Note: Descriptions are shown in the official language in which they were submitted.
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This in~ention relates to a high frequency semiconductor device,
and more particularly, to the structure of such a device which incorporates
a circuit substrate for mounting active elements such as transistors, and
passive elements such as capacitors and resistors all mounted in a package.
According to existing technology, in order to form such a high
frequency semiconductor device, for example, a single stage microwave amp-
lifier, a transistor which is hermetically sealed to prevent degradation of
characteristics and has leads for connection with other circuit elements is
mounted on a circuit substrate. The transistor is connected with the other
elements which are also mounted on the same circuit substrate and are requir-
ed for forming an amplifier via circuits formed on said substrate. Then the
circuit substrate is housed in a metal case.
Because the amplifier is hermetically sealed it occupies a large
space, requiring a large size of circuit substrate in order to mount it and
a resultant large case.
In the case of multi-stage amplifiers the overall size is large
because each stage involves the use of a large size case.
According to one existing idea for solving this disadvantage, tran-
sistor chips are mounted together with other necessary circuit elements on
the circuit substrate provided on a metal base without individual hermetical
sealing and then such circuit substrate is accommmodated in a metal case after
which this metal case is hermetically sealed. This structure has an advantage
that the physical dimensions are reduced but, at the same time, it has the
disadvantage that perfect sealing becomes difficult because the hermetic
sealing is required over longer distances.
An object of the present invention is to provide a high frequency
semiconductor device which may be compact as a whole even when connected as
a ~ulti-stage device, without detriment to the necessary hermetical sealing.
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Another object of the present invention is to provide a high fre-
quency semiconductor device having such a configuration that a plurality of
high frequency semiconductor devices respectively functioning as amplifiers
are directly cascade-connected without intervention of a.ny elements so as to
form, for example, a multi-stage amplifier circuit.
According to the present invention, there is provided a high fre-
quency semiconductor device comprising a metal base serving as a support and
ground for a function device which comprises at least one semiconductor elementJ
a DC circuit for operating said semiconductor element and a high frequency
circuit for cascade-connecting said semiconductor element to an external cir-
cuit; an insulating substrate which is frame-shaped and surrounds said function
device and provides a plurality of independent metallized parts on its sur-
face for the connection with an external circuit; and a sealing part which fits
on to the insulating substrate and hermetically seals said function device.
Figure 1 is a perspective view of the uncovered outline of a high
frequency semiconductor device according to the present invention;
Figure 2A is a plan view of a metal base or substrate;
Figure 2B is a cross-sectional view of Figure 2A along the line A-A';
Figure 3A is a plan view showing an insulating substrate mounted on
the metal base of Figure 2;
Figure 3B is a cross-sectional view along the line A-A' of Figure 3A;
Figure 4A is a plan view showing an insulating frame mounted on the
insulating substrate and a circuit substrate disposed on a mounting portion of
the metal base substrate;
Figure 4B is a cross-sectional view along the line A-A' of Figure 4A;
Figure 5 is a plan view showing a cover 51 mounted on the insulating
frame;
Figure 5B is a cross-sectional view along the line A-A' of Figure 5A;
Figure 6 is an enlarged view showing the ci.rcuit components of a
-- 2 --
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high frequency semiconductor device of the present invention, particularly a
microwave amplifier circuit;
Figure 7 is a functional block diagram of the circuit shown in Figure 6.
Figure 8 shows an equivalent circuit of the amplifier shown in Figure7.
Figure 9 shows a three-stage microwave amplifier according to the
present invention; and
Figure 10 is a plan view of another embodiment of the present invention.
Figure 1 is a perspective view of a high frequency semiconductor
device of the present invention, from which a cover for hermetical sealing has
been removed. This high frequency semiconductor device is, for instance, a
microwave amplifier. The insulating substrate 3 consisting of insulating
material such as ceramic is provided on a metal base or substrate 1 provided
with mounting screw holes 2. The substrate may be made of non-acidic copper.
The insulating substrate 3 is provided with a central opening, and herein the
circuit substrate 4 on which various elements such as transistors, capacitors,
inductors and directional couplers are mounted to form microwave amplifier
circuits and matching circuits. Moreover, metallized layers or strips 5 and
6 for connecting between a microwave amplifier formed on the circuit substrate
4 and external circuits, are formed on the insulating substrate 3. The metal-
lized strip 5 shown in Figure 1 is, for example, the one for receiving the
high frequency signal input of a microwave amplifier circuit and it extends
right to the outer edge of the insulating substrate 3 from the central opening
of insulating substrate 3 as do the metallized strips 6. Directly opposite
layer 5 and on the other side of circuit substrate 4 is another metallized
strip 5 (not shown in Figure 1 but shown in Figure 3A) serving as a high
frequency signal output, for example.
As clearly seen in Figure 3A there are four strips 6, two of which
extend to the same edge of substrate 3 as one of the strips 5 and the other
two of which extend to the same edge of substrate 3 as the other strip 5.
-- 3 --
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The strips of each pair thus defined extend towards each other and end in pads
7 and 7', respectively which axe spaced slightly apart. Metallized strips 6
are used to connect via pads 7 and 7' circuit 4 to an external D.C. voltage
source (not shown). The metallized strips described above are formed by the
following process. A tungsten paste is coated by the screen printing method
and baked, and thereaftèr nickel plating or gold plating is performed. ~I the
insulating substrate 3, the insulating frame 8 consisting of ceramic material
is provided to cross these metallized strips, and moreover a cover (not illust-
rated) for sealing is placed thereon and sealing is effected.
On each metallized strip the insulating frame 8, a lead 9 for con-
nection to external circuit components may be provided as indicated in Figure 1.
One of the leads 9 has been omitted to show one of the strips 6.
The high frequency semiconductor device described above will now be
explained in more detail with reference to Figures 2-8.
Figure Z shows the metal base or substrate-l. The metal base 1 is
provided with a mounting portion 21 on which the circuit substrate is mounted
and projections 22, 22', 22" for grounding parts of the circuit on the circuit
substrate 4. A support 23 for supporting the insulating substrate 3 is pro-
vided as a wall surrounding the perimeter of mounting portion 21. Portion 21
is also formed with a peripheral recess which provides a shoulder 24 level
with the top of support wall 23.
Figure 3 shows the condition where the insulating substrate 3 is
mounted on the metal base substrate 1. The insulating substrate 3 is supported
by shoulder 24 and support 23. The metal base substrate 1 and insulating
substxate 3 are bonded together Witll silver solder 25. The insulating subst-
rate 3 is provided with a central opening 31 for acco~mnodating the circuit sub-
strate 4, and opening 31 is provided with widened portions 32 so that the plat-
ing solution does not remain in the gap between the base 21 and shoulder 24 of
support 23 and flows out therefrom when gold plating is performed on the metal
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base substrate 1 after mounting of the insulating substrate 3. At the surface
of insulating substrate 3, the metallized strips 5 and 6 are formed.
Figure 4 shows the condition where the insulating frame 8 is mounted
on the insulating substrate 3 and the circuit substrate 4 is mounted on portion
21 of metal base 1. The insulating substrate 3 and insulating frame 8 are
bonded with alumina.
The metallized strips 5 are connected with the input and output
ends of a directional coupler (not illustrated in Figure 4) via wires etc. at
the inside of the insulating frame 8. The metallized strips 6 are connected
via pads 7, 7' to elements formed on the circuit substrate 4 at the inside of
the insulating frame 8. In Figure 4, various elements formed on the circuit
sub-strate 4 are not illustrated since these will be explained later in detail.
Figure 5 shows the device after a cover 51 has been mounted on the
insulating frame 8.
The cover 51 is made of an insulator such as ceramic or a metal
element such as Kovar, and is bonded to the insulating frame 8 with an alloy
AuSn (20) of gold 'Au) and tin ~Sn).
The insulating frame 8 and cover 51 form the sealing part of a high
frequency semiconductor device of the present invention. The frame 8 and
cover 51 could be formed integrally of a metal, for example, Kovar, which is
a trade mark of Westinghouse Electric Corporation designating an alloy of
iron (54%), nickel (29%) and cobalt (17%). However, in that case, it should
be irrelevent that to prevent short-circuits between the metallized strips 5
and 6 an insulator has to be provided at the contact area of the metallized
strips 5 and 6. Moreover, coupling between the metallized strips can be pre-
vented by providing a metallized layer, which reaches the metal base substrate,
between the metallized layers for a high frequency signal and DC signal.
The above description has involved mainly the case accommodating
B
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the circuit substrate of a high frequency semiconductor deYice of the present
invention. ~ow, a microwave amplifier circuit formed on the circuit substrate
will be explained.
Figure 6 shows a high frequency semiconductor device of the present
invention, specifically a microwave amplifier. The amplifier circuit formed
on the circuit substrate 4 is a balance type amplifier circuit, showing nearly
symmetrical characteristics in the right and left sides. As shown in Figure
7, in the circuit configuration of this circuit substrate, a microqave input
signal fed to the input terminal IN of the directional (hybrid) coupler HC 1
is divided into a couple of signals therein and these divided signals are
respectively amplified by the amplifiers 71 and 72, and then combined by the
hybrid coupler HC 2. Thus, an amplified microwave signal is output from the
output terminal OUT.
Here, each end of the hybrid couplers HC 1 and HC 2 is respectively
terminated by the resistors RSl and RS2. Ca, Cb, Cc and Cd denote DC blocking
capacitors. The amplifiers 71 and 72 have a similar structure and an equiv-
alent circuit of the amplifier 71 is shown in Figure ~.
In this figure, 81 is the input end of amplifier 71 and the input
matching circuit is composed of inductors L2, L3 and capacitor C2, while the
output matching circuit is formed by inductors L4, L5 and capacitor C4; the
gate self-bias circuit is formed by inductor Ll, resistors Rl and R2, capac-
itor C3; and the drain bias circuit is formed by inductor L6, resistor R3 and
capacitor C5. 82 denotes the output end, while 83 denotes the DC bias input
end.
Figure 6 shows an enlarged vie~Y of the circuit substrate 4 on which
an a~plifier circuit is formed and the area near to the hole part of the in-
sulating substrate 3.
As can be seen from the figure, the input end IN of the hybrid
1~344~39
coupler HC 1 and the output end OUT of the hybrid coupler HC 2 are respect-
ively connected with the metallized strips 5, formed on the insulating sub-
strate, termination resistors Rsl, Rs2 and capacitors C2, C4, are connected
to the projections 22, 22', 22 " of the metal base 1. Moreover, the edges
7, 7' of metallized strips 6 for the DC power supply are connected to a
resistor R4 by wires and the resistor R4 is connected to one electrode of a
capacitor C6 the other electrode of which is connected to the metal base 1
for grounding as shown in Figure 6. A wire bridges the resistor R~ and the
input end 83 of the bias circuit and thereby a bias voltage is supplied from
an exte m al circuit to the resistor R3 forming a bias circuit. It is also
possible to bridge the metallized pads 7 and 7' by a wire in order to supply
the externally supplied bias voltage to the metallized pad 7' from pad 7,
but resonance sometimes occurs between the facing metallized pads 7 and 7'
and therefore grounding is made through the resistor M and capacitor C6 in
order to prevent such resonance. Various elements of these circuits may be
obtained as monolithic elements.
According to the present example of a microwave signal amplifier,
what is i~,portant is that the whole circuit including amplification element
such as a field effect transistor and ancillary circuits such as input/output
matching circuit and directional coupler etc. are housed in a single case.
Thus, a high frequency semiconductor device itself operates as a
self-contained amplifier without requiring connection with any external
matching circuit etc.
Where the device is used as a single stage amplifier, leads 9 are
simply applied to the metallized strips. A multi-stage amplifier can also
be formed using the deyice as shown in Figure 9.
When the ~icrowave amplifiers 91, 92, 93 are fixed side-by-side to
a metal case 94 by screws through holes 2 in the metal bases 1, the metall-
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ized strips 6 for DC and 5 for high frequency are arranged face to face re-
spectively. Thus, the microwave signal input from the input connector 9~ of
the metal case is amplified by amplifiers 91, 92, 93 of ~he three stages and
then output from the output connector 99. Wire or conductive ribbon may be
used for the connections. Thus, the high frequency metallized strip 5 of the
microwave amplifier 91 is connected to the strip line 95, the DC metallized
strips 6 are connected to the bias terminals 96 provided in the metal case 94
and the high frequency metallized layer 5 of the microwave amplifier 93 is
connected to the strip line 97. The bias voltage which is required for the
function of the three amplifier stages 91, 92 and 93 is supplied only by con-
necting the bias power supply to the bias terminals 96. The metal case 94
requires a cover but it doesn't require to be hermetically sealed because
each amplifier stage is already hermetically sealed.
As described above, a high frequency semiconductor device of the
present invention is completely self-contained. Therefore, in order to form
a system by using these devices, it is not necessary to connect a matching
circuit as an external circuit and the system can be formed with a block
diagram concept at the system design stage. For this reason, system assembl-
ing can be made very easily.
Figure 10 is a view similar to Figure 3A but showing another embod-
iment of the present invention indicating the structure before an insulating
frame is installed. The circuit substrate 4' which is housed in the central
opening of the insulating substrate 3 as before differs from the substrate
4 previously used.
In this embodiment, the hybrid couplers HCl, HC2 which are mounted
on the circuit substrate 4 in the first embodiment are provided, instead, on
the insulating substrate 3. The hybrid coupler used particularly in the bal-
ance type amplifier circuit of a high frequency semiconductor device cannot
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be reduced in size since the coupling part requires a length of 1/4 of the
wavelength of signal used.
Thus, the disposition of hybrid couplers on the insulating substrate
permits reduction in size of the circuit substrate 4'. In the case where an
expensive sapphire is used as the circuit substrate, many more circuit sub-
strates can be obtained from a sheet or wafer and therefore the cost per
circuit substrate can be reduced, thus realizing a low cost supply of the
devices. Not only the hybrid coupler but also other elements may be formed
on the insulating substrate.
As explained above, the present invention is capable of offering a
high frequency semiconductor device which is small in size, provides suffic-
ient sealing and ensures easy system assembling.
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