Design of Bubble Device Elements Employing Ion-Implanted Propagation Patterns (1980)

Experimental 8-μm period magnetic bubble devices have been made using 270/Ne/2E14 + 130/H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /2E16 patterned implants on YSm-LuCaGe-IG films previously implanted uniformly with 80/Ne/1E14. For subsequent alignments, the patterned implant was converted, in selected areas, into a relief pattern by phosphoric acid etching. A 2000 A.U. SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> prespacer was deposited next, followed by the deposition and ion beam delineation of 500 A.U. of Permalloy for detection. A subsequent 2000 A.U. spacer was then deposited and patterned with via holes for electrical connection between the Permalloy and a 5000 A.U. Al-Cu layer which was deposited and patterned with plasma etching or ion beam milling. Final passivation and opening of contact windows were standard. All designs at 8-μm period were implemented with 2-μm or larger features. Novel ion-implanted propagation patterns are shown which accomplish merge, inside turns, and double period propagation. A conventional hairpin shape was chosen for the generator, and the structure was placed in a cusp on the strong side of the major loop. Phase and current margins are presented. The minimum generator current varied with the starting anisotropy of the bubble film. The minimum current was about 100 mA in films with H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> around 1700 Oe, when the shallow implant was unpatterned. When the shallow implant was patterned, lower values were obtained. An N-shaped transfer gate was studied. The design provides both a strong gradient, to separate the bubble from the implant boundary, and a locally lowered bias region to trap the bubble until the correct in-plane field orientation results in normal propagation. Phase and current margins are shown for transfer-out. A hairpin linking cusps on the two sides of a horizontal loop was found to transfer both ways with good current margins. This gate can be used as an active merge or to reverse the order in a block to overcome topological difficulties in a G-type major-minor loop chip. Using the same idea, a transfer gate was designed which transferred through a write line to the bottom of the minor loops. Good phase and current margins were obtained. A combination of a 2-μm wide implanted channel, a hairpin canductor, and a symmetrically placed Permalloy serpentine has been studied in a nondestructive read-out (NDRO) mode. It appears that the serpentine has too few turns for good averaging of Permalloy domain effects, as these detectors are noisy. An alternate design used a simple Permalloy bar entirely over implanted material. The straight detector produced better signal-to-noise appearance, although at a lower signal level and higher stretch current. Two straight bars were used in conjunction with the channel design. Both detector and “dummy” sense the stripped-out bubble in this case. Low noise and the best figure of merit δV/V ∼ 0.38 percent were obtained In the destructive read-out (DRO) mode of operation. Good signals were also obtained from a straight Permalloy bar located over an unimplanted region, in the DRO mode, with a separated dummy. A valid chip organization for the DRO mode is offered. Thus, all necessary functions have been demonstrated for the design of 8-μm period maior-minor loop-organized bubble devices based on ion-implanted propagation. At least 20-Oe margins are shown for all functions at 40-Oe drive field.