Method for manufacturing a sensor and sensor manufactured by the method

Abstract

The present invention relates to a method for manufacturing a sensor (1) capable of measuring the concentration of CO2 in a gas, the method comprising the steps of: a) providing a substrate (2), b) arranging a plurality of conductive structures (3) on the substrate (2) at a predetermined distance (A) from one another, c) oxidizing the conductive structures (3) while forming oxide-based nanowires between the conductive structures (3), and d) depositing nanoparticles on the nanowires to enable the sensor (1) to measure CO2. The present invention also relates to a sensor (1) capable of measuring the concentration of CO2 in a gas, the sensor (1) comprising: a substrate (2), a plurality of conductive structures (3) arranged on the substrate (2) at a predetermined distance (A) from one another, and oxide-based nanowires formed between the conductive structures by oxidation of the conductive structures (3), wherein nanoparticles are arranged on the nanowires to enable the sensor (1) to measure CO2.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a sensor capable of measuring the concentration of CO2 in a gas.

[0002] Furthermore, the present invention relates to a sensor capable of measuring the concentration of CO2 in a gas.

[0003] Finally, the present invention relates to a method for measuring the CO2 concentration in a gas. [Background technology]

[0004] For various reasons, it is important to be able to measure the carbon dioxide (CO2) content in gases, especially in air. On the one hand, CO2 is considered one of the gases that contribute to global warming. On the other hand, it is important to be able to accurately determine the CO2 concentration locally, for example, in densely populated areas with high emissions of harmful substances. Furthermore, determining the CO2 content in gases is also important in other application areas, for example, during surgery with anesthesia, in which the CO2 content in the respiratory gas is monitored, or for determining the ovulation period in women based on the CO2 content in the respiratory gas.

[0005] Devices for measuring the CO2 concentration in gases such as air have been known in the prior art for quite some time. The current trend is to replace the known, relatively comprehensively assembled devices with smaller devices, in particular with miniaturized sensors. This makes it possible, for example, to integrate CO2 sensors into mobile phones. This opens up a wide range of possibilities. For example, a mobile phone owner can quickly call up the CO2 content at any time, in any location, for example, in urban areas as well as residential areas, and compare it with a target value. The mobile phone owner's breathing gas can also be analyzed easily and quickly.

[0006] To provide correspondingly miniaturized sensors, it has become known to fabricate CO sensors that operate using nanowires or nanowires. Sensitive CO measurements can be achieved using nanowires, typically formed with a cross-section of a few nanometers (nm) across their longitudinal axis (see Naama et al., CO gas sensor based on silicon nanowires modified with metal nanoparticles, Materials Science in Semiconductor Processing 38, 2015, 367). The use of correspondingly small components that are sensitive to one or more gases and integrated into the measurement circuit allows for miniaturization of the sensor, due to the space-dependent miniaturization requirements of the sensitive unit, here the nanowire or nanowire.

[0007] Although the use of nanowires, optionally functionalized, for the determination of CO2 in gases is known, it would be desirable to provide a method by which CO2 sensors can be produced particularly simply and with suitable sensitivity. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Naama et al.,CO2 gas sensor based on silicon nanowires modified with metal nanoparticles,Materials Science in Semiconductor Processing 38,2015,367 Summary of the Invention [Problem to be solved by the invention]

[0009] This is the starting point of the present invention. The object of the present invention is to provide a method of the type mentioned at the beginning, which allows a reliable sensor to be produced in a simple manner and which is sensitive to CO2.

[0010] It is a further object to provide a correspondingly manufactured sensor.

[0011] Finally, it is another object of the present invention to provide a method for measuring CO2 concentration in a gas that provides reliably reproducible measurements. [Means for solving the problem]

[0012] The problem with the method is that in a method for manufacturing a sensor capable of measuring the concentration of CO2 in a gas, the method comprises the steps of: a) providing a substrate; b) disposing a plurality of conductive structures on a substrate at predetermined intervals from one another; c) oxidizing these conductive structures while forming oxide-based nanowires between these conductive structures; d) Depositing nanoparticles onto the nanowires to enable the sensor to measure CO2. is resolved when scheduled.

[0013] The advantage achieved by the present invention is that it provides a particularly simple method for producing miniaturized sensors that are particularly reactive or sensitive to CO2, thereby enabling the reliable determination of the CO2 content in gases, such as ambient air, or, for example, in the exhaust gases of an internal combustion engine. To this end, in a first step, a substrate is prepared. This substrate can essentially be any object. A silicon wafer can also be used. This substrate can also be part of an electronic chip that will later be integrated into a mobile phone. A plurality of conductive structures are arranged on this substrate, with a specific spacing between them. In a next step, the conductive structures are oxidized, forming nanowires or nanowires between the conductive structures that are or will be integrated into a circuit. Finally, nanoparticles are additionally attached to the nanowires, thereby enabling the sensor to measure CO2.

[0014] Therefore, the method according to the present invention is also characterized by its geometric flexibility with respect to predetermined spatial limitations, for example, when integrating it into an electronic chip, since it allows the deposition of any conductive structure on a large number of substrates. The spacing between the individual conductive structures is selected so that the nanowires or nanowires can form bridges from one conductive structure to the next. The nanowires themselves are oxide-based nanowires, typically composed of one or more oxides of metals, depending on the intended oxidation. The additional deposition of nanoparticles on the nanowires can increase the nanowire's sensitivity to CO2. The sensor thus produced allows for reliable and reproducible measurements of CO2, is easy to manufacture, and the measurement results are, moreover, at least largely independent of the humidity in the gas being tested.

[0015] The oxidation of the conductive structures to form oxide-based nanowires between them can, in principle, be carried out by any method known to those skilled in the art. Preferably, the oxidation in step c) is carried out at elevated temperatures. This oxidation can be carried out in air. In other words, the oxygen present in air is quite sufficient to oxidize at least the surface of the conductive structures within a substantial period of time. However, it is of course possible to increase the oxygen content of the oxidizing gas atmosphere above that of air, even using pure oxygen. It is also possible to use gas mixtures, such as mixtures of oxygen with an inert gas such as argon. For elevated-temperature oxidation, temperatures above 280°C, preferably 280°C to 420°C, and especially 300°C to 400°C, are preferred. It has been shown that nanowires or nanowires form between the regularly spaced conductive structures at temperatures of approximately 280°C. If the conductive structures are made of copper, CuO is first formed during oxidation, and the thickness of the copper layer decreases as the CuO layer forms. This is followed by the formation of CuO on the CuO layer. Subsequently, oxide-based nanowires grow from the CuO layer, bridging the gaps between the conductive structures. The conductive structures, which are exclusively composed of copper at the start of the growth process, may have a core made of copper and other portions made of copper oxide at the end of the growth process. For the purpose of producing sensors in the context of the subject invention, the optimal temperature range for producing the corresponding structures has been found to be between 280°C and 420°C, in particular between 300°C and 400°C.

[0016] The conductive structure is generally made of metal, which is then oxidized. For this purpose, copper or zinc has proven to be particularly suitable. Both metals can be easily deposited into the desired shape first, and then oxidized to form nanowires. In this case, it is also advantageous to select a mild temperature range for both method steps, that is, on the one hand, depositing the metal and on the other hand, oxidizing the metal. This is particularly important when the sensor is part of a relatively large unit that cannot withstand extremely high temperatures, for example, when the sensor is arranged on an electronic chip.

[0017] To apply the conductive structures, any method that allows applying multiple conductive structures to one another at preselected intervals on a substrate can be used. This includes, for example, electrochemical deposition processes in selected areas, targeted material removal methods such as laser ablation or stamping processes. However, it is particularly preferred that the conductive structures are deposited from the vapor phase in step b). For this purpose, a mask is usually used, which is placed on or above the substrate. The mask may be a mask produced using photolithography. In this case, a layer of polymer is deposited on the substrate, and then the polymer is selectively removed in the areas where the conductive structures will later be formed. After the corresponding areas are exposed, the conductive structures can be applied, particularly by deposition from the vapor phase. It is also possible to first deposit a bonding layer on the substrate and then deposit the conductive structures. In this case, the bonding layer is located below the conductive structures. The bonding layer is provided solely for the purpose of bonding the conductive structures deposited thereon and therefore may be relatively thin, for example, less than 100 nm, particularly less than 50 nm, and particularly preferably less than 10 nm. For this purpose, metals such as titanium or chromium are suitable. The conductive structures required for the formation of the nanowires and which are otherwise functional parts of the sensor are then deposited with a thickness of less than 750 nm, preferably between 200 nm and 600 nm.

[0018] The spacing between the conductive structures can, in principle, be freely chosen within a wide range. However, it is preferable that this spacing be calculated so that nanowires with sufficient mechanical stability are formed between the conductive structures within a reasonable time. Therefore, this spacing can be preferably adjusted to about 1 μm to 6 μm, preferably 2 μm to 5 μm. If this spacing is not greater than the stated maximum, sufficient stability of the nanowires between the individual conductive structures is ensured. In this case, the individual nanowires may overlap without the disadvantage of functional loss, forming a dense network between the conductive structures.

[0019] The sensor manufactured using the method according to the present invention is preferably operated at elevated temperatures, for example, in the temperature range of 300°C to 400°C. To this end, the sensor can be subsequently equipped with or connected to a heating element, so that the region containing the conductive structures and the nanowires associated with them can be brought to the corresponding temperature. However, it is particularly preferred to provide a substrate including a heating element in step a). This has the advantage that the oxidation process, and thus the formation of the nanowires, can be carried out precisely using the heating element originally required for adjusting the elevated measurement temperature. In this case, the heating element can be, in particular, a micro-hotplate. The micro-hotplate can have dimensions of less than 100 μm × 100 μm. The thickness can be selected to be less than 20 μm. Such elements are also referred to as microelectromechanical systems (MEMS). If such a micro-hotplate is provided, the elevated temperature for oxidation in step c) can be adjusted by heating using this micro-hotplate. The micro-hotplate can, in particular, be arranged on a chip. Such chips can be used, for example, in mobile phones. Hereafter, to allow for correspondingly high measurement temperatures, the micro-hotplate is insulated from the surrounding environment and connected to the remaining components of the chip only via the necessary electrical contacts, so that even elevated temperatures in the range of 300°C to 400°C do not adversely affect other units or areas of the electronic chip.

[0020] The nanoparticles that sensitize the nanowires to CO2 usually have an average size of less than 20 nm, in particular less than 10 nm. They can contain, for example, zirconium oxide and / or gold. Nanoparticles made of silver can also be used. Nanoparticles made of barium carbonate or barium titanate, as well as mixtures of these materials, are also suitable.

[0021] Nanoparticles are applied to nanowires using coating methods such as dip coating.Processes that can achieve a relatively high degree of structuring are also possible.For this purpose, inkjet printing is particularly suitable for this method.Nanoparticles are generally stabilized with organic ligands, so that the nanoparticles must be heated to a high temperature in order to burn off the organic ligands.If metal nanoparticles, especially nanoparticles made of gold, are intended, they can also be formed by sputtering or evaporation and subsequent temperature treatment.Because during this temperature treatment, separation of the deposited material into nanoparticles occurs.

[0022] A further object of the present invention is achieved by a sensor capable of measuring the concentration of CO2 in a gas, comprising a substrate, a plurality of conductive structures arranged on the substrate at a predetermined distance from one another, and oxide-based nanowires formed between the conductive structures by oxidation of the conductive structures, with nanoparticles deposited on the nanowires in order to enable the sensor to measure CO2.

[0023] The sensor according to the invention is characterized by a robust, easily manufacturable, and stable design that enables reliable measurement of CO. The sensor operates at particularly elevated temperatures, preferably in the temperature range of 300°C to 400°C, and is sufficiently insensitive to air humidity, so that in principle no special calibration in this regard is required.

[0024] The conductive structure may be formed from fully or partially oxidized copper or fully or partially oxidized zinc, both of which are particularly suitable for the simple manufacture of the sensor for the reasons already explained.

[0025] The conductive structures are preferably formed to a thickness of 750 nm, preferably 200 nm to 600 nm, such that the conductive structures are spaced apart by approximately 1 μm to 6 μm, preferably 2 μm to 5 μm, to provide sufficient material for oxidation and for forming nanowires relative to adjacent conductive structures.

[0026] When copper or zinc is oxidized for the conductive structure, the nanowires are formed substantially from copper oxide or zinc oxide.

[0027] It is particularly preferred that the sensor is equipped with a heating element, which allows for the measurement of CO2 concentrations at elevated temperatures. In this case, the heating element is arranged so that the associated conductive structures and nanowires can be brought to the desired temperature, for example, in the temperature range of 300°C to 400°C. For this purpose, the substrate supporting the conductive structures can be connected to a separate support that supports the heating element. It is also possible for the substrate to be equipped with a heating element before the deposition of the conductive structures. This can in particular be a micro-hotplate, preferably a micro-hotplate with the dimensions described above. In this case, the conductive structures can be heated, in particular to temperatures above 300°C, using the micro-hotplate. If the micro-hotplate is already connected to the substrate or integrated into the substrate before the conductive structures are placed thereon, this micro-hotplate or possibly another type of heating element has three tasks: i) adjusting the elevated temperature for nanowire formation; ii) adjusting the elevated temperature after application of the nanoparticles to burn off the organic ligands of the nanoparticles; iii) Adjusting the measurement temperature to be higher than room temperature.

[0028] When nanoparticles are formed by evaporation, sputtering, etc., and separation at elevated temperatures, four challenges are posed.

[0029] In particular, the micro-hotplate may be arranged on a CMOS chip, and thus, in general, a chip with a sensor according to the present invention may be formed. It is also possible for a single chip to have multiple sensors.

[0030] Within the scope of the present invention, it has been determined that the sensor according to the invention has a high sensitivity to CO2 in gases, in particular at temperatures above 250° C. The invention therefore provides in another aspect a method for measuring the CO2 concentration in gases, in which a sensor according to the invention is used and the measurement is carried out at temperatures above 250° C., in particular above 300° C.

[0031] Further features, advantages and operations of the present invention will become apparent from the following examples of embodiments, the drawings to which reference is made in the following: [Brief explanation of the drawings]

[0032] [Figure 1] 1 illustrates steps for photolithographically fabricating conductive structures on a substrate. [Figure 2a] 1 shows possible shapes of conductive structures on a substrate. [Figure 2b] 1 shows possible shapes of conductive structures on a substrate. [Figure 3] 1 shows a scanning electron microscope image of conductive structures and a close-up of nanowires formed between the conductive structures. [Figure 4] The structure of the CO2 sensor is shown. [Figure 5] 1 shows a scanning electron microscope view of a microhotplate integrated into a chip. [Figure 6] The schematic structure of the CO2 sensor incorporated in the chip is shown. [Figure 7] Graphs for CO2 measurements are shown. DETAILED DESCRIPTION OF THE INVENTION

[0033] The sensor 1 according to the invention can in principle be manufactured on any substrate 2. In the following, two exemplary manufacturing examples are given.

[0034] Manufacturing Example 1 The sensor 1 according to the invention can be arranged on a silicon substrate. For this purpose, a wafer cut into pieces measuring 2 cm x 2 cm can be used. The thickness of the wafer can be approximately 700 μm. A suitable substrate 1 typically comprises thermally oxidized silicon dioxide with a layer thickness of 300 nm. This oxide layer can be important when several sensors 1 are arranged in parallel on one substrate.

[0035] In particular, the sensor 1 can be fabricated when a substrate 2 is prepared. Subsequently, a conductive structure 3 is placed on the substrate 2 by photolithography and metal deposition or alternatively by electron beam lithography. This is shown schematically in Figure 1. Any geometric pattern can be applied. Non-limiting examples are shown in Figures 2a and 2b.

[0036] The metal can be, for example, copper or zinc. As can be seen in Figures 2a and 2b, the metal first forms the electrical structure 3 on the substrate 2. The deposition of copper or zinc can be carried out in a vacuum in a Univex Evaporator 450 from Leybold GmbH. Typical layer thicknesses of the metal layer are between 200 nm and 600 nm. Prior to the deposition of the conductive structure 3, it is also possible to deposit a relatively thin bonding layer, in particular made of a metal, for example titanium or chromium. The bonding layer can be used to avoid or at least reduce stresses in the conductive structure 3 and improve adhesion. Subsequently, in a further step, the conductive structure 3 is thermally oxidized, resulting in the formation of nanowires or nanolines between adjacent conductive structures 3. As can be seen in Figure 2a, the spacing A can be, for example, between 2 μm and 4 μm. Tables 1 and 2 below identify the individual process steps and typical process parameters for copper or zinc as the metal.

[0037] Table 1: Process parameters for copper oxide nanowires [Table 1]

[0038] Table 2: Process parameters for zinc oxide nanowires [Table 2]

[0039] Figure 3 shows a scanning electron microscope image of conductive structures 3 connected by nanowires. As can be seen in this section, the individual nanowires extend over the free distance or spacing A between the conductive structures.

[0040] As can be seen in FIG. 3, these nanowires are subsequently or optionally sensitized with nanoparticles at a later stage in the manufacture of sensor 1. The nanoparticles can comprise, in particular, zirconium oxide (ZrO) and / or gold (Au). Suitable nanoparticles are commercially available and can have an average particle size of less than 20 nm. Sensor 1 is particularly suitable for measuring the CO content in gases, which is performed at elevated temperatures, particularly above 200°C, for example, in the temperature range of 300°C to 400°C. For this purpose, sensor 1 may have a separate support 5 carrying and / or supporting a heating element, such as a microhotplate 4. This support 5, together with the heating element, may be connected to substrate 2 and the electrically conductive structure 3 arranged thereon or to sensor 1 by gluing or using an adhesive 7. Furthermore, a thermocouple 6 may be provided. This is shown in FIG. 4. Although not shown in detail, the individual components are also electrically connected, as far as necessary for the measurement or for the operation of these components.

[0041] Manufacturing Example 2 In accordance with Example 1, essentially any substrate 2 is suitable for the realization of the sensor 1. In a preferred variant, the sensor 1 is mounted on a chip, in particular a CMOS chip, which is already formed with a micro-hotplate 4. Other bases with a micro-hotplate 4 are also contemplated. Figure 5 shows a top view under a scanning electron microscope of a chip with an integrated micro-hotplate 4.

[0042] Figure 6 depicts a schematic diagram of the structure. A heat distribution element 8 is located above the microhotplate 4, although this element is optional. A thermally insulated, narrowly defined sensor device is located on top of it. As is apparent from Figure 5, the entire structure is only connected to the rest of the chip by a spider's web of electrical connections and is otherwise unsupported. This allows the microhotplate 4, despite being integrated onto the chip, to be easily heated to temperatures of, for example, 400°C without adversely affecting the remaining components of the chip. For this purpose, a recess is created below the microhotplate 4 by removing silicon. The corresponding material removal is achieved by an etching process. Together with the microhotplate 4, the entire unsupported sensor arrangement concept is well insulated from the surrounding environment. A thermocouple 6 may be provided, but this is not required.

[0043] Measurement results The sensor according to the invention can be used to determine the CO2 content particularly sensitively by resistance measurement, especially in the temperature range of 300°C to 400°C. In this case, the measurement results are largely independent of the air humidity in the investigated gas, which means that for many purposes no calibration is necessary.

[0044] As is evident from Figure 7, the sensor 1 fabricated according to the two aforementioned fabrication examples responds sensitively to variations in CO2 concentration. The operating temperature was 300 °C for the measurements shown in Figure 7. As is evident, the measurement results depend only to a tolerably small extent on the air humidity, which was varied between 25% and 75% according to the dashed line. It is also evident that within the relevant concentration range of 250 ppm to 2000 ppm, the measurement results correlate with the CO2 pulses shown as rectangles. In the presence of CO2 molecules, charge carrier exchange (electron transfer) occurs between the gas-sensitive oxide layer and the CO2 molecules. The electrical resistance of this sensor layer increases with increasing CO2 concentration.

[0045] The sensor 1 according to the present invention is easy to manufacture, robust, and particularly suitable for measuring the CO2 concentration in gases, even at elevated temperatures. In particular, such a sensor 1 can be integrated on an electronic chip, for example in combination with a micro-hotplate 4. In this case, the micro-hotplate 4 can be used for oxidizing the conductive structure 3 and for burning off the organic components of the deposited nanoparticles during manufacture, which is advantageous for simple manufacture. Furthermore, the micro-hotplate 4 ensures the desired high temperature during operation for determining the CO2 content. The thermally insulated arrangement of the micro-hotplate 4 including the sensor 1 allows the corresponding sensor device to be integrated on a single electronic chip, since only a localized high temperature is achieved that is not critical to the surrounding environment.

[0046] In addition to the application fields mentioned at the beginning, the sensor 1 according to the invention may also be intended for a range of other uses, for example for monitoring the indoor air in buildings, for inspecting the working environment of individuals, or for condition monitoring in machines that generate gases whose operation or other processes can infer the state of the machine.

Claims

1. Steps below a) providing a substrate; b) disposing a plurality of conductive structures on said substrate at a predetermined spacing (A) from one another; c) oxidizing the plurality of conductive structures while forming oxide-based nanowires between the plurality of conductive structures; d) CO ２ The sensor is a CO ２ depositing nanoparticles on the oxide-based nanowires to enable measurement of Including, The nanoparticles include barium carbonate, barium titanate, silver, zirconium oxide, and / or gold. CO in the gas ２ The method for manufacturing the sensor is capable of measuring the concentration of

2. 10. The process of claim 1, wherein the oxidation in step c) is carried out at elevated temperature.

3. 3. The process of claim 2, wherein the oxidation in step c) is carried out at a temperature above 280°C.

4. The method of claim 3, wherein the oxidation in step c) is carried out at a temperature between 280°C and 420°C.

5. The method of claim 4, wherein the oxidation in step c) is carried out at 300°C to 400°C.

6. The method of claim 1 , wherein the plurality of conductive structures are formed from copper or zinc.

7. The method of claim 1 , wherein the plurality of conductive structures are deposited in step b) from the gas phase.

8. The method of claim 1 , wherein in step b) a bonding layer is deposited on the substrate, followed by deposition of the plurality of conductive structures.

9. The method of claim 1 , wherein the plurality of conductive structures are deposited to a thickness of less than 750 nm.

10. The method of claim 9, wherein the plurality of conductive structures are deposited to a thickness of 200 nm to 600 nm.

11. The method according to any one of claims 1 to 10, wherein the distance (A) is adjusted to 1 µm to 6 µm.

12. The manufacturing method according to claim 11, wherein the distance (A) is adjusted to 2 μm to 5 μm.

13. The method of any one of claims 1 to 12, wherein in step a) a substrate is provided which comprises a heating element.

14. The method of claim 13 , wherein the heating element is a micro-hotplate.

15. The method of claim 14, wherein the elevated temperature for oxidation in step c) is adjusted by heating using the microhotplate.

16. The manufacturing method according to claim 14 or 15, wherein the micro-hotplate is arranged on one chip.

17. The method of any one of claims 14 to 16, wherein the micro-hotplate is thermally insulated.

18. 18. The method of any one of claims 1 to 17, wherein in step d) nanoparticles having an average size of less than 20 nm are deposited on the oxide-based nanowires.

19. 20. The method of claim 18, wherein in step d) nanoparticles having an average size of less than 10 nm are deposited on the oxide-based nanowires.

20. a substrate; a plurality of conductive structures arranged on the substrate at predetermined intervals (A) from each other; and oxide-based nanowires formed between the plurality of conductive structures by oxidation of the plurality of conductive structures; ２ The sensor is a CO ２ nanoparticles are deposited on the oxide-based nanowires to enable measurement of The nanoparticles include barium carbonate, barium titanate, silver, zirconium oxide, and / or gold. CO in the gas ２ A sensor capable of measuring the concentration of

21. 21. The sensor of claim 20, wherein the plurality of conductive structures are formed from fully or partially oxidized copper or fully or partially oxidized zinc.

22. 22. The sensor of claim 20 or 21, wherein the plurality of conductive structures are formed to a thickness of less than 750 nm.

23. 23. The sensor of claim 22, wherein the plurality of conductive structures are formed to a thickness of 200 nm to 600 nm.

24. The sensor according to any one of claims 20 to 23, wherein the spacing (A) between the conductive structures is between 1 μm and 6 μm.

25. 25. The sensor of claim 24, wherein the spacing (A) between the plurality of conductive structures is between 2 μm and 5 μm.

26. 26. The sensor of any one of claims 20 to 25, wherein the oxide-based nanowires are formed from copper oxide or zinc oxide.

27. 27. The sensor of any one of claims 20 to 26, wherein the substrate comprises a heating element.

28. 28. The sensor of claim 27, wherein the heating element is a micro-hotplate.

29. 30. The sensor of claim 28, wherein the plurality of conductive structures are heatable to a temperature in excess of 300°C using the micro-hotplate.

30. 30. The sensor of claim 28 or 29, wherein the micro-hotplate is disposed on a CMOS chip.

31. An electronic chip comprising a sensor according to any one of claims 20 to 30.

32. CO in gases using a sensor according to any one of claims 20 to 30, the measurement being carried out at temperatures above 250°C. ２ How to measure concentration.

33. CO in gases using a sensor according to any one of claims 20 to 30, the measurement being carried out at temperatures above 300°C. ２ How to measure concentration.

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