Cryogenic Test-Bed Applied to 9 K NbN RSFQ Devices Operation

NbN RSFQ circuits operating at 9 K reduce the cooling constraints especially for portable, remote, telecoms or medical imaging applications. We have developed a test-bed to study the operating temperature of the various mixed RF and digital circuit blocks of NbN `HyperSCAN´ project test vehicle 1 cm<sup>2</sup> chips. The use of a widespread helium cryostat (`Orange-ILL´) allows us to stabilize the chip temperature in the range 2.9 K-20 K with thermal oscillations lower than 0.1 K. The chip is mounted on a PCB and shielded from the external field: the PCB provides a multi-connection packaging used in order to study temperature and frequency operation of 30 GHz NbTiN CPW filters, RSFQ gates, analog SQUID and NbN/TaN/NbN SNS junctions arrays. The comparison between electrical simulations and tests is made on flexible, ~ 56 cm long, micro-strip line ribbon cable carrying 32 signals each including bias lines, in the range of DC-3 GHz, combined with 4 semi-rigid ~ 40 GHz coaxial cables. By removing spurious resonances, it is expected to take full benefit of the large bandwidth, low insertion loss and low thermal conductivity of the set-up. We emphasis on the flexibility, large yield, reliability and reduced cost of such packaging coupled to He cooling exchanger for applying to testers and to future 9 K NbN multi-ADC green and remote systems when only low electrical power sources are available.