Fluid sensor and method for examining a fluid

Abstract

A fluid sensor (100) with a substrate (80) having a recess (70) for receiving a fluid to be examined, wherein the fluid sensor (100) further comprises a transistor (90) configured to detect an electrical change caused by the fluid to be examined as a potential change in the recess (70), and wherein the fluid sensor (100) further comprises an external electrode (10), wherein the external electrode (10) at least partially surrounds the recess (70) and is connected or connectable to a reference potential, wherein the transistor (90) is configured as a field-effect transistor with an insulated gate (30).

Description

Technical area

[0001] Embodiments relate to a fluid sensor and a method for examining a fluid. background

[0002] Potential changes at a solid surface due to chemical reactions are known from conventional technology. For example, these potential changes can be measured using a so-called "Kelvin probe", which uses a plate capacitor with a mechanically moved electrode. The mechanical movement causes a charge shift, which is detected via the voltage (difference between the surface potentials of the two electrodes, or "contact potential difference" (CPD)). If a chemical reaction changes the charge on an electrode surface, the resulting change in CPD, i.e. the change in the electric field, can be measured. To achieve reliable measurements, it is desirable for one of the two electrodes to be chemically non-reactive, i.e. inert, e.g. as a reference electrode. Otherwise, a reaction of the chemically sensitive electrode may not be determined correctly.

[0003] Numerous further developments have been made based on the Kelvin probe. To avoid the mechanically moving electrode, field-effect transistors (FETs) were used, in which a change in potential leads to a shift in the threshold voltage and thus to a change in the current. FETs with a metal-insulator-semiconductor structure, also known as "metal-insulator-semiconductor" FETs (MIS-FETs), have proven particularly suitable. The metal-insulator-semiconductor structure can form a capacitance between a metal layer and a semiconductor layer. The MIS capacitor can induce a charge in the semiconductor with the help of a voltage across the metal (also known as the "gate"). This charge controls the current between two electrodes (also known as "source, drain").

[0004] For the application of MISFETs as gas and / or liquid sensors, an air gap is created between the metal and the insulator, and a chemically sensitive layer is applied to the side of the metal facing the insulator. Examples include the suspended gate FET (SGFET), the hybrid SGFET (HSGFET), and the charge-coupled FET (CCFET). The additional air gap can reduce the MIS capacitance, thus reducing the current control factor for the transistor and thus also the sensitivity to chemically induced potential changes. An improvement can be achieved by using an insulated gate, also known as a floating gate (FGFET). In this case, a center tap is inserted into an air-gapped MIS capacitor, which acts as a floating / insulated electrode connected to a conventional metal-oxide-film FET (MOSFET).

[0005] Although the capacitive voltage division reduces the chemically induced potential change at the center tap, an overall improvement in sensitivity can result, as the gain factor of the MOSFET can be fully utilized. In this concept, the gate electrode of the MIS capacitor is coated with a chemically sensitive layer, which can be problematic. The opposite electrode is covered with an insulator. The air gap is located between this insulator and the gate electrode. The exposed insulator surface can be problematic, as it may also react chemically, e.g., due to moisture, corrosion, etc.

[0006] In addition, a free surface has a finite resistance, which can lead to drift phenomena due to the electric fields within the capacitor.

[0007] For applications as liquid sensors, the metal electrode (the gate in the MIS-FET) is replaced by a conductive liquid (ISFET). If the liquid is provided with a reference electrode, a space charge zone forms at the insulator-liquid interface, the width of which depends on the ion concentration. The resulting capacitance change changes the current control factor of the transistor and thus enables the measurement of the ion concentration in the liquid. A stable reference electrode in the liquid is also important here.

[0008] Further details on the state of the art can be found in the documents: • EP 1 103 808 A2, Gas sensor and method for its production: A gas sensor based on the work function measurement principle is implemented in field-effect transistors using hybrid technology. The described gas sensor has at least two field-effect transistors whose control behavior is adjusted by approximately equal air gaps between the gate and channel, and whose sensor layers can be read separately. • DE 198 14 857 A1, Gas sensor based on the principle of work function measurement: A hybrid flip-chip gas sensor based on the work function measurement principle is presented, using a low-cost CMOS transistor. This consists of an electrically insulating ceramic substrate with electrical conductors and contacting elements. A gas-sensitive layer is part of the gate insulation. The CMOS transistor with source (s) and drain (D) is mounted on the ceramic substrate using flip-chip technology and is contacted with the conductors. • US 2006 / 0 154 399 A1, ULTRA-FAST NUCLEIC ACID SEQUENCING DEVICE AND A METHOD FOR MAKING AND USING THE SAME; • DE 10 2013 001 035 A1, A chemical species sensor and a method for detecting a chemical species; • US 2013 / 0 056 367 A1, INTEGRATED SENSING DEVICE AND RELATED METHODS; • WO 00 / 75 649 A1, LOW POWER SENSOR; • DE 37 27 805 A1, Chemical sensor device with a field effect transistor; • DE 102 11 900 A1, Biosensor for detecting macromolecular biopolymers and method for producing a biosensor for detecting macromolecular biopolymers; • WO 2012 / 170 630 A2, NANOSCALE WIRES, NANOSCALE WIRE FET DEVICES, AND NANOTUBE-ELECTRONIC HYBRID DEVICES FOR SENSING AND OTHER APPLICATIONS; and • US 2011 / 0 108 892 A1, DETECTOR OF BIOLOGICAL OR CHEMICAL MATERIAL AND CORRESPONDING ARRAY OF DETECTORS. Summary

[0009] It is therefore desirable to create an improved concept for a fluid sensor.

[0010] The invention is based on the core concept that a recess in a substrate can be used to analyze a fluid, e.g., a gas, a liquid, or a plasma. A fluid sensor, chemical sensor, or chemosensor is created with a substrate that has a recess for receiving a fluid to be analyzed. The fluid sensor is designed to detect electrical changes in the recess caused by the fluid to be analyzed. Embodiments therefore simplify the construction of a fluid sensor. Using a recess in the substrate can result in simple manufacturing and a favorable arrangement of the electrodes.

[0011] A further core idea of ​​embodiments is to at least partially reduce, control, or shield an electric field in the recess caused by external influences. The fluid sensor further comprises an outer electrode that at least partially surrounds the recess and is connected or connectable to a reference potential. In this respect, embodiments can reduce the influence of external electric fields on a measurement with the fluid sensor. In further embodiments, the outer electrode can correspond to a delimited doping region of the substrate. In other words, a substrate can be used that corresponds, for example, to a semiconductor substrate and that comprises one or more doping regions with different doping levels. The outer electrode can then be realized in the substrate in a cost-effective manner via doping.In some embodiments, the outer electrode may also be designed in a protected manner, ie such that there is no direct contact between the outer electrode and the fluid to be examined and the outer electrode is inert.

[0012] Furthermore, in some embodiments, the outer electrode can be used to adjust an operating point of the fluid sensor or a transistor of the fluid sensor via the reference potential, in particular to switch the fluid sensor on and off, for example, to ensure energy-efficient operation of the sensor outside of measurement phases, or to replace it in a sleep mode in which energy consumption is reduced compared to a measurement mode. In some embodiments, the fluid sensor can also be completely switched off via the reference potential, i.e., essentially placed in a currentless or powerless mode.

[0013] Some embodiments can avoid an open reference electrode and still achieve shielding, such as with a Faraday cage. The shield or outer electrode has openings for the access of gases and / or liquids. For example, in a plate capacitor, two electrodes are used and the electric field inside is constant. With a Faraday cage, an essentially self-contained electrode (except for the aforementioned openings) can be used and a potential inside can be kept nearly constant. This makes it easier to implement or avoid a "chemically inert" second electrode, or to circumvent critical effects associated with an open electrode.

[0014] Some embodiments therefore comprise a Faraday cage or an electrode that is essentially self-contained and thus at least almost forms a Faraday cage, wherein the Faraday cage is provided with one or more openings that allow gas or liquid access. This can be, for example, a conductive hollow cylinder, a conductive trench structure, a conductive sphere with openings, etc. If a potential is applied to the conductive structures from the outside, the potential inside the structure can be kept essentially constant, apart from edge effects at the openings, and in some embodiments even essentially field-free. In order to make the edge effects negligible, the length (extension in the direction perpendicular to the essentially circular base area) can be much greater than a diameter of the base area, for example in an embodiment as a hollow cylinder.In an embodiment as a trench, a trench depth can be much larger, e.g. twice as large, than a trench width.

[0015] Another key idea is that a chemically sensitive layer can be applied inside the Faraday cage, in which charges and / or dipole moments can form due to gases or liquids, for example, and thus the potential inside can be changed. The value of the potential change can be measured, for example, using an insulated, or "floating" electrode, which is connected to the gate of a MOSFET, as in a "floating gate" FET (FGFET), as will be explained in more detail below. Furthermore, embodiments can be based on the knowledge that absolute potential measurements can be carried out instead of potential difference measurements or relative potential measurements (for example using capacitances), and that a counter electrode in the conventional sense can be dispensed with for these potential measurements.Deviations attributable to a non-inert second electrode can thus be reduced or eliminated. Embodiments can thus enable more reliable or temporally stable detection of the electrical changes. Embodiments therefore provide a fluid sensor configured to detect an absolute potential change at an electrode, such as a gate of a FET, caused by a fluid under investigation.

[0016] Embodiments further provide a method for examining a fluid. The method includes passing the fluid through a recess in a substrate and detecting an electrical change in the recess.

[0017] In embodiments, the fluid sensor can comprise a transistor that is designed to detect the electrical changes in the recess as potential changes. In this respect, the transistor can be integrated into the sensor; for example, the transistor can be formed on the same substrate as the sensor or integrally with the sensor, thus enabling a compact sensor and a simple manufacturing process. The transistor is designed as a field-effect transistor with an insulated gate. The insulated gate can be arranged at least partially in the recess. In this way, an efficient fluid sensor with sufficient sensitivity can be provided, wherein the transistor can also be arranged outside the recess. In embodiments, the fluid sensor can have a chemically sensitive layer that is at least partially arranged in the recess.In this respect, electrical changes caused, for example, by chemical reactions, the passage of ions, physical adsorption, chemical adsorption, etc., can be detected and measured or further processed. As already mentioned above, an operating point of such a transistor, which can occur in self-conducting (normally conducting) or self-blocking (normally blocking) form in exemplary embodiments, can be defined, thus enabling various operating modes of the fluid sensor.

[0018] Another key idea is that in a fluid sensor, an insulated gate of a field-effect transistor is at least partially shielded by an electrode so that electrical changes, e.g. a potential change, which are attributable to a fluid to be analyzed can be detected by the gate and thus the transistor. Embodiments provide a fluid sensor with a transistor which is designed to detect an electrical change caused by a fluid to be analyzed, e.g. a chemically sensitive layer. The transistor is designed as a field-effect transistor with an insulated gate, and the insulated gate and a recess for receiving the fluid to be analyzed are at least partially surrounded by a common shielding electrode. Some embodiments can thus reduce the influence of interference and / or increase the sensitivity of a fluid sensor.The recess can be located outside a substrate on which the transistor is formed and can be located at least partially in the insulated gate.

[0019] In further embodiments, the chemically sensitive layer in the recess forms a boundary layer to the fluid to be examined. In other words, the chemically sensitive layer can be directly exposed to the fluid to be examined, for example when the fluid flows through the recess in the substrate, and thus make electrical changes measurable. In some embodiments, the chemically sensitive layer can surround the fluid to be examined in the recess at least in sections and at least with respect to two spatial directions. In this respect, the chemically sensitive layer and / or the outer electrode can form a passage, channel or trench for the fluid to be examined. In this respect, embodiments can create an arrangement in different layers that can be produced inexpensively using appropriate processes, e.g. thin-film coating processes.

[0020] Some embodiments include the insulated gate and the outer electrode described above. The insulated gate can be at least partially disposed between the chemically sensitive layer and an outer electrode, such that an electric field at the insulated gate can be influenced by the chemically sensitive layer and the gate is at least partially shielded by the outer electrode. In further embodiments, the fluid sensor further comprises at least one insulating layer disposed at least partially between the substrate and the chemically sensitive layer. The insulated gate can be at least partially separated from the chemically sensitive layer and the outer electrode by one or more insulating layers.In this respect, embodiments may comprise several layers, for example a substrate, an outer electrode, an insulating layer, a gate, a further insulating layer, a chemically sensitive layer.

[0021] Some embodiments of the fluid sensor may include a gate oxide layer for the transistor that is thinner than the one or more insulation layers. Some embodiments may thus realize improved sensitivity.

[0022] The recess can have a vertical extent that is at least twice as large as a lateral extent of the recess along other spatial directions. In this respect, the recess can have an elongated shape, for example in the form of a bore, a tunnel, etc. In embodiments, the extent of the recess along a path taken by the fluid to be examined in the recess can therefore be greater than extents of the recess in directions orthogonal to this path. The recess can be designed, for example, in the form of a trench, in the form of a passage, or in the form of a gap. In some embodiments, the recess can be designed as a passage through the substrate from a first side of the substrate to a second side of the substrate, for example as an opening, through-passage, bore, or contact hole (also known as a “via”).

[0023] Another core idea is to provide a passage in a substrate of a fluid sensor, in which passage an electrical change can be detected by means of a chemically sensitive layer. Embodiments therefore create a fluid sensor that has a chemically sensitive layer in a passage of a substrate for receiving a fluid to be examined. The sensor further comprises a transistor that is designed to detect an electrical change in the chemically sensitive layer in the passage caused by the fluid to be examined. Embodiments can therefore provide a fluid sensor for a fluid at low cost. In some embodiments, the passage can be substantially hollow-cylindrical. The transistor can be designed as a field-effect transistor with an insulated gate. The insulated gate can extend at least partially along a wall of the hollow-cylindrical recess of the substrate.The fluid sensor may further comprise an outer electrode that at least partially surrounds the recess, or shields it, or at least reduces external field influences on a field within the recess. The substrate may, for example, be at least part of a semiconductor wafer. Short character description

[0024] Exemplary embodiments are explained in more detail below with reference to the accompanying figures. They show: Fig. 1a shows an embodiment of a fluid sensor from two perspectives with an optional outer electrode; Fig. 1b shows another embodiment of a fluid sensor from two perspectives with an optional chemically sensitive layer; Fig. 1c shows another embodiment of a fluid sensor from two perspectives with an optional insulated gate of a field effect transistor; Fig. 2 illustrates an embodiment of a fluid sensor in the form of a hollow cylinder in a sectional view; Fig. 3 illustrates an embodiment of a fluid sensor in the form of a hollow cylinder in plan view; Fig. 4 shows an embodiment of a fluid sensor with a field effect transistor with a recess in an insulated gate; Fig. 5 shows another embodiment of a fluid sensor with a field effect transistor with a recess in an insulated gate; and Fig. 6 shows a block diagram of an embodiment of a method for examining a fluid. Description

[0025] Various embodiments will now be described in more detail with reference to the accompanying drawings, in which some embodiments are illustrated. In the figures, the thickness dimensions of lines, layers, and / or regions may be exaggerated for clarity.

[0026] In the following description of the attached figures, which show only a few exemplary embodiments, identical reference numerals may designate identical or comparable components. Furthermore, collective reference numerals may be used for components and objects that appear multiple times in an exemplary embodiment or in a drawing, but are described together with respect to one or more features. Components or objects described with identical or collective reference numerals may be identical with respect to individual, several, or all features, for example, their dimensions, but may also be different, unless the description explicitly or implicitly indicates otherwise.

[0027] Although embodiments are susceptible to various modifications and variations, embodiments are illustrated in the figures as examples and will be described in detail herein. It should be understood, however, that embodiments are not intended to limit the specific forms disclosed, but rather, embodiments are intended to cover all functional and / or structural modifications, equivalents, and alternatives within the scope of the invention. Like reference numerals designate like or similar elements throughout the description of the figures.

[0028] Note that an element described as "connected" or "coupled" to another element may actually be directly connected or coupled to the other element, or there may be intervening elements. Conversely, when an element is described as "directly connected" or "directly coupled" to another element, no intervening elements are present. Other terms used to describe the relationship between elements should be interpreted similarly (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments. As used herein, the singular forms "a," "an," "another," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. Further, it is to be understood that terms such as "includes," "including," "comprises," "comprising," "has," and / or "having," as used herein, indicate the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more features, integers, steps, operations, elements, components, and / or groups thereof.

[0030] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as one of ordinary skill in the art to which the embodiments belong. Furthermore, it should be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless expressly defined herein.

[0031] In the following figures, three orthogonal spatial directions can be distinguished (Cartesian coordinate system according to x, y, z), these are indicated on the right edge of the figures. Fig. Figure 1a shows an embodiment of a fluid sensor 100 from two perspectives. The upper illustration shows a sectional view along an axis AB, which is also visible in the plan view shown below. In the embodiment shown in Fig. 1a, the fluid sensor 100 comprises a substrate 80 having a recess 70 for receiving a fluid to be examined. In this and the following embodiments, any substrate 80 can be used. For example, circuit boards, glass, porcelain, etc. are just as conceivable as semiconductor materials, e.g., silicon (Si), germanium (Ge), gallium arsenide (GaAs), indium antimonide (InSb), zinc selenide (ZnSe), or cadmium sulfide (CdS), etc., in various dopings and designs or forms, e.g., as a disk (also known as a wafer). In some embodiments, the substrate 80 is at least part of a semiconductor wafer.

[0032] The fluid sensor 100 is according to the Fig. 1a is designed to detect electrical changes in the recess 70 caused by the fluid to be examined. Accordingly, the dimensions of the recess 70 are selected such that the fluid to be examined can enter or pass through the recess, e.g., the recess 70 can correspond to an opening or trench through the substrate 80, which has a diameter of less than 1 cm, 1 mm, 1 µm, etc. As explained in detail below, a recess 70a of the same dimensions can also be located in a gate of a transistor. The fluid here and below can correspond to a substance that is in liquid or gaseous form or as a plasma and is to be examined, detected, or monitored or controlled for chemical changes, for example.

[0033] This can then be done according to Fig. 1a due to chemical changes caused in the recess 70, which cause electrical changes.

[0034] Here, electrical changes are understood to mean changes in electrical properties. For example, the fluid can cause changes in charge, potential, potential difference, relative dielectricity, currents, voltages, etc. For example, the fluid can form dipoles or alter their formation, so that a change in dipole moments can be detected by the fluid sensor as a measure of spatial charge separation.

[0035] The Fig. 1a illustrates a further embodiment in which the fluid sensor 100 optionally (dashed lines) further comprises an outer electrode 10. The outer electrode 10 at least partially surrounds the recess 70 and is connected or connectable to a reference potential (e.g., ground potential). The outer electrode 10 can influence an electric field inside the recess 70; for example, it can shield the recess 70 from external fields or specify a defined field, e.g., a homogeneous field. In some embodiments, the outer electrode 10 can also form a type of Faraday cage with respect to the recess 70.

[0036] The outer electrode 10 can be formed, for example, by a correspondingly designed or shaped conductor, e.g., by a metal or a metal coating on the substrate 80. In some embodiments, the outer electrode 10 can correspond to a defined doping region of the substrate, e.g., a p- or n-doping of the substrate 80. This defined doping region is defined, for example, by a pn junction from an adjacent substrate region, so that a desired potential can be applied to the defined doping region.

[0037] Fig. 1b shows a further embodiment of a fluid sensor 100 from two perspectives analogous to Fig. 1a. The Fig. 1b shows the fluid sensor as it has already been described in the Fig. 1a, with the substrate 80 and the recess 70, wherein the fluid sensor 100 in the Fig. 1b optionally has a chemically sensitive layer 50. The chemically sensitive layer 50 is at least partially arranged in the recess 70. The exemplary embodiment shows an arrangement of the chemically sensitive layer 50 around the recess 70. In further exemplary embodiments, a partial or section-wise arrangement of the chemical layer 50 in the recess 70 is also conceivable. The chemically sensitive layer 50 is designed to convert, for example, chemical reactions, the passage of ions, physical adsorption, chemical adsorption, changes in dipole moments, etc., into electrical changes, for example by changing the charge state or the dielectric constant.

[0038] Another embodiment of a fluid sensor 100 is shown in Fig. 1c shown from two perspectives. The Fig. 1c shows the fluid sensor as it has already been described in the Fig. 1a, with the substrate 80 and the recess 70. In this exemplary embodiment, the fluid sensor 100 optionally comprises an insulated gate 30 of a field-effect transistor, which is at least partially arranged in the recess 70. For example, a contact lug or a contact of the gate 30 can protrude into the recess 70 or be at least partially surrounded by the recess 70. The gate 30 is then designed to detect electrical changes in the recess 70 and to make them measurable or analyzable via the transistor.

[0039] The Fig. 2 and Fig. 3 illustrate an embodiment of a fluid sensor 100 in the form of a hollow cylinder in a sectional view ( Fig. 2) and in plan view ( Fig. 3), with the section axis AB being illustrated in both views. In the embodiment shown in the Fig. 2 and Fig. 3, the substrate is a Si semiconductor substrate, which in this example is initially p-doped. Generally, embodiments with dopings complementary to those described here are also conceivable. In other embodiments, the substrate may also be n-doped. Fig. 2 and Fig. 3 show the recess 70 in the center, which is designed here as a passage through the substrate 80. In other words, the recess 70 in the embodiment shown is designed as a passage through the substrate 80 from a first side (in Fig. 2 above) of the substrate 80 to a second side (in Fig. 2 below) of the substrate. Furthermore, the Fig. 2, the substrate 80 and the outer electrode 10 are coupled to a reference potential in this embodiment. Electrical coupling of the substrate 80 is achieved here via a p+-doped region.

[0040] In general, in the present embodiment, an operating point of the transistor 90 and thus also of the fluid sensor 100 can be set via the reference potential. In other words, the reference potential can be used to set a specific sensitivity of the channel to potential changes of the gate on the characteristic curve of the transistor 90. In this respect, with a reference potential that corresponds to earthing / mass, a normally off or normally off FET can be essentially switched off, so that it then essentially consumes no power. This can be advantageous, for example, in mobile applications in battery-operated devices with regard to the energy efficiency of the device. In other embodiments, however, the use of normally on or normally conducting FETs is also conceivable. In this respect, the Fig. 2-5 each comprise a fluid sensor 100 which is designed to detect an absolute potential change at an electrode 30 caused by a fluid to be examined.

[0041] In other embodiments, the recess 70 may also be formed in the form of a trench, in the form of a passage, or in the form of a gap, which extend from a main surface of the substrate into the substrate or through the substrate. A main surface of a semiconductor substrate 80 is, for example, a surface of the semiconductor substrate 80 on which further layers may be located, e.g., metal layers, insulation layers, passivation layers, etc. The main surface of such a substrate therefore extends in the lateral direction and is delimited, for example, by edges that are provided by the singulation of individual chips or by boundaries of a wafer. In the embodiments of the Fig. 1a-c would be in the representation of the Fig. 1a-c above and in the Fig. 2 the main interface above, the lower display respectively. Fig. 3 show plan views of the main surface. The main surface can be considered to be essentially flat, e.g., neglecting unevenness resulting from the semiconductor structure or a manufacturing process (e.g., due to the recess). The main surface can therefore also be considered a transition region between the substrate 80 or semiconductor material and any other layers, such as insulation, passivation, or metallization.

[0042] In the examples of the Fig. 1abc-3, the recess 70 has a vertical extension, ie perpendicular to the main surface of the substrate 80. Furthermore, it is assumed that the extension in the vertical direction of the recess 70 is at least twice as large as a lateral extension of the recess 70 along other spatial directions, ie in the lateral direction with respect to the main surface.

[0043] In the Fig. 2 and Fig. 3, the fluid sensor 100 further comprises a transistor 90, which is designed to detect the electrical changes in the recess 70, e.g., as potential changes. The transistor 90 is designed as a field-effect transistor with an insulated gate 30, wherein the insulated gate 30 is at least partially arranged in the recess 70. In other embodiments, other transistor types may also be used, for example, bipolar transistors. The transistor 90 is in the Fig. 2 and Fig. 3 is realized by two n+-doped regions separated by a gate insulation layer 60. The actual gate 30 or gate electrode 30 then lies partially above the gate insulation layer 60, thus influencing the channel between the source and drain (here, n+ regions). Therefore, in the illustrated embodiment, the transistor 90 is arranged outside the recess 70.

[0044] The fluid sensor 100 has in the Fig. 2 and Fig. 3, the sensor further comprises a chemically sensitive layer 50. The chemically sensitive layer 50 is at least partially arranged in the recess 70. The chemically sensitive layer 50 is designed to convert, for example, chemical reactions, the passage of ions, physical adsorption, chemical adsorption, etc., into electrical changes, for example, changes in the charge state or the dielectric constant. These electrical changes then affect the gate 30 and the transistor 90, or its switching or conduction state, so that a chemical change in the fluid to be examined, e.g., ionization or chemical composition, leads to an electrical signal change, which can then be evaluated.Embodiments are not limited to a specific chemically sensitive material for the chemically sensitive layer 50; for example, materials such as tin(IV) oxide (SnO2) change their conductivity under the influence of gas. Other materials include zinc oxide, titanium dioxide, or organic semiconductor materials such as MePTCDI (MePTCDI or DiMePTCDI, N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic diimide). The specific selection of the material for the chemically sensitive layer 50 will therefore depend on the specific application, e.g., which gas or liquid is to be detected, the temperature range in which the sensor is used, the area of ​​application, etc.

[0045] In other words, a chemically sensitive layer 50 can be applied inside the Faraday cage, where charges and / or dipole moments can develop due to gases or liquids, thus changing the potential within. The value of the potential change can be measured, for example, by an insulated, floating electrode or gate 30, which, as in a floating gate FET (FGFET), is connected to the gate of a MOSFET.

[0046] Possible areas of application include safety technology such as explosion protection, methane and carbon monoxide detection in mines, hydrogen detection in fuel cells, gas leak detection (e.g., in natural gas or liquefied petroleum gas supply systems), poisoning protection (e.g., personal carbon monoxide and hydrogen sulfide monitoring), leak detection (e.g., in the monitoring of chemical storage facilities containing volatile organic components, solvents, or coolants), fire detectors (e.g., for fire gas detection using intelligent detectors), drug testing (e.g., breathalyzer tests for road traffic), detection of chemical warfare agents (e.g., explosives or poison gas). Other areas of application include emissions measurement, engine control via lambda probes, vehicle diagnostics, measurement of gaseous emissions in urban traffic, comfort (e.g., indoor air quality), automatic ventilation flaps in cars, building management, extractor hoods, humidity sensors, etc.

[0047] As the Fig. 2 and Fig. 3, the chemically sensitive layer 50 in the recess 70 forms a boundary layer to the fluid to be examined, so that the chemically sensitive layer 50 can provide direct, relatively large-area contact with the fluid to be examined. Furthermore, it can be seen that the chemically sensitive layer 50 surrounds the fluid to be examined in the recess 70, at least in sections and at least in two spatial directions. In other words, Fig. 2 and Fig. 3 distinguish three orthogonal spatial directions (Cartesian coordinate system according to x, y, z) as they are also indicated on the right edge of the figures. In the Fig. 1abc to 3, it can be seen that the recess 70, which here is essentially hollow-cylindrical in shape, surrounds a fluid flowing through it in a type of channel. It can also be seen that the recess 70 has a vertical extent (in the z-direction, perpendicular to the main surface) that is at least twice as large as a lateral extent of the recess 70 along other spatial directions (x, y directions). In other words, it can be seen that the recess extends in the z-direction and that it extends further in the z-direction (at least twice as far) than in the x, y directions.

[0048] In the exemplary embodiment, it can also be seen that the insulated gate 30 is at least partially disposed between the chemically sensitive layer 50 and an outer electrode 10. This arrangement can enable an improved electrical response of the gate 30 to an electrical change in the chemically sensitive layer 50.

[0049] The Fig. 2 and Fig. 3 further show that the fluid sensor 100 in this embodiment comprises at least one insulation layer 20, 40, which is at least partially arranged between the substrate 80 and the chemically sensitive layer 50. The insulated gate 30 is at least partially separated from the chemically sensitive layer 50 and the outer electrode 10 by one or more insulation layers 20, 40, in the embodiment of the Fig. 2 and Fig. 3 by the two insulation layers 20 and 40. The transistor 90 further includes a gate oxide layer 60, which is thinner than the one or more insulation layers 20, 40. This can contribute to improved sensitivity of the transistor 90 or the sensor 100. Oxide layers, for example, are conceivable as insulation / passivation materials, e.g., silicon dioxide, but in other embodiments also silicon nitride, hafnium dioxide, polymers, etc.

[0050] The structure of the Faraday cage 10 consists of the Fig. 2 and Fig. 3 consists of the outer electrode 10, to which a potential is applied from the outside, here a reference potential or ground. This potential defines the at least virtually constant potential inside the cage 10. The "floating electrode" or gate 30 is insulated by a first insulator layer 20 and a second insulator layer 40. The chemically sensitive layer 50, which is responsible for the chemical reaction and is not electrically contacted, is applied to the insulator layer 40. This layer can be insulating, semiconducting, or conductive. The "floating electrode" is connected to the gate 30 of the MOS transistor 90, wherein the area outside the Faraday cage 10 is smaller than the area inside the Faraday cage.In general, it can be assumed that the area outside the Faraday cage 10 should be small to minimize external potential influences and / or edge influences. The gate oxide 60 of the transistor 90 is significantly thinner than the insulation oxides 20 and 40. Any charge shift, work function change, etc., of the chemically sensitive layer 50 inside the cage 10 leads to a potential change. This also changes the potential of the "floating electrode" 30, which controls the source / drain current of the field-effect transistor 90. For conductive liquids, a potential or reference contact can be provided outside the cage 10 to avoid charging effects.

[0051] In addition, the Fig. 2 and Fig. 3 also shows a fluid sensor 100 in which a chemically sensitive layer 50 is arranged in a passage 70 of a substrate 80 for receiving a fluid to be analyzed. The sensor 100 further comprises a transistor 90, which is designed to detect an electrical change in the chemically sensitive layer 50 in the passage 70 caused by the fluid to be analyzed. The passage 70, in this exemplary embodiment, is essentially hollow-cylindrical, with the transistor 90 being designed as a field-effect transistor with an insulated gate 30. The insulated gate 30 extends at least partially along a wall of the hollow-cylindrical recess 70 of the substrate 80. The fluid sensor 100 further comprises an outer electrode 10, which at least partially surrounds the recess 70.

[0052] In the exemplary embodiments, it can further be seen that the area of ​​the gate 30 in the region of the shielded area, ie in the recess 70 and within the outer electrode 10, is larger than its area outside the shielded area. The ratio of these areas can, in exemplary embodiments, determine the influence of external fields on the fluid sensor 100. It can be assumed that within the shielded area, electrical changes in the gate 30 are mainly caused by the fluid, since external influences are essentially shielded. Outside the shielded area, for example in the Fig. 2 and Fig. 3, in the region to the left of the recess 70 in which the gate electrode 30 extends toward the source and drain terminals, i.e., to the actual gate of the FET, this can also be influenced by external fields due to the lack of shielding in this exemplary embodiment. Therefore, in exemplary embodiments, an area of ​​the insulated gate electrode 30 located within the outer electrode 10 or the recess 70 can be larger, e.g., at least twice or three times as large, than an area of ​​the gate electrode 30 located outside the outer electrode 10 or the recess 70.

[0053] The Fig. 2 and Fig. 3 also illustrate a fluid sensor 100 with a transistor 90 and other optional components. Fig. Figure 4 shows an embodiment of a fluid sensor 100 with a transistor 90 having a recess 70a in an insulated gate 30 in a sectional view (see the specified coordinate system). The fluid sensor is designed to detect an electrical change caused by a fluid to be analyzed, e.g., a chemically sensitive layer 50. The transistor 90 is designed as a field-effect transistor with an insulated gate 30, and the insulated gate 30 and a recess 70a for receiving the fluid to be analyzed are at least partially surrounded by a common shielding electrode 10. The recess 70a lies outside a substrate 80 on which the transistor 90 is formed. Fig. 4 further illustrates the gate oxide layer 60 of the transistor. In the embodiment of Fig. 4, the outer electrode 10 is formed, for example, by an n+-doped region in the substrate 80, two contact holes or vias, and an overlying metal layer. These components at least partially enclose the recess 70a. The gate 30 protrudes into the recess 70a and is at least partially shielded by the outer electrode 10. In this embodiment, the recess 70a is formed with respect to the gate 30 and, together with the gate 30, lies outside the substrate 80.

[0054] Fig. 5 shows a further embodiment of a fluid sensor 100 with a field effect transistor 90 with a recess 70a in an insulated gate 30 in a sectional view (cf. specified coordinate system). In the Fig. In the embodiment shown in Figure 5, the transistor 90 is formed on the substrate 80 by means of the n+-doped regions for source and drain already described above, as well as by means of the gate oxide layer 60, which is thinner than the insulation layer 20 located on the substrate 80. The Fig. 5 further shows the gate 30, which in the present case is formed in a cup shape over the substrate 80 and which extends from a region above the gate oxide layer 60 away from the substrate 80.

[0055] The pot-shaped gate 30 is further surrounded by a second insulation layer 40 and lies, at least in this embodiment, between the two insulation layers 20 and 40. As the Fig. 5 shows, the pot-shaped gate 30 is at least partially surrounded laterally by the outer electrode 10. By means of a potential applied to the outer electrode 10, the potential in the pot-shaped gate 30 can be predetermined, ie kept constant, or the interior 70a of the gate 30 can be kept essentially field-free. The innermost layer shows the Fig. 5 furthermore a chemically sensitive layer 50, which fulfils the functions already explained above. In this respect, the Fig. 5 shows a further embodiment in which the recess 70a is formed with respect to the gate 30 and lies outside the substrate 80.

[0056] Fig.6 shows a block diagram of an embodiment of a method for examining a fluid. The method for examining the fluid comprises passing the fluid 112 through a recess 70 of a substrate 80. The method further comprises detecting 114 an electrical change in the recess 70. Such a method can also be carried out automatically, for example, with the aid of a computer program that issues corresponding control commands to valves or other components in order to detect and evaluate the electrical changes in the recess 70, e.g., as potential changes with the aid of the transistor 90.

[0057] The features disclosed in the above description, the following claims and the attached figures can be important and implemented both individually and in any combination for the realization of an embodiment in its various forms.

[0058] Although some aspects have been described in connection with a device, it is understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Similarly, aspects described in connection with or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device.

[0059] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein.

Claims

[1] A fluid sensor (100) with a substrate (80) which has a recess (70) for receiving a fluid to be examined, wherein the fluid sensor (100) further comprises a transistor (90) which is designed to detect an electrical change caused by the fluid to be examined as a potential change in the recess (70), and wherein the fluid sensor (100) further comprises an outer electrode (10), wherein the outer electrode (10) at least partially surrounds the recess (70) and is connected or connectable to a reference potential, wherein the transistor (90) is designed as a field-effect transistor with an insulated gate (30). [2] Fluid sensor (100) according to claim 1, wherein the outer electrode (10) corresponds to a defined doping region of the substrate. [3] Fluid sensor (100) according to claim 1, wherein the insulated gate (30) is at least partially arranged in the recess (70). [4] Fluid sensor (100) according to one of claims 1 to 3, wherein the transistor (90) is arranged outside the recess (70). [5] Fluid sensor (100) according to one of the preceding claims, which has a chemically sensitive layer (50), wherein the chemically sensitive layer (50) is arranged at least partially in the recess (70). [6] Fluid sensor (100) according to claim 5, wherein the chemically sensitive layer (50) in the recess (70) forms a boundary layer to the fluid to be examined. [7] Fluid sensor (100) according to one of claims 5 or 6, wherein the chemically sensitive layer (50) surrounds the fluid to be examined in the recess (70) at least in sections and at least with respect to two spatial directions. [8] The fluid sensor (100) of any one of claims 5 to 7, further comprising the insulated gate (30) of claim 3 and the outer electrode (10) of claim 2, wherein the insulated gate (30) is at least partially disposed between the chemically sensitive layer (50) and the outer electrode (10). [9] Fluid sensor (100) according to one of claims 5 to 8, further comprising at least one insulation layer (20; 40) arranged at least partially between the substrate (80) and the chemically sensitive layer (50). [10] Fluid sensor (100) according to claims 8 and 9, wherein the insulated gate (30) is at least partially separated from the chemically sensitive layer (50) and the outer electrode (10) by the one or more insulation layers (20; 40). [11] The fluid sensor (100) of claim 9 or 10, further comprising a gate oxide layer (60) of the transistor (90) that is thinner than the one or more insulation layers (20;40). [12] Fluid sensor (100) according to one of the preceding claims, wherein the recess (70) has a vertical extent which is at least twice as large as a lateral extent of the recess (70) along other spatial directions. [13] Fluid sensor (100) according to one of the preceding claims, wherein the recess (70) is formed in the form of a trench, in the form of a passage, or in the form of a gap. [14] Fluid sensor (100) according to one of the preceding claims, wherein the recess (70) is formed as a passage through the substrate (80) from a first side of the substrate (80) to a second side of the substrate. [15] Fluid sensor (100) according to one of the preceding claims, wherein the recess (70) corresponds to a passage, wherein the passage is formed in the shape of a hollow cylinder, wherein the transistor (90) is formed as a field effect transistor with an insulated gate as the electrode (30), wherein the insulated gate extends at least partially along a wall of the hollow cylindrical recess (70) of the substrate (80). [16] Fluid sensor (100) according to one of the preceding claims, wherein the substrate (80) is at least a part of a semiconductor wafer. [17] A fluid sensor (100) comprising a transistor (90) configured to detect an electrical change caused by a fluid to be examined, wherein the transistor (90) is configured as a field-effect transistor with an insulated gate (30), and the insulated gate (30) and a recess (70a; 70) for receiving the fluid to be examined are at least partially surrounded by a common shielding electrode (10). [18] The fluid sensor (100) according to claim 17, wherein the recess (70a) is located outside a substrate (80) on which the transistor (90) is formed. [19] Method for examining a fluid with a fluid sensor (100) according to claim 1, comprising the method steps Passing the fluid (112) through the recess (70) of the substrate (80); and Detecting (114) the electrical change as potential changes in the recess (70).

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