ИСТИНА

We consider a possibility of the scaling of superconducting digital circuits down to nanometers. For this purpose, we analyze different options for the implementation of nano-scale Josephson junction. Such a junction should possess high values of the critical current, Ic, and the normal state resistance, Rn, as well as being well reproducible for providing fast and reliable operation of the circuits. We argue that a Superconductor - Normal metal - Superconductor (SNS) Josephson junction of variable thickness bridge geometry is a unique choice to meet these requirements. Theoretical analysis of this junction is presented under the assumption that its dimensions are comparable or smaller than the coherence length of N-material. The results show that the junction with high (sub-millivolt) IcRn value and the area comparable to the one of semiconductor transistors fabricated in the frame of a 32-nm process can be obtained using broadly utilized Nb/Al or Nb/Cu pairs of materials. At the same time, the transition to nanometers is impossible with the current presentation of information as magnetic flux quanta. Here we introduce the concept of superconducting digital circuits that do not utilize magnetic flux and have no inductances. The key idea of our approach is the utilization of bistable Josephson structures for information storage. We consider the design methodology of the all-Josephson junction (all-JJ) circuits on the example of utilization of recently developed 2-JJs with halved periodic current-phase relation (CPR), though other types of junctions having non-sinusoidal CPR including -, -, and 0- JJs are also suitable. Besides some broadly used basic cells, we present an all-JJ 8-bit parallel adder to illustrate the applicability of the proposed approach to the development of complex logic circuits. The presented concept of the scaling can be readily implemented using standard fabrication processes. Our results show that the capabilities of superconducting technology in the aspect of a circuit complexity can be close to the one of CMOS technology reaching several billion JJs on 1 cm2.