Improvement of NDRO characteristics of fine-striped magnetic thin film memory element

This paper reports the improvements of the NDRO characteristics in the FSM element achieved with combined application of multilayer film technology and topography control, and an improved process in forming the closed flux path structure. To form the adaptable closed flux path structure the following multistep procedure was developed: 1) deposition of magnetic film on the insulating surface; 2) deposition of Cu stripes over the film; 3) further deposition of magnetic fdm; and 4) removal of magnetic film between stripes by photoetching to form independent digit stripes. This improved method ensures a complete closed flux path between the magnetic films at the bottom and top. Thus, uniform memory characteristics and reproducibility are achieved. The bottom magnetic film is a four-layer film composed of Ni-Fe and Ni-Co films. On this film, Cu stripes, 2 μm thick and 100 μm wide, are deposited. Furthermore, a Ni-Fe film, 1 μm thick, is deposited. Nodules, 1-1.5 μm in diameter, formed on the Cu stripes by controlling deposition conditions, provide the top magnetic film with NDRO characteristics through the topography effect. The sense signal at 4 mV output from two intersections per bit is obtained with a word current at 150 mA having a rise time of 25ns.