FR2875299A1 - Electromagnetic radiation e.g. infrared radiation, detecting component for e.g. mobile telephone, has part including reception area in its top part for receiving optical system, which is transparent to infrared radiations - Google Patents

Abstract

The component has a case including a base (12) on which a part (17) is disposed in a perpendicular manner. The part includes soldered units and a reception area (10) in its top part for receiving an optical system (8), which is transparent to infrared radiations. The part is extended by a cover that is integrated to the case bottom, where the cover and the bottom constitute a single monolithic unit.

Description

COMPONENT FOR DETECTION OF ELECTROMAGNETIC RADIATION The invention

  relates to a component for detecting electromagnetic radiation, particularly in the visible and infrared range.

  These components traditionally integrate a radiation detection circuit in question, conventionally deposited on a substrate of appropriate nature, for example of the semiconductor type (monocrystalline silicon, germanium, etc ...), for transforming said radiation into electrical signals, said detection circuit being associated with a read circuit, able to exploit these signals for the purpose of rendering them in particular in visual form.

  In the context of the application of some of these components, especially for the detection of infrared radiation, these components must be immersed in a neutral atmosphere (rare gas), or even under vacuum more or less pushed.

  For this purpose, such a component is encapsulated in a casing providing the required hermeticity, said casing then being provided with a window positioned facing the radiation detection circuit in question, and transparent to the latter, hermetically sealed on said casing .

  In addition, for optical reasons, and in particular for forming the image to be acquired, one or more optical systems located upstream of said window are also necessary. These optical systems are conventionally constituted by one or more lenses, integrated within a structure that must allow the centering of said optical system (s) with respect to the optical axis of the detection circuit.

  Moreover, in the context of the integration of this type of component into more complex devices, such as for example a camera, there is also associated an additional optical system, generally an objective, as well as an external electronic card relative to to the component itself, and intended to process the detected signals.

  For example, there is shown in relation to FIG. 1 a component of the prior art devoid of any upstream optical system. It consists essentially of a hybrid or monolithic assembly (2) associating a detection circuit and a read circuit, encapsulated in a housing (1). At least part of one of the faces of said housing is sealed by a window (5), typically constituted by a parallel-sided blade, and transparent to the radiation to be detected.

  Said housing (1) associated with the window (5) defines a sealed enclosure (4), inside which is located said hybrid or monolithic assembly (2). The signals detected by the latter are transferred outside the housing (1) by means of connections (3) (see Figure 2, which also relates to a device of the prior art).

  In the example described with reference to FIG. 1, the detection circuit (2) is secured, for example by gluing, to a thermoelectric module (13) of the PELTIER type, itself fixed by brazing on a support or base. (12), made of a dielectric or metallic material. The implementation of such a PELTIER module is typical uncooled detection devices based for example micro-bolometers. The housing itself is defined by this base (12) and by side walls (17) extending substantially perpendicular to the base (12). These side walls (17) are extended by a cover (9), in this case substantially horizontal, at the free end which is sealed said window (5).

  FIG. 2 shows an example of integration of optical systems and an optical detection component known from the prior art. Thus, said housing (1), defined by the base (12) and by a side wall (17), is extended by a holding and centering member (6) of three lenses (7), respectively positioned according to their focal length, with respect to the upper surface of the detection circuit (2). This holding and centering member (6) is itself received in a support (20), hermetically sealed on the side wall (17) defining said housing, and furthermore, on which the window (5) is hermetically joined. ).

  This support (20) for example has on its inner wall a thread of adjustment screw, intended to cooperate with the outer wall of the holding member and centering (6). Once the adjustment made during manufacture, the positioning of the member (6) within the support (20) is fixed by means of an adhesive point.

  It is conceivable that according to such a configuration, which is also frequently encountered in traditional imagers in the field of mobile telephony, and other PDA (personal digital assistant), it is necessary to provide a step of mechanical maintenance of said lenses in addition to a step of centering them, making the process of producing the component more complex, and consequently, increasing its manufacturing cost.

  Among the optical systems used, the so-called Petzval objective is conventionally encountered, consisting of two lenses, generally convergent, separated by an interval whose order of magnitude is half of the focal length of the system. The advantage of such an objective lies mainly in the fact that it makes it possible to correct the aberrations for large-field systems, with relatively high numbers of openings, thus proving to be quite interesting in the context of infrared detection.

  In the field of infrared detection, the detector used is often of a bolometric nature, and is composed of a reading circuit generally made according to a CMOS technology, on which are deposited and then etched different layers, thus producing a so-called monolithic structure. .

  According to this technology, a suspended membrane is formed to form a resonant cavity around the desired wavelength. The bolometric material, which constitutes one of the upper layers of the cavity, is made of a material whose electrical resistance varies with temperature.

  The scene to be detected is measured in terms of the apparent temperature variation, observed through the optics positioned upstream of the detector itself, and which therefore creates a temperature variation of the upper membrane and, consequently, a variation of the electric current flowing between the two pads supporting each pixel (for picture element or image element) of this upper matrix membrane.

  Conventional means of addressing integrate, sample and multiplex this electric current, so as to provide an image signal of the scene.

  In the context of such a bolometric detector, or more precisely of such a matrix of bolometric detectors, the upper membrane must be thermally insulated from the reading substrate, so that a temperature difference can be established between the membrane and the substrate. .

  For this purpose, the electronic component in question is enclosed in a housing, in which a relatively high vacuum is achieved (104 to 10-Z millibars). Alternatively, one can leave a low pressure of rare gas with low thermal conductivity or heavy gas, such as Xenon.

  In both cases, the housing must be sealed by a window transparent to the radiation of the desired spectral band.

  Whatever the detector constituting the component in question put in place, the implementation on the one hand, a window transparent to the radiation to be detected, hermetically attached or sealed on the housing, and on the other hand a system optical, induces a complexification of the process of achieving the assembly, in addition to an increase in size.

  However, in the context of the implementation of these particular systems, it is sought as much as possible to reduce this congestion to achieve the greatest possible miniaturization, given the integration of such a system in more devices. complex.

  One of the objectives of the present invention is to overcome these disadvantages. It proposes a component for detecting electromagnetic radiation, in particular infrared radiation, comprising: a housing containing one or more optical detection electronic circuits, and provided with a part transparent to the electromagnetic radiation to be detected; an optical system intended to modify the wavefront that passes through it.

  It is characterized in that the part transparent to the electromagnetic radiation to be detected is constituted by the optical system itself.

  In other words, part of the walls of the sealed volume constituting the housing and closing the electronic detection circuit or circuits, is constituted by an active optical element, that is to say likely to affect the propagation of electromagnetic radiation to detect, and more generally likely to change the wavefront that passes through it, if only in direction, depending on the type of detector used, and in particular the type of radiation to be detected. In short, the window conventionally known and placed generally at the level of the upper face of the housing, and usually consisting of a single element with substantially parallel plane faces, is replaced by a lens, and generally by an optical system. active, which in addition to its optical functions (other than simple transparency), also provides a hermeticity function, or, more simply, a mechanical function of rigidification part of said housing and therefore protection.

  In addition to simplifying the realization of the component resulting from this particular arrangement by reducing the number of elements then used, it is also worth emphasizing the decisive advantage provided by it, consisting in fact by optimizing the opening, and corollary, during the implementation of bolometric detectors (thus in infrared imaging), the increase of the thermal resolution and therefore, the detection capabilities.

  The invention thus makes it possible to retain the functionalities of the various elements forming part of the constitution of the components of the prior art, while at the same time leading to a simplification of their realization.

  According to the invention, the optical system consists for example of: a convergent lens, simply acting as an objective; a plane blade at one of its faces, and having on the other face a diffractive element such as a diffraction grating, intended for example to ensure the correction of the chromatism; a combination of these two types of optical system, to allow the correction of the chromatism of the material if it is dispersive, or to athermalise the entire building in the case of a weakly dispersive material as in Germanium for far infrared (LWIR); a lens made according to conventional technologies (for example polishing or molding) so as to correct the field curvature of the objective disposed upstream, and in particular that of the camera in which the system may be integrated into the system optical of the invention; - A flat blade on one of its faces and having on the other side a microlens array; such an optical system makes it possible to provide a Shack-Hartmann type interferometric function, for the purpose, for example, of analyzing the beam or the wavefront (optical metrology); a plane blade on one of its faces, and having on the other face a diffractive element or diffraction grating; such an optical system allows spectroscopic analysis of the detected scene.

  According to the invention, in order to take into account the dimensional dispersions of manufacture of said optical systems and of the various elements involved in its constitution, in particular in terms of tolerance in terms of their focal length, a shim or spacer is inserted in the housing in order to be able to have the desired draw, that is to say the distance between the last dioptre of said optical system and the detection circuit.

  This shim or spacer is inserted at one of the interfaces of the component parts of the housing, and in particular: either at the bottom of the housing, between the base and the optical detection circuit or circuits, against one or other of the faces of the support constituting the thermoelectric module, if it is provided with it: it is then the height of the focal plane which is adjusted; - Or the optical interface side cover interface defining the housing, so in the upper position within it; either at the interface between the side wall and the top cover of the housing, or at the interface between the side wall and the base of the housing.

  The manner in which the invention can be realized and the advantages which result therefrom will emerge more clearly from the following exemplary embodiments, given by way of nonlimiting indication, in support of the appended figures.

  Figure 1 is, as already said, a schematic representation in section of a prior art component devoid of any optical system.

  FIG. 2 is also a diagrammatic representation in section of a component of the prior art with integration of the optical system.

  Figure 3 is a schematic representation in section of a component according to a first embodiment of the invention.

  Figure 4 is a schematic representation in section according to a second embodiment of the invention.

  FIG. 3 shows a sectional view of a non-cooled infrared detector, implementing the features of the present invention. This may include a support (13). In the case of uncooled infrared detectors, this support (13) is constituted at least in part by a thermoelectric module, conventionally called peltier element, for regulating the temperature of the focal plane. This Peltier element (13) is surmounted by a reading and detection circuit (2).

  The detection circuit (2) is for example made monolithically or hybridized on a read circuit, typically developed using a CMOS technology.

  The assembly constituting the reading and detection circuit is glued for example by means of an epoxy adhesive on the support (13) or brazed on the latter. The reading circuit communicates with the outside of the housing, hereinafter described in more detail, by means of through metal connections (16), and in a known manner.

  Said housing comprises a base (12) made of a dielectric material or metal or mixed, on which is joined by brazing, or monolithically, a portion (17) substantially perpendicular to said base (12), and therefore in this case substantially vertical, and suitable to form the base of said housing. This part (17), possibly itself consisting of several elements brazed together, is provided in its upper part with a receiving zone (10) of an optical system (8), characterizing the invention.

  Optionally, and as otherwise represented in FIG. 3, the part (17) is extended by a cover (9), laterally in the described configuration, and no longer horizontal as in the prior art or in the form of FIG. embodiment of Figure 4. This is intended to define the receiving zone (10) independently of the dimensions of the base (17). This cover (9) is typically metallic, and is brazed to the base (17). According to a variant shown in FIG. 4, the cover (9) and the base (17) constitute a single monolithic element.

  According to one characteristic of the invention, the housing is closed at its upper face by an optical system (8), coming to be positioned at said receiving zones (10) above. This optical system (8) is essentially transparent to the electromagnetic radiation to be detected. Said optical system (8) is hermetically sealed at this level.

  This optical system may consist of a single objective, advantageously reduced to a convergent lens of traditional invoice, whose focal length is chosen to correspond to the draw of the component.

  However, and for the sake of reducing the costs of producing the component, and to take account of manufacturing tolerances, in particular dimensional, both of said optical system, and of the characteristics of the case (typically more or less 500 m), and to result in reproducible nature of the technical and physical characteristics of the component, the positioning of said optical system is adjusted by means of shims or spacers according to different possible modes.

  Firstly and when the heat dissipation by the base (12) allows it, this shim (14) is positioned at the support (13), and in particular under the latter, and therefore at the bottom and inside of the housing. contact of the base (12). This wedge, identified in this case by the reference (18), can also be inserted at the level of the housing / optical system interface, ie at the receiving zones (10) of the side walls (17) or the hood (9). ) of said housing. The securing of this wedge, whatever its location within the housing, is achieved by brazing. This provides the hermeticity required at the link box / optical system.

  Finally, this shim, then identified by the reference (11), can be interposed at the base interface (17) and side cover (9) constituting the housing, or at the interface between the side wall (17). ) and the base (12), as suggested in Figure 4.

  In general, this wedge can be inserted at any mechanical interface assembly between the optical system (8) and the base of the housing, always by hermetic welding.

  In known manner, a physical screen (19) for defining the angle of view and also constituting a pupil for the optical system (8) is advantageously secured to the support (13). In the configuration according to which the support (13) is a thermoelectric module, the screen (19) is naturally brought to the temperature of the upper face of said module, thus advantageously constituting a thermalized pupil.

  The constituent lens of the optical system (8) may furthermore undergo anti-reflection optical treatments on the one hand, and high-pass or bandpass on the other hand, conventionally carried out at the level of the transparent windows implemented in the In doing so, by replacing the conventional windows of the components of the prior art with a lens optimized in terms of optical quality, the device of the invention has the advantage of improving the thermal resolution, since it is possible to have a more open system (larger field) in a smaller footprint, while optionally benefiting from a thermalized pupil, particularly appreciable for this type of component.

  Furthermore in terms of optical transmission, it also leads to an optimization with the device of the invention, since the number of optical elements implemented is reduced.

  Another embodiment of the invention is shown in connection with FIG. 4, which lends itself to numerous optical arrangements.

  Thus, while the component shown in Figure 3 is self-sufficient, that shown in Figure 4 is part of a more complex imager, for which the implementation of an objective is necessary.

  In this configuration, there is an active optical system upstream of the object of the invention, and in this case constituted by an objective. Typically, the active optical element integrated in the housing, is a so-called field lens capable of being able to correct in particular the possible curvature of the objective positioned upstream, particularly in the context of the integration of the component in a camera or any other imaging device.

  The power of the lens implemented in this configuration has in this case only a small effect, by its function, on the overall power of the complete optical system, but it contributes to significantly improve the edge of the field, in particular if upstream, the lens is lightened to a single lens.

  The definition of the field lens is then directly dependent on the objective 25 arranged upstream.

  It is therefore conceivable the whole point of the component according to the invention.

  First of all, a significant reduction in the cost of producing such components, which is inherent in the reduction of the number of elements used for its construction, will be emphasized.

  It will also highlight the decrease in the size and weight of these components, also inherent in reducing the number of elements involved in its constitution.

  Note also the improvement of the overall transmission along the optical path, due to the reduced number of diopters.

  Finally, mention will be made of the possibility of integrating additional functions at the level of the traditional transparent window for closing the case.

  The examples described have been related to the detection of infrared radiation.

  In this field, it is applicable to both cooled detectors and uncooled detectors (bolometers or other). It should be emphasized that the invention is also applicable in the field of detection in the visible. In this field, it is generally not necessary to use solder at the mechanical assemblies. Indeed, a bonding may be sufficient to ensure the integrity and functionality of the component.

Claims (1)

11 CLAIMS   An electromagnetic radiation detection component, particularly an infrared, comprising: a housing (9, 12, 17) containing one or more optical detection electronics (2), and having a portion transparent to the electromagnetic radiation to be detected; an optical system (8) for modifying the wavefront passing therethrough; characterized in that the portion transparent to the electromagnetic radiation to be detected is constituted by the optical system (8).   2. Electromagnetic radiation detection component according to claim 1, characterized in that the optical system (8) limitatively fulfills an optical function, besides the hermeticity function, and consists of an element chosen from the group comprising: a convergent lens, acting as a lens; - A plane blade at one of its faces, and having on the other side a diffractive element such as a diffraction grating for the correction of chromaticism or athermalize the optical system; a combination of the two preceding elements; a complex lens, suitable for correcting the field curvature of an objective arranged upstream, in the typical setting of integrating said component into a more complex device of the camera type.   a plane blade on one of its faces and comprising on the other face a microlens array, so as to be able to provide a Shack-Hartmann type interferometric function; a plane blade on one of its faces, and having on the other face a diffractive element, such as a diffraction grating, so as to be able to perform a spectroscopic analysis of the detected scene.   3. An electromagnetic radiation detection component according to claim 1, characterized in that the optical system (8) also provides a diffractive function, including particular allow said component performing a spectroscopic analysis of the detected scene.   4. Electromagnetic radiation detection component according to one of claims 1 to 3, characterized in that it incorporates one or more optical adjustment wedges or spacers, so as to compensate for most of the dimensional dispersions manufacturing system optical and other elements in its constitution.   5. The electromagnetic radiation detection component according to claim 4, characterized in that the wedge or shims are inserted at one of the interfaces of the constituent parts of the housing.