Long term stability of magnetoresistive bubble detectors

Various failure modes of Permalloy magnetoresistors are evaluated. Magnetic failure of magnetoresistors can be eliminated by passivation with evaporated SiO and sputtered Al2O3and Si3N4films. Effect of the permalloy/Au interaction at the sensor/lead metallization interface was investigated by high current and temperature stressing (5.5 × 10⁶A/cm²and 330°C) of actual sensors, and by He-ion nuclear backscattering and x-ray diffraction analysis of Au/permalloy sheet film couples. Stripe cracking failures occur at the negative terminal. Significant interdiffusion of Au/permalloy can occur. However, the interdiffusion is not particularly deleterious to sensor performance.