Characterization of scalable Josephson memory element containing a strong ferromagnet

Abstract

Josephson junctions (JJs) containing ferromagnetic (F) materials are being considered for applications as cryogenic random access memories (RAM). In this work, we report on the fabrication and characterization of tunnel JJs, based on Nb technology with a strong ferromagnetic interlayer Ni80Fe20 alloy (Permalloy), which is suitable for the realization of devices with reduced area and guarantees relative low saturation and coercive fields in the use of JJs as RAM elements. We have successfully realized Josephson memory elements that work well down to 7 μm2 preserving high values of the characteristic voltage. We have also investigated the role of the F layer thickness, and by measuring the critical current dependence on the external applied magnetic field, we have optimized our devices as memory elements using thin ferromagnetic layers with thickness down to 3 nm. We have experimentally proved their functioning as memory elements by applying magnetic field pulses in opposite directions that can change the F layer magnetization.