A MULTI CHANNEL FILTER FOR LOW ELECTRON TEMPERATURES

Abstract

A multi-channel filter with a PCB with a first side with signalling tracks and shielding tracks between neighbouring signalling tracks. On the second side, a conductive layer is provided. The signalling tracks are covered by an electromagnetically absorbing material, such as a powder of an electrically conducting material is provided. The filter may have sections with reversed structure where the conductors are on the second side and the layer on the first side, where the conductors on opposite sides are interconnected. The filter may be rolled or folded.

Claims

1.-13. (canceled)

14. A multi-channel filter comprising: a printed circuit board comprising: a plurality of first elongate signal tracks each formed by an electrically conducting path on a first surface of the printed circuit board, each first signal track is not galvanically connected to any other first signal track, one or more first elongate shielding tracks each formed by an electrically conducting or absorbing path on the first surface, one of the first elongate shielding track(s) being positioned between each pair of neighbouring first elongate signal tracks, a first electrically conducting or absorbing layer on a second surface of the printed circuit board, the first and second sides being opposite sides of the printed circuit board, and a first electromagnetically absorbing material covering the first elongate signal tracks.

15. The filter according to claim 14, further comprising two first outer elongate shielding tracks positioned on the first surface, all first elongate signal tracks and all first elongate shielding tracks being positioned between the two first outer elongate shielding tracks.

16. The filter according to claim 14, further comprising one or more electrical connections between the first elongate shielding tracks and the first electrically conducting or absorbing layer.

17. The filter according to claim 16, wherein at least one of the electrical connections is a connection through the printed circuit board.

18. The filter according to claim 14, further comprising a second electromagnetically absorbing material in contact with the first electrically conducting or absorbing layer.

19. The filter according to claim 18, wherein the first electrically conducting or absorbing layer is electrically conducting and in galvanic contact with the second electromagnetically absorbing material.

20. The filter according to claim 14, wherein the printed circuit board is flexible.

21. The filter according to claim 14, further comprising a first electrically insulating material covering the elongate signal tracks,

22. The filter according to claim 14, wherein the printed circuit board comprises at least two sections along a longitudinal direction, wherein: in a first section: the first elongate signal tracks and first elongate shielding tracks are provided at the first side of the printed circuit board and the first electrically conducting or absorbing layer is provided on the second side of the printed circuit board, in a second section adjacent to the first section, the filter comprises: a plurality of second elongate signal tracks each formed by an electrically conducting path on the second surface of the printed circuit board, each second signal track is not galvanically connected to any other second signal track, one or more second elongate shielding tracks each formed by an electrically conducting and/or absorbing path on the second surface, a second elongate shielding track being positioned between each pair of neighbouring second elongate signal tracks, a second electrically conducting or absorbing layer on the first surface of the printed circuit board, and a third electromagnetically absorbing material covering the second elongate signal tracks, and where a first signal track is connected to a second signal track.

23. The filter according to claim 22, wherein the printed circuit board is folded to form at least two at least substantially parallel printed circuit board portions.

24. The filter according to claim 22, wherein the printed circuit board is rolled into a roll.

25. The filter according to claim 14, wherein the first and/or second insulating material has a thickness of 0.001-500 μm.

26. A method of using the filter according to claim 14, the method comprising: cooling the first electromagnetically absorbing material, the first electrically conducting signal tracks and the first shielding tracks to a temperature below 110K, and feeding signals through the first electrically conducting signal tracks.

Description

[0092] In the following, preferred embodiments will be described with reference to the drawing, wherein:

[0093] FIG. 1 illustrates a filter according to a first embodiment of the invention,

[0094] FIG. 2 illustrates the filter of FIG. 1 seen from the end,

[0095] FIG. 3 illustrates a filter according to a second embodiment of the invention,

[0096] FIG. 4 illustrates a filter according to a third embodiment of the invention,

[0097] FIG. 5 illustrates a filter according to a fourth embodiment of the invention

[0098] FIG. 6 illustrates a filter according to a fifth embodiment of the invention,

[0099] FIG. 7 illustrates an interface useful in the embodiment according to FIG. 3,

[0100] FIG. 8 illustrates a container for providing an absorbing material to a PCB, and

[0101] FIG. 9 illustrates a folded PCB structure with cooling fins.

[0102] In FIG. 1, a filter 10 is illustrated which is formed by a printed circuit board, or PCB, 12 having thereon a plurality of elongate signal tracks 14. A number of elongate shielding tracks 16 and two outer shielding tracks 18 may be provided along with a number of vias 22.

[0103] The conductors 14 are covered by an insulating material 24, and an electromagnetically absorbing material 26 (see FIG. 2) of an electrically conducting material is provided on the insulating material.

[0104] A filter of this type is used for e.g. conditioning electric signals for a quantum computer processor. Then, the filter is cooled to less than 1K, such as less than 10 mK.

[0105] In FIG. 1, two different shapes of the conductors 14 are illustrated—a straight shape and a sine-shaped or more meandering shape. Any shape or combination of shapes may be used. These include meandering and sine-shapes with multiples of different pitches, or random lines to reduce resonance effects.

[0106] Preferably, the signal conductors 14 extend at least substantially parallel so as to not overlap. Also, this may allow a shielding track 16 to be provided there between in order to prevent cross talk from one signal conductor 14 to another. Clearly, signal conductors 14 may be meandering and an equally meandering shielding conductor may be provided there between, but any shape, including straight, are useful.

[0107] Naturally, any number of signal conductors 14 may be provided. Preferably, a shielding conductor 16 is provided between each pair of neighbouring signal conductors 14. Also, preferably, outer conductors 18 are provided. Also, neighbouring conductors 14 may be aligned intentionally to reduce crosstalk and noise, i.e. by aligning a meandering pattern in phase or out of phase.

[0108] The conductors 14, as well as optional conductors 16 and 18, are provided on a first side 121 of the PCB.

[0109] On the other side 122 of the PCB 12, a conducting layer 20 may be provided which preferably covers all of the second side of the PCB or at least all of an area of the first side on which the conductors 14, 16 and 18 are provided (when projected on to a plane of the first side 121.

[0110] In this manner, the signal conductors 14 can be covered at all sides by the layer 20, the outer conductors 18, the shielding conductors 16 and the layer 20 and electromagnetically absorbing material 26.

[0111] FIG. 2 illustrates the filter structure 10 of FIG. 1 seen from the end, such as from the left. A number of the conductors and some of the electromagnetically absorbing material have been left out, but the upper outer conductor 18, signal conductor 14 and shielding conductor 16 are illustrated. It is seen that an electrically insulating material 24 is provided on the signal conductor 14 so as to prevent direct contact between the electromagnetically absorbing material and the signal conductor.

[0112] The insulating material may also be provided over the outer conductors 18 and/or the shielding conductors 16, but this is not required. A better cooling is seen when these conductors are in direct, galvanic contact with the electromagnetically absorbing material.

[0113] The same is the situation for the layer 20 which may be used also for cooling, so that it is preferably un-isolated and in galvanic contact with the electromagnetically absorbing material or another layer 261 of electromagnetically absorbing material at the second side 122 of the PCB 12.

[0114] Furthermore layer 20 may be thermally anchored to the cooling system to provide optimal cooling of the electromagnetically absorbing material in contact with the layer.

[0115] Often the electromagnetically absorbing material comprises a glue, such as epoxy, or other fluid so as to be fixed in relation to the layers and not shift during thermal cycling (heating and cooling). Also, later compaction of e.g. a loose powder may generate voids which could generate less cooling to certain elements in the filter structure.

[0116] In order to obtain a better cooling and shielding/grounding of the shielding tracks, vias 22 may be provided from the shielding tracks to the plane 20. Vias may also be provided from the outer tracks to the plane if desired.

[0117] The filter structure of FIGS. 1 and 2 is illustrated as a straight structure. However, as the PCB 12 is flexible, it is configured to be bent/rolled, deformed or shaped in other manners in order to take up less space, such as if made very long. Often, it is desired that the conductors 14, or the PCB 12, have a length of more than 10 cm, such as longer than 50 cm, such as longer than 100 cm.

[0118] In FIG. 4, a coiled shape is seen. When the PCB is coiled, the first side with the conductors 14/16/18 faces the second side with the layer 20, so that the isolation or shielding, if desired, is maintained. In this manner, the conductors 14 are engageable at one end at the inner portion of the coil and at the other end at the outer portion of the coil. In one embodiment, the filter is bent at its centre (as explained below in relation to FIG. 5) and rolled so that both ends of the conductors 14 are engageable from the outer portions of the coil. In this case, however, the first side will be facing the first side, which may not be preferred, at least if no electromagnetically absorbing material is present between the facing first sides.

[0119] In FIG. 3, another embodiment of a filter may be seen which has three sections, I, II and III. In the upper illustration, the first side, 121, is seen and in the lower illustration, the other side 122 is seen. Sections I and II are of the type seen in FIG. 1 where the conductors 14, 16 and 18 are provided on the first side 121 and the plane on the second side 122.

[0120] In section II, however, the conductors 14, 16 and 18 are provided on the second side 122 and the layer on the first side 121.

[0121] Vias 24 are provided for connecting a conductor 14 in section II with a conductor 14 in section I and in section III. Vias 22 may also be used for connecting the conductors 16 and 18 to the corresponding conductors in the other sectors, but these may additionally or alternatively be connected directly to the plane 20 in the neighbouring section.

[0122] Clearly, the vias 22 described in relation to FIGS. 1 and 2 for connecting the conductors 16/18 to the plane 20 through the PCB may also be provided.

[0123] A filter of this type may be used in a number of manners. One manner is seen in FIG. 5, where a filter with two sections, such as sections I and II of FIG. 3 is provided, where the sections I and II have the same length. The PCB 12 is then folded at the centre, i.e. around the vias 24, where after the folded PCB is coiled. In this manner, both outer ends of the conductors 14 are engageable at the outer portions of the coil. In addition, due to this structure of the sections, the folding will have the layer 20 of section II face the conductors 14 of section I, so that the coiling again will have the conductors face the layer, so that optimal shielding is obtained. Clearly, also 4, 6 or any other even number, for rolls, of sections may be used.

[0124] A preferred manner of interfacing between the sections and the two sides is seen in FIG. 7.

[0125] In FIG. 6, another filter structure is seen in which the PCB 12 is zig-zagged or guided over a number of pins 26 each folding the PCB 12 gently 180 degrees. The equidistant positioning of the pins has the advantage that the distance between the parallel portions of the PCB 12 are equidistant. Alternatively, the pins may be positioned with a lower distance, making the PCB define more wedge-shaped portions, making the overall filter smaller. The pins 26 may be omitted and the PCB folded over itself or over other types of elements. Equidistance may be provided using only the electromagnetically absorbing material, for example. Any number of sections may be used in this context.

[0126] In this embodiment, the electromagnetically absorbing material may be fed into a casing also comprising the pins and the PCB. The electromagnetically absorbing material may have a higher or lower viscosity. If the viscosity is low, it may be desired to feed the electromagnetically absorbing material on both sides of the PCB in order to prevent that the PCB ends up in a shape different from a straight line between the pins.

[0127] The upper portion of FIG. 6 illustrates how the second side 122 will face the same side after a bend around a pin 26, if no sections are used. Naturally, around the next bend, the first sides 121 will then face each other.

[0128] At the lower portion of FIG. 6, it is illustrated how the embodiment of FIG. 3 will act, when the sectors I and II are made to intersect at the pin 26. In this manner, the second side will always face the first side. In this manner, the number of sectors will correspond to the number of parallel portions of the filter in the set-up. In FIG. 6, this would be 6.

[0129] Naturally, the electromagnetically absorbing material is preferred also in the coiled/folded embodiments, but it is not required in the situations where the layer of the second surface 122 faces the first layer conductors, as the layer will then perform the shielding function which the electromagnetically absorbing material would perform in the straight case.

[0130] In general, the PCB may require or prefer being heated or otherwise softened prior to and/or during bending/folding. The PCB may be rigid or fragile when in room temperature, where the softening may be chemical (addition of a softener, such as oil, phthalates or the like) or heating.

[0131] The PCB may have a core material which is permanently deformable, so that the bent/folded state is maintained once provided. Alternatively, the folded/bent shape may be maintained by adhesion, such as by the electromagnetically absorbing material adhering the portions of the PCB in the desired relative positions.

[0132] In another alternative embodiment, the absorbing material may be a paint or lacquer which may be applied on the PCB.

[0133] In another embodiment, the absorbing material is provided as a slurry of a powder and a liquid. The liquid may be an adhesive, as it may be able to harden or set.

[0134] The PCB 12, folded/rolled or straight, may be provided in a container (see FIG. 8) into which the slurry 40 is provided. Upon pouring into the container, the powder of the slurry will settle at the bottom and thus around the filter, generating a lower portion 42 with a higher concentration of the powder than the original slurry, and an upper portion 44 with a lower concentration of the powder. Thus, the filter may be provided with (or inside) a material with a high powder concentration.

[0135] When the liquid has hardened or set, the portion 44 may be removed if desired, or the absorbing material around the filter 12 may be machined to arrive at a desired size.

[0136] Preferably, the PCB and the signal tracks are cooled to close to 0K. In this connection, the function of the absorbing material may be to absorb energy from electrons travelling in the signal track. This absorbed energy will heat the absorbing material and preferably is removed. The absorbing material may have a high thermal conduction and thus be able to transport such energy to a surface thereof, such as a surface connected to a cooling surface. Alternatively or additionally, cooling elements or thermal conductors may be provided in the absorbing material, such as the layer C of FIG. 6 or a laminated layer between the windings of the coils of FIGS. 4 and 5. This layer C may merely extend inside the absorbing material to distribute or transport the energy therein, such as to a surface of the absorbing material. Alternatively, the layer C may extend to outside of the absorbing material in order for itself to be cooled, such as if connected to a cooling surface.

[0137] In FIG. 9, another or an alternative cooling manner may be seen in which the PCB itself is provided with cooling fins 32 which may extend into the absorbing material, if provided also at the width of the PCB, or to the surroundings of the PCB or filter structure to be cooled, such as by connection to a cooling surface. The fins 32 may be connected to the signal track(s) but preferably are extensions of the layer 20 so as to be able to cool a larger portion of the PCB.