Cooled IR Detector

Abstract

An IR radiation detector comprising: a tubular base (1) carrying an outer casing (3) in which is located one end of a cold finger (2) extending into the tubular base; a ceramic plate (5) mounted in the outer casing on the end of the cold finger; an inner casing (12) having a perimeter continuously fixed to the plate (5); the plate having at least one peripheral portion (5.2') projecting outside the inner casing; and an IR radiation-sensitive sensor (11) fixed to the plate in the inner casing and having electrical inputs and outputs connected to electrically conductive tracks (7) of the plate extending to the peripheral portion outside the inner casing. (Figure from the abstract: Fig. 1)

Description

Title of invention: Cooled IR detector

[0001] The present invention relates to the field of infrared radiation detectors (hereinafter referred to as IR detectors), and more particularly cooled IR detectors.

[0002] BACKGROUND OF THE INVENTION

[0003] A cooled IR detector generally comprises a tubular base having a first end carrying an external protective titanium casing provided with a first germanium window and a second end secured to a cold finger connected to a cold machine. The cold finger extends into the tubular base and has one end projecting into the external protective casing. On this end of the cold finger, the bottom of a titanium cup is fixed which is surmounted by an internal aluminum casing having a second germanium window opposite the first germanium window. An infrared sensor is fixed to the bottom of the cup in the extension of the cold finger and opposite the germanium windows.

[0004] In this arrangement, the annular edge of the inner casing is fixed to the periphery of the cup and has openings in which relay wedges extend which are mounted on the periphery of the cup and which have terminals connected to the sensor by first electrically conductive wires generally made of gold and to an electronic processing circuit, located outside the outer protective casing, by second electrically conductive wires.

[0005] The openings made in the annular edge of the internal casing are a source of parasitic infrared radiation. To limit the disturbances generated by this parasitic radiation, the part of the cup on which the sensor is fixed is slightly raised relative to the edge of the cup. This requires having relatively long and fragile first electrically conductive wires, which risk breaking under the effect of shocks and vibrations experienced by the detector.

[0006] SUBJECT OF THE INVENTION

[0007] The invention aims in particular to provide a reliable cooled IR detector. Summary of the invention

[0008] For this purpose, according to the invention, an IR radiation detector is provided, comprising: - a tubular base carrying an outer casing in which is located one end of a cold finger extending into the tubular base, - a ceramic plate mounted in the outer casing on the end of the cold finger, - an internal envelope having a perimeter fixed continuously on the plate, the plate having at least one peripheral portion projecting outside the internal casing, - an IR radiation sensitive sensor which is fixed to the board in the inner casing and which has electrical inputs and outputs connected to electrically conductive tracks of the board which extend to the peripheral portion outside the inner casing.

[0009] Thus, the edge of the inner envelope is free from any opening that is a source of stray radiation leakage and the electrical conduction of the signals coming from the sensor is ensured by the electrically conductive tracks which are less fragile than electrically conductive wires. In addition, the ceramic may preferably be a ceramic having better thermal conductivity than titanium such as aluminum nitride ceramics. In addition, the continuous bonding of the edge of the inner envelope with the plate improves the heat transfer between the plate and the inner envelope.

[0010] Other characteristics and advantages of the invention will emerge from reading the following description of a particular and non-limiting embodiment of the invention. Brief description of the drawings

[0011] Reference will be made to the accompanying drawings, among which:

[0012] [Fig.l] [Fig.l] is a perspective view of an IR detector according to the invention;

[0013] [Fig.2] [Fig.2] is a partial perspective view of this IR detector in section according to plan II of [Fig.l];

[0014] [Fig.3] [Fig.3] is a partial exploded perspective view of this IR detector;

[0015] [Fig.4] [Fig.4] is a partial top view of this IR detector without the internal and external envelopes;

[0016] [Fig.5] [Fig.5] is a top view of the plate of this IR detector;

[0017] [Fig.6] [Fig.6] is a top view of the plate of this IR detector, without the electrically insulating layer;

[0018] [Fig.7] [Fig.7] is an enlarged view of zone VII of [Fig.5];

[0019] [Fig.8] [Fig.8] is a partial bottom view of the plate of this IR detector. DETAILED DESCRIPTION OF THE INVENTION

[0020] With reference to the figures, the cooled IR detector according to the invention, generally designated D, comprises a tubular base 1 having a first end 1.1 fixed to a base 2.1 of a cold finger 2 and a second end 1.2 provided with a collar 1.3 on which is fixed in a sealed manner an annular edge of an external protective casing 3 having a top provided with a first window 4. The tubular base 1 is made of glass, the external casing 3 is made of titanium and the first window 4 is made of germanium.

[0021] The cold finger 2 extends from the base 2.1 into the tubular base 1 and has a closed free end 2.2 which extends out of the tubular base 1 projecting into the outer casing 3.

[0022] On the free end 2.2 of the cold finger 2, a plate generally designated 5 is fixed.

[0023] More precisely, the plate 5 comprises a substrate having a first main face 5.1 on the side of the free end 2.2 of the cold finger 2 and on the opposite side a second main face 5.2. The substrate of the plate 5 is here made of a ceramic based on aluminum nitride AIN.

[0024] The first main face 5.1 of the substrate of the plate 5 is covered with a reflective layer 6 with respect to IR radiation. The reflective layer 6, here made of gold, has a central opening 6.1 leaving a central zone (spare) of the first main face 5.1 uncovered. The free end 2.2 of the cold finger 2, which is closed by a flat transverse partition, bears on the reflective layer at a periphery of the opening 6.1 in such a way that the free end 2.2 is spaced from the first main face 5.1 by a distance equal to the thickness of the reflective layer 6, namely here 25 μm. The plate 5 is fixed by gluing to the end 2.2 of the cold finger 2.

[0025] The second main face 5.2 of the substrate of the plate 5 carries electrically conductive tracks 7 having ends 7.1, 7.2 forming contact pads and two electrically conductive tracks 9 having ends 9.1, 9.2 forming contact pads. The second main face 5.2 of the substrate of the plate 5 and the electrically conductive tracks 7, 9 are covered with an electrically insulating layer 8 that absorbs infrared radiation. The layer 8, here made of polyimide, has a main opening 8.1 leaving a central area of ​​the second main face 5.2 bare. Part of the ends 7.1 are in the main opening 8.1 and the other ends 7.1 open into secondary openings of the layer 8. The ends 9.1 of the two electrically conductive tracks 9 open into an opening 8.2 of the layer 8 which is located in the vicinity of the opening 8.1 and which accommodates a temperature probe 10.The temperature probe 10 is bonded to the substrate in the opening 8.2 and has connectors connected to the ends 9.1. The layer 8 leaves exposed the annular peripheral portion 5.2' of the second main face 5.2 and the ends 7.2 and 9.2 of the electrically conductive tracks 7 and 9 which are on said peripheral portion 5.2'.

[0026] An infrared radiation sensor, or IR sensor 11, is fixed on the periphery of the main opening 8.1 and has electrical inputs and outputs connected to the ends 7.1 of the conductive tracks 7 by electrically conductive wires here made of gold. The IR sensor 11 is of the FPA (or “Focal Plan Array”) type and is here glued on the periphery of the main opening 8.1.

[0027] The plate 5 carries an internal envelope 12 surrounding the sensor 11. The internal envelope 12 has a periphery (or annular edge) fixed continuously (and therefore sealed) on the layer 8 so that the annular peripheral portion 5.2' extends projecting outside the internal envelope 12. The internal envelope 12 (or "cold screen") is made of aluminum and comprises a window 13 (or cold filter) made of germanium in alignment with the IR sensor 11 and the window 4. Said periphery of the internal envelope 12 is fixed by gluing here by means of a flexible glue capable of absorbing the differential expansions between the aluminum and the ceramic. The glue is here a silicone glue having a low degassing coefficient, such as that of reference DC93500 produced by the company Dow Corning.

[0028] The plate 5 comprises a transverse channel 18 connecting the interior of the internal envelope 12 with the exterior, that is to say the interior volume of the external envelope 3; and the external envelope 3 itself comprises a pipe 14 making it possible to create a vacuum in the external envelope 3 and in the internal envelope 12 via the transverse channel 18.

[0029] The detector D finally comprises pins 15 which pass through the collar 1.3 to each have: - a first end which is located in the external enclosure 3 and which is connected by an electrically conductive wire 16 to one of the ends 7.2, 9.2, and - a second end which is located outside the external enclosure 3 and is connected by a conductive cable to an electronic processing unit 17.

[0030] The base 2.1 of the cold finger 2 is connected to a cold machine M which implements a Stirling cycle to supply the cold finger 2 with cooled helium under pressure.

[0031] The operation of the detector D is known in itself and will not be detailed here.

[0032] During this operation, the cold finger 2 undergoes a helium compression / expansion cycle and it is necessary to prevent a deformation of the cold finger 2 from exerting a stress on the IR sensor 11 (the latter generally being made of piezoelectric material, this stress would generate a parasitic electrical signal at the level of the IR sensor 11). The fact that the end of the cold finger 2 is spaced from the first face 5.1 of the substrate makes it possible to prevent said end from touching the substrate and exerting a stress on the IR sensor 11. This ensures mechanical decoupling.

[0033] It is noted that the fact of providing that the plate 5 comprises a housing (here the opening 8.2) which is open on the side of the internal casing 12 to receive the temperature probe 10 connected to the electrically conductive tracks 9 of the plate 5 greatly simplifies the integration of said temperature probe.

[0034] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the re- sales.

[0035] In particular, the structure of the detector D may be different from that described.

[0036] The ceramic may be a multi-layer ceramic. The ceramic may comprise an internal layer on which at least one conductive track is made.

[0037] The electrically insulating layer may be a layer of black paint.

[0038] The electrically insulating layer may extend only at the connection with the internal envelope.

[0039] The electrically insulating layer is optional if the internal envelope is made of electrically insulating material or if the electrically conductive tracks are slightly recessed relative to the main face of the plate.

[0040] Although the ceramic used here is aluminum nitride given its good thermal conduction, other ceramics can be used and for example an aluminum oxide of type A12O3.

[0041] The peripheral portion of the plate extending outside the internal casing 12 may not be annular in shape but comprise one or more spaced ears.

Claims

Claims

1. IR radiation detector, comprising: - a tubular base (1) carrying an outer casing (3) in which there is one end of a cold finger (2) extending into the tubular base, - a ceramic plate (5) mounted in the outer casing on the end of the cold finger, - an inner casing (12) having a periphery fixed continuously on the plate (5), the plate having at least one peripheral portion (5.2') projecting outside the inner casing, - a sensor (11) sensitive to IR radiation which is fixed to the plate in the inner casing and which has electrical inputs and outputs connected to electrically conductive tracks (7) which extend on a main face of the plate up to the peripheral portion outside the inner casing, said main face extending on the side of the inner casing (12) and the electrically conductive tracks (7) extending under an electrically insulating layer (8) leaving uncovered contact pads (7.1, 7.2) of the electrically conductive tracks, the electrically insulating layer (8) being made of a material ensuring absorption of IR radiation.

2. Detector according to claim 1, in which the plate (5) comprises another main face (5.1) located on the side of the end of the cold finger (2), the main face located on the side of the end of the cold finger (2) being covered with a reflective layer (6) with respect to IR radiation, the layer comprising an opening (6.1) leaving the main face, located on the side of the end of the cold finger (2), uncovered in line with the sensor (11) and the end of the cold finger resting on the reflective layer at a periphery of said opening of the reflective layer.

3. A detector according to claim 1, wherein the electrically insulating layer (8) is polyimide.

4. Detector according to any one of the preceding claims, in which the plate (5) comprises a transverse channel (18) bringing into co- communication between the interior of the internal envelope (12) and the exterior.

5. Detector according to any one of the preceding claims, in which the plate (5) comprises a housing (8.2) which is open on the side of the internal casing (12) and which receives a temperature probe (10) connected to electrically conductive tracks (9) of the plate.

6. Detector according to any one of the preceding claims, in which the outer casing (3) has a periphery fixed on an outer collar (1.3) of the tubular base (1).

7. A detector according to any preceding claim, wherein the ceramic is one of the following ceramics: aluminum nitride, aluminum oxide.

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