Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of biasing or erasing
Reexamination Certificate
2000-04-04
2002-10-29
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of biasing or erasing
C360S324200
Reexamination Certificate
active
06473257
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention mainly relates to a method and apparatus for measuring characteristics of a ferromagnetic tunnel magnetoresistance effect element. The ferromagnetic tunnel magnetoresistance effect element is, among magnetoresistance effect films for reading the magnetic field intensity of a magnetic recording medium or the like as a signal, an element which is capable of reading a small magnetic field change as a greater electrical resistance change signal. The ferromagnetic tunnel magnetoresistance effect element is mainly installed in, for example, a hard disk drive.
2. Description of the Related Art
Following the high densification of hard disks (HD), highly sensitive magnetic heads with high outputs have been demanded. In response to these demands, attention has been paid to a ferromagnetic tunnel magnetoresistance effect element having a multilayered structure composed of ferromagnetic layer/tunnel barrier layer/ferromagnetic layer, which utilizes a ferromagnetic tunnel magnetoresistance effect.
The ferromagnetic tunnel magnetoresistance effect is a phenomenon that when a current is applied in a laminate direction between a pair of ferromagnetic layers which sandwich a tunnel barrier layer, a tunnel current flowing in the tunnel barrier layer changes depending on a relative angle of magnetization between both ferromagnetic layers.
In this case, the tunnel barrier layer is a thin insulation film which allows electrons to pass therethrough while keeping spins of the electrons due to the tunnel magnetoresistance effect. Generally, the tunnel barrier layer is obtained by oxidizing a thin metal, such as Al, layer of about 10 Å in thickness.
When the relative angle of magnetization between both ferromagnetic layers which sandwich the tunnel barrier layer therebetween is decreased, the tunneling probability is increased and, therefore, the resistance to current flowing therebetween is decreased. In contrast, when the relative angle of magnetization between both ferromagnetic layers is large, the tunneling probability is lowered, thus, the resistance to current flowing therebetween is increased.
When applying the TMR element to a HDD head, it is essential to lower the electrical resistance of the element. The reason is as follows: Specifically, the resistance of a TMR element is basically expressed by the following equation (1).
R
&sgr;
=C
&sgr;
exp
(2
&kgr;d
)&kgr;=(2
m &phgr;/h
2
)
½
(1)
wherein d represents a thickness of a barrier, &phgr; represents a magnitude of a barrier potential measured from the Fermi level, and C
94
represents an amount determined by an electron state of an insulation layer and magnetic layers, and may be considered to be an amount which is approximately proportional to the product of the Fermi levels of the two magnetic layers.
According to the foregoing equation (1), it is understood that lowering of the resistance of the element can be achieved by reducing the thickness d of the barrier. By reducing the resistance of the element, a larger current is allowed to supply, thus, a greater output can be achieved. In addition, in order to prevent the electrostatic discharges, it is desirable to lower the resistance of the element.
In the TMR element, the resistance value drastically varies depending of the thickness d of the barrier layer. For example, when the thickness d of the barrier layer varies about ±1 Å, the order of the resistance value may vary about 1 figure, and in the worst case, dispersion among the resistance values of the TMR elements may be in the range of about 1 to 100 &OHgr; due to small dispersion in thicknesses of the barrier layers during the layer forming process.
Under these circumstances, for example, in a conventional method for measuring electromagnetic transduction characteristics using a constant measuring current on the order of 10 mA, some TMR elements, particularly having high resistances (&OHgr;), are subjected to extremely high voltages. As a result, the original characteristics of these TMR elements may be degraded or the elements may be destroyed.
The present invention has been made under these circumstances and has an object to provide a method and an apparatus for measuring characteristics of a tunnel magnetoresistance effect element without degrading the original characteristics of the element or destroying the element, and has a further object to provide a hard disk drive.
The TMR characteristics such as the TMR ratio and the resistance value vary depending on the magnitude of the voltage applied to the element. Therefore, when measuring characteristics of TMR elements having a broad resistance value distribution caused by small dispersion in production thereof, it is desirable to independently supply sense currents for applying the constant voltage to all the elements. In this event, it is required to provide a method and an apparatus for measuring characteristics of a tunnel magnetoresistance effect element and a hard disk drive which can provide a current for applying a given voltage “without damaging or destroying elements” and “in an effective way”.
SUMMARY OF THE INVENTION
For solving the foregoing problems, according to one aspect of the present invention, there is provided a method for measuring characteristics of a tunnel magnetoresistance effect element having a tunnel multilayered film comprising a tunnel barrier layer and a first and a second ferromagnetic layer formed to sandwich the tunnel barrier layer therebetween, wherein the method comprising the steps of:
setting an initial current value I
0
which does not destroy the element to be measured;
measuring, using the current value I
0
, a first resistance value R
1
as an approximate resistance value of the element, and defining, based on the first resistance value R
1
and a voltage value Vs which is a measurement standard for the element, an inspection current value Is (Is=Vs/R
1
); and
measuring the characteristics of the element using the inspection current value Is.
According to another aspect of the present invention, there is provided a method for measuring characteristics of a tunnel magnetoresistance effect element having a tunnel multilayered film comprising a tunnel barrier layer and a first and a second ferromagnetic layer formed to sandwich the tunnel barrier layer therebetween, wherein the method comprising the steps of:
setting an initial current value I
0
which does not destroy the element to be measured;
measuring, using the initial current value I
0
, a first resistance value R
1
as an approximate resistance value of the element, and defining, based on the first resistance value R
1
and a voltage value Vs which is a measurement standard for the element, a first modified current value I
1
(I
1
=Vs/R
1
);
measuring, using the first modified current value I
1
, a second resistance value R
2
as an approximate resistance value of the element, and defining, based on the second resistance value R
2
and the voltage value Vs which is the measurement standard for the element, an inspection current value Is (Is=Vs/R
2
); and
measuring the characteristics of the element using the inspection current value Is.
According to another aspect of the present invention, there is provided a method for measuring characteristics of a tunnel magnetoresistance effect element having a tunnel multilayered film comprising a tunnel barrier layer and a first and a second ferromagnetic layer formed to sandwich the tunnel barrier layer therebetween, wherein the method comprising the steps of:
setting an initial current value I
0
which does not destroy the element to be measured;
measuring, using the initial current value I
0
, a first resistance value R
1
as an approximate resistance value of the element, and defining, based on the first resistance value R
1
and a voltage value Vs which is a measurement standard for the element, a first modified current value I
1
(I
1
=Vs/R
1
);
measuring, using the first modified cu
Araki Satoru
Morita Haruyuki
Shimazawa Koji
Hudspeth David
Kapadia Varsha A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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