Study of Components for $\hbox {MgB}_{2}$ RSFQ Digital Circuits

In order to realize superconducting circuits using MgB₂, an in-depth study was conducted to generate a baseline of parameters necessary for circuit design. With a transition temperature (T_c) of 39 K, devices and circuits can be made to operate at low temperatures to achieve higher operating frequencies, and at high temperatures to lower the cooling requirements. The Josephson junction critical current density (J_c) and the product of critical current (I_c) and normal resistance (R_n) are necessary design parameters along with the sheet inductance (L_sq) of a superconducting microstrip. The need for a shunt resistor is also required for low-temperature operation. This paper describes the current status of these parameters for the multilayer process of all-MgB₂ Josephson junctions. The study includes the fabrication of Josephson junctions and DC SQUIDs to perform microstrip inductance measurements as well as research on materials suitable for an on chip resistor. The results have been used to design a Rapid Single Flux Quantum Toggle-Flip-Flop circuit operating at around 20 K.