Magnetic memory device with moving magnetic domain walls

A magnetic memory device includes a plurality of first metal lines arranged in parallel on a substrate and including a plurality of magnetic domains with variable magnetization directions. A plurality of second metal lines is arranged on the substrate perpendicular to the first metal lines. The plurality of second metal lines each has a tunnel through which the plurality of first metal lines pass. First input units are connected to the plurality of first metal lines and supply a current to drag or move the plurality of magnetic domains. Second input units are connected to the plurality of second metal lines to supply a current for switching the magnetization directions of magnetic domains inside the tunnels. Sensing units are connected to the plurality of second metal lines for sensing an electromotive force caused by magnetic domain walls passing through the tunnels.

PRIORITY STATEMENT

This non-provisional U.S. patent application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2006-0018881, filed on Feb. 27, 2006, in the Korean Intellectual Property Office (KIPO), the entire contents of which is incorporated herein by reference.

BACKGROUND

Description of the Related Art

Related art magnetic memory devices read and write information by detecting resistance changes of magnetic tunneling junction (MTJ) cells. Resistance of the MTJ cells changes according to magnetic polarization directions of two magnetic films with a thin insulating layer there between. For example, the resistance of the MTJ cells may changes according to whether magnetic polarization directions of the two magnetic films are equal or different from each other.

Unless the thin insulating layer is sufficiently clean when the MTJ cells are stacked, a resistance difference distinguishing states, such as, “1” and “0” (e.g., a resistance difference according to the magnetic polarization directions of the upper and lower magnetic films) is negligible. This is because a resistance change rate between a resistance when the MTJ cells are in state “0” and a resistance when the MTJ cells are in state “1” may be limited to about 40% and when the insulating layer is not sufficiently clean, the resistance change rate may be reduced to about 20 to 30%. In this example, information may not be read accurately, which may limit the practical use of memory devices employing MTJ cells.

In addition, because related art magnetic memory devices store only 1-bit information in a single memory area, manufacturing large capacity magnetic memory devices is relatively difficult.

SUMMARY

Example embodiments relate to magnetic memory devices, for example, magnetic memory devices which may read and/or write information using metal lines between which cross points are formed.

Example embodiments provide magnetic memory devices with a structure capable of reading and writing information accurately and/or storing multi-bit information.

According to at least one example embodiment, a magnetic memory device may include a plurality of first metal lines arranged in parallel on a substrate. The plurality of first metal lines may have a plurality of magnetic domains with variable magnetization directions. A plurality of second metal lines may be arranged on the substrate perpendicular or substantially perpendicular to the first metal lines and may include tunnels through which the plurality of first metal lines pass. First input units may be connected to the plurality first metal lines and may supply a current to drag or move the plurality of magnetic domains. Second input units may be connected to the plurality of second metal lines to apply a current for switching the magnetization directions of the plurality of magnetic domains inside the tunnels. Sensing units may be connected to the plurality of second metal lines and may sense an electromotive force caused by magnetic domain walls passing through the tunnels. In at least some example embodiments, the substrate may be a plastic substrate.

According to another example embodiment, a memory device may include a plurality of magnetic memory devices formed on a plurality of substrates stacked on one another. Each magnetic memory device may include may include a plurality of first metal lines arranged in parallel on a substrate. The plurality of first metal lines may have a plurality of magnetic domains with variable magnetization directions. A plurality of second metal lines may be arranged on the substrate perpendicular or substantially perpendicular to the first metal lines and may include tunnels through which the plurality of first metal lines pass. First input units may be connected to the plurality first metal lines and may supply a current to drag or move the plurality of magnetic domains. Second input units may be connected to the plurality of second metal lines to apply a current for switching the magnetization directions of the plurality of magnetic domains inside the tunnels. Sensing units may be connected to the plurality of second metal lines and may sense an electromotive force caused by magnetic domain walls passing through the tunnels. In at least some example embodiments, the substrate may be a plastic substrate.

In at least some example embodiments, the magnetic memory device may further include a plurality of insulating layers interposed between the plurality of first metal lines and the plurality of second metal lines. Each of the plurality of first metal lines may be fin-shaped and/or formed of a ferromagnetic material. In each of the plurality of first metal lines, a single memory area may be formed between adjacent tunnels, wherein a plurality of (e.g., n) magnetic domains may be formed in the single memory area. The single memory area may include a first magnetic domain disposed inside the tunnel. The first magnetic domain may have a reference magnetization direction. When magnetization directions of an (i+1)th magnetic domain and an (i)th magnetic domain are the same, a first data (e.g., information “0”) may be recorded, and when magnetization directions of the (i+1)th magnetic domain and the (i)th magnetic domain are different from each other, a second data (e.g., information “1”) may be recorded.

In at least some example embodiments, the plurality of magnetic domains corresponding to the memory area and magnetic domain walls between the plurality of magnetic domains may be formed on an end of the first metal line to control dragging or moving of the plurality of magnetic domains within the memory area. A magnetic domain wall stopper for stopping the magnetic domain walls may be formed on the end of each of the plurality of first metal lines. The magnetic domain wall stopper may be a notch formed between the plurality of magnetic domains. The first magnetic domain may be formed inside the tunnel.

A dummy magnetic domain for temporarily changing magnetization direction when information is recorded on other of the plurality of first metal lines may be formed on each of the plurality of first metal lines.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Various example embodiments will now be described more fully with reference to the accompanying drawings in which some example embodiments are shown. In the drawings, the thicknesses of layers and regions are exaggerated for clarity.

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

FIG. 1is a partial perspective view of a magnetic memory device, according to an example embodiment. Referring toFIG. 1, a magnetic memory device may include a plurality of first metal lines100and a plurality of second metal lines200which may be arranged on a plastic substrate300perpendicular or substantially perpendicular to each other. For example, the plurality of second metal lines200may orthogonally crossover the plurality of first metal lines100. The second metal lines200may have tunnels corresponding to cross points between the first and second metal lines100and200, and the first metal lines100may pass through the tunnels. The magnetic memory device may read information (e.g., single or multi-bit data) by detecting a magnetic flux change at the cross points. In doing so, the magnetic memory device may utilize an electromotive force induced when a magnetic flux is changed by moving a magnet back and forth inside a circular coil. The first metal lines100may function as the magnet and the second metal lines200may function as the coil.

Because the first metal lines100function as the magnet, each of the first metal lines100may be formed of a ferromagnetic material such as CoFe, NiFe, or the like and may have a relatively thin fin shape to allow more easy formation and dragging of magnetic domains. In at least one example embodiment, the first metal lines100may have a square wave shape.

Each of the second metal lines200may be formed of a conductive metal. Insulating layers400may be interposed between the first and second metal lines100and200to suppress (e.g., prevent) a pulse voltage and/or a current applied to the first metal lines100from flowing into the second metal lines200.

FIG. 2is a plan view illustrating two memory areas of the magnetic memory device, according to an example embodiment.

Referring toFIG. 2, a plurality of (e.g., four) magnetic domains D1through D4may be formed in a first memory area M1and a plurality of (e.g., four) magnetic domains D5through D8may be formed in a second memory area M2. The magnetic domains D1and D5may serve as reference magnetic domains. The width W of the second metal lines200may be less than the length L of the reference magnetic domains of the first metal lines100. The reference magnetic domains D1and D5may be disposed under the tunnels T.

Magnetization directions or polarization of the reference magnetic domains D1and D5may be the same. A magnetic domain wall DW may be formed between the domains D1and D2whose magnetization directions are different from each other in the first memory area M1. Magnetic domain walls DW may be formed between the magnetic domains D5and D6and between the magnetic domains D7and D8in the second memory area M2.

First input units500may supply a current to the magnetic domains D1through D8. Second input units600may apply a current to the second metal lines200to switch the magnetization directions of the magnetic domains under the tunnels. Sensing units700(e.g., voltmeters, Ammeters, etc.), may be connected to the second metal lines200to sense an electromotive force caused by the change in magnetic flux when the magnetic domain walls DW pass through the tunnels T.

When a positive dragging pulse current is applied to the first metal line100through the first input unit500, the magnetic domains D1through D8may move in a direction indicated by an arrow A, and the magnetic domain walls DW pass through the tunnels through the second metal lines200such that a magnetic flux changes and an electromotive force in the second metal line200is induced.

When the magnetization direction of the magnetic domain D2is different from the magnetization direction of the reference magnetic domain D1, a magnetic flux in the memory area M1may change such that an electromotive force is generated. The generated electromotive force may be sensed by sensing unit700connected to a second metal line200to read first information (e.g., a data bit “1”). When a positive current is again applied to the first metal line100, because the magnetization direction of the magnetic domain D3is the same as the magnetization direction of the magnetic domain D2which becomes a new reference magnetic domain, an electromotive force is not generated, and a second information (e.g., data bit “0”) may be read.

FIG. 3is a plan view illustrating a method of controlling the dragging of magnetic domains recorded in a memory, according to an example embodiment.

Magnetic domain walls DW may be formed on ends of the first metal lines100. The number of the magnetic domain walls DW may correspond to the number of information pieces stored in each memory area. For example, a plurality of (e.g., four) magnetic domains may be formed in one memory area inFIG. 2, but information may be stored in only a portion of (e.g., three) magnetic domains. Consequently, for the sake of clarity only a portion of the magnetic domain walls DW are shown inFIG. 3.

Magnetic domain wall stoppers may be formed to stop the respective magnetic domain walls DW. Referring toFIG. 3, a pair of facing notches110may serve as the magnetic domain wall stoppers. When a dragging pulse current above a threshold level flows through the first metal line100via first input unit500, the magnetic domain wall DW may pass through the first set of notches110and stop at the next set of notches110. Notches110enable each of the magnetic domain walls DW to be dragged or moved a distance corresponding to one magnetic domain.

In a write mode, a positive or negative dragging current may be applied to the first metal lines100to locate the magnetic domains of the memory areas under the second metal lines200. A write current may be applied to the second metal lines200to change or switch magnetization directions of the magnetic domains and portions of the memory areas at which the first metal lines100, receiving the dragging current, and the second metal lines200, receiving the write current, cross each other may be addressed. Dummy magnetic domains (not shown) may be formed in the first metal lines100such that the magnetization directions of magnetic domains of other first metal lines100, crossing over the second metal lines200receiving the write current, may not change. The dummy magnetic domains may be formed on ends of the first metal lines100so as not to affect the other magnetic domains.

Magnetic memory devices, according to at least some example embodiments, may be manufactured by creating patterns of the first and second metal lines100and200on the plastic substrate300using, for example, a photolithographic process including at least exposing and etching.

While related art magnetic memory devices using MTJ cells recognize information by detecting a voltage difference, magnetic memory devices, according to at least some example embodiments, recognize information by detecting the existence of an electromotive force. This may improve accuracy in writing and/or reading information.

Because the amount of bit information that may be stored in one memory area corresponds to a number of magnetic domains for data storage formed therein, magnetic memory devices, according to at least some example embodiments, may store multi-bit data or information.

FIG. 4is a cross-sectional view of a magnetic memory device, according to another example embodiment. The same elements as those inFIG. 1are designated by the same reference numerals. A detailed explanation of these elements has been omitted for the sake of brevity.

Referring toFIG. 4, a plurality of first metal lines101and a plurality of second metal lines201may be formed on a first substrate301. Insulating layers401may be interposed between the plurality of first metal lines101and the plurality of second metal lines201. A second substrate302may be formed on the second metal lines201. A plurality of first metal lines102and a plurality of second metal lines202may be formed on the second substrate302. Insulating layers402may be interposed between the plurality of first metal lines102and the plurality of second metal lines202. The first substrate301and the second substrate302may be plastic substrates.

Compared to related art magnetic memory devices having MTJ cells using a silicon substrate, magnetic memory devices, according to at least this example embodiment, may increase memory capacity per unit area. For example, silicon substrates of related art magnetic memory devices are grown on a single crystal, which may be affected by impurities. Thus it may be more difficult to grow a second silicon substrate on a first silicon substrate. Because magnetic memory devices, according to at least this example embodiment, form metal lines on a general plastic substrate, a stacked magnetic memory device may be more easily manufactured.

As described above, magnetic memory devices according to at least this example embodiment, may be more easily manufactured and/or more easily stacked to increase memory capacity per unit area because the magnetic memory devices may be manufactured by crossing metal lines on plastic substrates.

Because magnetic memory devices, according to at least some example embodiments, recognize bit information by detecting the existence of an induced electromotive force, reading accuracy may be improved. In addition, because the magnetic memory device may store multi-bit information in a single memory area, magnetic memory devices, according to at least some example embodiments, may have greater storage capacity as compared to related art magnetic memory devices.