Non-Evacuated, Rapidly Coolable Housing for an Opto-Electronic Semiconductor Component

The invention relates to a housing for an opto-electronic semiconductor component operable at low temperatures, with the housing being in communication with a cooler operating in accordance with the Joule-Thomson effect.

Certain semiconductor components have to be cooled down to low temperatures in order to attain their optimum performance data. This is particularly true for infrared sensitive detectors and infrared lasers. Typical operating temperatures of these semiconductor components are the boiling temperatures of nitrogen (77.degree. K.), air (79.degree. K.) or argon (87.degree. K.).

The housing for such a detector generally consists of an evacuated double-walled container comprising a window for transmission of the infrared radiation and electric bushings for the current supply and/or the signal evaluation of the semiconductor component. The immediate surrounding area of the semiconductor component is cooled with a cooler operating in accordance with the Joule-Thomson principle, the Peltier principle or the Stirling principle.

With the known devices of this type it is possible to reach the required low operating temperatures within a few minutes. The operating time of the semiconductor component is unlimited as long as the cooling of the cooler employed continues to be effective. For certain applications, however, the comparatively slow cooling down of the semiconductor component is undesirable, and long maintenance of the operating temperature is not required. In these cases, rapid cooling down within, for example, less than ten seconds, is desired, while the maximum operating duration may be less than 1 to 5 minutes.

The object underlying the invention is to indicate a housing for a radiation sensitive semiconductor component which may be cooled down to the required operating temperature very rapidly, for example, within a few seconds, and with which the operating state need only be maintained for a short time.

According to the invention, this object is attained with a housing of the type described at the outset in that the non-evacuated housing comprises several sections, wherein the first section of the housing which is directly connected with the cooler exhibits low thermal conductivity and capacity, while the housing end section comprising a radiation transmitting window exhibits high thermal conductivity and capacity.

The invention is based on the realization that only as small as possible an area of the housing around the semiconductor component must be cooled. This area ought to be of such mass and material as to exhibit as low a thermal capacity as possible. A simplification and decrease in cost of the housing are achieved by it not being evacuated, but rather filled with air or a suitable gas. Hermetic sealing between the individual housing sections is necessary in order to exclude condensation of penetrating water vapor and corrosion of the semiconductor component. Cooling down of the outer surface of the inlet window below the dew point of the surrounding atmosphere should be avoided during the required operating time of less than 1 to 5 minutes. To this end, the window and the area surrounding the window exhibit high thermal capacity and thermal conductivity as regards mass and material.

The advantageous embodiments of the housing according to the invention for the radiation sensitive semiconductor component operable at low temperatures are apparent from the subclaims.

The invention will now be explained in greater detail with reference to an embodiment example.

FIG. 1 shows the individual sections of the housing in a position suitable for assembly.

FIG. 2 shows the assembled housing which is also enclosed by a further stainless steel housing.

The housing shown in FIG. 1 mainly consists of four sections which are held together by screws or threaded plugs 22. The housing section 2 serves to support the carrier plate 11 for the semiconductor component 7 and to accomodate the cooler 1 operating in accordance with the Joule-Thomson principle.

The housing end section 3 contains the radiation transmitting window 4 which is arranged in such a way that the infrared rays entering through the window hit the semiconductor component 7. An intermediate section 5 is arranged between the housing end section 3 and the housing section 2. The electric connection leads 6 are conducted outwardly in an insulated manner between this intermediate section and the housing section 2. The fourth section of the housing is formed by the bottom plate 8 which is likewise screwed to the remaining housing sections and presses the cooler 1 against the outside wall of the recess 12 provided to accommodate it in the housing section 2.

The cooler 1 operates according the Joule-Thomson principle and consists in a manner known per se of a conical or cylindrical hollow body with a pipe coil which is arranged on the casing surface and through which the cooling agent flows. The cone angle is generally between 0 and 90 degrees; a known cooler consisting of a 90.degree. conical hollow body is shown in FIG. 1.

The cooling medium consisting of air, argon or nitrogen is fed into the pipe coil 19 through an inlet opening 9, flows through this pipe coil, and exits through the opening 14 directly opposite the carrier member 11 for the semiconductor component 7. The Joule-Thomson effect ensures that with expansion of the gas conducted through the pipe coil under high pressure, the gas cools down on exiting from the opening 14, so that the returning gas effects a pre-cooling of the gas flow following through the pipe coil. In this way, it is ensured that the exiting gas is liquefied only a few seconds later, with the result that the semiconductor component 7 is cooled down to the boiling temperature of the cooling medium. The bottom plate 8 contains outlet openings 10 for the returning gas. The bottom plate 8 also contains bores 21 by means of which this bottom plate is mechanically fixedly connected and hermetically sealed to the other sections of the housing by screws 22. During assembly, the cooler 1 is pressed against the outside wall 13 of the recess 12 adapted to the cone in the housing section 2 by the bottom plate 8 by means of springs, for example, Belleville springs 18. The bottom plate 8 is of stable design and may, for instance, consist of copper, another metal or plastics material.

The housing section 2 contains the recess 12 precisely adapted to the cone angle of the cooler 1, with a thin housing wall 13 which may be mechanically reinforced by means of suitable structures, for example, by means of webs or ribs. The recess 12 is closed off towards the housing interior by means of the carrier plate 11 for the semiconductor component 7. This plate 11 is made of a material of good thermal conductivity but low thermal capacity. Suitable materials are, for example, sapphire or molybdenum. The carrier plate 11 is adhered or soldered to the housing section 2 after prior metallization of the contact surfaces.

The housing section 2 contains groove 20 for a sealing ring 17 and bores 21 for the connecting screws 22.

The housing section 2 is made of a material with low thermal conductivity and low thermal capacity. A suitable material is, for example, polyimide plastic which may be filled with a foreign material reinforcement comprised of glass fibers or teflon. Other materials such as glass, metal or ceramics are also suited to meet the aforementioned thermal conditions.

Section 5 is an intermediate plate with a central opening 29 for the path of rays.

This intermediate plate 5 is sealed off from the housing section 2 and the housing end section 3 by means of sealing rings 16 and 15 which are inserted into grooves 20. Like the sealing ring 17, these sealing rings 15 and 16 preferably consist of rubber or indium. The intermediate section 5 is made of a sufficiently stable and resistant material, more particularly, of the same material as the housing section 2. The housing end section 3 contains the window 4 which may also be in the form of a lens, and consist, for example, of sapphire or germanium and have an antireflection coating. The material surrounding the window has a high thermal capacity as well as a high thermal conductivity. It consists, for example, of copper. Another suitable material is Kovar whose expansion coefficient is well adapted to most window materials, ensuring that the sections can be soldered to each other firmly and enduringly. The high thermal conductivity and thermal capacity of the housing end section 3 ensure that the window 4 does not fog up during the brief time of operation.

Thin, narrow metal foil strips 6 arranged radially are used for the electric current supply and/or signal evaluation. If the sealing rings 16 and 17 are made of a conductive material, the metal foils must be insulated on both sides. The insulation may, for example, consist of a polyimide coating. A so-called superinsulation may be arranged between the pipe coil 19 and the housing section 2 in the housing according to FIG. 1. This superinsulation preferably consists of a thin, single- or multi-layered foil made, for example, of polyimide. This makes for a further improvement of the heat insulation as compared to the housing section 2, with the result that the returning gas following its spiral-shaped path between the housing section 2 and the pipe coil 19 to the gas outlet port 10 effects an improved pre-cooling of the gas flowing through the pipe coil.

According to FIG. 2 the multi-sectioned housing for the detector component according to the invention may be built into an additional housing 23 if adverse environmental conditions, particularly high air humidity or aggressive vapors prevail. This housing 23 preferably is made of stainless steel and comprises a further window 24 which is located above the window 4 and permits transmission of infrared radiation. The electric leads 6 for the semiconductor component are also conducted through the second outer housing in a tight and electrically insulated manner.

The outer housing 23 may be screwed or soldered to the housing section 2 of the inner housing. To this end, the outer housing comprises a bottom plate 26 which is tightly and mechanically fixedly connected to the underside of the housing section 2. The bottom plate 8, which also holds the cooler 1, may then be rigidly connected to this bottom plate 26 of the outer housing. For screwing the sections to each other, the bottom plate 26 of the outer housing contains, for example, threaded blind holes 27 and 28 for the screws 30 and 31. The outer housing is also preferably not evacuated, but rather contains air or gas, for example, argon.

With the arrangement according to the invention, and a suitable choice of cooler, cooling times of the semiconductor component to the required operating temperature of under one second is attained. The possible operating time constituted values of more than five minutes.