Development of Fast NbN RSFQ Logic Gates in Sigma-Delta Converters for Space Telecommunications

Abstract

In the future generations of telecommunication satellites, it will be necessary to reduce the analog part in reception systems and achieve RF front-end at higher carrier frequencies with higher sensitivity and higher bandwidth. RSFQ (Rapid Single Flux Quantum) superconducting logic is suitable to process very high speed digital data processing with very low power dissipation and with performances well beyond what should be possible with CMOS technology in the next decades. The RSFQ circuit technology based on superconducting niobium nitride (NbN) presently developed at CEA-G involves NbN/Ta(sub X)N/NbN internally shunted Josephson junctions with high critical current density and high maximum switching frequency close to 1THz, as required by ultra-fast RSFQ electronics. Very low power dissipation and very low noise level of fast NbN RSFQ gates designed and fabricated at CEA-G are presented. The RSFQ circuit for a sampling comparator has been studied operating in a sigma-delta modulator with a 30 GHz sinusoidal input carrier signal and high sampling clock frequency of about 200 GHz. We will present the thermal noise and how it influences the phase fluctuations. Such a nitride technology has been recently demonstrated to be fully compatible with large scale integration on 200 mm diameter silicon wafer at reasonable fabrication cost in a micro-nano-electronic platform at CEA-Leti. The applicability of NbN RSFQ digital functions in the next decade Space Telecoms will finally be possible thanks to the development of reliable, low power consuming, space qualified cryocoolers operating at about 10K. Moreover semiconductor system design and integration techniques can be simply adapted to superconductivity, to fit the rules of any RSFQ library-foundry network, such as "CONNECT" for Japan and "FLUXONICS" for Europe.