Magnetpwiderstandsdetektoren für bubblespeicher

Abstract

The principles of magnetoresistive permalloy detectors for bubble sensing and methods for increasing the bubble signal are briefly discussed. To completely utilize the magnetoresistive properties of the detector material, galvanic decoupling of the domain stretcher from the sensor strip must be provided. The characteristics of thin-film chevron stretcher detectors are presented which are galvanically decoupled from the stretcher bars by an insulating layer. For the chevron stretcher detectors usually employed, the domain signal is created when the sensor magnetization lies nearly parallel to the input current. Due to the cos 2 θ dependence of the magnetoresistance, the optimum signal sensitivity will be obtained near the 45° orientations. This condition can be fulfilled by positioning the sensor strip asymmetrically with respect to successive chevron columns of the domain stretcher. By this arrangement, the signal sensitivity is improved by about 50% compared to the sensor symmetrically positioned. Furthermore, in a strobe window which is about 20% of the read cycle and coincides with the signal peak, considerable improvement of the ONE/ZERO ratio is obtained. Operating the asymmetrical sensor in a 4 kbit bubble memory chip at 100 kHz drive field frequency, a signal sensitivity of 2 mV/mA was obtained. In a 2 μs wide strobe window, the ONE/ZERO ratio was ⩾20 dB. Finally, the properties of a thick-film serpentine-type detector are discussed in comparison with thin-film sensors.