Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Insulating material
Reexamination Certificate
1999-09-27
2001-08-28
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Insulating material
C257S728000, C257S729000, C257S707000
Reexamination Certificate
active
06281574
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to high power transistor amplifiers and more particularly to packaging arrangements for removing heat from transistors used in such amplifiers.
As is known in the art, high power microwave amplifiers have a wide range of applications. Many applications, such as Continuous Wave (CW), (i.e., high duty cycle), Class C operation, require that, for practical use such amplifiers must operate with high power, high efficiency and be of low cost. These applications require a technique for efficiently removing heat from the transistor. One technique used to remove such heat is by the packaging arrangement shown in
FIGS. 1A and 1B
. As shown therein, a semiconductor chip
10
, having a bipolar transistor configured in a common base configuration, is shown. The semiconductor chip
10
is disposed on a thermally conductive, electrically insulating, beryllium oxide (BeO), heat sink
12
. The heat sink
12
is mounted to a thermally conductive mounting flange
14
. A dielectric corral
16
, here a ceramic such as alumina, has an aperture
18
in an inner region thereof. The chip
10
with the heat sink
12
is disposed in the aperture
18
so the outer portion of the coral
16
encloses or encases, the sidewalls of the beryllium oxide heat sink
12
. The corral
16
has electrical conductors
21
passing therethrough to enable connection of input signals, and bias voltages to the amplifier of chip
10
and to enable the amplified signal to be coupled out of the packaging arrangement. More particularly, the amplifier of the chip
10
is electrically connected to the conductors
21
by wires
22
(FIG.
1
B). A cover
24
, for example Kovar or Alloy
42
material, is used to shield the amplifier of chip
19
. The width of the aperture
18
is typically less than &lgr;/4 where &lgr; is the wavelength of the nominal microwave operating frequency of the amplifier.
Another packaging arrangement is shown in FIG.
2
. Here, a diamond insert
26
is placed in the central region of the beryllium oxide heat sink
12
. The semiconductor chip
12
is mounted to the upper surface of the diamond insert
26
and the lower surface of the diamond insert
26
is mounted on the mounting flange
14
. Thus, the diamond insert
26
is enclosed, or encased around the sidewalls thereof by the beryllium oxide corral
16
. Testing such an arrangement showed a temperature reduction of less than 3 degrees Centigrade when operating under the same conditions as the packing arrangement shown in
FIGS. 1A and 1B
.
In spite of this improvement, such device has not been found adequate for Class C operation with high duty cycle, (i.e., substantially CW) operation, at high power levels. Further, beryllium oxide is a highly toxic, and therefore undesirable, material.
SUMMARY OF THE INVENTION
In accordance with the present invention, a transistor structure is provided. The structure includes a mounting thermally conducting mounting flange. An isomorphic, thermally conductive material is disposed on the flange. A semiconductor chip is disposed on a portion of a surface of the isomorphic, thermally conductive material, other surface portions of the thermally conductive material extending laterally beyond the portion of the material having the semiconductor chip disposed thereon.
With such an arrangement, the isomorphic material is able to spread heat generated in the semiconductor chip laterally beyond the region thereon directly below the semiconductor chip and thereby increase the heat removal efficiency of the arrangement.
In accordance with another feature of the invention, wherein the isomorphic material is an isothermal conductive material.
In accordance with another feature of the invention wherein the isomorphic material is diamond or silicon carbide.
In accordance with another feature of the invention, a transistor structure is provided. The structure includes a mounting thermally conducting mounting flange. Diamond is disposed on the flange. A semiconductor chip is disposed on a portion of a surface of the diamond, other surface portions of the diamond extending laterally beyond the portion of the diamond.
In accordance with another feature of the invention, the packaging arrangement is provided. The arrangement includes a mounting thermally conducting mounting flange. An isomorphic, thermally conductive material is disposed on the flange. A circuit, comprising a semiconductor chip having a transistor arranged as an amplifier and adapted to operate at a nominal microwave frequency with a band of frequencies is disposed on a portion of a surface of the isomorphic, thermally conductive material. Other surface portions of the thermally conductive material extend laterally beyond the portion of the material having the semiconductor chip disposed thereon. A corral having an aperture through an inner region thereof, the isothermal material being disposed within the aperture. An outer region of the corral is mounted to surface portions of the flange.
In accordance with another feature of the invention, wherein the aperture has a length less than &lgr;/4, where &lgr; is the wavelength of the nominal operating microwave frequency of the amplifier.
In accordance with another feature of the invention, the circuit is configured to bias the amplifier for Class C operation. Further, the amplifier is configured to amplify pulsed microwave signals with for example, pulse widths greater than 750 microseconds and duty cycles of about 25 percent or more. Thus, the amplifier is now able to operate with a continuous wave input signal.
In accordance with yet another feature of the invention, a method is provided for operating a microwave amplifier. The method includes providing a packaging arrangement having: (i) a mounting thermally conducting mounting flange; (ii) an isomorphic, thermally conductive material disposed on the flange; (iii) a circuit comprising a semiconductor chip having a transistor arranged as the amplifier, such amplifier being adapted to operate at a nominal microwave frequency with a band of frequencies, disposed on a portion of a surface of the isomorphic, thermally conductive material, other surface portions of the thermally conductive material extending laterally beyond the portion of the material having the semiconductor chip disposed thereon; (iv) a corral having an aperture through an inner region thereof, the isothermal material being disposed within the aperture, such corral having an outer region thereon mounted to surface portions of the flange. The amplifier is biased for Class C operation.
In one embodiment, the method includes feeding pulsed microwave signals to the amplifier for amplification thereby.
In one embodiment, the pulses have pulse widths greater than 750 microseconds and have a duty cycle of about 25 percent or more. Thus, the amplifier is now able to operate with a continuous wave input signal.
REFERENCES:
patent: 4360965 (1982-11-01), Fujiwawa
patent: 4425195 (1984-01-01), Papanicolaou
patent: 5886407 (1999-03-01), Polese et al.
patent: 6081028 (2000-06-01), Ettehadich et al.
patent: 0 932 199 A2 (1981-10-01), None
patent: 56-125849 (1981-10-01), None
patent: 60-127750 (1981-10-01), None
Drake Peter R.
Kessler Keith R.
Clark Sheila V.
Daly, Crowley & Mofford LLP
Raytheon Company
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