Two-stage HEMT LNA room-temperature broadband 
response. 
1 1 I 1 I I I I I I 1 
10 11111111111 
4j 
1 1 I I I I I I I I I 
26 27 28 29 30 31 32 33 34 35 36 37 
FREQUENCY. GHz 
Fig. 8. Three-stage HEMT LNA room-temperature broadband 
response. 
78 
LN2 COLD AMBIENT 
HOT LOAD 
WAVEGUIDE SWITCH 
NITROGEN 
WG CHOKE INPUT 
KAPTON WINDOW 
(AT PORTS) 
STAINLE 
(Cu PLAT 
STEEL WAVEGUIDE 
1 
-50 K ANCHOR 
-12 K ANCHOR 
I 
REFRIGERATOR 
I ,  
I 
I 
lsoLAT0!$ FET AMP 
U 
- 
LO 
Fig. 9. 32-GHz cryogenic noise temperature measurement system. 
79 
350 
300 
250 
Y 
w' 
LL 
3 
Le 
w 
2 200 
n 
I 
52 
0 z 
150 
w 
100 
50 
a 
I I 
v v  
VD1 = 2.5 V 
ID1 = 3 . 0 m A  
VD2= 2.0 V 
ID2 = 5 . 0 m A  
0 0  
V 
V 
V 
V 
0 
0 
0 
0 
V 
V 
0 0  
0 
0 NOISE TEMPERATURE 
v ASSOCIATED GAIN 
FREQUENCY = 32 GHz 
50 100 150 200 250 300 
PHYSICAL TEMPERATURE, K 
Fig. 10. Two-stage HEMT LNA noise temperature and gain cooling curve. 
I I I 
VD1 = 2.5 V 
ID1 = 3 . 0 m A  
VD2 = 2.0 V 
ID2 = 5 . 0 m A  
VD3 = 2.0 V 
ID3 = 5 . 0 m A  0 
0 
0 0  
0 
w 
Q V  
O 8  0 
0 B 
8 
0 
0 '  
0 NOISE TEMPERATURE 
V ASSOCIATED GAIN 
FREQUENCY = 32 GHz 
01 1 I I I I 
0 50 100 150 200 250 31 
PHYSICAL TEMPERATURE, K 
m 
U 
f 
6 
CI 
0 
w 
I- 
V 
m a 
9 
8 
Fig. 11. Threestage HEMT LNA noise temperature and gain cooling curve. 
80 
8o  2o 
80 
70' 
Y 
W' 5 6 0 -  
5 
Le 
n z 
W 
5 0 -  
I? 
0 z 
40 
30 
70 c 
I I I 35 
- 30 
I _ v v v " v  
v v ~ v v v v v v v v v v  
ID1 =3.0mA ?i 
VD2 = 2.0 V - 20 9 
n 
V ASSOCIATED GAIN + 
- 1 5  2 
v.  
L'25 
m VD1 = 2.5 V v 
w ID2 =5.0mA 0 NOISE TEMPERATURE 
VD3= 2.0 V 
ID3 = 5.0 mA PHYSICAL TEMPERATURE = 12.5 K 
() 
0 -(>lo 
0 0  
0 0 0 0  O 0 0  0 0 0  
o o o  
0 0 0  
- 
- 5  
. I I I 0 
v v  V V 
V D l  = 2.5 V 
ID1 =3.0mA 
VD2= 2.0 V 
ID2 =5.0mA 
30 40L 31 .O 31.5 
V 
v v v  
V 
V 
V 
0 0 0  
0 0 
I 
32.0 
0 
0 
- 
u 
0 v) 
2 1 0 NOISE TEMPERATURE V ASSOCIATED GAIN PHYSICALTEMPERATURE = 14 K 5 
32.5 33.0 
FREQUENCY, GHz 
Fig. 12. Two-stage HEMT LNA at 14-K noise temperature and gain. 
Fig. 13. Three-stage HEMT LNA at 12.5-K noise temperature and gain. 
81 


On 32-GHz cryogenically cooled HEMT low-noise amplifiers

On 32-GHz cryogenically cooled HEMT low-noise amplifiers

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