Following on from the posts about miniature circuits here and here, I thought I’d show some pictures of the sample box where the chips are housed before they are cooled down in the dilution refigerator.
As you might expect, there is more signal filtering before the DC lines enter the sample box. The filtering is again done by powder filters. These are housed in antechambers surrounding the main sample space. Here is a picture showing the coils which form the inductive component of these LC filters before they have been ‘potted’. You can also see the feedthrough capacitors entering the main sample chamber.
And here is one after showing the filters after they have been filled with stycast:
In the centre of the sample box is the sample space containing a chip carrier, the 4 filtered DC lines and 2 RF lines (which have not been connected yet here). It is important that the chip sits on a copper chip carrier which is screwed down tightly to the sample box. This is due to the physics of conductivity at low temperatures. If the chip carrier is glued down, there would not be very much thermal connection between the sample box and the chip carrier, as glues become very good thermal insulators at low temperatures. The best way to make thermal contact at low temperatures is to have two clean metal surfaces in hard contact. The sample box itself is attached to the mixing chamber of the dilution refrigerator, the part that does the cooling, so this too must be screwed down tightly.
The connectors on the outside of the box are MCX-style jacks for the DC lines and SMA jacks for the RF lines.
There is also a tapped hole on the back of the sample box where a calibrated Ruthenium Oxide thermometer is mounted.