Nucleation of 1-µm bubbles via charged walls

The propagation and transfer of 1-μm bubbles via charged walls in ion-implanted contiguous-disk devices was previously reported. A novel bubble nucleator utilizing charged walls to provide a portion of the nucleation field, helping to define the spot where nucleation occurs and also reducing the required current, is described. Controlled nucleation of 1-μ bubbles and propagation away from the nucleation site have been tested in several double garnet composites with different material Q factors (2 to 4) in the storage garnet layer. Typically, using a 0.1-μs current pulse along a 5-μm wide conductor, the nucleation current increases from 200 mA to over 800 mA over the entire bias field range (∼15 percent) for propagation as the Q factor increases from 2 to 4. Compared to nucleators without charged wall assistance, the reduction in current level attributable to the charged wall is approximately 30-40 percent. This and other data are consistent with a model which assumes that nucleation takes place at the interface between the implanted and unimplanted layers, and that the charged wall contributes a field on the order of 0.5 × 4πM to the nucleation process. The collective operating margins for propagation (350 kHz), generation, transfer and annihilation of 1-μm bubbles along a short contiguous-disk pattern with a 4.5-μm device period are presented.