Design of Passive Transmission Line by Adjusting Intrinsic Parameters of Josephson Junctions

Abstract

Along with the improvement of integration and the requirement of high-speed operation, the passive transmission line (PTL) plays a significant role in superconducting integrated circuits due to its intrinsic advantage of extremely low propagation delay and low signal loss in long-distance transmission. Good impedance matching is critical to reduce the signal reflection in the transmission line and maximize the power transferred. Based on the PTL wiring layer selection under SIMIT-Nb03 process, we studied the equivalent input/output impedance for Josephson junction (JJ) at the IO port and explored a method of impedance matching in rapid-single-flux-quantum (RSFQ) circuits by adjusting the Stewart McCumber parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\beta_c$</tex-math></inline-formula> of the JJ in the design of the PTL's driver and receiver. Furthermore, the accompanying influence from the JJ's modified <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\beta_c$</tex-math></inline-formula> on the performance of the driver and receiver is evaluated to maximize the profit of the functional circuits. The common-used serial resistor is removed to obtain a balanced bias margin for the PTL circuits. The proposed PTL has been designed and tested based on SIMIT-Nb03 fabrication process. ±30% bias margin for the PTL is achieved at low frequency and high frequency (40 GHz) contrast tests, including operation speed and transmission length as test vector. Additionally, a frequency sweep for 1 mm PTL is performed by the designed ring oscillator on the chip. The maximum working frequency is up to 129 GHz, with a margin duration of 8%.