Conductor propagation circuits for high-density bubble- domain memories

Garnet epitaxial wafers are now available [1,2] which permit data to be stored at densities greater than one million bits per square inch (>200 000/cm2) and which allow data to be shifted at rates greater than one megahertz. We are developing circuits to fully utilize these materials which will be directly compatible with integrated-circuit peripherial electronics. They contain a number of independent storage loops, typically 512 bits, which are randomly accessible. Data is read by propagating the domain stream past a magnetoresistance domain detector element when the peripheral electronics applies a series of bipolar pulses (typically 2 volts and 8 mA) to the single-conductor propagation circuit of the loop to be read. The propagation circuit consists of a pattern of serrated-edge grooves etched into the epitaxial garnet layer [3,4] and overlapped with a serpentine conductor [5]. Information has been coded onto a complete stream of domains (one per bit) by using the lateral displacement technique [6]. Memory chips of the type described here are easily designed into small or large systems since the only external mechanical requirements are a constant magnetic bias field (supplied by a permanent magnet) and a reasonable amount of shielding from stray magnetic fields.