Sensor element with overvoltage protection

Abstract

The invention relates to a sensor element with overvoltage protection, comprising: a carrier element; a sensor structure applied or attached to the carrier element for detecting a measurement variable, the sensor structure having a first electrical contact point and a second electrical contact point, the sensor structure being operable by applying a voltage between the first electrical contact point and the second electrical contact point; and an overvoltage protection element applied to the carrier element and comprising a sub-element pair consisting of a first sub-element comprising a first conductor rail and a first pad and a second sub-element comprising a second conductor rail and a second pad spaced apart from the first pad, a first conductor rail electrically connects the first electrical contact to the first pad and a second conductor rail connects the second electrical contact to the second pad, the first pad and the second pad being designed and arranged on the carrier element at a first distance from each other such that a spark gap is formed between the first pad and the second pad.

Description

Technical Field

[0001] This invention relates to a sensor element. Background Technology

[0002] Many sensor elements for determining physical, chemical, and / or biological measurement variables of a measurement medium or environment are known from the existing technology.

[0003] For example, temperature sensors are known for measuring the temperature of a measuring medium. They are manufactured using thin-film or thick-film techniques and have a functional layer on a substrate, which is, for example, made of platinum. This functional layer can be used to determine the temperature of the medium that thermally interacts with it. This measuring medium is, in particular, a gaseous or liquid fluid.

[0004] Another example is a heat flow sensor, which typically consists of one or more temperature sensors and at least one heating element.

[0005] Other examples of sensor elements are humidity sensors, strain sensors, gas sensors, and light sensors. The portion of the sensor element used to detect the measured variable is referred to below as the sensor structure. In addition to the sensor structure, the sensor element particularly includes a carrier element or substrate, conductor rails, contact pads, and (if necessary) electronic components and / or circuitry.

[0006] All of these sensor elements are sensitive to electrostatic discharge (ESD). This manifests as voltage breakdown due to a high potential difference. These voltage breakdowns briefly generate high currents, which can irreversibly damage components of the sensor element, especially the sensor structure.

[0007] Starting with this problem, the object of the present invention is to provide a sensor element with integrated protection that prevents damage caused by electrostatic discharge. Summary of the Invention

[0008] This objective is achieved by a sensor element, which includes:

[0009] -Carrier element;

[0010] - A sensor structure, applied to or attached to a carrier element, for detecting physical, chemical, and / or biological measurement variables, wherein the sensor structure has a first electrical contact and a second electrical contact, and wherein the sensor structure is operable by applying a voltage between the first electrical contact and the second electrical contact; and

[0011] - An overvoltage protection element is applied to a carrier element and includes a pair of sub-elements consisting of a first sub-element and a second sub-element, wherein the first sub-element includes a first conductor rail and a first pad, wherein the second sub-element includes a second conductor rail and a second pad spaced apart from the first pad, wherein the first conductor rail electrically connects a first electrical contact to the first pad, wherein the second electrical conductor rail connects a second electrical contact to the second pad, wherein the first pad and the second pad are designed and arranged on the carrier element at a first distance from each other, such that a spark gap is formed between the first pad and the second pad.

[0012] The sensor element according to the invention has an integrated structure in the form of an overvoltage element connected in parallel with the sensor structure. The overvoltage element essentially consists of a spark gap formed between two pads. This provides reliable ESD protection.

[0013] Instead of voltage, current or power can be applied to operate the sensor structure.

[0014] One embodiment of the sensor element provides that a first pad and a second pad are arranged such that when a voltage exceeding a first threshold exists between the first contact point and the second contact point, current discharges parallel to the sensor structure via an overvoltage protection element. Provided, this threshold is a multiple of kV. Below this threshold, the applied (operating) voltage generates the desired current, by means of which the sensor element operates, and this current is required to determine the measured variable. Electrostatic discharge causes short-term voltages many times higher than typical operating voltages (e.g., 5V). If a voltage exceeding this threshold exists, the air gap between the pads of the overvoltage protector is ionized, causing a high discharge current to discharge through the thus ionized air gap, and therefore without damaging the parallel-connected sensor structure.

[0015] The threshold value is specifically defined by the length of the spark gap (i.e., the distance between the second pad and the first pad). Generally, a longer length defines a higher threshold.

[0016] Based on the development of sensor elements, an overvoltage protection element is provided having one or more additional sub-element pairs, each additional sub-element pair including an additional first sub-element and an additional second sub-element, each additional first sub-element having an additional first pad and an additional first conductor rail, each additional second sub-element having an additional second pad and an additional second conductor rail, wherein the additional first conductor rail connects a second electrical contact to a corresponding additional first pad in each case, wherein the additional second conductor rail connects a second electrical contact to a corresponding additional second pad in each case, wherein the additional first pad and the additional second pad are designed to be spaced apart from each other by an additional distance and are arranged on a carrier element in each case such that an additional spark gap is formed between the corresponding additional first pad and the corresponding additional second pad in each case.

[0017] In this case, it can be provided that, when multiple additional pairs of sub-elements are provided, the additional distances to each other are different from the first distance.

[0018] In each case, an additional distance or multiple additional distances define an additional threshold for the applied voltage.

[0019] In this way, multi-level protection can be provided to cope with different overvoltage levels.

[0020] Advantageous embodiments of the sensor element provide that a first pad and a second pad, together with the distance between them, and / or additional first pads and additional second pads, or a plurality of additional first pads and a plurality of additional second pads, together with corresponding additional distances, are covered by a layer of dielectric material. Using this material, the threshold can be influenced or adjusted. For example, covering the air gap with glass will produce a higher threshold. Conversely, by covering the air gap while maintaining the same threshold, the desired distance between the pads can be influenced.

[0021] According to the first variant, the carrier element is provided as a substrate made of metallic, ceramic, or semiconductor material, particularly a planar substrate. The sensor structure can be applied to the carrier element using thick-film or thin-film processes.

[0022] PVD or CVD processes are suitable as thin-film processes. The materials for the sensor structure are particularly metallic, such as platinum in the case of a temperature sensor. A suitable thick-film process, for example, is screen printing, where the material used for the sensor structure is initially in paste form and includes metals or conductive ceramics. After printing, the sensor structure must be heat-treated, such as heated, to remove the liquid components of the paste.

[0023] According to the second variation, the carrier element is a printed circuit board. The sensor structure can then be electronic components, particularly SMD or THT components.

[0024] Advantageous embodiments of the sensor element provide that an overvoltage protection element is applied to the carrier element by means of a thick-film or thin-film process. Where the sensor structure is also applied by means of a thick-film or thin-film process, the sensor structure and the overvoltage protection element can be manufactured in a single process step.

[0025] According to one embodiment of the sensor element, an overvoltage protection element and a sensor structure are provided to be applied to or attached to a common side of the carrier element. Alternatively, the overvoltage protection element and the sensor structure may be provided to be applied to or attached to different sides of the carrier element. Attached Figure Description

[0026] The invention will be explained in more detail with reference to the following figures, in which:

[0027] Figure 1 A first embodiment of a sensor element according to the present invention is shown;

[0028] Figure 2 A second embodiment of the sensor element according to the present invention is shown;

[0029] Figure 3 A third embodiment of the sensor element according to the present invention is shown;

[0030] Figure 4 A fourth embodiment of the sensor element according to the present invention is shown; and

[0031] Figure 5 A fifth embodiment of the sensor element according to the present invention is shown. Detailed Implementation

[0032] Figure 1 A first exemplary embodiment of the sensor element 1 according to the present invention is shown in a plan view of the sensor element 1. The sensor element 1 comprises a carrier element 110 in the form of a planar substrate. The substrate is made of, for example, a ceramic material.

[0033] The sensor structure 120 has a first electrical contact 121 in the form of a contact pad and a second electrical contact 122 in the form of a contact pad, and the sensor structure 120 is applied to the carrier element 110. The sensor structure 120 with two contacts 121, 122 is made of a metallic material (especially platinum) and is applied to the carrier element 110 by means of a sputtering process or a screen printing process in the present case.

[0034] Sensor structure 120 is used for temperature detection. For this purpose, sensor structure 120 has a tortuous portion with a thin cross-section. The resistance of this tortuous portion can be detected by applying a voltage or current between two contact points 121, 122. Since this is temperature-dependent, the temperature of the environment or medium can be determined.

[0035] In this embodiment and the following embodiments, a temperature sensor is described. However, other types of sensor structures can also be used, as long as they can be supplied with voltage via two or more contact points 121, 122. Electronic components, such as diodes or transistors, can also be provided as sensor structure 120.

[0036] To protect the sensitive sensor structure 120 from electrostatic discharge, an overvoltage protection element 130 is applied to the carrier element 110. The overvoltage protection element 130 consists of a first sub-element and a second sub-element. The first sub-element has a first pad 132 and a first conductor rail 131 connecting the first pad 132 to the first contact point 121. The second sub-element has a second pad 134 and a second conductor rail 133 connecting the second pad 134 to the second contact point 122.

[0037] The overvoltage protection element 130 may be made of the same material as the sensor structure 120 and may be applied to the carrier substrate 110 by means of the same process in the same process steps.

[0038] The first and second sub-components are arranged such that the two pads 132 and 134 have a first distance d1 from each other, that is, the two pads 132 and 134 do not contact each other. This creates a so-called spark gap between the two pads 132 and 134. This means that when a low voltage is applied, no current flows from the first contact point 121 to the second contact point 122. Only when a first threshold is exceeded does a flashover occur from the first pad 132 to the second pad, whereby the current discharges parallel to the tortuous structure via the overvoltage protection element 130.

[0039] See below, Table 1 shows possible dimensions and example thresholds. In this case, the first distance between pads 132 and 134 is 200µm. Therefore, the first threshold is 4kV.

[0040] In this way, a simple and reliable overvoltage protector is created for sensor element 1 and can be directly integrated with sensor structure 120 on common carrier element 110.

[0041] Figure 2 A second embodiment of sensor element 1 is shown in cross-section. The dimensions of sensor element 1 substantially correspond to... Figure 1The dimensions of the sensor element in the exemplary embodiment shown are illustrated. However, the overvoltage protection element 130 is not applied to the same side of the carrier element 110, but is located on the side of the substrate 110 opposite to the sensor structure 120. Here, the conductor rails 131, 133 contact the corresponding contact points 121, 122 by means of through-holes passing through the carrier element 110.

[0042] Figure 3 A third exemplary embodiment of sensor element 1 is shown as a plan view. The dimensions of sensor element 1 substantially correspond to... Figure 1 The dimensions of the sensor element in the exemplary embodiment shown are illustrated. However, the overvoltage protection element 130 is extended in this exemplary embodiment: in addition to the first and second sub-elements, there are two additional sub-elements. Therefore, a third pad 136 and a fourth pad 138 are provided, each connected to corresponding contacts 121 and 122 by means of additional conductor rails 135 and 137. In this case, the first conductor rail 131 and the additional first conductor rail 135 can be at least partially combined, and the second conductor rail 131 and the additional second conductor rail 137 can be at least partially combined.

[0043] The additional first pad 136 has a second distance d2 from the additional second pad 138. This provides an additional threshold for overvoltage. See below, Table 1 shows the possible dimensions and example thresholds. In this case, the first distance d1 between pads 132 and 134 is 200µm. Therefore, the first threshold is 4kV. The additional distance d2 between pads 136 and 138 is 300µm. Therefore, the additional threshold is 8kV.

[0044] Figure 4 A fourth exemplary embodiment of sensor element 1 is shown as a plan view. The dimensions of the sensor element 1 substantially correspond to... Figure 2 The dimensions of the sensor element in the exemplary embodiment shown are illustrated. Layer 139 is also shown, applied to pads 132, 134, 136, 138 and formed in the associated spark gaps between pads 132, 134, 136, 138. Layer 139 is composed of a dielectric material and is applied by means of a thick-film or thin-film process.

[0045] The dielectric material affects the corresponding threshold of the spark gap. This threshold can be precisely selected by choosing the material. Therefore, the distance between pads 132, 134, 136, and 138 can be affected while keeping this threshold constant.

[0046] In this example, glass is chosen as the dielectric material. See Table 1 below, which shows the possible dimensions and example thresholds for this case. In this case, the first distance d1 between pads 132 and 134 is 5 µm. The first threshold is 3 kV because of the presence of glass layer 139. The additional distance d2 between pads 136 and 138 is 10 µm. This additional threshold is 4 kV because of the presence of glass layer 139.

[0047] Figure 4 A fourth exemplary embodiment of sensor element 1 is shown as a plan view. The dimensions of the sensor element 1 substantially correspond to... Figure 2 The dimensions of the sensor element in the exemplary embodiment shown are illustrated. The substrate is replaced here by a printed circuit board serving as the carrier element 110. The sensor structure 120 is designed here as an electronic component (a temperature sensor with a housing) soldered to contacts 121, 122. An overvoltage protection element 130 is applied as described in the previous example. Distances d1, d2, and the threshold correspond to... Figure 4 The distances and thresholds shown in the embodiments.

[0048]

[0049] Table 1

[0050] List of reference numerals

[0051] 1 Sensor Component

[0052] 110 carrier element

[0053] 120 sensor structure

[0054] Electrical contact points 121 and 122

[0055] 130 Overvoltage Protection Component

[0056] 131 First Conductor Rail

[0057] 132 First pad

[0058] 133 Second Conductor Rail

[0059] 134 Second Pad

[0060] 139 Layers of dielectric material

[0061] d1 First distance

[0062] d2 Other distance

Claims

1. A sensor element (1), comprising: -Carrier element (110); - A sensor structure (120) is applied to or attached to the carrier element (110) for detecting physical, chemical and / or biological measurement variables, wherein the sensor structure (120) has a first electrical contact (121) and a second electrical contact (122), wherein the sensor structure (120) is operable by applying a voltage between the first electrical contact (121) and the second electrical contact (122); as well as - An overvoltage protection element (130) is applied to the carrier element (110) and includes a pair of sub-elements consisting of a first sub-element and a second sub-element, wherein the first sub-element includes a first conductor rail (131) and a first pad (132), wherein the second sub-element includes a second conductor rail (133) and a second pad (134) spaced apart from the first pad (132), wherein the first conductor rail (131) electrically connects the first electrical contact (121) to the first pad (132), wherein the second electrical conductor rail (133) connects the second electrical contact (122) to the second pad (134), wherein the first pad (132) and the second pad (134) are designed and arranged on the carrier element (110) at a first distance (d1) from each other, such that a spark gap is formed between the first pad (132) and the second pad (134).

2. The sensor element according to claim 1, wherein, The first pad (132) and the second pad (134) are arranged such that when a voltage exceeding a first threshold exists between the first contact point (121) and the second contact point (122), current discharges through the overvoltage protection element (130) parallel to the sensor structure (120).

3. The sensor element according to claim 1 or claim 2, wherein, The overvoltage protection element (130) has one or more additional sub-element pairs, each additional sub-element pair including an additional first sub-element and an additional second sub-element, each additional first sub-element having an additional first pad (136) and an additional first electrical conductor rail (135), each additional second sub-element having an additional second pad (138) and an additional second electrical conductor rail (137), wherein the additional first electrical conductor rail (135) in each case connects the first electrical contact (121) to the corresponding additional first pad (136), wherein the additional second electrical conductor rail (137) in each case connects the second electrical contact (122) to the corresponding additional second pad (138), wherein the additional first pad (136) and the additional second pad (138) are designed to be spaced apart from each other by an additional distance (d2) and are arranged on the carrier element (110) in each case such that an additional spark gap is formed between the corresponding additional first pad (136) and the corresponding additional second pad (138) in each case.

4. The sensor element according to claim 3, wherein, In the case of providing multiple additional pairs of sub-elements, the additional distance (d2) to each other is different from the first distance (d1).

5. The sensor element according to claim 3 or claim 4, wherein, The additional distance (d2) or the plurality of additional distances each defines an additional threshold for the applied voltage.

6. The sensor element according to any one of the preceding claims, wherein, The first pad (132) and the second pad (134), together with the distance (d1) between them and / or the other first pad (136) and the other second pad (138) or a plurality of the other first pads and a plurality of the other second pads, together with the corresponding other distance (d2), are covered by a layer of dielectric material (139).

7. The sensor element according to any one of the preceding claims, wherein, The carrier element (110) is a substrate made of metallic, ceramic or semiconductor material, and the substrate is particularly planar.

8. The sensor element according to claim 7, wherein, The sensor structure (120) is applied to the carrier element (110) by means of a thick film or thin film process.

9. The sensor element according to any one of the preceding claims, wherein, The carrier element (110) is a printed circuit board.

10. The sensor element according to claim 9, wherein, The sensor structure (120) is an electronic component, particularly an SMD or THT component.

11. The sensor element according to any one of the preceding claims, wherein, The overvoltage protection element (130) is applied to the carrier element (110) by means of a thick film or thin film process.

12. The sensor element according to any one of the preceding claims, wherein, The overvoltage protection element (130) and the sensor structure (120) are applied to or attached to the common side of the carrier element (110).

13. The sensor element according to any one of claims 1 to 11, wherein, The overvoltage protection element (130) and the sensor structure (120) are applied to or attached to different sides of the carrier element (110).

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