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These results rank among the best obtained to date when the
diodes are measured using similar equipment.
Diode fabrication: In our method, an n+ wafer (antimony or
arsenic-doped, with resistivity of 002 Q-cm) rather than an
n++ wafer is the starting substrate. A thick layer of n material
is formed on the n+ substrate using the epireactor (Fig. 3); it is
arsenic-doped to a concentration of 3—3-5 x 1015 cm" 3 . Next,
the p + + layer is formed by a 50 keV, 1 X B + ion implant with a
fluence of 1-5 x 10 15 cm" 2 . Following thermal annealing, the
implanted side of the wafer is metallised to act both as a heat
sink and a handle for further processing. The wafer is thinned
down to 10 fim or less (Fig. 4), after which the n+ layer is
ion-implanted to reduce ohmic contact resistance and to form
the n + + contact.
It is important to note that, due to the metallisation on the
opposite side, laser annealing is required to anneal the implant
damage in the n + layer. Laser annealing is performed with a
pulsed N d : YAG laser. The laser beam has a pulse width of 15
ns, repetition rate of 10 pps, energy density of 1-3 J/cm 2 and
contains both the 106 //m and the 0-53 /zm components. This is
achieved by passing the fundamental output of the two-stage
pulsed N d : Y A G laser through a type II, KD*P crystal
frequency doubler which has a conversion efficiency of ~30%.
The dual-output pulses are collinear and are optically scanned
over the target wafer. The laser beam spot has a diameter of 6
mm with ~ 5 0 % overlap between adjacent spots.
After pulsed laser annealing of the n + + -implanted layer, the
wafer is metallised, mesa-etched, diced and packaged for
testing.
InP GUNN OSCILLATORS IN V-BAND
Indexing terms: Semiconductor devices and materials, Gunn
devices, Oscillators
Output powers of 200 mW and efficiencies up to 6-5% have
been achieved with CW InP Gunn oscillators in V-band
(50-75 GHz). Fixed frequency as well as frequency tunable
oscillators have been developed. Tuning bandwidths of 19%
and 6-1 % have been achieved with mechanical and varactor
tuning, respectively.
It is the purpose of this letter to report results obtained with
CW InP Gunn oscillators in F-band. The oscillators described
here are fixed frequency as well as mechanically and varactor
tuned oscillators. The performance reported here equals or
exceeds that of GaAs Gunn oscillators previously reported in
the literature for frequencies above 50 GHz. 1 ^ 3
InP material used to fabricate devices was grown by vapour
phase epitaxy. Diodes had a two-layer device structure. The
two-layer structure consists of an n+ buffer layer and an active
layer. The buffer layer is doped at 1-5 x 10 17 /cm 3 with a typical length of 3 /im. The best output powers and tuning ranges
obtained thus far are from wafers with an active layer doping
of 8 x 10 15 /cm 3 and thickness ranging from 1-5-20 //m.
An integral heat sink process was used to fabricate the
diodes. This process produces device mesas that are approximately 75 nm in diameter on 25 /im-thick plated Au heat sinks.
The overall height of the InP mesa is between 20 to 40 /zm. The
fabrication sequence used has been described in previous
literature. 4
The diode is packaged in Varian Associates N-35 package.
The N-34 package consists of a 3 mm diameter flange, 0-5 mm
thick on top of a threaded stud. Mounted on the flange is a 0-25
mm high ceramic ring metallised on top with gold. The outer
diameter of the ceramic is 0-76 mm and the inner diameter is
0-3 mm. The diode is placed inside the ceramic on top of a
fold-plated copper pedestal. Gold-tin solder is used to bond
the integral heat sink of the diode to the pedestal, and gold
ribbon is used to make electrical contact from the diode to the
top of the ceramic. A cap 013 mm thick and 0-76 mm in
diameter is then soldered to the metallisation on the ceramic.
High output powers and efficiencies were achieved with a
fixed frequency oscillator design. This design uses a coaxwaveguide configuration. The packaged device is put in a
copper heat sink and then screwed into the cavity where it
terminates the end of a coaxial line. The coaxial line is then
magnetically coupled through an iris to a full height wave708
Conclusion: The use of ion implantation and laser annealing
for p+ + and n++ ohmic contacts, coupled with the epigrowth
technique for low-impurity concentration, allows reproducible
fabrication of varactor diodes. Epigrowth reactors remain
clean and uncontaminated for continued and repeatable
operation.
Acknowledgment: The authors wish to acknowledge motivating discussions on the various fabrication schemes with Dr. H.
Huang. An expression of thanks is also due to J. Corboy and E.
Miller for providing the epigrown wafers.
A. ROSEN
C. P. WU
M. CAULTON
A. GOMBAR
P. STABILE
12th August 1981
RCA Laboratories
Microwave Technology Center, Princeton, NJ 08540, USA
References
1
SWARTZ, c A., WERN, D. w., and ROBINSON, p. H. : 'Large-area varac-
tor diode for electrically tunable, high-power U H F bandpass filter',
IEEE Trans., 1980, ED-27
2
wu, c. P., and ROSEN, A.: US patent 4, 230, 505, Oct. 28, 1980
3
ROSEN, A., CAULTON, M., STABILE, P., GOMBAR, A., JANTON, W., WU, C.
p., CORBOY, J., and MAGEE, C. W.: 'Millimeter-wave device technology', IEEE Trans., 1982, MTT-30, to be published
0013-5194/81/190707-02$! .50/0
guide. Results obtained with this circuit are shown in Table 1.
Efficiencies as high as 6-5% have been achieved in this circuit.
Mechanical and varactor tuning were achieved in a reduced
height waveguide circuit. A single step provides the transformation to 6 1 % of the full height of WR-15 waveguide. The
device is mounted in a heat sink and then placed into the cavity
where it sits on the bottom wall of the reduced height section of
waveguide. Bias is applied to the cap of the package by a metal
post. An anodised aluminium sliding short behind the diode is
used for mechanical tuning.
Table 1 R F PERFORMANCE O F FIXED
FREQUENCY InP GUNN OSCILLATORS
Device
Output power
Efficiency
GHz
mW
56-4
56-8
56-8
660
200
157
125
115
%
6-35
4-86
4-50
410
Frequency
EE209
EE210
EE201
EE196
The reactance of the sliding short is coupled to the packaged
device through the reactance of the post. By varying the position of the sliding short the impedance presented to the diode
can be altered, thereby changing the frequency of operation.
This provides the means for mechanically tuning the circuit.
Output power and frequency are shown as a function of the
short position in Fig. 1. The graph shows a tuning bandwidth
of 15-4% from 59-8 GHz to 69-8 GHz. Tuning bandwidth is
20r
45 50 5-5
short position,mm
Fig. 1 Output power and frequency against sliding short position for a
mechanical tuned InP Gunn oscillator
ELECTRONICS LETTERS
17th September 1981
Vol.17
No. 19
defined as the tuning-range/centre-frequency of that range. The
power variation is seen to be 30 dB. Tuning bandwidthsup to
19 % with power variations of 2-7 dB or better have been seen
in this circuit.
The circuit used for varactor tuning is similar to that used
for mechanical tuning. The varactor is placed on the bottom
wall of the reduced height section of waveguide behind the
Gunn device, centred at the sidewall. Bias is applied by a metal
post to the cap of the diode. The varactor is magnetically
coupled through this post to the waveguide fileds. The
diameter of the post and its distance behind the Gunn device
are parameters varied to achieve the desired coupling.
The varactor used was a GaAs p-n junction device made by
Varian Associates. The total capacitance C, of the packaged
varactor against voltage is shown in Fig. 2. This shows a capacitance variation of 4:1 for bias voltage ranging from 0 to
- 40 V. Typical Qs for similar devices range from 4000-7000 at
50 MHz. Fig. 2 also shows typical performance of a varactor
tuned InP Gunn oscillator. Output power and frequency are
plotted as a function of varactor bias. A tuning bandwidth of
2-6 dB. Tuning bandwidths up to 61 ° o have been noted with
this circuit.
It can be seen by the results stated in this report that high
powers and efficiencies as well as wide tuning ranges can be
achieved from InP Gunn devices in K-band. Both methods of
tuning (mechanical and varactor) showed smooth frequency
tuning while exhibiting a reasonable amount of power variation
with frequency.
The authors wish to acknowledge Dominic Tringali for the
growth of epitaxial InP, Stan Lombardi and Jan van Gorder
for fabrication and packaging of devices, and Dave Humber
for fabrication of circuits.
J.
B.
J.
F.
1-5r 15]
J. SOWERS
A. JAMS
D. CROWLEY
B. FANK
12th August 1981
Varian Associates
611 Hansen Way, Palo Alto, CA 94303, USA
References
1
SUN, c , BENKO, E., and TULLY, j . w.: 'A tunable high power K-band
oscillator, IEEE Trans., 1979, MTT-27, pp. 512-514
2 RUTTAN, T. c : 'High frequency Gunn oscillators', ibid., 1974,
MTT-22, pp. 142-144
3 RUTTAN, T. G.: 'Gunn-diode oscillator at 95 GHz', Electron. Lett.,
1975, 11, (14), pp. 293-294
4
Fig. 2 Output power, frequency and CT against varactor bias for a varactor tuned InP Gunn oscillator
METHOD FOR DIRECT MULTIWAY
BRANCHING IN MICROPROGRAM CONTROL
Indexing terms: Computers, Microprogramming, Programmable logic arrays, Associative memories
A new technique is proposed for simultaneously executing
multiway branching with PLAs. The basic structure consists
of three units: the microcode ROM, the microsequencer PLA
and a register counter. The main idea is to store only branching information in PLA, exploiting the associative addressing properties of the latter. Benefits in speed and memory
space are obtained.
Introduction: It is well known that microprograms contain
many branch microinstructions, typically about 30% of the
total number.1 In fact, many of these microprogram branches
are nonbinary or multiway (Fig. 1), i.e. they involve more than
two branching conditions. For example, at the end of a macroinstruction fetch phase, a microprogram multiway branch may
occur depending on the macroaddressing mode (direct, indirect, indexed etc.). Although a multiway branch can be implemented by a sequence of binary branches, this increases the
required number of microinstructions and hence the execution
time. Direct implementation of multiway branching results in
benefits such as microprogram compaction, concurrency and
increased speed. It may also enhance microprogram development and documentation.
Conventionally, multiway branching is implemented by explicit or implicit methods. In the first, the jump addresses are
each contained in distinct microinstruction fields; this results
in excessive control word lengths. In the second, the jump
address is formed by substituting certain status bits for some
bits of the microinstruction address field; this may result in
inflexible address assignments. In the following we describe a
new technique for direct multiway branching using programmable logic arrays (PLAs). Details on PLAs are in References
2 and 3.
Principal ideas: Every microprogram structure must execute
two essential control tasks: declaration of the current state
(microcode) and generation of the next state (micro x
ELECTRONICS LETTERS
17th September 1981
CROWLEY, J. D., SOWERS, J. J., JANIS, B. A., a n d FANK, F. B.: ' H i g h
efficiency 90 GHz InP Gunn oscillators', ibid., 1980, 16, (18),
pp. 705-706
0 3 6 9 12 15 18 21 24 27 30 33 363942
varactor bbs.V
SLM]
Vol.17
0013-5194/81/190708-0211.50/0
sequencing).4 As far as microprogram addressing is concerned,
the transitions, conditional or unconditional, among the
microinstructions may be distinguished into: (a) continue-type,
i.e. transitions with (next address) = (current address) + 1, and
(b) jump-type, i.e. not continue-type (Fig. 1). The transition
structure of a microprogram may be described by ASM-like
charts or graphs.5 The essential information for a microprogram jump may be represented compactly by the following
four-field format:
/branch condition/current address/next address/output/
current
address
jump 1
Fig. 1 Illustrating multiway branching: a 3-way branch involving three
jump-type microprogram transitions
We employ these principles in our approach by partitioning
the above microcoding and microsequencing tasks such that
the latter is entirely embedded in PLAs and the former in
ROMs. An important feature is that only microprogram jumps
need to be stored in the PLA; continue-type transitions are
implicitly generated by a counter. Our method exploits the
conditional matching properties of PLAs (Fig. 2) as follows. The
three P-terms, Pu P2, Pi, are each accessible by address 0101.
However, Pj or P 2 is matched whenever condition Cx or C2,
No. 19
709
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