FR2949561A1 - MICROSYSTEM SENSOR FOR MEASURING OR DETECTING ENCRYPTION - Google Patents

Abstract

The present invention relates to a sensor for measuring or detecting fouling produced according to microelectronic manufacturing technologies, comprising, arranged on the same face (12a) of a thermal conductive substrate (12): - at least one heating element (14) which is able to generate, on command, a homogeneous controlled heat flow and to diffuse it into the substrate, - at least one element (16) for measuring temperature (Tw) which is subjected to the action of the heat flux diffused by the substrate, the sensor comprising, arranged on the opposite face of the substrate, at least one interface element (18).

Description

The invention relates to a sensor for measuring or detecting the fouling of a reactor or a pipe containing a compressible or incompressible fluid in circulation. In industrial processes, we find different types of installations (tube, heat exchanger, membrane separation processes, mix agitation tank, etc.) in which fluids of various natures (Newtonian and non-Newtonian fluids, charged fluids in particles) are set in motion. These installations generally comprise a circulation of fluids (pump, agitation), conduits in which fluids circulate and may also include reactors (in the unitary operating sense as defined by the Industrial Process Engineering), for example parietal heat exchangers (conductive-convective transfer) either tubular or plate. In this specific case, the fouling of such installations can be detrimental insofar as it affects the performance of the unit operation and therefore of the entire process (for example, the drop in the global coefficient of heat exchange implies also a decrease in the energy efficiency of the process). Fouling of equipment leads to a deterioration in the performance of unit operations in terms of heat transfer, material or momentum. In addition, when fouling is formed on the inner wall of a pipe or a reactor, it should be cleaned at the right time. Cleaning operations are either unavoidable to maintain the proper functioning of a process (eg chemical industries), or mandatory to ensure the quality and safety of products (eg: agro-food industries).

However, this fouling must be continuously detectable by the operators or the maintenance staff of the installation in order to be able to assess, as part of a preventive maintenance, the best time to carry out the cleanings.

In any case, the fouling irregularly cause the shutdown of the installation and this, for a sometimes indeterminate duration, which strongly penalizes the course of the industrial process. These interventions can be painful tasks for the staff, especially if the fouling has been detected only late and if its thickness is too great. The frequency and duration of cleaning operations, the consumption of specific chemical formulations and the production of effluent during these operations have economic, energy, human and environmental impacts.

This de-clogging has a significant economic cost since it is appropriate to include in the cost of maintenance operations the cost of the temporary shutdown of the operation. It will also be noted that as the heat exchangers become fouled, a progressive loss of efficiency ensues (reduction of the overall exchange coefficient, increase of the linear load losses), before a shutdown. potential of the installation or part of the installation including these exchangers. On the other hand, in domestic hot water systems and open industrial cooling towers, bacteria can develop inside the network and the cooling circuit. This bacterial development is commonly in the form of a microbiological deposit called biofilm or biofouling. Similarly, a risk of legionella (Legionella pneumophila) contamination is possible and statistically coupled with drift in biofilm thickness in the sense of the health risk assessment.

At present, it is advisable to carry out a regular control of the installations by foreseeing points of stitching in the pipes or in the reactors where circulate the fluids which are likely to cause a fouling. These stitches also make it possible to take samples and then analyze them in the laboratory in order to obtain either a measurement of the fouling or an analysis of the type of fouling formed (nature, composition, etc.). On certain industrial lines, global thermal or hydraulic approaches are used to estimate the thickness of the fouling layer formed inside the walls of a pipe or a reactor.

Hydraulic methods involve a measurement of the pressure drop generated along the process. The appearance of a deposit reduces the passage section and induces the increase of the pressure drop. The thermal methods are based on the measurement of the overall exchange coefficient or, in the absence of a simple drift, of the logarithmic difference of the inlet and outlet temperatures of the primary and secondary fluids. These last measurements however have real disadvantages insofar as: - they do not make it possible to obtain a local information, - they rest on multiple measurements of temperatures or of loss of load and flow rates, - they are not repeatable even for identical operating conditions (example: evolution of the pressure drop as a function of time). Document FR 2 885 694 discloses a method for locally and on-line measurement of fouling in a reactor or pipe that uses two temperature probes. More particularly, these two probes are introduced into a pipe respectively through two stitching points and one of these probes measures the temperature of the fluid, while the other probe measures the wall temperature of a heat generator. According to this method, it is made, first, to obtain a temperature difference between the wall temperature and the fluid temperature as close to zero as possible. A heat generator emits a heat flux while the temperature difference between the wall temperature and that of the fluid is measured over time, the reactor fouling condition being determined from the measurement of this temperature. temperature difference.

This method and the associated system, however, have certain disadvantages limiting their use in an industrial environment. Indeed, because of the thermal inertia of the system response times may be too long for certain applications or induce a phase shift between measurements of fluid and wall temperatures.

Moreover, with this system it is difficult to detect the first phases of the start of formation of a fouling deposit (limits of detection and quantification). Finally, for the monitoring of fouling generating low thermal resistances, it would be desirable to increase the sensitivity and accuracy of the measurements. In view of the foregoing, it would be interesting to have a new sensor for determining the fouling of a reactor of simplified design and which provides reliable measurements over time. The subject of the present invention is thus a measurement or dirt detection sensor produced according to microelectronic manufacturing technologies, comprising, arranged on the same face of a thermal conductive substrate: at least one heating element which is capable of generating, on command, a homogeneous controlled heat flow and diffusing it into the substrate, at least one temperature measuring element (Tw) which is subjected to the action of the thermal flux diffused by the substrate, the sensor comprising, arranged on the opposite face of the substrate, at least one interface element. In a first configuration of the microsystem sensor according to the invention, said at least one heating element and said at least one temperature measuring element are one and the same element. This element is therefore able both to generate a heat flux and to measure a temperature. In this first configuration, the microsystem sensor according to the invention may comprise a single temperature measuring element or two temperature measuring elements as described below. In a second configuration, said at least one heating element and said at least one temperature measuring element are two different elements of the microsystem sensor according to the invention. In this configuration, the sensor may comprise only one temperature measuring element or two temperature measuring elements as described below. The use of microelectronic technology makes it possible to manufacture on a single plate or wafer a large number of devices / sensors, for example several thousand. Thus, the reproducibility is ensured from one device / sensor to the other on the same plate, which avoids the problems of dispersion during manufacture. The devices / sensors thus manufactured in series of several thousands at a time are therefore more reliable in their operation and less expensive to produce. In addition, the reduced dimensions of such a sensor relative to the sensor of the prior art discussed above have the consequence of reducing the energy consumption of this sensor. In comparison with a sensor structure having the same functional elements but which would not be realized in microelectronic technology: the microsystem sensor has reduced dimensions and therefore reduced thermal inertia, which makes it possible to reduce its response time; the measurement element or elements are much more sensitive in the miniaturized sensor, which makes it possible to reduce the limit of detection and of quantification; the microsystem sensor has a greater sensitivity to measuring the thickness of a fouling layer in terms of detection limit (for example of the order of a few pm instead of a few hundreds of pm in the case of a deposit characterized by a thermal conductivity close to that of water), which makes it possible to improve its accuracy; - In terms of quantification limit, the microsystem sensor is capable of providing a fouling thickness within a few pm in the case of a deposit characterized by a thermal conductivity close to that of water. Moreover, insofar as the sensor is very sensitive, the thermal flux density diffused by the heating element (s) can be greatly reduced.

It will be noted that the sensor according to the invention is capable of determining the fouling formed on the latter when it is placed in a fluid or in contact with a fluid. Determination of fouling is the calculation of a fouling layer thickness already formed or being formed on the sensor and / or the detection of a fouling layer being formed. According to one characteristic, the sensor according to the invention is part of a system which is intended to measure and / or to detect fouling formed or being formed inside a container containing a fluid. Such a container is, for example, a reactor or a pipe carrying a fluid.

It will be noted that the measurement and / or the detection of the level of fouling are carried out continuously and almost in real time, whatever the evolutions of the conditions of the measuring medium (for example the temperature of the uncontrolled fluid). In order to carry out the measurement and / or the detection of the level of fouling, the system of which the sensor is part includes means for supplying energy to the functional elements of the sensor and means for processing the data provided by these elements. These means are offset with respect to the sensor or integrated therewith.

It will be noted that the system further comprises, optionally, means for displaying the results (example: measurement curve of the measured temperature as a function of time, curve of thickness of fouling as a function of time, etc.) and or means for remotely transmitting information relating to the quantitative data (temperature, thickness, etc.) and / or qualitative data (presence or absence of fouling, etc.). Thanks to the sensor according to the invention the measurements are reliable in the time. According to one characteristic, said at least one temperature measuring element (Tw) at least partially surrounds said at least one heating element. Alternatively, it can only be arranged next to it. In another configuration, it may even be surrounded by the heating element. According to one characteristic, the sensor further comprises at least one other temperature measuring element (Tb) which is thermally insulated from the at least one heating element. Thus, said at least one other temperature measuring element (Tb) will not be disturbed by the heat flux generated by said at least one heating element. It is thus possible to measure the fluid temperature using the same sensor, either in its first configuration or in its second configuration. According to one characteristic, said at least one other temperature measuring element (Tb) at least partially surrounds said at least one heating element. According to one characteristic, said at least one other temperature measuring element (Tb) is arranged on one side of a second substrate which is thermally insulated from the first substrate on which said at least one heating element is arranged. According to one characteristic, the second substrate at least partially surrounds the first substrate. According to one characteristic, the thermal insulation is performed by a static gas blade, for example air, which constitutes a very good thermal insulator.

According to one characteristic, the thermal insulation is made by a thermal insulation material disposed between said at least one other temperature measuring element (Tb) and the first substrate. Achieving this thermal insulation provides the advantage of stiffening the overall structure of the sensor and, therefore, to increase its robustness. According to one characteristic, said at least one interface element which is arranged on the opposite faces of the two substrates takes the form of a bonding membrane which interconnects these substrates. It will be noted that the membrane may consist of a SiO 2 and Si, Ny bilayer or, alternatively, a single layer made of SiO, Ny or polymer. According to one feature, the bonding membrane has a small thickness with low thermal resistance to the axial heat flux generated by said at least one heating element and a high thermal resistance to lateral heat losses from the first to the second substrate. When the two substrates are independent of one another, each of said at least one interface element arranged on the opposite face of each substrate is a thermal conductor to promote thermal conduction through the thickness of said at least one interface element considered. For example, each interface element is metallic. In each of these different arrangements one or more heating elements are made in microelectronic technology by optimizing the available surface area on the substrate.

According to one characteristic, the embodiment of said at least one temperature measuring element (Tw) and / or of said at least one other temperature measuring element (Tb), when it is present, and / or of said at least one heating element is performed by ion implantation, thermal diffusion or metal deposition.

It is possible in the context of ion implantation, thermal diffusion or metal deposition to select the length and width of the constituent resistances of the aforementioned elements. It should be noted, however, that the temperature measuring elements may alternatively not be made in the form of resistors but, for example, diodes. In general, it is sought to increase the value of the electrical resistance to increase the sensitivity of the sensor.

To do this, it is possible to act on two parameters, namely the electrical resistivity (p) and a shape parameter (LIS). The resistance of an element is given by the following formula: R = p (L / S) where p is the resistivity of the material constituting the element, L is the length of the wire constituting the element, S is the surface of the element defined by the following formula, S = h * I where I is the width of the element and h is its height.

It will be noted that the resistivity depends on the temperature and the thermo-dependence relation is of the type p = po * (1 + aT + (3T2) where a and R are first and second order temperature coefficients. ion implantation, it is possible to vary one and / or the other of the following parameters to adjust the electrical resistivity: the implantation dose, the implantation energy (this determines the depth of the zone in which is implanted) and the species or species implanted.It is also possible to act on the design or geometry of the implanted area in order to modify the aforesaid shape parameter, it is thus possible to vary the length and / or In the context of thermal diffusion, the electrical resistivity is adjusted by the choice of one or more implanted species, by the conditions of realization of the thermal diffusion (temperature, duration, etc.) and also by speak choosing a drawing or a geometry for the diffused zone in order to modify the shape parameter already mentioned. With regard to the metallic deposit, in order to be able to adjust the electrical resistance, it is possible to select the most suitable metal and / or to act on the design or geometry of the implanted zone in order to modify the aforesaid shape parameter ( it is thus possible to vary the length and / or the surface of the deposit). By modifying the value of the resistance of the metal deposit, which is particularly simple to achieve in microelectronic technology, one can very simply modify the heating power of the sensor to achieve the required flow density. According to one characteristic, the metal deposit forming one of the aforementioned elements takes the form of one or more coils or lines clamped together so as to obtain a large length of metal tracks on a relatively small surface. According to one characteristic, in the case of ion implantation, the temperature coefficient of the resistance or resistors is adjusted by the choice of the species to be implanted and / or the ion implantation dose.

According to one characteristic, in the case of ion implantation, the high resistivity of the implanted resistor or resistors makes it possible to obtain a more compact design and therefore a smaller sensor than with metal deposits. According to one characteristic, the substrate is made of silicon. According to one characteristic, the sensor comprises a thermal insulation element which limits the heat dissipations on the side of the face on which said at least one heating element and said at least one temperature measuring element (Tw) are arranged. Thus, the propagation of the thermal flux towards the opposite face of the substrate is favored. According to one characteristic, the sensor comprises, on the side of the face where is arranged said minus an interface element, a thermal conduction element and an interface material, said thermal conduction element being disposed between said at least one element of interface and the interface material. In this variant, said at least one sensor interface element is not in direct contact with the fluid.

According to one characteristic, said at least one heating element and said at least one temperature measuring element (Tw) are one and the same element.

The subject of the invention is also a method for manufacturing a sensor for measuring or detecting fouling according to microelectronics manufacturing technologies. This method comprises the following steps carried out from a thermal conductive substrate: formation on the same side of the substrate, on the one hand, of at least one heating element and, on the other hand, of at least one element temperature measuring device (Tw), - formation on the opposite side of the substrate of at least one interface element.

The integration of the temperature measuring element (Tw) and the heating element on the same side of the substrate (and for example in the same plane) makes it possible to simplify the manufacturing process of the sensor and also to simplify the process. establishing the electrical connections of these elements. According to one characteristic, the method comprises a step of forming at least one other temperature measuring element (Tb) on the face of the substrate carrying said at least one heating element and said at least one temperature measuring element (Tw ). The arrangement of the other temperature measuring element (second temperature measuring element (Tb)) on the same side of the substrate as the first temperature measuring element and the heating element simplifies the manufacturing process of the sensor. and also to simplify the establishment of all the electrical connections of these three components. According to one characteristic, the method comprises a step of producing a thermal insulation between, on the one hand, said at least one other temperature measuring element (Tb) and, on the other hand, said at least one heating element and said at least one temperature measuring element (Tw). According to one characteristic, said at least one heating element and said at least one temperature measuring element (Tw) being formed in a first portion of the substrate, said at least one other temperature measuring element (Tb) being formed in a second portion of the substrate separated from the first portion by a third substrate portion, the method comprises a step of removing the third substrate portion. This removal of material produced for example by chemical and / or physical etching makes it possible to achieve thermal insulation between the first and second portions. According to one characteristic, thermal insulation is achieved by the presence of a static gas blade (for example air) in the space left free by the removal of the third substrate portion. This way of achieving thermal insulation is particularly simple and the resulting insulation is particularly effective. According to an alternative characteristic, the method comprises a step of filling, by at least one thermal insulating material, the space left free by the removal of the third substrate portion. This additional step makes it possible, in addition to the thermal insulation that it provides, to mechanically stiffen the overall structure of the sensor comprising the two substrate portions. According to one characteristic, said at least one interface element extends over the entire opposite face of the substrate and forms a bonding membrane which interconnects the first and second substrate portions. According to one feature, the method comprises a step of establishing connections between said at least one heating element, said at least one temperature measuring element (Tw), said at least one other temperature measuring element (Tb), when it is present, and a suitable electronics. The invention further relates to a measurement or fouling detection system formed inside a container containing a fluid, characterized in that it comprises a sensor for measuring or detecting fouling. as briefly mentioned above.

The features and advantages already described in relation to the sensor also apply to the system and will not be recalled here.

According to one characteristic, the sensor is associated with a wall of the container in order to fulfill its function of measurement or detection of fouling. According to one characteristic, said at least one interface element of the sensor is in direct contact with the fluid or in indirect contact via an interface material. It should be noted that the direct contact with the fluid offers a greater sensitivity of measurement and / or detection and therefore better performance of the sensor.

In addition, the presence of the additional interface material in contact with the fluid, in flow, protects the sensor, at least mechanically, or even chemically, and makes it robust to external aggressions, in particular from the fluid. According to one characteristic, said at least one interface element or the interface material is mounted flush with respect to the wall. Thus, the fluid is not disturbed by the presence of the sensor. A fouling deposit composed of one or more types of bodies present in the fluid may be formed on said at least one interface element or on the interface material, in the same manner as if it were formed on the inner face of the container wall. In the case where an interface material is used in addition to said at least one interface element, the sensor can be manufactured in a very large series in its simplest structure including the heating element or elements, the or the temperature measuring elements and said at least one interface element and making only the additional interface material, made separately, which will be in contact with the fluid. Other features and advantages will become apparent from the following description, given solely by way of nonlimiting example and with reference to the accompanying drawings, in which: FIG. 1a is a general schematic view of a sensor according to a first embodiment of the invention and associated means for its implementation; FIG. 1b is a general schematic view of an alternative embodiment of the sensor of FIG. 1a; - Figure 2 is a general schematic view of a sensor according to a second embodiment of the invention and associated means for its implementation; - Figure 3 is a general schematic view of a sensor according to a third embodiment of the invention and associated means for its implementation; FIG. 4 is a general schematic view of an alternative embodiment of the sensor of FIG. 3; FIG. 5 is a bottom view of the first substrate of the sensor of FIG. 4 showing the arrangement of the heating element and the first temperature measuring element; FIG. 6 is a bottom view of the second substrate of the sensor of FIG. 4 showing only the arrangement of the second temperature measuring element; FIGS. 7 and 8 schematically illustrate respectively two different embodiments by ion implantation / thermal diffusion and by metal deposition of the measuring and heating elements of the sensor according to the invention; FIGS. 9a to 9k schematically illustrate the manufacturing steps of a sensor according to the invention; - Figure 10 is a schematic view showing the implantation of a sensor according to the invention in a body mounted in a wall of a container; FIG. 11 is a schematic view showing the implantation of a sensor according to a variant of the invention in a body mounted in a wall of a container. It is an object of the present invention to provide, using microsystem technology, a small sensor capable of determining fouling in a flowing fluid. More particularly, the subject of the invention is a microsystem intended to measure the thermal resistance and / or the thermal properties (thermal conductivity, heat capacity) of a fouling within a reactor (in the sense of process engineering) of which nature and intensity can be very varied and / or known. As shown diagrammatically in FIG. 1a, a sensor 10 according to a first embodiment made in microsystem technology comprises several functional elements assembled on a thermal conductive substrate 12. This substrate is, for example, silicon. However, it could alternatively be made of another material that promotes the diffusion of heat. More particularly, the sensor comprises the following elements 20 arranged on the same face 12a (lower face in Fig.1 a) of the substrate: - at least one heating element 14, which is able to generate, on command, a homogeneous heat flow controlled and diffuse into the substrate to a measuring medium which is here a fluid; at least one temperature measuring element (Tw) 16, which is subjected to the action of the thermal flux diffused by the substrate. It is considered here that there is only one element of temperature measurement (Tw), but several elements are possible according to the applications and the configurations of sensor. The temperature measuring element 16 is located in close proximity to the heating element 14 in order to benefit directly and without delay from the heat flux. Note that due to the small dimensions of the substrate and its good thermal conductivity, we can neglect the thermal gradients inside this substrate. This temperature measuring element 16 may for example at least partially surround said at least one heating element, as shown in Figure 5 which will be described later. The heating element 14 is supplied by electrical energy supply means 20 via connection means 22. The heating element is ideally an electrical resistance whose thermo-dependence of the resistivity is known.

The dimensioning of the heating element is performed by determining the heat flow necessary to be able to detect a fouling on the surface of the sensor according to the intended application. The injection of an electric current or a voltage (supply means 20) into the heating resistor generates an overheating thereof. A heat flux is then generated and varies according to the power injected into the heating element. The value of its resistance to rest is calculated according to the power of the heat flow to be generated. Note that the resulting voltage across the resistor is measured. The temperature measuring element 16, placed in this heat flow, measures the temperature continuously or discontinuously (as a function of the command applied to the sensor) and transmits these measurements, via the connection means 24, to a control unit. data processing 26 (for example, a calculator). The sensor also comprises, arranged on the opposite face 12b (upper face in FIG. 1a) of the substrate, at least one interface element 18 which is a thermal conductor made for example in the form of a layer or a bilayer deposited on the substrate 12. The interface element 18 transmits the thermal flux to the outside of the sensor, towards the measuring medium (fluid) with which it is in contact, in order to dissipate this heat. The data collected by the unit 26 are, after processing, displayed by the display means 28, for example in the form of curves representing the temporal evolution of the temperature and / or the thickness of the fouling layer formed on the surface of the sensor and which is determined from measured temperature differences. The processed data and / or other information such as those indicating the presence or absence of fouling on the surface of the sensor can be transmitted remotely by transmission means 30. An alarm signal to prevent an operator in case of detection of fouling can, for example, be transmitted to a remote monitoring center.

It will be noted that the heating element 14 and the temperature measuring element 6 are arranged on the same side of the substrate 12, which facilitates, on the one hand, their implantation on the substrate and, on the other hand, the establishment of their electrical connections with the elements 20 and 26 above. It will be noted that the measuring element comprises connection tracks or pads which make it possible to supply this element with the necessary electrical energy coming from the device 20 and to collect, at the computer 26, the temperature data. The measurement made at the terminals of the element 16 can be carried out using, for example, the well-known technique of the two points which allows, knowing the voltage and the electrical intensity, to deduce in a direct way the value of the resistance. . This measurement is used when the measurement or measurement noise is not too high. When the noise is too high the measurement across the element 16 can be implemented using for example the well-known technique of the four points. According to this indirect measurement technique, the value of the voltage imposed on the terminals is known, the value of the intensity is measured and the value of the resistance is deduced therefrom. The realization of the temperature measuring element (Tw) and / or the heating element is performed on the face 12a of the substrate by ion implantation / thermal diffusion or by metal deposition.

In a manner not shown in FIG. 1a, the sensor may comprise a thermal insulation element which limits the heat dissipations on the side of the face 12a on which are arranged the heating element and the temperature measuring element (Tw). . Such an element is shown in FIGS. 10 and 11. According to a variant not shown here, the sensor may comprise, on the side of the opposite face 12b where said minus is arranged an interface element 18, a thermal conduction element and a interface material, said thermal conduction element being disposed between said at least one interface element and the interface material. The sensor is then in contact with the fluid via the interface material and not with the element 18 of FIG. 1. Such a variant is illustrated in FIG. 11 which will be described later.

The following description illustrates a more elaborate version of a microsystem sensor according to a second embodiment shown in FIG. 2. The elements common to FIGS. 1a and 2 which are shown in FIG. 2 retain the same references and will not be described. again here.

The sensor 40 differs from the sensor 10 of Figure la in that it comprises at least one other temperature measuring element (Tb) noted 42. This other temperature measuring element 42 (second element) is arranged on a face 44a a second substrate 44 (for example silicon as the first substrate 12) which is thermally insulated from the first substrate 12 on which the heating element 14 and the first temperature measuring element 16 are arranged. Indeed, it is important that the second measuring element 42 is not influenced by the dissipated heat flow. The thermal insulation is here carried out by a static gas, for example air. However, another insulating material could be interposed between the two substrates.

The function of this measuring element is to measure the temperature of the fluid, for example, continuously or discontinuously (depending on the control applied to the sensor). The measuring element 42 transmits these measurements, via the connection means 48, to the data processing unit 26. The face on which the second measuring element 42 is arranged is on the same side as the face 12a so, again , to enjoy the same advantages as those described in relation to Figure 1a. The sensor also comprises, arranged on the opposite face 44b (upper face in FIG. 2) of the substrate, at least one interface element 46 made for example in the form of a layer or a bilayer deposited on the substrate 44. The second substrate 44 is also a thermally conductive material so that the temperature of the fluid which is in contact with the interface element 46 can be measured by the second measurement element 42. It will be noted that according to a variant not shown, the other temperature measuring element (Tb) can at least partially surround the heating element. More particularly, the second substrate itself may at least partially surround the first substrate as illustrated in FIGS. 4 and 6 which will be described hereinafter. According to a variant illustrated in Figure 1b, the heating element and the temperature measuring element are one and the same element 15 arranged on the face 12a of the substrate. It should be noted that this variant can also be applied to the configurations of FIGS. 2 to 4 described below. The element 15 is therefore, on the one hand, able to generate, on command, a homogeneous controlled heat flow in the substrate 12 and, on the other hand, to measure the temperature of the substrate thus heated. The connections 22 and 24 similar to those of FIG. 1a allow the power supply from the unit 20 and the delivery of measurement signals to the unit 26.

The sensor 11 thus designed is even simpler to manufacture than that of FIG. Thermal flow generation and temperature measurement can be performed in different, time-spaced and alternating phases. Alternatively, the generation of heat flow and temperature measurement can be performed almost simultaneously but with a slight shift in time. As shown in FIG. 2, the two substrates 12 and 44 are independent of one another. Each of the respective interface elements 18, 46 arranged on the opposite side of each substrate is a thermal conductor to promote thermal conduction through the thickness of the considered interface element. Each interface element 18, 46 thus offers a very low thermal resistance. Thus, this makes it possible to promote the heat exchange between the fluid and the substrate and, therefore, the second measurement element 42 makes it possible to measure the temperature of the fluid more reactively. This also allows the flow generated by the heating element 14 to dissipate rapidly in the fluid. Figure 3 illustrates a third embodiment of a micro-system sensor. The elements common to FIGS. 2 and 3 which are shown in FIG. 3 retain the same references and will not be described again here. The sensor 50 differs from the sensor 40 of FIG. 2 in that the interface element which is arranged on the opposite faces of the two substrates 12b and 44b takes the form of a securing membrane 52. This membrane extends on each of said faces and extends between the substrates in order to mechanically connect them to one another. The securing membrane constitutes a mechanical holding element of the monolith thus constituted. This thin membrane 30 offers a low thermal resistance to the axial flow generated by the heating element 14 (first substrate 12) and a high thermal resistance to lateral heat losses (losses to the second substrate 44).

It will be noted that the thermal resistance varies linearly with the thickness (thermal resistance proportional to the thickness) of the substrate towards the fluid (axial direction) and inversely proportional to this thickness (thermal resistance proportional to the inverse of the 'thickness) in a lateral direction. Thus, by decreasing the thickness of the membrane, the thermal resistance thereof, from the substrate towards the fluid, tends to a zero value, while the lateral thermal resistance, that is to say from the central part towards the peripheral part, tends towards an infinite value and thus opposes the passage of the flow in this direction.

Furthermore, as shown in Figure 3, a thermal insulation is formed between the two substrates 12 and 44 by a static gas blade (for example air) which is a good insulator. According to a variant not shown, the thermal insulation is produced by a thermal insulation material disposed between the second substrate 44 where is implanted the second temperature measuring element (Tb) 42 and the first substrate 12. Such an arrangement allows to to increase the robustness of the structure of the microsystem sensor. As for the previous embodiments, the production of the first and second temperature measuring elements and the heating element is performed by ion implantation / thermal diffusion or by metal deposition. FIG. 4 illustrates an alternative embodiment of the microsystem sensor of FIG. 3. The elements common to FIGS. 3 and 4 which are shown in FIG. 4 retain the same references and will not be described again here. The sensor 60 differs from the sensor 50 of FIG. 3 by the arrangement of the two substrates 62 and 64 with respect to each other, as well as by the configuration of the two temperature measuring elements and the heating element. one against another.

Thus, the structure of the microsystem sensor 60 includes a central portion 62 forming the first substrate and a peripheral portion 64 forming the second substrate and completely surrounding the central portion as shown in Figures 4 and 6 (in Figure 6 the central portion n ' was not represented). The central portion 62 is for example formed by a monolithic block of silicon whose thickness is defined by the dimensions of the plate used for the technological realization of the sensor, typically of the order of 300 to 500pm. This central block of silicon has minimum dimensions of 1 mm side. It is on the lower face 62a of this silicon block that the heating element 66 and the first element for measuring the wall temperature (Tw) 68 are integrated. The heat flux generated by the heating element is transmitted to the fluid due to the conduction properties of silicon (λ = 150W / m / K at room temperature). As shown in FIG. 5, the temperature measuring element 68 takes for example the shape of a U which partially surrounds the heating element 66. Thus, the measuring element 68 receives, in a relatively homogeneous manner, the flow of heat. generated by the heating element 66. Note that, in a variant not shown, the temperature measuring element 68 can completely surround the heating element 66 to take advantage of even more homogeneous heat flow. The peripheral portion 64, also made of silicon, supports, on its lower face 64a, a second temperature measuring element 70 intended to measure the temperature of the fluid. Here too, the conduction properties of silicon are used to capture the temperature of the fluid. As shown in FIGS. 4 and 6, the second temperature measuring element 70 partially surrounds the central portion 62 and, therefore, the first temperature measuring element 68 and the heating element 66. As for the previous embodiments, the heating element and the two temperature measuring elements are made for example: either by ion implantation / thermal diffusion; it is a technique which has the advantages of offering a minimal bulk of the device made, a choice of the resistivity of the resistance and the temperature coefficient in a range ranging, for example, from 0 to 7000ppm / ° C ; - Or by a metal deposit, for example, platinum or nickel. All the components integrated on the sensor are accessible on the same side of the substrate leading to a simple electrical schematic comprising at least six connection pads in this configuration.

The two parts 62 and 64 are held together by the dielectric membrane 52 located on the faces opposite to those on which the temperature measuring elements are integrated. This membrane is an electrical and thermal insulator (for example, at <1.5W / m / K) whose thickness does not exceed 10pm. This membrane may be in direct contact with the measuring medium (fluid), as shown in FIG. 4. Alternatively, an additional interface material may be interposed between the membrane and the measuring medium, as illustrated in FIG. will be described later. The membrane 52 is known to have minimal mechanical stresses. This membrane may be, for example, the choice: a bilayer composed of silicon oxide SiO 2 (800 nm) and non-stoichiometric silicon nitride SiXNy (600 nm); a silicon oxynitride SiOXNy (1 to 10 μm); a polymer or a resin (several micrometers thick). It will be noted that the sensor 60 shown in FIG. 4 is perfectly flat on the surface of the membrane 52, which is preferable when this membrane is in direct contact with the measuring medium, in order to disturb the latter as little as possible.

The flatness of the sensor is also sought when additional material must be arranged facing the membrane in order to obtain as intimate contact as possible between the elements and, therefore, in order to reduce the thermal resistances as much as possible. The thermal insulation between the two parts 62 and 64 is obtained by the deep etching of the silicon around the central portion to provide a peripheral space 72. The thermal insulation between the central portion and the peripheral portion is then provided by the simple presence of a static gas (for example air) between these two parts or, in a variant not shown, using an insulating material to increase the robustness of the microsystem. Note that the sensor 60 has a generally square shape whose side does not exceed 5mm in length. FIG. 7 illustrates an exemplary configuration for a microsystem sensor 80 in which the heating element 82 and the two temperature measuring elements 84 and 86 are made by ion implantation or thermal diffusion. In the central part of the sensor, the first temperature measuring element 84 which has for example the general shape of the lying digit 2 is arranged next to the heating element 82, while in the peripheral part the second element of the sensor Temperature measurement 86 partially surrounds the first temperature measuring element and the heating element. The zone 88 in the form of a square which surrounds the central part of the sensor represents the zone of thermal insulation (for example, it is a space left free and occupied by air) between the two parts of the sensor. Connection pads 82a, 82b, 84a, 84b, 86a-d are provided for each measuring element and for the heating element in order to allow electrical connections to be made with elements 20 and 26 shown in FIG. FIG. 8 illustrates an exemplary configuration for a microsystem sensor 90 in which the heating element 92 and the two temperature measuring elements 94 and 96 are made by metal deposition. In the central portion of the sensor, the first temperature measuring element 94 is strongly interwoven with the heating element 92. The outer connection pads 94a, 94b of the measuring element and the inner ones 92a, 92b of the heating element are represented. In the peripheral portion, the second temperature measuring element 96 partially surrounds the first temperature measuring element 94 and the heating element 92.

Each of the heating elements 92 and first temperature measuring element 94 is made in the form of metal resistors which take the form of coils or lines arranged on the surface of the substrate in a very tight manner in order to obtain a very long deposit length. metal in a small footprint. The drawings of the two elements are thus strongly intertwined, which allows, on the one hand, the two elements to occupy less surface and, on the other hand, to the element of measurement to be more intimately placed in the flow homogeneous thermal generated by the heating element. The second temperature measuring element 96 also takes the form of coils or lines arranged very closely for the same reasons. The general shape of the measuring element 96 is for example that of a U. Connection pads 96a-d are provided for the second measuring element in order to allow the establishment of electrical connections with the elements 20 and 26. represented in FIG. 4. An exemplary embodiment of a method for manufacturing a microsystem sensor according to the invention will now be described with reference to FIGS. 9a to 9k. The sensor is made from a substrate 100, for example silicon, which is polished on its two opposite faces 100a, 100b and which can be initially doped with a known species and concentration (FIG. 9a). Doping is, for example, of the P type. This doping is for example carried out with boron (1015 atoms per cm3). The thickness of the substrate is conventionally between 300 and 500 micrometers and is for example equal to 400 microns. In a second step illustrated in FIG. 9b, thermal oxidation of the substrate is carried out at high temperature, for example on the two faces 100a and 100b in order to obtain an oxide layer 102, 104 respectively on each of the faces 100a, 100b of the substrate. The oxide layer is for example formed of SiO 2 with a thickness, for example equal to 800 nanometers.

It will be noted that it is possible to be content with the single oxide layer 104 arranged on the upper face 100b instead of an oxide layer on both sides of the substrate. FIG. 9c illustrates a third step of the manufacturing process during which a layer of SiXNy is deposited on each of the oxide layers 102 and 104 and in order to obtain the layers 106 and 108. It will be noted here again that the formation of the layer 106 (just like that of the layer 102) is not always necessary. The layers 106 and 108 are for example made by a known low pressure chemical deposition technique LPCVD (acronym for Low Pressure Chemical Vapor Deposition). These deposits of a thickness for example equal to 600 nanometers are for example made at a temperature of 800 ° C for a period of 96 min. The following figure 9d illustrates a first photolithography step which aims to prepare the locations where will be integrated the various functional components of the sensor (heating element and temperature measuring elements). During this step, an engraving of the RIE type, for example, is performed in order to create openings in the lower double layer 102, 106. A plurality of openings 110, 112 and 114 are thus created on the side of the lower face 100a. substrate, leaving areas with the two superimposed layers 102 and 106 locally. It will be noted that the microsystem structure is three-dimensional and that the two open zones marked by the arrow 110 constitute a single opening which constitutes a trench having the shape of the resistance to integrate. The same is true for the zones indicated by the arrow 112. The following figure 9e corresponds to the first integration step 30 of the functional components of the sensor.

In this embodiment, the various functional components (heating element and temperature measuring elements) are produced by ion implantation / thermal diffusion. In the openings 110, 112 and 114 created in step 9d, an ion implantation is carried out, for example with phosphorus. It will be noted that the zones formed by portions of superimposed layers 102 and 106 situated on either side of the aforementioned openings have been voluntarily left as these zones make it possible to easily locate the implanted zones.

The ion implantation is more particularly carried out by N type doping (with a pentavalent material such as phosphorus, for example) or P type (with a trivalent material such as boron, for example), with an energy that can from 20keV to 200 keV which determines the depth of the implanted zone. In the example, phosphorus N type doping can be retained with an implantation energy equal to 20keV. Several implantation doses can be used as desired, which makes it possible to modify the dopant concentration and thus to adjust the electrical resistivity of the implanted zone, as well as its temperature coefficient. In general, the higher the dose, the lower the resistivity.

By way of example, doses of 1013, 1014 or 1015 atoms per cm2 are used. The step illustrated in the following figure 9f aims to reorganize the crystal lattice and to diffuse the dopants (redistribution) so that the silicon atoms and the implanted ions are reorganized in a regular network. To do this, it is intended to anneal in an oxidizing atmosphere such as an oxygen atmosphere, for example, for a period of 2 hours at a temperature of about 1050 ° C. At the end of this step, an oxide layer 130, 132 and 134 is formed on the surface of each implanted zone 120, 122 and 124.

The local oxide layer thus prevents the implanted ions from re-diffusing into the atmosphere (exodiffusion phenomenon). The next step illustrated in FIG. 9g is a second photolithography step.

During this step, the oxide formed on the local portions 130, 132 and 134 of FIG. 9f is locally removed in order to create openings in which metallic contacts will subsequently be formed. These contacts will make it possible to establish the connections of the functional components of the sensor with the electronics for supplying and analyzing measurement signals of the sensor. As shown in FIG. 9g, openings 140, 141, 142, 143, 144 and 145 are formed in the oxide layer portions 130 to 132, 134. These openings are formed, for example, by a conventional photolithography technique. using a resin mask and then etching the oxide with hydrofluoric acid. During the step illustrated in FIG. 9h, a metallization operation is carried out on the entire lower face of the substrate shown in FIG. 9g (full plate metallization).

This step is intended to achieve the metal contacts / connection pads that will allow the establishment of electrical connections of the functional components of the sensor with the power electronics and analysis of the measurement signals. Thus, a metal deposit 152 is formed on the entire surface in relief of the underside of the substrate illustrated in FIG. 9g. This metallization step is for example carried out using aluminum and a thickness of 500 nanometers and is thus deposited at each location of the surface (full plate). It will be appreciated that other metals may alternatively be used such as, for example, titanium and / or gold. The next step illustrated in FIG. 9i is a third photolithography step.

During this step etching or chemical etching of the metallization carried out in the previous step is carried out, in order to leave the metal areas at the appropriate places so that they thus form the connection pads mentioned above.

Alternatively, for the realization of metal contacts, it is possible to perform a step known as the lift-off. This step is followed by an activation annealing operation which aims to interpenetrate the metal atoms deposited in the ionically implanted resistors and to order the metal atoms.

This annealing is a metal annealing performed for example at a temperature of 450 ° C for 20 minutes. After etching, the remaining metal areas are areas 154, 156, 158, 160, 162 and 164 as shown in FIG. 9i. It is these areas that will allow the establishment of connections with the functional components of the sensor. The step illustrated in FIG. 9j is then followed at a fourth photolithography step. This step is intended to prepare a next step of deep etching in the substrate 100 in order to achieve thermal insulation between two portions of this substrate. As represented in FIG. 9j, a deposit of a protective resin on the rear face of the substrate is carried out on the areas to be protected and which are those comprising the functional components and the metal contacts, as well as certain zones coated with the two layers 102. 106.

The resin is thus deposited on the entire rear face and, by photolithography, the resin is left on a central zone 192 of the central part of the substrate and on a peripheral zone 194 surrounding the central zone. It will be noted that the remaining protective resin on the zone 194 takes for example the shape of a square surrounding the central zone 192, in order to eventually lead to the shape illustrated in FIGS. 4 and 6.

The next step illustrated in FIG. 9k comprises two RIE etching steps. A first step consists in etching the bilayer 102, 106. The second step is an etching step DRIE, (an acronym for Deep Reactive Ion Etching), which is carried out as far as the layer 104, in order to physically separate a first central portion substrate 100c of a second peripheral portion of the substrate 100d. This deep etching makes it possible to remove a third portion of substrate situated between the first and second portions and denoted 100e in FIG. 9j.

This third portion is a trench-shaped portion of square section that surrounds the first portion 100c. Thus separated the first and second portions are thermally insulated from each other by the space 196 surrounding the first portion 100c and which has been left free after the removal of the third portion 100e.

Alternatively, the step illustrated in Figure 9k can be performed by chemical etching. Note that in an alternative embodiment not shown in the figures, this free space 196 can be filled with a thermally insulating material between the first and second substrate portions.

The microsystem structure obtained in FIG. 9k thus comprises, arranged on a face 100a of the substrate, in the central part, functional components 122 and 124 and in the peripheral part of the functional component 120. More particularly, the component 122 takes the form of a resistance obtained by implantation and which partially surrounds a central resistance 124 obtained by implantation. The central resistor 124 plays the role of the heating element 66 of FIG. 5, while the resistor 122 plays the role of the first temperature measuring element 68 of FIG.

Moreover, the functional component 120 of the second peripheral portion 100d is a resistance obtained by implantation and which plays the role of the second temperature measuring element 70 of FIG.

In addition, on the face of the substrate which is opposite to that on which the aforementioned functional components are implanted, the double layer 104, 108 described in connection with FIGS. 9a to 9c plays the role of the securing membrane 52 illustrated in FIG. 4. It thus connects together the first substrate portion 100c and the second substrate portion 100d. Thus, the sensor is manufactured from a single block or substrate, for example silicon, which is micro-machined to differentiate two heat exchange surfaces with the fluid, isolated from each other by micromachining. One surface, the largest, equilibrates with the temperature of the fluid and the other takes a different temperature between the fluid temperature and that of a hot source (heating element) integrated in the silicon. Thanks to the microsystem technology, the temperature measuring element has a very high temperature sensitivity which is, for example, less than 0.05 ° C.

In addition, microsystem technology enables the design of a sensor with the following characteristics and advantages: - small size (a few hundred micrometers), - low power (a few milliwatts), - high sensitivity of the measuring element (less than 0, 05 ° C), - proximity of the functional elements to each other, - very low response time. When the sensor is used, the securing membrane acts as an interface element and can be in direct contact with the fluid as shown in FIG. 10 or in indirect contact via additional elements (FIG. 11). . According to an alternative embodiment, the functional components of the microsystem sensor according to the invention can be produced by metal deposition and non-ion implantation or thermal diffusion. According to this variant, a structure similar to that of FIG. 9c described above but without a bilayer is produced on the lower face of the substrate 100.

To do this, either one starts from the structure obtained in FIG. 9c and one removes the double layer 102, 106 from the lower face, or one forms a double layer only on the upper face of the substrate. Subsequently, from the substrate 100 provided with the double layer 104, 108, a metal deposit, for example nickel, is made on the lower face 100a of the substrate. This deposit is for example made by the known lift-off technique. During a next step, the formation of the metal contacts (connection pads) is carried out by the above-mentioned lift-off technique using, for example, aluminum as metal. This step is followed by a metallization annealing. This results in a substrate provided on its upper face with a double layer of interface elements (layers 104 and 108) and on its underside functional components required for the sensor and made in the form of metal resistors obtained by deposition. metallic. In the context of this variant, a deep etching of the substrate is then carried out, as indicated above with reference to FIGS. 9j and 9k, in order to obtain the microsystem structure already described above.

FIG. 10 illustrates an exemplary embodiment in which the microsystem sensor 200 of FIG. 9k (which is also that of FIG. 4) is associated with a wall 202 of a container 204 (for example a chemical reactor or a vessel) wherein a flowing fluid symbolized by the arrow F is present. It will be noted that the container 204 containing the fluid may be of another type such as a pipe or pipe of an industrial installation, .... It will also be noted that the fluid present in the container is not necessarily at rest but may be in flow. The microsystem sensor 200 is mounted in one of the walls of the container as shown in Figure 10 through a body 206 in which the microsystem is integrated. More particularly, the sensor 200 is arranged in a hollow cylindrical envelope 208 provided at one of its longitudinal ends 208a of a plate 210 forming a shoulder and which has for example a disc or pellet shape. This plate is for example welded to the cylindrical casing 208. The opposite end 208b is, for its part, open on the outside. It will be noted that other body shapes can be envisaged without calling into question the operation of the sensor. The plate 210 forming a shoulder is intended to be inserted in a corresponding arrangement provided in the wall 202 of the container to be mounted flush with respect thereto. This plate 210 is open in its central part, in order to receive the sensor. The latter is in contact with the fluid F by the outer face of the bilayer 104, 108 (bonding membrane). Such an arrangement makes it possible to confer on the sensor an increased sensitivity with respect to what is described in FIG. 11. It will be noted that the external face of the sensor, the external face 210a of the shoulder and the surface 202a of the wall are arranged in FIG. the same coast so as not to introduce a disturbance in the flow. Furthermore, as shown in FIG. 10, the microsystem sensor is mounted on a support 212 such as a printed circuit board whose role is to create the necessary electrical contacts between this microsystem sensor and the part of the associated system which ensures power supply and information processing of this sensor. These electrical contacts cooperate with the tracks or pads illustrated for example in Figures 7, 8 and 9k and briefly described above via connecting son 211a and 211b (Figure 10).

Note also that the support is connected to the elements 20, 26, 28 and 30 of Figure 4 by connections 213a and 213b. In order to dissipate as much as possible the homogeneous and controlled thermal flow generated by the heating element towards the front of the microsystem sensor, that is to say towards the fluid, a thermal insulation element 214 is introduced into the body 206 by the rear end. This element 214, such as a paste with a low coefficient of thermal conductivity, is placed against the rear face of the support 212 in order to form a heat shield at the rear of the body and thus to channel the heat flow towards the front of said body. body. The membrane plate 104, 108 acting as an interface with the fluid is adapted so that its outer face 108a is representative of the surface state of the wall 202 of the container so that the deposition of a fouling layer on the face 108a is made almost identically to the deposition of a fouling layer on the inner face 210a of the wall of the container. Indeed, it is on the outer face 108a that the fouling phenomenon will be followed according to the invention, it being understood that this phenomenon occurs of course at other locations of the inner surface 202a of the wall. Thus, the determination of fouling formed on the face 108a, determination which corresponds either to a fouling measurement or to a detection of fouling, will be particularly reliable given the nature of this external face.

So that the outer face 108a is representative of the surface condition of the wall of the container, it is preferable that this face is in the same material and has a roughness equivalent to that of the wall. Thus, for example in the context of an agri-food application, the wall 202 may be made of stainless steel and the face 108a of the sensor will have the same roughness, as the face 202a of the wall. Preferably, the outer face 108a is made of a material of the same nature as that of the wall of the container. If this material is not identical, it must at least be of a nature compatible with that of the material constituting the wall, the operation of the process and the fluid. FIG. 11 schematically illustrates another possible installation of a microsystem sensor such as that of FIG. 4 in the wall 202 of the container 204. In this embodiment, the sensor 200 is in contact with the fluid F through the face external 220a of an additional interface material 220. This is the only difference with the system of Figure 10. The elements of Figure 10 are shown in Figure 11 with the same references and will not be described again.

This interface material may be a separate element of the body 206 or may constitute a thinned central region of the plate 210. All the characteristics described above with reference to FIG. 10, especially with regard to the surface condition of the face external sensor 108a here apply to the outer face 220a of the interface material 220. The interface material 220 is for example made of a material identical to that of the wall of the container. In this example, the plate 210, like the cylindrical envelope 208 are made of stainless steel, which material is used for the wall 202 and in particular its inner surface 202a. The thermo-physical properties of the interface material (s), in particular its thickness E [m] between the temperature measuring element and the measurement medium, and its thermal conductivity λ [Wm -. K - '] , its specific heat Cp [J.kg - 'K-1] and its density p [kg / m3] are perfectly known. Thus, knowing that the edge effects and heat losses are negligible, it is easy to calculate the precise temperature Tp at the surface of the interface material or materials which is in contact with the fluid and therefore offered to a user. fouling.

T = T - x p w r, where P is the power dissipated through the heating element [W] and S is the area of the active area, ie the area of the heated area [m2]. Note that in the absence of interface material (E = 0): TW = Tp. In order to maximize the heat exchange between the microsystem sensor heating element and the internal surface 220b of the material 220, a heat transfer element 222, such as a thermal paste with a high coefficient of thermal conductivity, is placed in contact with the microsystem and the internal face 220b. It should be noted that in the presence of interface material the temperature difference Tp Tb is preferably followed. The sensor which has just been described with reference to FIGS. 1 to 11 may be used in steady state or periodic thermal mode under stationary or unsteady conditions for measuring and / or detecting the fouling formed on the external face 108a of FIG. on the external face 220a of the additional interface material of FIG. 11. By fouling is meant any deposit forming on the external face of the element under consideration from bodies that are present in the fluid temporarily or permanently. Note also that one can thus perform the measurement and / or the detection of fouling on site and in real time. It is therefore not necessary to carry out on-site sampling, followed by subsequent analyzes of the samples taken for measurement and / or fouling detection. The sensor illustrated in FIG. 1 a can for example be used by alternating heating phases (control of the diffusion of a heat flow by the heating element 14) and non-heating (non-diffusion of a heat flux) on a given duration. One can thus choose to perform this alternation of heating and non-heating phases throughout the course of an industrial process or only during certain stages thereof. During these heating and non-heating phases, the measuring element 16 continuously measures the temperature. When the surface condition is clean (no fouling), the heat flux produced by the heating element is transferred to the measuring element and the interface element (or, as the case may be, to the material of the interface as in Figure 11), and then broadcast in the measuring medium (fluid). The temperature measured by the measuring element then remains substantially constant and close to the temperature of the medium. On the other hand, when fouling is formed on the outer face of the interface element 18 in FIG. 1a or the aforementioned interface material, the heat flux generated by the heating element will cause a rise in temperature at the of the interface element or the interface material.

Indeed, the fouling layer that is formed acts as a thermal insulator that reduces the heat exchange with the measuring medium and thus the dissipation of the flow. Under these conditions, there is an increasing temperature difference between the temperature measured by the measuring element in the heating phase and the temperature measured in the non-heating phase. This temperature difference is representative of the fouling formed at the instant corresponding to the measurements made. This temperature difference is more particularly representative of the thickness of the fouling layer. This thickness is obtained by formulas well known to those skilled in the art and which depend on the geometric configuration of the sensor, namely a planar geometry for the sensors of Figures 1 to 11 and the thermal regime retained. It should be noted that the greater the thickness of the deposit formed on the surface of the sensor, the higher the temperature rise will be for a given power. In practice, the operating mode of the sensor makes it possible to impose a given temperature difference set point, for example of the order of 1 ° C., and to regulate the supply power of the heating element as a function of this instruction. Thus, the heating element is provided with electrical energy so that the generated heat flow produces a desired temperature increase. This mode of operation provides a very good signal-to-noise ratio and thus contributes to a reliable and high quality measurement. From a practical point of view, the temperature difference mentioned above is determined using linear and / or non-linear regression algorithms between two non-heating phases that frame a heating phase. It should be noted that the simple detection of a significant difference in temperature, such as, for example, a difference of 1 ° C., provides important information since it is representative of a fouling formed inside a container containing a fluid as the container 204 of Figures 10 and 11.

Such information may for example give rise to the sending of an alarm signal by the means 30 illustrated in Figure la to prevent an operator or maintenance personnel of the installation. This detection function can of course be coupled to the fouling measurement function in order to also be able to provide quantitative information on the thickness of the deposit thus formed. The operating mode of the sensor illustrated in FIGS. 2 to 4 is different insofar as this sensor comprises a second temperature measuring element which provides a measurement of the temperature of the fluid.

This sensor thus makes it possible to overcome variations in the temperature of the fluid. The sensor illustrated in one or the other of the figures provides, continuously and in real time, a temperature difference to determine the fouling formed on the surface of the interface element of this sensor or, according to The case of the additional interface material as illustrated in FIG. 11. The sensor comprising two temperature measuring elements as illustrated in FIGS. 2 to 4, 10 and 11 may function as taught in document FR 2 885 694. It should also be noted that a sensor incorporating two different temperature measuring elements, like that of FIGS. 2 to 4, 10 and 11, can also be used by alternating heating and non-heating phases. Thus, during a non-heating phase, the temperatures measured by the two measuring elements must normally provide the same temperature measurement.

A measurement gap observed between these two elements, during a non-heating phase, reflects a drift of the properties of one measuring element relative to the other. Thus, the monitoring of the temperatures measured by the two measuring elements during a non-heating phase of the sensor constitutes a step of checking the proper functioning of these elements.

Claims (28)

REVENDICATIONS1. Measuring or dirt detection sensor produced according to microelectronic manufacturing technologies, comprising, arranged on the same face (12a) of a thermal conductive substrate (12): - at least one heating element (14) which is capable of generating, on command, a controlled homogeneous heat flow and diffusing it into the substrate, at least one temperature measuring element (16) which is subjected to the action of the thermal flux diffused by the substrate, the sensor comprising, arranged on the opposite face of the substrate (12b), at least one interface element (18). 2. Sensor according to claim 1, characterized in that said at least one temperature measuring element (Tw) at least partially surrounds said at least one heating element. 3. Sensor according to claim 1 or 2, characterized in that it further comprises at least one other element (42) for measuring temperature (Tb) which is thermally insulated from said at least one heating element. 4. Sensor according to claim 3, characterized in that said at least one other element (42) for measuring temperature (Tb) at least partially surrounds said at least one heating element. 5. Sensor according to claim 3 or 4, characterized in that said at least one other element (42) for measuring temperature (Tb) is arranged on one face (44a) of a second substrate (44) thermally insulated from the first substrate (12) on which said at least one heating element is arranged. 6. Sensor according to claim 5, characterized in that the second substrate (44) at least partially surrounds the first substrate (12). 7. Sensor according to claim 5 or 6, characterized in that said at least one interface element (52) which is arranged on the opposite faces of the two substrates (12, 44) takes the form of a bonding membrane which interconnects these substrates. 8. Sensor according to claim 7, characterized in that the bonding membrane (52) has a small thickness with a low thermal resistance to the axial heat flux generated by said at least one heating element and a high thermal resistance to thermal side losses of the first to the second substrate. 9. Sensor according to one of claims 3 to 8, characterized in that the thermal insulation is performed by a static gas blade. 10. Sensor according to one of claims 3 to 8, characterized in that the thermal insulation is formed by a thermal insulation material disposed between said at least one other element (42) for measuring temperature (Tb) and the first substrate (12). 11. Sensor according to one of claims 5 to 8, characterized in that the two substrates (12, 44) are independent of each other, each of said at least one interface element (18, 46) arranged on the opposite face (12b, 46b) of each substrate being a thermal conductor to promote thermal conduction through the thickness of said at least one interface element considered. 12. Sensor according to one of claims 1 to 11, characterized in that the embodiment of said at least one temperature measuring element (Tw) and / or said at least one other temperature measuring element (Tb) when is present and / or of said at least one heating element is carried out by ion implantation, by thermal diffusion or by metal deposition. 13. Sensor according to one of claims 1 to 12, characterized in that the substrate is silicon. 14. Sensor according to one of claims 1 to 13, characterized in that it comprises a thermal insulation element which limits the heat dissipation on the side of the face on which are arranged said at least one heating element and said at least one heating element. a temperature measuring element (Tw). 15. Sensor according to one of claims 1 to 14, characterized in that it comprises, on the side of the face where is arranged said minus an interface element, a thermal conduction element (222) and a materialaud'interface (220), said thermal conduction element being disposed between said at least one interface element and the interface material. 16. A sensor according to claim 1, characterized in that said at least one heating element and said at least one temperature measuring element (Tw) are one and the same element (15). 17. A method of manufacturing a sensor for measuring or detecting fouling according to microelectronics manufacturing technologies, comprising the following steps performed from a thermal conductive substrate: forming on the same side of the substrate; on the one hand, of at least one heating element and, on the other hand, of at least one temperature measuring element (Tw), -formation on the opposite face of the substrate of at least one interface element . 15 18. The method of claim 17, characterized in that it comprises a step of forming at least one other temperature measuring element (Tb) on the face of the substrate which carries said at least one heating element and said at least one a temperature measuring element (Tw). 19. A method according to claim 18, characterized in that it comprises a step of producing a thermal insulation between, on the one hand, said at least one other temperature measuring element (Tb) and, on the other hand, on the one hand, said at least one heating element and said at least one temperature measuring element (Tw). 20. The method of claim 19, characterized in that said at least one heating element and said at least one temperature measuring element (Tw) being formed in a first portion of the substrate, said at least one other measuring element of said Since the temperature (Tb) is formed in a second portion of the substrate separated from the first portion by a third substrate portion, the method includes a step of removing the third substrate portion. 21. The method of claim 20, characterized in that said at least one interface element extends over the entire opposite face of the substrate and forms a bonding membrane which interconnects the first and second substrate portions. 22. The method of claim 20 or 21, characterized in that thermal insulation is achieved by the presence of a static gas blade (eg air) in the space left free by the removal of the third portion of substrate. 23. The method of claim 20 or 21, characterized in that the method comprises a step of filling, by at least one thermal insulating material, the space left free by the removal of the third substrate portion. 24. Method according to one of claims 18 to 23, characterized in that it comprises a step of establishing connections between said at least one heating element, said at least one temperature measuring element (Tw), said at least one other temperature measuring element (Tb) and a suitable electronics. 25. Measurement or detection system for fouling formed inside a container (204) containing a fluid, characterized in that it comprises a sensor (200) for measuring or detecting the fouling according to the invention. one of claims 1 to 16. 26. System according to claim 25, characterized in that the sensor is associated with a wall (202) of the container. 27. The system of claim 25 or 26, characterized in that said at least one interface element (108, 104) of the sensor is in direct contact with the fluid or in indirect contact via a material of interface (220). 28. System according to claims 26 and 27, characterized in that said at least one interface element (108, 104) or the interface material (220) is mounted flush with respect to the wall (202).