Process for producing magnetoresistive transducers

Details Process for producing magnetoresistive transducers Process for producing magnetoresistive transducers

1996-07-10

1999-10-05

Brenemar, R. Bruce

Etching a substrate: processes

Forming or treating article containing magnetically...

2960301, 360113, B44C 122

Patent

active

059618485

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a process for producing a magnetoresistive transducer and more particularly a magnetoresistive transducer having perpendicular transport.
The process of the invention furthermore makes it possible to produce a large number of these transducers in the same step, which transducers may or may not be connected together.
2. Discussion of the Background
In the various fields of application of thin-film magnetoresistive materials (read head for magnetic recording, magnetometers, compasses, various types of sensors, etc.), all the components are nowadays produced with thin layers of magnetic alloys such as "Permalloy": Ni80Fe20.
The discovery of a giant magnetoresistive effect in magnetic metallic Baibich et al., Physical Review Letters 61, p 2472, 1989 and in the document by T. Valet et al, Applied Physics Letters 61, p 3187, 1992. It is already accepted that these materials exhibit superior performance compared to those of magnetic alloys used hitherto.
The physical origin of this effect resides in the spin dependence of the scattering of carriers in magnetic metals and their alloys (see the document by A. Campbell et al., "Transport Properties of Ferromagnets" which appeared in Ferromagnetic Material, published by Wohlfarth, Amsterdam, 1982, vol 3) and in the existence of two magnetic states in these multilayers: a state in which the magnetizations of the magnetic layers all point in the same direction and which will be denoted P and the other state in which the magnetizations are alternately in one direction and then in the other and which will be denoted AP.
Switching from one state of alignment to the other causes a variation in the resistivity which may be written in the form:
Two types of geometry are possible, the first denoted CIP (the one which has been studied most) in which the current I.sub.0 flows parallel to the layers (see FIG. 1A), and the second denoted CPP in which the current I.sub.90 flows perpendicularly to the layers (see FIG. 1B).
As has been demonstrated by theoretical work (see the document by T. Valet et al., Physical Review, B 48, No. 10, p 7099, 1993) and experimental work (see the document by W. P. Pratt, Physical Review Letters, 66, p 3060, 1991), the second configuration is potentially more promising. Nevertheless, the difficulties encountered when implementing it have limited its study.
In order to clarify this point, it is necessary to calculate not the resistivity variation .alpha. of the multilayer, which is an intrinsic variation, but that of the total resistance which is the experimentally accessible quantity.
The resistance R of an object of resistivity .rho., of cross-section S and of length l is expressed in the following manner:
For a set of resistances in series, the total resistance will be the sum of all these resistances. Thus, in both the abovementioned cases (CIP and CPP), denoting by R.sub.m the resistance of the multilayer, by R.sub.f that of the current leads and by R.sub.c that resulting from the contact between the multilayer and these leads, the total resistance is given by:
In the general case in which the lines of current I.sub..theta. make an angle .theta. with respect to the planes of the layers (FIGS. 1a and 1b), the resistance variation associated with the situations on switching from ##EQU1## .phi..sub.m.sup.G.AP means resistivity in the antiparallel state of the CIP or CPP geometry for the magnetic layer, CPP geometry for the magnetic layer. a.sub.G is a mixture of the effects obtained in the two geometries.
In addition, these formulae show that the value of the measured effect is attenuated by the contact resistances and by the resistances of the on:
Thus, in order to get at the intrinsic value .alpha..sub.m of the effect, which is the maximum variation which it is possible to obtain, it is necessary to decrease the resistance ratio (R.sub.f +R.sub.c)/R.sub.m and, in order to decouple the .alpha..sub.m CIP and .alpha..sub.m CPP effects, to produce a structure in which the

REFERENCES:
patent: 5446613 (1995-08-01), Rottmayer
Gijs et al. "Perpendicular Giant Magnetoresistance of Microstructured Fe/Cr Magnetic Multilayers from 4.2 to 300 K"; "1993 The American Physical Society", pp. 3343-3346.

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