Superconductor Integrated Circuit (IC) Testing With the Integrated Cryogenic Electronics Testbed (ICE-T)

Future development of superconductor digital and mixed-signal ICs requires extensive testing with a large number of input/output (I/O) lines for applying independent bias controls, injecting test signals, and monitoring outputs of different subcircuits. There is a growing need for a standardized test apparatus for a variety of complex superconducting chips and multichip modules (MCMs). Such a test apparatus must support many I/O lines, be easy and cost-effective to operate, and support prolonged automated testing. Existing test apparatus include liquid He cryoprobes and cryocooled custom digital-RF systems, both of which have drawbacks. LiquidHe cryoprobes with universal wiring, such as 40 or 80 coaxial cables, are convenient to use. Cooled by immersion in a tank filled with liquid He, these cryoprobes allow rapid cool-down and warm-up. However, large consumption of liquid He, the cost of which has been steadily increasing worldwide, makes this solution rather expensive and wasteful. On the other hand, one can exploit the modular reconfigurability of HYPRES' digital-RF receiver product to create a testbed for different ICs. Such a system uses the smallest commercially available closed-cycle refrigerator (similar to 1.2 kW) and has negligible operating cost. However, reconfiguration takes time and expertise since these products are specially designed with customized chip package and wiring tominimize the thermal load on the cryocooler. These low-maintenance systems are ideal for prolonged operation of a single chip, which is invaluable for superconductor electronics system developers and end-users. The integrated cryoelectronics testbed (ICE-T) combines the advantages of the liquid He cryoprobe and the cryocooled digital-RF product. By using a more powerful, commercially available, electrically powered closed-cycle refrigerator (7 kW), ICE-T alleviates the thermal constraints on wiring while maintaining very low operating cost. By separating the electrical and thermal subsystems, it maintains modularity without sacrificing the universality of the cryoprobe. A set of universal and custom electrical modules can be independently built and inserted in ICE-T. Universal inserts with 40 and 80 coaxial cables accommodate all chips with standard I/O pads like the familiar liquid He cryoprobes. Custom inserts for different classes of chips and MCMs are designed and built according to user requirements and specifications. The utility of the ICE-T was successfully demonstrated by testing a benchmark superconducting digital circuit at low frequency and an analog-to-digital converter chip clocked above 20 GHz.