An all-NbN time domain reflectometer chip functional above 8 K

Niobium nitride has a superconducting transition temperature nearly twice that of niobium. A 5-ps time-domain reflectometer chip based on NbN technology has been designed, fabricated, and tested. The circuit is operable up to 9 K. The NbN process and limitations are discussed, and present drawbacks in the junction fabrication method are pointed out. Electrical properties are discussed, the circuit operation is described, and simulations are presented that are based on model parameters extracted from device measurements. The actual output of the circuit is presented as evidence of basic functionality. This is the first demonstration of a functional high-speed circuit based entirely on a compound superconductor technology and operable at temperatures above 8 K.>