Radiation Tolerance of Bubble-Domain Materials and Devices

Following a brief outline of magnetic bubble domain technology and possible radiation effects, the results of radiation effects experiments are presented. Permanent damage experiments on materials consisted of characterizing samples of Y3 (FeGa)5O12, Er3(FeGa)5O12, and (YGdTm)3 (FeGa)5O12 films before and after exposure to neutrons from a TRIGA reactor and to Co60 gammas. Parameter measurements included saturation magnetization, wall energy, defect density, wall mobility, coercivity, and saturation velocity. No significant changes in these parameters were observed after 1015 n/cm2 (1 MeV equivalent) and 5 × 107 rads. Permanent damage experiments on devices included measurements of propagation and annihilation margins, and domain sensor output (for shift registers) before and after exposure to reactor neutrons and Co60 gammas. Again no significant change was found after 4 × 1014 n/cm2 (1 MeV equivalent) and 5 × 107 rads for devices with hard-bubble suppression. Magnetoresistive parameters of a thin, permalloy domainsensor film were also unchanged after 1015 n/cm2 and 5 × 107 rads. Information stored in a shift register was read electrically immediately before and after exposure to a 30 ns pulse of 1.5 MeV electrons with a dose of 3 × 104 rads(Si) and found unchanged. A similar experiment, using optical determination of the stored information, indicated no change after a 1.7 × 105 rad pulse.