Tunneling magnetoresistive head and a process of tunneling...

Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head

Reexamination Certificate

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C428S611000, C428S621000, C428S629000, C428S632000, C428S637000, C428S668000, C428S682000, C428S212000, C428S409000, C428S692100

Reexamination Certificate

active

06710986

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a tunneling magnetoresistive element, and also to a magnetic head and memory device utilizing the tunneling magnetoresistive element. The present invention relates also to a method of manufacturing these devices.
As an example of the magnetic sensor based on: tunneling magnetoresistance effect (TMR), a TMR element is proposed by S. Jagadeesh Moodera and Lisa R. Kinder (J. Appli. Phys. Vol.79 (1996), No. 8, pp.4724) (Publication 1); and by J. C. Slonczewski (Physical Review B Vol.39 (1989), No. 10, pp.6995) (Publication 2). Since this TMR element is capable of exhibiting a large magnetoresistance effect as compared with the conventional magnetoresistive element (MR element), the application thereof as a read magnetic head is highly expected.
This TMR element is constructed as shown in
FIG. 1
such that a tunnel barrier layer
300
is sandwiched between a first magnetic layer
200
and a second magnetic layer
100
. In this case, the first magnetic layer
200
is formed on the surface of a lead wire layer
400
formed on a substrate
500
and is connected with an external electric circuit. On the other hand, the second magnetic layer
100
is also connected with the external electric circuit. If, in the case, these two kinds of magnetic layers
100
and
200
differ in coercivity from each other, there will be generated a phenomenon that, the orientation of the magnetization of these magnetic layers
100
and
200
becomes parallel or anti-parallel with each other corresponding to the changes in external magnetic field
800
.
Meanwhile, when a bias voltage V is applied between these two kinds of magnetic layers
100
and
200
, a tunnel current I is allowed to flow therebetween through the tunnel barrier layer
300
with the tunnel resistance R in this case being defined by R=V/I. It will be recognized through the observation of the magnitude of the tunnel resistance R whether the orientation of the magnetization of the two magnetic layers
100
and
200
is parallel or anti-parallel. A device which is capable of outputting the changes of tunnel resistance R of a TMR element corresponding to the change of the external magnetic field
800
is the aforementioned magnetic sensor based on tunneling magnetoresistance effect.
As disclosed in the aforementioned publication No. 1, the magnitude of changes of tunnel resistance R is mainly determined by the value of the polarizability P
1
of a magneticllayer
100
and also by the value of the polarizability P
2
of a magnetic layer
200
. The value of “polarizability” is closely related to the magnitude of magnetization (=spin polarizability) of a substance, and the magnitude of magnetization is a value which is specific to a substance. As the magnitude of “polarizability” becomes closer to
1
, the magnitude of changes of tunnel resistance R would become larger.
For each magnetic layer, the value of “polariziability” can be determined by finding the number of electronic state which is capable of contributing to the tunnel conduction. Namely, the “polarizability” inside each magnetic layer is determined by a difference between the number of spin-up state and the number of spin-down state, both of which are capable of contributing to the tunnel conduction. A difference in number between the number of spin-up state and the number of spin-down state also becomes an issue on the occasion of determining the magnetization of a metallic magnetic body. The numbers of electronic state to be employed for defining the value of “polarizability” here differs from that to be employed for determining the ordinary magnetization in the respect that only the electronic states which are capable of contributing to the tunnel conduction is taken up out of the possible electronic states inside the magnetic layers. In other words, when only the electron which is capable of contributing to the tunnel conduction is taken into consideration, the value of “polarizability” discussed herein is not necessarily identical with the value of ordinary magnetization.
An object of the present invention is to provide a tunneling magnetoresistive element which is capable of obtaining a higher “polarizability” and hence capable of achieving a larger magnitude of changes in tunnel resistance R, which can be realized by optimizing the selection of electronic states that can contribute to the tunnel conduction even though a magnetic material having the same magnetization is employed.
Another object of the present invention is to provide a high sensitivity magnetic head and the method of manufacturing such a magnetic head.
A further object of the present invention is to provide a magnetic memory which is non-volatile and is capable of reading and writing data at a high speed, and the method of manufacturing such a magnetic memory.
SUMMARY OF THE INVENTION
First of all, the meaning of the state called “an electronic state that can contribute to the tunnel conduction” will be explained. This electronic state may be summarized in such a way that it is (1) an electronic state in the vicinity of Fermi surface and at the same time, (2) an electronic state having a wavevector which is perpendicular to tunnel junction plane (i.e. parallel with the direction of thickness of tunnel barrier). When these electronic states of the magnetic material are located in the wavevector space, the aforementioned electronic states that can contribute to the tunnel conduction are specified by the wavevectors which are roughly normal to the tunnel junction plane and which have the lengths that roughly correspond to the length of the Fermi energy of the direction.
The aforementioned requirement (2) are brought about by the wavevector selectivity of the tunnel barrier. As reported by E. Wolf, in “Principles of Electron Tunneling Spectroscopy” Oxford University Press, Oxford, 1989, pp. 23 (Publication 3), in the case of ideal dielectric tunnel barrier which is constituted by infinite planes and where alumina, etc. is employed, the transmission factor of tunneling electron becomes maximum when the wavevector of tunneling electron that can be described by a plane wave is parallel with the normal line of tunnel barrier. However, when the wavevector begins to include a component perpendicular to the normal line of the tunnel barrier, the transmission factor of tunneling electron will be sharply decreased. When it is assumed that the barrier height is 2 eV, the thickness of tunnel barrier is 1 nm, and Fermi level is 5 eV, the angle between the direction of normal line and the wavevector as the transmission factor of tunneling electron falls down to 1/e (e: the base of natural logarithm) would become only around 8 degrees. Namely, the wavevector of the tunneled electron is very well aligned. It may be said in view of this fact that the tunnel barrier where the flatness thereof is sufficiently ensured is a device exhibiting a highlyefficient wavevector selectivity. In other words, the electronic state of the electron that has been taken up by the tunneling from the magnetic layer can be said to be only the electronic states included in a region of a very small solid angle which spreads around the gamma (&Ggr;) point in the wavevector space.
Therefore, it is very likely that the tunneling electron to be obtained from a group of electronic states where the direction of wavevector is very sharply aligned is characteristically very sensitive to the anisotropy of the Fermi surface, i.e. the crystal anisotropy.
Such a characteristic of the tunneling electron can be inferred also from the experiment of magnetic Compto scattering where circular polarized X-ray is employed as set forth by Yoshidazu Tanaka, Nobuhiko Sakai, Yasunori Kubo and Hiroshi Kawata in “Physical Review Letters”, Vol. 70, No.10, 1993, pp.1537-1540 (Publication 4). In this experiment, the polarizability of electron taken up from the surface of iron by means of circular polarized X-ray is directly measured, obtaining the result that the polarizability of electron to be released in

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