Analysis of thin film detector for bubble devices

Thin (35 nm) permalloy is being considered for magnetoresistive bubble detection because of the improved performance compared to the thick (400 nm) MR serpentine detector. The key reason for the significant performance improvement is that the thick permalloy which provides the bubble drive also shields the detector from the external rotating field allowing the detector to deliver 1-1.5% MR signal. A model of this shielding will be described. The dependence of the relevant signal characteristics: amplitude, pulse position, pulse width, and zero signal on geometry, position, temperature and sense current are given. R has a temperature coefficient ranging from 0 to 0.6%/°C depending on the geometry of the detector. Within wide limits, the pulse position is not a function of alignment, but is synchronized to the rotating field phase.