Apparatus and method for cryocooled devices thermalization with RF electrical signals

Abstract

Cryogenic device comprising at least two chambers at two different temperatures, a first chamber at a first temperature T1 accommodating a sample, and a second chamber at a second temperature T2 greater than T1 and being adapted to accommodate a cooling device, said cooling device being adapted to cool wirelines connecting said sample to an external element detector, wherein said cooling device is an IMS thermalization plate comprising at least one wire-guide having an input for plugging a wire line connected to the sample and an output for plugging a wire line connected to said external element, said wire-guide being thermally connected to the first chamber.

Claims

1. A cryogenic device comprising at least two chambers at two different temperatures, a first chamber at a first temperature T1 accommodating a sample, and a second chamber at a second temperature T2 greater than T1 and being adapted to accommodate a cooling device, said cooling device being adapted to cool wirelines connecting said sample to an external element, wherein said cooling device is an IMS thermalization plate comprising at least one wire-guide having an input for plugging a wire line connected to the sample and an output for plugging a wire line connected to said external element, said wire-guide being thermally connected to the first chamber.

2. The cryogenic device according to claim 1, wherein said thermalization plate (170) is mounted on a mechanical attachment made of a thermally conductive material and thermally connected to the first chamber.

3. The cryogenic device according to claim 1, wherein the thermalization plate embeds an active device for signal amplification or processing.

4. The cryogenic device according to claim 1, wherein the wirelines are coaxial cables.

5. The cryogenic device according to claim 1, wherein the thermalization plate is located in the second chamber.

6. The cryogenic device according to claim 1, wherein the thermalization plate comprises a first layer comprising a material with high thermal conductivity; a second layer made of a thin dielectric material as an insulating layer; a third layer is made of conductive material used for forming circuitry enabling wire thermalization; and two layers which are a solder mask and a solder paste.

7. The cryogenic device according to claim 1, wherein the thermalization plate is adapted to fit a specific impedance value.

8. The cryogenic device according to claim 1, wherein the chambers are electrically connected to each other through feeding through-holes provided in walls of the chamber.

9. Process for installing an IMS thermalization board inside the cryogenic device of claim 1 comprising the steps of: putting the IMS plate in contact with a part of cryostat at T1; connecting an output cable on and output connector of the plate; connecting an input cable to an input connector on the same wire-guide as the output cable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

(2) FIG. 1ais a schematic view of a cryostat apparatus of the invention;

(3) FIG. 1bis an enlarged schematic view of a cooling system of included in the cryostat of FIG. 1a;

(4) FIG. 2ais an upper view of the thermalization plate with and without active devices;

(5) FIG. 2bis a cross-section view of the thermalization plate of FIG. 2a;

(6) FIG. 3is a picture and diagram of the method associated to the apparatus embodiment;

(7) FIG. 4ais a graph presenting measurement results without the thermalization plate.

(8) FIG. 4bis a graph presenting measurements results with a thermalization plate.

DETAILED DESCRIPTION OF THE BEST MODE OF THE INVENTION

(9) The invention description is based on the attached FIGS. 1a to 4b.

(10) A best mode of the invention is described here where a thermalization plate is preferably made with IMS technology which combines the properties presented above. It is of particular interest, that IMS has never been specified at cryogenic temperatures, and the inventors surprisingly found that such a plate made with this technology was compatible with the thermal (high heat dissipation) and electrical requirements (impedance matching and high bandwidth) of the present device.

(11) FIG. 1a shows a cryostat 100 is made of three chambers 110, 120 and 130 at three different temperatures T3, T2 and T1 with preferably, T3>T2>T1. As an example T3 may be in the order of magnitude of few hundred Kelvin (typically 200K), T2 at the order of 20K and T1 at the level of 2K. Each chamber is connected electrically to the other through feeding through-holes 030 provided in the walls of the chamber. These three chambers 110, 120, 130 enable to have a smooth temperature transition from T3 (typically in the range of 200K) in the third chamber 110 to T1 (typically in the range of 2K) in the first chamber 130 comprising an analyzed sample 131 by using cold finger 010 filed with He that is provided second chamber 120.

(12) FIG. 1b is an enlarged view of chambers 120 and 130. One can see the sample 131 to be measured in the first chamber 130 in cryogenic conditions, that is at temperature T1 and that is attached to the cold finger 010 and thermally and mechanically anchored using appropriate screws in order to be cooled to cryogenic temperature. In order to acquire sample signals, sample 131 is connected to the higher temperature chamber 120 through wires 160 used for data acquisition. A first wire 160 is connected from the sample 131 to a thermalization plate 170. A second wire 150 is connecting the thermalizing plate 170 to the external environment. Preferably, the apparatus used for thermalization 170 is mechanically and thermally connected to the cryostat last chamber baseline 020 at T1 thanks to a mechanical attachment 140. Being thermally coupled to the first chamber 130, the mechanical attachment 140 acts like a thermal drain. This thermal drain ensures thermal dissipation and temperature transition from T2 to T1.

(13) Therefore, the general idea of the invention is to connect the sample 131 located in the chamber 130 at cryogenic temperature T1 to a thermalization plate 170 with at least one wire 160. Further preferably, the thermalization plate 170 is connected to the external environment through a wire that may be a coaxial cable 150

(14) FIG. 2a shows a preferred embodiment of the thermalization plate 170. This thermalization plate is preferably an IMS plate and is preferably composed of N wirelines connected to N inputs 105 ports and N output ports 106 connected by wires of length L 108. Thermalization plate input temperature is at T1 and output temperature is at T2. This plate is adapted with 50 impedance so that so that high-frequency (above 1 GHz) and weak signals may be transmitted without any attenuation. By doing so, one of the main advantages is that any suitable cable type may be used between the sample 131 and thermalization plate 170, whereas the output thermalization plate 170 may consist in cables adapted to avoid thermal dissipation such as coaxial cables. With this embodiment, wire length L 108 is adapted in order to ensure a gradient from T1 which is the temperature of the first cryostat chamber (at the level of 2K) at the input to T2 which is the temperature of the second cryostat chamber (at the level of 20K) at the output. Therefore, with this thermalization plate 170 one can, from the electrical point of view, adapt wirelines with high bandwidth signals which means, low attenuation at high frequencies and it is possible to design easily wirelines in order to adapt their impedance to the input/output impedance. Finally, from a thermal point of view the thermalization plate ensures that all parts of the coaxial cable, namely the shield and conductive core, are thermally anchored at the required temperature of T1, avoiding excessive heating of the sample.

(15) The first thermalization plate 170 described is composed of inactive components, namely wires used to transmit electrical signals. Alternatively, the thermalization plate may embed active device for signal amplification or processing. This can have several advantages among them, the proximity to the signal source leading to lower interference pickup, lower noise or increase system bandwidth.

(16) FIG. 2b shows the thermalization plate 170 structure based on IMS technology used within a cryostat and used for wirelines thermalization. It has been mechanically adapted as described below for working in cryostat conditions. The IMS plate is composed of at least five (5) layers each of them in charge of a specific function.

(17) First layer 206 is dedicated to heat dissipation through conduction phenomenon, and consists in a layer made with a material with high thermal conductivity. As an example it may be Al or Cu. This heat dissipation layer helps to spread thermal energy at the lower bound of the thermalization plate.

(18) Second layer 205 is an insulator layer made of a thin dielectric layer enabling to separate and discriminate electrically conductive layers from heat dissipation layer.

(19) Third layer 204 is made of conductive material used for forming the circuitry enabling wire thermalization.

(20) Above these conductive tracks, two additional layers 203, and 202 are preferably used for thermal and electrical insulation which are namely the solder mask and solder paste.

(21) Therefore, wirelines realized on IMS board enables to thermalize wirelines from temperature T1 to temperature T2 and spread thermal power through thermal drain

(22) FIG. 3 depicts the IMS thermalization board, ready to be installed inside a cryostat. In order to get this IMS thermalization board within a cryostat, the following method may be used.

(23) The first step 301 consists in putting the IMS plate 170 in contact with a part of cryostat at T1. The thermalization plate 170 may be placed outside the T1 chamber at cryogenic temperature 120. It is outside the T1 cryogenic chamber, and then the thermalization plate 170 may be fixed to a mechanical attachment 140 (optionally made of metal or the like) acting in this case as a thermal drain which can be considered as an additional step 301 of the present method.

(24) The second step 302 consists in connecting the cable 150 coming from the outside of the chamber 110 at temperature T2 on one of the output connectors of the plate 106.

(25) The third step 303 consists in connecting the corresponding cable 160 coming from the chamber 130 at temperature T1 to the connector 105 on the plate linked to the previously cited connector through the wire-guide. Note that it is important that two cables that have to be linked together are connected to the same wire-guide.

(26) FIG. 4 shows, as previously described, that the disclosed invention relies on the exploitation of IMS board technology for cryostat and wire line thermalization. In this figure two graphs are presented based on the characterization of an SNSPD detector without a thermalization plate (a) and with a thermalization plate (b).

(27) These two graphs plot the Detection Efficiency as a function of the bias current in (A). Experiment without thermalization plate shows that typical saturation plateau can not be obtained above 5.5 A. In the opposite, with thermalization plate, a detection plateau 401 is obtained from 5.0 A to 6.2 A corresponding to the maximum detection efficiency. This detection plateau 401 is clearly one of the characteristics of the single-photon detection regime corresponding to weak signal detection. Moreover, this detection plateau 401 corresponds to the regime where the internal quantum efficiency of the single photon detector is near 100%. Clearly this regime is sought after in applications using SNSPDs since higher detection efficiency typically means better performance. The fact that the saturation plateau without the thermalization plate is smaller, shows that the SNSPD device is being heated by heat flow through the center core of the coaxial cable, which is badly thermalized, hence reducing the performance of the SNSPD. In that specific case, the thermalization plate allow proper functioning of the SNSPD detector

LIST OF REFERENCE SIGNS

(28) TABLE-US-00001 (100) - Cryostat (010) - Cryostat cold finger (020) - T1 cryostat chamber baseline (030) - Feed through hole (120) - 2.sup.nd Cryostat chamber (at T2) (105) thermalization plate input (106) thermalization plate output (108) L thermalization plate wire length (110) - 3.sup.rd cryostat chamber (At T3) (130) - 1.sup.st Cryostat chamber (at T1) (131) - Device/Sample (140) - Mechanical attachment/Thermal drain (150) Outside cable (160) wires used for data acquisition (170) Thermalization plate (206) Thermalization plate first layer - heat spreader (205) Second layer - insulating layer (204) third layer - conducting wires (203) Fourth layer - solder mask (202) Fifth layer - solder paste (301) - First method step (302) - Second method step (303) - Third method step (401) - Detection Efficiency Plateau