We report the fabrication and testing of a 10 GHz grid amplifier utilizing sixteen GaAs chips each

containing an HBT differential pair plus integral bias/feedback resistors. The overall amplifier consists of

a 4x4 array of unit cells on an RT Duroid™ board having a relative permittivity of 2.2. Each unit cell

consists of an emitter-coupled differential pair at the center, an input antenna which extends horizontally

in both directions from the two base leads, an output antenna which extends vertically in both directions

from the two collector leads, and high inductance bias lines. In operation, the active grid array is placed

between a pair of crossed polarizers. The horizontally polarized input wave passes through the input

polarizer and couples to the input leads. An amplified current then flows on the vertical leads, which

radiate a vertically polarized amplified signal through the output polarizer. The polarizers serve dual

functions, providing both input-output isolation as well as independent impedance matching for the input

and output ports. The grid thus functions essentially as a free-space beam amplifier. Calculations indicate

that output powers of several watts per square centimeter of grid area should be attainable with optimized

structures

Hacker, J. B.

Ho, W. J.

Kim, Moonil

Rosenberg, James J.

Rutledge, David B.

Smith, R. Peter

Sovero, E. A.

English

The authors report the fabrication and testing of a 10-GHz grid amplifier utilizing 16 GaAs chips each containing an HBT (heterojunction bipolar transistor) differential pair plus integral bias/feedback resistors. The AlGaAs-GaAs HBT material was grown by molecular-beam epitaxy. The amplifier exhibits a peak gain of 12 dB at 9.9 GHz, with a 3 dB bandwidth which extends from 9.55 and 10.3 GHz. The peak gain and bandwidth are sensitive to polarizer position, indicating that the polarizers provide good matching to free space. Output power is linear with input power, indicating that the grid operates as an amplifier rather than as an injection-locked oscillator. Gain saturation can be observed at low DC bias and high-input RF levels

Kim, Moonkil

Rutledge, D. B.

Caltech Authors - Main

I I 
IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 39, NO. 11, NOVEMBER 1992 2667 
preparation was an RCA clean and a dehydration bake. 
The FET’s were fabricated in a concentric ring structure 
in order to eliminate parasitic conduction paths between 
the source and drain. The device gate length was 2 pm 
and the gate width was 314 pm. Source and drain contacts 
were formed by electron-beam evapora$on of Ti/Au. 
Gold was evaporated on top of a 750-A-thick layer of 
Si02 to form the gate electrode. At room temperature, the 
source to drain resistance was greater than 2 G 0  and the 
characteristics were nonlinear. This was due to a low con- 
centration of activated carriers at room temperature. The 
zero gate bias drain-to-source current at 23°C was -7 nA 
at -20 V. Although the current levels were low, the three- 
terminal characteristics of the device still showed current 
modulation with varying gate voltage. Following room- 
temperature characterization, the devices were tested at 
elevated temperatures in atmosphere. As the temperature 
was increased, the current level increased significantly. 
At a temperature of 150”C, the zero gate bias drain-to- 
source current was -34 nA at -20 V and the channel 
resistance had dropped to 990 M0. The drain to source 
I-V characteristics were linear at this temperature. Gate 
voltages were applied in 8 V steps while the drain-to- 
source voltage was swept from 0 to - 30 V. The I-V char- 
acteristics clearly showed evidence of saturation. Also, at 
applied gate biases in excess of 32 V, the active channel 
is pinched off. The peak transconductance at 150°C was 
6.4 nS/mm. Device ‘failure occurred at a temperature 
above 200°C and was due to failure of the gate oxide 
layer. Although the device characteristics are less than 
perfect, they are still much better than any previously re- 
ported for polycrystalline diamond FET’s and indicate that 
there is a promising future for PCD in active electronic 
devices. 
[ l ]  C. R .  Zeisse, C. A.  Hewitt, R.  Nguyen, J .  R.  Zeidler, and C. G .  
Wilson, IEEE Electron Device Lett., vol. 12, p. 602, 1991. 
[2] A. J .  Tessmer, D. L. Dreifus, and K. Das, Diamond and Relured Mu- 
rerials, vol. 1 ,  pp. 89-92, 1992. 
[3] H. Kiyota, K .  Okano, T. Iwasaka, H. Izumiya, Y.  Akiba, T. Kurosa, 
andM. Iida,Jupun. J .  Appl. Phys., vol. 30, no. 12A, p. L2015, 1991. 
VB-1 A 10-GHz Quasi-Optical Gr id  Amplifier Using 
Integrated HBT Differential Pairs-Moonil Kim, Di- 
vision of Engineering and Applied Science, California In- 
stitute of Technology, Pasadena, CA 91 125; E. A. Sov- 
ero, W. J. Ho, Science Center, Rockwell International 
Corporation, P. 0. Box 1085, 1049 Camino Dos Rios, 
Thousand Oaks, CA 91358; J. B. Hacker, David B. Rut- 
ledge, Division of Engineering and Applied Science, Cal- 
ifornia Institute of Technology, Pasadena, CA 91 125; 
James J. Rosenberg, Germanium Power Devices Corpo- 
ration, P. 0 Box 3065 SVS, Andover, MA 01810; and R. 
Peter Smith, Center for Space Microelectronic Technol- 
ogy, Jet Propulsion Laboratory, 4800 Oak Grove Drive, 
Pasadena. CA 91 109. 
We report the fabrication and testing of a 10-GHz grid 
amplifier utilizing 16 GaAs chips each containing an HBT 
differential pair plus integral biadfeedback resistors. The 
overall amplifier consists of a 4 x 4 array of unit cells on 
an RT DuroidTM board having a relative permittivity of 
2.2. Each unit cell consists of an emitter-coupled differ- 
ential pair at the center, an input antenna which extends 
horizontally in both directions from the two base leads, 
an output antenna which extends vertically in both direc- 
tions from the two collector leads, and high-inductance 
bias lines. In operation, the active grid array is placed 
between a pair of crossed polarizers. The horizontally po- 
larized input wave passes through the input polarizer and 
couples to the input leads. An amplified current then flows 
on the vertical leads, which radiate a vertically polarized 
amplified signal through the output polarizer. The polar- 
izers serve dual functions, providing both input-output 
isolation as well as independent impedance matching for 
the input and output ports. The grid thus functions essen- 
tially as a free-space beam amplifier. Calculations indi- 
cate that output powers of several watts per square cen- 
timeter of grid area should be attainable with optimized 
structures. 
Quasi-optical grid devices including oscillators, multi- 
pliers, mixers, and beam steerers have already been dem- 
onstrated [ 11-[4]. Motivation for studying quasi-optical 
devices is twofold: free-space power combining is more 
efficient at high frequencies than power combining in 
guided wave structures, and transmitting and receiving 
systems based on monolithic implementations of quasi- 
optical elements have the potential for being smaller, 
lighter, and substantially less costly than conventional 
phased-array systems. 
The AlGaAs/GaAs HBT material was grown by MBE. 
~~ 
Thickness Doping AlAs 
Layer (pm) Type ( ~ m - ~ )  Fraction 
Cap 0.16 n+ 5 x l o h 8  0 
Emitter 0.1 n 0.5-1.5 x loh8 0-0.25-0 
Base 0.07 p+ 0.5-1.0 x 10’’ 0 
Collector 0.7 n 0 3-6 x IOh6 
Subcollector 0 . 6  n+ 6 x 10l8 0 
The devices are implant-isolated and have an active 
emitter area of 40 pm2. The transistors exhibit fT = 65 
GHz, andf,,, = 90 GHz. Each chip contains a differen- 
tial pair with 1.7-k0 collector-base feedback resistors and 
a 250-0 emitter bias resistor which also serves to supress 
common mode gain. 
The amplifier exhibits a peak gain of 12 dB at 9.9 GHz, 
with a 3 dB bandwidth which extends from 9.55 to 10.3 
GHz. The peak gain and bandwidth are sensitive to po- 
larizer position, indicating that the polarizers provide good 
matching to free space (as a reference point, the transis- 
tors have 18-dB unilateral gain at 10 GHz). Output power 
is linear with input power, indicating that the grid oper- 
ates as an amplifier rather than as an injection-locked os- 
cillator. Gain saturation can be observed at low dc bias 
and high-input RF levels. 
This amplifier represents a significant advance over the 
previously reported grid amplifier [5] beyond its higher 
, 
I I 
2668 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 39, NO. I I ,  NOVEMBER 1992 
operating frequency, larger gain, and wider bandwidth. 
Where the previous grid required both front and backside 
wiring on the substrate (which would be cumbersome in 
a monolithic implementation), this amplifier utilizes 
frontside wiring only. Where the previous amplifier uti- 
lized packaged discrete MESFET’s, in this amplifier the 
contents of each unit cell are monolithically integrated 
with the exception of the metal lines which make up the 
antenna array. This amplifier therefore represents a sub- 
stantial step toward monolithic integration of an entire 
grid, which will be required for higher frequency opera- 
tion and low cost. 
Z.  B. Popovic, M. Kim, and D. B. Rutledge, “Grid oscillators,” In?. 
J .  Infrared and Millimeter Waves, vol. 9 ,  no. 7,  pp. 647-654, 1988. 
R. J .  Hwu, L. P. Sadwick, N. C. Luhmann, D. B. Rutledge, M. So- 
kolich, and B. Hancock, “Theoretical and experimental investigation 
of watt-level wafer scale integration of microwave and millimeter-wave 
GaAs and AlGaAs frequency multipliers,” presented at the 47th De- 
vice Research Conference, Boston, MA, June 1989. 
J .  B.  Hacker, R. M. Weikle 11, M. Kim, M. P. Delisio, and D. B. 
Rutledge, “A 100-element planar Schottky diode grid mixer,” IEEE 
Trans. Microwave Theory Tech., vol. 40, no. 3, Mar. 1992. 
M. Kim, R. M. Weikle 11, J. B. Hacker, and D. B. Rutledge, “Beam 
diffraction by a planar grid structure at 93 GHz,” presented at the IEEE 
Antenna and Propagation Society Symp., London, Ont., Canada, June 
1991. 
M. Kim, J .  J .  Rosenberg, R. P. Smith, R. M. Weikle, J .  B.  Hacker, 
M. P. DeLisio, and D. B. Rutledge, “A grid amplifier,” IEEE Micro- 
waveand Guided WaveLe?., vol. 13, no. 1 1 ,  pp. 322-324, 1991. 
VB-2 Monolithic High-Power Millimeter-Wave 
Quasi-Optical Frequency Multiplier Arrays Using 
Quantum Barrier Devices-Hong-Xia L. Liu, X-H. Qin, 
L. B. Sjogren, E. Chung, C. W. Domier, and N. C. 
Luhmann, Jr., University of California, Los Angeles, CA. 
90024 (310) 206-8133. 
Monolithic solid-state device arrays are under devel- 
opment for application as millimeter and submillimeter 
sources. Current efforts are focused on frequency multi- 
plication up to = 1 0 0  GHz at the 1-50-W power level. 
However, the intrinsic capabilities of several of the de- 
vices should permit the extension of this work to frequen- 
cies of several terahertz. 
GaAs barrier-N-N+ (BNN) diode arrays have been suc- 
cessfully designed and fabricated. Frequency doubling to 
66 GHz has been successfully achieved with an output 
power of 2.4-2.6 W and an efficiency in excess of 10%. 
In addition to the BNN arrays, a number of new device 
concepts have been developed in the course of this re- 
search which offer the promise of more efficient frequency 
multipliers with both higher cutoff frequency and higher 
power handling capability. These include the multi-quan- 
tum-bamer varactor (MQBV), and the Schottky-quan- 
tum-bamer varactor (SQBV). 
It is well known that a varactor’s efficiency degrades 
significantly at high pumping power level, which is pri- 
marily due to the increase of the effective series resistance 
resulting from the electric field dependence of the electron 
mobility. This results in a reduction in cutoff frequency 
and efficiency. The MQBV and SQBV can suppress these 
effects dramatically. The doping profile of the fabricated 
MQBV array involves the epitaxial stacking of six single 
quantum barriers (utilizing a back-to-back fabrication 
method). In addition to the current work involving array 
fabrication for the first time instead of discrete waveguide 
mounted devices, it also employs epitaxial stacking which 
offers a number of important advantages over the single- 
barrier devices previously utilized. First, the stacking 
structure results in several capacitances in series, which 
significantly reduces the resultant C,,, . Alternatively, the 
device area can be increased, thereby reducing the series 
resistance and improving the power handling ability. Sec- 
ond, since each single barrier only shares a portion of the 
pump power, the electric field in the n regions, as well as 
the thermionic current, can be reduced for a given total 
input power. This results in the reduction in series resis- 
tance associated with the maintenance of electric fields 
sufficiently low to provide high mobility. Third, the 
stacking structure also increases the overall device break- 
down voltage. Finally, the symmetric structure makes the 
back-to-back fabrication method feasible, which doubles 
the number of barriers and improves the array yield. 
Measured C-V characteristics of the MQBV (4 X 20 
pm2) show a Cm,,/Cmln ratio of 5 with a C,,, of 10 fF. In 
excess of 10 times reduction in thermionic current com- 
pared to the single-barrier device has also been obtained. 
The performance of the MQBV can be further improved 
by incorporating a Schottky-barrier structure on multi- 
quantum barriers to form the Schottky-quantum-barrier 
varactor (SQBV). The SQBV has two major advantages 
over the MQBV. First, the significantly higher Schottky 
barrier further suppresses the thermionic current. As a re- 
sult, the thermal heating effect from the dc current can be 
neglected. Second, the Schottky contact eliminates the 
specific contact resistance associated with the Ohmic con- 
tact. A SQBV array with a Schottky-barrier structure in 
series with six quantum barriers has been successfully 
fabricated with a yield of 99% (1300 devices), and an 
output power of 3.8-10 W with an efficiency of 1.7-4% 
at 99 GHz has been achieved. 
In addition to the thick quantum-barrier-based devices, 
resonant tunneling diode (RTD) arrays have also been 
fabricated. An output power of 33 mW at 99 GHz has 
been obtained. I 
VB-3 Picosecond Duration, Large-Amplitude Im- 
pulse Generation Using Electrical Soliton Effects on  
Monolithic GaAs Devices-Michael Case, Eric Carman, 
Ruai Yu, and M. J.  W. Rodwell, Department of Electri- 
cal and Computer Engineering, University of California, 
Santa Barbara, CA 93106 (805) 893-3244; Masayuki 
Kamegawa, Shimadzu Corporation, Kyoto, Japan. 
We report two devices which generate picosecond du- 
ration electrical impulses using soliton propagation ef- 
fects. A high repetition-rate device has generated an 


A 10 GHz Quasi-Optical Grid Amplifier Using Integrated HBT Differential Pairs

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