Current-Access Magnetic Bubble Circuits

Abstract

Experimental and theoretical results from our work on current‐access technology show promise for high‐density, ∼107 bits/cm2, and high‐frequency, f > 1 MHz, bubble devices. We have operated current‐access devices where the bubble‐driving fields derive from two patterned conducting sheets instead of orthogonal field coils. Margins for generation, propagation, and transfer were studied on 8‐μm periods at 1 MHz. These 8‐μm period structures typically required 1.5 mA/μm per conducting sheet and dissipated 14 μW/bit. Single conducting‐sheet, current‐access circuitry also propagates bubbles but offers less design flexibility. We present design criteria, magnetic field equations, and design curves. Implementation of these devices required new magnetic materials with quality factor Q comparable to available garnets, yet higher mobility and lower dynamic coercivity. Of the three systems, (YLuSmCa)3(FeGe)5O12, (LaLuSmCa)3(FeGe)5O12, and (LaLuSm)3(FeGa)5O12, the last appears best suited; some room temperature characteristics of the composition La0.6Lu2.1Sm0.3Ga0.9Fe4.1O12 are 4πMs = 470G, μ = 750 cmS−1‐Oe−1, d = 1.6 μm, and ΔHc = 2 Oe across a bubble for the threshold of motion. Necessary improvements in processing were made with a radio‐frequency, chlorine‐containing plasma etch which produced metal patterns identical to those of the etch mask. We anticipate that current‐access devices, when compared to conventional field‐access devices, will achieve higher data rates, lower power consumption per bit, and greater storage densities with existing processing technologies.

Measurement of the Induced Magnetic Field in a Flawed Tube

“…A straightforward calculation shows that the normal magnetic field component at the edge of a hole in a current carrying sheet is a rapidly decreasing function of increasing distance above the surface of the sheet [5]. It is therefore important to bring the radial sensor as close as possible to the wall of the tube.…”

“…It is therefore important to bring the radial sensor as close as possible to the wall of the tube. The significant perpendicular magnetic fields that exist at the edges of holes in current carrying sheets find technological application elsewhere as well; this effect is used to constrain magnetic bubbles in a current access bubble memory [5].…”

High frequency propagation of magnetic bubbles in dual conductor devices

“…In conventional films having uniaxial anisotropy the maximum velocity is about 20 m/s and the frequency in current access devices (a J.lm period) processed on these films is limited to about 1.5 MHz [1). When the bit frequency increases, the voltage across the coils and the heat dissipation in these coils rise to unpractical values.…”

Abstract: Recent advances in the design of dual-conductor bubble devices (invited)

“…Dual-conductor bubble circuits were announced in 1979 (1) and reviewed at the 1980 Intermag Conference (2). Work continued toward the design of a fully functional chip and, although problems remain, we report some of the progress that has been made.…”