Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2000-10-25
2002-11-12
Nguyen, Viet Q. (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C365S173000, C360S110000, C360S112000, C428S611000
Reexamination Certificate
active
06480411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a memory that utilizes magnetoresistance effect. More particularly, it relates to a magnetoresistance effect type memory requiring only a small power consumption at the time of reproduction, improved in memory characteristics and utilizable as an inexpensive memory adapted to computer peripheral equipment, the memory being preferable as peripheral circuits are made high-speed, and a reproduction method and a reproducing device which make use of such a memory.
2. Related Background Art
Memories used in computers or electronic instruments are under strong competition in their technical development. Techniques progress at a rapidly advancing rate, and various new memory devices are proposed. In recent years, giant magnetoresistance (GMR) effect has been discovered in magnetoresistive films holding a non-magnetic layer between ferromagnetic layers, and magnetic sensors and memories that utilize this phenomenon are attracting notice. In the following description, memories that utilize magnetoresistive films are generically called MRAM.
In the MRAM, a triple-layer structure having two ferromagnetic layers and a thin non-magnetic layer held between them forms a basic structural unit where information is recorded. Between the two ferromagnetic layers holding a non-magnetic layer between them, the state of “0” or “1” is recorded by utilizing a phenomenon that resistance values differ between a case where their directions of magnetization are identical and a case where they are antiparallel.
When recorded information is read, an alternating magnetic field weaker than that at the time of writing is applied to cause only one ferromagnetic layer to change in its direction of magnetization, where changes in resistance values are measured to read the state of “0” or “1”. The MRAM has an advantage that it has a good resistance to radiations, is non-volatile in principle, is high-speed and is not limited in the number of times for writing, because the information is magnetically recorded. Appropriation of existing semiconductor techniques can afford to perform high-density recording with ease, and hence there is an expectation of its substitution for DRAM in future. For example, Japanese Patent Application Laid-open No. Hei6-243673 discloses a proposal relating to its utilization as a memory.
The operating principle of the MRAM is shown below.
FIG. 5A
illustrates the construction of an MRAM. The MRAM is so constructed as to have on a substrate a first magnetic layer
11
, a non-magnetic layer
12
, a second magnetic layer
13
, an insulating layer
80
and a write wire (word wire)
51
in this order. The magnetoresistive film portion formed of combination of ferromagnetic layers with a non-magnetic layer may have a multi-layer structure.
Two ferromagnetic layers, the first magnetic layer
11
and second magnetic layer
13
, are formed of combination of a soft magnetic material and a hard magnetic material. The soft magnetic material forms a reproducing layer from which information is read, and the hard magnetic material forms a memory layer in which information is stored. In the MRAM shown in
FIG. 5A
, the first magnetic layer
11
serves as a reproducing layer making use of the soft magnetic material, and the second magnetic layer
13
as a memory layer making use of the hard magnetic material. A buffer layer of SiN, Ta or the like may also be provided between the substrate and the first magnetic layer
11
.
Recording operation of the MRAM is performed by changing the direction of magnetization of the memory layer second magnetic layer
13
by means of a magnetic field generated in the write wire.
FIG. 5B
shows a case where “0” is written. A recording electric current is flowed through the write wire from the back to the front in the vertical direction as viewed on the drawing, whereupon a magnetic field is generated in the direction of arrows. When information is recorded, the magnetic field generated is made strong, so that the directions of magnetization not only of the reproducing layer first magnetic layer
11
but also of the memory layer second magnetic layer
13
are written in the rightward direction as viewed on the drawing. This state is “0”.
FIG. 5C
shows a case where “1” is written. A recording electric current is flowed through the write wire from the front to the back in the vertical direction as viewed on the drawing, whereupon a magnetic field is generated in the direction of arrows. When recorded, the magnetic field generated is made strong, so that the directions of magnetization not only of the reproducing layer first magnetic layer
11
but also of the memory layer second magnetic layer
13
are written in the leftward direction as viewed on the drawing. This state is “1”.
On the other hand, when information is reproduced, reproducing electric current pulses weaker than those at the time of recording are flowed through the write wire sequentially in the both directions to reverse the magnetization of the reproducing layer, and a change in resistance at that moment is read, thus the reproduction is accomplished.
FIGS. 5D
to
5
G are a series of views showing the reproducing operation. In the state the “0” is kept recorded as shown in
FIG. 5B
, the directions of magnetization of the magnetic layers change as shown in
FIG. 5D
when first a reproducing electric current is flowed through the write wire from the front to the back in the vertical direction as viewed on the drawing, and change as shown in
FIG. 5E
when next the electric current is flowed in the opposite direction.
When first the reproducing electric current is flowed through the write wire as shown in
FIG. 5D
, from the front to the back in the vertical direction as viewed on the drawing, a weak magnetic field is generated in the direction of an arrow. At such a magnetic field strength, the reproducing layer first magnetic layer
11
reverses in magnetization, but the magnetization of the memory layer second magnetic layer
13
remains kept in the direction of “0”. When next the reproducing electric current is flowed through the write wire as shown in
FIG. 5E
, from the back to the front in the vertical direction as viewed on the drawing, a weak magnetic field is generated in the direction of an arrow. At such a magnetic field strength, the reproducing layer first magnetic layer
11
reverses in magnetization, but the magnetization of the memory layer second magnetic layer
13
remains kept in the direction of “0”.
Take note of the directions of magnetization of the two magnetic layers. When first the reproducing electric current is flowed through the write wire from the front to the back in the vertical direction as viewed on the drawing, the directions of magnetization of the first magnetic layer
11
and second magnetic layer
13
stand antiparallel. When next the reproducing electric current is flowed through the write wire from the back to the front in the vertical direction as viewed on the drawing, the directions of magnetization of the first magnetic layer
11
and second magnetic layer
13
stand parallel. Hence, in the course where electric current pulses are flowed in the two directions, the resistance of the write wire changes from a high resistance in an antiparallel state to a low resistance in a parallel state. The state where resistance values change from a high resistance to a low resistance in this way is read to be “0”.
On the other hand, in the state the “1” is kept recorded as shown in
FIG. 5C
, the directions of magnetization of the magnetic layers change as shown in
FIG. 5F
when first a reproducing electric current is flowed through the write wire from the front to the back in the vertical direction as viewed on the drawing, and change as shown in
FIG. 5G
when next the electric current is flowed in the opposite direction.
When first the reproducing electric current is flowed through the write wire as shown in
FIG. 5F
, from the front to the back in the vertical direction as viewed on the drawin
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Viet Q.
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