Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
1999-09-22
2001-01-09
Zarabian, A. (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000
Reexamination Certificate
active
06172903
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hybrid device and a memory apparatus realized by using such hybrid devices. It also relates to an information reading method.
2. Related Background Art
Various devices utilizing the magnetoresistance effect such as thin film magnetic heads have been developed in recent years. In the course of developing such devices, magnetic thin film memories using magnetoresistance elements that can replace currently popular DRAMs and EEPROMs have been proposed. Since the electric resistance of a magnetoresistance element varies remarkably depending on its state of magnetization, non-volatile solid-state memories can be realized by combining such elements and semiconductor elements in a manner referred to as hybridization.
For instance, Japanese Patent Application Laid-Open No. 6-84347 describes a magnetic thin film memory comprising memory cells that are formed by combining magnetoresistance elements and switching elements such as field effect transistors (hereinafter referred to as FETs).
FIG. 1
of the accompanying drawings schematically illustrates the circuit configuration of a magnetic thin film memory proposed in the above cited patent document.
FIG. 1
is a schematic circuit diagram of a known memory apparatus realized by using known memory devices (hybrid devices of magnetic thin film elements/semiconductor elements).
FIGS. 2A and 2B
illustrate two different arrangements of magnetic thin films in a memory device as shown in FIG.
1
.
FIGS. 3A and 3B
illustrate two different states of magnetization of a magnetoresistance element as shown in FIG.
1
.
Referring to
FIG. 1
, the memory apparatus comprises a plurality of memory cells, each having a magnetoresistance element
1
for storing information as a function of the state of magnetization of the magnetic material of the element and a switching element
2
for recording/reproducing information. Typically, FETs are used for the switching elements
2
and a write line
5
is connected to the source electrode of each of the FETs. Each of the magnetoresistance elements
1
is connected at an end thereof directly to the write line
5
of the device and the other end to the ground potential.
The memory apparatus additionally comprises a plurality of selection lines
4
for applying a voltage to each of the switching elements
2
to turn it on or off and a plurality of data lines
3
for writing data to or reading data from each of the memory cells, said selection lines
4
and said data lines
3
being arranged to form a grid. Memory cells are arranged at the respective intersections of the selection lines
4
and the data lines
3
. The gate electrodes of the FETs of the memory cells of each row are commonly connected to the related selection line
4
, whereas the drain electrodes of the FETs of the memory cells of each column are commonly connected to the related data line
3
. A resistor
6
is connected to each of the data lines
3
so that information is recorded in each of the memory cells by applying a predetermined voltage to the related data line
3
by way of the related resistor
6
.
In
FIG. 1
, the magnetoresistance elements
1
are discriminated from each other by means of reference symbols
1
aa
through
1
ac
and
1
ba
through
1
bc
, whereas the switching elements
2
are discriminated from each other by means of reference symbols
2
aa
through
2
ac
and
2
ba
through
2
bc
. Similarly, the write lines
5
are identified by respective reference symbols
5
aa
through
5
ac
and
5
ba
through
5
bc
, whereas the data lines
3
are identified by respective reference symbols
3
a
through
3
c
and the selection lines
4
are discriminated from each other by means of reference symbols
4
a
and
4
b.
As seen from
FIGS. 2A and 2B
, a magnetoresistance element
1
is formed from a giant magnetoresistance (GMR) film obtained by laying a magnetic layer
20
showing a large coercive force and a magnetic layer
21
showing a small coercive force repeatedly for several times with a non-magnetic layer
22
interposed therebetween to produce a multilayer structure. A GMR film has a remarkable property that it shows a small electric resistance when both the magnetic layers showing a large coercive force and the magnetic layers showing a small coercive force are magnetized in a same direction whereas it shows a large electric resistance when the magnetic layers showing a large coercive force and the magnetic layers showing a small coercive force are magnetized in opposite directions.
Now, a method of recording information to and reproducing information from a memory apparatus as shown in
FIG. 1
will be discussed below.
When storing “1” in the magnetoresistance element
1
ac
, a voltage of +V
3
is typically applied to the data line
3
c
. When a voltage V
4
is applied to the selection line
4
a
under this condition, the switching element
2
ac
is turned on and a relatively large electric current I
1
flows to the magnetoresistance element lac and the write line
5
ac
in a direction running from the bottom surface to the top surface of FIG.
3
A. Then, a magnetic field H
1
is applied to the magnetoresistance element lac due to the electric current I
1
so that consequently the direction of magnetization of the magnetic layer b operating for storing information and showing a small coercive force is made to agree with the direction of the magnetic field H
1
, or the leftward direction in FIG.
3
A.
When, on the other hand, storing “0” in the magnetoresistance element
1
ac
, a voltage of −V
3
is typically applied to the data line
3
c
. When a voltage V′
4
is applied to the selection line
4
a
under this condition, the switching element
2
ac
is turned on and a relatively large electric current I
0
flows to the magnetoresistance element lac and the write line
5
ac
in a direction running from the top surface to the bottom surface of FIG.
3
B. Then, a magnetic field H
0
is applied to the magnetoresistance element lac due to the electric current I
0
so that consequently the direction of magnetization of the magnetic layer b operating for storing information and showing a small coercive force is made to agree with the direction of the magnetic field H
0
, or the rightward direction in FIG.
3
B.
Since the switching element
2
ac
is turned on only when a predetermined voltage is applied to the related selection line
4
a
, no electric current will flow to the magnetoresistance element
1
bc
commonly connected to data line
3
c
with the magnetoresistance element
1
ac
. Additionally, since no electric current flows to the data lines
3
except the data line
3
c
to which a predetermined voltage is applied, no electric current will flow to the magnetoresistance elements
1
aa
,
1
ab
commonly connected to selection line
4
a
with the magnetoresistance element
1
ac.
The magnetic layer
20
showing a large coercive force is normally magnetized in the rightward direction in
FIGS. 2A and 2B
and, therefore, the resistance of the magnetoresistance element
1
ac
is relatively large when “1” is stored in it but relatively small when “0” is stored in it.
When reproducing the information stored in the magnetoresistance element
1
ac
, a constant electric current I
3
is made to flow through the data line
3
c
for data reproduction and an appropriate voltage is applied to the selection line
4
a
to turn on the switching element
2
ac
. Then, an electric current flows to the write line
5
ac
and the magnetoresistance element
1
ac
as a result. Therefore, a potential difference V
&agr;&bgr;
will be produced between point &agr; (the drain voltage of the switching element
2
ac
) and point &bgr; (ground potential).
As pointed out above, the electric resistance of the magnetoresistance element
1
ac
varies depending on the state of magnetization so that consequently the value of the potential difference V
&agr;&bgr;
also varies. Therefore, the state of magnetization of the magnetoresistance element
1
ac
and henc
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Zarabian A.
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