WO2010003438A1

WO2010003438A1 - A high current transmission line and a method for transmitting high currents

Info

Publication number: WO2010003438A1
Application number: PCT/EP2008/005645
Authority: WO
Inventors: Marcus Müller; Heinz NÜSSLE; Claus PLÖTZ
Original assignee: Verigy Singapore Pte Ltd
Current assignee: Verigy Singapore Pte Ltd
Priority date: 2008-07-10
Filing date: 2008-07-10
Publication date: 2010-01-14
Anticipated expiration: 2011-01-10

Abstract

A high current transmission line for guiding a current (I) along a current path comprises a first, a second and a third conducting layer (110, 120, 130) and a first and a second isolating layer (210, 220). The first, second and third conducting layers (110, 120, 130) are arranged as a layer stack such that the second conducting layer (120) is arranged between the first and third conducting layers (110, 130). The first isolating layer is arranged between the first conducting layer (110) and the second conducting layer (120) and the second isolating layer (220) is arranged between the second and third conducting layer (120, 130).

Description

A High Current Transmission Line and a Method for Transmitting High Currents

Background of the Invention

Embodiments according to the invention relate to a high current transmission line and a method for transmitting high currents. Some embodiments relate to an ultimate performance high current transmission line to a device under test (DUT) .

In order to perform an operational test and/or a characterization of electronic devices under test or a group of devices (especially in testing semiconductor devices) it is needed that these devices are tested during operation - either during the manufacturing or after the manufacturing thereof. In modern semiconductor technology usually multiple devices are tested simultaneously at the same time (multi-site testing) . Depending on a number of devices under a simultaneous test, high currents are needed in such tests. For example, up to about 1000 Amperes or up to about 10.000 Amperes per testing unit are needed. Therefore, high currents should be provided to the testing unit and ideally, the applied voltage is independent from the load current (no voltage drop during the test) .

Therefore, the testing unit should comprise (or is connected to) a current transmission line, in which rapidly- changing currents do not result in a voltage drop such that multiple devices can be tested in parallel. At high currents and especially at rapidly changing currents, the voltage drop (or the attainable voltage constancy) depends on the quality of the transmission line between the current source and the device under test.

A high (or best) quality transmission line exhibits the following electrical or physical properties: (a) A low Ohmic resistance - to be zero in the ideal case;

(b) A lowest possible electrical inductance - to be zero in the ideal case; and

(c) A highest possible electrical capacitance - to be infinite in the ideal case.

These electrical or physical properties imply lowest possible impedance, which vanishes in the ideal case or may be, for example, below 1 Ohm or below 3 Ohm or below 10 Ohm.

In order to achieve this objective, a conventional transmission line (either as a cable or as a current bar) is formed with a large cross section and/or is realized in a co-axial shape, in which an outer conductor surrounds an inner conductor. Both conductors comprise, for example, a same cross-sectional area and both conductors are separated by dielectric material. This conventional shape of a transmission line aims to solve the aforementioned objective of the lowest possible impedance.

Hence, there is a need to provide an alternative transmission line, which provides an improved compromise of electrical and mechanical characteristics. An alternative transmission line comprises a different geometrical shape, but obeys nevertheless the electrical and physical properties (see above) with optimal electrical parameters (Ohmic resistance, inductance, capacitance, etc.), so that a high quality transmission line is achieved (with very low impedance, e.g. < 10 Ohm) .

This objective is solved by a high current transmission line according to claim 1 or claim 10 and a method for transmitting high currents according to claim 14. According to embodiments of the present invention, a high current transmission line for guiding a current along a current path comprises at least a first, second and third conducting layer and, in addition, a first and second isolating layer. The first, second and third conducting layers are arranged as a layer stack, such that the second conducting layer is arranged between the first and third conducting layer. The first isolating layer is arranged between the first and second conducting layer and the second isolating layer is arranged between the second and third conducting layer.

Hence, embodiments solve the aforementioned objective by a layer stack of multiple layers of conducting material, wherein the geometry, especially the cross-section and the shape of the^" conducting layers, is such that the electromagnetic (inductive) fields of adjacent forward and reverse conducting layers may at least approximately cancel against each other. As a result, the transmission line exhibits a high quality with respect to the criteria (a) to (c) mentioned above.

Therefore, embodiments provide a high current transmission line, which is applicable for high voltage and/or high currents - especially for rapidly changing currents while the voltage remains constant or only a minor drop in the applied- voltage occurs without loosing transmission performance. Embodiments of the present invention may be used in particular between a power supply and a device under test within semiconductor testing units.

In comparison to conventional round cables, advantages of an arrangement of conducting layers according to embodiments can be summarized as follows.

To verify the desired low impedance, note that the impedance is given by the square root of the inductance or inductance per unit length divided by the capacitance or capacitance per unit length of the conductor (Z²=L/C) . On the one hand, the inductance L of a conductor is geometrically related to the thickness of the conductor. Thin conductors comprise a higher inductance than thick conductors do. If the magnetic field caused by the electric current is spread over a large surface area, a small inductance can be achieved. Thus, flat conductors with the same cross section comprise a smaller inductance than round conductors do.

The electric capacitance C of a forward and a reverse conductor, on the other hand, is geometrically related to the area over which a dielectricum or a dielectric layer separates the forward and reverse conductor. In addition, the distance between both conductors relates to the capacitance as well. These are the known relations implying the higher the area the higher the capacitance and the higher the distance the lower the capacitance. If both conductors (the forward and the reverse conductor) are in a face-to-face arrangement, the area between both conductors is maximal and, hence, the capacitance is high. Correspondingly, for a small area between both conductors, the capacitance of the arrangement is decreasing. For a round conductor, the surface (or the circumference) fixes or determines the cross section uniquely. This constitutes a disadvantage of round conductors, since a fixed cross section implies a fixed capacitance, which is not the case for flat conductors.

For flat conductors, the ratio (surface area to the cross- sectional area) can be adjusted by a variation of the geometrical parameter and, hence, can be optimized accordingly. In a multi-stack arrangement with alternating forward and backward conducting layers, the inductance of the transmission line can be significantly decreased and, at the same time, the resulting capacitance can be significantly increased. As a result, the quotient of the inductance and the capacitance and, therefore, the impedance can be made extremely small.

A further advantage of a multi-stack arrangement of conducting layers lies in the possibility of effectively carrying away produced heat. Every conductor is heated by high currents accordingly to the relationship that the electrical power equals the Ohmic resistance times the square of the current (P=R*I²) . Especially for high (electric) currents, this results in an undesired strong heating of the conductor. With respect to this effect, the described arrangement comprises a two-fold advantage:

• The flat layer design of conductors in a multi-stack technique allows, in a given space, to form conductors with a relatively high cross-sectional area, which decreases the Ohmic resistance; and

• By a flat arrangement of the conductor, the surface area is maximized and, therefore, the whole layer arrangement is able to release the produced heat in an optimal way to the surrounding.

In comparison, conventional round conductors comprise a minimal surface area for a fixed cross-sectional area, which may result in an insufficient heat delivery to the surrounding of the conductor. The middle conductor of a coax cable, for example, can release its heat only by heating the surrounding cable. Therefore, both cables (the inner conductor and the outer conductor of the coaxial cable) may comprise a different temperature and therewith a different resistance.

Embodiments of the present invention will be explained in the following with reference to the accompanying drawings, in which: Fig. 1 shows a schematic view on high current transmission line formed as a layer stack, according to embodiments of the present invention;

Fig. 2 shows a cross-sectional view of the high current transmission line comprising two conducting layers and one insulating layer;

Fig. 3 shows a further embodiment for the high current transmission line;

Fig. 4 shows an overview of the high current transmission line; and

Fig. 5 shows an overview of details of one end of the high current transmission line.

Before embodiments of the present invention are explained in detail in the following based on the drawings, it is pointed out that equal elements or elements operating in an equal way are provided with the same or similar reference numerals in the Fig., and that a repeated description of these elements is omitted.

Fig. 1 shows a high current transmission line for guiding a current I along a current path, both in forward direction and reverse direction. The current I in forward direction is divided in a first forward current Il and a second forward current 12. The current in the reverse direction is designate as reverse current 13. The high current transmission line of Fig. 1 comprises a first conducting layer 110, a second conducting layer 120 and a third conducting layer 130, wherein the second conducting layer 120 is arranged in-between the first conducting layer 110 and the third conducting layer 130. The first conducting layer 110 and the second conducting layer 120 are electrically isolated by a first isolating layer 210. Similarly, the second conducting layer 120 is electrically isolated from the third conducting layer 130 by a second isolating layer 220. The forward current I may be equal to the reverse current - at least up to a tolerance of +/-10% or +/- 20 %.

For the embodiment of Fig. 1, the high current transmission line comprises a length L measured along the current path or the main current-flow direction. Perpendicular to the current path or main current flow direction, the high current transmission line comprises a cross section, wherein the first, second and third conducting layer comprise a width B. The width B may comprise, for example, the same value for the first, second and the third conducting layer, as shown in the embodiment of Fig. 1. The third conducting layer comprises a thickness C and the second isolating layer comprises a thickness A. The first as well as the second conducting layer 110, 120 may comprise the same thickness C as the third conducting layer 130 and, similarly, the first isolating layer 210 may comprise the same thickness A as the second isolating layer 220. In further embodiments, however, the thicknesses of the conducting layers as well as the thicknesses of the isolating layers separating the conducting layers may differ from one another. The thicknesses may optionally be such that the total cross section (or cross-sectional area) of all forward current paths (sum of the cross sections or cross-sectional areas) equals the total cross section or cross-sectional area of the sum of reverse current paths.

In some embodiments, the widths B of the conducting layers may be different.

Fig. 2 shows a cross section perpendicular to the current path or main current-flow direction of the high current transmission line (therefore, the current path or the main current-flow direction is perpendicular to the drawing plane) . The high current transmission line as shown in Fig. 2 comprises only two conducting layers - the first conducting layer 110 and the second conducting layer 120, which are electrically isolated by the first isolating layer 210. In this embodiment, the first isolating layer 210 comprises a layer thickness A, which comprises, for example, the same value as the second isolating layer 220 shown in Fig. 1. The first and second conducting layers 110, 120 can be flush with each other in a direction perpendicular to the current path and comprise a width B. The width B can be such that the cross-sectional area Fl of the first conducting layer 110 and/or the cross-sectional area F2 of the second conducting layer 120 comprise a predetermined value. This predetermined value is related, for example, to the total current I (sum of all forward currents) transmitted by the high current transmission line, for example, by an upper limit for the Ohmic resistance, which the high current transmission line applies to the total current. The first conducting layer 110 and the second conducting layer 120 may, for example, comprise the same layer thickness C. Therefore, the cross- sectional area of the first conducting layer is given by F1=B*C1 and the cross-sectional area of the second conducting layer 120 is also given by F2=B*C2.

With this geometry of the high current transmission line, the impedance Z₀ can be expressed as follows:

wherein εo,_r denote dielectric constants and μo,_r the permeability (of the vacuum or of the dielectric material arranged between the layers) . The inductance and capacitance per length unit can be calculated by:

L¹= μ— ; C = ε — . B A As an example, the following values can be taken:

ε_r = 3;

A = 0.10mm;

B = 40mm; μ₀ = 1.257 • 10^"6 -; m ε₀ = 8.854 • Kr¹² — , m

which yield:

Z₀ = 0.54 Ω;

L'= 3.14^; m

C= 10.06 — m

In general, an increase in the number of layers yields a further decrease in the impedance Z as well as a decrease in the inductance L and the Ohmic resistance - in accordance with the basic idea of embodiments of the present invention.

Fig. 3 shows a high current transmission line according to a further embodiment comprising seven conducting layers: The first conducting layer 110, the second conducting layer 120, the third conducting layer 130, ... , and the seventh conducting layer 170. The conducting layers 110, ... ,170 are arranged as a layer stack, wherein neighboring conducting layers are separated from each other by an isolating layer. For example, the first isolating layer 210 separates the first and second conducting layers 110, 120, and the second isolating layer 220 isolates the second and third conducting layers 120, 130, and so on, up to the sixth and seventh conducting layers 160, 170, which are separated from each other by the sixth isolating layer 260. All conducting layers can be flush with their corresponding neighboring conductive layers in a lateral direction perpendicular to the current I or the main current flow direction thereof.

Assuming a continuous numbering of the conducting layers, the conducting layers are electrically connected in a way that the odd-numbered conducting layers (the first, third, fifth and seventh conducting layers 110, 130, 150, 170) are electrically connected to a first terminal 310a on one end (on the left hand side in Fig. 3) and to a second terminal 310b on the other end of the transmission line. Similarly, the even-numbered conducting layers (the second, fourth and sixth conducting layers 120, 140, 160) are electrically connected with each other, so that on one end of the transmission line, the even-numbered conducting layers are connected to a further first terminal 320a and to a further second terminal 320b at the other end of the transmission line. When applying a forward current I_f to the first terminal 310a, the current path for the forward current I_f is split into four parallel current paths for four currents: II, 13, 15 and 17, which are combined again at the second terminal 310b and can, for example, be used for a device under test. When applying a reverse current I_r to the further second terminal 320b, the further second terminal 320b being connected to the even-numbered conducting layers (the second, fourth and sixth conducting layer 110, 130, 150), the reverse current I_r is divided into three parallel reverse currents or reverse current portions: A first reverse current 12, a second reverse current 14 and a third reverse current 16. These three reverse currents are combined at the first end of the transmission line and guided to the further first terminal 320a.

Hence, current paths or the main current directions of neighboring conducting layers are reverse with respect to each other so that two forward current paths are separated from each other by a reverse current path, and vice-versa. In further embodiments, the odd-numbered (or even-numbered) conducting layers are not connected to each other and hence may provide current paths to different devices under test. It is also possible that only at the first end, the even- numbered and the odd-numbered conducting layers are connected to each other and that at the second end of the transmission line, every conducting layer can be used for connecting a different device under test. In further embodiments, more than seven conducting layers are stacked in a layer stack (or an even number of conducting layers is stacked) . In addition, the cross-sectional areas of the different conducting layers can be different. For example, the cross-sectional areas can be chosen such that a given conducting layer comprises a predetermined Ohmic resistance (for example, within a predetermined range) .

Fig. 4 shows an overview or top-view of a transmission line, wherein the first end is drawn below the second end of the transmission line and the first end comprises six terminals: A first terminal 310a, a second terminal 320a, a third terminal 330a, ..., a sixth terminal 360a. Similarly, the second end of the transmission line also comprises six terminals: A second terminal 310b, a further second terminal 320b, ..., a sixth terminal 360b.

In this overview, only the first conducting layer 110 is shown and the other conducting layers are arranged beneath this first conducting layer 110. Moreover, in this embodiment, the first conducting layer is separated into a first part 110a and a second part 110b, which parts provide parallel current paths taking over the functionality of the first current path 110. In this embodiment, the terminals at the first end and the terminals at the second end of the transmission line are not connected to each other. For example, it can be of advantage if separate current paths are used for different devices under test so that no interconnections between some of the conducting layers are needed. Similar to the first conducting layer 110, which is separated into a first part 110a and a second part 110b, the remaining conducting layers (the second, third, ... , conducting layers 120, 130, ...) can also be separated into first parts and second parts. In this way, each of the current paths over a given conducting layer is separated into a first part and a second part.

Fig. 5 shows a detailed overview or top-view of the first end of the transmission line comprising six terminals (310a, 320a, 330a, ... , 360a) . These six terminals may be connected to different conducting layers, which are electrically isolated from each other. As explained taking reference to Fig. 4, the first conducting layer 110 is divided into the first part 110a and the second part 110b and both parts can be electrically isolated along the line 112. In this way, the first current Il through the first conducting layer 110 is in turn divided into a first part Ila and a second part lib.

The high current transmission line as shown in Figs. 4 and 5 may comprise for example the following properties: The width B may be approximately 40 mm, and the length may be approximately 0.35m, which gives a surface area of 280cm².

In further embodiments, the high current transmission line comprises, for example, eight layers of conducting material (alternating three force layers and four return layers) . One of the eight layers may be reserved for different tasks or applications (for example other than power supply) . The capacitance C is approximately 7nF and the inductance L is approximately 2OnH. In this example, connectors, which are not shown in the Figs. 4 and 5, may be included and, therefore, the layer stack may comprise even better inductance L. Hence, per length, the inductance comprises a value of 20nH/0.35m = 57nH/m. The cross-sectional area A comprises, for example, a value of 6qmm. These values can be compared to a conventional power coax cable, which, for a cross-sectional area of 6qmm, comprises a diameter of 5.5mm, a circumference of approximately 17.2mm. Such conventional coax cable yields an inductance of 75nH/m (without connectors) . The capacitance of this conventional power coax cable comprises a value of lnF/m and, hence, the conventional coax cable comprises an impedance of approximately 8.66 Ohm.

The comparison of embodiments of the present invention to conventional coax cable with the different parameters given above yields the following results:

1) Surface area used for heat release: If both surfaces are compared with each other, a factor of (2 x 40mm) /17.2mm = 4.65 is achieved.

2) Inductance: Each of the coax cables comprises an inductance of 33nH/m so that in parallel, it yields a value of approximately 16.7nH/m. The flat inductor (high current transmission line according to embodiments) comprises a value (see above) of approximately 57nH so that the improvement factor is 75/57 = 1.3. These values include, for example, the connectors and the results would be even better without the connectors.

3) Capacitance: The coax cable comprises a capacitance of approximately lnF/m and the transmission line according to embodiments comprises a capacitance of approximately 20nF/m so that the improvement factor is approximately 20/1 = 20.

4) Impedance: The coax cable comprises a value of approximately 8.66 Ohm, whereas the transmission line according to an embodiment comprises a value of approximately ^57nH / 2OnF =1.68Ω so that the improvement factor becomes approximately 8.66/1.68 = 5.13. These values denote only one example to show the advantage of embodiments of the present invention in comparison to conventional coax cables.

Possible materials for the conducting layers are copper, aluminum or other metals. The transmission line may be flexible and the electric connections of the different conducting layers may comprise wires or other low Ohmic connections (for example, below 1 Ohm or below 3 Ohm or below 10 Ohm) . The low Ohmic connection between two conducting layers may in further embodiments even comprise a resistance below 10 mOhm. For example, the low Ohmic connection may comprise a plurality of vias circuited in parallel between two conducting layers. The ratio of the width B to the thickness C may comprise, for example, at least a value of 10 or 100 or 200 or 400, or may lie within a range between 10 and 10000 or within a range between 50 and 500. The impedance of the transmission line comprises, for example, a value below 20 Ohm, or below 10 Ohm, or below 1 Ohm.

High current transmission lines in embodiments are, for example, capable of carrying at least 1 A or 10 A or 100 A at a temperature increase of less than 20 K.

Further embodiments also comprise a method for guiding an electrical current, which comprises a forward current and a reverse current, along a current path. The method comprises splitting the forward current into a plurality of parallel forward currents flowing in conductive forward current layers and combining the parallel forward currents at an end of the current path. The method further comprising returning the reverse current such that at least a part of the reverse current is guided in a conductive reverse current layer arranged between two parallel forward currents . Moreover, embodiments comprise also a method of manufacturing a high current transmission line, comprising the steps of arranging alternating conducting and isolating layers, wherein isolating layers are arranged between two conducting layer. The method further comprising connecting the conducting layers to terminals such that a forward current and a backward current is directed such that the backward current path is in-between two neighboring forward currents .

Claims

1. A high current transmission line for guiding a current

(I) along a current path, the high current transmission line comprising:

a first, a second and a third conducting layer (110, 120, 130);

a first and a second isolating layer (210, 220),

wherein the first, second and third conducting layers (110, 120, 130) are arranged as a layer stack such that the second conducting layer (120) is arranged between the first and third conducting layers (110, 130), and

wherein the first isolating layer is arranged between the first conducting layer (110) and the second conducting layer (120) and wherein the second isolating layer (220) is arranged between the second and third conducting layer (120, 130) .

2. The high current transmission line of claim 1, wherein the first and third conducting layers (110, 130) are electrically connected by a low Ohmic connection.

3. The high current transmission line of claim 1 or claim 2, wherein each conducting layer comprises an elongate cross section perpendicular to the current path.

4. The high current transmission line of claim 3, wherein the cross section comprises a width (B) and a thickness (C) such that a ratio of width to thickness comprises a value of more than 10 or more than 100.

5. The high current transmission line of one of the preceding claims, wherein the first, second and third conducting layers (110, 120, 130) are flush with each other in a lateral direction perpendicular to the current path.

6. The high current transmission line of one of the preceding claims, wherein the layer stack is flexible.

7. The high current transmission line according to one of the preceding claims, wherein the impedance of the transmission line is below 10 Ohm.

8. The high current transmission line according to one of the preceding claims, wherein each conducting layer forms a flat conductor.

9. The high current transmission line of one of the preceding claims, wherein the first, second and third conducting layers (110, 120, 130) comprise copper or aluminum or a different metal.

10. A high current transmission line comprising

a plurality of isolating layers;

a first plurality of conducting layers;

a second plurality of conducting layers, the first and second plurality of conducting layers being arranged as a layer stack such that the layer stack comprises an alternating arrangement of layers of the first and second plurality of layers, wherein the layers or the first plurality of conducting layers are isolated from the layers of the second plurality of conducting layers by isolating layers of the plurality of isolating layers, and

wherein the first plurality of layers defines a plurality of forward current paths and the second plurality of layers defines a plurality of reverse current paths, wherein the forward current paths and the reverse current paths are anti-parallel with respect to each other.

11. The high current transmission line of claim 10, wherein the conducting layers of the first plurality of conducting layers are electrically connected with each other at a first end of the high current transmission line and at a second end of the high current transmission line, and wherein the second plurality of conducting layers are electrically connected with each other at the first end of the high current transmission line and at the second end of the high current transmission line.

12. An apparatus for guiding a high current along a current path, the apparatus comprising:

a current or a voltage supply;

an electrical device; and

a high current transmission line according to one of the claims 1 to 11, which connects the electric device to the current or voltage supply, to supply the electric device with energy.

13. The apparatus of claim 12, wherein the high current transmission line comprises first terminal (310a) and a further first terminal (320a) at one end, and a second terminal (310b) and a further second terminal (320b) at another end, and

wherein the high current transmission line comprises a stack of layers, the stack of layers comprising, in an alternating arrangement, forward current layers and reverse current layers, wherein the first terminal (310a) and the second terminal (310b) are both connected to the forward current layers and wherein, the further first terminal (320a) and the further second terminal (320b) are both connected to the reverse current layers.

14. A method for guiding an electrical current, which comprises a forward current and a reverse current, along a current path, the method comprising:

splitting the forward current into a plurality of parallel forward currents flowing in conductive forward current layers;

combining the parallel forward currents at an end of the current path;

returning the reverse current such that at least a part of the reverse current is guided in a conductive reverse current layer arranged between two parallel forward currents.

15. The method of claim 14, further comprising:

splitting the reverse current into parallel reverse currents at a first end of the current path such that the current path comprises a stack of conducting layers comprising, in an alternating arrangement, forward current layers in which portions of the forward current are flowing and reverse current layers in which portions of the reverse current are flowing; and;

combining the parallel reverse currents at another end of the current path.