Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2002-09-30
2004-09-14
Elms, Richard (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C257S295000, C438S003000
Reexamination Certificate
active
06791866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive film made of a ferrimagnetic material whose major constituents are a rare earth metal and a transition metal, and more particularly to a magnetoresistive film that exhibits a relatively large magnetoresistive effect, a method of manufacturing the magnetoresistive film, and a memory that uses such a magnetoresistive film.
2. Related Background Art
In recent years, a semiconductor memory which is a solid state memory has been used extensively in information equipment. Semiconductor memories are in variety of types and include DRAMs, (dynamic random access memory), FeRAMs (ferroelectrics random access memory), and flash EEPROM (electrically erasable programmable read only memory). These semiconductor memories have advantages and disadvantages. No one type of semiconductor memory meets all requirements of information equipment in current use. For example, DRAMs have a high recording density and can be rewritten a large number of times. However, DRAMs are volatile, so that when the memory is turned off, the stored information is lost. Flash EEPROMs are non-volatile but take a long time for erasing information and therefore do not lend themselves to the high-speed processing of information.
In contrast to semiconductor memories, a memory based on magnetoresistive effect (MRAM: magnetic random access memory) is non-volatile and a potential material that will meet all the requirements of current information equipment including write time, read time, recording density, the number of times that information can be rewritten, and power consumption. Especially, an MRAM using a spin dependent tunnel magnetoresistance (TMR) provides a large read signal and is therefore advantageous in designing a memory of high recording density or high-speed reading. Recent researches showed the feasibility of a memory using the MRAM.
A basic configuration of a magnetoresistive film used as an MRAM element is a sandwich structure in which a non-magnetic layer is sandwiched between magnetic layers. Materials as the non-magnetic layer include, for example, Cu and Al
2
O
3
. A magnetoresistive film using, for example, Cu as a non-magnetic layer is referred to as GMR (giant magneto-resistance) film while a magnetoresistive film based on insulators such as Al
2
O
3
is referred to as a spin dependent tunnel magnetoresistive (TMR) film. Typically, TMR films have larger magnetoresistances than GMR films.
FIGS. 6A and 6B
illustrate a magnetoresistive film of a configuration where two magnetic layers are laminated with a non-magnetic layer sandwiched therebetween. Arrows indicate the direction of magnetization of the respective magnetic layers. As shown in
FIG. 6A
, if the magnetization directions of the two magnetic layers are oriented parallel, the electrical resistance (electrical resistance between the two magnetic layers) of the magnetoresistive film is relatively low. If the directions of magnetization are anti-parallel as shown in
FIG. 6B
, the electrical resistance is relatively high. Thus, by using one of the two magnetic layers as a memory layer and the other as a detecting layer and making use of the aforementioned property, reading information can be accomplished. For example, a magnetic layer
13
located on a non-magnetic layer
12
operates as a memory layer and a magnetic layer
11
under the non-magnetic layer
12
operates as a detecting layer. The information stored is assumed to be “1” when the magnetization direction of the memory layer (magnetic layer
13
) is rightward and “0” when the magnetization direction is leftward.
If the magnetization directions of the magnetic layers
11
and
13
are both rightward as shown in
FIG. 7A
, the electrical resistance of the magnetoresistive film is relatively low. If the magnetization direction of the magnetic layer
11
is rightward and the magnetization direction of the magnetic layer
13
is leftward as shown in
FIG. 7B
, the electrical resistance of the magnetoresistive film is relatively high. Likewise, if the magnetization direction of the magnetic layer
11
is leftward and the magnetization direction of the magnetic layer
13
is rightward as shown in
FIG. 7C
, the electrical resistance of the magnetoresistive film is relatively high. If the magnetization directions of the magnetic layers
11
and
13
are both leftward as shown in
FIG. 7D
, the electrical resistance of the magnetoresistive film is relatively low. When the magnetization direction of the detecting layer
11
is rightward, a relatively high electrical resistance indicates that the memory layer
13
holds “0” and a relatively low electrical resistance indicates that the memory layer
13
holds “1”. Alternatively, when the magnetization direction of the detecting layer
11
is leftward, a relatively high electrical resistance indicates that the memory layer
13
holds “1” and a relatively low electrical resistance indicates that the memory layer
13
holds “0”.
Thus, the constituents of the magnetic layers
11
and
13
are selected such that the detecting layer
11
has a relatively large coercive force and the memory layer
13
has a relatively small coercive force. Information can be written by magnetizing the detecting layer
11
in one direction and applying a magnetic field to the memory layer
13
in such a way that the memory
13
is changed in the direction of magnetization but the detecting layer
11
is not reversed in the direction of magnetization. Information can be read by detecting the electrical resistance of the magnetoresistive film.
MRAMs use a surface magnetization film as a magnetic layer. If the size of the magnetoresistive film is made smaller in an attempt to increase the recording density of MRAM, the magnetoresistive film cannot hold information because of the demagnetizing field or curling of magnetization of the end surface of the element. One way of avoiding this problem, for example, is to make the magnetic layer rectangular. However, this approach cannot increase the recording density significantly because the element size cannot be smaller.
As described in, for example, U.S. Pat. No. 6,219,275, the Applicant of the present invention has proposed the use of a vertically magnetizing film to solve the aforementioned problem. The use of the vertically magnetizing film will not increase the demagnetizing field even if the element size is made smaller. Thus, the use of a vertically magnetizing film can implement a magnetoresistive film having a smaller size than a MRAM that uses a surface magnetizing film.
Just as in a magnetoresistive film using a surface magnetizing film, a magnetoresistive film using a vertically magnetizing film exhibits a relatively low resistance if the two magnetic layers are magnetized in parallel directions, and a relatively high resistance if the two magnetic layers are magnetized in anti-parallel directions. The magnetic layer
23
formed on the non-magnetic layer
22
is used as a memory layer and the magnetic layer
21
formed under the non-magnetic layer
22
is used as a detecting layer. The information stored in the magnetoresistive film is assumed to be “1” if the memory layer
23
is magnetized upward and “0” if the memory layer
23
is magnetized downward. When the magnetic layers
21
and
23
are both magnetized upward as shown in
FIG. 8A
, the electrical resistance of the magnetoresistive film is relatively low. When the detecting layer
21
is magnetized downward and the memory layer
23
is magnetized upward as shown in
FIG. 8C
, the electrical resistance of the magnetoresistive film is relatively high. Likewise, when the detecting layer
21
is magnetized upward and the memory layer
23
is magnetized downward as shown in
FIG. 8B
, the electrical resistance of the magnetoresistive film is relatively high, and when both the magnetic layers
21
and
23
are magnetized downward as shown in
FIG. 8D
, the electrical resistance is relatively low. In other words, when the detecting layer
21
is magnetized
Canon Kabushiki Kaisha
Elms Richard
Fitzpatrick ,Cella, Harper & Scinto
Le Toan
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