A housing for a radiation sensitive semiconductor component

The present invention relates to a package for an optoelectronic semiconductor component, operating at low temperatures, and connected to a heat sink operating by the Joule-Thomson effect.

Some semiconductor components must be cooled to low temperatures to exhibit their optimum characteristics. This is particularly the case with infrared sensitive detectors and infrared lasers. Typical operating temperatures for these semiconductor components are the boiling point of nitrogen (77 K), air (79 K) or argon (87 K).

The housing of such a detector is generally constituted by an evacuated double-walled container, comprising a window transparent to infrared radiation and electrical feedthroughs for supplying and processing the signal of the semiconductor component. The immediate vicinity of the latter is cooled by a radiator operating by the Joule-Thomson effect, the Peltïer effect or the Stirling effect.

Known devices of this type make it possible to reach the necessary low operating temperatures in a few minutes. The service life of the semiconductor component is unlimited in the case of continuous cooling by the heat sink used.

The relatively slow cooling of the semiconductor component, however, is not desired for some applications and prolonged maintenance of the operating temperature is unnecessary. In these cases, rapid cooling is sought in less than 10 seconds, for example, while the maximum operating time may be less than 1-5 minutes.

The object of the invention is a housing for a semiconductor component sensitive to radiation, which can be cooled very quickly to the required operating temperature, in a few seconds for example, and which only has to be maintained in the operating state for a period of time. short.

According to an essential characteristic of the invention, the non-evacuated housing is made in several parts; the first part of the housing connected to the radiator has low thermal conduction and capacity; and the end of the housing, having a window transparent to radiation, has high thermal conduction and capacity.

The invention starts from the following observation: only an area as small as possible of the package, surrounding the semiconductor component, needs to be cooled. The mass and material of this area should be such that it has as low a heat capacity as possible. A simplification and a reduction in the price of the housing is obtained by the fact that it is not evacuated, but filled with air or a suitable gas. A hermetic seal between the various parts of the housing is necessary to reliably prevent condensation of the penetrating water vapor and corrosion of the semiconductor component. Cooling of the outer surface of the inlet window, below the dew point of the surrounding atmosphere, should be avoided for the required service life of less than 1-5 minutes. The mass and material of the window and the area around it have a high capacity and thermal conduction for this purpose.

Other characteristics and advantages of the invention will be better understood with the aid of the detailed description below of an exemplary embodiment and of the appended drawing in which: FIG. 1 represents the various parts of the housing in a suitable position for their assembly; and Figure 2 shows the assembled housing, which is further surrounded by a second stainless steel housing.

According to FIG. 1, the housing is essentially made up of four parts, joined together by screws or threaded studs 22. The part 2 of the housing fixes the support plate 11 of the semiconductor component. 7 and serves as a housing for the radiator 1 operating by the Joule-Thomson effect.

The end piece 3 of the housing comprises the window 4 transparent to radiation and arranged so that the infrared rays which pass through it reach the semiconductor component 7. An intermediate part 5 is arranged between the end piece 3 and the part 2 of the housing. The electrical connections 6 are output with insulation between this intermediate part 5 and the part 2 of the housing. The fourth part of the housing is formed by the base 8, which is also screwed with the other parts of the housing and applies the radiator 1 to the outer wall of the recess 12 provided in the part 2 for its housing.

The radiator 1, operating by the Joule-Thomson effect, is constituted in a known manner by a conical or cylindrical hollow body bearing on its casing a coil through which the coolant passes. The angle at the apex of the cone is usually between 0 and 90 °; Figure 1 shows a known radiator, consisting of a 90 ° conical hollow body

The refrigerant, consisting of air, argon or nitrogen, is introduced through an inlet opening 9 into the coil 19, passes through the latter, then leaves through the orifice 14, facing the support 11 of the semiconductor component 7. The gas circulating under high pressure in the coil is cooled by expansion according to the Joule-Thomson effect when it leaves through the orifice 14, so that the refluxing gas ensures a precooling of the gas flow circulating in the coil. Liquefaction of the escaping gas is thus obtained in a few seconds, so that the semiconductor component 7 is cooled to the boiling temperature of the refrigerant. The base 8 has outlet orifices 10 for the flowing gas. It further comprises holes 21 allowing its mechanical attachment to the other parts of the housing, using screws 22, as well as thermal sealing. During assembly, the base 8 applies with the aid of springs, such as Belleville springs 18, the radiator 1 on the outer wall 13 of the recess 12 of the part 2 of the housing, adapted to the cone. This base 8 is stable and for example made of copper, another metal or a plastic material.

The part 2 of the housing comprises the recess 12, adapted exactly to the angle at the top of the radiator 1 and thin-walled 13, which can be mechanically reinforced by suitable structures, such as ribs. The recess 12 is closed towards the inside of the case by the support plate 11 of the semiconductor component 7. This plate 11 is made of a material with good thermal conduction, but low thermal capacity. Sapphire or molybdenum are suitable materials, for example. The support plate 11 is glued or, after metallization of the contact faces, welded to part 2 of the housing.

Part 2 of the housing has grooves 20 for seals 17 and holes 21 for assembly screws 22.

Part 2 of the housing is made of a material with poor thermal conduction and low thermal capacity. A suitable material is, for example, polyimide, which can be loaded with fiberglass or Teflon. Other materials which meet the above thermal conditions are suitable, such as glass, metal or ceramic.

Part 5 is an intermediate plate having a central opening 29 for the passage of spokes.

The seal between this intermediate plate 5, the part 2 and the end piece 3 of the housing is ensured by gaskets 16 and 15 housed in grooves 20. These gaskets 15 and 16 are advantageously produced, like the gasket. sealing 17, rubber or indium. The intermediate part 5 is made of a sufficiently stable and resistant material, and in particular of the same material as the part 2 of the housing. The end piece 3 of the case comprises the window 4, which can also be produced in the form of a lens, in sapphire or germanium, for example with, where appropriate, an antireflection layer. The material surrounding the window has good heat capacity and high thermal conductivity. It is for example made of copper. Another suitable material is Kovar, the coefficient of expansion of which is well suited to most window materials, so that the parts can be welded together strong and durable. The high thermal conductivity and capacity of the end cap 3 of the housing prevent condensation on the window 4 during the short service life.

Thin and narrow ribbons 6 of metal film, arranged radially, are used for power supply or signal processing. The metallic films must be insulated on both sides when the seals 16 and 17 are made of a conductive material. The insulation is for example constituted by a layer of polyimide. In the housing according to FIG. 1, a superinsulation can be arranged between the coil 19 and the part 2 of the housing. This superinsulation is advantageously constituted by one or more layers of a thin film of polyimide, for example. The thermal insulation with respect to part 2 of the housing is thus further improved, so that the gas flowing back to the outlet 10, following its spiral path between part 2 of the housing and the coil 19, ensures better pre-cooling of the gas. feed into the coil.

According to figure 2, the multi-part housing according to the invention for the detector element can be accommodated in an additional housing 23 in the case of very severe environmental conditions, and in particular high relative humidity or vapors. corrosive. This housing 23 is advantageously made of fine steel and comprises, above the window 4, a second window 24 transparent to infrared radiation. The electrical connections 6 of the semiconductor component are also output through the second outer housing, with sealing and electrical insulation.

The outer casing 23 can be screwed or welded to the part of the inner casing. To do this, the outer casing comprises a base 26, secured with sealing to the underside of part 2 of the casing. The base 8, which simultaneously fixes the radiator 1, can then be made integral with this base 26 of the outer casing. For the assembly of the parts by screwing, the base 26 of the outer casing comprises, for example, blind tapped holes 27 and 28 for the screws 30 and 31. The outer casing is advantageously not also evacuated, but contains air or a gas such as argon.

By means of an appropriate choice of the radiator, the device according to the invention makes it possible to obtain cooling times of the semiconductor component to the required operating temperature of less than 2 seconds. The possible operating time is more than 5 minutes.

Of course, various modifications can be made by those skilled in the art to the principle and to the devices which have just been described by way of nonlimiting examples, without departing from the scope of the invention.