Device and method for reversible contacting

Abstract

Contacting device (1) with an electrically conductive contact (4) for reversible contacting of a measuring object (5), characterized in that the contacting device further comprises a plurality of electrically conductive particles (3) which can be introduced between the contact (4) and the surface (51) of the measuring object (5) and the contacting device (1) further comprises a first magnetic field generating device (21) with which a magnetic field penetrating the conductive contact (4) can be generated, wherein the plurality of particles (3) can be deposited on the contact along the field lines of the magnetic field.

Description

[0001] The invention relates to a contacting device with an electrically conductive contact for the reversible contacting of a test object. The invention further relates to a measuring device equipped with the contacting device and a method for determining the electrical parameters of a test object, in which the test object is reversibly contacted with at least one conductive contact. Devices and methods of this type can be used to determine the electrical resistance and derived parameters of single layers or layer systems.

[0002] A plug-and-receptacle pair is known from US Patent 5,235,743 A. The plug has a flat, plate-like electrical contact section. The receptacle has a tubular body and an electrical contact portion bent at an obtuse angle, projecting from the tubular body so that it is located within the tubular body, and an electrical contact projection positioned on the tubular body such that the projection faces an upper surface of the electrical contact portion. The contact section, the electrical contact portion, and the electrical contact projection are coated with a mixture of Teflon and a powder of tin, nickel, or the like to reduce the insertion force of the plug into the receptacle.

[0003] DE 690 27 171 T2 discloses an electrical test unit with many test electrodes and an anisotropically electrically conductive film. This film has conductive sections filled with electrically conductive particles. Adjacent conductive sections are separated from each other by insulating sections that do not contain particles.

[0004] US Patent 5,945,834 A discloses a holding plate that holds a semiconductor wafer with a variety of integrated circuit connections for testing a semiconductor chip. This plate is positioned opposite a test plate that has a variety of test circuit connections electrically linked to their corresponding integrated circuit connections.

[0005] In practice, it is known to use test pins or contact probes made of a metal or alloy and to bring them into contact with the object being measured. This allows a current to flow between the conductive contact and the object, so that, for example, a current can be inscribed or a potential difference can be measured. After the measurement, the conductive contacts can be lifted from the object. Ideally, the contacts can be removed without leaving any residue, and the object remains completely unaffected by the measurement.

[0006] However, it has been shown that, particularly with test objects featuring sensitive interface or functional layers with thicknesses ranging from a few nanometers to several tens of micrometers, damage to these layers cannot be ruled out. Furthermore, very rough surfaces cannot be reliably contacted, as the contact between the test object and the conductive contact only occurs at the surface roughness elevations, resulting in a limited number of current-carrying paths. This often leads to inaccurate, non-reproducible, and drifting measurements, which provide little or no meaningful information about the parameters being measured.

[0007] Based on the state of the art, a contacting device, a measuring device and a measuring method should therefore be provided which, on the one hand, avoid damage to sensitive surfaces and, on the other hand, enable reliable measurement results.

[0008] The object of the invention is achieved by a contacting device according to claim 1, a measuring device according to claim 7, and a method for determining electrical parameters according to claim 11. Advantageous embodiments of the invention are found in the dependent claims.

[0009] According to the invention, a contacting device is proposed which has an electrically conductive contact. In some embodiments of the invention, the electrically conductive contact can have a diameter or circumference of approximately 1 mm to approximately 20 mm. The contact can be polygonal or round. The contact can contain a metal or an alloy. The contact can have a surface facing the object being measured, which is provided for contacting the object being measured. In addition, the contact has a further connection point for a measuring lead in order to connect the contact, and thus ultimately the object being measured, to a measuring instrument known per se, a current source, or a voltage source.

[0010] For example, the contact can have a cuboid or cylindrical shape. In other embodiments of the invention, the contact can be made of a sheet metal part which, in addition to the contact surface provided for contacting the object being measured, has a connecting lug. A wire can be attached to this connecting lug by soldering, crimping, or spot welding.

[0011] In some embodiments of the invention, the conductive contact can contain or consist of copper, aluminum, silver, nickel silver, and / or gold. The contact can optionally have a coating that improves conductivity or corrosion protection, or by means of which the work function is adjusted to a predefinable target value.

[0012] According to the invention, it is proposed that the electrically conductive contact is not placed directly onto the surface of the object being measured. Instead, a highly deformable, flowable material is introduced between the conductive contact and the surface of the object. This material has the property of conforming to any surface roughness of the object, thus increasing the contact area and consequently the number of current paths formed or that can be formed. Furthermore, the relatively soft material prevents damage to sensitive surfaces that can occur when the metallic material of the conductive contact is placed directly onto the object.

[0013] The material used according to the invention between the conductive contact and the object being measured contains dust or a plurality of particles which are displaceable relative to one another and can thus penetrate the troughs of surface roughness to increase the contact area. Furthermore, the particles can prevent large forces or mechanical stresses from occurring on the surface of the object being measured, which could lead to damage. After measurement, the particles can be removed from the surface of the object without leaving any residue, for example by blowing them off with a gas stream or by cleaning in an ultrasonic bath.

[0014] According to the invention, the contacting device comprises a first magnetic field generation unit with which a magnetic field penetrating the conductive contact can be generated, whereby the majority of particles can be deposited onto the contact along the field lines of the magnetic field. This enables simple handling of the contacting device according to the invention, since the particles can be bound to the contacting device by magnetic forces. This allows not only for easy contacting of the object being measured, but also for easy disconnection of the contact, with the majority of the particles remaining magnetically attached to the contacting device, so that only minimal or no contamination needs to be removed from the object being measured. In some embodiments of the invention, a cleaning step after the measurement can therefore be omitted.

[0015] To magnetically couple the particles to the conductive contact, some embodiments of the invention provide for the particles to be ferrimagnetic, paramagnetic, or ferromagnetic. This allows the particles to adhere to the contact along the magnetic field lines; that is, as long as the magnetic field exists, the particles form elongated dendrites or threads extending from the surface of the conductive contact. Since the particles remain displaceable relative to one another, the tips of the dendrites can adapt to the surface of the object being measured, thus preventing damage to the object and reliably filling in surface roughness with the particles.

[0016] In some embodiments of the invention, the magnetic field generation device may include a permanent magnet. This allows for reliable and continuous operation of the contacting device, since no auxiliary energy is required to bind the particles to the conductive contact.

[0017] In some embodiments of the invention, the first magnetic field generating device can comprise at least one coil or an electromagnet with a coil and a core. This allows the magnetic field to be switched on and off, so that the particles can be easily removed from the contacting device, for example, to use different particles for different measurements.

[0018] In some embodiments of the invention, the particles can have a diameter of approximately 0.5 µm to approximately 50 µm. In other embodiments of the invention, the particles can have a diameter of approximately 10 µm to approximately 40 µm. In still other embodiments of the invention, the particles can have a diameter of approximately 15 µm to approximately 30 µm. Such particles have dimensions that are smaller than typical surface roughness, so that the particles can easily penetrate the valleys of the roughness to fill them. This increases the number of current paths and thus the effective contact area on rough surfaces.

[0019] In some embodiments of the invention, the particles may contain or consist of ferrite, stainless steel, and / or carbonyl iron. These particles are ferrimagnetic or ferromagnetic and can therefore be reliably bound to the conductive contact of the contacting device by the magnetic field generating device.

[0020] In some embodiments of the invention, the particles can additionally contain nickel and / or manganese and / or zinc and / or barium and / or strontium. This allows the desired hard or soft magnetic properties to be adjusted depending on the intended application of the contacting device. In some embodiments of the invention, the particles contain barium ferrite and / or strontium ferrite and / or nickel-manganese ferrite and / or manganese-zinc ferrite. In some embodiments of the invention, the particles contain nickel-containing stainless steel and / or manganese-containing stainless steel and / or zinc-containing stainless steel. In yet other embodiments of the invention, the particles contain nickel-containing carbonyl iron and / or manganese-containing carbonyl iron and / or zinc-containing carbonyl iron.

[0021] In some embodiments of the invention, the particles are provided with a coating. The coating of the particles can increase the electrical conductivity, passivate the surface of the particles and / or adjust the work function to predefinable target values, so that both ohmic contacts and Schottky contacts can be formed on semiconductor surfaces with the contacting device according to the invention.

[0022] In some embodiments of the invention, the coating of the particles can be achieved electroplating or plasma PVD coating. This makes it easy and cost-effective to produce the particles with the desired properties.

[0023] In some embodiments of the invention, the coating of the particles can contain or consist of silver and / or gold and / or copper and / or nickel. This can increase the conductivity of the particles, thus further increasing the measurement accuracy.

[0024] In some embodiments of the invention, it relates to a measuring device for determining the electrical parameters of a test object, comprising at least one of the aforementioned contacting devices. The electrical parameters determined by the measuring device can be selected from electrical resistance, charge carrier density, charge carrier mobility, breakdown field strength, or other parameters not mentioned here. The measurements can include the measurement of the layer resistance, i.e., the contacting devices are arranged side by side on the same surface of the test object. In other embodiments of the invention, the through-resistance of the test object can be determined, i.e., the contacting devices are located on opposite surfaces of the test object.In other embodiments of the invention, a measurement of the Hall effect can be carried out using the contacting device according to the invention.

[0025] In some embodiments of the invention, the measuring device can have a second magnetic field generating device arranged opposite the contacting device, with the gap formed between the contacting device and the second magnetic field generating device serving to hold the object being measured. The second magnetic field generating device can generate an approximately homogeneous magnetic field with approximately parallel field lines on the surface of the object being measured. Since the particles align themselves along the field lines, the effective diameter of the contacting device on the surface of the object being measured can be reduced. The second magnetic field generating device can also include a permanent magnet or a current-carrying coil, so that the magnetic field can be varied in strength and direction.

[0026] In some embodiments of the invention, the measuring device can further include a positioning device with which the gap between the contacting device and the object being measured can be adjusted. The positioning device can be selected from a piezoelectric actuator, a linear motor, a spindle drive, or other positioning aids known per se. This allows the height or distance of the contacting device to be controlled relative to the surface of the object being measured, thus preventing accidental contact of the conductive contact with the surface. This ensures that the electrical contact is established exclusively via the particles that can be moved relative to each other and that no significant forces act on the object being measured that could lead to its destruction.

[0027] In some embodiments of the invention, the measuring device may further include a control unit with which the positioning device can be controlled. By comparing the target value with the actual value, accidental damage to the object being measured is prevented, and at the same time, reliable contact is ensured, which is a prerequisite for reliable measured values.

[0028] In some embodiments of the invention, the particles can be present in air or in a gas atmosphere. This allows for easy handling of the measuring device and / or a simple execution of the method according to the invention. In other embodiments of the invention, the particles can be bound in a ferrofluid. This allows for a more reliable measurement.

[0029] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention. This will show Fig. 1 a first embodiment of the contacting device according to the invention. Fig. Figure 2 shows a microscopic image of the particles at the contacting device according to the invention. Fig. Figure 3 shows a particle in cross-section. Fig. Figure 4 shows an electron micrograph of the particles. Fig. Figure 5 shows an embodiment of a measuring device according to the invention. Fig. Figure 6 shows a second embodiment of the contacting device according to the invention. Fig. Figure 7 shows comparative measurements of the contacting device according to the invention compared to known contacting devices using a first application example. Fig. Figure 8 shows comparative measurements of the contacting device according to the invention against known contacting devices using a second application example.

[0030] Based on Fig. 1 A first embodiment of a contacting device 1 according to the invention is explained.

[0031] The contacting device 1 has a shaft 10 with which the contacting device can be mechanically fastened. The mechanical fastening can be carried out by means of a positioning device 70, as will be shown below with reference to Fig. 5 is explained.

[0032] Furthermore, the contacting device 1 comprises a first magnetic field generating device 21. In the illustrated embodiment, the magnetic field generating device 21 includes a permanent magnet. In other embodiments of the invention, a current-carrying coil can be used so that the magnetic field can be varied in direction, strength, and timing. Since the magnetic field is not permanently switched on, the particles 3 can be easily removed from the contacting device 1 by switching off the magnetic field.

[0033] Furthermore, the contacting device has a conductive contact 4. In the illustrated embodiment, the conductive contact 4 is formed from a sheet metal which can have a thickness of approximately 0.1 mm to approximately 1 mm. The conductive contact 4 can contain or consist of copper, aluminum, gold, and / or silver. The conductive contact 4 can be provided with a coating that passivates the surface and / or increases the electrical conductivity.

[0034] Unlike conventional contacting devices, the conductive contact 4 is not brought into direct contact with the material being measured. Instead, particles 3 are provided, which are bound to the conductive contact 4 by the magnetic field of the first magnetic field generating device 21.

[0035] Since the particles 3 are very small and can be displaced relative to each other, they can penetrate surface roughness on the object being measured and thus increase the number of conductive current paths between the contact 4 and the surface of the object. Furthermore, the particles 3 allow the object to be contacted with low contact forces, preventing damage to sensitive surfaces. Finally, the particles 3 can be easily and completely removed from the object when the contacting device 1 is removed from the surface of the object after the necessary measurements have been completed.

[0036] The particles 3 are based on Fig. 2 explained in more detail. Due to the diverging dipole field of the magnetic field generating device 21 and the fact that the particles 3 align themselves along the field lines, they form elongated dendrites or tufts which extend radially outwards from the surface of the contact 4, similar to a brush or paintbrush.

[0037] The dendrites of particle 3 become thinner towards their tip due to the decreasing magnetic field strength. As shown in the smaller illustration in Fig. As shown in Figure 2, the tips of the dendrites often contain only single particles, so that the tips of the dendrites have a diameter the size of the particles. In some embodiments, the tip can therefore have a diameter between approximately 0.5 µm and approximately 50 µm, or between approximately 5 µm and approximately 50 µm, or between approximately 10 µm and approximately 30 µm.

[0038] Fig. Section 3 illustrates the structure of a particle 3 by way of example. The particle 3 according to Fig. 3 has a core 31 and a coating 32.

[0039] The core 31 can contain a ferrimagnetic or ferromagnetic material to enable good magnetic coupling to the conductive contact 4. In some embodiments of the invention, paramagnetic materials can also be used for the core 31. For example, carbonyl iron, stainless steels, or ferrites are suitable materials for the core 31.

[0040] The core 31 is provided with a coating 32, which can consist of a material exhibiting higher conductivity than the core material. This reduces the contact resistance of the contacting device according to the invention. For example, the coating 32 can contain or consist of gold, silver, and / or copper. The coating 32 can be deposited using wet chemical processes, for example, without external current, or electroplating. Alternatively, the coating 32 can be applied using a sputtering process or a plasma PVD process.

[0041] Fig. Figure 4 shows particle 3 as an example in an electron microscope image. The example in Fig. The 4 particles shown have a core 31 made of ferrite and a coating 32 made of silver.

[0042] Based on Fig. Figure 5 describes an embodiment of a measuring device according to the invention. The measuring device 5 shows a measuring object 5 with a surface 51. The measuring object 5 can, for example, be a metallized foil for the manufacture of a battery, a capacitor, or a fuel cell. In other embodiments of the invention, the measuring object 5 can be a semiconductor device or a semiconductor wafer.

[0043] The contacting device 1 is intended to reliably contact the object 5 via its surface 51 with low contact resistance, so that electrical parameters of the object 5 can be recorded. For example, the electrical film resistance can be determined using a four-point measurement known per se. In other embodiments of the invention, charge carrier densities or charge carrier mobilities can be determined, for example by means of the Hall effect.

[0044] The object 5 is located on a sample holder 50, which can be equipped with a multi-axis manipulation in a manner known per se to position the object 5 in the measuring instrument. In the illustrated embodiment, the sample holder 50 also serves as a conductive back contact to measure the volume resistance of the object 5. Optionally, the sample holder 50 can also be heated or cooled to enable measurements at different temperatures. For measuring the coating resistance, the sample holder 50 can also be designed to be insulating, in which case one or more contact devices 1 are additionally attached for measurement.

[0045] The contacting device 1 has a shaft 10 and a first magnetic field generating device 21, as described above. A conductive contact 4 is located at the end of the magnetic field generating device 21 facing the object 5 being measured. The conductive contact 4 extends beyond the magnetic field generating device 21 on at least one side and forms a contact lug there, which allows the conductive contact 4 to be connected to a measuring device, a current source, or a voltage source.

[0046] The surface of the conductive contact 4 located beneath the magnetic field generating device 21 is covered with particles 3, which are fixed to the contact 4 by the magnetic field generating device 21. The particles are designed, on the one hand, to be held to the contact by the magnetic forces of the magnetic field generating device 21 and, on the other hand, to have good electrical conductivity in order to enable sufficiently good electrical contact with the object being measured 5.

[0047] In the illustrated embodiment, a gap 55 exists between the particles 3 and the surface 51 of the object 5 being measured. The size of this gap 55 can be varied by a linear actuator 70, which increases or decreases the distance between the contacting device 1 and the surface 51 of the object 5. In one measuring position of the contacting device 1, the particles 3 are in contact with the surface 51. Nevertheless, a gap remains between the conductive contact 4 and the surface 51, which is filled by the particles 3. By avoiding direct mechanical contact between the conductive contact 4 and the surface 51, mechanical damage to the surface 51 by the contact 4 is prevented.

[0048] The control of the gap 55, and thus the control of the linear drive 70, can be carried out by a control device 6. The control device 6 can include a PID controller, which is known per se. This has the advantage that no overshoot occurs when approaching the setpoint of the measuring position; that is, the conductive contact 4 does not even briefly touch the surface 51 when approaching the measuring position. The actual value of the gap 55 can be continuously detected by a sensor and supplied to the control device 6. In the illustrated embodiment, a light barrier or a camera 74 is used as the sensor, which detects the position of the contacting device 1 without contact.

[0049] Furthermore, in Fig. Figure 5 shows an optional second magnetic field generating device 22. The second magnetic field generating device 22 serves to shape the magnetic field generated by the first magnetic field generating device 21. This allows the particles 3 to be arranged more uniformly on the contacting device 1, so that, when the second magnetic field generating device 22 is in operation, for example a cuboid or cylindrical cross-section is formed instead of the one shown in Figure 5. Fig. This results in the meniscus-shaped cross-section shown in Figure 5. This allows the effective contact area to be increased, enabling more accurate measurement.

[0050] Fig. Figure 6 shows a second embodiment of the contacting device according to the present invention. Identical components of the invention are provided with the same reference numerals, so that the following description is limited to the essential differences.

[0051] As in Fig. As shown in Figure 6, this embodiment of the invention has two first magnetic field generating devices 211 and 212. Each magnetic field generating device is associated with a conductive contact 41 and 42. At the end of the conductive contacts 41 and 42, there are a plurality of particles 310 and 320, respectively. The contacting device 1 according to the second embodiment is thus suitable for generating two contact points at a defined distance on the surface 51 of the object 5 to be measured. Since both contacts are connected to a common linear drive by a single shaft 10, the distance between the two contacts can be kept constant with high accuracy during different measurements. This allows the layer resistances and, consequently, the specific resistance of the measured layer to be determined with high accuracy.

[0052] Furthermore, the contacting device has a position sensor 75 which continuously detects the distance to the surface 51 of a measuring object 5 and transmits this information to a control device. This enables the placement of the object in Fig. The double contact shown in section 6 can be operated with great accuracy without damaging the surface 51.

[0053] The in Fig. The position sensor 75 shown in Figure 6 can, for example, be an ultrasonic sensor, a capacitive sensor, or a laser sensor to detect the distance without contact. Alternatively, the position sensor 75 can also have a spring-loaded pin that acts on a sliding resistance, so that the distance of particles 310 and 320 from the surface can be determined by the measured resistance value. In further embodiments of the invention, the position sensor 75 can be designed as a force transducer, which determines the contact closure from the applied force.

[0054] In Fig. Figure 7 shows comparative measurements demonstrating the advantageous effect of the contacting device according to the invention. The figures show the volume resistances of approximately 3 µm thick preparation layers on aluminum foil. Both layers were produced using different manufacturing processes, which are described in Figure 7. Fig. 7 are each labelled “Primer 1” and “Primer 2”.

[0055] Fig. Figure 7A shows the result of the measurement of the contact resistance using a cylindrical test probe with a diameter of 3 mm. The test probe has a flat contact surface and is gold-plated to ensure an inert surface and low resistivity. Fig. Figure 7A shows the arithmetic mean of the through-resistance as well as the error bars that occurred during the measurement.

[0056] Out of Fig. As shown in section 7A, no significant differences in contact resistance can be determined using the known test probe. Therefore, the measurement is not suitable for detecting different properties of differently prepared layers.

[0057] Fig. Figure 7B shows measurements that were carried out in the same way using a known contact stamp. This contact stamp is also made of a metallic material with a flat contact surface 10 mm in diameter.

[0058] Based on Fig. 7B shows that the arithmetic mean of the measured values ​​varies for the differently produced layers. Therefore, a distinction is possible in principle.

[0059] However, due to highly fluctuating measured values, the measurements exhibit a large error bar. This leads to partial overlap of the measurements, meaning that the differently manufactured layers cannot always be distinguished.

[0060] Fig. Figure 7C shows measurements which were carried out in the same manner with the contacting device according to the invention. The arithmetic mean of the contact resistances is again shown. Fig. Figure 7c shows that the differently manufactured layers exhibit significantly different resistance values. The error bar is also so small that the layers can be distinguished in each individual measurement.

[0061] Based on the Fig.Figure 8 presents a second application example demonstrating the measurement of the contact resistance of two samples. The use of the previously described contact probe is compared with the contacting device according to the invention. Both samples consist of aluminum foil (Al foil) bearing a 30-50 µm thick cathode coating. The difference between the samples is that the first sample contains conventional aluminum foil (bar A), while the second sample contains functionalized aluminum foil (bar B). Conventional aluminum foil is known to always have a native Al₂O₃ interface layer on its surface, a few nanometers thick, which causes high electrical resistance. In the functionalized aluminum foil, the Al₂O₃ layer and its dielectric properties are no longer present.

[0062] Accordingly, the measured values ​​of the two samples with the cathode coating are as follows, using the two measurement methods: High through-resistances in the cathode with conventional aluminum foil contrast with low through-resistances in the cathode with functionalized aluminum foil.

[0063] Comparing the degree of resistance reduction that occurs with the two measurement methods, the reduction is approximately 0.25 for the contact stamp compared to approximately 0.05 for the contacting device according to the invention.

[0064] This finding can be explained by the fact that the contact stamp must be subjected to force, which causes mechanical stress on the sample structure. In the case of conventional aluminum foil + cathode coating, the dielectric Al₂O₃ layer present at the interface between the aluminum foil and cathode coating is damaged and partially rendered ineffective. The volume resistance is reduced by the invasive contacting, the measured values ​​appear lower than in reality, and are therefore inaccurate. In contrast, the contacting device according to the invention provides plausible values ​​and increases the safety and reliability of the measurement.

[0065] When using the contacting device according to the invention, the contact resistance through the carbon layer increases by a factor of 20. This means that the functionalization layer is damaged by the contact plunger, thus distorting the measured values. In contrast, the contacting device according to the invention increases the safety and reliability of the measurement.

[0066] Naturally, the invention is not limited to the embodiments illustrated in the figures. The preceding description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Where the claims and the preceding description define "first" and "second" embodiments, this designation serves to distinguish between two similar embodiments without establishing any hierarchy. Features from different embodiments of the invention can be combined at any time to obtain further embodiments of the invention.

Claims

[1] Contacting device (1) with an electrically conductive contact (4) for reversible contacting of a measuring object (5), characterized by , that the contacting device further comprises a plurality of electrically conductive particles (3) which can be introduced between the contact (4) and the surface (51) of the object being measured (5) and the contacting device (1) further comprises a first magnetic field generating device (21) with which a magnetic field penetrating the conductive contact (4) can be generated, wherein the plurality of particles (3) can be deposited on the contact along the field lines of the magnetic field. [2] Contacting device according to claim 1, characterized by that the first magnetic field generating device contains at least one coil. [3] Contacting device according to claim 1 or 2, characterized by, that the particles (3) have a diameter of about 0.5 µm to about 50 µm or of about 5 µm to about 50 µm or of about 10 µm to about 40 µm or of about 15 µm to about 30 µm. [4] Contacting device according to any one of claims 1 to 3, characterized by , that the particles (3) contain or consist of ferrite and / or barium ferrite and / or strontium ferrite and / or nickel-manganese ferrite and / or manganese-zinc ferrite and / or nickel- and / or manganese- and / or zinc-containing stainless steel and / or nickel- and / or manganese- and / or zinc-containing carbonyl iron. [5] Contacting device according to any one of claims 1 to 4, characterized by that the particles (3) are provided with a coating (32). [6] Contacting device according to claim 5, characterized by that the coating (32) is available by plasma-PVD and / or that the coating (32) contains or consists of silver and / or gold and / or copper and / or nickel. [7] Measuring instrument for determining electrical parameters of a measuring object (5) with at least one contacting device (1) according to one of claims 1 to 6. [8] Measuring device according to claim 7, characterized by , that a second magnetic field generating device (22) is arranged opposite the contacting device (1), wherein the object to be measured (5) can be inserted into the gap (55) between the at least one contacting device (1) and the second magnetic field generating device (22). [9] Measuring device according to one of claims 7 or 8, further comprising a positioning device (70) with which the gap (55) between the contacting device (1) and the object being measured (5) can be adjusted. [10] Measuring device according to claim 9, further comprising a control device (6) with which the positioning device (70) can be controlled. [11] Method for determining electrical parameters of a measurement object (5) in which the measurement object (5) is reversibly contacted with at least one conductive contact (4), characterized by , that the conductive contact (4) is penetrated by a magnetic field and a plurality of electrically conductive particles (3) attach themselves to the contact along the field lines of the magnetic field. [12] Method according to claim 11, characterized by that the particles have a diameter of approximately 5 µm to approximately 50 µm or of approximately 10 µm to approximately 40 µm or of approximately 15 µm to approximately 30 µm and / or that the particles contain or consist of a ferro- or ferrimagnetic material. [13] Method according to one of claims 11 or 12, characterized by , that the particles (3) are provided with a coating (32) which contains a material which has a lower specific resistance than the material of the particles. [14] Method according to any one of claims 11 to 13, characterized by , that a magnetic field is generated by a second magnetic field generation device (22) on the side of the object being measured (5) opposite the conductive contact (4). [15] Method according to any one of claims 11 to 14, characterized by , that the particles (3) are part of a ferrofluid. [16] Method according to any one of claims 11 to 15, characterized by , that an electrical resistance and / or a breakdown field strength and / or a charge carrier density and / or a charge carrier mobility and / or a specific resistance is determined.

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