Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Magnetic field
Reexamination Certificate
2001-09-07
2003-08-26
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Magnetic field
C257S422000
Reexamination Certificate
active
06611034
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
A magnetic device according to the present invention can be utilized over a wide range such as a magnetic memory, a magnetic sensor and a spin operational device. Particularly, the present invention is useful as a part of a solid-state magnetic memory device.
2. Related Background Art
Conventionally, for a solid-state memory device, DRAM, SRAM, flash memory, EEPROM and FeRAM have been used. In recent years, however, from the viewpoints of non-volatility, higher speed and higher density, a magnetic solid memory, particularly a memory using a TMR or GMR effect has attracted much interest and its study has advanced. In the following description, a solid-state magnetic memory closely related to the present invention will be described.
First, a giant magneto-resistance (GMR) will be simply described. As regards the GMR, a magnetio-resistive change larger than an AMR (Anisotropic Magnetic Resistance) was discovered with ferromagnetic (Fe)
on-magnetic (Cr) (Chromium) artificial lattices by Fert et al. and Grunberg et al. in 1986 to 1988, and this has been called “Giant Magneto-Resistance, GMR”. This GMR has a special feature that it has a negative rate of change of resistance with respect to an applied magnetic field and has a great (a few tens percent) change in resistivity. The cause of GMR is qualitatively explained as follows. First, when there is no magnetic field, magnetic layers of the artificial lattice are arranged in an antiferromagnetic way (interlayer antiferromagnetism). When a magnetic field is applied in this case, magnetization of each layer is arranged in parallel. At this time, conduction arranged electrons are strongly scattered in a magnetizing non-parallel state, and the electric resistance decreases by the magnetic field by means of a mechanism having a dependence on such a spin as weakly scattered in a magnetizing parallel state. Theoretically, non-parallelism of interlayer magnetization has been studied by the use of a RKKY type long-distance exchange interaction or a quantum well model, and interlayer spin-dependent scattering has been discussed by a theory based on a binary fluid model of conduction electrons.
In order to utilize this GMR effect as a device such as a memory, the orientation of magnetization of a partial ferromagnetic layer is fixed while the orientation of magnetization of the other ferromagnetic layer is changed to use it as a memory. A device having such a structure is called “spin valve type”. Also, a layer (layer having a high coercive force), the orientation of magnetization of which remains unchanged, is called “hard layer (pin layer)” while a layer (layer having a low coercive force), the orientation of magnetization of which is changed, is called “free layer”. Contrary to this, there has also been adopted a method of reading a state of magnetization (memory state) from the change in resistance by recording on the hard layer and reversing the free layer.
Concerning this GMR, there have been known CIP (Current in Plane) type, CPP (Current Perpendicular to Plane) type, CPA (Current at an Angle) type, which is a type of their mixture, granular alloy type or the like. Generally, the CIP structure has most been studied in terms of its ease of fabrication. However, the CIP type, in which electric current flows in parallel with a lamination interface, has a change in resistivity being 40 to about 50% because of contribution of conduction electrons which do not interface spin scattering, or the like. In contrast, the CPP type, in which electric current flows in a direction perpendicular to the lamination interface, may have a change in resistivity exceeding 100% because of all electrons being exposed spin scattering having a dependence on the spin state on the lamination interface, an effect of increased Fermi velocity based on an energy gap resulting from the laminated structure, or the like, and the CPP type has better basic characteristics.
However, since the CPP type flows electric current in a direction perpendicular to the film surface, its resistance itself tends to become a very small value. For this reason, a pore enveloping the laminated structure must be made into a shape having a very small cross-sectional area.
In the CPP type GMR device into a pore, as an example of a structure which is not a simple laminated structure having a ferromagnetic layer
on-magnetic layer, there is one specified in Applied Physics Letters Vol. 70, 396 (1997). In this paper, there is specified an example in which lamination is performed with three-layer structure of NiFe alloy/Cu/NiFe alloy interposed between thick Cu layers, and this operation provides an effect in which the saturation magnetic field decreases. In this example of configuration, however, any sufficient memory effect has not yet appeared.
Also, as an example showing the memory effect, there is one specified in Applied Physics Letters Vol. 76, 354 (2000). In this paper, it is specified that the configuration is arranged such that a ferromagnetic layer (free ferromagnetic layer
14
) having a thin layer is interposed between a ferromagnetic layer (hard layer
61
) having such a thick layer as shown in
FIG. 6A and a
non-magnetic layer
62
for lamination, whereby a memory effect having a change in resistance being about 10% is exhibited. However, the reversal of this memory state is not clear.
<Tunnel Type Magnetic Memory>
As a memory cell using a tunnel junction, such a spin valve type as disclosed in U.S. Pat. No. 5,764,567 specification has generally been used. Such a cell has a laminated structure of a pin layer, an insulating layer, a ferromagnetic layer or the like. The orientation of magnetization in the ferromagnetic layer is directed toward one of the longitudinal axes of an ordinary cell. Particularly when the orientations of two ferromagnetic layers with an insulating layer interposed therebetween are same, the tunneling current is increased, and the cell resistance value decreases. On the contrary, when the orientations of two ferromagnetic layers with an insulating layer interposed therebetween are opposite, the tunneling current decreases, and the cell resistance value is increased. As shown in
FIG. 6B
, as regards the orientation of magnetization of this ferromagnetic material layer, of two magnetic material layers normally, one magnetic material layer (pin layer
61
) is left fixed with an antiferromagnetic layer
63
, and the orientation of magnetization of the other magnetic material layer (free ferromagnetic layer
14
) is changed. In the figure, the non-magnetic layer
62
is the insulating layer. The orientation of magnetization of this free ferromagnetic layer
14
is controlled and held by a magnetic field generated by electric current flowing through up and down wiring of the element. Generally, by means of a vector sum of the magnetic field to be generated by the up and down wiring orthogonally intersecting, only a selected cell portion is written. Reading-out is performed through a reading-out line or the like wired on the cell. The cell is selected by MOSFET or the like.
The rate of change of resistance of the TMR type can be made infinitely high in calculation, but values which can actually be fabricated are about 40 to about 60%. Also, it is how to fabricate the insulating layer and dependency of the rate of change of resistance on bias that most matter in fabrication and characteristics. More specifically, it is necessary to uniformly fabricate insulating layers having thickness of about 1 nm, but it is difficult to fabricate. Also, when the voltage is made higher, there arises a problem of dependency on bias that the rate of change of resistance will greatly decrease. These problems did not exist with the GMR device.
Since the present invention uses the GMR structure of CPP type, a pore having a large aspect ratio becomes necessary. As a method of obtaining this structure, a membrane filter using track etching and anodized alumina are known. Hereinafter, the detailed description will be made of the
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nelms David
Tran Long
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