Patent Application
20070055815
The invention relates to a storage system comprising a record carrier and a storage device, the record carrier having an information plane that is provided with an electro-magnetic material constituting an array of bit locations, a magnetic state of said material at a bit location representing the value thereof.
The invention further relates to a record carrier comprising an information plane on a substrate that is provided with a layer of an electro-magnetic material constituting an array of bit locations, a magnetic state of said material at a bit location representing the value thereof.
The invention further relates to a storage device.
A storage system, record carrier, and a device for storing information are known from U.S. Pat. No. 5,956,216. Data storage systems using magnetic material on a disc-type record carrier are well known, for example a removable type magnetic record carrier like the floppy disk. The document describes a magnetic record carrier of a patterned type. The record carrier has an information plane that is provided with a magnetic layer that can be magnetized by a suitable magnetic field from a write head. In particular the information plane is provided with a non-magnetic substrate and magnetic domain elements that can have two magnetization values. The magnetic domain elements constitute bit locations for storing a single bit of data. The device has a head and a write unit for recording information in a track constituted by the bit locations on the record carrier. The value of a bit location must be set or retrieved by positioning a read/write head opposite the bit location, e.g. by scanning the track. A problem of the known magnetic storage system is that the scanning does not allow immediate random access to any bit location. The process of positioning the head via a jump to a required part of the track is time consuming.
Therefore it is an object of the invention to provide a system comprising a record carrier and a device for storing information that allows fast access to the bit locations.
According to a first aspect of the invention the object is achieved with a storage system as defined in the opening paragraph, the storage device having an interface surface for cooperating with the information plane, which interface surface is provided with an array of electro-magnetic elements that are sensitive to said magnetic state of the electro-magnetic material, which record carrier can be coupled to and removed from the storage device, and which system has alignment means for positioning the bit locations near the electro-magnetic elements within a near-field working distance between a bit location and the corresponding electro-magnetic element during said coupling.
According to a second aspect of the invention the object is achieved with a record carrier as defined in the opening paragraph, characterized in that the record carrier comprises alignment means for positioning the bit locations near the electro-magnetic elements within a near-field working distance between a bit location and the corresponding electro-magnetic element during said coupling.
According to a third aspect of the invention the object is achieved with a device as defined in the opening paragraph, characterized in that the device comprises an interface surface for cooperating with the information plane, which interface surface is provided with an array of electro-magnetic elements that are sensitive to said magnetic state of the electro-magnetic material, and alignment means for positioning the electro-magnetic elements near the bit locations within a near-field working distance between an electro-magnetic element and the corresponding bit location during said coupling.
The effect of the array constituted by electro-magnetic elements cooperating with the information plane is that data from a large number of bit locations can be retrieved simultaneously via electro-magnetic interaction. This has the advantage that data can be accessed at a high speed. In particular the alignment is different from a scanning system in that the array is aligned to the bit locations parallel to the information plane and also in height with respect to the information plane. Compared to scanning magnetic hard-disk systems the advantage is that no high scanning speed between a head and the disk is needed, which prevents fatal head-disk interactions like a head-crash.
The invention is also based on the following recognition. The magnetic hard-disk storage system provides a non-removable record carrier that can be recorded by magnetizing material in a layer or pattern in a user device. However removable magnetic discs like floppy discs are slow and large, and require a scanning mechanism which is sensitive to mechanical shocks. The inventors have seen that data on a record carrier can be accessed fast and reliably by bringing the surface of the information plane into close vicinity of an array of electro-magnetic elements. The elements can detect a magnetic state within a predefined near-field working distance, which is in practice in the same order of magnitude as the minimum dimensions of the bit location. Alignment is required to bring the elements opposite and close to the bit locations within the near-field working distance. Suitable read/write elements can be produced using solid state production methods, e.g. known from producing MRAM magnetic storage devices.
In an embodiment of the record carrier the substrate is of a flexible material for allowing positioning of the bit locations near the electro-magnetic elements within the near-field working distance between a bit location and the corresponding electro-magnetic element. A rigid substrate requires a highly level plane. The flexible material has the advantage that close contact between the bit locations and the electro-magnetic elements is easily achieved by applying pressure on the flexible material.
Further preferred embodiments of the record carrier and storage device according to the invention are given in the further claims.
These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which
a shows a storage device (top view) and record carrier,
b shows a storage device (side view) and record carrier,
c shows a record carrier in a cartridge,
In the Figures, elements which correspond to elements already described have the same reference numerals.
It is noted that other combinations of an electro-magnetic material and a sensor unit can be chosen. In another embodiment the sensor units are arranged for emitting light as the electro-magnetic field for affecting the state of the material, e.g. phase-change material known from CD-RW, and detecting the effect of the material on a near-field working distance from the source of light. The further embodiments described below are based on using magnetic material. A suitable material is a hard magnetic material and a suitable electro-magnetic element is based on the magneto-resistive effect. An example is described below with reference to
a shows a storage device (top view) and record carrier. The storage device has a housing 35 and an opening 36 for receiving a record carrier 40.
The record carrier 40 includes an information carrier part 10 that has an information plane that has an array of bit locations 11 as described above with reference to
When coupling the record carrier 40 to the storage device 35 the record carrier is placed on the opening 36. The opening 36 is provided with an interface surface 32 on a read-out unit 30 as described above with reference to
In an embodiment the opening 36 is a recess in the surface of the housing, the recess having precisely shaped walls as alignment elements for cooperating with the outer perimeter of the record carrier 40 for aligning the information carrier part.
In an embodiment the storage device is provided with processing circuitry for analyzing the read-out signals of the electro-magnetic elements for eliminating influences of neighboring bit locations. Any electro-magnetic element may be influenced somewhat by adjacent bit locations, in particular due to some remaining misalignment. However, by analyzing the read-out signals of neighboring electro-magnetic elements and subtracting some of those from the current read-out signal, the detected value of the current bit location is improved. Hence electronic correction of inter-symbol interference is provided. The analysis may be controlled by global information about the remaining misalignment, for example indicating which of the neighboring read-out signals must be subtracted and to which extent.
In the direction perpendicular to the interface surface some pressure is required to make sure that the distance of the bit locations to the electro-magnetic elements in the read-out part is within the near-field working distance. The pressure may be provided by a user just pressing the record carrier to the storage device, or by a resilient lid or cover on top of the record carrier (not shown). Other options for achieving close physical contact are well-known to a skilled man.
In an embodiment of the record carrier the information plane is provided on a flexible substrate. The device is provided with a pressure system for bringing the flexible substrate in close contact with the interface surface, for example by creating a low pressure or vacuum between the substrate and the interface surface. In an embodiment the device is provided with a generator for generating an attracting field for attracting the information carrier to the interface surface. The type of attracting field is different from the field used by the sensor element. For example an electrostatic field is generated for attracting a record carrier of a magnetic type. Alternatively a magnetic field is generated for a record carrier based on capacitive read-out.
In an embodiment the alignment elements 38 on the device are connected to actuators for moving the record carrier with respect to the interface surface 32. Only a small movement, in the order of magnitude of the dimensions of a single bit location (i.e. a few μm), is sufficient to align the electro-magnetic elements with the bit locations. For the actuators several types may be used, e.g. voice coil type, piezo type or electrostatic type. In an embodiment the actuators are controlled by detecting misalignment of the bit locations. The misalignment can be derived from read-out signals of the electro-magnetic elements. For example if there is a substantial misalignment the electro-magnetic elements will cover adjacent bit locations. Read-out signals of adjacent locations having the same value will be different from read-out signals of adjacent locations having differing values. Hence if such differences occur, i.e. if the read signals of some bit locations have values at an intermediate level between the maximum and minimum levels of other bit locations, misalignment is detected. It is noted that in non correlated data the intermediate levels will occur in substantially 50% of the bit locations due to the fact that the respective neighboring location has a same or different logical value. In an embodiment predefined control patterns having known neighboring bits are included for misalignment detection. A control signal is generated to activate the actuators, and after applying the control signal the read-out signal is again analyzed. In an embodiment the record carrier is provided with optical marks for alignment, and the device is provided with separate optical sensors for detecting the optical marks for generating a misalignment signal.
In an embodiment of the storage system the pitch of the array of electro-magnetic elements is larger than the pitch of the array of the bit locations, for example by an integral factor n=2 in one or both planar dimensions. Some stepwise movement of the information carrier part relative to the read-out part is provided to read-out positions in each direction in which the pitch differs to access every bit location. The movement may be provided as indicated above, e.g. by the actuators. Such scanning over small distances by means of micro-mechanic means can make it possible to use media with a higher bit density than the density of the read-out part.
In an embodiment of the record carrier the information plane is provided with position mark patterns that are unique patterns in the information plane within a predefined area of the information carrier. The storage device is provided with a processor for applying techniques of pattern recognition for detection the absolute position of the position mark patterns with respect to the electro-magnetic elements array by analyzing the signals detected from the electro-magnetic elements. For example the position mark patterns may comprise a large area of material at a predefined magnetic state which is larger than any initial mechanical misalignment. The large area is surrounded by a contour with material having a different state in a predetermined pattern. Hence some electro-magnetic elements will always initially be covered by said large area. By analyzing the surrounding electro-magnetic elements the misalignment can be detected easily.
In an embodiment the array of electro-magnetic elements is substantially smaller than the information plane, e.g. 4 times smaller. The device is provided with actuators that are arranged for positioning the record carrier or the array of electro-magnetic elements at a few, e.g. 4, read-out positions for reading areas of the information plane.
In an embodiment the alignment elements of the record carrier are constituted by oblong protruding guiding bars, and the complementary guiding elements on the device are slots or grooves. The alignment by these elements is effective in one planar dimension. The alignment in the other planar dimension may be provided by a wall or protruding stopping pin on the device. Alternatively there may be no specific stopping position in the second planar dimension, but the information is retrieved from the bit locations while the record carrier is being propelled along that second direction, e.g. by the user pushing the record carrier via a guiding slot. Such constellation is advantageous for one-time reading of data from the record carrier, e.g. in an application like a personal passport carrying biomedical or DNA information for access control at an airport.
b shows a storage device (side view) and record carrier. The storage device has a housing 45 and an opening 43 for receiving a record carrier 40. When coupling the record carrier 40 to the storage device 45 the record carrier is placed on the opening 43. Close contact between the two parts is obtained by pressing (possibly with contact liquid) the read-out array against the information carrier when the slot of the reader is closed. The opening 43 is provided with an interface surface 32 on a read-out unit 30 as described above with reference to
c shows a record carrier in a cartridge. The record carrier has a cartridge 47 enclosing the information carrier part 10. The cartridge 47 has a movable cover 48 that effectively seals off the information plane from contamination (dust and fingerprints) when the record carrier is not coupled to a storage device. A storage device has an opening mechanism (not shown) for moving the cover aside during said coupling. Several options for slidable covers are known from optical or magnetical recording disc cartridges and cooperating devices.
In an embodiment the cartridge comprises a cleaning pad 46. The pad 46 is located on and/or moved by the cover 48 for wiping the information plane and/or the interface surface when the cover is moved. Alternatively the pad or other cleaning units such as a brush may be placed on the cartridge itself. In an embodiment the cartridge is provided with a dust attracting inner layer for attracting any dust particles that may have entered the closed cartridge in spite of the cover 48.
In the array electro-magnetic elements may be read-only elements only having the parts needed for read-mode as described with
In the storage system data are represented by magnetization directions occurring at a sensor element due to the bit location opposite the sensor on the information plane. In the sensor element the read-out is done by a resistance measurement which relies on a magnetoresistance (MR) phenomenon detected in a multilayer stack. Sensor elements can be based on the anisotropic magnetoresistance (AMR) effect in thin films. Since the amplitude of the AMR effect in thin films is typically less than 3%, the use of AMR requires sensitive electronics. The larger giant magnetoresistance effect (GMR) has a larger MR effect (5 à 15%), and therefore a higher output signal. The magnetic tunnel junctions use a large tunnel magnetoresistance (TMR) effect, and resistance changes up to ≈50% have been shown. Because of the strong dependence of the TMR effect on the bias voltage, the useable resistance change in practical applications is at present around 35%. In general, both GMR and TMR result in a low resistance if the magnetization directions in the multilayer stack are parallel and in a high resistance when the magnetizations are oriented antiparallel. In TMR multilayers the sense current has to be applied perpendicular to the layer planes (CPP) because the electrons have to tunnel through the barrier layer; in GMR devices the sense current usually flows in the plane of the layers (CIP), although a CPP configuration might provide a larger MR effect, but the resistance perpendicular to the planes of these all-metallic multilayers is very small. Nevertheless, using further miniaturization, sensors based on CPP and GMR are possible.
In an embodiment a number of sensor elements are read at the same time. The addressing of the bit cells is done by means of an array of crossing lines. The read-out method depends on the type of sensor. In the case of pseudo-spin valves a number of cells (N) can be connected in series in the word line, because the resistance of these completely metallic cells is relatively low. This provides the interesting advantage that only one switching element (usually a transistor) is needed per N cells. The associated disadvantage is that the relative resistance change is divided by N. The read-out is done by measuring the resistance of a word line (with the series of cells), while subsequently a small positive plus negative current pulse is applied to the desired bit line. The accompanying magnetic field pulses are between the switching fields of the two ferromagnetic layers; thus the layer with the higher switching field (the sensing layer) will remain unchanged, while the magnetization of the other layer will be set in a defined direction and then be reversed. From the sign of the resulting resistance change in the word line it can be seen whether a ‘0’ or a ‘1’ is stored in the cell at the crossing point the word and the bit line. In an embodiment spin valves with a fixed magnetization direction are used and the data is detected in the other, free magnetic layer. In this case the absolute resistance of the cell is measured. In an embodiment the resistance is measured differentially with respect to a reference cell. This cell is selected by means of a switching element (usually a transistor), which implies that in this case one transistor is required per cell. Besides sensors with one transistor per cell, alternatively sensors without transistors within the cell are considered. The zero-transistor per cell sensor elements in cross-point geometry provide a higher density, but have a somewhat longer read time.
The storage system according to the invention is in particular suitable for the following applications. A first application is a portable device that needs removable memory, e.g. a laptop computer or portable music player. The storage device has low power consumption, and instant access to the data. The record carrier can also be used as a storage medium for content distribution. A further application is a memory that is copyright-protected. In contrast to existing solutions it has all the following properties: easily replicable, copy-protected, instant-on, fast access time, robust, no moving parts, low power consumption.
Although the invention has been mainly explained by embodiments using the TMR effect, any suitable read/write element for cooperating with the magnetic material can be used, e.g. based on coils. It is noted, that in this document the verb ‘comprise’ and its conjugations do not exclude the presence of other elements or steps than those listed and the word ‘a’ or ‘an’ preceding an element does not exclude the presence of a plurality of such elements, that any reference signs do not limit the scope of the claims, that the invention may be implemented by means of both hardware and software, and that several ‘means’ or ‘units’ may be represented by the same item of hardware or software. Further, the scope of the invention is not limited to the embodiments, and the invention lies in each and every novel feature or combination of features described above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 02079079.6 | Oct 2002 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB03/04007 | 9/12/2003 | WO | 3/29/2005 |
