Electrochemical sensor and method for its manufacture

Description

[0001] The invention relates to an electrochemical sensor and a method for its production. In particular, the invention relates to the structure of a sensor in the area that is in contact with the measuring medium during use of the electrochemical sensor.

[0002] Conventional electrochemical or potentiometric sensors, particularly those for measuring the pH value of a measuring medium, are designed as so-called glass electrodes. They usually have a glass shaft with a roughly spherical or hemispherical glass membrane made of electrochemically active pH glass, which is firmly connected, i.e. fused, to the glass shaft at the end of the shaft that faces the measuring medium or is immersed in the measuring medium during use. The measuring rod formed in this way is filled with a buffer solution. Depending on the pH value of the measuring medium, a potential difference develops across the glass membrane. This potential difference is measured using a metal electrode immersed in the buffer solution as a discharge element, compared to the equilibrium potential of a reference electrode as a reference point.

[0003] Furthermore, so-called ion-sensitive field-effect transistor sensors (ISFET) are known, in which the pH value of a measuring medium or the concentration of a specific ion, for which the sensor has a sensitive layer, is measured by a change in the source-drain current of the transistor.

[0004] In contrast to conventional potentiometric sensors, the ISFET sensor has a largely flat or planar measuring element as the sensitive area, which is facing the measuring medium during use.

[0005] US 6,464,940 B1 describes the design, manufacture, and measuring principle of a pH measuring cell designed to determine extremely small volumes of measuring medium, i.e., the size of a drop. An annular wall made of Pyrex glass serves as a reservoir for the measuring medium, arranged on an insulating layer applied to a semiconductor substrate and coated with a metal electrode so that the latter can come into contact with the measuring medium. The side of the substrate opposite the reservoir is also coated with a metal electrode. Thus, at a frequency of around 1 MHz, a capacitance-voltage characteristic can be measured between the electrode that is in contact with the measuring medium during use and an electrode attached to the back of the semiconductor substrate, which varies depending on the pH value of the measuring medium.

[0006] While the production of conventional electrochemical glass sensors is complex and the glass measuring cells must be produced individually, they also exhibit high sensitivity and long-term stability. ISFET sensors, or those with a flat or planar measuring element, as disclosed, for example, in US Pat. No. 6,464,940 B1, can be manufactured on a large scale using wafer technology. However, in terms of stability and resistance to aggressive media, ISFET sensors do not achieve the values ​​inherent in electrochemical glass sensors. Compared to electrochemical glass sensors, ISFET sensors exhibit less favorable drift stability and are less suitable for process measurement technology.

[0007] Electrochemical sensors are therefore desirable whose measuring element, for example the pH-sensitive glass membrane in electrochemical glass sensors, is designed as a flat measuring element; since the sensor elements having such a measuring element can be produced on an industrial scale using wafer technology.

[0008] It has been shown that in an electrochemical sensor with a flat measuring element, which is installed in a sensor shaft in conjunction with a sensor element, measurement errors can occur if a sealing element, which prevents the penetration of a medium during use—usually a measuring medium or a cleaning medium—rests directly on the measuring surface of the measuring element. Such measurement errors can occur in the form of reduced slope or a long response time, meaning the stability and reproducibility of the electrochemical sensor could suffer.

[0009] The object of the invention is to propose an electrochemical sensor with a precisely defined measuring surface, i.e., a defined area, in terms of its size or area. This means that when the sensor is immersed in a measuring or cleaning medium during use, the measuring element of the sensor has a precisely defined wetted area, while simultaneously ensuring a good seal between the sensor and the measuring or cleaning medium.

[0010] This object is achieved by an electrochemical sensor according to claim 1 and a manufacturing method of the electrochemical sensor according to claim 11, including the incorporation of a sensor element into a sensor shaft. Advantageous embodiments are set forth in the dependent claims.

[0011] An electrochemical sensor has a sensor element with a measuring surface that, during use, faces a measuring medium. This sensor element comprises a flat measuring element. Furthermore, the electrochemical sensor is provided with a sensor shaft that has a window with a frame at its end facing the measuring medium during use, and into which sensor shaft the sensor element is installed in the region of the window. The electrochemical sensor has an annular sealing element that is arranged between the sensor element and the frame. An insulator element is firmly and inseparably connected to the measuring element of the sensor element, leaving the measuring surface free or cut out. The sealing element, which protects the sensor against the penetration of the measuring medium, is sealingly arranged between the insulator element and the frame.

[0012] In the present context, a flat measuring element is to be understood as a substrate provided with a flat sensitive area forming a measuring surface on one side - for example in the form of a sensitive layer as sensitive material - or a disc-shaped measuring element made of sensitive material that is largely flat on both sides.

[0013] In the electrochemical sensor according to the invention, an insulator element consisting of insulating material forms a common structure with the measuring element, ie is inseparably connected to it.

[0014] The sensing element and the insulator element are not necessarily homogeneous. They can also be constructed in multiple layers; for example, the sensing element can comprise one or more sensitive layers.

[0015] The measuring element and the insulator element form the sensor element, optionally with the inclusion of further elements necessary for the function of an electrochemical sensor - which, however, are not the subject of the invention.

[0016] A sealing element serves to seal the interior of the electrochemical sensor's sensor shaft against a measuring or cleaning medium, into which the sensor is immersed at one end during use. The sealing element comprises a chemically and thermally resistant polymer or elastomer material.

[0017] The release or recess of a measuring surface of the measuring element refers to the area that faces the measuring environment of the sensor and is in contact with the measuring medium during use.

[0018] The design of an electrochemical sensor according to the invention enables large-scale production of the sensor element as well as the construction of a wafer-based mold suitable for installation in a sensor shaft. In particular, the insulator element, which is inseparably bonded to the measuring element in the area of ​​its contact with the measuring medium, ensures a precisely defined measuring surface in contact with the measuring medium during use, i.e., a medium-wetted surface. Furthermore, the insulator element, together with the annular sealing element, ensures a good seal by preventing the measuring medium from penetrating between the sealing element and the measuring surface. This ultimately results in improved sensor slope and increased long-term stability.

[0019] The sensor element of the electrochemical sensor according to the invention comprises a flat, planar disc made of electrochemically active pH glass as the measuring element. However, the measuring element can also be designed as a planar layer or layer structure comprising electrochemically active pH glass.

[0020] In an advantageous development of the electrochemical sensor, the insulating element comprises a thermally and chemically resistant insulating glass whose thermal expansion coefficient is matched to that of the measuring element, in particular, identical to the thermal expansion coefficient of the measuring element. An identical expansion coefficient is understood here to mean one with a deviation between the insulating glass and the pH glass of less than 5e -7< / K.

[0021] Alternatively, the insulator element can comprise an insulator layer, particularly made of silicon nitride, applied by physical or chemical deposition processes. In this case, due to the thinness of such an insulator layer, the thermal expansion coefficient of the insulator element does not have to correspond to that of the measuring element.

[0022] In another embodiment, the sensor shaft is cylindrical, and the window, and thus the clearance or recess, is located on the end face of the sensor shaft. This creates an easy-to-handle electrochemical sensor.

[0023] In a further embodiment, the sensor shaft is cylindrical and the window is arranged in a flattened region of the cylinder jacket of the sensor shaft.

[0024] Depending on the arrangement of the window and thus the clearance or recess on the end face or in a flattened area of ​​the cylinder surface of the sensor shaft, the measuring surface of the measuring element can take on various shapes. It can be circular, elliptical, or rectangular. The requirement for a larger measuring surface than a circular one, as is usually the case with a sensor element built into the end face of the sensor shaft, can favor an elliptical or rectangular shape of the measuring surface. However, it is always necessary that the clearance area is slightly smaller than the sealing surface to prevent direct contact between the seal and the active measuring surface.

[0025] Due to the embodiment of an electrochemical sensor according to the invention, in which the sensor shaft is made of thermally and chemically resistant metallic material or plastic, a robust, largely unbreakable electrochemical sensor is made possible, which can also be used in harsh chemical environments and is autoclavable.

[0026] The method for producing an electrochemical sensor according to the invention with a flat sensitive measuring surface facing a measuring medium during use comprises the following steps: Producing an inseparable connection of a wafer comprising a sensitive material with an insulating material to form a wafer with at least two layers; generating a predefined thickness by processing the sensitive material and, if applicable, the insulating material connected thereto; structuring the insulating material while exposing a measuring surface in the sensitive material to form one or more measuring elements, wherein the measuring element comprises a flat, planar disc made of electrochemically active pH glass or a flat, planar layer or layer structure comprising electrochemically active pH glass; cutting the wafer with at least two layers from connected sensitive material and structured insulating material in the regions of insulating material present to form sensor elements provided with insulating elements;Installation of a sensor element produced in this way into a shaft, wherein a sealing element is sealingly inserted between the insulator element and a casing at the end of the sensor shaft facing the measuring medium during use.

[0027] This process allows for large-scale production of the sensor elements and provides a cost-effective electrochemical sensor.

[0028] In an advantageous embodiment of the method, the sensitive material comprises an electrochemically active pH glass and the insulator material comprises a thermally and chemically resistant insulator glass with a thermal expansion coefficient adapted to the sensitive material, in particular identical to it, wherein the insulator material is inseparably bonded to the sensitive material by means of "direct bonding" or "fusion bonding" to form a wafer with at least two layers.

[0029] In an alternative embodiment of the method, the insulating material comprises an insulating layer, in particular made of silicon nitride, which is applied to the sensitive material by means of a physical or chemical deposition process, bonded to it to form an at least two-layer wafer, and then patterned. In a further alternative, the insulating layer applied by means of a physical or chemical deposition process can be patterned in the form of insulating elements directly during deposition using a mask.

[0030] The structuring of the insulator material on the sensitive material can advantageously be carried out by means of etching technology, in particular wet chemically with hydrofluoric acid or by means of plasma etching.

[0031] The invention is explained below using the highly schematic drawings. They show: Fig. 1 shows an electrochemical sensor in the form of a pH measuring rod with a reference electrode in its overall view; Fig. 2 shows a partial view of an electrochemical sensor in the form of a pH measuring rod, with a sensor element built into the sensor shaft in a first embodiment; Fig. 3A shows a partial view of another embodiment of an electrochemical sensor in the form of a pH measuring rod, with a sensor element built into the sensor shaft; and Fig. 3B shows a measuring element of a sensor element connected to an insulator element according to Fig. 3A ; Fig. 4 the steps for manufacturing and installing a sensor element into a sensor shaft.

[0032] In the following, the invention will be described by way of example using a pH sensor with a sensor element having a flat measuring surface, for example made of electrochemically active pH glass.

[0033] It should be noted at this point that the individual components of the various embodiments of electrochemical sensors in the following figures are not drawn to scale.

[0034] Figure 1 shows an electrochemical sensor 1 in a highly schematic representation. The electrochemical sensor 1 shown forms a measuring rod, which, in conjunction with a reference electrode 16, is used to determine the pH value of a measuring medium. The sensor 1 and the reference electrode 16 are connected to a transmitter 17 via a line (shown in dashed lines in the figure).

[0035] The electrochemical sensor 1 has a window 13 at its end pointing downwards in the figure, in which a sensor element 15 is arranged. The sensor element 15 comprises a measuring element 2 and has, among other things, a flat layer, i.e. a flat surface or membrane made of electrochemically active pH glass. Alternatively, the measuring element 2 can also comprise a disc made of pH glass that is flat on both sides. The sensor element 15 is built into a sensor shaft 4. When the electrochemical sensor 1 is in use, it is partially immersed in a measuring medium 5, i.e. at least in the area comprising the window 13 with the sensor element 15, with a measuring surface 8 of the measuring element 2, forming a medium-contacting surface, facing the measuring medium 5. The electrochemical sensor 1 has a sensor head 3 at its end opposite the sensor element 16, which sensor head contains part of the sensor electronics.The latter is connected to a contact 6 via a line 7 for transmitting a measurement signal. Further components serving to detect the measurement signal can be arranged on the sensor element 15 inside the sensor shaft 4. However, these are not the subject of the present invention and will therefore not be discussed further below.

[0036] In Figure 2 is a sectional view of a partial view of the measuring medium 5 in use (see Fig. 1) facing end of the electrochemical sensor 1. The sensor element 15 built into the sensor shaft 4 can have a measuring element 2 made of electrochemically active pH glass. It is crucial that the medium-contacting surface of the measuring element 2 is flat. Advantageously, the measuring element 2 is designed as a flat disk. The electrochemical sensor 1 is sealed against the measuring medium 5 by means of an elastic sealing element 9. The sealing element 9 can preferably be formed as a sealing ring with a round or flat profile made of a chemically and thermally resistant polymer, such as PTFE (polytetrafluoroethylene), or an elastomer, in particular a perfluoroelastomer (FFKM). In addition to a circular shape, such a sealing ring can also take on other shapes, for example, be elliptical or rectangular.

[0037] An insulator element 10 is arranged between the sealing element 9 and the measuring surface 8 of the electrochemical sensor 1, which is in contact with the measuring medium 5 during use. This insulator element 10 has a structure with a precisely defined geometrical extent, medium-contacting clearance of the measuring surface 8 of the measuring element 2 during use. Figure 2 In the arrangement shown, the insulator element 10 is preferably annular, thus forming a circular clearance of the measuring surface 8 of the measuring element 2. The insulator element 10 is inseparably connected to the measuring element 2 by the so-called wafer bonding process, also called direct bonding or fusion bonding. This bonding process is sufficiently known from the MEMS packaging or microfluidics field and will not be explained further here.

[0038] In the case of a pH sensor with a flat measuring element 2 made of electrochemically active pH glass, the insulator element 10 is made of a similar material, namely an insulating glass, with a thermoelectric expansion coefficient adapted to the thermal expansion coefficient of the pH glass, in particular essentially the same. Due to the inseparable bond between the material of the measuring element, i.e., the sensitive material, and the material of the insulator element, i.e., the insulating material, the sensor is made of at least two-layer wafer material.

[0039] The sensor shaft 4 is preferably made of metal, for example, stainless steel, titanium, or a chemically and thermally resistant hard polymer material, for example, PEEK, PVDF, or PFA (perfluoroalkoxy) or a comparable fluoropolymer, or even of a composite material. At its end immersed in the measuring medium during use, it has a bezel 11 extending toward the interior of the shaft. The dimensions of the sensor shaft 4 can be, for example, 12 mm for the diameter, 1 mm for the wall thickness, and the bezel 11 can extend approximately 1 mm toward the interior of the shaft. Of course, electrochemical sensors with different dimensions can also be manufactured.

[0040] The sealing element 9 is arranged sealingly between the enclosure 11 and the insulator element 10, i.e. the polymer or elastomer ring is slightly deformed by pressure between the enclosure 11 and the insulator element 10 in order to ensure the tightness of the electrochemical measuring probe 1 at its end immersed in the measuring medium or cleaning medium during use.

[0041] By fully supporting the sealing element 9 on the insulator element 10 instead of directly supporting the measuring element 2, it is prevented that, even with a complete sealing effect, measuring medium could be present between the measuring surface 8 and the elastic sealing element 9, which would lead to an undefined measuring surface 8. The solution according to the invention thus provides a measuring surface 8 with a precisely defined extent, which is not disturbed by edge effects and / or exchange effects in the sealing area.

[0042] Alternatively to an insulator element 10, which consists of a insulating, non-sensitive glass with a measuring element 2 made of If the measuring element 2 is manufactured from electrochemically active pH glass with a thermal expansion coefficient adapted to the sensor's specific needs, a layer produced by physical or chemical deposition processes, for example, from silicon nitride, can also form the insulator element 10. Due to the typical silicon nitride layer thicknesses of approximately 0.1 to 0.5 micrometers, no adaptation of the thermal expansion coefficients of the electrochemically active pH glass of the measuring element 2 and the insulator element 10 is necessary. Other insulating materials, such as silicon oxide, aluminum oxide, and the like, can also be considered for such applied insulator elements 10. Coatings with chemically and thermally resistant polymer materials are also conceivable.

[0043] The Figures 3A and 3Bshow partial views of another embodiment of an electrochemical sensor 101, with a sensor element 115 built into the sensor shaft 104: Figure 3A in a sectional drawing along the sensor shaft 104 and Figure 3B the measuring element 102 connected to the insulator element 110 in plan view.

[0044] In this embodiment, the sensor shaft 104 has, at its end facing the measuring medium 5 during use, a flattened area 112 with a window 113 on one side, in which the sensor element 115 is arranged. This sensor element 115, which is installed in the side wall of the sensor shaft 104 by means of a holding device 14, can have a measuring element 102 with a shape deviating from a circular shape, for example, oval or rectangular with rounded corners or the like. This embodiment enables the presence of a larger measuring surface 108 compared to the construction according to Figure 2, in which the sensor element 2 is installed transversely to the cylinder axis of the sensor shaft 4.

[0045] Also in the Figures 3A and 3B In the embodiment shown, an insulator element 110 is arranged between the sealing element 109 and the measuring surface 108 in contact with the measuring medium 5, which is inseparably connected to the measuring element 102. The corresponding insulator element 110 can be designed as an oval ring in this embodiment or, as in Figure 3B As shown, apart from the oval-shaped clearance of the measuring surface 108, the entire edge area of ​​the measuring element 102 is covered. It is important that the sealing element 109 rests completely on the insulator element 110, and that the measuring surface 108 resulting from the clearance is precisely defined in its size and extent.

[0046] The Figure 4illustrates by way of example the steps for manufacturing and installing the sensor element 15 in the sensor shaft 4 in the embodiment of an electrochemical sensor according to Figure 2 and for an insulator element 10 made of chemically and thermally resistant material connected to the measuring element 2 by means of wafer technology Isolator In step 20, a wafer approximately 50 to 100 mm in diameter made of electrochemically active pH glass with a thickness of 0.3 mm to 1.2 mm, preferably 0.6 mm, is bonded by direct bonding or fusion bonding to a wafer of the same size made of chemically and thermally resistant insulating glass with an adapted, in particular identical, thermal expansion coefficient. The aforementioned methods of so-called wafer bonding are known and therefore will not be described in detail.

[0047] After the formation of such an inseparably connected at least two-layer wafer from the measuring element 2 and the insulator element 10, the thickness of both layers of the wafer is reduced in step 30 by grinding and subsequent polishing: to approximately 0.1 mm for the insulator glass and approximately 0.1 to 0.2 mm for the pH glass.

[0048] Subsequently, in step 40, the insulator glass is structured by means of wet-chemical etching, a dry etching process, or a mechanical process such as powder plating or fluid jet polishing, and using masks. This creates a release of the pH glass in defined areas, creating precisely defined measuring surfaces 8 for the respective measuring elements 2 on the at least two-layer wafer. At the same time, the insulator glass remains in place in the edge areas in order to form the insulator elements 10 as a component of the sensor elements 15 after they have been separated.

[0049] In step 50, the separation into sensor elements 15 with the associated insulator elements takes place. They are preferably cut, for example by laser or diamond cutting, and if necessary, ground into a suitable shape. The cutting takes place in the areas of existing insulator material and into a shape suitable for installation in a sensor shaft 4, e.g., circular for a sensor according to Figure 2 or rectangular for a sensor according to Figure 3B .

[0050] A sensor element 15 is installed in step 60, possibly after further processing or the addition of further components that are necessary to establish the functionality of a sensor 1, into a sensor shaft 4, so that the insulator element 10 with the sensor 1 immersed in a measuring medium 5 in case of use faces the measuring medium 5. In this case, a sealing element 9 is sealingly arranged between a frame 11 and the insulator element 10, i.e. the sensor element 15 with the measuring element 2 and the insulator element 10 is held in place by controlled pressing in of a holding device 14 in the interior (see Figure 3A ) of the sensor shaft 4.

[0051] The production of a sensor that has an insulating layer created by physical or chemical deposition processes, such as a silicon nitride layer, is carried out in a similar manner. The coating process is preferably PECVD (plasma-enhanced chemical vapor deposition). The etching process for creating the exposed area is carried out by plasma etching.

[0052] Alternatively, the areas of the release could already be covered by masks on the wafer made of sensitive material and the insulator material - in this case silicon nitride - could be vapor-deposited or deposited in the same structured manner during application, e.g. by means of PVD (physical vapor deposition).

[0053] The invention has been shown and described with reference to preferred embodiments. However, other embodiments and developments of the invention not detailed here are also intended to be encompassed within the scope of protection. For example, when structuring the insulator material of the wafer, it is conceivable to create various patterns in the exposure, for example, islands and the like. List of reference symbols

[0054] 1, 101Electrochemical sensor 2, 102Measuring element 3Sensor head 4, 104Sensor shaft 5Measuring medium 6Contact 7Cable 8, 108Measuring surface 9, 109Sealing element 10, 110Insulator element 11, 111Bezel 112Flattened area of ​​the sensor shaft 104 13, 113Window 14Holding device 15, 115Sensor element 16Reference electrode 17Transmitter 20Wafer bonding 30Adjustment of the wafer thickness 40Structuring 50Separation 60Installation

Claims

1. An electrochemical sensor (1, 101), having a sensor element (15, 115) with a measuring surface (8, 108) facing a measuring medium (5) in use, which sensor element (15, 115) comprises a planar measuring element (2, 102); a sensor shaft (4, 104) having an aperture (13, 113) with a bezel (11, 111) at its end facing the measuring medium (5) in use, and in which sensor shaft (4, 104) the sensor element (15, 115) is installed in the area of the aperture (13, 113); an annular sealing element (9, 109) which is arranged between the sensor element (15, 115) and the bezel (11, 111); wherein the measuring element (2, 102) has a flat, planar disk of electrochemically active pH glass or has a flat, planar layer or layer structure comprising electrochemically active pH glass; wherein the sensor element (15, 115) has an insulator element (10, 110) which is firmly and inseparably connected with the measuring element (2, 102), exposing the measuring surface (8, 108); and wherein the sealing element (9, 109) is arranged between the insulator element (10, 110) and the bezel (11, 111) in a sealing manner, protecting the electrochemical sensor against the ingress of measuring medium (5).

2. The electrochemical sensor (1, 101) according to claim 1, characterized in that the insulator element (10, 110) has a thermally and chemically resistant insulator glass whose coefficient of thermal expansion is substantially identical to the coefficient of thermal expansion of the measuring element (2, 102).

3. The electrochemical sensor (1, 101) according to claim 1, characterized in that the insulator element (10, 110) has an insulator layer, in particular of silicon nitride, applied by means of physical or chemical deposition methods.

4. The electrochemical sensor (1, 101) according to any one of claims 1 to 3, characterized in that the sensor shaft (4, 104) is cylindrical and in that the aperture (13, 113) is arranged on the end face of the sensor shaft (4, 104).

5. The electrochemical sensor (1, 101) according to any one of claims 1 to 4, characterized in that the sensor shaft (4, 104) is cylindrical and in that the aperture (13, 113) is arranged in a flattened area (112) of the lateral surface of the cylinder of the sensor shaft (4, 104).

6. The electrochemical sensor (1, 101) according to claim 5, characterized in that the measuring surface (8, 108) of the measuring element (2, 102) is of circular or elliptical or rectangular shape.

7. The electrochemical sensor (1, 101) according to any one of claims 1 to 6, characterized in that the sensor shaft (4, 104) is made from thermally and chemically resistant metallic material or from thermally and chemically resistant plastic material.

8. The electrochemical sensor (1, 101) according to any one of claims 1 to 7, characterized in that the sealing element (9, 109) has a ring made of elastic polymer material or of an elastomer.

9. A method for fabrication of an electrochemical sensor (1, 101) with a planar measuring surface (8, 108) facing a measuring medium (5) in use, having the steps of: • fabricating an inseparable bond between a wafer having sensitive material and insulator material to form an at least two-layer wafer (20); • producing a predefined thickness by machining the sensitive material and, if applicable, the bonded insulator material (30); • structuring the insulator material by exposing or leaving blank a measuring surface (8, 108) in the sensitive material to form a measuring element (2, 102) (40), wherein the measuring element (2, 102) has a flat, planar disk made of electrochemically active pH glass or a flat, planar layer or layer structure, which comprises electrochemically active pH glass; • cutting the at least two-layer wafer of bonded sensitive material and structured insulator material in the areas of existing insulator material (50) to form sensor elements (15, 115) provided with insulator elements (10, 110); • installing a sensor element (15, 115) produced in this way in a sensor shaft (4, 104), wherein a sealing element (9, 109) is introduced (60) in a sealing manner between the insulator element (10, 110) and a bezel (11, 111) at the end of the sensor shaft (4, 104) facing the measuring medium (5) in use.

10. The method according to claim 9, wherein the sensitive material has an electrochemically active pH glass and wherein the insulator material has a thermally and chemically resistant insulator glass with a coefficient of thermal expansion identical to the sensitive material, which insulator material is inseparably bonded to the sensitive material by means of direct bonding or fusion bonding to form an at least two-layer wafer.

11. The method according to claim 9, wherein the insulator material comprises an insulator layer, in particular of silicon nitride, which is applied to the sensitive material by means of physical or chemical deposition methods and is bonded thereto to form an at least two-layer wafer.

12. The method according to claim 11, wherein the insulator layer applied by means of physical or chemical deposition methods is produced directly during deposition by a mask and in a structured manner in the form of insulator elements.

13. The method according to any one of claims 9 to 11, wherein the insulator material on the sensitive material is structured by means of etching technique, in particular wet-chemically with hydrofluoric acid or by means of plasma etching.