Device for determining the value of a measurable property of a fluid, method for operating a device for determining the value of a measurable property of a fluid

Abstract

Device (10) for determining a value of a property of a fluid (F) to be measured, comprising: a measuring capacitor device (12) which can be brought into contact with the fluid (F), wherein the measuring capacitor device (12) comprises a first electrode (14), a second electrode (16), a first dielectric layer (18) and a second dielectric layer (20); wherein the first electrode (14), the second electrode (16), the first dielectric layer (18) and the second dielectric layer (20) are arranged such that a first electrical capacitance (C1) of the measuring capacitor device (12) is at least partially attributable to the first and second electrodes (14, 16) in conjunction with the first and with the second dielectric layer (18, 20); wherein a first dielectric constant of the first dielectric layer (18) upon contact with the fluid (F) depends on the property of the fluid (F) to be measured; wherein a second dielectric constant of the second dielectric layer (20) is essentially independent of the property of the fluid (F) to be measured; a compensation capacitor device (22) comprising the second dielectric layer (20), a third electrode (24) and a fourth electrode (26); wherein the second dielectric layer (20), the third electrode (24) and the fourth electrode (26) are arranged such that a second electrical capacitance (C2) of the compensation capacitor device (22) is at least partially attributable to the third and fourth electrodes (24, 26) in conjunction with the second dielectric layer (20); wherein the compensation capacitor device (22) is connected in parallel or can be connected in parallel with the measuring capacitor device (12); a measuring device (40) by means of which a first current capacitance value of a total electrical capacitance of an electrical parallel circuit of the measuring capacitor device (12) with the compensation capacitor device (22) can be measured; a determining device (42) by means of which, based on the measured first current capacity value, a sensitivity of the device (10) to the property to be measured can be determined; and a computing device (44) by means of which, based on the determined sensitivity of the device (10) and based on a measured second current capacitance value of the first electrical capacitance (C1) of the measuring capacitor device (12) and / or based on a measured third current capacitance value of the total electrical capacitance of the parallel connection of the measuring capacitor device (12) with the compensation capacitor device (22), the value to be determined of the property to be measured of the fluid (F) can be determined.

Description

[0001] The present invention relates to a device for determining the value of a measurable property of a fluid, in particular a device that is at least partially micromechanical. It further relates to a method for operating a device for determining the value of a measurable property of a fluid, in particular for operating a device according to the invention for determining the value of the measurable property of the fluid. Finally, the present invention also relates to a method for manufacturing a device for determining the value of a measurable property of a fluid, in particular a method for manufacturing a device according to the invention for determining the value of the measurable property of the fluid.

[0002] A fluid is understood to be, in particular, a gas or a liquid. The property of the fluid to be measured is, in particular, a physical and / or a chemical property. This property could, for example, be a gas concentration, such as humidity, a pH value, or something similar. The value to be determined is understood to be a numerical value that the property of the fluid exhibits at the time of measurement, for example, a pH value of 7, a carbon dioxide concentration of 5%, etc. State of the art

[0003] A micromechanical sensor for determining air humidity, also known as relative humidity, is described, for example, in DE 102 53 913 A1. A pair of opposing, comb-shaped electrodes with teeth are formed on a substrate. The teeth of the electrodes generally have a uniform width and interlock. The teeth of one electrode are separated from the teeth of the other electrode by a generally uniform gap. The micromechanical sensor has a humidity-sensitive film whose capacitance changes with humidity. This film covers the electrodes and an area between them. Humidity is detected based on changes in capacitance between the electrodes in response to changes in the humidity of the ambient air.

[0004] German patent DE 37 81 500 T2 describes a differential sensor for detecting analytes in a liquid medium, comprising an analyte sensor and a reference capacitor. The reference capacitor consists of a layer of insulating material between two electrodes. The analyte sensor is identical to the reference capacitor, except that it additionally has an active layer between its electrodes, which has a relatively high affinity for nonpolar molecules. The reference capacitor compensates for changes in the dielectric constant of the liquid medium caused by variations in temperature, ion concentration, pH, composition, and physical and chemical state.

[0005] WO 85 / 04 718 A1 describes a measuring sensor with two electrodes and a non-conductive membrane arranged between the electrodes, wherein the electrodes have an insulating coating.

[0006] In DE 196 44 290 A1 a sensor element for measuring two different properties of a chemically sensitive substance is described.

[0007] German patent application DE 10 2006 019 534 A1 describes a microsensor comprising a first and a second electrode and at least one sensitive layer between the electrodes and an insulating substrate on which the electrodes and the at least one sensitive layer are arranged. The electrodes are located at approximately the same distance from the substrate. The electrode surfaces adjacent to the sensitive layer are arranged on the substrate surface at an inclination to the vertical. The inclination of the electrodes is oriented such that the distance of the respective opposite electrode surfaces to the substrate decreases.

[0008] German patent DE 10 2004 042 729 A1 describes a biochip with an electrode array on a substrate for the electrical, in particular capacitive, detection of biochemical molecules. The electrodes are each connected via an electrical conductor through the substrate to an electrically conductive contact surface.

[0009] In GB 2 136 130 A, a device and a method for chemical analysis are described. The device comprises a thin-film capacitor, which is at least partially covered with a thin layer selected to be reactive with a species to be detected. A non-reactive insulating layer may be arranged between the electrodes of the capacitor, which may be configured as an interdigital capacitor.

[0010] Further state of the art is also known from the patent application US 2004 / 10 182 153 A1. Disclosure of the invention

[0011] The present invention discloses a device having the features of claim 1 and a method having the features of claim 8.

[0012] Advantageously, the properties of the second dielectric layer in the measuring and compensation capacitor devices are essentially identical. In particular, both the material parameters and the manufacturing-related variations in the geometric parameters of the second dielectric layer, which are to be determined for the capacitance, behave essentially the same. A thickness of the second dielectric layer that is essentially the same in both the measuring and compensation capacitor devices is particularly preferred.

[0013] The compensation capacitor device is connected in parallel with the measuring capacitor device, in particular permanently connected in parallel, or can be connected in parallel.

[0014] A capacitor assembly, i.e., the measuring capacitor assembly and the compensation capacitor assembly, shall in particular comprise a capacitor of any type, for example, a plate capacitor, wound capacitor, interdigital capacitor, spherical capacitor, etc. Furthermore, a capacitor assembly may include electrical connections, links, protective layers, insulating layers, housings, seals, etc.

[0015] The term "connected in parallel" is understood to mean, in particular, that the measuring capacitor device and the compensating capacitor device are connected in a circuit such that the first electrical capacitance of the measuring capacitor device and the second electrical capacitance of the compensating capacitor device can be represented in an equivalent circuit diagram for the circuit by a first and second electrical capacitance connected in parallel. According to a further development, the parallel connection is permanent, that is, permanently connected.

[0016] The term "parallel-connectable" means that the parallel connection is not permanent but can be established, for example, by means of a switch or an integrated circuit. Advantageously, the parallel connection is achieved using an electronic circuit, in particular an integrated electronic circuit, especially automatically as a result of a program sequence. Furthermore, "parallel-connectable" also specifically implies reversible parallel connection. This means that the parallel connection can also imply that the compensation capacitor circuit can be decoupled from the measuring capacitor circuit.

[0017] Furthermore, a method with the features of claim 8 is provided. Advantages of the invention

[0018] The fundamental insight of the present invention is that, in devices, particularly at the wafer level, for measuring the physical properties of materials, manufacturing-related deviations from target values, such as target values ​​for the thickness of functional layers, can lead to errors in measurement results as soon as the determination of the measurement results is based on the target values. The measurement methods described in this application are capacitive measurement methods, meaning that the functional layers are dielectric layers, i.e., layers whose dielectric constants are measured during the intended use of the device according to the invention, either individually or in a combination of capacitive elements, for example, in a series or parallel circuit, such as in the sense of an equivalent circuit diagram.The term "dielectric constant" is historically determined and does not imply that the parameter referred to as the dielectric constant is constant; in particular, the described measurement methods are based on a change in the variable dielectric constant of a functional layer upon contact with a fluid.

[0019] For example, a polyimide layer can change its dielectric constant under the influence of the moisture content of a fluid, such as atmospheric humidity. Atmospheric humidity refers specifically to the concentration of water vapor in the air. It is also possible to form at least one functional dielectric layer from one or more materials that changes its dielectric constant upon contact with a liquid based on the pH value of the liquid. Furthermore, it is also possible to form at least one functional dielectric layer from one or more materials that changes its dielectric constant upon contact with a fluid based on the carbon dioxide concentration in the fluid.

[0020] A crucial step in sensor manufacturing is calibration. This involves first determining how the sensor's measurement result—that is, the signal at the end of a signal chain (e.g., capacitance-to-voltage converter and voltage-to-numerical value converter)—behaves depending on the applied stimulus (e.g., humidity) or stimuli (e.g., humidity and temperature). Then, in one or more iterations, parameters can be determined that allow the stimulus to be calculated from the final result of the signal chain. This can be achieved either by (preferably iteratively) manipulating the signal chain or by using a second signal chain or processing chain downstream of the first. Applying the stimuli is cost-relevant, and it is desirable to minimize the number of defined calibration points required. If only one known stimulus is applied, this is called "single-point calibration."

[0021] The idea underlying the invention is to take into account the knowledge described above by designing a device for determining a value of a property of a fluid to be measured with a measuring capacitor device, which mainly serves to determine the value, and with a compensation capacitor device, which is suitable for reducing the influence of manufacturing-related deviations from the target values ​​on the determination of the value, in particular on the preceding determination of the sensitivity of the device to a change in the property to be measured.By reducing this influence, the errors in determining the value can be reduced to such an extent that even with a single-point adjustment for calibrating the device, the errors in determining the value remain within relatively small error thresholds, for example within + / - 5%, preferably within + / - 3% or even less. The error thresholds can also be arranged asymmetrically around the exact value, for example from -1% to +3%.

[0022] In a single-point calibration, a single measurement point is generated for an individual component, here one of the devices according to the invention, under controlled conditions, specifically by measuring a reference value of the property to be determined. Single-point calibration is technically less complex than multi-point calibration. Each individual component is subject to manufacturing-related variations, i.e., deviations from target values. Based on the single measurement point, the individual component is calibrated. In this case, as part of the calibration, the sensitivity of the individual device according to the invention to a change in the fluid property to be determined is also established.

[0023] Knowing the sensitivity, a current value of the fluid's property can be determined from a current measurement point by comparing it to a known measurement point obtained under controlled conditions. For example, if it is known that the electrical capacitance of a device has an offset of one unit when the relative humidity is 10%, and if the sensitivity of the device is also known—that is, how much the electrical capacitance of the device changes with a given change in relative humidity—then the current relative humidity can be determined from a current measurement point that yields, for example, a current electrical capacitance of three units.

[0024] In multi-point measurement, two or more measurement points are determined for an individual component, between which, for example, a linear relationship is assumed. This can improve the accuracy of the calibration, but also increase the required calibration effort.

[0025] Based on Fig. Section 9 describes a simple one-point calibration using an exemplary device 1 for the capacitive measurement of air humidity. A functional layer 3 made of a polyimide is arranged between three capacitor plates 2. The dielectric constant of this polyimide depends on the humidity H of the ambient air due to the material properties of the polyimide. The capacitor plates 2 and the functional layer 3 are arranged on a substrate 5, with an insulating layer 4 electrically isolating the substrate 5 from the capacitor plates 2.

[0026] A voltage can be applied via two contact devices 6 to measure the electrical capacitance of the device 1.

[0027] The formula for the electrical capacitance C(H) as a function of the humidity H of this arrangement is: C(H)=ε0εpol(H)Ad

[0028] Here, ε0 is the electric constant, ε pol The dielectric constant of the polyimide used is dependent on humidity, A is the effective area of ​​the parallel-plate capacitor, and d is the effective distance between the two capacitor plates of the parallel-plate capacitor, which is perpendicular to the effective area A. Both the effective area A and the distance d can be subject to manufacturing-related deviations from their respective target values. The deviations of the area A from the target value are not considered in this application; they are often relatively small compared to the area A itself.

[0029] The sensitivity to humidity is the total derivative of the electrical capacitance with respect to humidity H: S=δC(H)δH=ε0Adδεpol(H)δH

[0030] If the above capacity C(H0) of the humidity H is measured at a predetermined reference value H0, the term can be derived from this single-point measurement. ε0Ad=C(H0)εpol(H0) be determined, where ε pol (H0) is known from tables and / or measurement series. With the value for, which is also known from tables and / or measurement series, δεpol(H)δH Thus, the sensitivity S can be calculated with particular accuracy. S=C(H0)εpol(H0)δεpol(H)δH.

[0031] If a capacitance C(H1) is then measured at a humidity value H1 in the actual measurement, this humidity value H1 can be determined in the simplest way by H1=H0+S[C(H1)−C(H0)], This means that the humidity value H1 is the sum of the reference value H0 of the humidity as an offset, and the product of the sensitivity S and the difference between the capacitance in contact with air at humidity value H1 and the capacitance in contact with air at humidity value H0. Instead of speaking of a capacitance, it would be more accurate to speak of a current capacitance value of the electrical capacitance.

[0032] Electrodes of such devices for the capacitive determination of values ​​for measured properties of a substance can be provided with protective layers, for example, oxygen-impermeable protective layers to prevent oxidation of the electrodes or moisture-impermeable protective layers to prevent corrosion of the electrodes and thus to extend the service life of the device and to stabilize its behavior over its service life. This can result in a capacitive series circuit whose total electrical capacitance includes, as unknowns, the thickness of both the protective layer and the thickness of the functional layer used in the device, whose dielectric constant changes upon contact with the fluid.

[0033] According to the inventive concept of the present patent application, a single-point adjustment, i.e., calibration based on a single-point measurement, can also be performed for a device for determining the value of a measured property of a fluid, thereby minimizing measurement errors that are based on manufacturing-related deviations from target values. For the calculations, the target value for one of the dielectric layers of the device, whose dielectric constant does not depend on the value of the measured property of the fluid, for example, a protective layer, can be used. According to the invention, the errors that can occur when determining the sensitivity of the device due to manufacturing-related deviations in the thickness of this dielectric layer can be reduced by means of the compensation capacitor device.

[0034] The described methods for operating the device to determine the value of the fluid property to be measured can include several steps for calibrating the respective individual device. These steps primarily involve determining the device's sensitivity and an offset. The sensitivity and offset can be determined, for example, using… Fig. 9 described above. Due to the associated effort, the calibration steps can advantageously be performed only once, while the subsequent steps, i.e., the actual determination of the value of the fluid property to be measured, can be performed any number of times after the calibration steps.

[0035] Advantageous embodiments and further developments are described in the dependent claims and in the description with reference to the figures.

[0036] According to a preferred embodiment of the device according to the invention, the first dielectric layer and the second dielectric layer are formed between the first electrode and the second electrode. According to a further preferred embodiment, the second dielectric layer is formed between the third electrode and the fourth electrode. Advantageously, only the second dielectric layer is formed between the third electrode and the fourth electrode. This further improves the measuring accuracy of the device according to the invention.

[0037] According to the invention, the device comprises a measuring device by means of which a first current capacitance value of the total electrical capacitance of an electrical parallel circuit of the measuring capacitor device with the compensation capacitor device can be measured. According to the invention, the device comprises a determining device by means of which, based on the measured first current capacitance value, the sensitivity of the device to the property to be measured can be determined.

[0038] According to the invention, the device comprises a computing unit by means of which, based on the determined sensitivity of the device, a measured second current capacitance value of the first electrical capacitance of the measuring capacitor unit, and / or a measured third current capacitance value of the total electrical capacitance of the parallel connection of the measuring capacitor unit and the compensation capacitor unit, the value of the fluid property to be measured can be determined. This allows the device to be designed in a particularly compact manner. Furthermore, manufacturing steps can be combined, especially at the wafer level, thus reducing the technical effort required to manufacture the device.

[0039] The determining device and / or the computing device can, for example, be designed as a computer of a balancing system.

[0040] According to a further preferred embodiment, the first dielectric layer comprises or consists of a polyimide. Polyimides exhibit dielectric constants that change almost linearly with an applied, i.e., contacted, relative humidity. Therefore, polyimides are particularly suitable for a device for measuring humidity, especially relative humidity, according to the present invention. Furthermore, the drift of properties in polyimides is relatively low. Polyimides can be integrated in a variety of ways and, depending on their size, can lead to capacitance changes in the range of one hundred to one thousand femtofarads, and even several tens of thousands of femtofarads, depending on the dimensions of the polyimides, over an exemplary measuring range between 0% and 100% relative humidity.As described below, such changes in capacitance can easily be evaluated using integrated circuits to determine humidity.

[0041] According to a further preferred embodiment, the measuring capacitor device is configured as a plate capacitor or as an interdigital capacitor. If the measuring capacitor device is configured as a plate capacitor, one or more electrodes of the measuring capacitor device can consist of a porous or moisture-permeable material, so that the fluid or its moisture can penetrate through this electrode. According to a further preferred embodiment, the compensation capacitor device is configured as a plate capacitor or as an interdigital capacitor. Such capacitor configurations for the capacitor devices are particularly compact and easy to manufacture.

[0042] According to a further preferred embodiment, the fluid is a gas or a gas mixture, and the property of the gas or gas mixture to be determined is the concentration of a predetermined substance in the gas or gas mixture, for example, the carbon dioxide content in the air. According to a particularly preferred embodiment, the fluid is a gas or gas mixture, for example, air, and the property to be determined is the concentration of water vapor in the gas or gas mixture, wherein the first dielectric constant of the first dielectric layer changes substantially depending on the concentration of water vapor in the gas or gas mixture.

[0043] According to a further preferred embodiment, the fluid is a liquid and the property of the liquid to be determined is the pH value of the liquid.

[0044] According to a further preferred embodiment, the device includes a controllable circuit by means of which the compensation capacitor assembly can be electrically connected in parallel with the measuring capacitor assembly and / or electrically decoupled from the measuring capacitor assembly. At least the measuring capacitor assembly and the compensation capacitor assembly are formed on one and the same substrate. According to a further preferred embodiment, the controllable circuit is designed as an application-specific integrated circuit arranged on the substrate. Thus, the device can be manufactured in a particularly compact form and at the wafer level with particularly low technical effort. By decoupling the compensation capacitor assembly, it can be ensured that it is not constantly subjected to load during the actual measurement.This can be advantageous if, for example, the compensation capacitor device is expected to age differently, e.g., faster, than the measuring capacitor device, or if no information is available on its long-term behavior.

[0045] According to a further preferred embodiment, the circuit device is designed as an application-specific integrated circuit that is separate from the substrate and electrically connected to the measuring capacitor device and the compensation capacitor device.

[0046] According to a preferred embodiment, the inventive method for operating a device for determining the value of a measured property of a fluid comprises the following further steps: measuring a fourth current capacitance value of the first electrical capacitance of the measuring capacitor device when the measuring capacitor device is in contact with the reference fluid, wherein the reference fluid has a predetermined reference value of the measured property of the reference fluid; bringing the measuring capacitor device into contact with the fluid with the measured property; measuring a second current capacitance value of the measuring capacitor device when the measuring capacitor device is in contact with the fluid with the measured property; calculating the value of the measured property of the fluid based on the measured second current capacitance value.further based on the determined sensitivity of the device to the property to be measured; as well as based on the measured fourth current capacity value. This allows the measurement accuracy of the method according to the invention to be further improved.

[0047] According to a further preferred embodiment, the method comprises the step of determining a difference value between the measured first and the measured fourth current capacity value; wherein the calculation of the value to be determined of the property to be measured of the fluid is carried out based on the determined difference value between the measured first and the measured fourth current capacity value.According to a further preferred embodiment, the method comprises the steps of: bringing the measuring capacitor device into contact with the fluid with the property to be measured; measuring a third current capacitance value of the total electrical capacitance of the measuring capacitor device with the compensation capacitor device when the measuring capacitor device is in contact with the fluid; calculating the value of the property of the fluid to be measured based on the measured third current capacitance value; and furthermore based on the determined sensitivity of the device to the property to be measured.

[0048] To manufacture a device, the first dielectric layer and the second dielectric layer can be formed between the first and second electrodes. According to a further preferred embodiment, the second dielectric layer is formed between the third and fourth electrodes.

[0049] According to a further preferred embodiment, the second dielectric layer is formed between the first and second electrodes, as well as between the third and fourth electrodes, in the same manufacturing step. Thus, manufacturing-related deviations in the properties, particularly dimensions, including layer thickness, of the second dielectric layer affect both the measuring capacitor device and the compensation capacitor device equally and can therefore be compensated for. This means that the influence of these deviations on determining the sensitivity of the device to changes in the fluid property being measured can be reduced.

[0050] Insofar as elements are referred to as "first", "second", "third", "nth", etc., in this description and the claims, it should be understood that this is not a numerical enumeration but merely different designations. Thus, a particular embodiment may well contain an element designated as "second" without necessarily also containing an element designated as "first". Brief description of the characters

[0051] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawings. These show: Fig. 1 a schematic block diagram of a device for determining a value of a property of a fluid to be measured according to a first embodiment of the present invention; Fig. 2 a schematic cross-sectional view of a measuring capacitor device of the apparatus according to the first embodiment of the present invention; Fig. 3 a schematic longitudinal sectional view of the measuring capacitor device of the apparatus according to the first embodiment of the present invention; Fig. 4 a schematic cross-sectional view of a compensation capacitor device of the apparatus according to the first embodiment of the present invention; Fig. 5 an equivalent circuit diagram for the measuring capacitor device and the compensation capacitor device of the apparatus according to the first embodiment of the present invention in parallel connection; Fig. 6 a schematic flowchart to explain a method for operating a device for determining a value of a property to be measured of a fluid according to a second embodiment of the present invention; Fig. 7 a schematic flowchart to explain a method for operating a device for determining a value of a property to be measured of a fluid according to a third embodiment of the present invention; Fig. 8 a schematic flowchart to explain a manufacturing process for a device for determining a value of a measurable property of a fluid according to a fourth embodiment of the present invention; and Fig. 9 A schematic cross-sectional view through an exemplary device for capacitive measurement of air humidity.

[0052] In all figures, identical or functionally equivalent elements and devices are provided with the same reference numerals unless otherwise specified. Detailed description of the exemplary implementations

[0053] Fig. Figure 1 shows a schematic block diagram of a device 10 for determining the value of a measurable property of a fluid F according to a first embodiment of the present invention. For details, reference is also made to the following Fig. 2 to 5 referred.

[0054] According to the first embodiment, the device 10 has a measuring capacitor assembly 12 which can be brought into contact with the fluid F. For this purpose, the measuring capacitor assembly 12 can be arranged on an outer surface of the device 10. In particular, according to the first embodiment, the device 10 is a device for measuring air humidity, i.e., the concentration of water in air as fluid F.

[0055] Fig. Figure 2 shows a schematic cross-sectional view of a measuring capacitor device 12 of the device 10 according to the first embodiment. The measuring capacitor device 12 is designed as an interdigital capacitor; see also Fig. 2 and Fig. 3. Such an interdigital capacitor has interlocking, comb-shaped electrodes arranged interdigitally (between fingers). The individual teeth of the comb-shaped electrodes are referred to below as "electrode fingers".

[0056] The measuring capacitor device 12 comprises a first electrode 14 with a first plurality of electrically connected first electrode fingers 17-1 and a second electrode 16 with a second plurality of electrically connected second electrode fingers 17-2. Except for electrode fingers 17-1, 17-2 formed at an edge of the measuring capacitor device 12, each first electrode finger 17-1 engages in a space between two of the second electrode fingers 17-2, and each second electrode finger 17-2 engages in a space between two of the first electrode fingers 17-1. The first and second electrodes 14, 16 are made of a conductive material, in particular polysilicon, or of a metal, preferably aluminum, copper, titanium, or tungsten.One or more of the electrodes can be made of a porous metal to allow better access of the fluid F to or onto the measuring capacitor device 12.

[0057] The electrode fingers 17-1, 17-2 are perpendicular in cross-section to a common imaginary axis A-A'. In a respective plane perpendicular to the axis AA', each of the first and second electrode fingers 17-1, 17-2 is essentially formed as a plate. The electrode fingers 17-1, 17-2 each have a width B perpendicular to the axis AA' and a thickness D parallel to the axis AA'. It should be understood that, due to the manufacturing processes used, the shapes can only be specified in general terms. Instead of an ideal plate with rectangular cross-sections, the electrode fingers 17-1, 17-2 may, for example, have one or more trapezoidal, triangular, and / or pentagonal cross-sections, etc.

[0058] The first and second electrodes 14, 16 and the associated first and second electrode fingers 17-1, 17-2 are made of an electrically conductive material, in particular a metal. The first electrode 14 can be electrically contacted via a first electrical contact device 19-1, for example a bond pad. The second electrode 16 can be electrically contacted via a second electrical contact device 19-2, for example a bond pad. A first dielectric layer 18 is formed between the electrode fingers 17-1, 17-2 of the first and second electrodes 14, 16, which will be explained in more detail below.

[0059] Fig. Figure 3 shows a schematic longitudinal sectional view of the device according to the first embodiment, which includes the axis AA' and is perpendicular to the cross-section according to Fig. 2 is displayed. As in Fig. As shown in Figure 3, the electrode fingers 17-1, 17-2 according to the first embodiment are each configured with a height H perpendicular to the axis AA'. The first and second electrodes 14, 16 are formed on a common substrate 50. The substrate is preferably a non-conductive silicon substrate, for example made of silicon oxide, although other materials are also conceivable. The first and second electrodes 14, 16 are configured in the same plane and are insulated from each other.

[0060] The substrate is formed, for example by etching before or after the application of the electrode fingers 17-1, 17-2 to the substrate 50, with spaced-apart pedestals P. The pedestals P essentially have a pedestal height h relative to the substrate 50, as well as a thickness D and a width B. Each of the first and second electrode fingers 17-1, 17-2 is formed with a height H on a pedestal P of the substrate 50. An insulating layer, for example an oxide layer, such as silicon oxide, can be formed between the pedestals P and the electrode fingers 17-1, 17-2. Alternatively, the electrode fingers 17-1, 17-2 can also be formed directly on the substrate 50. The pedestals P can help to prevent unwanted electrical connections between the first and second electrodes 14, 16 during the formation of the electrode fingers 17-1, 17-2.

[0061] The electrode fingers 17-1, 17-2 are coated with a second dielectric layer 20 as a protective layer, which can serve in particular to improve the reliability and / or extend the service life of the measuring capacitor device 12. According to the first embodiment, the second dielectric layer 20 consists of silicon nitride. The silicon nitride layer 20 can, for example, be vapor-deposited onto the substrate 50 with the electrode fingers 17-1, 17-2 arranged thereon. Alternatively, the second dielectric layer can also consist, for example, of gold, another silicon oxide, or another gas-tight, non-oxidizing material.

[0062] The silicon nitride layer 20 is formed with a first layer thickness d1 on surfaces 21-1 to 21-7 of the electrode fingers 17-1, 17-2, which face one or more other electrode fingers 17-1, 17-2. On surfaces 23-1 to 23-4 facing away from the substrate 50, the silicon nitride layer 20 is formed with a second layer thickness d2, wherein the first layer thickness d1 is smaller than the second layer thickness d2.

[0063] Between the electrode fingers 17-1, 17-2 and on a side of the first and second electrodes 14, 16 facing away from the substrate 50, the first dielectric layer 18 is formed as a polyimide layer. In particular, the spaces 15 between the electrode fingers 17-1, 17-2 are filled as completely as possible with the second dielectric layer 20. The space width d4 of the spaces 15 between the electrode fingers 17-1, 17-2 is preferably between 200 nanometers and 2000 nanometers, and particularly between 500 nanometers and 1500 nanometers. The third layer thickness d3 of the first dielectric layer 18 between the electrode fingers 17-1, 17-2 can be thinner than the space width d4, in particular between 100 nanometers and 500 nanometers.

[0064] Advantageously, the gap width d4 is essentially uniform for all electrode fingers 17-1, 17-2. A distance d5 between the tips of the electrode fingers 17-1, 17-2 and a main body of the first and second electrodes 14, 16, from which the electrode fingers 17-1, 17-2 extend, is shown in Figure 1. Fig. 2, can advantageously be between half and twice the gap width d4. In particular, the distance d5 can also be equal to the gap width d4.

[0065] The first electrical capacitance C1 of the measuring capacitor device 12 therefore exhibits a first and a second capacitance component Cm, Cp. The first capacitance component Cm is due to the first and second electrodes 14, 16 in conjunction with the first dielectric layer 18, i.e., the polyimide layer. The polyimide layer is designed such that the polyimide or polyimides of the second dielectric layer are selected such that, depending on the humidity of the ambient air (the fluid F), the first dielectric constant of the first dielectric layer 18 is variable, i.e., it changes depending on the humidity. Thus, the first capacitance component Cm is also dependent on the humidity. Based on this, a capacitive measurement can be performed to determine the humidity, a property of the air to be determined.

[0066] The second capacitance component Cp of the first electrical capacitance C1 of the measuring capacitor device 12 is due to the first and second electrodes 14, 16 in conjunction with the second dielectric layer 20, i.e., the silicon nitride layer. The second dielectric layer, formed as a silicon nitride layer, has a second dielectric constant, which is essentially independent of the humidity.

[0067] Thus, the second capacitance component Cp is also essentially independent of the humidity, which can reduce the sensitivity of the measuring capacitor device to changes in humidity. From an electrical engineering perspective, the first and second capacitance components Cm and Cp are connected in series (see figure). Fig. 5, which creates the first electrical capacitance C1.

[0068] The first layer thickness d1 of the second dielectric layer 20 is subject to variations depending on the chosen manufacturing process, for example, vapor deposition. A target value for the first layer thickness d1 can be, for example, between 30 and 250 nanometers, preferably between 40 and 150 nanometers, and particularly between 60 and 100 nanometers. A difference in layer thickness at the end and flank faces of the electrode fingers 17-1, 17-2 is possible due to the manufacturing process. For example, the first layer thickness d1 can be 40% smaller than the second layer thickness d2. Manufacturing-related variations of, for example, plus or minus 10% can occur.Since the first dielectric layer 18 is filled into the spaces 15 with the space width d4 between the electrode fingers 17-1, 17-2 after the formation of the second dielectric layer 20 on the electrode fingers 17-1, 17-2, a third layer thickness d3 of the first dielectric layer 18 between the electrode fingers 17-1, 17-2 is also subject to manufacturing-related variations.

[0069] The sensitivity of the device 10 to a change in humidity is due to a change in the first capacitance fraction Cm. The greater the change in the first capacitance fraction Cm – particularly as a percentage of the first capacitance fraction Cm – between contact with air at approximately 0% relative humidity and contact with air at approximately 100% relative humidity, the greater the sensitivity of the device 10 to the change in humidity.

[0070] A single-point calibration is advantageously used to determine the sensitivity. The device 10 is brought into contact with a reference fluid with a predetermined reference value for the fluid property to be determined; in the example described here, this is air with a relative humidity of 50%. Based on this, the sensitivity of the device 10 is determined as described in more detail below, where target values ​​are assumed for the first and third layer thicknesses d1 and d3. A target value for the third layer thickness d3 can, for example, be between 100 and 2000 nanometers, advantageously between 200 and 1500 nanometers, particularly between 300 and 1300 nanometers, and most preferably 300 nanometers. Because the first and third layer thicknesses d1 and d3 deviate from the target values ​​due to manufacturing processes, the sensitivity of the device 10 is thus determined with a certain degree of error.By means of the compensation capacitor device 22, the dependence of the determination of the sensitivity on the manufacturing-related deviations of the first and third layer thicknesses d1, d3 is reduced, so that even with a single-point adjustment the resulting error in the determination of the sensitivity remains relatively small.

[0071] Therefore, it is advantageous if the fluctuations, particularly in the first and third layer thicknesses d1, d3, result in the smallest possible error when determining the humidity value based on measured electrical capacitances, which include the first capacitance component Cm. This is achieved by means of a compensation capacitor device 22, as described in more detail below.

[0072] Referring again to Fig. 1 The device 10 further comprises a compensation capacitor device 22, which according to the first embodiment is designed as a plate capacitor.

[0073] Fig. Figure 4 shows a schematic cross-sectional view of a compensation capacitor device 22 of the device 10 according to the first embodiment. According to the first embodiment, the compensation capacitor device 22 is designed as a plate capacitor on a surface 50-S of the substrate 50, on which the measuring capacitor device 12 is also formed.

[0074] An electrically insulating layer, in particular an oxide layer 27, is formed on a surface 50-S of the substrate 50. On, and in particular on, a surface 27-S of the oxide layer 27 facing away from the substrate, a third electrode 24 and a fifth electrode 25 are formed, spaced apart from each other by a gap 51. The third and fifth electrodes 24, 25 consist of an electrically conductive material, in particular polysilicon or a metal, preferably aluminum, copper, titanium, or tungsten. The third and fifth electrodes 24, 25 of the compensation capacitor device 22 can advantageously be manufactured in the same manufacturing step and using the same method as the first and second electrodes 14, 16 of the measuring capacitor device 12.

[0075] The second dielectric layer 20 is formed on, and in particular on, a surface 24-S of the third electrode 24 facing away from the oxide layer 27. A section 20' of the second dielectric layer 20, which is part of the compensation capacitor arrangement 22, can be separate and spaced apart from a section of the second dielectric layer 20, which is part of the measuring capacitor arrangement 12. For this purpose, the second dielectric layer 20 can be structured, for example by etching.

[0076] Alternatively, the second dielectric layer 20 can also be formed continuously, i.e., in one piece, so that the section 20' of the second dielectric layer 20, which is part of the compensation capacitor device 22, and the section of the second dielectric layer 20, which is part of the measuring capacitor device 12, are connected to each other within the second dielectric layer.

[0077] According to the first embodiment, the entire second dielectric layer 20 has been formed within one manufacturing step, so that manufacturing-related deviations from target values, in particular with regard to the dimensions of the second dielectric layer 20, especially with regard to the layer thicknesses d1, d2 of the second dielectric layer 20, are reflected equally in the measuring capacitor device 12 as well as in the compensation capacitor device 22.

[0078] According to the first embodiment, section 20' of the second dielectric layer 20 partially covers, preferably more than 50%, and particularly more than 90%, the surface 24-S of the third electrode 24 facing away from the oxide layer 27. Furthermore, section 20' of the second dielectric layer 20 partially covers, preferably more than 50%, and particularly more than 90%, the surface 25-S of the fifth electrode 254 facing away from the oxide layer 27. An intermediate space 51 formed between the third electrode 24, the fifth electrode 25, and the oxide layer 27 is also substantially filled by section 20' of the second dielectric layer. "Substantially" here means that manufacturing-related deviations, such as small bubbles, may be included.

[0079] A fourth electrode 26 is formed on a surface 20-S of the first section 21-1 of the second dielectric layer 20, facing away from the third and fifth electrodes 24, 25, and also facing away from the substrate 50. The section 20' of the second dielectric layer is thus formed between the third electrode 24 and the fourth electrode 26, which can be considered capacitor plates. Due to the manufacturing process, the section 20' of the second dielectric layer also has the second layer thickness d2, as does the section of the second dielectric layer 20 arranged in the measuring capacitor device. A ratio between the first layer thickness d1 and the second layer thickness d2 may be known from the known manufacturing step for producing the second dielectric layer and may, for example, be 5:3.

[0080] The compensation capacitor device 22 thus has a second electrical capacitance C2, which is partly attributable to the third and fourth electrodes 24, 26 in conjunction with the second dielectric layer 20. The third electrode 24 can be electrically contacted via a third electrical contact device 19-3, for example, a bond pad. The fifth electrode 25 can be electrically contacted via a fourth electrical contact device 19-4, for example, a bond pad. A third electrical capacitance can therefore be measured between the third and fourth electrical contact devices 19-3, 19-4, which is attributable to the third and fourth electrodes 24, 26 in conjunction with the second dielectric layer 20, as well as to the fourth and fifth electrodes 26, 25 in conjunction with the second dielectric layer 20.The second electrical capacitance C2 and the third electrical capacitance are essentially independent of the humidity, while the first electrical capacitance C1 depends on the humidity being measured.

[0081] Referring again to Fig. 1, the measuring capacitor device 12 and the compensation capacitor device 22 are connected in parallel or can be connected in parallel by means of a circuit device 46 which is arranged on the substrate 50.

[0082] Fig. Figure 5 shows an equivalent circuit diagram for the measuring capacitor device 12 and the compensating capacitor device 22 of the device according to the first embodiment in parallel connection.

[0083] Fig. Figure 1 further shows a measuring device 40 of the device 10, by means of which a first current capacitance value of the total electrical capacitance of the electrical parallel circuit of the measuring capacitor device 12 with the compensation capacitor device 22 can be measured. The measuring device 40 is electrically connected to the circuit device 26. A measurement using the measuring device 40 can be based, for example, on measuring an RC time constant, a phase shift, a frequency modulation, and / or an amplitude modulation. The measuring device 40 can comprise corresponding electronic components.

[0084] According to the first embodiment, the device 10 further comprises a determination device 42, by means of which the sensitivity of the device 10 to atmospheric humidity can be determined based on the measured first current capacitance value. The determination device 42 is electrically connected to the measuring device 46 in order to receive at least the first current capacitance value measured by the measuring device 40. The determination device 42 can, for example, be configured as a computer of a balancing system. The determination of the sensitivity can be carried out by means of one of the methods according to the invention, as described in more detail below.

[0085] The device 10 further comprises a computing unit 44, by means of which the value of the relative humidity can be determined based on the determined sensitivity of the device 10 and on a measured third current capacitance value of the total electrical capacitance of the parallel connection of the measuring capacitor unit 12 with the compensation capacitor unit 22. The computing unit 44 has a non-volatile data memory 45 for storing calculation parameters. The determination of the relative humidity can be carried out according to one of the methods according to the invention, as described in more detail below.

[0086] The device 10 further comprises an interface 48, through which the results of determining the humidity value can be output. This interface can be a wireless interface, such as a radio interface, or a simple wired interface, through which an analog or digital signal containing the determined humidity value can be transmitted. The data content of the data memory 45 can also be adapted via the interface 48, for example, a control program stored in the data memory 45 that automatically controls the determination of the value to be determined by the device 10.

[0087] Fig. Figure 6 shows a schematic flowchart to explain a method for operating a device for determining a value of a measurable property of a fluid F according to a second embodiment of the present invention, in particular a method for operating the device 10 for determining a value of the relative humidity according to the first embodiment of the present invention. The method according to the second embodiment is explained below mainly with reference to the device 10 according to the first embodiment of the present invention. For the method according to the second embodiment, the measuring capacitor device 12 and the compensation capacitor device 22 should be able to be connected in parallel and also disconnected from each other.

[0088] In step S01, the measuring capacitor device 12 is brought into contact with a reference fluid, wherein the reference fluid has a predetermined reference value for the property to be determined. According to the second embodiment, the reference fluid is air with a predetermined reference value of relative humidity, for example, 50% relative humidity. Alternatively, a relative humidity of 0% or 100% can also be used as the reference value, within the limits of technical feasibility. According to the second embodiment, the entire device 10 is placed in a sealed chamber containing air with a reference value of 10% relative humidity as the reference fluid.

[0089] In step S02, while the measuring capacitor device 12 is in contact with the reference fluid, an initial current capacitance value of the total electrical capacitance of an electrical parallel circuit of the measuring capacitor device 12 with the compensation capacitor device 22 is measured. The measurement S02 can be based, for example, on a measurement of an RC time constant, a phase shift, a frequency modulation, and / or an amplitude modulation.

[0090] In step S03, based on the measured first current capacity value and the predetermined first reference value of the property of the reference fluid to be measured, the sensitivity of the device 10 to the humidity is determined.

[0091] Predetermined parameters are taken into account when determining the sensitivity of the device 10. A predetermined parameter can, for example, specify the average sensitivity of a large number of devices manufactured in the same way as the present device 10, depending on the respective first measured capacitance value, i.e., upon contact with the reference fluid.

[0092] Further predetermined parameters used to determine the sensitivity are known properties of the polyimide from which the first dielectric layer 18, formed as a polyimide layer, is formed, in particular a function which specifies the dielectric constant of the polyimide used as a function of the humidity.

[0093] Other predetermined parameters used to determine the sensitivity are known dimensions, in particular target values ​​of the dimensions of the measuring capacitor device 12 and the compensation capacitor device 22.

[0094] Another predetermined parameter used to determine sensitivity is the reference value of the reference fluid.

[0095] In step S04, a fourth current capacitance value of the first electrical capacitance of the measuring capacitor device 12 is measured when the measuring capacitor device 12 is in contact with the reference fluid, for example, using the measuring device 40 of the device 10 according to the first embodiment. The designation "fourth current capacitance value" was chosen because a "second current capacitance value" and a "third current capacitance value" are defined elsewhere. The reference fluid has the predetermined reference value of the property to be measured, i.e., air with a relative humidity of 10%. For step S04, the parallel connection of the measuring capacitor device 12 and the compensation capacitor device 22 was removed, for example, using the circuit device 46 according to the first embodiment.The S04 measurement can be based on, for example, measuring an RC time constant, a phase shift, a frequency modulation and / or an amplitude modulation.

[0096] In step S05, a difference value is determined between the measured first and the measured fourth current capacitance values. This difference value indicates the extent to which the compensation capacitor device 22 influenced the total electrical capacitance. The difference value is calculated, for example, by the computing unit 44 of the device 10 according to the first embodiment and stored in the non-volatile data memory 45 of the computing unit 45.

[0097] This completes the calibration of the individual device. Steps S01 to S05 can, for example, be performed once for each individual device, which can then be used to determine the value of the measured property F once or several times without requiring further calibration. The subsequent steps S06 to S08 can therefore be performed as often as necessary, particularly after steps S01 to S05.

[0098] In step S06, the measuring capacitor device 12 is brought into contact with the fluid F with the property to be measured.

[0099] In step S07, a second current capacitance value of the measuring capacitor device 12 is measured when the measuring capacitor device 12 is in contact with the fluid F with the property to be measured, for example by means of the measuring device 40 of the device 10 according to the first embodiment. The measurement S07 can be based, for example, on measuring an RC time constant, a phase shift, a frequency modulation and / or an amplitude modulation.

[0100] In step S08, the value to be determined for the measured property of the fluid F is determined based on the measured second current capacitance value, the determined sensitivity of the device to the property to be measured, and the calculated difference between the measured first and fourth current capacitance values. Specifically, the difference can be added to the measured second current capacitance value to obtain an effective capacitance value, on which the further determination of the value is based—instead of directly on the measured second current capacitance value. Furthermore, the reference value, for example as an offset, can also be used, as described above. Fig. 9 described, in which determining the value to be determined is used.

[0101] Fig. Figure 7 shows a schematic flowchart to explain a method for operating a device for determining a value of a measurable property of a fluid F according to a third embodiment of the present invention, in particular a method for operating the device 10 for determining a value of the relative humidity according to the first embodiment of the present invention. The method according to the third embodiment is also described mainly with reference to the device 10 according to the first embodiment, which can be configured to carry out both the method according to the second and the method according to the third embodiment.

[0102] The method according to the third embodiment is a variant of the method according to the second embodiment, sharing steps S01 to S03 with it. For the method according to the third embodiment, the measuring capacitor device 12 and the compensating capacitor device 22 can be connected in parallel and also disconnected from each other, with measurements only being performed when the measuring capacitor device 12 and the compensating capacitor device 22 are connected in parallel. Alternatively, the measuring capacitor device 12 and the compensating capacitor device 22 can also be permanently connected in parallel for the method according to the third embodiment.

[0103] In the method according to the third embodiment, the calibration of the individual device can be completed with steps S01 to S03. Steps S01 to S03 can, for example, be performed once for each individual device, which can then be used to determine the value of the measured property of fluid F once or several times without requiring further calibration. The subsequent steps S04' to S06' can therefore be performed any number of times, particularly after steps S01 to S03.

[0104] According to the second embodiment, in step S04' the measuring capacitor device 12 is brought into contact with the fluid F with the property to be measured.

[0105] In step S05', a third current capacitance value of the total electrical capacitance of the parallel connection of the measuring capacitor device 12 with the compensation capacitor device 22 is measured when the measuring capacitor device 12 is in contact with the fluid F, for example by means of the measuring device 40 of the device 10 according to the first embodiment.

[0106] In step S06', the value to be determined for the measured property of the fluid F is calculated based on the measured third current capacitance value and the determined sensitivity of the device to the measured property. This is done by calculating the product of the sensitivity and the difference between the measured third current capacitance value and the measured first current capacitance value. This product can be added to a predetermined offset, for example, the reference value, to obtain the value to be determined. The reference value can be stored in the data memory 45 of the computing unit 44.

[0107] Fig. Figure 8 shows a schematic flowchart illustrating a manufacturing process for a device for determining the value of a measurable property of a fluid F according to a fourth embodiment of the present invention, in particular a manufacturing process for the device 10 according to the first embodiment of the present invention. In particular, in the described manufacturing process, the reference numerals of the steps are not intended to imply a chronological sequence. In particular, the individual steps can also be carried out partially simultaneously.

[0108] In step S21, a measuring capacitor device 12 is formed, in particular on a substrate 50, which can be brought into contact with the fluid F.

[0109] The formation of the measuring capacitor device 12 S21 is carried out in such a way that the measuring capacitor device 12 is formed with a first electrode 14 and a second electrode 16 as well as with a first dielectric layer 18 and a second dielectric layer 20.

[0110] The formation of S21 is further carried out in such a way that a first dielectric constant of the first dielectric layer 18 upon contact with the fluid F depends on the property of the fluid F to be measured, and that a second dielectric constant of the second dielectric layer 20 is essentially independent of the property of the fluid F to be measured.

[0111] The formation of S21 continues in such a way that the measuring capacitor device 12 has a first electrical capacitance C1, which is at least partly due to the first and second electrodes 14, 16 in conjunction with the first dielectric layer 18 and the second dielectric layer 20.

[0112] In step S22 a compensation capacitor device 22 is formed, which has the second dielectric layer 20, a third electrode 24 and a fourth electrode 26.

[0113] The compensation capacitor device 22 is further designed such that the compensation capacitor device 22 has a second electrical capacitance C2, which is at least partly due to the third and fourth electrodes 24, 26 in conjunction with the second dielectric layer 20.

[0114] Advantageously, the measuring capacitor device 12 and the compensation capacitor device 22 are designed such that the second electrical capacitance C2 is between 1% and 400% of the first electrical capacitance C1, preferably between 5% and 300%, in particular between 10% and 200%, and most preferably between 20% and 50%.

[0115] According to the fourth embodiment, the first dielectric layer 18 and the second dielectric layer 20 are formed between the first electrode 14 and the second electrode 16. Furthermore, the second dielectric layer 20 is formed between the third electrode 24 and the fourth electrode 26.

[0116] Furthermore, the second dielectric layer 20 is formed between the first electrode 14 and the second electrode 16 as well as between the third electrode 24 and the fourth electrode 26 in the same manufacturing step, so that the second dielectric layer 20 of both the measuring capacitor device 12 and the compensation capacitor device 22 has the same manufacturing-related deviations from target values, in particular with regard to the first and second layer thickness d1, d2 of the second dielectric layer 20.

[0117] Advantageously, both the formation S21 of the measuring capacitor device 12 and the formation S22 of the compensation capacitor device 22 are carried out at the wafer level. This allows a large number of devices to be manufactured simultaneously with a particularly low overall technical effort.

[0118] According to a fifth embodiment of the present invention, both the measuring capacitor device and the compensation capacitor device are designed as interdigital capacitors. The fifth embodiment is a variant of the first embodiment, wherein the compensation capacitor device 22 according to the first embodiment is replaced by a compensation capacitor device designed as an interdigital capacitor.

[0119] The compensation capacitor device designed as an interdigital capacitor according to the fifth embodiment is a variant of the one described in Fig. 2 and Fig. The measuring capacitor device 12 shown in Figure 3 is designed according to the first embodiment, wherein, instead of the first dielectric layer 18, an electrically conductive layer made of an electrically conductive material, for example a metal, is formed. It is preferred that the conductive material has essentially no sensitivity to the property of the fluid to be measured, i.e., a dielectric constant independent of the property to be measured.

[0120] The dimensions, in particular layer thicknesses, of the compensation capacitor device designed as an interdigital capacitor according to the fifth embodiment can also differ from those of the measuring capacitor device 12 according to the first embodiment. In particular, it can be advantageous if the gap width between the electrode fingers of the compensation capacitor device is 0.5 to 2 times larger than the gap width, d4 in Fig. 3, between the electrode fingers of the measuring capacitor device, in particular 0.75 times to 1.5 times as large, particularly preferably the same size.

[0121] In the measuring and compensation capacitor devices designed as interdigital capacitors, the second dielectric layer 20 is formed in the same manufacturing step from the same material and in the same way, for example by vapor deposition. Thus, the properties of the second dielectric layer 20 are essentially identical in the measuring and compensation capacitor devices. In particular, the material parameters as well as the manufacturing-related variations in the geometric parameters of the second dielectric layer 20, which are to be determined for the capacitance, are essentially identical. This applies especially to the first and second layer thicknesses d1, d2 of the second dielectric layer 20, which are therefore identical in the measuring and compensation capacitor devices according to the fifth embodiment, regardless of any differences in the dimensions of the electrode fingers.

[0122] Although the present invention has been described above with reference to preferred embodiments, it is not limited thereto, but can be modified in a variety of ways. In particular, the invention can be altered or modified in many ways without deviating from the core of the invention. For example, further protective layers, as well as layers made of or containing plastic, epoxy, etc., can be arranged between the substrate 50 and the first to fifth electrodes 14, 16, 24, 25, 26.

[0123] For example, both the measuring capacitor device and the compensating capacitor device can be designed as interdigital capacitors, or both as plate capacitors, or as capacitors of another type. Particularly simple manufacturing is possible if the measuring capacitor device and the compensating capacitor device are designed as capacitors of the same type, even if they may have different dimensions, such as the electrodes and / or electrode fingers.

Claims

[1] Device (10) for determining a value of a property to be measured of a fluid (F) comprising: a measuring capacitor device (12) which can be brought into contact with the fluid (F), wherein the measuring capacitor device (12) has a first electrode (14), a second electrode (16), a first dielectric layer (18), and a second dielectric layer (20); wherein the first electrode (14), the second electrode (16), the first dielectric layer (18), and the second dielectric layer (20) are arranged such that a first electrical capacitance (C1) of the measuring capacitor device (12) is at least partially attributable to the first and second electrodes (14, 16) in conjunction with the first and second dielectric layers (18, 20); wherein a first dielectric constant of the first dielectric layer (18) upon contact with the fluid (F) is dependent on the property of the fluid (F) to be measured; wherein a second dielectric constant of the second dielectric layer (20) is substantially independent of the property of the fluid (F) to be measured; a compensation capacitor device (22) comprising the second dielectric layer (20), a third electrode (24) and a fourth electrode (26); wherein the second dielectric layer (20), the third electrode (24) and the fourth electrode (26) are arranged such that a second electrical capacitance (C2) of the compensation capacitor device (22) is at least partially attributable to the third and fourth electrodes (24, 26) in conjunction with the second dielectric layer (20); wherein the compensation capacitor device (22) is connected or can be connected in parallel with the measuring capacitor device (12); a measuring device (40) by means of which a first current capacitance value of a total electrical capacitance of an electrical parallel circuit of the measuring capacitor device (12) with the compensation capacitor device (22) can be measured; a determination device (42) by means of which a sensitivity of the device (10) with respect to the property to be measured can be determined based on the measured first current capacitance value; and a computing device (44) by means of which the value to be determined of the property of the fluid (F) to be measured can be determined based on the determined sensitivity of the device (10) and based on a measured second current capacitance value of the first electrical capacitance (C1) of the measuring capacitor device (12) and / or based on a measured third current capacitance value of the total electrical capacitance of the parallel connection of the measuring capacitor device (12) with the compensation capacitor device (22). [2] The device (10) of claim 1, wherein the first dielectric layer (18) and the second dielectric layer (20) is formed between the first electrode (14) and the second electrode (16) and wherein the second dielectric layer (20) is formed between the third electrode (24) and the fourth electrode (26). [3] Device (10) according to one of the preceding claims 1 to 2, wherein the first dielectric layer (18) comprises or consists of a polyimide. [4] Device (10) according to one of the preceding claims 1 to 3, wherein the measuring capacitor device (12) is designed as a plate capacitor or as an interdigital capacitor and / or wherein the compensation capacitor device (22) is designed as a plate capacitor or as an interdigital capacitor. [5] Device (10) according to one of the preceding claims 1 to 4, wherein the fluid (F) is a gas (F) or gas mixture and wherein the property of the gas (F) to be determined is a concentration of a predetermined substance in the gas (F) or gas mixture. [6] Device (10) according to one of the preceding claims 1 to 4, wherein the fluid (F) is a liquid and wherein the property of the liquid to be determined is a pH value of the liquid. [7] Device (10) according to one of the preceding claims 1 to 6, comprising: a controllable circuit device (46) by means of which the compensation capacitor device (22) can be electrically connected in parallel with the measuring capacitor device (12) and / or electrically decoupled from the measuring capacitor device (12); wherein at least the measuring capacitor device (12) and the compensation capacitor device (22) are formed on a substrate (50); and wherein the controllable circuit device (46) is designed as an application-specific integrated circuit (46) arranged on the substrate (50) or as an application-specific integrated circuit separate from the substrate (50) and electrically connected to the measuring capacitor device (12) and the compensation capacitor device (22). [8] Method for operating a device (10) for determining a value of a property to be measured of a fluid (F), in particular a device (10) according to one of claims 1 to 7, comprising the steps: Bringing (S01) a measuring capacitor device (12) into contact with a reference fluid, wherein the reference fluid has a predetermined reference value of the property to be determined; wherein a first electrical capacitance (C1) of the measuring capacitor device (12) is composed of a first capacitance component (Cm) and a second capacitance component (Cp); wherein the first capacitance component (Cm) upon contact with the reference fluid depends on the property to be measured; and wherein the second capacitance component (Cp) is substantially independent of the property to be measured; Measuring (S02), while at least the measuring capacitor device (12) is brought into contact with the reference fluid, a first current capacitance value of an electrical total capacitance of an electrical parallel circuit of the measuring capacitor device (12) with a compensation capacitor device (22); wherein the compensation capacitor device (22) has a second electrical capacitance (C2); wherein the second electrical capacitance (C2) is substantially independent of the property to be measured; and wherein the second electrical capacitance (C2) is in a substantially known ratio to the second electrical capacitance component (Cp) of the measuring capacitor device (12); and Determining (S03), based on the measured first current capacitance value and the predetermined first reference value of the property of the reference fluid to be measured, a sensitivity of the device (10) with respect to the property to be measured. [9] Method according to claim 8, comprising the further steps: Measuring (S04) a fourth current capacitance value of the first electrical capacitance of the measuring capacitor device (12) upon contact of the measuring capacitor device (12) with the reference fluid, wherein the reference fluid has the predetermined reference value of the property of the reference fluid to be measured; Bringing (S06) the measuring capacitor device (12) into contact with the fluid (F) having the property to be measured; Measuring (S07) a second current capacitance value of the measuring capacitor device (12) upon contact of the measuring capacitor device with the fluid (F) having the property to be measured; Calculating (S08) the value to be determined of the property to be measured of the fluid (F) based on the measured second current capacitance value; further based on the determined sensitivity of the device (10) to the property to be measured; and based on the measured fourth current capacitance value. [10] Method according to claim 9, comprising the further step: Determining (S05) a difference value between the measured first and the measured fourth current capacitance value; wherein the calculation (S08) of the value to be determined of the property of the fluid (F) to be measured is carried out based on the determined difference value between the measured first and the measured fourth current capacitance value. [11] Method according to one of the preceding claims 8 to 10 with the further steps: Bringing (S04') the measuring capacitor device (12) into contact with the fluid (F) having the property to be measured; Measuring (S05') a third current capacitance value of the total electrical capacitance of the measuring capacitor device (12) with the compensation capacitor device (22) upon contact of the measuring capacitor device (12) with the fluid (F); Calculating (S06') the value to be determined of the property to be measured of the fluid (F) based on the measured third current capacitance value; and further based on the determined sensitivity of the device (10) to the property to be measured.

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