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Balanced Resistance Magnetoresistive Head Compensated against Thermal and Piezoresistive Effects

IP.com Disclosure Number: IPCOM000083302D
Original Publication Date: 1975-Apr-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

Anderson, R: AUTHOR [+4]

Abstract

The structure and method of fabrication of a balanced resistance magnetoresistive (MR) head, offers compensation against thermal and piezoresistive effects. Any change in the resistance of a magnetoresistive sensor element which results from external influences, other than the field to be sensed, yields an unwanted signal from the head. A thermal spike in a magnetoresistive head causes a corresponding spurious output from the head, because heating of the MR stripe results in a change in its resistivity. Similarly, stresses cause the piezoresistive effect and extraneous signals.

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Balanced Resistance Magnetoresistive Head Compensated against Thermal and Piezoresistive Effects

The structure and method of fabrication of a balanced resistance magnetoresistive (MR) head, offers compensation against thermal and piezoresistive effects. Any change in the resistance of a magnetoresistive sensor element which results from external influences, other than the field to be sensed, yields an unwanted signal from the head. A thermal spike in a magnetoresistive head causes a corresponding spurious output from the head, because heating of the MR stripe results in a change in its resistivity. Similarly, stresses cause the piezoresistive effect and extraneous signals.

The balanced structure shown in Fig. 1 compensates against thermal and piezoresistive effects, as discussed in patent No. 3,860,965 issued to O. Voegeli. A magnetoresistive head 30 for sensing magnetic recordings on media, such as tape comprises MR elements S1 and S2 adjacent to each other that are magnetostatically coupled to one another. The MR elements may be formed as thin-ferromagnetic films parallel to one another and are separated by a thin- insulating layer L.

The elements S1 and S2 have low anisotropy and a high-magnetoresistance coefficient. The MR elements are matched to each other and have substantially the same thickness, dimensions, resistance, coefficient of thermal expansion, resistivity and shape anisotropy. The MR elements S1 and S2 have a common junction 45 which is connected through a conductor 49 to a reference voltage source, such as ground terminal 46. The elements S1, S2 receive current from a constant-current source 50 applied through conductors A and B. The conductors A, B and 49 are deposited over the ends of the MR elements.

A differential amplifier 10 is connected to the output of the elements. Accordingly, the voltage difference signal across the MR elements S1, S2 is sensed by the amplifier 10, and appears after amplification at output terminal 57. Thus, when a drive current from source 50 is applied through conductors A and B to the elements, the drive current through MR element S1 energizes that element and serves to magnetically bias magnetoresistive element S2. Similarly, the drive current through MR element S2 energizes that element and serves to magnetically bias element S1. The drive current required is relatively low.

Magnetically, the current I2 (indicated by the arrow) in stripe S2 biases stripe S1 and vice versa, so the stripes are biased in opposite directions. A common magnetic field sensed by both stripes results in increased resistance in one stripe and a decrease in the other. Amplifier 10 senses the resulting difference in voltage between A and B.

The coupling of the elements is illustrated schematically in Fig. 2A, which is a partial front view of Fig. 1 showing the elements S1 and S2. Fig. 2B is a right elevation of Fig. 1 showing the exterior of element S1. H1 is the magnetic field acting on MR element S2 due to...