Effects of annealing on propagation in ion-implanted contiguous-disk bubble devices

Bubble propagation margins are found to be affected by heat treatment in ion-implanted contiguous-disk devices fabricated on LPE-grown double-layer garnet films which support 1 μm bubbles. When an optical reflector is deposited directly on the driving layer, interfacial diffusion takes place, and this raises the coercivity of implanted layer which in turn causes a severe degradation of propagation margins. For example, in devices fabricated with a Ti reflector, bubble propagation ceases after a 350°C annealing for 30 min. However, a thin diffusion barrier such as 100Å thick SiO2prevents such diffusion for temperature up to 550°C. The adverse effects of annealing on propagation margins are stronger in populated minor loops due to interaction of long-range charged walls as compared with isolated loops and isolated disks. After a series of isochronal annealing, populated loops cease to propagate bubbles after annealing in the temperature range of 350-400°C, whereas the loss of margins in isolated loops and disks are typically less than 30% after 600 to 650°C anneals. In singly implanted devices with a nominal dose of 3 × 10¹⁵He+/cm², an annealing at C generally increases margins to a value obtained in doubly-implanted samples in which little improvement is obtained by annealing. Stress gradients caused by the discontinuity in the overlay patterns contribute significantly to the increase of threshold drive field after annealing, The rapid degradation of propagation margins found after annealing in the temperature range of 350 to 400°C in all samples is caused by reordering of the damaged lattice as observed previously in ion-implanted semiconductor devices in which reordering of lattice disorder occurred at temperatures as low as 260°C in Si and 180°C in Ge for low doses ( /cm²) and 570°C and 380°C, respectively, f- - or higher doses ( /cm²).