Resistor layout for pressure sensor

Abstract

The invention relates to a resistor layout (1) for a Wheatstone bridge comprising four electrical resistance elements (2, 3), wherein the structures of the four resistance elements are arranged concentrically around a common center point (M) and extend in a radial and a tangential direction to the center point, wherein the first resistance elements extend tangentially around the center point by a defined angle α and the second resistance elements extend tangentially around the center point by a defined angle β.

Description

[0001] The present invention relates to a resistor layout, the use of a resistor layout for a pressure sensor and a pressure sensor.

[0002] Sensor elements with a sensitive electrical layer are known from the prior art, particularly from US patent US 11 378 478 B2.

[0003] Due to the manufacturing process, such sensor elements often have membranes with thickenings in the center of the circular diaphragm, which influence the measurement result. The thickening of the diaphragm has a particularly local impact on its deflection under pressure.

[0004] Exemplary resistor layouts for pressure sensors according to the state of the art are also known from DE 10 2011 109 461 A1 and DE 10 2018 121 294 A1. An alternative solution for a pressure sensor is also known from JP H10 - 90 093 A.

[0005] One object of the present invention is therefore to position the resistors on the surface of the sensor element in a suitable manner in order to achieve the highest possible sensitivity.

[0006] The problem is solved by the embodiments of the invention.

[0007] The invention is defined by the claims.

[0008] The invention relates in particular to a resistor layout (hereinafter sometimes referred to simply as "layout") for a Wheatstone bridge (hereinafter sometimes referred to simply as "bridge" or "bridge", always meaning the Wheatstone bridge). In other words, the invention relates to a Wheatstone bridge, wherein the resistor elements of the bridge are arranged in a defined configuration.

[0009] The measuring bridge according to the invention comprises four electrical resistance elements (hereinafter also referred to as "elements"), wherein two of the resistance elements form two parallel-connected electrical voltage dividers. Thus, one voltage divider consists of two resistance elements. The two voltage dividers also form two parallel electrical conductors. All four elements form the measuring bridge according to the known principle of the Wheatstone bridge.

[0010] The first two of the four resistor elements each have the same structure and preferably the same length. Likewise, the second two of the four resistor elements, which are not the first elements, each have the same structure. The first and second resistor elements have different structures.

[0011] Both of the two voltage dividers each comprise a first and a second resistive element. The first and second resistive elements are connected in parallel in each case. That is, a first resistive element in the first voltage divider is arranged in parallel to a second resistive element in the second voltage divider, or vice versa. This corresponds to the well-known principle of the Wheatstone bridge.

[0012] The structures of the four resistance elements are arranged and structured concentrically around a common center point according to the layout of the invention. This means that the structures of the resistance elements are also aligned concentrically towards the common center point and only have sections that are oriented radially or tangentially to the center point.

[0013] Thus, when using the resistor layout in a sensor according to the invention, the influence of radial or tangential mechanical stresses on the measurement result of the sensor can be directly adjusted.

[0014] The first resistance elements extend tangentially around the center point at a defined angle α, and the second resistance elements extend tangentially around the center point at a defined angle β. The resistance elements thus extend within circular sectors around the common center point, leaving the area immediately surrounding the center of the circle unobstructed. Angles α and β are the central angles that define the extent of the circular sectors. Angles α and β are each greater than 0° and less than 180°.

[0015] According to one embodiment, angles α and β are arranged with maximum offset, thus minimizing their overlap. Therefore, when using this layout, different areas of a deformation body, such as a membrane (see below), can be covered by the resistance elements.

[0016] According to one embodiment, the two first resistance elements and the two second resistance elements are each arranged and structured in an axially symmetrical manner relative to each other.

[0017] According to one embodiment, the two first resistance elements and the two second resistance elements are each arranged and structured in a rotationally symmetrical manner relative to each other.

[0018] According to one embodiment, the two first resistance elements and the two second resistance elements are each arranged and structured in a way that is both axially symmetric and rotationally symmetric to each other.

[0019] The axes of symmetry each pass through the common center point, and the point of symmetry is the common center point.

[0020] According to one embodiment, the first resistance elements are arranged closer to the common center point than the second resistance elements and thus serve, for example, to detect mechanical stresses that occur further away from the center point.

[0021] “Symmetrically structured” here means that the structures of the resistance elements, e.g. the meander structures executed later, are also designed and constructed symmetrically to each other.

[0022] Each of the four electrical resistance elements is designed as a meander structure with the same meander length.

[0023] The meandering structures each have sections in the tangential and radial directions, which are connected by a defined number of bends by 90°, i.e. from the tangential to the radial direction.

[0024] According to a preferred embodiment, the meander structures each have exclusively sections in the tangential and radial directions, which are connected by a defined number of bends by 90°, i.e. from the tangential to the radial direction.

[0025] The meandering structures each have the same width, which is preferably constant along the entire meandering structure.

[0026] The meandering structures each have the same height, which is preferably constant along the entire meandering structure.

[0027] Height and width are dimensions always defined in directions perpendicular to the length of the meandering structure. Height is the dimension in the direction of a deformation body on which the resistance layout is applied.

[0028] The meandering structures are each internally symmetrical. The axis of symmetry preferably runs through the center point.

[0029] According to one embodiment, the tangential sections of the first resistance elements are longer than the radial sections, so that when used as a sensor, the first resistance elements primarily detect tangential deformations or tangential mechanical stresses. In this application, the tangential stresses are always positive when the deforming body is stretched.

[0030] According to one embodiment, the first two resistance elements are each designed as double meanders.

[0031] A double meander comprises two meander parts, whereby the two meander parts of the double meander are axially symmetric to each other.

[0032] Preferably, the two meander sections of the double meander are connected by a tangential section that is located closest to the center point in the meander structure.

[0033] The meander sections are preferably arranged concentrically to the center point and rotationally symmetrical around the center point with respect to the other first resistance element, which also has a double meander structure.

[0034] According to one embodiment, all tangential sections of a meander part lie next to each other in a radial direction, and all tangential sections of a meander part, except for the outermost tangential section of the meander part, extend around the center point by the same angle γ.

[0035] The angle γ is smaller than α / 2 (half of α). By definition, the angle γ is greater than 0° and less than 90°.

[0036] "Outside" is the side facing away from the center, "inside" is the side facing the center.

[0037] According to one embodiment, the outermost sections of the first resistive elements are tangential sections whose length is adapted so that they contact radial conductor tracks via 90° bends, which establish the contact between the first and second resistive elements. The electrical resistance of the conductor tracks is added to the electrical resistance of the resistive elements.

[0038] According to one embodiment, all radial sections of the first resistive elements have the same length. The influence of radial deformations or radial mechanical stresses on the electrical resistance is thus easily scalable, in particular by adjusting the number of bends or radial sections, or by adjusting the angle γ. If the angle γ is larger, the influence of the tangential stresses increases; if the angle γ is smaller, the influence of the radial stresses on the first resistive elements increases. With a larger angle γ, the length of the entire meandering structure or the entire resistive element also increases, and the resulting electrical resistance therefore becomes greater.

[0039] According to one embodiment, the radial sections of the second resistance elements are longer than the tangential sections, so that when used as a sensor, the second resistance elements primarily detect radial deformations or radial mechanical stresses. If the tangential stresses are positive, the second resistance elements are preferably arranged in accordance with the Wheatstone bridge such that negative radial stresses are detected, which, for example, in the application shown in the figures, occur primarily in the outer regions of the deformed body (see also the diagrams in the Fig. 6 and Fig. 7).

[0040] According to one embodiment, all radial sections of the second resistance elements have the same length. Preferably, these lie next to each other in the tangential direction. The influence of radial deformations or radial mechanical stresses on the electrical resistance is thus easily scalable.

[0041] According to one embodiment, all tangential sections of the second resistance elements extend around the center point at the same angle δ and connect two radial sections in the meandering structure. The tangential sections are significantly shorter than those of the first resistance elements because the influence of tangential stresses is less pronounced further away from the center point.

[0042] According to one embodiment, the outermost sections of the second resistive elements are radial sections that preferably extend directly into the radial conductor tracks described above. Unlike the first resistive elements, the second resistive elements therefore have no bends at their outer ends.

[0043] According to one embodiment, the first resistor elements have the same number of bends as the second resistor elements, including the outermost bends that connect the first resistor elements to the conductor tracks. This enables the described clear layout (see also figures).

[0044] According to one embodiment, the resistor layout comprises four of the conductor tracks, wherein the two outermost sections of the second resistor elements are radial sections ending towards the center, and wherein the two outermost sections of the first resistor elements are the tangential sections located furthest from the center within the first resistor elements, and wherein the first and second resistor elements are electrically connected to each other in a radial direction by one of the four conductor tracks.

[0045] The preferred design is also evident from the figures.

[0046] According to one embodiment, the resistive elements and the conductive tracks consist of the same material, which has piezoelectric properties.

[0047] According to one embodiment, the four resistive elements and the conductive traces each have the same thickness and width, preferably constant along their length. This simplifies the dimensioning and scaling of the measuring bridge.

[0048] According to one embodiment, the resistor layout is designed such that, according to the principle of the Wheatstone bridge, an electrical voltage is or can be applied between the two conductor tracks arranged between the parallel-connected voltage dividers in the operating state, and that a voltage measuring device is or can be connected between the remaining two conductor tracks.

[0049] According to one embodiment, no resistance element is arranged at the center point and all resistance elements have a defined minimum distance from the center point.

[0050] If the resistance layout is applied to a deformation body such as a membrane that has a thickening in the middle, the resistance element should only be applied to the deformation body outside the thickening, since the deformation body deforms differently (less) at the point of the thickening, as also shown in the diagrams in the figures.

[0051] In other words, the resistor layout (= "pattern") according to the invention is characterized by a geometric symmetry of the resistor elements forming a resistive bridge and their tangential and radial sections. This symmetry applies both to the cumulative length of the respective radial and tangential resistive sections within the resistor elements and to the number of 90° bends (= "deflections") for their electrical connection. Preferably, the total resistive lengths of the first resistor elements can be varied and simultaneously adjusted by modifying the angle γ. The described symmetry is a prerequisite for optimal bridge imbalance (= voltage offset) of the resistive bridge with a target value of 0 millivolts (= no bridge imbalance).

[0052] The electrical connections of the resistive elements form conductive tracks in a radial direction as resistive bridges, which also serve to supply (electrical contacting) or as output (voltage tap, also referred to as tap in the text) of the resistive full bridge.

[0053] The exact position of the contact points on the conductor tracks for electrical contact or for tapping the output voltage can be moved longitudinally (here radially) along the conductor tracks for fine-tuning the bridge fundamental detuning.

[0054] According to the invention, the previously described resistor layout, according to any embodiment or combination of embodiments, is particularly suitable for use in a pressure-measuring sensor element, wherein the resistor elements are pressure-dependent. This use is part of the invention.

[0055] Furthermore, the invention relates to a sensor element for pressure measurement with the previously described resistance layout according to any embodiment or combination of embodiments, comprising: - a sensor body with a membrane, which is a general round deformation body with a central center point that can deform under pressure, whereby mechanical stresses arise in tangential and radial directions during deformation, and an edge zone arranged around the membrane, - a piezoelectric layer comprising a first area arranged above the membrane in which pressure-dependent resistance elements and conductor tracks are structured according to the described resistance layout.

[0056] The sensor body can, in particular, have a hollow cylindrical pot shape, with the membrane forming the pot base and the rim forming the pot wall. The pot wall is preferably significantly thicker than the pot base, as can be seen in the figures.

[0057] The sensor geometry is not limited to a hollow cylindrical shape. The shape can be any suitable form, e.g., but not exclusively, a hollow ellipsoidal or spherical segment or a circular plate.

[0058] The membrane is designed as a pressure-sensitive zone of the sensor body in such a way that, when the sensor is in operation, the membrane deforms depending on a pressure difference between the top and bottom of the membrane, while the edge zone is designed as a pressure-insensitive zone of the sensor body.

[0059] In particular, this allows the pressure of fluids such as liquids and gases, i.e., their fluid pressure, to be measured.

[0060] One exemplary application is the measurement of CO2 gas pressure (carbon dioxide gas pressure) in air conditioning systems or similar applications. Another example application would be the monitoring of pressures in hydraulic systems, e.g., in commercial vehicles or construction machinery.

[0061] The fluid preferably presses on the membrane from the inside of the pot or hollow cylinder, while the electronics are mounted on the outside of the membrane. In this text, the side of the membrane facing the inside of the pot is defined as the bottom, and the other side as the top.

[0062] In one embodiment, the sensor element is also designed for temperature measurement, wherein the piezoelectric layer comprises a second area that is arranged above the edge zone and in which at least one temperature-dependent resistor is formed.

[0063] This resistance should be affected as little as possible by mechanical deformations.

[0064] The temperature-dependent resistor preferably comprises a piezoelectric material, preferably the same material as the pressure-sensitive resistance elements, or consists of it.

[0065] In one embodiment, the first and second regions of the piezoelectric layer are electrically isolated from each other by an insulating zone. Such an insulating layer is advantageous or necessary when the sensor body is electrically conductive.

[0066] The insulation zone is an area in the piezoelectric layer between the actual piezoelectric elements, i.e., the resistive elements and the conductive traces, which consists of or comprises insulating material, e.g. silica.

[0067] In one embodiment, the sensor body comprises or consists of stainless steel. Other materials such as silicon, silica, other metals and metal alloys, metal oxides, ceramics, or plastics are also possible.

[0068] In one embodiment, a first electrical insulating layer is formed between the sensor body and the piezoelectric layer. Such an insulating layer is advantageous or necessary if the sensor body is electrically conductive.

[0069] In one embodiment, an electrically conductive electrode structure for contacting the conductor tracks of the piezoelectric layer is applied above the piezoelectric layer on the side facing away from the sensor body.

[0070] In one embodiment, a second electrical insulation layer is formed above the piezoelectric layer and the electrode structure.

[0071] The second electrical insulation layer preferably also serves as a protective layer against moisture and mechanical damage. Openings for electrical contacting the electrode structure, e.g., bond or solder joints, are preferably provided in the second electrical insulation layer.

[0072] The electrode structure incorporates features for applying, tapping, and measuring an electrical voltage across the Wheatstone bridge of the resistor layout. Short circuits are prevented by insulating intermediate material, analogous to the insulating zone in the piezoelectric layer. The electrode structures preferably utilize well-known, highly electrically conductive metals or alloys, such as silver, copper, nickel, or precious metals and / or their alloys.

[0073] In one embodiment, the first and / or the second electrical insulation layer comprises or consists of silicon dioxide.

[0074] In one embodiment, the membrane has a thickening in its middle and is less pressure-sensitive in the area of ​​the thickening than in the remaining area without thickening.

[0075] In one embodiment, therefore, no resistance element is arranged in the area of ​​the membrane thickening.

[0076] The invention will now be described in more detail with reference to exemplary embodiments and accompanying figures.

[0077] Similar or seemingly identical elements in the figures are marked with the same reference symbol. The figures and their proportions are not to scale.

[0078] The features of the exemplary embodiments can be combined in any way desired.

[0079] The examples of implementation are not limiting. Fig. Figure 1 shows an exemplary resistor layout according to the present invention. Fig. Figure 2 shows a sensor element with a membrane with an applied resistance layout according to the invention. Fig. Figure 3 shows half a cross-section of the sensor element. The center of the membrane, with its pronounced manufacturing-related thickening, is shown on the far left. The left half of the sensor element's cross-section is obtained by mirroring the right half of the sensor element's cross-section shown. Fig. Figure 4 shows half a cross-section of the sensor element. The center of the membrane, with its slight manufacturing-related thickening, is shown on the far left. The left half of the sensor element's cross-section is obtained by mirroring the right half of the sensor element's cross-section shown. Fig. Figure 5 shows half a cross-section of the sensor element. The center of the membrane without thickening is shown on the far left. The left half of the sensor element's cross-section is obtained by mirroring the right half of the sensor element's cross-section shown. Fig. Figure 6 shows a diagram representing the mechanical radial stresses in the sensor element versus the radial distance from the center of the membrane. Fig. Figure 7 shows a diagram representing the mechanical tangential stresses in the sensor element versus the radial distance from the center of the membrane.

[0080] Two curves are shown. One curve indicates a greater stress at the center point if the area around the center point is not thickened (see figure). Fig. 5) The other curve shows a lower stress at the center point in the case where the area around the center point is thickened (see figure). Fig. 3 or Fig. 4).

[0081] In Fig. Figure 1 shows an exemplary embodiment of the resistor layout according to the invention.

[0082] The resistor layout 1 serves in particular as a resistor layout for a pressure sensor or deformation sensor.

[0083] As in Fig. As shown in Figure 1, the resistor layout 1 according to the invention comprises four resistor elements forming a bridge circuit. In particular, the resistor layout 1 comprises two first resistor elements 2 and two second resistor elements 3.

[0084] All four resistance elements 2 and 3 are arranged concentrically around a common center point. The structures of the resistance elements are always oriented tangentially or radially to the common center point.

[0085] As in Fig. As shown in Figure 1, the first two resistor elements 2 are arranged closer to the center point, while the second two resistor elements 3 are arranged further away from the center point. The center point is located in the Fig. 1 is labelled with M.

[0086] Both the first resistance elements 2 and the second resistance elements 3 are arranged axially and rotationally symmetrically around the center point. The axis of symmetry (first axis) runs through the center point. Furthermore, the resistance elements are also axially symmetrical about a second axis through the center point, perpendicular to the first axis. This means that axial symmetry is present in the structure of each of the individual resistance elements 2 and 3.

[0087] No resistance element is formed in the area above and directly around the center point. The area above and at least immediately around the center point remains free of resistance elements.

[0088] Each first resistive element 2 and a second resistive element 3 form a voltage divider A and B respectively, wherein the two voltage dividers A and B are electrically connected in parallel.

[0089] In particular, in the parallel circuit a first resistance element 2 is connected in parallel to a second resistance element 3 and a second resistance element 3 is connected in parallel to a first resistance element 2.

[0090] Within the voltage dividers A and B, the two different resistance elements 2 and 3 are each connected in series, whereby the order of the voltage dividers A and B is different in the two voltage dividers.

[0091] The voltage is tapped and measured at conductor tracks 4 between the two series-connected resistor elements 1 and 2.

[0092] To provide such a Wheatstone bridge, a conductor track 4 is provided between each pair of different resistive elements 2 and 3.

[0093] In this example, the voltage is applied between the two diagonally arranged conductor tracks 4A and the voltage is measured between the two other diagonally arranged conductor tracks 4B, or vice versa, as is known in principle as the setup for a Wheatstone bridge.

[0094] The two diagonally arranged conductor tracks 4A and the two diagonally arranged conductor tracks 4B are each arranged symmetrically about an axis through the center point.

[0095] The conductor tracks 4 preferably comprise or consist of the same material as the resistive elements 2 and 3.

[0096] Resistor elements 2 and 3 are each structured as meanders. The meanders comprise a meandering conductor track. The thickness and width of the meandering conductor tracks are constant.

[0097] Each meander comprises tangential and radial sections of the conductor track, each viewed from the common center point. In other words, the sections are arranged tangentially or radially to the center point, but not obliquely.

[0098] The radial sections are executed along an imaginary circular radius radiating from the center. In other words, the radial sections are aligned along rays radiating outwards from the center, while the area around the center itself remains untouched.

[0099] The tangential sections are circular arcs along ring segments around the center point at various distances from the center point.

[0100] Tangential and radial sections preferably alternate, each connected by bends of 90°.

[0101] The first two resistance elements 2 each lie within a circular sector around the center point, which encloses the defined angle α.

[0102] The first resistance elements 2 are structured as a double meander. Each double meander comprises two meander sections 5 extending around the angle γ. Both meander sections 5 are arranged axially symmetrically within the double meander and exhibit the same meandering structure.

[0103] Each meander part 5 comprises the same number of tangential sections of the conductor track and radial sections of the conductor track.

[0104] In the first resistance elements 2, the tangential sections are each longer than the radial sections. All tangential sections of a meander segment 5 lie within a circular sector enclosing the defined angle γ and are at different distances from the center point. All tangential sections extend through the entire angle γ around the center point. The angle γ can take a value between 0° and 90° (excluding both).

[0105] By definition, the angle α is greater than 2 x γ (2 times γ) and therefore less than 180°.

[0106] Thus, there are tangential sections that lie further out in the radial direction and therefore have a greater length than tangential sections that lie further inwards in the radial direction, i.e., closer to the center.

[0107] The radial sections in the meander parts 5 between the tangential sections preferably have the same length in the first resistance elements 2, which is shorter than that of the radial sections.

[0108] Every second radial section in the meander segments 5 is radially adjacent to the penultimate radial section. Radially adjacent means adjacent along the radius as seen from the center point, i.e., along the same ray as seen from the center point, without one or more further sections being arranged in between along the ray.

[0109] Adjacent to the "penultimate" radial section means that every second radial section is arranged on the same beam. Thus, every first, third, fifth section, etc., is arranged on the same beam, and every second, fourth, sixth section, etc., is arranged on the same beam.

[0110] The two rays on which the radial sections of a resistance element are arranged form the outer boundaries of the tangential sections along the angle γ of the meander part 5.

[0111] The two meander parts 5 of the first resistance element 2 are connected to each other by a connecting tangential section 5A, which is located inside the meander structure of the first resistance element 2, i.e. closest to the center.

[0112] The connecting tangential section 5A extends around the entire angle α around the center point.

[0113] The outermost tangential sections of the two meander parts 5 of the first resistance elements 2, viewed from the center point in the radial direction and which also form the outermost sections of the resistance elements 2, do not necessarily extend over the entire angle γ, but are designed in such a way that they are in contact with the radial conductor tracks 4.

[0114] In other words, the tangential sections of the first resistive elements 2, which are furthest from the center, form the tangential connections to the radially arranged conductor tracks 4, which connect the first and the second resistive elements 2 and 3.

[0115] The two second resistance elements 3 are preferably designed as two axially symmetric circular sectors with angle β around the center point, which overlap as little as possible with the circular sectors with angle α. The sum of two angles α and two angles β preferably yields at least 360°.

[0116] In one exemplary embodiment, two angles α and two angles β add up to exactly 360°. In this case, the angle ranges α and β do not overlap. In other embodiments, the two angles α and the two angles β add up to more than 360° and thus overlap.

[0117] In another embodiment, the sum of two angles α and two angles β is greater than 360°, namely 360° + x. Then, the angle ranges α and β preferably overlap by exactly x.

[0118] The meandering conductor tracks of the second resistive elements 3 also have radial and tangential sections, with the radial sections of the second resistive elements all having the same length and being longer than the tangential sections of the second resistive elements 3.

[0119] The radial sections of the second resistance element 3 are tangentially adjacent, meaning they are arranged side by side along a circle around the center point. In other words, the radial sections are all equidistant from the center point. The distance between any two adjacent radial sections is always the same.

[0120] All radial sections of the second resistance elements 3 are thus bounded externally by an outer circumferential line, which is a circle and the center point, and internally by an inner circumferential line, which is a circle around the center point.

[0121] Each pair of adjacent radial sections is connected by a tangential section, the tangential sections of the second resistance elements 3 being arranged alternately along an outer circumferential line of the radial sections and along an inner circumferential line of the radial sections.

[0122] The tangent sections all occupy an equally sized arc segment of a circle, extending around the center at an angle δ. The tangent sections on the outer perimeter are therefore longer than the tangent sections on the inner perimeter.

[0123] Between the radial and tangential sections, there are bends of 90°. The two outermost sections of the second resistive elements 3 are two radial sections that transition directly into the conductor tracks 4, which extend radially to the first resistive elements, in particular to their previously described outer tangential sections.

[0124] All meandering structures or their conductor tracks and the remaining conductor tracks 4 have the same width and thickness.

[0125] The total length of each meander of all four resistor elements is the same. However, the total length of the resistors can be slightly varied, if necessary, by adjusting the precise position of the electrical contact or voltage tap (see also below).

[0126] The first resistive elements 2 preferably have the same number of 90° bends as the second resistive elements 3. In the example, the first resistive elements 2 have exactly 26 bends, including the outermost bends between the first resistive elements 2 and the conductor tracks 4, and the second resistive elements 3 also have exactly 26 bends.

[0127] The conductor tracks 4 run in a straight radial direction and connect the first and second resistor elements. The length of the conductor tracks 4 can be adjusted. The radial distance between the first resistor elements 2 and the second resistor elements 3 is then correspondingly large. By adjusting the precise position of the electrical contact or voltage tap on the conductor tracks, the length ratios of the total resistances can be slightly varied if necessary, since the resistances of the corresponding length segments of the conductor tracks 4 between the contact / voltage tap position and the resistor elements add up to the resistances of the respective resistor elements (see also below).

[0128] The first resistance elements 2 therefore mainly comprise tangential sections, which serve to measure a tangential resistance and its change, e.g. as a result of a tangential deformation, i.e. a deformation / compression / elongation in the tangential direction and the resulting stress in the tangential direction.

[0129] The second resistance elements 3 mainly comprise radial sections, which serve to measure a radial resistance and its change, e.g. as a result of a radial deformation in a radial direction.

[0130] By simultaneously lengthening or shortening the meanders of the first and second resistance elements 2, 3, the total resistance of the resistance bridge can be easily adjusted. The bridge's fundamental detuning should be zero. Furthermore, as described previously, the exact position of the voltage tap can also be varied, thus providing additional "fine-tuning" to compensate for any unwanted non-zero bridge fundamental detuning.

[0131] Due to the symmetrical geometry and arrangement, it is particularly easy to adjust the first two resistance elements and the second two resistance elements analogously, if necessary, in order to fulfill the principle of the Wheatstone bridge (or measuring bridge).

[0132] Due to the clear and multiply symmetrical arrangement described in resistor layout 1, the bridge resistors of the formed Wheatstone bridge can be easily scaled and adjusted.

[0133] For example, the bridge resistances, i.e., the resistances of the resistor elements and the two voltage dividers formed from them, can be easily changed and modified as described above.

[0134] Furthermore, a tension offset (detuning), i.e., a tension in the Wheatstone bridge that deviates from 0 in the unloaded or unstressed state, which is generally undesirable, can be easily modified by appropriate adjustments to the corresponding radial or tangential sections. Additionally, as previously described, the exact position of the tension tap can also be varied, thus allowing for "fine-tuning."

[0135] Furthermore, such modifications are visually striking and therefore easily recognizable. For example, to increase the tangential resistance, the meanders of the first two resistance elements 2 can be extended by the same length, for example by two bends and conductor track sections each.

[0136] It is therefore easy to adjust the two tangential resistors analogously as required, for example by adding the same number of additional sections and bends to both resistor elements.

[0137] Alternatively, the angle α can be varied. By definition, a larger angle α means longer tangential sections in the first resistance element, and vice versa (smaller angle α → shorter tangential sections).

[0138] Similarly, the radial resistance can be varied by extending the second resistance elements 3, which primarily comprise radial sections, for example by adding further sections and bends. This corresponds to changing the angle β, i.e., the angle by which the second resistance elements extend around the center point.

[0139] Furthermore, as described above, in the case of a voltage offset, especially a comparatively small one, the point at which the voltage is applied can simply be changed, particularly if the total electrical resistance of one of the voltage dividers is greater or less than the total resistance of the parallel voltage divider.

[0140] For this purpose, the location of the external electrical contact on the conductor tracks 4A can be easily varied by moving the position of the contact in a radial direction.

[0141] The contact is made, for example, by an electrode structure applied over the resistor layout 1.

[0142] Alternatively or additionally, the point of tapping the electrical voltage on conductor tracks 4B can also be varied or moved.

[0143] As in Fig. Figure 2 shows the entire resistor layout 1 applied to the surface of a sensor element 10.

[0144] The sensor element 10 preferably comprises or consists of a metal, e.g., stainless steel, in particular stainless steel. In further embodiments, the sensor element 10 comprises or consists of other materials such as ceramics, silicon, metals or metal oxides, alloys, plastics, etc.

[0145] The sensor element 10 comprises a pressure-sensitive, easily deformable membrane 11 and a thickened and therefore less pressure-sensitive edge area 12.

[0146] The membrane 11 forms the bottom of the pot and the edge area the wall of a pot with a preferably cylindrical surface.

[0147] In particular, the membrane is made of or consists of stainless steel.

[0148] The resistive elements 2 and 3 and the conductive traces 4 of the resistive layout 1 are applied to the membrane 11. The resistive layout 1, or rather the Wheatstone bridge formed from it, serves here as a deformation and pressure sensor, i.e., to convert the deformations and mechanical stresses into electrical signals.

[0149] The resistor layout 1 is applied such that the center point of the membrane 11 corresponds to the center point M of the resistor layout 1.

[0150] Membrane 11 can be used as in the Fig. 3 and Fig. Figure 4 shows that the area around the center point is thickened due to manufacturing processes and is therefore less deformable.

[0151] Therefore, according to the resistance layout 1, an area around the center of the membrane 11 is free of resistance elements, since the deformations and stresses are lower here and more difficult to measure.

[0152] Alternatively, the membrane can also be non-thickened around the center point, as in Fig. 5 shown.

[0153] The Fig. 3, Fig. 4 and Fig. Figure 5 shows half of the cross-section of the sensor element 10. The center of the membrane 11 is shown on the far left. The left half of the cross-section of the sensor element 10 is obtained by mirroring the right half of the cross-section of the sensor element 10 shown.

[0154] In the embodiment shown, a temperature-sensitive resistance element 13 for detecting an ambient temperature is applied to the pressure-insensitive edge area 12.

[0155] Since it has been empirically established that mechanical stresses in the radial direction also occur further away from the center point during deformation of the membrane 11, in an outer region of the membrane near the edge region 12, while mechanical stresses in the tangential direction occur primarily in the region around the center point, as shown in the diagrams in the Fig. Figures 6 (radial voltages) and 7 (tangential voltage) show that the first resistive elements 2 are expediently arranged closer to the center M than the second resistive elements 3, as previously described.

[0156] Furthermore, it should be noted that for the Wheatstone bridge to function correctly, the deflections at the first and second resistance elements 2 and 3 should each have opposite signs. The tangential stresses at the first resistance elements 2 have a positive sign, and the radial stresses in the outer region, where the second resistance elements 3 are advantageously positioned, have a negative sign.

[0157] The first resistance elements 2 primarily detect tangential stresses, the second resistance elements 3 primarily detect radial stresses.

[0158] All resistance elements shown preferably comprise or consist of the same piezoelectric material or piezoelectric metal, which changes its electrical resistance depending on the deformation.

[0159] All resistive elements 2 / 3 / 13 and conductor tracks 4 are formed in a plane called the piezoelectric layer, since the resistive elements and conductor tracks are preferably made of the piezoelectric material.

[0160] All resistive elements 2 / 3 / 13 and conductor tracks 4 have the same height, which corresponds to the height of the piezoelectric layer.

[0161] Insulating material, e.g. based on silicon dioxide, is preferably applied around the structures of the resistive elements 2 / 3 / 13 and conductor tracks 4, so that an insulating zone is formed around the resistive elements and no short circuits occur between the resistive elements 2 / 3 / 13 or with the environment.

[0162] Electrically insulating layers, e.g. based on silicon dioxide, silica, are also preferably provided below and above the piezoelectric layer or the electrode structure in order to avoid electrical short circuits between the piezoelectric layer and the sensor element 10 or the environment.

[0163] In particular, the lower insulating layer, between the membrane 11 and the resistor layout 1, preferably has dimensions in the micrometer range (up to 10 µm), while the upper insulating layer, above the resistor layout 1 and the electrode structure, is preferably 100 nm to preferably 500 nm thick, but less than 1 µm thick.

[0164] The electrode structure is preferably designed as a layer with electrically conductive elements that contact the conductor tracks 4A and / or 4B and with insulating zones arranged between them above the piezoelectric layer. Reference symbol list 1 Resistor layout 2 first resistance elements 3 second resistance elements 4, 4A, 4B conductor tracks 5 meander sections of the double meander 5A Tangential section connecting the meandering parts in the first resistance element 10 sensor elements 11 Membran 12 Edge area 13 Resistance element in the edge area A, B voltage divider M Center of the resistor layout and the membrane

Claims

[1] Resistor layout (1) for a Wheatstone bridge comprising four electrical resistance elements (2,3), wherein two of the resistance elements (2,3) form two parallel-connected voltage dividers (A, B), wherein two first resistance elements (2) have the same structure and two second resistance elements (3) have the same structure and the first and second resistance elements (2,3) have different structures, wherein both voltage dividers (A, B) each comprise a first and a second resistive element (2,3), and wherein a first and a second resistive element (2,3) are connected in parallel, wherein the structures of the four resistance elements (2,3) are arranged and structured concentrically around a common center point (M) and extend in a radial and a tangential direction to the center point (M), wherein the first resistance elements (2) extend tangentially around the center point (M) at a defined angle α and the second resistance elements (3) extend tangentially around the center point (M) at a defined angle β, wherein each of the four electrical resistance elements (2,3) is designed as a meander structure with the same meander length, wherein the meander structures each have sections in the tangential and radial directions which are connected by a defined number of bends by 90°, i.e. from the tangential to the radial direction and which each have the same width and thickness, and wherein the meander structures are each axially symmetric are structured. [2] Resistor layout (1) according to claim 1, wherein the angles α and β are greater than 0° and less than 180° and overlap as little as possible. [3] Resistor layout (1) according to one of claims 1 or 2, wherein the two first resistance elements (2) and the two second resistance elements (3) are each arranged and structured in an axially symmetrical and rotationally symmetrical manner relative to each other, wherein the axes of symmetry pass through the common center point (M) and wherein the point of symmetry is the common center point (M). [4] Resistor layout (1) according to one of claims 1 to 3, wherein the first resistance elements (2) are arranged closer to the common center point (M) than the second resistance elements (3). [5] Resistor layout (1) according to one of claims 1 to 4, wherein the tangential sections of the first resistance elements (2) are longer than the radial sections. [6] Resistor layout (1) according to claim 5, wherein the two first resistance elements (2) are each designed as double meanders, each connected by a tangential section (5A) of the meander structure located closest to the center point (M), wherein the two meander parts (5) of the double meanders are arranged axially symmetric to each other and concentric to the center point (M). [7] Resistance layout (1) according to claim 6, wherein all tangential sections of a meander part (5) lie next to each other in the radial direction and all tangential sections of a meander part (5) except the outermost tangential section of the meander part (5) extend by the same angle γ around the center (M), wherein the angle γ is greater than 0° and less than 90°. [8] Resistor layout (1) according to one of claims 1 to 7, wherein the outermost sections of the first resistor elements (2) are tangential sections. [9] Resistor layout (1) according to any one of claims 1 to 8, wherein all radial sections of the first resistance elements (2) have the same length. [10] Resistor layout (1) according to one of claims 1 to 9, wherein the radial sections of the second resistance elements (3) are longer than the tangential sections of the second resistance elements (3). [11] Resistor layout (1) according to one of claims 1 to 10, wherein all radial sections of the second resistance elements (3) have the same length and lie next to each other in the tangential direction. [12] Resistor layout (1) according to one of claims 1 to 11, wherein all tangential sections of the second resistor elements (3) extend by the same angle δ around the center point (M). [13] Resistor layout (1) according to one of claims 1 to 12, wherein the outermost sections of the second resistance elements (3) are radial sections. [14] Resistor layout (1) according to any one of claims 1 to 13, wherein the first resistive elements (2) have the same number of bends as the second resistive elements (3). [15] Resistor layout (1) according to any one of claims 1 to 14, further comprising four conductor tracks (4, 4A, 4B), wherein the two outermost sections of each of the second resistive elements (3) are radial sections terminating towards the center (M) and wherein the two outermost sections of the first resistance elements (2) are the tangential sections which are at their maximum distance from the center point (M) within the first resistance elements (2) and wherein the first and second resistance elements (2,3) are electrically connected to each other in a radial direction by one of the four conductor tracks (4, 4A, 4B). [16] Resistor layout (1) according to claim 15, wherein the resistive elements (2,3) and the conductor tracks (4, 4A, 4B) are made of the same material which has piezoelectric properties. [17] Resistor layout (1) according to claim 15 or 16, wherein the four resistive elements (2,3) and the conductor tracks (4, 4A, 4B) each have the same thickness and width. [18] Resistor layout (1) according to one of claims 15 to 17, such that, according to the principle of the Wheatstone bridge, an electrical voltage is applied in the operating state between the two conductor tracks (4A) which are arranged between the parallel-connected voltage dividers (A, B) and that a voltage measuring device is connected between the remaining two conductor tracks (4B). [19] Resistor layout (1) according to any one of claims 1 to 18, wherein no resistor element is arranged at the midpoint (M) and all resistor elements (2,3) have a defined minimum distance to the midpoint (M). [20] Use of the resistor layout (1) according to one of the preceding claims for a sensor element (10) for pressure measurement, wherein the resistor elements (2,3) are pressure-dependent. [21] Sensor element (10) for pressure measurement with a resistance layout (1) according to any one of claims 1 to 20, comprising: - a sensor body with a membrane (11) and an edge zone (12) arranged around the membrane (11), - a piezoelectric layer comprising a first area arranged above the membrane (11) in which pressure-dependent resistance elements (2, 3) and conductor tracks (4, 4A, 4B) are structured according to the resistance layout (1), - wherein the membrane (11) is designed as a pressure-sensitive zone of the sensor body such that the membrane (11) assumes a deformation depending on a pressure difference between the top and bottom of the membrane (11), - wherein the edge zone (12) is designed as a pressure-insensitive zone of the sensor body. [22] Sensor element (10) for pressure measurement according to claim 21, which is further configured for temperature measurement, wherein the piezoelectric layer comprises a second area which is arranged above the edge zone (12) and in which at least one temperature-dependent resistance (13) is formed. [23] Sensor element (10) according to claim 22, wherein the first and the second region of the piezoelectric layer are electrically isolated from each other by an insulating zone. [24] Sensor element (10) according to one of claims 21 to 23, wherein the sensor body comprises or consists of stainless steel. [25] Sensor element (10) according to one of claims 21 to 24, wherein a first electrical insulating layer is formed between the sensor body and the piezoelectric layer. [26] Sensor element (10) according to claim 25, wherein an electrically conductive electrode structure for contacting the conductor tracks (4, 4A, 4B) of the piezoelectric layer is applied above the piezoelectric layer on a side facing away from the sensor body. [27] Sensor element (10) according to claim 26, wherein a second electrical insulation layer is formed above the piezoelectric layer and the electrode structure, which preferably has openings for electrical contacting the electrode structure. [28] Sensor element (10) according to claim 27, wherein the first and / or the second electrical insulation layer comprises or consists of silicon dioxide. [29] Sensor element (10) according to one of claims 21 to 28, wherein the membrane (11) has a thickening in its middle and the membrane (11) is less pressure-sensitive in the area of ​​the thickening than in the rest of the area. [30] Sensor element (10) according to claim 29, wherein no resistance element is arranged in the area of ​​the thickening of the membrane (11).

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