Information storage devices and methods of operating the same

This application claims the benefit of Korean Patent Application No. 10-2008-0059771, filed on Jun. 24, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

1. Technical Field

The present invention relates to information storage devices, and more particularly, to information storage devices using magnetic domain wall motion and methods of operating the same.

2. Description of the Related Art

Examples of conventional nonvolatile information storage devices in which recorded information is retained even when power is cut-off include hard disk drives (HDDS) and nonvolatile random access memories (RAMs).

Conventional HDDs use a rotating part to store information. However, the rotating part may wear down over time, thereby increasing the likelihood of operational failure and thus reducing reliability.

An example of a conventional non-volatile RAM is a flash memory. Although the flash memory does not use a rotating part, it has relatively slow reading and writing speeds, a relatively short life span, and a relatively small storage capacity when compared to a conventional HDD. Flash memories may also have relatively high manufacturing costs.

Another conventional information storage device uses the principle of magnetic domain wall motion of a magnetic material. In these conventional magnetic information storage devices, a minute magnetic region that constitutes a ferromagnetic substance is referred to as a magnetic domain. A boundary portion between magnetic domains having different magnetization directions is referred to as a magnetic domain wall. The magnetic domains and the magnetic domain walls may be moved by applying current to a magnetic layer.

However, the information storage device using the magnetic domain wall motion is still in an initial stage of development and some problems still need to be resolved before it can be practically used. In particular, an improved information recording method is required to enable practical use of information storage devices using magnetic domain wall motion.

Example embodiments of the present invention provide information storage devices facilitating recording information and methods of operating the same.

According to an aspect of the present invention, there is provided an information storage device including: a magnetic layer having a plurality of magnetic domain regions and a magnetic domain wall interposed between the magnetic domain regions; a first unit disposed on a first region which is one of the plurality of magnetic domain regions for recording information to the first region; a second unit connected to the first unit for inducing a magnetic field so as to record information to the first region.

Through the second unit, a current may be applied to the first unit and the magnetic field is generated by the current flowing through the second unit.

The first unit may record information by using a spin transfer torque.

The first unit may include: a first pinned layer disposed on one of a lower surface and an upper surface of the first region; and a first separation layer interposed between the first pinned layer and the first region.

The first unit may further include: a second pinned layer having a magnetization direction opposite to that of the first pinned layer, the second pinned layer being disposed on the other one of the lower surface and the upper surface of the first region; and a second separation layer interposed between the second pinned layer and the first region.

The first unit may further include: an electrode layer disposed on the other one of the lower surface and the upper surface of the first region; and a resistive layer having a higher electric resistance than that of the magnetic layer, the resistive layer being interposed between the electrode layer and the first region.

The second unit may include at least one conducting wire connected to the first unit.

The first unit may include a lower unit and an upper unit respectively disposed on the lower surface and the upper surface of the first region, any one of the lower unit and the upper unit being connected to a first conducting wire and the other one of the lower unit and the upper unit being connected to a second conducting wire, and at least one of the first and second conducting wires being included in the second unit.

The first conducting wire may include a first portion extending from the first unit and the first portion of the first conducting wire is disposed on a first plane that is parallel to the magnetic layer.

The second conducting wire may include a first portion extending from the first unit and the first portion of the second conducting wire is disposed on a second plane that is parallel to the magnetic layer.

The first portion of the first conducting wire and the first portion of the second conducting wire may extend in a same direction.

The first conducting wire may further include a second portion extending from the first portion and surrounding at least a portion of the first unit on the first plane.

The first conducting wire may further include a second portion extending from the first portion of the first conducting wire and surrounding at least a portion of the first unit on the first plane.

The second conducting wire may further include a second portion extending from the first portion of the second conducting wire and surrounding at least a portion of the first unit on the second plane.

The direction in which the second portion of the first conducting wire extends and the direction in which the second portion of the second conducting wire extends may be opposite to each other.

The device may further include: a first line that is parallel to the magnetic layer; second and third lines crossing the first line; and a switching device disposed at the intersection of the first wire and the second wire; wherein the switching device and the third line are respectively connected to the first conducting wire and the second conducting wire.

The second line may be included to pass above the first unit and the third line may be included to space apart from the second line by a predetermined interval.

The second and third lines may be spaced apart from one side of the first unit by a predetermined interval.

The device may further include fourth and fifth lines respectively connected to one end and another end of the magnetic layer.

The device may further include another switching device disposed at least one of between the one end of the magnetic layer and the fourth line and between the other end of the magnetic layer and the fifth line.

The device may further include a sixth line connected to the other switching device which crosses the fourth and fifth lines.

The first and sixth lines may be word lines and the second through fifth lines may be bit lines.

The first unit may further include an information reproduction function.

The first unit may be disposed at the center portion of the magnetic layer.

The magnetic layer, the first unit, the first conducting wire, and the second conducting wire may be included in one unit memory region, and the information storage device may include a plurality of unit memory regions equivalent to the unit memory region.

According to another aspect of the present invention, there is provided a method of operating the information storage device of claim 1 , the method including: recording information to the first region by applying a write current to the first unit through the second unit.

The method may further include moving magnetic domains and magnetic domain walls in the magnetic layer in units of bits by applying a current to between one end and another end of the magnetic layer.

The method may further include reproducing information recorded in the magnetic layer by applying a read current to between any one of both ends of the magnetic layer and the first unit.

The above and other features and advantages of the present invention will become more apparent by describing in detail example embodiments thereof with reference to the attached drawings in which:

FIGS. 1 through 3 are perspective views of information storage devices according to embodiments of the present invention;

FIGS. 4A and 4B are cross-sectional views of an information storage device according to an embodiment of the present invention for illustrating a write operation;

FIGS. 5 , 6 , and 7 are perspective views of information storage devices according to embodiments of the present invention, illustrating magnetic fields generated by applying a write current to the information storage devices;

FIG. 8 is a perspective view of an information storage device according to another embodiment of the present invention;

FIG. 9 is a graph showing a magnetization reversal characteristic of a magnetic layer of an information storage device according to an embodiment of the present invention and an information storage device according to a comparison example;

FIG. 10 is a circuit diagram illustrating a unit memory region of an information storage device according to an embodiment of the present invention;

FIGS. 11 through 13 are circuit diagrams illustrating a method of operating the information storage device of FIG. 10 ;

FIG. 14 is a layout view of an information storage device according to an embodiment of the present invention;

FIG. 15 is a cross-sectional view of the information storage device of FIG. 14 taken along the line I-I′ of FIG. 14 ;

FIG. 16 is a layout view of an information storage device according to another embodiment of the present invention; and

FIG. 17 is a cross-sectional view of the information storage device of FIG. 16 taken along the line II-II′ of FIG. 16 ;

Various example embodiments will now be described more fully with reference to the accompanying drawings in which some example embodiments are shown.

Detailed illustrative example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. This invention may, however, may be embodied in many alternate forms and should not be construed as being limited to only the example embodiments set forth herein.

Accordingly, while example embodiments are capable of various modifications and alternative forms, these embodiments are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but on the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the invention. Like numbers refer to like elements throughout the description of the figures.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the example embodiments. As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element or layer is referred to as being “formed on,” another element or layer, it can be directly or indirectly formed on the other element or layer. That is, for example, intervening elements or layers may be present. In contrast, when an element or layer is referred to as being “directly formed on,” to another element, there are no intervening elements or layers present. Other words used to describe the relationship between elements or layers should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the example embodiments. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements.

FIGS. 1 through 3 are perspective views of information storage devices according to embodiments of the present invention.

Referring to FIG. 1 , a magnetic layer 100 illustrated is, which extends in a predetermined direction, for example, an X-axis direction. The magnetic layer 100 may include a plurality of continuous magnetic domain regions D. A magnetic domain wall region DW may be interposed between two adjacent magnetic domain regions D. The magnetic domain disposed in the magnetic domain regions D and the magnetic domain wall disposed in the magnetic domain wall region DW may be moved in a predetermined direction due to a current applied to the magnetic layer 100 . That is, the magnetic layer 100 may have a magnetic domain wall motion characteristic. Such a magnetic layer 100 may be an information storage layer formed of a ferromagnetic substance.

A writing unit 200 may be provided on a first region R 1 which is one of the magnetic domain regions D in the magnetic layer 100 . The writing unit 200 may be a device for recording information to the first region R 1 using a spin transfer torque. For example, the writing unit 200 may be a device using a tunnel magneto resistance (TMR) effect (hereinafter, referred to as a TMR device) or may be a device using a giant magneto resistance (GMR) effect (hereinafter, referred to as a GMR device). More specifically, the writing unit 200 may include a first pinned layer 40 a disposed on one of a lower surface and an upper surface of the first region R 1 , for example, the lower surface of the first region R 1 , and may include a first separation layer 20 a interposed between the first pinned layer 40 a and the first region R 1 . As such, the first separation layer 20 a and the first pinned layer 40 a disposed on the lower surface of the first region R 1 may be denoted as a lower unit of the writing unit 200 . Moreover, the writing unit 200 may further include a second pinned layer 40 b disposed on another one of a lower surface and an upper surface of the first region R 1 , for example, the upper surface of the first region R 1 , and may further include a second separation layer 20 b interposed between the second pinned layer 40 b and the first region R 1 . The second separation layer 20 b and the second pinned layer 40 b disposed on the upper surface of the first region R 1 may be denoted as an upper unit of the writing unit 200 . The first separation layer 20 a and the second separation layer 20 b may be insulation layers or conductive layers. When the first separation layer 20 a and the second separation layer 20 b are the insulation layers, the writing unit 200 is the TMR device and when the first separation layer 20 a and the second separation layer 20 b are the conductive layers, the writing unit 200 is the GMR device. When the first separation layer 20 a and the second separation layer 20 b are the conductive layers, a resistive layer (not shown) having a higher electric resistance than that of the magnetic layer 100 may be further interposed between the first region R 1 and the first separation layer 20 a and between the first region R 1 and the second separation layer 20 b . When a current for the magnetic domain and magnetic domain wall motion is applied to the magnetic layer 100 , the resistive layer may function as an electric barrier which prevents the current from being leaked to the writing unit 200 and when a current is applied between a first conducting wire 300 a and a second conducting wire 300 b , the resistive layer may not disturb the flow of current. Accordingly, the resistive layer may be formed of a material having an appropriate electric resistance with an appropriately small thickness. For example, the specific resistance of the resistive layer may be 500-10000 times higher than that of the magnetic layer 100 , for example, 1000-3000 times higher. In order to achieve this resistance difference, the magnetic layer 100 may be formed of any one of NiFe, Co, CoNi, CoFe, CoCr, CoCu, NiCu, FePt, FePd, CoCrPt, CoFeTb, CoFeGd, CoTb, and CoFeNi and the resistive layer may be formed of any one of amorphous CoZrNb and CoFeB or may be formed of a magnetic material including impurities such as Si and B so as to have a high resistivity. The first pinned layer 40 a and the second pinned layer 40 b may be ferromagnetic layers of which magnetization directions are fixed and the magnetization directions of the first pinned layer 40 a and the second pinned layer 40 b may be opposed to each other. Arrows illustrated in the first pinned layer 40 a , the second pinned layer 40 b , and the first region R 1 of FIG. 1 indicate each of the magnetization directions thereof. The directions of the arrows are in a z-axis direction or a reversed direction thereof. That is, when the first pinned layer 40 a , the second pinned layer 40 b , and the first region R 1 have perpendicular magnetic anisotropy, these arrows indicate the magnetization directions of the first pinned layer 40 a , the second pinned layer 40 b , and the first region R 1 . The magnetization directions of the first pinned layer 40 a and the second pinned layer 40 b may be switched around and the magnetization direction of the first region R 1 may be opposite to that of the arrow shown in FIG. 1 . The first region R 1 may not be in a magnetized state in a specific direction. When the magnetic layer 100 , the first pinned layer 40 a , and the second pinned layer 40 b have horizontal magnetic anisotropy, the first region R 1 , the first pinned layer 40 a , and the second pinned layer 40 b may have magnetization directions that are parallel to an x-axis (or a y-axis). Although not shown in FIG. 1 , other magnetic domain regions D, except for the first region R 1 , may also be magnetized in a direction that is the same as the first region R 1 or a direction that is opposite to the first region R 1 in the magnetic layer 100 .

The first conducting wire 300 a and the second conducting wire 300 b may be respectively disposed on the lower surface and the upper surface of the writing unit 200 . In other words, the first conducting wire 300 a may be disposed on the lower surface of the lower unit of the writing unit 200 and the second conducting wire 300 b may be disposed on the upper surface of the upper unit of the writing unit 200 . A predetermined write current may be applied to the writing unit 200 through the first conducting wire 300 a and the second conducting wire 300 b . The first conducting wire 300 a may include a first portion 1 a extended in a predetermined direction from the lower surface of the writing unit 200 . Similarly, the second conducting wire 300 b may include a first portion 1 b extended in a predetermined direction from the upper surface of the writing unit 200 . The first portion 1 a of the first conducting wire 300 a and the first portion 1 b of the second conducting wire 300 b may be extended in a direction perpendicular to the writing unit 200 . In other words, the first portion 1 a of the first conducting wire 300 a and the first portion 1 b of the second conducting wire 300 b may be disposed on each different plane (hereinafter, respectively referred to as a first XY plane and a second XY plane) parallel to the plane on which the magnetic layer 100 is formed. The first portion 1 a of the first conducting wire 300 a and the first portion 1 b of the second conducting wire 300 b may be extended in the same direction. In the current embodiment, the first portion 1 a of the first conducting wire 300 a and the first portion 1 b of the second conducting wire 300 b are extended in a Y-axis direction. However, the first portion 1 a of the first conducting wire 300 a and the first portion 1 b of the second conducting wire 300 b may be extended in various directions. That is, the directions in which the first portion 1 a of the first conducting wire 300 a and the first portion 1 b of the second conducting wire 300 b are extended may be arbitrarily determined within the first XY plane and the second XY plane on which the first portions 1 a and 1 b are respectively disposed.

Although not shown in FIG. 1 , at least one layer may be further interposed between the first pinned layer 40 a and the first conducting wire 300 a so as to fix the magnetization direction of the first pinned layer 40 a . Similarly, at least one layer may be further interposed between the second pinned layer 40 b and the second conducting wire 300 b so as to fix the magnetization direction of the second pinned layer 40 b . The at least one layer used to fix the magnetization direction of the first pinned layer 40 a or the second pinned layer 40 b may include anti-ferromagnetic layer and may have various structures. The structure would have been obvious to one of ordinary skill in the art and it would also have been obvious to one of ordinary skill in the art to further include a contact electrode layer respectively between the first conducting wire 300 a and the writing unit 200 , and the second conducting wire 300 b and the writing unit 200 .

According to other embodiments, the first conducting wire 300 a and/or the second conducting wire 300 b in the information storage device of FIG. 1 may have various forms. Examples of these forms are described with reference to FIGS. 2 and 3 .

Referring to a perspective view and a partial plan view illustrated in FIG. 2 , a first conducting wire 300 a ′ may include the first portion 1 a extended from the lower surface of the writing unit 200 and may further include a second portion 2 a extended from the first portion 1 a . The second portion 2 a may surround at least some portion of the writing unit 200 on the plane on which the first portion 1 a is formed, that is, on the first XY plane. The second portion 2 a may have an angulated structure in which at least one straight line constituent is connected. In the current embodiment, the second portion 2 a includes a first constituent 2 aa , a second constituent 2 ab , a third constituent 2 ac , and a fourth constituent 2 ad , wherein the first constituent 2 aa is extended in an x-axis direction from the first portion 1 a , the second constituent 2 ab is extended in a negative y-axis direction from the first constituent 2 aa , the third constituent 2 ac is extended in a negative x-axis direction from the second constituent 2 ab , and the fourth constituent 2 ad is extended in a y-axis direction from the third constituent 2 ac . However, the present invention is not limited thereto. For example, the fourth constituent 2 ad or the third constituent 2 ac and the fourth constituent 2 ad or the second constituent 2 ab through the fourth constituent 2 ad may not be included in the second portion 2 a and another conducting wire constituent may be further included in the end of the second portion 2 a . Moreover, the second portion 2 a may have a curved structure, instead of the angulated structure.

The second conducting wire 300 b of FIG. 2 may also be transformed as in the first conducting wire 300 a.′ An example is shown in FIG. 3 .

Referring to FIG. 3 , a second conducting wire 300 b ′ may include the first portion 1 b extended from the upper surface of the writing unit 200 and may further include a second portion 2 b extended from the first portion 1 b . The second portion 2 b may surround at least some portion of the writing unit 200 on the plane on which the first portion 1 b is formed, that is, the second XY plane. The second portion 2 b of the second conducting wire 300 b ′ may be extended from the first portion 1 b in a direction opposite to the direction in which the second portion 2 a of the first conducting wire 300 a ′ is extended from the first portion 1 a . The second portion 2 b of the second conducting wire 300 b ′ may also have various transformed structures as in the second portion 2 a of the first conducting wire 300 a′ . The direction to which the second portion 2 a of the first conducting wire 300 a ′ is extended and the direction to which the second portion 2 b of the second conducting wire 300 b ′ may be switched around. Also, the first conducting wire 300 a′ in FIG. 3 may be transformed as in the first conducting wire 300 a of FIG. 1 . Moreover, the first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ may be close to the first region R 1 .

In the information storage device of FIGS. 1 through 3 , the first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ may be configured to apply a predetermined magnetic field to the first region R 1 while a write operation is being performed. The magnetic field may be applied to the first region R 1 in a direction suitable to support the write operation. That is, the first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ may induce the magnetic field to record information in the first region R 1 by a current passing therethrough. Thus, the first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ are means for applying the magnetic field to record information in the first region R 1 and may be denoted as a ‘second unit’ for information recording. More specifically, when a write operation is performed for recording information to the first region R 1 by applying a write current to the writing unit 200 through the first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ , the magnetic field for supporting the write operation is generated in the first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ by the write current. Of course, a spin transfer torque is applied from the writing unit 200 to the first region R 1 by the write current. In other words, in the current embodiment, the spin transfer torque of the writing unit 200 and the magnetic field generated in the first conducting wires 300 a and 300 a ′ and the second conducting wires 300 b and 300 b′ are used to perform the write operation. Accordingly, according to the current embodiment of the present invention, the write operation can be easily performed even with a small current density. When the write current density decreases, consumed power can be reduced and reliability of the writing unit 200 can be improved. When the write current density is high as is generally the case, characteristics of the writing unit 200 may be degraded and when the first and second separation layers 20 a and 20 b are the insulation layers, the first and second separation layers 20 a and 20 b may be broken down.

Hereinafter, an information recording method using an information storage device according to an embodiment of the present invention will be described in more detail.

FIGS. 4A and 4B are cross-sectional views of an information storage device according to an embodiment of the present invention for illustrating a write operation. In FIGS. 4A and 4B , a partial cross-sectional configuration of an information storage device according to an embodiment of the present invention is illustrated and the cross-sectional configuration may be the same with those of FIGS. 1 through 3 .

Referring to FIG. 4A , when a first write current is applied from the first conducting wire 300 a or 300 a′ to the second conducting wire 300 b or 300 b′ and electrons are moved from the second conducting wire 300 b or 300 b′ to the first conducting wire 300 a or 300 a′ , electrons E 1 having a magnetization direction M 1 that is the same as the magnetization direction of the second pinned layer 40 b (hereinafter, referred to as a first direction) are moved from the second conducting wire 300 b or 300 b′ to the first region R 1 . These electrons E 1 magnetize the first region R 1 in the first direction M 1 . Meanwhile, in the first pinned layer 40 a, electrons having a magnetization direction M 2 that is the same as the magnetization direction of the first pinned layer 40 a (hereinafter, referred to as a second direction) flow out to the first conducting wire 300 a or 300 a′ through the first pinned layer 40 a. However, electrons E 2 having magnetization directions that are opposite the magnetization direction of the first pinned layer 40 a cannot flow out through the first pinned layer 40 a and instead, are returned and accumulate in the first region R 1 . These electrons E 2 magnetize the first region R 1 in the first direction M 1 . As such, the first region R 1 may be magnetized in the first direction M 1 by the spin transfer torque applied from the first pinned layer 40 a and the second pinned layer 40 b to the first region R 1 . When the first region R 1 is magnetized in the second direction M 2 before the first write current is applied thereto, the magnetization direction of the first region R 1 may be reversed to be in the first direction M 1 by the first write current.

Referring to FIG. 4B , when a second write current is applied from the second conducting wire 300 b or 300 b′ to the first conducting wire 300 a or 300 a′ and electrons are moved from the first conducting wire 300 a or 300 a′ to the second conducting wire 300 b or 300 b′ , electrons E 3 magnetized in the second direction M 2 are moved from the first conducting wire 300 a or 300 a′ to the first region R 1 . These electrons E 3 magnetize the first region R 1 in the second direction M 2 . Meanwhile, in the second pinned layer 40 b , electrons magnetized in the first direction M 1 flow out to the second conducting wire 300 b or 300 b′ through the second pinned layer 40 b . However, electrons E 4 magnetized in the second direction M 2 cannot flow out through the second pinned layer 40 b and instead, are returned and accumulate in the first region R 1 . These electrons E 4 magnetize the first region R 1 in the second direction M 2 .

When the first region R 1 is magnetized in the first direction M 1 before the second write current is applied thereto, the magnetization direction of the first region R 1 may be reversed to be in the second direction M 2 by the second write current.

The magnetic domains and the magnetic domain walls may be moved in a predetermined direction within the magnetic layer 100 by one bit-distance due to a predetermined current applied to the magnetic layer 100 during operations between FIG. 4A and FIG. 4B , before the operation of FIG. 4A , or after the operation of FIG. 4B . While the magnetic domains and the magnetic domain walls are moved within the magnetic layer 100 in units of bits, the magnetic domains located in the first region R 1 are magnetized in a desired direction using the operation of FIG. 4A or FIG. 4B so that predetermined information can be recorded to a part of or to the entire magnetic layer 100 .

As such, since the first pinned layer 40 a and the second pinned layer 40 b which are magnetized in each different direction are respectively disposed on the lower surface and the upper surface of the magnetic layer 100 in the information storage device according to the current embodiment, information can be recorded by the spin transfer torque induced from both the first pinned layer 40 a and second pinned layer 40 b . Thus, the write current density may be reduced and the write operation is rapidly performed, compared to when one pinned layer is used.

In addition, in the information storage device according to an embodiment of the present invention, the magnetic field to support the write operation is generated in the first conducting wire 300 a or 300 a′ and the second conducting wire 300 b or 300 b′ by the write current (the first and second write current), as described above. Therefore, the write current density may be reduced more and the write operation may be performed more rapidly, due to the magnetic field. This will be described in more detail with reference to FIGS. 5 through 7 .

FIG. 5 illustrates a first magnetic field F 1 and a second magnetic field F 2 when the write current is applied from the first conducting wire 300 a to the second conducting wire 300 b in FIG. 1 , the first magnetic field F 1 being induced from the first conducting wire 300 a by the write current and the second magnetic field F 2 being induced from the second conducting wire 300 b by the write current. These first and second magnetic fields F 1 and F 2 are generated in compliance with the right hand rule. Although not shown in FIG. 5 , a magnetic field is also generated surrounding the writing unit 200 by the write current passing through the writing unit 200 . Such a magnetic field is also generated in FIGS. 6 and 7 .

The first and second magnetic fields F 1 and F 2 of FIG. 5 may act advantageously for the magnetization reversal (e.g., write operation) of the first region R 1 . The X-axis magnetic field of approximately −47 Oe is applied to a first point p 1 of the first region R 1 . This denotes that a relatively strong magnetic field is applied to the first point p 1 in a negative X-axis direction. The first point p 1 is a central point at the center of one end in the Y-axis direction. The relatively strong magnetic field is applied to the first point p 1 in a negative X-axis direction because the first and second conducting wires 300 a and 300 b in FIG. 5 are extended to the Y-axis and the first and second magnetic fields F 1 and F 2 generated from the first and second conducting wires 300 a and 300 b has directions opposite to the X-axis at the first point p 1 . The magnetic field is applied to most of the first region R 1 in a direction opposite to the X-axis based on the first point p 1 . The X-axis constituent magnetic field supports the first region R 1 in magnetization reversal during the write operation as in FIG. 4A . That is, when the magnetization direction of the first region R 1 of FIG. 4A is changed from the second direction M 2 to the first direction M 1 that is the direction opposite to the second direction M 2 , the X-axis constituent magnetic field may act advantageously for the magnetization reversal of the first region R 1 .

The Y-axis magnetic field of approximately 20 Oe and −20 Oe is respectively applied to two points (hereinafter, referred to as a second point p 2 and a third point p 3 ) located at both sides of the first region R 1 . This is because the magnetic field is applied to the second point p 2 in the Y-axis direction by the writing unit 200 of FIG. 5 and the magnetic field is applied to the third point p 3 in a direction opposite to the Y-axis direction by the writing unit 200 of FIG. 5 . However, the Y-axis constituent magnetic field may not be applied to most of the first region R 1 . Thus, the Y-axis constituent magnetic field may not affect the magnetization reversal of the first region R 1 .

The Z-axis constituent magnetic field which is applied to the magnetic layer 100 is 0 Oe. This denotes that the available magnetic field constituent applied to the magnetic layer 100 in the Z-axis direction or a direction opposite to the Z-axis direction does not exist.

FIG. 6 illustrates a first magnetic field F 1 ′ and the second magnetic field F 2 when the write current is applied from the first conducting wire 300 a′ to the second conducting wire 300 b in FIG. 2 , the first magnetic field F 1 ′ being induced from the first conducting wire 300 a′ by the write current and the second magnetic field F 2 being induced from the second conducting wire 300 b by the write current. The first magnetic field F 1 ′ may be classified into a first portion magnetic field F 1 a induced from the first portion 1 a and the second portion magnetic field F 2 aa +F 2 ab +F 2 ac +F 2 ad induced from the second portion 2 a . The first portion magnetic field F 1 a may be equivalent to the first magnetic field F 1 of FIG. 5 .

The first and second magnetic fields F 1 and F 2 of FIG. 6 may act advantageously for the magnetization reversal (e.g., write operation) of the first region R 1 . (X) and (Y) in FIG. 6 are respectively similar to (X) and (Y) in FIG. 5 . However, referring to (Z) in FIG. 6 , unlike (Z) in FIG. 5 , the magnetic field of approximately 6.6 Oe is applied to the first region R 1 in a Z-axis direction. This may be caused by the second portion magnetic field F 2 aa +F 2 ab +F 2 ac +F 2 ad . The Z-axis constituent magnetic field supports the first region R 1 in magnetization reversal during the write operation as in FIG. 4A . More specifically, when the magnetization direction of the first region R 1 of FIG. 4A is changed from the second direction M 2 to the first direction M 1 that is the direction opposite to the second direction M 2 , it may be advantageous that the Z-axis constituent magnetic field be applied to the first region R 1 so as to perform the magnetization reversal. That is, since the Z-axis constituent magnetic field is applied to the first region R 1 in the first direction M 1 of FIG. 4A , the magnetization direction of the first region R 1 may be easily changed to the first direction M 1 .

As shown in FIG. 6 , since the X-axis and Z-axis constituent magnetic fields support the magnetization reversal of the first region R 1 , the magnetization reversal of the first region R 1 may be more facilitated than the case of FIG. 5 in which the Z-axis constituent magnetic field is not applied to the first region R 1 .

In FIG. 7 , when the write current is applied from the first conducting wire 300 a′ to the second conducting wire 300 b′ , the first magnetic field (not shown) is induced from the first conducting wire 300 a′ by the write current and a second magnetic field F 2 ′ is induced from the second conducting wire 300 b′ by the write current. The first magnetic field (not shown) may be the same as the first magnetic field F 1 ′ of FIG. 6 . The second magnetic field F 2 ′ may be classified into a first portion magnetic field F 1 b induced from the first portion 1 b and the second portion magnetic field F 2 ba +F 2 bb +F 2 bc +F 2 bd induced from the second portion 2 b.

The first and second magnetic fields F 1 and F 2 of FIG. 7 may act advantageously for the magnetization reversal (e.g., write operation) of the first region R 1 . (X) and (Y) in FIG. 7 are respectively similar to (X) and (Y) in FIG. 5 . Meanwhile, referring to (Z) in FIG. 7 , the magnetic field of approximately 13 Oe is applied to the first region R 1 in a Z-axis direction. The intensity of the magnetic field is approximately double the intensity of the Z-axis constituent magnetic field of FIG. 6 . The Z-axis constituent magnetic field may be caused by the magnetic field generated from the second portion 2 a of the first conducting wire 300 a in FIG. 7 (same as F 2 aa +F 2 ab +F 2 ac +F 2 ad in FIG. 6 ) and by the second portion magnetic field F 2 ba +F 2 bb +F 2 bc +F 2 bd generated from the second portion 2 b of the second conducting wire 300 b . Since the Z-axis constituent magnetic field of FIG. 7 is stronger than that of FIG. 6 , magnetization reversal of the first region R 1 may be more facilitated in FIG. 7 .

In FIGS. 5 through 7 , the write current is applied from the first conducting wires 300 a and 300 a′ to the second conducting wires 300 b and 300 b′ and the first region is magnetized in a Z-axis direction. However, the effect of the magnetic field described above is similar when the write current is applied from the second conducting wires 300 b and 300 b′ to the first conducting wires 300 a and 300 a′ and the first region R 1 is magnetized in a direction opposite to the Z-axis direction. That is, when the write current is applied from the second conducting wires 300 b and 300 b′ of FIGS. 5 , 6 , and 7 to the first conducting wires 300 a or 300 a′ , the magnetic field may be applied to the first region R 1 of FIGS. 5 , 6 , and 7 in an X-axis direction and the magnetic field may be applied to the first region R 1 of FIGS. 6 and 7 in a direction opposite to the Z-axis direction. Due to these magnetic fields, the write operation magnetizing the first region R 1 in a Z-axis direction may be facilitated.

In addition, in FIGS. 5 through 7 , the magnetic fields supporting the write operation are generated from all first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ . However, according to other embodiments, any one of the first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ may be changed so as not to generate the magnetic field which substantially supports the write operation. That is, the magnetic fields generated from all first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ are not always needed for the advantage of the present invention. In other words, the advantage of the present invention can be obtained only with the magnetic field generated from at least one of first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′.

The information storage device of FIGS. 1 through 3 respectively includes the first pinned layer 40 a and the second pinned layer 40 b on the lower surface and the upper surface of the first region R 1 in the magnetic layer 100 . However, in another embodiment, only one pinned layer may be used and an example thereof is illustrated in FIG. 8 .

FIG. 8 is a perspective view of an information storage device according to another embodiment of the present invention.

Referring to FIG. 8 , a resistive layer 30 and an electrode layer 50 are sequentially disposed in that order on the first region R 1 and the second conducting wire 300 b is disposed on the electrode layer 50 .

The resistive layer 30 is a layer having a higher electric resistance than that of the magnetic layer 100 and may function as an electric barrier to prevent a current from being leaked to the electrode layer 50 , when the current for the magnetic domain wall motion flows through the magnetic layer 100 . However, when the write current is applied from the first conducting wire 300 a to the second conducting wire 300 b or vice versa, the resistive layer 30 may not prevent the write current from flowing. Properties and forming materials of the resistive layer 30 may be the same as those of the resistive layer described with reference to FIG. 1 . In some cases, the second conducting wire 300 b may be directly disposed on the resistive layer 30 without the electrode layer 50 . The lower structure of the first region R 1 in FIG. 8 may be the same as that of FIG. 1 . That is, the first separation layer 20 a , the first pinned layer 40 a , and the first conducting wire 300 a may be sequentially disposed in this order on the lower surface of the first region R 1 . When the first separation layer 20 a is a conductive layer, another resistive layer (not shown) may be interposed between the first region R 1 and the first separation layer 20 a . The other resistive layer (not shown) may be similar to the resistive layer 30 . The first conducting wire 300 a and/or the second conducting wire 300 b of FIG. 8 may be transformed as in the first conducting wire 300 a′ and/or the second conducting wire 300 b′ of FIG. 3 .

FIG. 9 is a graph showing a magnetization reversal characteristic of the magnetic layer of the information storage device according to an embodiment of the present invention and an information storage device according to a comparison example. In FIG. 9 , a first graph G 1 indicates a magnetization reversal characteristic of the first region R 1 using the information storage device having the structure described in FIG. 1 . A second graph G 2 indicates a magnetization reversal characteristic of the first region R 1 when the write current is applied between the first pinned layer 40 a and the second pinned layer 40 b in a structure where the first and second conducting wires 300 a and 300 b are removed, as illustrated in FIG. 1 . That is, the result of the second graph G 2 corresponds to when the effects of the magnetic fields induced from the first and second conducting wires 300 a and 300 b in FIG. 1 are removed. A damping constant, a magnetic anisotropy energy density, saturation magnetization Ms, and an exchange constant of the magnetic layer 100 used in obtaining the result of FIG. 9 are approximately 0.1, 10 6 erg/cc, 200 emu/cc, and 10 6 erg/cm, respectively. The write current density used for magnetization reversal is approximately 3.8×10 7 A/cm 2 .

Referring to FIG. 9 , a Z-axis magnetization Mz changes in the first graph G 1 5 ns earlier than a Z-axis magnetization Mz changes in the second graph G 2 . This denotes that the magnetization reversal (that is, information recording) is rapidly and easily performed by the magnetic fields induced from the first and second conducting wires 300 a and 300 b in the information storage device.

FIG. 10 is a circuit diagram illustrating a unit memory region of the information storage device according to an embodiment of the present invention. In FIG. 10 , a direction indicator indicating the XY coordinates indicates directions of first and second word lines WL 1 and WL 2 and first through fourth bit lines BL 1 through BL 4 , and the directions of the magnetic layer 100 and a first unit 200 are indicated as in the direction indicator illustrated in FIG. 1 .

Referring to FIG. 10 , the first and second word lines WL 1 and WL 2 are illustrated extending in a predetermined direction, for example, an X-axis direction, and the first through fourth bit lines BL 1 through BL 4 crossing the first and second word lines WL 1 and WL 2 are also illustrated. A first transistor T 1 may be disposed at the intersection of the first word line WL 1 and the first bit line BL 1 and a second transistor T 2 may be disposed at the intersection of the first word line WL 1 and the fourth bit line BL 4 . Gates of the first and second transistors T 1 and T 2 are connected to the first word line WL 1 . The magnetic layer 100 in which one end and the other end thereof are respectively connected to the first and second transistors T 1 and T 2 may be interposed between the first and second transistors T 1 and T 2 . The first unit 200 may be disposed in a predetermined region of the magnetic layer 100 , for example, the center portion of the magnetic layer 100 (hereinafter, referred to as the first region R 1 ). The configuration of the magnetic layer 100 and the first unit 200 may be the same as that of the magnetic layer 100 and the writing unit 200 of FIGS. 1 through 3 . One end of the first unit 200 , for example, the upper surface, may be connected to the third bit line BL 3 and the other end of the first unit 200 , for example, the lower surface, may be connected to a third transistor T 3 disposed at the intersection of the second word line WL 2 and the second bit line BL 2 . The gate of the third transistor T 3 is connected to the second world line WL 2 . A conducting wire W 1 connecting the other end of the first unit 200 to the third transistor T 3 and a conducting wire W 2 connecting the one end of the first unit 200 to the third bit line BL 3 may include the same structure as that of the first conducting wires 300 a and 300 a′ and the second conducting wires 300 b and 300 b′ of FIGS. 1 through 3 or a structure derived therefrom.

In FIG. 10 , since the first through third transistors T 1 through T 3 are kinds of switching devices, they may be replaced with switching devices having other structures, for example, a diode. At least one of the first and second transistors T 1 and T 2 may not be included and the location of the second transistor T 2 may be changed. For example, the third transistor T 3 may be disposed at the intersection of the second word line WL 2 and the third bit line BL 3 , instead of at the intersection of the second word line WL 2 and the second bit line BL 2 . Also, the configuration of the first unit 200 of FIG. 10 may be replaced with the writing unit of FIG. 8 .

Hereinafter, a method of operating the information storage device having the structure as illustrated in FIG. 10 is described with reference to FIGS. 11 through 13 .

<Write Operation>

Referring to FIG. 11 , while the gate of the third transistor T 3 is open by applying a predetermined voltage V 2 to the second word line WL 2 , a predetermined positive voltage is applied to any one of the second bit line BL 2 and the third bit line BL 3 and voltage of 0 V is applied to the other one of the second bit line BL 2 and the third bit line BL 3 . Then, the write current may flow in a predetermined direction to the first region R 1 through the first unit 200 . According to the direction of the write current, the magnetization direction of the first region R 1 may vary. In addition, as described above, the magnetic field generated from at least any one of the upper and lower conducting wires connected to the first unit 200 by the write current may support changing of the magnetization direction of the first region R 1 .

Referring to FIG. 12 , while the gates of the first and second transistors T 1 and T 2 are open by applying a predetermined voltage V 1 to the first word line WL 1 , a predetermined positive pulse voltage is applied to any one of the first bit line BL 1 and the fourth bit line BL 4 and voltage of 0 V is applied to the other one of the first bit line BL 1 and the fourth bit line BL 4 . Then, a pulse current may flow through the magnetic layer 100 due to the pulse voltage and thereby, the magnetic domains and magnetic domain walls may be moved by a unit bit in a predetermined direction.

When the operations of FIG. 11 and FIG. 12 are alternately and repeatedly performed, the magnetic domains D disposed one side of the first unit 200 , for example, left of the first unit 200 , are moved to the other side of the first unit 200 , for example, to the right of the first unit 200 , and predetermined information can be recorded to the magnetic domains D.

<Read Operation>

Referring to FIG. 13 , while the gates of the first through third transistors T 1 through T 3 are open by applying predetermined voltages V 1 and V 2 to the first and second word lines WL 1 and WL 2 , a predetermined read current can be applied between the first bit line BL 1 and the second bit line BL 2 . The read current may flow via a portion of the first unit 200 (for example, a lower portion of the first region R 1 ) and the first region R 1 and the intensity of the read current may be significantly affected by the magnetization direction of the first region R 1 . That is, according to the magnetization direction of the first region R 1 , an electric resistance between the first bit line BL 1 and the second bit line BL 2 may significantly vary. Therefore, the recorded information can be read by application of the read current. The intensity of the read current is relatively smaller than that of the write current so that a magnetization state of the first region R 1 does not change. Instead of applying a predetermined read current between the first bit line BL 1 and the second bit line BL 2 , a predetermined read current may be applied between the second bit line BL 2 and the fourth bit line BL 4 , thereby performing a read operation. In addition, when the third transistor T 3 is disposed at the intersection of the second word line WL 2 and the third bit line BL 3 , instead of the intersection of the second word line WL 2 and the second bit line BL 2 , the read current may be applied to between the third bit line BL 3 and the first bit line BL 1 or between the third bit line BL 3 and the fourth bit line BL 4 and thus, information may be reproduced. Accordingly, according to the current embodiment, the read current is applied to between any one of both ends of the first unit 200 and any one of the both ends of the magnetic layer 100 and thus information recorded to the first region R 1 can be reproduced. Thus, in the current embodiment of the present invention, at least some portion of the first unit 200 may be used as a device for reproducing information. Therefore, the first unit 200 may be denoted as a read/write unit having both a write function and a read function. However, the first unit 200 may be only used as a write unit and a read unit may be separately installed. In this case, the read unit may be a TMR sensor, a GMR senor, or another type of sensor.

The information reading operation as in FIG. 13 and moving the magnetic domains and the magnetic domain walls in units of bits as in FIG. 12 can be alternately and repeatedly performed. Accordingly, the magnetic domains D disposed on one side of the first unit 200 , for example, left of the first unit 200 , are moved to the other side of the first unit 200 , for example, to the right of the first unit 200 , and information recorded to the magnetic domains D can be reproduced.

The information storage device according to another embodiment of the present invention may include a plurality of the unit memory regions illustrated in FIG. 10 and examples with regard to this are illustrated in FIGS. 14 and 16 .

FIG. 14 is a layout view of the information storage device according to an embodiment of the present invention.

Referring to FIG. 14 , illustrated are first through fourth word lines WL 1 through WL 4 and the first through fourth bit lines BL 1 through BL 4 crossing the first through fourth word lines WL 1 through WL 4 .

The first transistor T 1 is disposed near to the intersection of the first word line WL 1 and the first bit line BL 1 and the second transistor T 2 is disposed near to the intersection of the first word line WL 1 and the fourth bit line BL 4 . The first transistor T 1 includes a first source S 1 and a first drain D 1 at both sides of the first word line WL 1 and the second transistor T 2 includes a second source S 2 and a second drain D 2 at both sides of the first word line WL 1 . The magnetic layer 100 in which one end and other end thereof are respectively connected to the first and second transistors T 1 and T 2 may be provided between the first and second transistors T 1 and T 2 . The first source S 1 and the first drain D 1 of the first transistor T 1 are respectively connected to the first bit line BL 1 and one end of the magnetic layer 100 and the second source S 2 and the second drain D 2 of the second transistor T 2 are respectively connected to the fourth bit line BL 4 and the other end of the magnetic layer 100 . The first unit 200 may be disposed on a predetermined region of the magnetic layer 100 , for example, the center portion of the magnetic layer 100 (hereinafter, referred to as the first region R 1 ). The second bit line BL 2 may pass over the first unit 200 . The third bit line BL 3 may be disposed in such a manner as to be spaced apart from the second bit line BL 2 by a predetermined interval. The upper surface of the first unit 200 may be electrically connected to the third bit line BL 3 by the second conducting wire 300 bb . The connection between the upper surface of the first unit 200 and the third bit line BL 3 and the connection between the lower surface of the first unit 200 and a third source S 3 will be described more fully with reference to FIG. 15 . The third transistor T 3 is disposed near to the intersection of the second word line WL 2 and the second bit line BL 2 . The third transistor T 3 respectively includes the third source S 3 and a third drain D 3 at both sides of the second word lines WL 2 . The third source S 3 is electrically connected to the lower surface of the first unit 200 and the third drain D 3 is electrically connected to the second bit line BL 2 . In the first through third transistors T 1 through T 3 , functions of the first through third sources S 1 through S 3 and the first through third drains D 1 through D 3 may be switched around.

The configuration of the unit memory region CB 1 in FIG. 14 may correspond to the unit memory region illustrated in FIG. 10 . In FIG. 14 , the unit memory region CB 1 is repeatedly arranged in a Y-axis direction. However, a plurality of the unit memory regions CB 1 may be arranged to configure a plurality of columns and lines in X-axis and Y-axis directions.

FIG. 15 is a cross-sectional view of the information storage device of FIG. 14 taken along the line I-I′ of FIG. 14 .

Referring to FIG. 15 , the lower surface of the first unit 200 is connected to the third source S 3 by the first conducting wire 300 aa and the upper surface of the first unit 200 is connected to the third bit line BL 3 by the second conducting wire 300 bb. The configuration of the second conducting wire 300 bb is similar to that of the second conducting wire 300 b in FIG. 1 . Thus, information can be recorded by the magnetic field generated in the second conducting wire 300 bb and the spin transfer torque of the first unit 200 . In FIG. 15 , a substrate 10 is illustrated and the third source S 3 is disposed within the substrate 10 , which is also the case in FIG. 17 .

FIG. 16 is a layout view of an information storage device according to another embodiment of the present invention. In the current embodiment, the information storage device is transformed from that of FIG. 14 . Thus, a repeated description will be omitted and only a portion that is different will be described.

Referring to FIG. 16 , the second and third bit lines BL 2 and BL 3 are moved more right, compared with those illustrated in FIG. 14 . That is, the second and third bit lines BL 2 and BL 3 are disposed in such a manner as to be spaced apart from the first unit 200 in a predetermined interval at one side of the first unit 200 , for example, right of the first unit 200 . The upper surface of the first unit 200 may be electrically connected to the third bit line BL 3 by the second conducting wire 300 bb′ . The connection between the first unit 200 , the third bit line BL 3 , and the third source S 3 is described more fully with reference to FIG. 17 .

FIG. 17 is a cross-sectional view of the information storage device of FIG. 16 taken along the line II-II′ of FIG. 16 .

Referring to FIG. 17 , the lower surface of the first unit 200 is connected to the third source S 3 by the first conducting wire 300 aa ′ and the upper surface of the first unit 200 is connected to the third bit line BL 3 by the second conducting wire 300 bb′. The configurations of the first conducting wire 300 aa′ and the second conducting wire 300 bb ′ may be respectively similar to those of the first conducting wire 300 a and the second conducting wire 300 b in FIG. 1 . Thus, information can be recorded by the magnetic field generated in the first conducting wire 300 aa′ and the second conducting wire 300 bb′ and the spin transfer torque of the first unit 200 .

The connection between the first unit 200 , the third bit line BL 3 , and the third source S 3 illustrated in FIGS. 14 through 17 is only an example. That is, the form of the first conducting wires 300 aa and 300 aa′ and the second conducting wires 300 bb and 300 bb′ are only an example. When the layout of the device is changed, the first conducting wires 300 aa and 300 aa′ and/or the second conducting wires 300 bb and 300 bb′ may be similar to the first conducting wire 300 a′ and/or the second conducting wire 300 b′ or may have a structure that is modified from the first conducting wire 300 a′ and/or the second conducting wire 300 b′.

While the example embodiments have been described in the detailed description above, it will be understood that the embodiments may be preferred examples, rather than limitations of scope of the embodiments. For example, it would have been obvious to one of ordinary skill in the art to vary structures illustrated in FIGS. 1-3 , 8 , 10 , and 14 - 17 and to vary the method of operating illustrated in FIGS. 11-13 . In addition, it would have been obvious to one of ordinary skill in the art to apply an idea of the example embodiments not only to an information storage device using movement of the magnetic domain walls but also to other information storage devices. Therefore, the scope of the example embodiments will be determined by technical ideas defined in the following claims, instead of preferred examples described in the detailed description above.