SENSOR, INCLUDING A DIAPHRAGM THAT IS OPEN THROUGH A CLEARANCE, FOR MEASURING THE CONCENTRATION OF AN ANALYSIS FLUID

Abstract

A sensor for measuring a concentration of an analysis fluid based on a thermal conductivity principle. The sensor includes at least one analysis heating element, situated on a measuring diaphragm, for heating the analysis fluid, and a reference heating element, situated on a reference diaphragm, for heating at least one reference gas. The measuring diaphragm and the reference diaphragm are adjacently situated between a sensor substrate and a cap substrate. The measuring diaphragm is situated in a measuring volume and the reference diaphragm is situated in a reference volume. The measuring diaphragm and the reference diaphragm each include at least one coating. The measuring diaphragm is opened by at least one clearance. A method for manufacturing a sensor is also described.

Claims

1-11. (canceled)

12. A sensor for measuring a concentration of an analysis fluid based on a thermal conductivity principle, the sensor comprising: at least one analysis heating element, situated on a measuring diaphragm, configured to heat the analysis fluid; a reference heating element, situated on a reference diaphragm, configured to heat at least one reference fluid, the measuring diaphragm and the reference diaphragm being adjacently situated between a sensor substrate and a cap substrate, the measuring diaphragm being situated in a measuring volume and the reference diaphragm being situated in a reference volume, wherein the measuring diaphragm and the reference diaphragm are situated in the form of a diaphragm layer between the sensor substrate and the cap substrate and each include at least one coating, and wherein at least one clearance is situated in the measuring diaphragm.

13. The sensor as recited in claim 12, wherein the at least one analysis heating element and the at least one reference heating element are connectable to a sensor-external or sensor-internal evaluation electronics system for measuring a change in resistance of the analysis heating element relative to an electrical resistance of the reference heating element, caused by the analysis fluid.

14. The sensor as recited in claim 12, wherein the coating is a one-sided or two-sided coating.

15. The sensor as recited in claim 12, wherein the reference volume is open at a front side and/or at a rear side, or the reference volume is a closed volume, the reference diaphragm being formed as a closed diaphragm or as a diaphragm that is provided with a clearance.

16. The sensor as recited in claim 12, wherein the measuring volume includes at least one fluid channel that is connected at a front side, and/or a rear side, and/or a lateral side, the fluid channel being introduced into a cap substrate, and/or a base substrate, and/or the sensor substrate.

17. The sensor as recited in claim 12, wherein the coating includes at least one nitride, and/or silicon, and/or oxide, and/or plastic, and/or ceramic.

18. The sensor as recited in claim 12, wherein the measuring volume and the measuring diaphragm and/or the reference volume and the reference diaphragm, have a rectangular, or square, or oval, or circular cross section.

19. The sensor as recited in claim 12, wherein the measuring volume and the reference volume have the same size or have different sizes.

20. The sensor as recited in claim 12, wherein the sensor includes at least two analysis heating elements and at least two reference heating elements, the analysis heating elements and the reference heating elements being usable as heating elements and/or measuring elements for a change in resistance.

21. The sensor as recited in claim 12, wherein the reference diaphragm separates a first reference volume, introduced into the cap substrate, from a second reference volume introduced into the sensor substrate, the first reference volume and the second reference volume being filled with the same fluid or with different fluids.

22. A method for manufacturing a sensor, comprising the following steps: providing a wafer-shaped sensor layer; depositing a diaphragm layer on the sensor layer; applying analysis heating elements and reference heating elements in the form of electrically conductive structures to the diaphragm layer; depositing at least one coating as protection for the electrically conductive structures; introducing clearances into the diaphragm layer by material removal; situating a cap layer that is closed or provided with openings on the diaphragm layer or on the coating of the diaphragm layer; exposing the diaphragm layer by material removal of the sensor layer to form reference volumes and measuring volumes; situating a base layer that is closed, or open at least in areas, on the sensor layer; and carrying out a separation operation to form a plurality of sensors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 shows a schematic sectional illustration of a sensor according to a first specific embodiment of the present invention, with an open reference volume.

[0036] FIG. 2 shows a schematic sectional illustration of a sensor according to a second specific embodiment of the present invention, with a closed reference volume.

[0037] FIG. 3 shows a schematic sectional illustration of a sensor according to a third specific embodiment of the present invention, with two reference volumes that are separate from one another.

[0038] FIG. 4 shows a schematic sectional illustration of a sensor according to a fourth specific embodiment of the present invention, with a laterally extending fluid channel.

[0039] FIG. 5 shows a schematic sectional illustration of a sensor according to a fifth specific embodiment of the present invention, with a measuring volume that is open on two sides.

[0040] FIGS. 6 through 11 show a schematic sequence for illustrating a method for manufacturing the sensor, in accordance with an example embodiment of the present invention.

[0041] FIG. 12 shows a top view onto the electrical strip conductors of the sensor according to a first exemplary embodiment of the present invention.

[0042] FIG. 13 shows a top view onto the electrical strip conductors of the sensor according to a second exemplary embodiment of the present invention, with a connected evaluation electronics system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0043] FIG. 1 shows a schematic sectional illustration of a sensor 1 according to a first specific embodiment, with an open reference volume 2. Sensor 1 includes a measuring volume 4 in addition to reference volume 2. A reference diaphragm 6 is situated in reference volume 2. Measuring volume 4 includes a measuring diaphragm 8. In particular, reference volume 2 and measuring volume 4 are divided in areas by reference diaphragm 6 and measuring diaphragm 8, respectively, and also by cap substrate 18 and base substrate 20.

[0044] Electrically conductive structures 10 that may be electrically contacted via electrical connections 11 or bond pads are introduced on reference diaphragm 6 and measuring diaphragm 8. Electrically conductive structures 10, illustrated in FIGS. 12 and 13, are designed here as reference heating elements 12 for heating at least one reference fluid, and as analysis heating elements 14 for heating an analysis fluid. Reference heating elements 12 and analysis heating elements 14 are simultaneously used for heating and for measuring changes in resistance or differences in resistance.

[0045] Reference volume 2 and measuring volume 4 are introduced in the form of cavities into a sensor substrate 16, and extend up to a cap substrate 18. A base substrate 20 is situated at sensor substrate 16 on a side opposite from cap substrate 18. In vertical direction V, cap substrate 18 is spaced apart from sensor substrate 16 via diaphragms 6, 8.

[0046] Substrates 16, 18, 20 are flatly extended, and enclose reference volume 2 and measuring volume 4 at least in areas. Reference volume 2 is closed on the base side by base substrate 20. Measuring volume 4 is closed on the cap side by cap substrate 18.

[0047] Fluid channels 24 used for supplying an analysis fluid into measuring volume 4 are introduced into base substrate 20. Arrow 26 illustrates the inflow of the analysis fluid.

[0048] Measuring diaphragm 8 and reference diaphragm 6 include a coating 28 that covers electrically conducting structures 10 on the cap side and thus protects them. Coating 28 may be made of a nitride, for example. In addition, each diaphragm 6, 8 includes at least one clearance 30 through which a fluid may pass through diaphragm 6, 8 without mechanical stress.

[0049] In the illustrated exemplary embodiment, measuring volume 4 is closed in the area of cap substrate 18. Reference volume 2 is provided with an opening 22 via which reference volume 2 may carry out a gas exchange with surroundings U.

[0050] Due to measuring volume 4 which is closed on the cap side, an analysis gas such as H2 may flow through fluid channels 24 into measuring volume 4, and may remain there at least temporarily. The analysis gas may also contain water vapor or moist air. Alternatively, the analysis fluid may be present in liquid form or may be made of a liquid. The concentration of any other heat-conducting gas, such as O2, CO2, He, moist air, and the like, may also be measured. Reference volume 2 is open with respect to a housing or an electronics system, not illustrated, and exposed to environmental influences.

[0051] FIG. 2 shows a schematic sectional illustration of a sensor 1 according to a second specific embodiment, with a closed reference volume 2. In contrast to the first exemplary embodiment, reference volume 2 is filled with a reference gas that experiences no exchange with surroundings U.

[0052] Due to a closed reference volume 2, fluctuations in the ambient air such as changes in moisture or influences from interfering gases from the surroundings may be avoided. Reference volume 2 may be flooded beforehand with a suitable reference fluid, for example during attachment of base substrate 20 or cap substrate 18, for example for bonding with glass frit 32. A reference fluid may be, for example, synthetic air, N2, O2, CO2, methane, and the like.

[0053] In addition to expansion of the field of application of sensor 1 for areas with high pressures and/or pressure fluctuations, further advantages are simplified handling during manufacture. For typical semiconductor processes, deposits or residues made up, for example, of ash from lacquer stripping, cleaning solutions, or sludge from sawing the wafer assemblies, may form on diaphragms 6, 8. A closed cap substrate 18 may prevent such deposits.

[0054] FIG. 3 shows a schematic sectional illustration of a sensor 1 according to a third specific embodiment, with two reference volumes 2, 3 that are separate from one another. For this purpose, reference diaphragm 6 has a closed design, i.e., without a clearance 30, as the result of which different fluids are introducible above and below reference diaphragm 6 in vertical direction V.

[0055] For example, different gases that are not miscible with one another and that allow a reduction of a variable field may be introduced into reference volumes 2, 3. For example, H2 gas may be led into a first reference volume 2 on the cap side, and O2 gas may be led into a second reference volume 3 on the base side. Creation of further gas-filled reference cavities is also possible.

[0056] FIG. 4 shows a schematic sectional illustration of a sensor 1 according to a fourth specific embodiment, with a laterally extending fluid channel 24. The fluid channel extends not through base substrate 20 in vertical direction V, but, rather, laterally or transversely with respect to vertical direction V along a boundary between base substrate 20 and sensor substrate 16, up to measuring volume 4.

[0057] FIG. 5 shows a schematic sectional illustration of a sensor 1 according to a fifth specific embodiment, with a measuring volume 4 that is open on two sides. It is possible to supply an analysis fluid on the cap side and on the base side. Fluid channels 23 are provided which extend through cap substrate 18 and up to measuring volume 4. Fluid channels 24 are likewise situated in substrate 20 on the base side, through which the analysis fluid may pass into measuring volume 4. The analysis fluid may continuously flow through measuring volume 4 due to such an arrangement.

[0058] FIGS. 6 through 11 illustrate a schematic sequence for explaining a method for manufacturing sensor 1. FIGS. 6 through 11 show details of a wafer-shaped arrangement, which is separated to form multiple sensors 1 in a last step. The separation step is not described or illustrated in greater detail.

[0059] FIG. 6 illustrates a step in which a wafer-shaped sensor layer 34 is provided. Sensor layer 34 may be coated with a dielectric 36, for example. The dielectric may be designed as a first diaphragm layer.

[0060] Electrically conductive structures 10 are applied to dielectric 36 in a further step shown in FIG. 7. This step may take place, for example, by sputtering of platinum or some other metal. Structuring via a lithographic method in combination with an etching process may be subsequently carried out.

[0061] Analysis heating elements 14 and reference heating elements 12 in the form of metal coatings may be applied to diaphragm layer 36 via the application of electrically conductive structures 10.

[0062] Clearances 30 may be subsequently introduced into electrically conductive structures 10 and diaphragm layer 36. Deposition of a coating 28 that is used as protection for electrically conductive structures 10 takes place in a further step. Alternatively or additionally, clearances 30 in electrically conductive structures 10 may also be provided after application of coating 28, or may be provided through coating 28.

[0063] For example, coating 28 may be made of an oxide or a nitride, or both. Pressure compensation openings or clearances 30 may be formed in a further step. Clearances 30 may be introduced into diaphragm layer 36, coating 28, and electrically conductive structures 10, for example using a gas-phase etching process or a plasma etching process.

[0064] FIG. 8 shows a further step in which a cap layer 38 that is closed or provided with openings 22, 23 is situated on coating 28 of diaphragm layer 36. The adhesion between cap layer 38 and coating 28 may be enabled by applying glass frit 32. Cap layer 38 may already include cavities, which are necessary for forming electrical connections 11, reference volume 2, and measuring volume 4.

[0065] In addition, an adhesion promoter layer 35 is also applied to sensor substrate 34 in order to improve the joining process of base substrate 34. This adhesion promoter layer 35 may be made, for example, of an oxide and/or a combination of oxide, nitride, or metal oxides. Depending on the design of sensor 1, this adhesion promoter layer 35 may likewise be structured.

[0066] FIG. 9 shows a further step for manufacturing sensor 1. Diaphragm layer 36 is exposed to form reference volume 2 and measuring volume 4 by material removal of the sensor layer. The material removal may take place in one or multiple steps. For example, the material removal may take place by grinding or full-surface thinning and/or via an etching process. The base-side exposure of diaphragm layer 36 may take place using a trench etching process, for example.

[0067] A base layer 40 that is closed, or open at least in areas, is subsequently situated on sensor layer 34. This step is illustrated in FIG. 10. The introduction of fluid channels 24 into base layer 40 is shown in FIG. 11, cap layer 38 and base layer 40 being ground to the final dimensions.

[0068] A plurality of sensors 1 is formed using a separation operation.

[0069] Alternatively or additionally, for introducing fluid channels 24 into base layer 40, openings 22, 23 may also be formed in cap layer 38. Furthermore, introducing openings 22, 23 in cap layer 38 through clearances 30 is possible.

[0070] By use of the method, depths of all cavities or of volumes 2, 4 are controllable in the micron range. The heat transfer may thus be controlled by a targeted flat or particularly deep cavity in cap substrate 18 or sensor substrate 16, and by the shape of volumes 2, 4. For example, the shape of volumes 2, 4 may have a symmetrical or asymmetrical design. For example, depths in the range of 6 μm to 600 μm may be created.

[0071] FIG. 12 shows a top view onto electrically conductive structures 10 that are designed as electrical strip conductors of sensor 1. Electrically conductive structures 10 form a cost-efficient form of wiring, since they include only one strip conductor crossing 42 on sensor 1.

[0072] Reference heating elements 12 and analysis heating elements 14 are simultaneously used for heating and for measuring changes in resistance or differences in resistance.

[0073] Two resistors R1 through R4 that are formed by electrically conductive structures 10 are situated on reference diaphragm 6 and measuring diaphragm 8. These resistors R1 through R4 are connected to one another in the form of a Wheatstone bridge circuit. Resistors R1 and R4 are situated on measuring diaphragm 8, and resistors R2 and R3 are situated on reference diaphragm 6.

[0074] A difference of medium voltage taps between resistors R1 and R3 or between R2 and R4 is sensitive to changes in the resistance values, and may therefore be used as a measuring signal.

[0075] Resistors R1 through R4 are used both as heating elements and measuring elements. A design in which heating elements and measuring elements are separate is likewise possible.

[0076] In the specific embodiment illustrated in FIG. 12, diaphragms 6, 8 or corresponding volumes 2, 4 are the same size and have a square cross section.

[0077] FIG. 13 shows a top view onto electrically conductive structures 10 of sensor 1 according to a second exemplary embodiment, with a connected evaluation electronics system 44. In contrast to the exemplary embodiment shown in FIG. 12, in this case no strip conductor crossing 42 is provided on sensor 1. For implementing a Wheatstone bridge circuit, the design of strip conductor crossing 42 is displaced on evaluation electronics system 44. The bond pads or electrical connections 11 may be mounted at some other edge of sensor 1. For example, electrical connections 11 may be rotated by 90° in order to simplify or optimize a subsequent installation of the sensor.

[0078] In addition, reference volume 2 has a larger design than measuring volume 4. This is illustrated by reference diaphragm 6, which has a larger design compared to measuring diaphragm 8.

[0079] Alternatively, additional measuring resistors or heating resistors may also be provided, for example to measure the ambient temperature or to condition sensor 1 uniformly or at a constant thermal temperature.