Two-inch-diameter wafers containing 56 bubble memory chips of 16 kbit capacity each were fabricated by electroplating. A three-mask level design with a thin-film detector and a minimum feature of 1.5 μm were used. The NiFe films, plated out of a NiFe-sulfamate or a NiFe-citrate bath, had a coercivity of 1.5 Oe, a magnetostriction of 0 to -1 × 10-6a relative magnetoresistance of 1.8 percent at maxi...
The design and operation margins of a bubble memory chip 2,8 mm × 2,1 mm with 32 minor loops of 128 bits of storage capacity each are described. In a special package, designed for test purposes and containing the drive field coils and a variable bias magnet system, signals up to 10 mV are generated by bubbles of 6 μm diameter in a thin film detector. The X-bar propagation works well up to 500 kHz using garnets having the composition Y 1,6 Sm 0,4 Ca 1 Fe 3,9 Ge 1 Si 0,1 O 12 . Also the transfer is performed by special X-bar transfer gates.
Plated wire memory elements with good NDRW-characteristics can be produced by a sandwich diffusion technique. A thin layer of tin is placed between a smooth copper and the permalloy film and the wire has to be annealed before and after the plating of the permalloy. The reproducibility and the extrapolated long time stability were good. The parameters of this technology and the influence of the two annealing temperatures on the memory characteristics are described. The two fold diffusion of the tin film into the copper and permalloy layers produces the NDRW-behavior.
Bubble domain memory chips with micron dimension patterns have been fabricated by additive electroplating through photoresist windows using the conductor first processing. Etching defines the detector strips and removes the plating base. The various fabrication steps are described and discussed. The uniformity of the plated films is good and gives a reasonable yield. Nonmagnetic underlayers were plated below the NiFe bars. The gap width could be reduced by overplating the photoresist windows. 4 kbit chips have been fabricated with the processes described.
It is possible to improve the margins of propagation in field-access bubble memories considerably by a new arrangement of the Permalloy bars which constitute the propagation path. More slender bars of equal length become possible if the bars form an X-shaped pattern and the bubbles propagate at an angle of 45° with respect to the bars. U-turns and bubble gates have been designed and tested success...
The storage properties of flat thin Ni-Fe films can be improved by diffusing a nonmagnetic metal into them. Usually this metal is deposited on the Ni-Fe film in a vacuum chamber. By this well-known technique one can also electroplate the non-magnetic overlay. Several metals, e.g., Zn, Cd, Cu, Pb, Sn, Bi, and In have been tried. Tin gave the best reproducibility. The dispersion remains almost unchanged up to a ratio of 1, so that very good bit current margins are achieved. To avoid demagnetization effects, which could mask the film qualities, large spots were investigated. It was found that the creep threshold is independent of the film thickness (350-1000 Å). An explanation for this desirable behavior can be found if one assumes that the nonmagnetic metal fills up and enlarges easy-diffusion paths in the film and thus creates obstacles for a creeping wall. Despite the low diffusion temperature for Sn, 50-100°C, the long-time stability of the magnetic parameters is good, and it is possible to get uniform magnetic parameters on large memory planes.
