WO2024028209A1

WO2024028209A1 - Thermal detector of radiation

Info

Publication number: WO2024028209A1
Application number: PCT/EP2023/070916
Authority: WO
Inventors: Jean-Luc Garden; Charlotte LATARGEZ; Daniel Bourgault; Gaël MOIROUX
Original assignee: Centre National De La Recherche Scientifique
Priority date: 2022-08-01
Filing date: 2023-07-27
Publication date: 2024-02-08
Also published as: FR3138516A1

Abstract

The invention relates to a thermoelectric microsensor formed of a stack of layers comprising, from a lower face to an upper face of the microsensor, a support made from a thermally conducting material, a layer made from a dielectric material, at least a pair of layers, forming a thermocouple, the two layers of which are separated, by a trench, by a minimum distance in excess of 500 nm, a layer of metal partially covering the at least one pair of layers. In a first configuration of the microsensor, the layer of metal comprises a central portion which covers, at the least, a portion of each of the two layers of the at least one pair of layers which is adjacent to the trench. In a second configuration of the microsensor, a central portion of one of the two layers of the at least one pair of layers covers, at the least, a central portion of the other layer of the at least one pair of layers. The microsensor has, for a given range of measurement temperatures denoted [Tmin, Tmax], a parameter ZTeffective which is comprised between 0.1 and 1.9, ZT being the figure of merit of the microsensor, and T being the measurement temperature.

Description

DESCRIPTION

Thermal Radiation Detector

Technical area

The present invention relates to the field of high-resolution thermoelectric sensors for measuring low-power thermal radiation.

State of the prior art

Thermal detectors based on the principle of thermoelectric detection are known in the state of the art. However, these detectors are too insensitive and cannot measure powers below one microwatt.

The thermal detector according to the invention makes it possible to overcome this problem by offering high sensitivity and a low detection threshold. Indeed, the thermal detector according to the invention is capable of measuring temperature variations of between a few microkelvins and a few tens of millikelvins or variations of thermal radiation of between a few nanowatts and a few hundred microwatts.

High resolution detectors based on photodiodes whose measurement principle is quantum are also known in the state of the art. A problem with such sensors lies in the fact that detection is focused only on a small range of wavelengths which is specific to each photodiode. Another problem with photodiode detectors is their complexity of use and the need to calibrate the detector each time it is used.

The thermal detector according to the invention makes it possible to overcome these problems by making it possible to measure radiation over a wide band of wavelengths ranging from ultraviolet to medium and far infrared. Furthermore, the thermal detector according to the invention is very easy to use.

Finally, microbolometers are known in the state of the art, the measurement principle of which is based on the variation of electrical resistance as a function of temperature. Microbolometers have high detection sensitivity. On the other hand, they are very expensive and to have high sensitivity, they require complex conditions of use with cooling of the measurement electronics and the detector. They can be adapted to radiation measurements at room temperature but in this case they lack sensitivity. The thermal detector according to the invention has a low manufacturing cost. It can operate over a wide range of temperatures and, in particular, at room temperature while maintaining an exceptional level of sensitivity. Finally, the thermal detector according to the invention does not require cooling of the detector or the measurement electronics.

Another aim of the invention is, furthermore, to propose a rapid response thermal detector, that is to say having a response time of the order of a second up to a few milliseconds.

Presentation of the invention

For this purpose, a thermoelectric microsensor is proposed for measuring low-power thermal radiation, called a microsensor, formed by a stack of layers comprising, from a lower face to an upper face of the microsensor:

- a support made of thermally conductive material,

- a layer made of a dielectric material,

- at least one pair of layers forming a thermocouple, the at least one pair of layers is, preferably, arranged so that a trench separates, preferably completely or only partially, the two layers of the at least one pair of layers with a minimum distance greater than 500 nm,

- a layer of metal partially covering the at least one pair of layers, the metal layer comprises two annular portions per pair of layers and for each thermocouple one of the two annular portions covers a peripheral portion of one of the two layers of the at least one pair of layers and the other of the two annular portions covers a peripheral portion of the other layer of the at least one pair of layers.

In a first configuration of the microsensor, the microsensor is preferably arranged so that and/or the at least one pair of layers is preferably arranged so that the metal layer is preferably arranged so that the metal layer preferably comprises a central portion which covers, at least, a portion, preferably an upper surface, of each of the two layers of the at least one pair of layers which is adjacent to the trench.

In a second configuration of the microsensor, the microsensor is preferably arranged so that and/or the at least one pair of layers is preferably arranged so that and/or the metal layer is preferably arranged so that a central portion of one of the two layers of the at least one pair of layers covers, at least, a central portion of the other layer of the at least one pair of layers.

The microsensor presents, for a given measurement temperature interval, denoted [Tmin, Tmax], an effective ZT parameter of between 0.1 and 1.9, ZT is the figure of merit of the microsensor and T is the measurement temperature.

Preferably, the materials constituting the two layers of the at least one pair of layers are chosen so that, preferably the arrangement of the microsensor according to the invention associated with the choice of the materials constituting the two layers of the at least one pair of layers are such that, for a given measurement temperature interval denoted [Tmin, Tmax], said microsensor has an effective ZT parameter of between 0.1 and 1.9, ZT is the figure of merit of the microsensor and T is the measurement temperature.

Unless otherwise indicated, the entire description applies to the first and second configuration of the microsensor.

Microsensor can be understood as a sensor, a detector or a microdetector.

The thermally conductive material support may be a metal, for example copper, aluminum, silver or stainless steel, or glass or ceramic.

A layer of a pair of layers forming a thermocouple may comprise or be made of several different materials. A layer of a pair of layers forming a thermocouple may comprise several portions or segments each comprising or being made of a different material. A considered layer of a pair of layers may comprise a first segment extending from an end, called the proximal end, located on the side of the center of the microsensor of the layer considered up to half the distance separating the proximal end from the the end, called the distal end, located on the side of the external edge, of the layer considered and a second segment extending from the distal end of the layer considered to the first segment. The first segment can be made of a material making it possible to obtain a high temperature gradient along the first segment and the second segment can be made of a material making it possible to obtain a temperature gradient lower than the first segment, or even a low temperature gradient.

Preferably, for the second configuration, the trench separates, only partially, the two layers of the at least one pair of layers by a minimum distance greater than 500 nm. Preferably, for the second configuration, the proximal end of the layers of the at least one pair of layers corresponds to the central part of the layers of the at least one pair of layers.

Preferably, a trench, distinct from the trench separating, completely or only in part, the two layers of the at least one pair of layers, separates two adjacent layers of two pairs of different layers by a minimum distance greater than 500 nm .

Preferably, the center of the microsensor constitutes the detection zone or sensitive zone of the microsensor.

In the second configuration, the metal layer can also cover the central portion of the layer of the at least one pair of layers covering the central portion of the other layer of the at least one pair of layers.

Preferably, the metal layer does not extend over the entire upper face of the microsensor. Preferably, the metal layer is a discontinuous layer.

Preferably, the metal layer can extend in all or part of the trench separating the two layers of the at least one pair of layers.

According to the invention, the term “pair of layers” corresponds to a pair of layers of a thermocouple of the microsensor.

According to the invention, the operating principle of a thermoelectric sensor can be defined as consisting of converting, successively, a radiation power into thermal power then the thermal power into a temperature gradient then the temperature gradient into an electrical signal.

According to the invention, low-power thermal radiation can be understood as radiation whose power is between a few tens of micro Watts and a few tens of nano Watts.

Preferably, the layers of the stack of layers forming the microsensor are stacked along an axis extending between the lower face and the upper face of the microsensor.

According to the invention, the upper face of the microsensor can be understood as the face or surface of the microsensor comprising, at least in part, the metal layer. According to the invention, the bottom face of the microsensor can be understood as the face of the microsensor which is opposite the upper face of the microsensor.

It can be understood by face or upper surface, in particular of a layer of the stack of layers, the surface or face oriented towards the upper face of the microsensor. It can be understood by face or lower surface, in particular of a layer of the stack of layers, the surface or face opposite to the upper face or surface.

The upper face or the lower face of the microsensor can be oriented in the direction of the thermal radiation to be measured.

Preferably, the dielectric material has an electrical conductivity of less than 1.10' ¹¹ S.nr ¹ .

Preferably, the dielectric material has a thermal conductivity of less than 1 Wm^.K' ¹ .

Preferably, the dielectric material is a polyimide membrane.

Preferably, in the first configuration, the two layers of a pair of layers are adjacent or neighboring, in particular at the center of the microsensor. Preferably, in the first configuration, the two layers of a pair of layers are not in contact, preferably, and in particular, at the center of the microsensor.

Preferably, a given layer of a pair of layers is separated from a layer of another pair of layers which is neighboring or adjacent to the given layer. Preferably, no layer of the at least one pair of layers is in contact with another layer of the at least one pair of layers.

By trench can be understood a furrow or a space.

Preferably, in the first configuration, a distance separating two adjacent layers of the same pair of layers extends in a direction perpendicular to the direction of the stack of layers of the microsensor.

Preferably, a given layer of a pair of layers is separated by a trench or space from a layer of another pair of layers which is close to or adjacent to the given layer. Preferably, a distance separating two adjacent layers of two pairs of different layers extends in a direction perpendicular to the direction of the stack of layers of the microsensor. Preferably, a distance separating two adjacent layers of two pairs of different layers extends along the length of the layers of the pairs of layers. Preferably, the distance separating two layers, which can be defined as a width of the trench or the space, is between 0.5 pm and 100 pm.

Preferably, the sensitivity of the microsensor is proportional to the number of thermocouples, or pairs of layers, that the microsensor comprises.

Preferably, the metal layer partially covers an upper surface of the at least one pair of layers. The metal layer may comprise or consist of one or more metallic chemical elements. Preferably, in the first configuration, the function of the central portion of the metal layer is to ensure an electrical connection between the two layers of the at least one pair of layers of semiconductor material.

Preferably, the function of the central portion of the metal layer is to allow better absorption of the thermal radiation to be measured.

Preferably, the metal layer has a thermal conductivity greater than or equal to 10 W.nrTK' ¹ . Preferably, the metal layer has an electrical conductivity greater than or equal to 1.10 ⁶ S.nr ¹ .

Preferably, in the first configuration, the portion of the layers of the at least one pair of layers which is adjacent to the trench does not coincide with a geometric center of the microsensor. The geometric center of the microsensor can coincide with a geometric center of the layer of dielectric material. The center of the microsensor can be included in an axis of revolution of the microsensor. The axis of revolution of the microsensor can be parallel to the direction of the stack of layers of the microsensor.

Preferably, in the second configuration, the geometric center of the microsensor coincides with the central portion of the layer of the at least one pair of layers covering the central portion of the other layer of the at least one pair of layers.

Preferably, the effective ZT of the microsensor is greater than or equal to 0.1, more preferably 0.2, more preferably 0.3, more preferably 0.4, more preferably 0.5, even more preferably at 0.6, particularly preferably at 0.7, particularly advantageously at 0.8 and most particularly advantageously at 0.9. Advantageously, the ZTeffective of the microsensor is equal to 1.

Preferably, the effective ZT of the microsensor is less than or equal to 1.9, more preferably 1.8, more preferably 1.7, more preferably 1.6, more preferably 1.5, even more preferably at 1.4, particularly preferably at 1.3, particularly preferably at 1.2, most preferably at 1.1 and most preferably at 1.05.

The effective figure of merit ZT of the microsensor can be defined as the thermoelectric figure of merit. In the state of the art, the thermoelectric figure of merit is used to evaluate the efficiency of thermoelectric refrigeration modules, typically the efficiency of Peltier modules. In this area, it is always sought to maximize the effective figure of merit ZT of the device to obtain maximum conversion efficiency.

According to the invention, the inventors have observed that the design of a thermal sensor arranged so that its effective ZT is close to 1 or equal to 1 makes it possible to obtain the best sensitivity and the best detection threshold. The arrangement of the layers of the stack of layers of the microsensor as described above makes it possible to obtain a microsensor whose ZTeffective is close to 1 or equal to 1.

Preferably, a thermal conductivity of the microsensor is less than or equal to 10 W.nrTK' ¹ .

Preferably, the thermal conductivity of the microsensor means the thermal conductivity measured between the two annular portions of the metal layer. Preferably, the thermal conductivity of the microsensor means the thermal conductivity measured between the two annular portions of each of the pairs of layers of the at least one pair of layers.

Preferably, the arrangement of the layers of the stack of layers of the microsensor as defined above makes it possible to minimize thermal losses between the layers of the stack of layers of the microsensor but also between the microsensor and its environment. Preferably, the arrangement of the layers of the stack of layers of the microsensor as defined above makes it possible to minimize thermal losses along the stack axis of the layers of the microsensor. Preferably, the arrangement of the layers of the stack of layers of the microsensor as defined above makes it possible to increase the sensitivity and the detection threshold of the microsensor. Furthermore, the arrangement of the layers of the stack of layers of the microsensor as defined above, although constituting an improvement of the invention, can contribute to obtaining an effective ZT close to or equal to 1.

Preferably, a thermal time constant, denoted tau, of the microsensor is less than or equal to 10 s, tau is equal to the ratio between a heat capacity of the microsensor and the thermal conductivity of the microsensor.

Preferably, the heat capacity of the microsensor means the heat capacity in a central zone of the microsensor. More preferably, the heat capacity of the microsensor means the heat capacity of a central zone and/or a portion of the layers of the stack of layers. The central area of the microsensor can be defined as the area of the microsensor where the power of thermal radiation is absorbed. Preferably, in the first configuration, the heat capacity of the microsensor means the heat capacity measured between the central portion of the metal layer and the portion of the layers of the at least one pair of layers covered by the central portion.

Preferably, in the second configuration, the heat capacity of the microsensor means the heat capacity measured between the central portion of the layer of the at least one pair of layers covering the central portion of the other layer of the at least one pair of layers. minus a pair of diapers.

Preferably, the arrangement of the layers of the stack of layers of the microsensor as defined above makes it possible to obtain such a thermal time constant. Preferably, the arrangement of the layers of the stack of layers of the microsensor as defined above making it possible to obtain such a thermal time constant makes it possible to reduce the response time of the microsensor.

More preferably, the arrangement of the microsensor according to the invention, more preferably the microsensor according to the invention whose effective ZT is between 0.1 and 1.9 and/or whose thermal conductivity of the microsensor is less than or equal to 10 W.nr ^K' ¹ and/or whose thermal time constant, denoted tau, of the microsensor is less than or equal to 10 s makes it possible to obtain a specific detectivity greater than the detectors of the state of the art. Preferably, the specific detectivity of the microsensor according to the invention is greater than or equal to 1.10 ⁹ cm.Hz°' ^5.W ¹ , preferably 5.10 ⁹ , more preferably 1.10 ¹⁰ , more preferably 5.1O ¹⁰ and even more preferably at 1.10 ¹¹ cm.Hz°' ^5.W ¹ .

Preferably, each of the layers of the at least one pair of layers has a ZT parameter of between 0.1 and 1.9.

Preferably, the ZT of each of the layers of the at least one pair of layers of semiconductor material is greater than or equal to 0.1, more preferably 0.2, preferably 0.3, more preferably at 0.4, more preferably at 0.5, even more preferably at 0.6, particularly preferably at 0.7, particularly advantageously at 0.8, very particularly advantageously at 0, 9. Advantageously, the ZT of each of the layers of the at least one pair of layers of semiconductor material is equal to 1.

Preferably, the ZT of each of the layers of the at least one pair of layers of semiconductor material is less than or equal to 1.9, more preferably 1.8, of preferably at 1.7, more preferably at 1.6, more preferably at 1.5, even more preferably at 1.4, particularly preferably at 1.3, particularly advantageously at 1 ,2, very particularly advantageously at 1.1 and most preferably at 1.05.

Layers of the at least one pair of layers having a ZT parameter of between 0.1 and 1.9, although constituting an improvement of the invention, can contribute to obtaining an effective ZT close to or equal to 1 .

Preferably, a ratio between a thickness, extending along the stacking axis of the layers of the microsensor, of a layer or layers of the at least one pair of layers and, for a layer considered of the at least one minus a pair of layers:

- in the first configuration, a distance (R.1-R.2) between the central portion of the metal layer covering the layer considered and the annular portion of the metal layer covering the layer considered is less than 0.1% , preferably at 0.05%, more preferably at 0.01%, or

- in the second configuration, a distance (R.1-R.2) between the central portion of the layer considered and the annular portion of the metal layer covering the layer considered is less than 0.1%, preferably 0 .05%, more preferably 0.01%; the distance (R.1-R.2) is included in a plane perpendicular to the stacking axis of the layers of the microsensor.

Preferably, the thickness of the at least one pair of layers is less than or equal to 10 μm.

It can be understood by edge, for example of the microsensor or of a layer, a border, a peripheral end, a contour or a periphery of the microsensor.

Preferably, the microsensor, more preferably each of the layers of the stack of layers forming the microsensor, has a spherical geometry. Preferably, the length of the layers of the at least one pair of layers, more preferably a length of each of the layers of the stack of layers forming the microsensor, extends radially from a center of the microsensor towards the edge of the microsensor .

The microsensor, more preferably each of the layers of the stack of layers forming the microsensor, can have a rectangular or square geometry. Preferably, the length of the layers of the at least one pair of layers, more preferably a length of each of the layers of the stack of layers forming the microsensor extends along a length or width of the square or rectangle, preferably from a center of the microsensor towards the edge of the microsensor.

Preferably, the arrangement of the layers of the at least one pair of layers respecting this ratio makes it possible to maximize the temperature gradient, in each of the layers of the at least one pair of layers, between the central portion of the layer of metal and the annular portions of the metal layer, for the first configuration, and between the central portions of the two layers of the at least one pair of layers and the annular portions of the metal layer. Preferably, the arrangement of the layers of the at least one pair of layers respecting this ratio makes it possible to minimize the temperature gradient, in each of the layers of the at least one pair of layers, between the metal layer and the layer of dielectric material. The arrangement of the layers of at least one pair of layers respecting this ratio, although constituting an improvement of the invention, can contribute to obtaining an effective ZT close to or equal to 1.

Preferably, in the first configuration of the microsensor, a contact surface between the central portion of the metal layer and the at least one pair of layers is greater than 0.1%, more preferably greater than 0.25%, so preferred at 0.5%, more preferably at 0.75%, more preferably at 1%, even more preferably at 2%, particularly preferred at 4%, particularly advantageously at 6%, very particularly advantageously at 8% and most preferably at 10%, of a total surface area of one face of the at least one pair of layers which faces the metal layer.

Preferably, in the second configuration of the microsensor, the contact surface between the central portions of the two layers of the at least one pair of layers is greater than 0.1%, more preferably greater than 0.25%, more preferably at 0.5%, more preferably at 0.75%, more preferably at 1%, even more preferably at 2%, particularly preferably at 4%, particularly advantageously at 6%, very particularly advantageous manner at 8% and most preferably at 10%, of a total surface area of one face of the layer of the at least one pair of layers whose central portion covers the central portion of the other layer of the at least one pair of layers and/or a total surface of one face of the layer of the at least one pair of layers whose central portion is covered by the central portion of the other layer of at least one pair of layers. Preferably, a contact surface between the two annular portions of the metal layer and the at least one pair of layers is greater than 10%, more preferably 20%, more preferably 30%, more preferably more than 30%. 40%, more preferably 50%, even more preferably 55%, particularly preferably 60%, particularly advantageously 70%, most particularly advantageously 80% and most preferably at 90%, of a total surface area of one side of the at least one pair of layers which faces the metal layer.

Preferably, such an arrangement of the contact surfaces between the metal layer and the at least one pair of layers, associated with the high thermal and electrical conductivity of the metal layer, makes it possible to reduce the contact resistances between the metal layer and the at least one pair of layers and, in addition, for the second configuration such an arrangement of the contact surface between the central portions of the two layers of the at least one pair of layers makes it possible to reduce the contact resistances at the level of the contact surface between the central portions of the two layers of the at least one pair of layers. Preferably, such an arrangement of the contact surfaces between the metal layer and the at least one pair of layers associated with the high thermal and electrical conductivity of the metal layer, and, in addition, for the second configuration such an arrangement of the contact surface between the central portions of the two layers of the at least one pair of layers, makes it possible to homogenize the temperature at the proximal end and the distal end of the layers of the at least one pair of layers . Preferably, such an arrangement of the contact surfaces between the metal layer and the at least one pair of layers, associated with the high thermal and electrical conductivity of the metal layer makes it possible to obtain an optimal compromise between a reduction in contact resistances between the metal layer and the at least one pair of layers, and good homogenization of the temperature between the metal layer and the at least one pair of layers and, in addition, for the second configuration such an arrangement of the surface of contact between the central portions of the two layers of the at least one pair of layers, makes it possible to obtain an optimal compromise between the central portions of the two layers of the at least one pair of layers, and good homogenization of the temperature between the central portions of the two layers of the at least one pair of layers. Although constituting an improvement of the invention, the arrangement of the contact surfaces between the metal layer and the at least one pair of layers, and, in addition, for the second configuration the arrangement of the contact surface between the central portions of the two layers of the at least one pair of layers, as described above, associated with the high thermal and electrical conductivity of the metal layer can contribute to obtaining an effective ZT close to 1 or equal to 1.

The microsensor may comprise, at the contact surface between the central portion of the metal layer and the at least one pair of layers, and, for the second configuration, between the central portions of the two layers of the at least one pair of layers, a thin intermediate layer aimed at reducing the contact resistance between the metal layer and the at least one pair of layers, and, for the second configuration, between the central portions of the two layers of the at least one pair of diapers. Preferably, the metallic layer and/or the at least one pair of layers of semiconductor material may comprise chemical elements constituting the thin intermediate layer having diffused in the metallic layer and/or in the at least one pair of layers in semiconductor material.

Preferably, the materials constituting the layers of the at least one pair of layers are:

- semiconductor materials comprising Telluride and/or Bismuth and/or Germanium and/or antimony, and/or

- Heusler alloys.

Preferably, the semiconductor material constituting the at least one pair of layers comprises, or is made up of at least 90%, in atomic percentage, of Bismuth Telluride or Germanium Telluride or Lead Telluride or Antimony Telluride. or an Antimony-Lead alloy or a Silicon-Germanium alloy.

Preferably, for a measurement temperature around 300 K, the semiconductor material is Bismuth Tellurium.

Preferably, for a measurement temperature around 700 K, the semiconductor material is an alloy comprising Tellurium, Antimony, Germanium and Silver or an alloy comprising Lead and Tellurium.

Preferably, for a measurement temperature around 900 K, the semiconductor material is an alloy comprising Zinc and Anitmony or its derivatives or skutterude.

Preferably, for a measurement temperature around 1200 K, the semiconductor material is an alloy comprising Silicon and Germanium. Preferably, the at least one pair of layers rests entirely on the layer of dielectric material.

Preferably, the entire surface or face of the at least one pair of layers which faces the layer of dielectric material is in contact with the dielectric material.

Preferably, the characteristic of the microsensor according to which all of the layers of the at least one pair of layers is in contact with the layer of dielectric material makes it possible to reduce the electrical losses or exchanges and/or the thermal losses or exchanges of the layers of the at least one pair of layers with the environment of the microsensor. Such an arrangement of the layers of the at least one pair of layers, although constituting an improvement of the invention, can contribute to obtaining an effective ZT close to or equal to 1.

Preferably, the microsensor comprises a layer of absorbent material covering, preferably covering only:

- in the first configuration, the central portion of the metal layer, or

- in the second configuration, the central portion of the layer of the at least one pair of layers covering the central portion of the other layer of the at least one pair of layers, said layer of absorbent material is capable of absorbing the heat over a wide wavelength range.

Preferably, the layer of absorbent material covers an upper surface of the central portion of the metal layer or an upper surface of the layer of the at least one pair of layers covering the central portion of the other layer of the at least one pair of layers. minus a pair of diapers.

A wide wavelength range can be understood as wavelengths between a hundred nanometers and a few hundred microns.

The absorbent material may be a dielectric material. The absorbent material may be carbon black, black gold or platinum black.

Preferably, the microsensor is arranged and/or comprises fixing means intended or capable of cooperating with a vacuum chamber so that the at least one pair of layers of semiconductor material and the metal layer and/or the layer of material absorbent and/or the layer of dielectric material and/or the support material of thermal conductor are maintained under primary or secondary vacuum. Preferably, the use of the microsensor under ambient pressure conditions offers sensitivities and detection thresholds lower than those of the state of the art. The use of the microsensor under vacuum is not necessary but allows the sensitivity and detection threshold of the microsensor to be further improved.

Preferably, a thickness, extending along the stacking axis of the layers of the microsensor, of the layers of the at least one pair of layers and/or a thickness, extending along the stacking axis of the layers of the microsensor, the central portion and/or the annular portions of the metal layer is between 0.01 and 10 pm and/or a thickness, extending along the stacking axis of the layers of the microsensor, of the layer of absorbent material is between 0.1 and 10 μm.

Preferably, the thicknesses of the layers of the stack of layers of the microsensor as described above make it possible to reduce, preferably to make negligible, the temperature gradient, in each of the layers of the stack of layers of the microsensor, according to the stacking axis of the layers of the microsensor. Preferably, the thicknesses of the layers of the stack of layers of the microsensor as described above make it possible to maximize the temperature gradient, in each of the layers of the at least one pair of layers, between the central portion of the layer of metal and the annular portions of the metal layer, for the first configuration, or between the central portions of the two layers of the at least one pair of layers and the annular portions of the metal layer, for the second configuration. The thicknesses of the layers of the stack of layers of the microsensor as described above, although constituting an improvement of the invention, can contribute to obtaining an effective ZT close to or equal to 1.

Preferably, the support made of thermally conductive material is annular and extends along a periphery of the lower face of the microsensor.

Preferably, the effect of the support in annular thermal conductive material extending along the periphery of the lower face of the microsensor makes it possible to generate a temperature gradient extending radially or from the center of the microsensor, where the power of the thermal radiation is absorbed, towards the periphery or the periphery of the microsensor.

Preferably, a thickness, extending along the stacking axis of the layers of the microsensor, of the part of the layer of dielectric material which is opposite the support of annular thermal conductive material is greater than the thickness of remainder of the layer of dielectric material. In other words, preferably, a thickness of the layer of dielectric material varies in the plane perpendicular to the stacking axis of the layers of the microsensor. Preferably, the layer of dielectric material comprises a part, called a central part, and an annular part which extends along a periphery of the layer of dielectric material. Preferably, the remainder of the layer of dielectric material corresponds to the central part of the layer of dielectric material. Preferably, the annular part of the layer of dielectric material corresponds to the part of the layer of dielectric material which faces the support of annular thermal conductive material. Preferably, the central part of the layer of dielectric material extends from a center of the layer of dielectric material to the annular part of the layer of dielectric material. Preferably, the center of the layer of dielectric material coincides or coincides with the axis of revolution of the microsensor.

Preferably, the thickness of the annular part of the layer of dielectric material has a thickness greater than the thickness of the central part of the layer of dielectric material.

Preferably, the thickness of the remainder of the layer of dielectric material is less than 20 pm, more preferably 18 pm, more preferably 16 pm, more preferably 14 pm, more preferably 12 pm, even more preferably at 10 pm. Preferably, the thickness of the remainder of the layer of dielectric material is less than 9 pm, more preferably 8 pm, more preferably 7 pm, more preferably 6 pm, more preferably 5 pm, even more preferably at 4 pm, particularly preferably at 3 pm, particularly preferably at 2 pm and most preferably at 1 pm.

Preferably, the dielectric material may comprise only an annular part. In other words, the dielectric material may not include a central part.

Preferably, the thickness of the part of the layer of dielectric material which faces the support of annular thermal conductive material is between 1 and 100 pm, more preferably between 12.5 and 50 pm.

Preferably, a length of the layer of dielectric material and/or a length of the support of thermal conductive material is greater than a length of the other layers of the stack of layers of the microsensor; for each of layers of the stack of layers of the microsensor, the length of a layer considered of the stack of layers of the microsensor is included in a plane perpendicular to the stacking axis of the layers of the microsensor and extends between a central portion and an edge, preferably an external edge, of the layer considered.

Preferably, the length of a layer considered of the stack of layers of the microsensor extends between an end, called proximal, located on the side of the center of the microsensor and an end, called distal, located on the side of the external edge, of the layer considered.

Preferably, the layer of dielectric material and/or the support of thermal conductive material extend, radially or in the direction connecting the center of the microsensor to the edges of the microsensor, beyond the other layers of the stack so as to prevent a short circuit between the at least one pair of layers and/or the metal layer and the support made of thermally conductive material.

According to the invention, a method of manufacturing a microsensor according to the invention is also proposed. The process comprises the steps consisting of:

- deposit a layer made of a dielectric material on a support made of thermally conductive material,

- carry out a first succession of microfabrication steps to form a first layer of a pair of layers, intended to form a thermocouple, covering a first part of the layer of dielectric material,

- carry out a second succession of microfabrication steps to form a second layer of the pair of layers, intended to form the thermocouple, covering a second part of the layer of dielectric material, the first and second layers of the pair of layers are separated , through a trench, with a minimum distance greater than 500 nm,

- carry out a third succession of microfabrication steps to form a metal layer partially covering the pair of layers, the metal layer comprises two annular portions per pair of layers, one of the two annular portions covers a peripheral portion of one of the two layers of the pair of layers and the other of the two annular portions covers a peripheral portion of the other of the two layers of the pair of layers; in a first configuration of the microsensor, the metal layer comprises a central portion which covers, at least, a portion of each of the two layers of the pair of layers which is adjacent to the trench, and in a second configuration of the microsensor, a central portion of the second layer of the pair of layers covers a central portion of the first layer of the pair of layers.

The method of obtaining the microsensor may also include one or more steps of processing the contact surface between the metal layer and the pair of layers making it possible to reduce the contact resistances between the metal layer and the pair of layers of semiconductor material. Preferably, such a treatment aims to reduce the contact resistance between the metal layer and the layers of semiconductor material.

The method according to the invention is particularly suitable, preferably even specially designed, for implementing the microsensor according to the invention. Thus, any characteristic of the microsensor according to the invention can be integrated into the method according to the invention and vice versa.

Description of figures

Other advantages and particularities of the invention will appear on reading the detailed description of implementations and embodiments in no way limiting, and the following appended drawings:

[Fig. 1] FIGURE 1 is a schematic representation in top view of a first embodiment of the thermoelectric microsensor according to the invention,

[Fig. 2] FIGURE is a schematic representation in sectional view of the microsensor illustrated in FIGURE 1,

[Fig. 3] FIGURE 3 is a schematic representation in sectional view of the microsensor illustrated in FIGURE 1,

[Fig. 4] FIGURE 4 is a schematic representation in sectional view of the microsensor illustrated in FIGURE 1,

[Fig. 5] FIGURE 5 is a schematic representation in top view of a second embodiment of a thermoelectric microsensor according to the invention, [Fig. 6] FIGURE 6 is a schematic representation in sectional view of the microsensor illustrated in FIGURE 5,

[Fig. 7] FIGURE 7 is a schematic representation in sectional view of the microsensor illustrated in FIGURE 5,

[Fig. 8] FIGURE 8 is a graph illustrating the temperature variations over time of a black body measured by the microsensor,

[Fig. 9] FIGURE 9 is a graph illustrating the temperature variations over time of a black body measured by the microsensor,

[Fig. 10] FIGURE 10 is a graph illustrating the variations in thermal power over time of a light-emitting diode measured by the microsensor,

[Fig. 11] FIGURE 11 is a graph illustrating the variations in thermal power over time of a light-emitting diode measured by the microsensor,

[Fig. 12] FIGURE 12 is a graph illustrating the variations in thermal power over time of a light-emitting diode measured by the microsensor,

[Fig. 13] FIGURE 13 is a graph illustrating the thermal power variations over time of a light-emitting diode measured by the microsensor. Description of embodiments

The embodiments described below being in no way limiting, we may in particular consider variants of the invention comprising only a selection of characteristics described, isolated from the other characteristics described (even if this selection is isolated within a sentence including these other characteristics), if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection includes at least one characteristic, preferably functional without structural details, or with only part of the structural details if this part only is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. .

With reference to FIGURES 1 to 7, a thermoelectric microsensor 1 according to the invention is presented. Microsensor 1 is formed by a stack of layers. The microsensor 1 is circular according to the embodiment presented. This geometry is not limiting and the arrangement currently described can be transposed directly to a microsensor 1 of any geometry, for example square or rectangular. As described below, the center or the central part of the microsensor 1 constitutes the detection zone onto which the thermal radiation to be detected is directed. According to the non-limiting embodiment, the detection zone is located on the upper face of the microsensor 1. The detection zone could very well be located in the center of the lower face of the microsensor 1.

The stack of layers comprises a support 2 made of thermally conductive material. Support 2 constitutes the lower layer of microsensor 1. According to the embodiment, support 2 is made of copper. The stack of layers comprises a layer 3 made of a dielectric material which rests on the support 2 made of copper. Layer 3 of dielectric material is made of Kapton according to the embodiment. The stack of layers comprises at least one pair of layers, two pairs 51, 52 and 53, 54 of layers 51, 52, 53, 54 according to the embodiment, forming a thermocouple, two thermocouples 61, 62 according to the mode of realization. Each layer of a pair 51, 52 and 53, 54 of layers is separated by a trench 83 from a layer of another pair 51, 52 and 53, 54 of layers. In other words, layer 51 of thermocouple 61 is separated by trench 83 from layer 53 of thermocouple 62 and layer 52 of thermocouple 61 is separated by trench 83 from layer 54 of thermocouple 62. The stack of layers comprises a metal layer 71, 72, 74, 75, 76 covering partially the two pairs 51, 52 and 53, 54 of layers 51, 52, 53, 54. The metal layer 71, 72, 74, 75, 76 comprises two annular portions 71, 72 and 71, 74 per pair 51, 52 and 53, 54 of layers 51, 52, 53, 54. According to the embodiment, the metal layer 71, 72, 74, 75, 76 therefore comprises three annular portions 71, 72, 74. For each thermocouple 61, 62 , one of the two annular portions 71, 72 or 71, 74 of a thermocouple 61, 62 covers a peripheral portion of one of the two layers 51 or 52 and 53 or 54 of one of the two pairs 51, 52 and 53, 54 of layers and the other of the two annular portions 71, 72 or 71, 74 covers a peripheral portion of the other layer 51 or 52 and 53 or 54 of the two pairs 51, 52 or 53, 54 of layers. The thickness of the metal layer is 1 μm according to the non-limiting embodiment. The metal layer 71, 72, 74, 75, 76 is a Nickel-Platinum bilayer according to the non-limiting embodiment.

Each thermocouple 61, 62 or each pair 51, 52 and 53, 54 of layers is arranged so that a trench 81, 82 separates the two layers 51, 52 and 53, 54 of a thermocouple 61, 62. The width of the trench 81, 82, denoted d, or the distance separating the two layers 51, 52 and 53, 54 of a thermocouple 61, 62 is 500 pm according to the non-limiting embodiment.

With reference to FIGURES 1 to 4, in a first configuration of the microsensor 1 according to the embodiment, the metal layer 71, 72, 74, 75, 76 comprises two central portions 75, 76. In practice, the microsensor 1 comprises a central portion 75, 76 by thermocouple 61, 62. Each of the central portions 75, 76 covers a portion, which is adjacent to the trench 81, 82, of each of the two layers 51, 52 and 53, 54 of a thermocouple 61, 62. The central portions 75, 76 of the metal layer have the effect of electrically connecting the two layers 51, 52 and 53, 54 of a thermocouple 61, 62. The central portions 75, 76 of the metal layer are located in the detection zone of the microsensor 1. In addition, the central portions 75, 76 of the metal layer 71, 72, 74, 75, 76 also have the effect of homogenizing the temperature at the level of each portion adjacent to the trench 81, 82, of each of the two layers 51, 52 and 53, 54 of a thermocouple 61, 62. Finally, the central portions 75, 76 of the metal layer 71, 72, 74, 75, 76 also have the effect of allowing better absorption of thermal radiation.

With reference to FIGURES 5 to 7, a second configuration of the microsensor 1 according to the embodiment is illustrated. The second configuration of the microsensor 1 differs from the first configuration of the microsensor 1 only in the central zone of the microsensor 1 and only with regard to the two layers 51, 52, 53, 54 of thermocouples 61, 62. Only the differences between the two configurations are therefore presented. In the absence of contrary indication, all of the characteristics described apply to the two configurations of the microsensor 1. In the second configuration of the microsensor 1 according to the embodiment, a central portion 91, 93 of a layer 51, 54 among the two layers 51, 52 and 53, 54 of each thermocouple 61, 62 cover a central portion 92, 94 of the other layer 52, 53. The covering of the central portions 91, 92 and 93, 94 of the layers 51, 52 and 53, 54 of each thermocouple 61, 62 has the effect of electrically connecting the two layers 51, 52 and 53, 54 of a thermocouple 61, 62. The central portions 91, 92, 93, 94 of the layers 51, 52 and 53 , 54 are located in the detection zone of the microsensor. In addition, the covering of the central portions 91, 92, 93, 94 of the layers 51, 52 and 53, 54 of each thermocouple 61, 62 also has the effect of homogenizing the temperature at each of the portions of the central portions 91, 92.

According to the invention, the materials constituting each of the two layers 51, 52, 53, 54 of each thermocouple 61, 62 are chosen so that, for a given measurement temperature interval, denoted [Tmin, Tmax], the microsensor 1 has an effective ZT parameter between 0.1 and 1.9, ZT is the figure of merit and T is the measurement temperature. It has been observed that the design of a microsensor 1 respecting the arrangement as described above, the effective ZT of which is close to 1 or equal to 1, makes it possible to obtain the best sensitivity and the best detection threshold. The arrangement of the layers of the stack of layers of the microsensor 1 modifies the effective ZT of the microsensor 1. In particular, the arrangement of the layers of the stack of layers modifies, among other things, the thermal conductivity and the electrical conductivity of the layers 51 , 52 and 53, 54 of the thermocouples 61, 62 and therefore their figure of merit. Also, it is necessary that the choice of materials constituting the layers 51, 52 and 53, 54 of the thermocouple 61, 62 takes into account the arrangement of the stack of layers of the microsensor 1 as a whole. Also, this effect is not, and cannot be, obtained by simply choosing the materials constituting the layers 51, 52 and 53, 54 of a thermocouple 61, 62 so that the figure of merit of the pairs of layers 51, 52 and 53, 54 of thermocouples 61, 62 either as high as possible or as small as possible. Also, by way of non-limiting example, according to the embodiment, and for an operating temperature close to 300 kelvins, the material used for layers 51 and 54 of thermocouples 61, 62 is Bismuth (III) tellurium, (BizTez.ySeo.s), p-doped and layers 52 and 53 of thermocouples 61, 62 are made of Bismuth tellurium (III), (Bio.5Sb1.5Te3), n-doped. In the case of Bismuth tellurium, the figure of merit of the layers 51, 52, 53, 54 of the thermocouples 61, 62 is of the order of 1 and the figure of merit of the microsensor 1 is of the order of 1.

In practice, according to the embodiment with two thermocouples 61, 62, the temperature measurement is carried out by measuring the potential difference which is established between the annular portions 72 and 74. The measured potential difference therefore corresponds to the difference potential across the two thermocouples 61, 62 connected in series.

For the first configuration, the central portion 75 connects the layer 52 to the layer 51 of the pair of layers 51, 52 of the thermocouple 61, the annular portion 71 connects the thermocouple 61 to the thermocouple 62 and the central portion 76 connects the layer 53 to the layer 54 of the pair of layers 53, 54 of the thermocouple 62.

For the second configuration, the central portions 93, 94 connect the layer 52 to the layer 51 of the pair of layers 51, 52 of the thermocouple 61, the annular portion 71 connects the thermocouple 61 to the thermocouple 62 and the central portions 91, 92 connect layer 53 to layer 54 of the pair of layers 53, 54 of the thermocouple 62.

This operating mode can be transposed and adapted to the number of thermocouples constituting the microsensor. In particular, for a microsensor comprising two or more thermocouples and comprising a total number N of layers forming the pairs of layers of the microsensor, the microsensor will comprise a number of annular portions connecting two adjacent layers each belonging to a pair of distinct layers is equal to ((N-2)/2). Such a microsensor will include a number denoted M of thermocouples which is equal to (N/2) and a number of annular portions N' which is equal to 2M + 1.

In an improvement of the microsensor 1, the support 2 is annular. The thickness of support 2 is 2 mm depending on the embodiment. Such a thickness makes it possible to have a significant thermal mass at the level of the support which defines a constant temperature. The arrangement of the support 2 makes it possible to maximize the radial temperature gradient, denoted AT2, extending laterally or perpendicularly relative to the layer stacking axis 4, establishing itself in the microsensor 1 when thermal radiation is absorbed in the center of the microsensor 1. Optimization of the temperature gradient AT2 will induce an increase in the potential difference, denoted AV, measured across the thermocouples 61, 62, that is to say between the portions annular rings 71, 72 and 71, 74 of the metal layer of a thermocouple 61, 62, and will therefore make it possible to increase the sensitivity and reduce the detection threshold of the microsensor 1.

In an improvement of the microsensor 1, the layer 3 has a thickness which varies laterally or radially. The thickness Z of the part of the layer 3 facing the annular support 2 is 25 μm. This thickness must be sufficient to ensure electrical insulation between the metal layer 71, 72 and 71, 74 and 75, 76 and the layers 51, 52, 53, 54 of the thermocouples 61, 62 and the support 2. Such an arrangement of the layer 3 makes it possible to reduce the temperature gradient AT3 between the support 2 and the layers 51, 52, 53, 54 of the thermocouples 61, 62 so as to maximize the temperature gradient AT2.

In addition, the thickness p of the part of the layer 3 extending from the center of the microsensor 1 to the interior or proximal edge of the support 2, that is to say the part having a diameter equal to twice that of Ri, is 1 pm. This thickness must be as small as possible to reduce the lateral temperature gradient AT'2 within layer 3 so as to maximize the lateral temperature gradient AT2 in layers 51, 52, 53, 54 of thermocouples 61, 62. Ideally, layers 51, 52, 53, 54 of thermocouples 61, 62 are suspended and layer 3 is annular.

In an improvement of the microsensor 1, the length or the radius R4 of the layer 3 is equal to the length R4 of the support 2. The radius 4 of the layer 3 is greater than the radius 3 of the layers 51, 52, 53, 54 of the thermocouples 61, 62 and at the radius of the annular portions 71, 72 and 71, 74 of the metal layer. In other words, the distal end of layer 3 extends radially beyond the distal end of layers 51, 52, 53, 54 of thermocouples 61, 62 and from the distal end to radius R3-R1 of the portions annular rings 71, 72 and 71, 74 of the metal layer. This has the effect of preventing a short circuit between layers 51, 52, 53, 54 of the thermocouples 61, 62 and/or the annular portions 71, 72 and 71, 74 of the metal layer and the copper support 2 .

In an improvement of the microsensor 1, a ratio between the thickness A of the layers 51, 52, 53, 54 of the thermocouples 61, 62 and the length, equal to R1-R2, of the layers 51, 52, 53, 54 of the thermocouples 61 , 62 is less than 0.1%. The ratio is of the order of 0.01% depending on the embodiment. An arrangement respecting such a ratio makes it possible to maximize the lateral temperature gradient AT2 in layers 51, 52, 53, 54 of thermocouples 61, 62. In addition, an arrangement respecting such a ratio makes it possible to minimize the vertical temperature gradient AT3 between layers 51, 52, 53, 54 of thermocouples 61, 62 and layer 3. In addition, for the first configuration, an arrangement respecting such a ratio makes it possible to minimize the vertical temperature gradient ATI between the layers 51, 52, 53, 54 of the thermocouples 61, 62 and the central portions 75, 76 of the metal layer.

In an improvement of the microsensor 1, the thermal time constant, denoted tau, of the microsensor 1 is less than or equal to 10 s. Such a time constant is obtained thanks to the arrangement of the layers of the stack of layers of the microsensor 1 as defined above. Such a thermal time constant makes it possible to reduce the response time of the microsensor 1.

In an improvement of the microsensor 1, the arrangement of the microsensor according to the invention makes it possible to obtain a specific detectivity greater than the detector of the state of the art. This specific detectivity is between 1.10 ⁹ and 1.10 ¹¹ cm.Hz°' ⁵ .W ¹ depending on the embodiment. Unlike the state-of-the-art detector, the specific detectivity of the microsensor 1 according to the invention depends only on the thickness A of the layers 51, 52, 53, 54 of the thermocouples 61, 62 and is inversely proportional to the thickness A of layers 51, 52, 53, 54 of thermocouples 61, 62. Consequently, the more the thickness A is reduced, the higher the specific detectivity of the microsensor 1 will be.

In an improvement of the microsensor 1, a contact surface between the annular portions 71, 72 and 71, 74 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62 is greater than 10% of the total surface. of the upper face of the layers 51, 52, 53, 54 of the thermocouples 61, 62 which is facing the metal layer. The ratio between the contact surface between the annular portions 71, 72 and 71, 74 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62 and the total surface of the upper face of the layers 51, 52, 53, 54 thermocouples

61, 62 which faces the metal layer is 55% depending on the embodiment. Such a ratio has the effect of reducing the contact resistances between the annular portions 71, 72 and 71, 74 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62. Such a ratio also has the effect of effect of homogenizing the temperature at the distal end of the layers 51, 52, 53, 54 of the thermocouples 61,

62. Such a ratio also makes it possible to obtain an optimal compromise between a reduction contact resistances between the annular portions 71, 72 and 71, 74 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62 and good thermal transfer between the annular portions 71, 72 and 71, 74 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62.

In an improvement of the first configuration of the microsensor 1, the contact surface between the central portions 75, 76 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62 is greater than 0.1% of the total surface of the upper face layers 51, 52, 53, 54 of the thermocouples 61, 62. The ratio is of the order of 2% depending on the embodiment. Such a ratio has the effect of reducing the contact resistances between the central portions 75, 76 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62. Such a ratio also has the effect of homogeneity. - ser the temperature at the proximal end of the layers 51, 52, 53, 54 of the thermocouples 61, 62. Such a ratio also makes it possible to obtain an optimal compromise between a reduction in the contact resistances between the central portions 75, 76 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62 and good thermal transfer between the central portions 75, 76 of the metal layer and the layers 51, 52, 53, 54 of the thermocouples 61, 62.

In an improvement of the second configuration of the microsensor 1, the contact surface between the central portions 91, 92 and 93, 94 of the layers 51, 52, 53, 54 of the thermocouples 61, 62 is greater than 0.1% of the surface total of an upper face of the layers 51, 52, 53, 54 of the thermocouples 61, 62. The ratio between the contact surface between the central portions 91, 92 and 93, 94 of the layers 51, 52, 53, 54 of the thermocouples 61, 62 and the total surface area of an upper face of the layers 51, 52, 53, 54 of the thermocouples 61, 62 is 2% according to the embodiment. Such a ratio has the effect of reducing the contact resistances between the central portions 91, 92 and 93, 94 of the layers 51, 52, 53, 54 of the thermocouples 61, 62. Such a ratio also has the effect of homogenizing the temperature at the level of the central portions 91, 92 and 93, 94 of the layers 51, 52, 53, 54 of the thermocouples 61, 62. Such a ratio also makes it possible to obtain an optimal compromise between a reduction in the contact resistances between the central portions 91 , 92 and 93, 94 of layers 51, 52, 53, 54 of thermocouples 61, 62 and good thermal transfer between the central portions 91, 92 and 93, 94 of layers 51, 52, 53, 54 of thermocouples 61, 62 . Finally, although not necessary for obtaining an effective ZT of the microsensor 1 close to or equal to 1, each of the improvements described above contribute to obtaining an effective ZT close to or equal to 1 by reducing the difference between the figure of merit ZT of the pairs of layers 51, 52 and 53, 54 of the thermocouples 61, 62 and the factor of merit ZTeffective of the microsensor 1.

An embodiment of the method of manufacturing the microsensor 1 according to the invention is also described. The method comprises the step of depositing the Kapton layer on the annular copper support 2. According to the non-limiting embodiment, the Kapton is glued to the copper support 2, preferably previously cleaned with ethanol. A press is placed on the copper ring and it is heated for around ten hours at 120°C in order to dry the glue.

The method then comprises the step of carrying out a first succession of microfabrication steps to form layers 51 and 54 each covering a first part of layer 3 in Kapton. According to the non-limiting embodiment, the first succession of steps comprising a spreading, by spin-coating, of positive resin S1818 at a rotation speed of between 6000 rpm/s and 4000 rpm/s for a duration of 30 s. The resin is then developed for 1 min in a 1:1 solution of microposit developer and deionized water. The resin is then exposed. A p-type BizTes film is deposited by magnetron-assisted cathode sputtering over the entire surface. The resin is then removed by immersing the sample for 5 min in acetone then 5 min in ethanol to obtain layers 51 and 54.

The method then comprises the step of carrying out a second succession of microfabrication steps to form layers 52 and 53 of n-type BizTes covering a second part of layer 3 of Kapton. The microfabrication steps implemented are identical to those of the first succession of steps.

The process further comprises annealing the layers 51, 52, 53, 54 under argon at a pressure of 600 mbar. Layers 51, 52, 53, 54 are annealed at 270°C between 2 hours and 3 hours.

The method then comprises the step of carrying out a third succession of microfabrication steps to form the three annular portions 71, 72, 74.

For the implementation of the microsensor 1 according to the first configuration, the third succession of microfabrication steps further comprises the production of the central portions 75, 76 of the metal layer which cover a portion of each of the two layers of the pair of layers which is adjacent to the trench. The microfabrication steps implemented during the third succession of steps are identical to those of the first and second successions of steps. The deposition of the Nickel-Platinum bilayer is carried out by X-ray magnetron-assisted cathode sputtering.

For the implementation of the microsensor 1 according to the second configuration, the first and second successions of microfabrication steps to form the layers 51, 52, 53 and 54 are carried out so that the central portions 91, 93 of the second layer of the pair of layers covers the central portion 92, 94 of the first layer of the pair of layers.

In a particular embodiment of the invention, the dimensions of the microsensor 1 are reduced, in particular the dimensions Ri, 2, 3, R4 are reduced, by way of non-limiting example, so that the distance 2. i is between 1 mm and 0.01 mm. Thus, it is planned to form a network or matrix of microsensors 1, distributed over a two-dimensional surface, thus constituting a thermal camera.

With reference to FIGURES 8 to 13, the performances of the microsensor 1 according to the invention are illustrated.

FIGURE 8 shows the temperature variations, measured by the microsensor 1, of a black body of constant temperature which is placed a few centimeters from the microsensor 1. The microsensor 1 displays a peak-to-peak noise of less than 10 microkelvins. The drifts are linked to variations in temperature of the room in which the microsensor 1 and the black body are placed. They are less than 80 microkelvins over the three hours of the experiment. Each experimental point is a measurement per second of the temperature.

FIGURE 9 shows the temperature variations, measured by the microsensor 1, of a black body placed a few centimeters from the microsensor 1. The temperature variations of the black body are a few hundred microkelvins and are imposed by the experimenter . Each experimental point is a measurement per second of the temperature.

FIGURE 10 shows the variations, measured by the microsensor 1, of the thermal power supplied by a light-emitting diode (LED) emitting at a wavelength of 680 nm. The light emitted by the LED is collimated to the center of microsensor 1. The power signal is recorded as a function of time with a point every 1.3 seconds. The microsensor 1 is capable of measuring variations in the power of the LED of 200 nW, 1 .W, 10pW, 100 |_iW and 1 mW. The dynamic measurement over time is presented in logarithmic scale. It was observed that microsensor 1 has an upper limit of measurable power of 600 mW.

With reference to FIGURES 11, 12 and 13 respectively, the variations, measured by the microsensor 1, of the value of the thermal power supplied by LED diodes emitting respectively at 680, 1050 and 1650 nm are illustrated. The light emitted by the LEDs is collimated to the center of microsensor 1. The power signal is illustrated as a function of time with a point recorded every 0.64, 1.3 and 1.3 seconds respectively. With reference to FIGURE 11, the microsensor 1 is capable of measuring a variation in the power of the LED of approximately 250 nW with a peak-to-peak noise of approximately 50 nW. With reference to FIGURE 12, the microsensor 1 is capable of measuring a variation in the power of the LED of approximately 250 nW with a peak-to-peak noise of approximately 50 nW. With reference to FIGURE 13, the microsensor 1 is capable of measuring a variation in the power of the LED of approximately 350 nW with a peak-to-peak noise of approximately 50 nW.

Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

Thus, in variants that can be combined with each other of the previously described embodiments:

- in the second configuration of the microsensor 1, the metal layer also covers the central portions 91, 93 of the layers 51, 54, and/or

- in the second configuration, the microsensor 1 comprises a layer of absorbent material covering the central portions 91, 93 of the layers 51, 54 or covering the layer of metal which covers the central portions 91, 93 of the layers 51, 54, and/or

- in the first configuration, the microsensor 1 comprises a layer of absorbent material covering the central portions 75, 76 of the metal layer.

In addition, the different features, shapes, variants and embodiments of the invention can be associated with each other in various combinations as long as they are not incompatible or exclusive of each other.

Claims

1. Thermoelectric microsensor (1) for measuring low-power thermal radiation, called a microsensor, formed by a stack of layers comprising, from a lower face to an upper face of the microsensor:

- a support 2 made of thermally conductive material,

- a layer 3 made of a dielectric material,

- at least one pair (51, 52), (53, 54) of layers (51, 52, 53, 54) forming a thermocouple (61, 62), the at least one pair of layers is separated by a distance minimum greater than 500 nm by a trench (81, 82),

- a metal layer (71, 72, 74, 75, 76) partially covering the at least one pair of layers, the metal layer comprises two annular portions (71, 72, 74) per pair of layers and for each thermocouple considered one of the two annular portions covers a peripheral portion of one of the two layers of the at least one pair of layers and the other of the two annular portions:

■ covers a peripheral portion of the other layer of the at least one pair of layers, and

■ for a number of thermocouples greater than or equal to 2, is connected to a peripheral portion of an adjacent layer belonging to a separate thermocouple;

• in a first configuration of the microsensor, the metal layer comprises a central portion (75, 76) which covers, at least, a portion of each of the two layers of the at least one pair of layers which is adjacent to the trench, Or

• in a second configuration of the microsensor, a central portion (91, 93) of one of the two layers of the at least one pair of layers covers, at least, a central portion (92, 94) of the other layer of the at least one pair of layers; said microsensor presents, for a given measurement temperature interval, denoted [Tmin, Tmax], an effective ZT parameter of between 0.1 and 1.9, ZT is the figure of merit of the microsensor and T is the measurement temperature.

2. Microsensor (1) according to claim 1, in which a thermal conductivity of the microsensor is less than or equal to 10 W.nrTK' ¹ .

3. Microsensor (1) according to the preceding claim, in which a thermal time constant, denoted tau, of the microsensor is less than or equal to 10 s, tau is equal to the ratio between a heat capacity of the microsensor and the thermal conductivity of the microsensor.

4. Microsensor (1) according to any one of the preceding claims, in which each of the layers (51, 52, 53, 54) of the at least one pair (51, 52), (53, 54) of layers presents a ZT parameter between 0.1 and 1.9.

5. Microsensor (1) according to any one of the preceding claims, in which a ratio between a thickness, extending along the stacking axis 4 of the layers of the microsensor, of the layers of the at least one pair (51 , 52), (53, 54) of layers (51, 52, 53, 54) and, for a layer considered of the at least at least one pair of layers:

- in the second configuration, a distance (R.1-R.2) between the central portion of the layer of the layer considered and the annular portion of the metal layer covering the layer considered is less than 0.1%, preferably at 0.05%, more preferably at 0.01% is less than 0.1%; the distance (Ri-R.2) is included in a plane perpendicular (x, y) to the stacking axis of the layers of the microsensor.

6. Microsensor (1) according to any one of the preceding claims, in which:

- in the first configuration of the microsensor, a contact surface between the central portion (75, 76) of the metal layer and the at least one pair (51, 52), (53, 54) of layers (51, 52, 53, 54) is greater than 0.1% of a total surface area of one face of the at least one pair of layers which faces the metal layer (71, 72, 74, 76), or

- in the second configuration of the microsensor, the contact surface between the central portions (91, 92) of the two layers of the at least one pair of layers is greater than 0.1% of a total surface of a face of the layer of the at least one pair of layers whose central portion covers the central portion of the other layer of the at least one pair of layers, and/or

- a contact surface between the two annular portions (71, 72, 74) of the metal layer and the at least one pair of layers is greater than 10% of a total surface area of one face of the at least one pair of layers which is opposite the metal layer.

7. Microsensor (1) according to any one of the preceding claims, in which the materials constituting the layers (51, 52, 53, 54) of the at least one pair (51, 52), (53, 54) of layers are:

- Heusler alloys.

8. Microsensor (1) according to the preceding claim, in which the semiconductor material comprises Bismuth Telluride or Germanium Telluride or Lead Telluride or Antimony Telluride or an Antimony-Lead alloy or an alloy of Silicon-Germanium.

9. Microsensor (1) according to any one of the preceding claims, in which the at least one pair (51, 52), (53, 54) of layers (51, 52, 53, 54) rests entirely on the layer 3 in dielectric material.

10. Microsensor (1) according to any one of the preceding claims, comprising a layer of absorbent material covering:

- in the first configuration, the central portion (75, 76) of the metal layer, or

- in the second configuration, the central portion (91, 93) of the layer of the at least one pair of layers covering the central portion (92, 94) of the other layer of the at least one pair of layers, said layer of absorbent material is capable of absorbing heat over a wide wavelength range.

11. Microsensor (1) according to any one of claims 1 to 4 and 6 to 10, in which a thickness, extending along the stacking axis 4 of the layers of the microsensor, of the layers (51, 52, 53 , 54) of the at least one pair (51, 52), (53, 54) of layers is between 0.01 and 10 pm.

12. Microsensor (1) according to any one of claims 1 to 4 and 6 to 10, in which a thickness, extending along the stacking axis of the layers of the microsensor, of the central portion (75, 76) and/or annular portions (71, 72, 74) of the metal layer is between 0.01 and 10 pm.

13. Microsensor (1) according to claim 10 or according to one of claims 11 or 12 taken in combination with claim 10, in which a thickness, extending along the stacking axis of the layers of the microsensor, of the layer of absorbent material is between 0.1 and 10 μm.

14. Microsensor (1) according to any one of the preceding claims, wherein the support (2) of thermally conductive material is annular and extends along a periphery of the lower face of the microsensor.

15. Microsensor (1) according to the preceding claim, in which a thickness, extending along the stacking axis (4) of the layers of the microsensor, of the part of the layer (3) of dielectric material which is in screw -with respect to the support (2) made of material annular thermal conductor is greater than the thickness of the rest of the layer of dielectric material.

16. Microsensor (1) according to any one of the preceding claims, in which a length of the layer (3) of dielectric material and/or a length of the support (2) of thermal conductive material is greater than a length of the other layers the stack of layers of the microsensor; for each of the layers of the stack of layers of the microsensor, the length of a layer considered of the stack of layers of the microsensor is included in a plane perpendicular (x,y) to the stack axis (4) of the layers of the microsensor and extends between a central portion and an edge of the layer considered.

17. Method for manufacturing a microsensor (1) according to one of claims 1 to 16, said method comprises the steps consisting of:

- deposit a layer (3) made of a dielectric material on a support (2) of thermally conductive material,

- carry out a first succession of microfabrication steps to form a first layer of a pair (51, 52), (53, 54) of layers (51, 52, 53, 54) intended to form a thermocouple (61, 62 ) covering a first part of the layer of dielectric material,

- carry out a second succession of microfabrication steps to form a second layer of the pair of layers intended to form the thermocouple covering a second part of the layer of dielectric material, the first and second layers of the pair of layers are separated by a minimum distance, through a trench (81, 82), greater than 500 nm,

- carry out a third succession of microfabrication steps to form a metal layer (71, 72, 74, 75, 76) partially covering the pair of layers, the metal layer comprises two annular portions (71, 72, 74) per pair of layers and for each thermocouple considered one of the two annular portions covers a peripheral portion of one of the two layers of the pair of layers and the other of the two annular portions:

■ covers a peripheral portion of the other of the two layers of the pair of layers, and

■ for a number of thermocouples greater than or equal to 2, is connected to a peripheral portion of an adjacent layer belonging to a separate thermocouple; in a first configuration of the microsensor, the metal layer comprises a central portion (75, 76) which covers, at least, a portion of each of the two layers of the pair of layers which is adjacent to the trench, and in a second configuration of the microsensor, a central portion (91, 93) of the second layer of the pair of layers covers a central portion (92, 94) of the first layer of the pair of layers.