JP2006504210A - Data storage device - Google Patents

Abstract

A data storage device for storing digital information in a readable form will be described. The storage device includes one or more storage elements, each of which includes a planar magnetic conduit that can maintain and further expand the domain wall formed in a continuous propagation path. Each continuous propagation path is provided with at least one, preferably a large number of inversion nodes, at which the domain wall magnetization direction extending along the conduit under the action of a suitable applied magnetic field, such as a rotating magnetic field. Will be changed.

Description

  The present invention relates to a data storage device for storing digital information such as computer files, digital music, digital video, and the like. Specifically, the present invention relates to a data storage device that can write and read data any number of times.

  In recent years, a wide range of data storage devices in which the medium area is used for a digital data storage application area has become available. Data storage devices have several different operating characteristics including capacity, access speed, write / rewrite capability, and the ability to stably hold data over a period of time (with or without power). It is made to correspond to.

  Known storage devices include magnetic tape storage devices, magnetic hard disk storage devices, and optical disk storage devices. Both of these have the advantages of significant storage capacity and relatively fast data access, and they can all be adapted for quick writing and rewriting of data. Both of these require moving parts in the form of electromechanical or optical readers. For this reason, the range in which an apparatus incorporating such a data storage medium can be reduced is limited, and the use of the device in a large vibration environment is limited. In any case, the surface medium is very important for the data storage device, but the associated mechanism requires fine-grained control of the properties of any support substrate. Therefore, such a device needs to have a finely controlled structure. In addition, both require a reader that can access the device surface, which may limit the degree of freedom in device design.

  It is an object of the present invention to provide an alternative digital data storage device that has flexibility in other situations. If specified, for example, it can be miniaturized and / or can be incorporated into another device such as a smart card, identification tag, and patch, and / or can be incorporated on a flexible substrate. It is possible to provide an alternative digital data storage device that can be used and / or used in a high vibration environment and / or is simple and inexpensive to manufacture.

  A particular object of the present invention is to provide a data storage device that allows digital data to be stored tightly and effectively, allowing data to be written to the device of the present invention and read back many times.

  Thus, in accordance with the present invention, a data storage device that stores digital information (such as computer files, digital music, digital video, etc.) in a readable form can include one or more, especially multiple storage devices. The device is provided. Each of these storage elements comprises a planar magnetic conduit that can sustain and widen the domain wall formed in a continuous propagation path. Each of the continuous paths is provided with at least one, a plurality, and more particularly a number of inversion nodes, with which the magnetization direction of the domain wall extending along the conduit under the action of a suitable applied magnetic field is at this node. Can be changed, especially reversed significantly.

  Each conduit is formed in a continuous conduction path. Conventionally, the conduit is provided with such a continuous propagation path by being formed in a closed loop. Such a loop is provided with at least one or a plurality, in particular a large number of inversion nodes. Data can move around the closed loop by this mechanism. This mechanism is outlined below. In a variant, the magnetic conduit is not a complete closed-loop node shape of the inversion node, but means to transfer data between its two ends so that it can still circulate around the externally closed loop. Form a linear chain of inversion nodes, for example, one end of the chain has a data write function, the other end has a data read function, and an electronic output from the chain output to the chain input In addition, an additional circuit for feeding back data is provided.

  Of a conduit adapted to change direction and to change the direction of magnetization of the domain wall spreading throughout the conduit under the action of a suitable applied magnetic field, such as a rotating magnetic field, and more preferably to significantly reverse the direction of magnetization. In terms of structure and shape, inversion nodes conventionally have features.

  However, the direction of the conduit and thus the direction in which the domain wall spreads needs to change at all points without significant disruption. Therefore, a conduit in the region of the inversion node and comprising the inversion node changes the magnetization direction of the domain wall extending throughout the conduit, preferably significantly reversing the magnetization direction, without significantly changing the propagation direction. It is necessary to have structural features.

  In a preferred embodiment, the reversal node includes a significant reversal of the magnetization direction at the reversal node. The reversal node is provided with a portion of the conduit where the direction changes away from the first path and then changes back to the first path, so that there is no direct propagation path throughout the deviation. Preferably it is not possible. In particular, the deviation includes a 90 degree deviation from the first path. For reasons already shown, the departure from the initial path is preferably made gradually as it moves away along the conduit.

  For example, the inversion node includes a cycloid portion within the conduit loop structure, in particular an inwardly facing cycloid portion, or a phase isomorphism of such a structure.

  Each loop is preferably provided with a plurality of such cycloid portions. Accordingly, the device according to the present invention comprises a number of magnetic conduits formed in a closed loop, each of which comprises a plurality of cycloids and functions to rapidly reverse the direction of magnetization of the domain wall moving through the entire conduit. Thus, it is preferable that an appropriate driving magnetic field functions as a domain wall inversion point when the domain wall is expanded along the conduit of the present invention.

  Each cycloid preferably has a radius of rotation in the range of 3 to 10 times the conduit width. As the domain wall passes through the cycloid, it is preferred that the cycloid significantly changes the magnetization direction, eg, reverses approximately 180 degrees.

  According to the present invention, the magnetic conduit needs to have a structure capable of maintaining and spreading the domain wall under the action of controlling the magnetic field. In the usual case, the magnetic conduit can be formed as a continuous path made of a magnetic material. Thus, the loop in the device according to the invention preferably comprises a magnetic wire, in particular a generally planar magnetic wire, on a suitable substrate.

  Thus, the data storage device uses a number of planar magnetic conduits, and particularly preferably a cycloid closed loop magnetic wire. In particular, the present invention uses magnetic nanoscale technology, and the device preferably comprises a number of planar magnetic nanowires formed in a plurality of closed loop shapes of cycloids.

  The width of the planar magnetic nanowire is preferably less than 1 μm and is formed on a suitable substrate. The width is a question of whether to prioritize using a thinner nanoscale wire to improve the storage capacity of the device and thereby increase the manufacturing cost and complexity. However, devices incorporating wires greater than 1 micron are not likely to be effective, and 50 nm is a lower limit at which the cost effectiveness of modern wire forming technology is likely to be realized. It should be emphasized that this is not the limit of the technical effect, and that if the manufacturing technique is improved, the apparatus can be further miniaturized and the present invention can be realized in a practical manner.

  The wire is placed on a thin layered substrate of magnetic material. The wire thickness is optimized for the optimal performance of the device and is generally a function of width. In particular, the thickness of the wire is generally about 1/40 of the width of the wire. The wire thickness is generally not less than 2 nm and preferably not less than 3 nm. In practice, the wire thickness cannot exceed 25 nm.

The wires can be manufactured by optical lithography, X-ray lithography, microcontact printing, e-beam lithography, shadow mask deposition, or other suitable methods. The wire is made from a magnetic material such as permalloy (Ni ₈₀ Fe ₂₀ ) or cobalt iron, or other soft magnetic material.

  A memory function is imparted to the inversion node by applying to the data storage device incorporating the inversion node a magnetic field that changes direction appropriately, particularly a rotating magnetic field, in the manner described in more detail below. By providing a plurality of loop arrays, each incorporating one or more inversion nodes, the device according to the present invention can store data in a circular sequence.

  It is possible to write data to the device of the present invention and read it back again and again. Unlike magnetic tape storage devices or magnetic hard disk storage devices, the present invention does not require moving parts. Therefore, it can be easily downsized and can be used in a large vibration environment. The principle of the present invention is very simple, and the manufacturing cost can be kept low. Furthermore, the product of the present invention does not require power for holding data in the memory when not in use.

  The product of the present invention uses a number of magnetic conduits such as planar magnetic wires. Planar wires are formed on a substrate, which, unlike microelectronic memories, does not play any role in the electronic or magnetic operation of the device, it simply performs the basic role of mechanical support. There are only. Although conventional silicon substrates can still be used, materials other than silicon, such as glass or plastic, can be used because the substrate function is not required. For example, polyimide such as Kapton, polyethylene terephthalate, or mylar type material, acetate, polymethyl methacrylate, and the like. The advantages of the plastic substrate are that it is low cost and not only easy to manufacture, but also has the potential to be mechanically flexible, so that the present invention can be used as a plastic card or apparel such as a smart card. It is suitable for incorporation into goods.

  Unlike compact disks, magnetic tapes, and magnetic hard disk storage devices, no mechanical access to the surface of the product is required, so multiple substrates are stacked on top of each other to form a three-dimensional memory cube. It is possible.

  The surface density of the storage device of the present invention is moderate, higher than that of the magnetic tape but lower than that of the hard disk. The data read / write speed can be increased as required and can be higher than the speed of the hard disk drive. However, since the present invention continuously stores data in a circular manner and the access time to a predetermined data block is relatively gradual, the present invention, which has a limited scope of application, can be used as it is. May be replaced with a disk drive.

  International patent application PCT / GB01 / 05072 applies and develops part of the principles of the above-mentioned papers by Cowburn and Welland, from nanometer-scale dot chains of magnetic materials, or nanometer-scale planar magnetic wires. It describes how a digital logic circuit can be constructed.

  In FIG. 1, the arrows indicate the direction of magnetization in a thin strip of magnetic material that constitutes the gate. The structure in the center of the gate reverses the magnetization direction from the left.

  In use, the gate is placed in a magnetic field whose vector rotates over time in the plane of the device. Although the device of the present invention is not limited by any theory of operation, it should be noted that the magnetization of the wire is generally limited due to the anisotropy of the magnetic shape and is along the long axis of the wire. I can do it. This means that there are two possible magnetization directions and therefore there is a natural binary representation. The domain wall is expanded by the applied magnetic field along the wire, but the magnetization direction is changed by the domain wall. The rotation of the applied magnetic field means that the domain wall can be conveyed so as to surround the corner.

  In accordance with the present invention, a NOT gate similar to that described above is manufactured by a suitable method. It is ideal that the gate shape has a cycloid shape with some modifications to the shape shown in FIG. The output of the gate is reconnected to its input using a suitable magnetic conduit such as a planar magnetic wire to form a closed loop. Such an array of loops forms the device of the invention according to this preferred embodiment. It comprises planar magnetic nanowires formed in a large closed loop shape of continuously connected cycloids, forming a chain of magnetic NOT gates. The output of the last NOT gate in each chain is fed back to the input of the first NOT gate by a planar magnetic wire, forming a closed loop for the data sequence to circulate.

  Cycloids, as described above, and as described in further detail below, under appropriate rotationally acting magnetic field effects, as domain nodes reverse through the nanowires as domain nodes reverse. Function. The inverted output appears only after a time delay equal to half of the rotating applied magnetic field period, so that each inverted node looks like a single memory cell or flip-flop. Thus, the cycloid loop has the same memory function as a continuous circular shift register and can function as a data storage device according to the present invention.

  According to another aspect of the present invention, it is possible to provide a data storage device including one or more of the above-described device elements and further including a magnetic field driver capable of controlling the magnetic field driving with time. The magnetic field driver is preferably set so that the magnetic field is applied to all cycloids of a given loop simultaneously and further to all loops of the system simultaneously. This gives the operating system a unique function. A magnetic field is applied to the entire loop at once so that all data bits travel simultaneously. This is in contrast to simply applying a magnetic field partially under the write head, as is the case with conventional magnetic data storage devices.

  Any suitable magnetic field can be envisaged. The magnetic field driver is preferably capable of controlling a magnetic field consisting of two orthogonal magnetic fields, preferably appearing alternately, operating in a predetermined sequence, and more preferably forming a clocked magnetic field in a clockwise or counterclockwise direction. By using such a system, data can be stored in the storage device according to the first aspect of the present invention.

  The system can comprise suitable electrical and / or data inputs and / or outputs to allow the data storage device to be used in memory storage and retrieval systems.

An example of the operation of a magnetic data storage device according to the principles of the present invention will now be described by way of example with reference to FIGS.
For such description, reference is made to FIGS. 1-8 of the accompanying drawings.

FIG. 2 is similar to FIG. 1 but shows a NOT gate having a cycloid shape, specially modified to be optimal for the present invention. The gate is created by focused ion beam milling of 5 nm thick permalloy (Ni ₈₀ Fe ₂₀ ) on a silicon substrate. Only the bright white shading is magnetic material and the other contrast is due to the multi-stage milling process used during gate fabrication. FIG. 2A shows a gate where the output is again connected to the input by using a planar magnetic wire to form a closed loop. FIG. 2B shows a close-up of a gate structure having a cycloid shape. A magneto-optical measurement at points I and II in response to an applied rotating magnetic field is shown in FIG. 2C. There is a 1/2 cycle delay between the input (trace I) change state and the output (trace II) change state equal to ½ of the applied rotating field period. This corresponds to the memory function.

  FIG. 3 illustrates the reversal action of the cycloid and in particular the onset of this delay.

  In low magnetic field conditions, the magnetization direction in a submicron ferromagnetic planar wire tends to be along the long axis of the wire. This is due to the anisotropy of the ferromagnetic shape. When magnets in two opposing directions meet in a wire, the reorganization of successive atomic magnetic moments is not abrupt and is gradually performed as a certain distance leaves, forming a domain wall.

  It is now known that domain walls can extend along a straight submicron magnetic wire by applying a magnetic field parallel to the wire. When using the present invention, by using a magnetic field with a vector that rotates over time at the sample surface, it is also possible to change direction and widen the domain wall along a magnetic wire that turns a corner. Magnetic field chirality is defined by clockwise or counterclockwise rotation. Given that the magnetic field and angular chirality are the same, the domain wall should extend around the magnetic wire. However, the chirality of the corner is determined by the direction of the domain wall, and in the rotating magnetic field of the predetermined chirality, the domain wall only passes through the predetermined corner in one direction. This meets the important requirement of any logic system that a certain signal flow direction needs to exist. These two stable magnetization directions in a submicron magnetic wire provide a unique means of representing two Boolean logic states. This forms the basis of the operation of each logical unit of the storage device together with the application of a rotating magnetic field.

  The cycloid shown in FIG. 3 has a reversal function and exhibits a NOT gate function when in a suitable rotating magnetic field. It is assumed that the magnetic field is rotating counterclockwise. The domain wall that reaches the end “P” of the joint (FIG. 3B) spreads around the first corner of the joint (FIG. 3C), and reaches the end “Q” when the applied magnetic field rotates from horizontal to vertical. To do. The magnetization between 'P' and 'Q' is here continuous (FIG. 3D). Next, as the magnetic field vector continues to rotate in the opposite horizontal direction, the domain wall extends around the second corner of the joint (FIG. 3E), exits from the end 'R', and 'Q' and 'R' Should return to continuous magnetization during Unlike the magnetization of the wire immediately before the bonding portion, the magnetization of the wire immediately after the bonding portion is reversed. Thus, the junction performs the desired NOT function with a 1/2 cycle propagation delay. This action is similar to a car that reverses its direction by performing a three-point rotation.

  Therefore, there is a delay of ½ cycle as a whole between the domain walls from reaching the input to leaving the output. In the present invention, this synchronization delay has an associated memory function that can be exploited by connecting a number of magnetic NOT gates together in series and then piping the output of the chain to the input. Authenticate.

  FIG. 4 shows a reduced version of the invention in which three NOT gates are connected in a chain and the output of the chain is fed back to the beginning of the chain by a planar magnetic wire. Two different data bit sequences were set in the device by specially applying a magnetic field, and then the data started to circulate around the loop by starting a rotating magnetic field.

  Trace I in FIG. 4B shows a simple bit sequence that circulates around the chain, ie the pattern repeats every 5 cycles of the rotating field. Trace II in FIG. 4B shows a more complex sequence that circulates around the loop in a 5-cycle period of the rotating field. The device is effectively acting as a 5-bit serial shift register. The data bit sequence operates one step to the right each time the rotating field cycle is completed. These data were obtained by using a magnetic field rotating counterclockwise, whereby the data was circulating counterclockwise around the magnetic field ring. By reversing the direction of rotation of the magnetic field, the data is found to reverse direction and begin to circulate clockwise around the magnetic field ring.

  FIG. 5 shows the test of the present invention using 11 NOT gates. FIG. 5B shows a simple bit sequence that circulates around the loop with a 13-cycle repetition of the rotating field.

  Data is written to each loop by a conductive lithographic wire that passes above or below the planar magnetic wire. By using a magnetic tunnel junction attached to a portion of the loop, or by measuring the electrical resistance of the domain wall present at one of the corners of the wire, or by reducing the electrical resistance of the domain wall present at one of the NOT gates. Data is read from each loop by measuring.

  FIG. 6 shows examples of these data input / output methods. Data is written into the loop by conductive electrolithographic wire (61) passing over or under the ring. Data circulates around the loop in the direction of arrow A. Data is obtained by forming a magnetic tunnel junction between two electrical contacts (62) at one point of the loop (upper panel) or by using two electrical contacts (63) and a small portion of the ring (lower panel) It is read out by measuring the resistance of any domain wall contained within.

  In a variant of the invention (not shown), the magnetic conduit itself does not form a closed loop of inversion nodes, but instead has a data write function at one end of the chain and a read at the other end of the chain. Form a linear chain of inverted nodes with functionality. In this case, the external control circuit electronically feeds back data from the output of the chain to the input of the chain, allowing the data to still circulate around the apparently closed loop.

  The data loop is located in the magnetic field and its vector rotates with time at frequencies in the range of 1 Hz-200 MHz in the plane of the loop. When rotating the magnetic field, the magnitude of the magnetic field may be constant, in which case a circular trajectory is formed with respect to the magnetic field vector, or the magnitude of the magnetic field may fluctuate. Form a trajectory. To achieve this, in a small area device, the electromagnetic strip line is placed under the loop, and then alternating current passes through the strip line. In an apparatus having a larger area, the substrate holding the loop is disposed inside the 4-channel electromagnet.

  The magnitude of the magnetic field needs to be strong enough to ensure that the domain wall can be pushed all the way to each NOT gate, but not so strong that the new domain wall can agglomerate regardless of the data input mechanism. .

  The magnetic field required to push the domain wall to each NOT gate can be adjusted by changing the thickness of the loop, the width of the loop, and the magnetic material used to make the loop. This magnetic field needs to be so large that the device is not removed from the stray surrounding magnetic field. When deletion of stray magnetic fields becomes a problem, the product of the present invention can be protected by using mu metal. The optimized device uses an applied magnetic field strength in the range of 50-200 Oe.

  The present invention can include multiple data loops on a single substrate, as shown in FIG. 7, and the correct loop can be addressed using electronic multiplexers and demultiplexers. A number of loops are shown between the data write driver and multiplexer (71) and the data read demultiplexer and amplifier (72).

  The optimum balance between the number of loops and the number of NOT gates in each loop is determined to suit a given application. It is very easy and inexpensive to incorporate a small number of loops each having a large number of NOT gates into a package, but if one of the NOT gates fails due to manufacturing defects, the entire device will fail. It is easy to happen. Such combinations also take time to access data. This is because a predetermined data block circulates around the reading position, and on average, a large number of clocks must be circulated before reaching this position. Many loops, each with a small number of NOT gates, are less prone to failure of individual NOT gates (the loop containing the failed gate can be taken out of the circuit without significantly reducing the overall capacity of the storage device), Although quick access is possible, the number of read and write points increases (and consequently increases cost) and the incorporation of multiple loops into a single integrated circuit package is complicated. All drawings in this document show a loop of 8 gates. This is just a comparison, and in practice each loop contains thousands of gates.

  A unique feature of the present invention is that the data loop placement is not limited to a two-dimensional plane. Unlike compact disks, magnetic tapes, and magnetic hard disk storage devices, no mechanical access is required on the surface of the product. As shown in FIG. 8, substrates can be placed on top of each other to form a three-dimensional data cube. This has the advantage that much higher data storage density can be achieved. If necessary, all the substrates in the cube can share the same applied rotating magnetic field. Thereby, the layers can be synchronized with one another and the device can be simplified.

  The present invention can be configured to input / output a single continuous data stream or, if desired, a multi-bit wide data word stream by using several rings or layers in parallel Can be stored.

Due to the low access time, the present invention is not suitable as an alternative to the main hard disk of a computer. However, applications can be sought in the following situations and some of the other situations.
Temporary storage of digital music for pocket digital audio players such as MP3 players. This application requires an inexpensive, non-volatile and rewritable storage device for digital information that is normally reproduced continuously. By using a planar wire with a width of 200 nm, the NOT gate occupies an area of 1 μm ² . Thus, a continuous data storage of 12 bytes is obtained with only one 1 cm ² layer covered with a data chain. This is every 12 minutes, and is sufficient for several hours of CD quality music. By layering, several hours of CD quality audio is provided very inexpensively.
Temporary storage of digital photographs in digital cameras. This function is currently achieved by flash electronic memory, but this is expensive and limits the number of rewrite cycles.
Non-volatile offline storage of mobile phones, personal organizers, palm top computers, and smart cards.

1 is a schematic diagram of a conventional magnetic NOT gate (see above). FIG. AC is a magnetic NOT gate modified to be used as a data storage device according to the present invention. FIGS. 2A to 2E are schematic diagrams illustrating the structure of the NOT gate of FIG. 2A and the influence of the NOT gate structure on the domain wall that enters from the point P under the action of the rotating magnetic field H. FIGS. A shows a 5-bit continuous shift register connected in a ring. The asterisk indicates the point in the loop where the measurement was made in FIG. 4B. B shows a situation where simple (trace I) and complex (trace II) bit sequences can be forced to rotate around the ring by applying a rotating magnetic field. A shows 11 magnetic NOT gates connected in a ring to form a 13-bit continuous memory. The asterisk indicates the point in the loop where the measurement is made in FIG. 4B. B shows a simple 13-bit data sequence that circulates around the loop under the action of a rotating magnetic field. FIG. 3 is a schematic diagram of a data writing and reading mechanism of the present invention. FIG. 2 is a schematic diagram of multiple magnetic loops on the same substrate individually addressed by an electronic multiplexer and demultiplexer. FIG. 3 is a schematic diagram of a stack of multiple substrates, each including multiple data loops to form a three-dimensional memory cube.

Claims (15)

  A data storage device that stores digital information in a readable form includes one or more storage elements, each of which is a planar magnetic that can maintain and expand a domain wall formed in a continuous propagation path state. A data storage device comprising a conduit, each continuous propagation path comprising at least one inversion node, wherein the magnetization direction of the domain wall extending along the conduit under the action of a suitable applied magnetic field is changed at the inversion node .   2. The data storage device according to claim 1, wherein each continuous path is provided with at least one reversal node, and the magnetization direction of the domain wall extending along the conduit under the action of a suitable applied magnetic field is greatly reduced at this reversal node. Data storage device to be inverted.   3. The data storage device according to claim 1 or 2, wherein each continuous path includes a large number of inversion nodes.   4. The data storage device according to claim 1, wherein the conduit is formed in a closed loop shape and includes a continuous propagation path.   5. A data storage device according to any of claims 1 to 4, wherein the conduits form a chain of inversion nodes rather than a complete closed loop, so that data can circulate around a loop that is apparently closed. Means for transferring data between the two ends of the inversion node, said means having a data writing function at one end of the chain and a data reading function at the other end of the chain; And a data storage device further comprising an additional circuit for electronically feeding back data from the output of the chain to the input of the chain.   6. A data storage device according to claim 1, wherein the inversion node is adapted to change the magnetization direction of the domain wall extending across the conduit under the action of a suitable applied magnetic field. A data storage device characterized by the above.   7. A data storage device according to claim 6, wherein the reversal node is characterized by the structure and shape of the conduit adapted to significantly reverse the direction of magnetization of the domain wall extending throughout the conduit under the action of a rotating magnetic field. apparatus.   8. The data storage device according to claim 6, wherein the inversion node includes a deviating portion that leads to a node that significantly reverses the magnetization direction, and further changes the direction away from the first path, and the subsequent direction is A data storage device in which a direct propagation path cannot be provided over the entire deviating portion because it includes a portion to be returned to the first route.   9. The data storage device of claim 8, wherein the deviation includes a 90 degree deviation from the initial path of the conduit.   10. The data storage device according to claim 8, wherein the inversion node includes a cycloid portion in a conduit loop structure or a phase isomorphism of the structure.   The data storage device according to claim 10, wherein the data storage device includes a plurality of such cycloid units provided in each loop.   12. The data storage device according to claim 11, comprising a plurality of magnetic conduits formed in a closed loop shape, each of the closed loops having a plurality of cycloids functioning to suddenly reverse the magnetization direction of the domain wall moving throughout the loop. Data storage device provided.   13. A data storage device according to claim 10, wherein each cycloid has a turning radius in the range of 3 to 10 times the width of the conduit.   14. A data storage device according to any of claims 1 to 13, wherein the magnetic conduit comprises a particularly common planar magnetic wire on a suitable substrate.   15. The data storage device according to claim 14, wherein the magnetic wire comprises a magnetic nanowire having a thickness of 2 nm to 25 nm and a width of 50 nm to 1 [mu] m.

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