HRP20040884A2 - Data storage device - Google Patents

Description

This invention relates to a device for storing digital information such as computer files, digital sound recording, digital image recording and the like. This invention particularly relates to a data storage device in which data can be written and read an unlimited number of times.

In recent years, a variety of data storage devices have become available that use a variety of media to store digital data. Data storage devices are designed to take advantage of some of their basic operating characteristics, including capacity, access speed, write/rewritable ability, ability to retain data over time (with or without power), size, robustness, portability, or the like.

Common data storage devices include magnetic tapes, hard drives, and optical storage drives. All of them offer the advantages of large storage capacity and relatively fast access, and can be configured to write and rewrite data. All versions require moving parts in the form of electromechanical or optical readers. These facts limit the possibility of using them in terms of further miniaturization and their use in an environment with strong vibrations. Regardless of everything in each of the mentioned cases, the surface medium is the key to data storage, the mechanism used requires precise control of the properties as well as any of the supporting substrates. Furthermore, such devices must be assembled with great care. Moreover, they all require the reader to have access to the surface of the device itself, which is a limitation on design freedom in the construction of the device.

The aim of the present invention is to provide an alternative device for storing digital data that enables usefulness in alternative situations, especially from the aspect of miniaturization, and/or when the device needs to be incorporated into other devices, e.g. smart-card, identification tags, "patches" or the like. .

The particular object of the invention is a device that enables data storage and that compactly and efficiently stores digital data and enables that data can be written and read an unlimited number of times in the mentioned device from the invention.

According to the invention itself, a device for storing digital information (such as computer files, digital sound recording, digital image recording and the like) contains one or more, and in particular a plurality of memory elements, where each memory element contains planar magnetic conductors capable of retaining and propagating magnetic a domain wall that forms on a continuous path of propagation, where each continuous path is equipped with at least one and optionally with more, and especially with a large number of nodes, where the direction of magnetization of the domain wall that propagates along the conductor and is acted upon by a corresponding field changes, and especially in a way to reverse it.

Each conductor is designed as a continuous propagation path. It is convenient to make a conductor made in the form of a closed loop containing such a continuous propagation path. Such a loop has at least one, optionally many, and especially a large number of inversion nodes. Data can pass around a closed loop as shown below. In the variant where the magnetic conductor does not form a completely closed loop of inversion nodes, but rather a linear chain of inversion nodes with a data transfer device between the two ends in such a way that the data still circulates as if it were a closed loop, for example that such a device contains the possibility writing data at one end and reading data at the other end of the chain, and additional circuitry for electronic data input from the end to the very beginning of the chain.

It is convenient for the inversion nodes to contain properties in the structure and shape of the conductor which are adjusted to cause a change in the direction of magnetization, and preferably to reverse the direction of magnetization of the domains themselves propagating through these nodes upon the appropriate application of a field, such as a field varying in direction, especially in a rotating magnetic field.

It is quite necessary that the direction of the conductor and thus the direction of propagation of the domain wall varies without sharp discontinuities at each point. Therefore, the conductor in the region containing the inversion node must have a configurational property such as a change in the direction of magnetization, preferably completely in the opposite direction to the direction of magnetization of the domain propagating through the node, but without any sharp variation in the direction of propagation.

In a preferred embodiment of the invention, the inversion node is such that it generally reverses the direction of magnetization. Preferably, the inversion node contains a part in which the direction of change outside the initial path and the subsequent change of direction to the initial path occur in the conductor in such a way that no direct propagation is possible through the deviation point. It is particularly desirable that the deviation contains a 90° deviation from the initial path. For the indicated reason, the deviation from the initial path preferably occurs graduated over the distance along the path of the conductor.

For example, an inversion node contains a cycloidal part within the conducting loop structure, particularly directed inward, or the topological equivalent of such a structure.

Preferably, a plurality of such cycloids form a loop. Accordingly, the device in accordance with the invention preferably contains a plurality of magnetic conductors that form a closed loop where each of them contains a plurality of cycloids whose purpose is to effectively reverse the magnetization of the domain wall passing through them and thus serve as inversion points for the domain walls while they are propagated through the guide that is the subject of the invention by a suitable excitation field.

Preferably, each cycloid has a radius of gyration that is in the range of three to ten times the width of the conductor itself. It is desirable that such a cycloid gives a substantial change, for example 180° in turning the direction of magnetization when the domain wall propagates through it.

In accordance with the invention, the magnetic conductors must have an architecture capable of retaining and propagating the magnetic wall under the influence of the control field. Typically, the magnetic conductor can be made as a continuous strip of magnetic material. Therefore, the loops in the device according to the invention are made of magnetic wires, especially magnetic wires placed planarly on a suitable substrate.

The data storage device therefore uses a plurality of planar magnetic conductors, particularly magnetic wires which are preferably formed into closed cycloidal loops. In particular, the invention uses magnetic nano-technology, the device comprises numerous planar magnetic nano-wires preferably formed into a plurality of closed cycloid loops.

Planar magnetic nanowires are preferably less than 1 μm in width and are fabricated on any suitable substrate. The width itself is determined by the relationship between the improved storage capacity due to the use of narrower nano-wires and the manufacturing costs and complexity of the same. Devices involving wires above one micrometer do not seem to be viable, and 50 μm seems to be the lower practical limit for a good investment-gain ratio according to the current possibilities of the method of formation and production. It should be emphasized that this is not a technical limit and that improving manufacturing techniques can provide further miniaturization making the performance practical.

The wires are applied to the substrate in the form of thin layers of magnetic material. Wire thickness is optimized for optimal device performance, and is largely a function of width. It is desirable that the thickness be about 1/40th of the width of the wire. The thickness of the wire is generally not less than 2 nm and preferably not less than 3 nm. The wires used in practice are no thicker than 25 nm.

Wires are fabricated by optical lithography, X-ray lithography, microcontact printing, electron lithography, shadow mask deposition, or some other convenient process. The wires can be made of a magnetic material such as Permalloy (Ni80Fe20) or CoFe or some other soft magnetic material.

The data storage device includes inversion nodes as described earlier and which are suitable for a suitable change of direction especially by means of a rotating magnetic field in a manner that will be described in detail below, in such a way that a memory function is attached to the inversion node. An embodiment with a plurality of loop arrays each including one or more inversion nodes allows a device according to the invention to store data serially in a ring.

According to the invention, data can be written and read from the device an unlimited number of times. Unlike magnetic tapes or magnetic hard disks, the invention does not require moving parts. Therefore, it can be easily miniaturized and used in a vibration-rich environment. The principle of the invention is very simple, the production costs can be low. More importantly, no power is required to keep data in the invention's memory when it is not in use.

The invention utilizes a plurality of magnetic conductors such as planar magnetic wires. The planar wires are made on the same substrate, but unlike the microelectronic memory, this substrate does not play any role in the electronic or magnetic performance of the device, and its purpose is solely to be a mechanical support. Standard silicon supports can be used, but since the substrate does not need to show any particularities, other materials can also be used, eg glass and plastic. Examples include polyamides such as Kapton, polyethylene terephthalate or Mylar-type materials, acetates, polymethylmethacrylates or others. Plastic substrates possess the advantages of cheap performance and simple fabrication, while at the same time providing the potential for mechanical flexibility that makes the invention suitable for incorporation into plastic cards such as smart-cards or clothing.

Considering that the mechanical accessibility of the surface of the invention itself is not necessary, as it is, for example, necessary with compact disks, magnetic tapes and hard disks, a large number of substrates can be stacked on top of each other in order to obtain a three-dimensional memory cube.

The data storage density according to the invention itself is average, higher than magnetic tapes but lower than magnetic hard disks. The speed of reading and writing data can be very high if required, and even higher than with hard disks. According to the invention, data is stored serially in a ring, so that the access time to a given block of data is relatively slow, which is why the invention itself has a limitation when applied as a direct replacement for the basic hard disk of a computer.

International patent application PCT/GB01/05072 applies and develops the same principles as the referenced Cowburn and Welland article, which describes how digital logic circuits can be made from chains of nanometer-scale magnetic material dots, or nanometer-scale planar magnetic wires. . The construction of the NE door, which is shown in drawing 1 of the subject patent application, is particularly described.

In drawing 1, the arrows show the direction of magnetization in the thin strip of magnetic material that forms the gate. The central gate structure reverses the magnetization coming from the left.

When using the aforementioned gates, they are placed in a magnetic field whose vector rotates in the plane of the device in time. While the device according to the invention is not limited by any method of execution, it is noticeable that due to the form of magnetic anisotropy, the magnetization of the wires is generally such that it lies along the axis of the wire itself. This means that there are two possible directions of magnetization, so there is a natural binary representation. The change in magnetization direction is mediated by a magnetic domain wall that moves along the wire driven by the applied field. The fact that the applied field rotates means that domain walls can be carried around corners.

According to the invention, NE-gates similar to those described are extracted by suitable procedures. Ideally for the purpose in question, the shape of the door is slightly modified from that shown in drawing 1 to obtain a cycloidal shape. The output of the gate is coupled back to the input using suitable magnetic conductors such as planar magnetic wires to form closed loops. The field of such loops is formed by the device according to the invention and according to the preferred embodiment it consists of planar magnetic nano-wires which form a large closed loop of serially connected cycloids to obtain a chain of magnetic NE-gates. The output of the last NE gate of each chain is led back to the input of the first NE gate by a planar magnetic wire in such a way that they form a closed loop for the data circulating around.

The cycloids serve as inversion nodes for the propagation of the domain walls as they propagate through the nanowires under the action of a suitable rotating field in the manner indicated before and described in detail below. The inverted output is generated after a time delay equal to one half of the rotation period of the applied field, which makes each inversion node as a one-bit memory cell or flip-flop. Therefore, cycloid loops have the same memory function as a serial circular shift register and can serve as a data storage device according to the present invention.

According to a further aspect of the invention, the data storage device comprises one or more elements as described above and further comprises a magnetic field drive to provide a controlled time-varying magnetic field. The magnetic field drive is designed in such a way that it is applied simultaneously to all cycloids in a given loop and can be applied simultaneously to all loops in the system. This gives a distinctive feature to the given system in its operation. The magnetic field is applied to the entire loop simultaneously so that all data advances together, rather than only locally under the action of the write head as is the case with conventional magnetic data storage devices.

Any suitable field can be used. Preferably, the magnetic field drive provides a controlled magnetic field consisting of two orthogonal fields acting in a predetermined sequence, preferably alternately, and more preferably in such a way as to form a pulsed field in a clockwise or counterclockwise direction. Using such a system, data can be stored in the data storage device(s) according to the first aspect of the present invention.

The system can further contain a suitable electrical and/or data input and/or data output that enables the stored data to be used further in the memory or in devices for data manipulation.

An exemplary operation of magnetic data storage according to the principles of the present invention will be further described by examples referring to drawings 2 through 8.

References are made to drawings 1 through 8 and supplement those drawings and serve as illustrations, showing:

Drawing 1 is a schematic representation of the prior art of magnetic NE-gates (see description earlier);

Figure 2 shows a magnetic NE gate modified for use as a data storage device in accordance with the present invention;

Drawing 3 is a schematic representation of the structure of the NE gate taken from drawing 2 (part A) and the action of that gate on the domain wall that enters at point P under the action of the rotating magnetic field H;

Figure 4 shows three magnetic NE gates connected in a ring to produce a 5-bit serial shift register in part A, and part B shows how a simple (trace I) and complex (trace II) sequence of bits can be made to cycle through the ring under the action of a rotating magnetic field (the asterisk in part A shows the point in the loop where the measurement shown in part B was performed);

Figure 5 shows eleven magnetic NE gates connected in a ring to form a 13-bit serial memory in part A, and part B shows how a simple 13-bit sequence of data circulates through the ring under the action of a rotating magnetic field (the asterisk in part A shows a point in the loop where the measurement shown in part B was performed);

Figure 6 provides a schematic view of the data write and read mechanism according to the present invention.

Drawing 7 is a schematic representation of numerous magnetic loops on the same substrate, individually addressed by electronic multiplexers and demultiplexers.

Figure 8 is a schematic representation of the stacking of a number of substrates each carrying a number of data loops to form a three-dimensional memory cube.

Drawing 2 shows a NE-gate similar to that of drawing 1, but specially adjusted and optimized according to the subject invention to have a cycloidal shape. The gate can be performed by a focused ion beam penetrating a 5 nm thin Permalloy (Ni80Fe20) film on a silicon substrate. Only the lighter trace represents magnetic material; the other contrast comes from the multi-step encroachment process that was used during the execution of the aforementioned door. Figure 2a shows a gate where the output is connected to the input using a planar magnetic wire to form a closed loop. Drawing 2b shows one gate (enlarged) which is cycloidal in shape. Magneto-optical measurements made at points I and II in response to an applied rotating magnetic field are given in Figure 2c. There is a half-cycle delay between the input (trace I) change of state and the output (trace II) change of state equal to half the period of the applied rotating magnetic field, which corresponds to a memory function.

Figure 3 provides an explanation of the inversion action of the cycloid and the reason for the observed delay.

Under the action of a small magnetic field, the magnetization along submicron-thick ferromagnetic wires tends to align with the longer axis of the wire itself due to strong magnetic anisotropy resulting from the shape. When two oppositely directed magnetizations meet inside the wire, a redistribution of the direction of the successive magnetic moments occurs, which is not interrupted but occurs graduated over the distance as a domain wall is formed.

It is known that domain walls can be propagated along flat sub-micron magnetic wires by applying a magnetic field parallel to the wire itself. As used in the present invention, a magnetic field is applied with a time-rotating field vector in the plane of the sample and used to propagate domain walls along magnetic wires that also change direction and rotate at angles. Clockwise or counterclockwise rotation defines the chirality of the magnetic field. Domain walls can propagate around the corners of magnetic wires provided that the field and the corner have the same chirality. However, the chirality of the angle itself depends on the direction of propagation of the domain wall in such a way that with a rotating magnetic field of a given chirality, the domain wall may be able to pass through the given angle in one direction. This satisfies the important requirement for any logic system to have a defined signal flow. The two stable directions of magnetization in sub-micron magnetic wires provide a natural representation of two Boolean logic states and this, together with the application of a rotating magnetic field, constitutes the basis for any logic unit of a memory device.

The cycloids shown in figure 3 perform an inverter function and show the functionality of a NO-gate when a suitable magnetic field is applied. Assume that the magnetic field rotates in a counter-clockwise direction. The domain wall comes to the point «P» (drawing 3B) of the joint itself and continues to move around the first corner (drawing 3C) until the end «Q», since the applied field rotates from the horizontal to the vertical direction. The magnetization between points «P» and «Q» is continuous (drawing 3D). After that, the magnetic field vector continues to rotate in the opposite horizontal direction, the domain wall propagates around the second corner of the junction (drawing 3E), thus exiting at the end of «R» and establishing a continuous magnetization between «Q» and «R». The magnetization of the wire immediately after the junction will be reversed compared to that before the junction. Such a connection will therefore enable the desired NO-function with a delay of half a cycle of the applied field. This operation is analogous to turning a car with three pivot points.

We can see that we have a half-cycle delay between the incoming wall at the entrance and the one coming out of the exit. According to the present invention, we identify this synchronous delay as an associated memory function that can be exploited by connecting a number of magnetic NO-gates together in series and connecting the output of such a chain back to the input.

Figure 4 shows a reduced version of the invention in which three NE gates are connected in a chain and the output of the chain is fed back to the input by a planar magnetic wire. We program two sets of different bit sequences into the device through a specific application of a magnetic field and then initiate a data cycle within the loop by turning on the rotating magnetic field.

Trace I in Figure 4b shows a simple sequence of bits circulating around the chain: the pattern is repeated every 5 cycles of the rotating field. Trace II on line 4b shows a more complex sequence circulating around the loop, with a period of 5 cycles of the rotating field. The device behaves as if it were a 5-bit serial shift register. The data sequence makes one step from the right for each cycle of the rotating field. This data is obtained by using a counter-clockwise rotating field so that the data circulates around the magnetic ring in a counter-clockwise direction.

Figure 5 shows an experiment according to the invention using 11 NE-gates. Figure 5b shows a simple bit sequence circulating around a loop with a repetition period of 13 cycles of the rotating field.

Data is written into each loop with a lithographically derived current-carrying wire passing over the top of a grid of planar magnetic wires. Data is read from each loop using a magnetic tunnel junction attached to one part of the loop or by measuring the electrical resistance of a domain wall present at one of the wire corners or by measuring the electrical resistance of a domain wall present in one of the NE gates.

Figure 6 shows examples of such input/output procedures. The data is written into the loop with the help of the current carried by the lithographic wires (61) that pass above or below the ring. The data circulates around the loop in the direction of arrow A. The data is read from the loop either by applying a magnetic tunnel junction between two electrical contacts (62) at one point of the loop itself (top image) or by applying two electrical contacts (63) to measure the resistance of a from the domain walls of a small part of the ring (bottom image).

In a variant of this invention (not shown in the drawings) the magnetic conductors themselves do not form a closed loop of inversion nodes but rather a linear chain of inversion nodes with read devices at one end and write devices at the other end. In this case, it is necessary for the external control circuits to return the data back electronically from the output of the chain to the input so that the data is still able to circulate around as in a closed loop.

The data loops lie in a magnetic field whose vector rotates in the plane with the frequency in the range 1Hz-200MHz. The amount of field can be constant as the field rotates forming a circular locus for the magnetic field vector, or it can vary to form an elliptical locus for the magnetic field vector. This can be achieved on a small area of the device by placing electromagnetic thin lines under the loops themselves and later passing alternating current through these lines. In devices with a larger area, the substrate carrying the loops is placed in a quadrupole electromagnet.

The amount of field must be large enough to allow domain walls to be pushed all the way through each NE gate, but not so large as to nucleate new domain walls independently of the data entry mechanism.

The field required to push the domain wall through each NE gate can be tuned by varying the thickness of the loop, the width of the loop, and the magnetic material used to make the loop. The field must be strong enough so that the device does not suffer from erasure caused by scattered magnetic fields from the environment. The invention can be shielded using MuMetal - material if scattered external fields are a problem. In the optimized device, fields of 50-200 Oe are applied.

The invention may include a large number of data loops on a single substrate with electronic multiplexers and demultiplexers used to address a particular loop, as shown in Figure 7. A number of loops are shown between the data write drive and the multiplexer (71) and the data read demultiplexer and amplifiers (72).

The optimal balance between the number of loops and the number of NE gates in each loop must be determined according to the given application. A small number of loops with a large number of NE gates is very easy and cheap to integrate into one package, but it will be more prone to errors of the whole device if only one NE gate has a manufacturing error. Such a combination requires a large access time and it is necessary to wait for a large number of clock cycles in order to access a data block on average until it arrives at the reading position. A large number of loops containing a small number of NE gates will be more resistant to the errors of individual NE gates (a loop containing a gate with an error can be removed from the circuit without significant loss of storage capacity) and a high access speed will be obtained using a larger number of write points. and reading (which makes the device more expensive) and all of that together will be more complicated for integrating a larger number of loops into one integrated circuit. All drawings in this document show 8-gate loops. This is purely figurative - practically every loop contains many thousands of gates.

A particular feature of the invention is that it is not limited to a two-dimensional plane for placing data loops. Unlike compact disks, magnetic tapes and magnetic hard disks, mechanical contact with the surface of the invention is not required. The substrates can be stacked on top of each other to form a three-dimensional data cube as shown in Figure 8. This has the advantage of allowing much higher recording densities to be achieved. If desired, all substrates in the cube can share the same applied rotating magnetic field, thus making the layers synchronized with each other, which reduces the complexity of the device itself.

The device can be configured as an input/output of a single serial data string, or if desired a string of words consisting of multiple bits stored using several loops or layers in parallel.

For reasons of slow access, the invention is not suitable as a replacement for the primary hard disk of the computer itself. However, the invention can find application in some of the following situations:

Temporary storage of digital music recordings for digital audio players such as MP3 players. Such an application requires inexpensive, resilient, and rewritable digital information that is typically reproduced serially. By using a 200 nm wide planar gate, the NE-gate occupies an area of about 1μm2. 1cm2 of one layer covered with data chains can store 12 Mb of serial data, which is enough for 12 minutes of CD-quality music. By layering it is possible to get several hours of CD-quality audio at a very low price.

Temporary storage of digital photos in digital cameras. This function is implemented today with FLASH electronic memory, which is expensive and has a limited number of possible rewrite cycles.

Reliable off-line storage for mobile phones, personal organizers, palm top computers and SMART cards.

Claims (13)

1. A device for storing data that is in digital form in a form that can be read, characterized by the fact that it contains one or more memory elements, where each of the elements contains a planar magnetic conductor that is capable of retaining and propagating a magnetic domain wall formed on a continuous propagation path , where each continuous path has at least one inversion node where the direction of magnetization of the domain wall propagating along that conductor changes under the action of the corresponding applied magnetic field, and each inversion node contains a part where the direction deviates from that in the initial part of the path and a continuous direction is changed according to that in the initial part in such a way that such a conductor does not allow a direct propagation path through the deviation area of the same conductor. 2. Data storage device according to claim 1, characterized in that each continuous track has at least one inversion node where the direction of magnetization of the domain wall propagating through the conductor is reversed under the action of a suitable external field. 3. Data storage device according to claim 1 or claim 2, characterized in that each continuous track contains a large number of inversion nodes. 4. A data storage device according to any one of the preceding claims, characterized in that the conductor is made in the form of a closed loop to contain a continuous propagation path. 5. A data storage device according to any of the previous requirements, characterized in that the conductor is not made in the form of a closed loop but as a chain of inversion nodes with means that enable the transfer of data between the two ends of the chain so that the data can still circulate around as if they are in a closed loop, and the mentioned devices contain devices that enable data entry at one end of the chain and a device for reading data at the other end of the chain and additional circuitry that returns data electronically from the output of the chain itself to the input of the same chain. 6. Data storage device in accordance with any of the previous requirements, characterized in that the deviation part makes a 90° deviation from the initial path of the conductor itself. 7. A data storage device according to any of the preceding requirements, characterized in that the deviation occurs graduated over the distance of the conductor path itself. 8. A data storage device in accordance with any of the preceding claims, characterized in that the inversion node contains a part made in the form of a cycloid within the conductive loop structure or a topological equivalent of such a structure. 9. A data storage device according to claim 8, characterized in that a plurality of such cycloid parts are contained in one loop. 10. A data storage device according to claim 9, characterized in that it contains a plurality of magnetic conductors formed into closed loops where each contains a plurality of cycloids that serve to turn the direction of magnetization of the domain wall passing through them. 11. Data storage device according to one of claims 8-10, characterized in that each cycloid has a turning radius that is three to ten times larger than the width of the conductor itself. 12. A data storage device according to any of the preceding claims, characterized in that the magnetic conductor comprises a generally planar magnetic wire on a suitable substrate. 13. Data storage device according to claim 12, characterized in that the magnetic wire contains magnetic nano-wires whose thickness is from 2 nm to 25 nm and width between 50 nm and 1 μm.