The design of magnetoresistive multitrack READ heads for magnetic tapes

Magnetoresistive (MR) elements linearized by barber pole stripes arranged symmetrically on both halves of the Permalloy sensor are particularly linear, generate almost no Barkhausen noise, and have a good stability against external easy axis fields. This is especially true if the barber pole stripes have a short distance. Experimental unshielded multitrack MR heads were fabricated from these symmetric barber pole sensors and tested. The multitrack heads consist of 32 MR sensors and are suited for the parallel reproduction of long to medium wavelength information, recorded with 250-tpi and 20-μm guard band on a normal cassette tape. During wafer prober experiments, almost no magnetic cross-coupling could be observed within the limits of tolerable field amplitudes. Some technological aspects of multitrack head fabrication are discussed. Multitrack heads with shielded symmetrical MR elements were also fabricated. From the results of wafer prober experiments, it was concluded that shielded heads with sensors considerably recessed from the head surface should deliver enough signal if a proper flux conductor is used in between both shields. Thus the sensitivity of MR heads to wear effects may be considerably reduced.