JP2005259206A - Magnetic associative memory and method for reading information therefrom - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic associative memory, having nonvolatile characteristics and high integration characteristics and is capable of reading at a high speed. <P>SOLUTION: A storage cell 1 constituted of a pseudo-spin valve membrane cell is arranged at a position corresponding to the point of intersection between a digit conductor 7 and a bit conductor 9 in a conductor matrix. The storage cell 1 has a structure, where soft and hard magnetic layers 3 and 5 face each other via a nonmagnetic layer 4. A plurality of storage cells 1, arranged in a columnar direction, are electrically connected in series by detection conductors 11A to 11C, to constitute a plurality of storage cell columns 13A to 13C. Bit conductors 9A to 9C are used as retrieval data input lines, and the detection conductors 11A to 11C are used as information reading output lines. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic associative memory and a method for reading information from the magnetic associative memory.

  Magnetic associative memories having nonvolatile characteristics and high integration characteristics are expected to be used in the following fields in which high-speed recognition processing is performed on large-capacity information such as moving images and voices in an environment where power consumption is limited.

・ Recognition technology field such as vision and hearing in the robotics industry ・ Image processing memory field (collision prevention function) indispensable to realize autonomous autonomous driving in the automobile industry
・ Information processing field (fingerprint detection technology) that processes vague image data with noise and data loss
-Mobile field such as portable cameras, portable audio devices, portable information terminals, wearable computers (ubiquitous information environment technology), etc. Conventional associative memories (CAM) have a complicated circuit configuration combining many CMOS, It is difficult to integrate. Non-Patent Documents 4 to 6 describe research on content addressable memory (CAM) using conventional semiconductor device integration technologies such as CMOS, DRAM, and SRAM.

  In the case of a CAM intended for high-speed operation, the stored data group is accumulated in the SRAM, so that information is lost when the power is turned off.

On the other hand, a magnetic random access memory (MRAM) in which magnetic cells having a magnetoresistive effect are integrated is attracting attention as a next generation memory that is nonvolatile and can be highly integrated. Non-Patent Documents 5 to 7 describe conventional MRAM technology [research on logical operation devices using MRAM cells].
S. Aragaki et al. "A high-density multiple-valued content-addressable memory based on one transistor cell", IEICE Trans. Electron. , E76-C (1993) 1649. " T.A. Yamagata et al. "A bitline control circuit scheme and redundancy technique for high-densitive dynamic addressable memories", IEICE Trans. Electron. , E76-C (1993) 1657. H. Kimura et al. "Implementation of a DRAM-cell-based multiple-valued logic-in-memory circuit", IEICE Trans. Electron. , E85-C (2002) 1814. K. Tamaru, “The trend of functional memory development”, IEICE Trans. Electron. , E76-C (1993) 1545. W. C. Black, Jr. et al. , "Programmable logic using giant-magnetoresistance and spin-dependent tunneling devices", J. et al. Appl. Phys. 87 (2000) 6664. R. Richter et al. "Nonvolatile field programmable spin-logic for reconfigurable computing", Appl. Phys. Lett. 80 (2002) 1291. A. T.A. Hanbicki et al. , "Nonvolatile reprogrammable logic elements using hybrid resonant tunneling diode-giant magnetism circuits", Appl. Phys. Lett. 79 (2001) 1190.

  Since the conventional magnetic associative memory uses the magnetization direction of the ferromagnetic material as an information carrier, the stored information is non-volatile, and practically unlimited repetitive writing is possible. Although a technique for configuring a CAM with MRAM memory cells has also been reported, since its functional operation is a method of accessing each memory cell individually, it is inherently difficult to operate at high speed, and the current of a conductor current magnetic field is extremely small. Since only a part is used for functional operation, energy utilization efficiency is poor, which is a major obstacle to practical use.

  An object of the present invention is to provide a magnetic associative memory having non-volatile characteristics and high integration characteristics.

  Another object of the present invention is to provide a magnetic associative memory capable of reading at high speed and a method of reading from the memory.

  The magnetic associative memory according to the present invention is arranged to form a matrix in a state where a plurality of digit conductive lines arranged in the column direction and a plurality of bit conductive lines arranged in the row direction are electrically insulated from each other. A conductive line matrix and a plurality of pseudo spin valve film cells arranged one by one at positions corresponding to the intersections of digit conductive lines and bit conductive lines in the conductive line matrix are provided. In the present specification, the column direction and the row direction are determined for convenience, and can be interpreted as one and the other of the two kinds of intersecting conductive lines in interpreting the scope of rights. Further, the digit conductive lines and the plurality of bit conductive lines constituting the conductive line matrix are not necessarily orthogonal to each other. The pseudo spin valve film cell is composed of at least one soft magnetic layer having a small magnetization reversal magnetic field and at least one hard magnetic layer having a large magnetization reversal magnetic field opposed to each other with a nonmagnetic layer having conductivity therebetween. . The direction of magnetization of the hard magnetic layer is determined by a magnetic field generated by passing a current through the digit conductive line and the bit conductive line. The direction of magnetization of the soft magnetic layer is determined by a magnetic field generated by passing a current through the bit conductive line. The soft magnetic layer may have any configuration as long as the magnetization direction is changed by the magnetic field applied from the bit conductive line, and may be configured by a plurality of layers. The hard magnetic layer may be formed of a plurality of layers as long as the magnetization direction is changed by the magnetic field applied from the bit conductive line and the digit conductive line.

  In the present invention, a plurality of pseudo spin-valve film cells arranged in the column direction are electrically connected in series by a detection conductive line to constitute a plurality of memory cell columns. Each of the plurality of bit conductive lines is used as a search data input line, and the plurality of detection conductive lines are used as information readout output lines.

  The soft magnetic layer can be made of NiFe, the nonmagnetic layer can be made of Cu, and the hard magnetic layer can be made of CoFe. The soft magnetic layer can be made of NiFe, the nonmagnetic layer can be made of Cu, and the hard magnetic layer can be made of NiFe. Furthermore, the soft magnetic layer may be made of CoFe, the nonmagnetic layer may be made of Cu, and the hard magnetic layer may be made of CoFe.

  In the method for reading information from the magnetic content addressable memory for reading information stored in the plurality of memory cell columns in the magnetic content addressable memory of the present invention, it is preferable to do as follows. Using the potentials of the plurality of bit conductive lines as potentials corresponding to the search data strings, the search data strings are transferred to the soft magnetic layers of the plurality of pseudo spin valve film cells that respectively constitute the plurality of memory cell strings. Then, the voltage change based on the magnetoresistive change of the plurality of pseudo spin valve film cells included in the memory cell columns respectively appearing at the output portions of the detection conductive lines of the plurality of memory cell columns after the transfer is obtained as a search data string and a memory cell string. The information stored in the plurality of storage cell columns is read out as the Hamming distance from the data column stored in the hard magnetic layer. The Hamming distance corresponds to the degree of approximation between the search data string and the data string stored in the hard magnetic layer of the memory cell string. For example, if the search data string and the data string stored in the hard magnetic layer of the memory cell string are the same, the Hamming distance is zero. If the data stored in the hard magnetic layer of one pseudo-spin valve film cell is different when comparing the search data string and the data string stored in the hard magnetic layer of the memory cell string, the Hamming distance is ΔR. ΔR is the amount of change in magnetoresistance of one pseudo spin valve film cell.

  According to the present invention, by using a pseudo spin valve film cell used in a magnetic memory device such as an MRAM as a storage cell of a magnetic associative memory, the associative memory can be made non-volatile and have a large capacity at the same time. Further, by designing a device so that a magnetic field can be applied simultaneously to a plurality of memory cell columns, the number of parallel operations (calculation speed) can be dramatically increased without increasing power consumption.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, one memory cell 1 of a magnetic associative memory has a pseudo spin in which a soft magnetic layer 3 having a small magnetization reversal magnetic field and a relatively large hard magnetic layer 5 are separated by a nonmagnetic layer 4 having conductivity. It is formed by a valve membrane cell. As shown in FIG. 2, the magnetic associative memory forms a matrix in which a plurality of digit conductive lines 7 arranged in the column direction and a plurality of bit conductive lines 9 arranged in the row direction are electrically insulated from each other. In this example, a conductive wire matrix (orthogonal conductor wire matrix) is provided. One memory cell 1 composed of a pseudo spin valve film cell is disposed at a position corresponding to the intersection of the digit conductive line 7 and the bit conductive line 9 in the conductive line matrix.

  The electric resistance (magnetoresistance) of the memory cell 1 is that of the magnetization of the soft magnetic layer 3 and the hard magnetic layer 5 compared to the case where the magnetization directions of the soft magnetic layer 3 and the hard magnetic layer 5 are parallel due to the giant magnetoresistance effect. When the direction is antiparallel, it increases by about 10%. The magnetization direction of the soft magnetic layer 3 is changed only by the magnetic field generated by the current Iw of the bit conductive line 9. The magnetization direction of the hard magnetic layer 5 can be reversed by simultaneously applying to the memory cell 1 the magnetic field generated by the current Iw flowing through the bit conductive line 9 and the magnetic field generated by the current Ia flowing through the digit conductive line 7. Further, the memory cell material (material of the soft magnetic layer 3, the nonmagnetic layer 4 and the hard magnetic layer 5) and the current intensity are designed. Specifically, the soft magnetic layer 3 can be made of NiFe, the nonmagnetic layer 4 can be made of Cu, and the hard magnetic layer 5 can be made of CoFe. The soft magnetic layer 3 can be made of NiFe, the nonmagnetic layer 4 can be made of Cu, and the hard magnetic layer 5 can be made of NiFe. Furthermore, the soft magnetic layer 3 may be made of CoFe, the nonmagnetic layer 4 may be made of Cu, and the hard magnetic layer 5 may be made of CoFe. Such a memory cell 1 is electrically connected in series via detection conductive lines (information read output lines) 11A to 11C called sense lines as shown in FIG. 3, and one memory cell column 13A to 13C is connected. Configured (in fact, there are a large number of memory cells). A plurality of memory cell columns are arranged in parallel to form a magnetic content addressable memory. In this magnetic associative memory, a plurality of bit conductive lines 9 are respectively used as search data input lines.

  In this magnetic associative memory, the magnetization direction of the soft magnetic layer 3 of each storage cell 1 is made to correspond to the search data 1 and 0, and the magnetization direction of the hard magnetic layer 5 of each storage cell 1 is set to 1 of the storage data. , 0 respectively. Therefore, when the storage data and the search data match, the magnetoresistance of the memory cell 1 is in a low resistance state, and when the storage data and the search data are different, the magnetoresistance of the memory cell 1 is in a high resistance state.

  As described above, by using the pseudo spin valve film cell used in the magnetic memory device such as the MRAM as the storage cell of the magnetic associative memory, the associative memory can be made non-volatile and have a large capacity at the same time. In addition, a device design is performed so that a magnetic field can be simultaneously applied to a large number of memory cells arranged corresponding to the intersection of the conductive matrix (specifically, directly below or immediately above the intersection of the two conductive lines 7 and 9). As a result, it is possible to dramatically increase the number of parallel operations without increasing the power consumption.

  Next, a method for reading information stored from the magnetic associative memory will be described. First, arbitrary information is stored in advance in the hard magnetic layer 5 of each of the memory cells 1a to 1i by flowing current through the bit conductive line 9 and the digit conductive line 7, respectively, by a current matching selection method. Here, the current coincidence selection method is a magnetization direction selection method in which the magnetization direction of the hard magnetic layer 5 changes depending on whether the current Iw flowing through the bit conductive line 9 and the current Ia flowing through the digit conductive line 7 coincide with each other. Means.

  In the case of FIG. 3, the hard magnetic layers of the memory cells 1a to 1c, 1d to 1f, and 1h constituting the memory cell rows 13A to 13C are respectively (1,0,0), (1,0,1). , (0, 1, 1), three types of 3-bit data are input. When data is stored, the magnetization direction of the hard magnetic layer 5 and the magnetization direction of the soft magnetic layer 3 coincide with each other as shown in FIG. That is, in the state where data is input, the magnetization directions of the soft magnetic layer and the hard magnetic layer of the memory cell column 13A have a relationship of (1, 1) (0, 0) (1, 1), respectively. Further, the magnetization directions of the soft magnetic layer and the hard magnetic layer of the memory cell row 13B have a relationship of (1, 1) (0, 0) (1, 1), respectively. Further, the magnetization directions of the soft magnetic layer and the hard magnetic layer of the memory cell array 13C are in a relationship of (0, 0) (1, 1) (1, 1), respectively.

  A case where data search is performed will be described. For example, when searching for data in which (1, 0, 1) data is stored in the hard magnetic layer 5 of the memory cell column, the potential applied to the bit conductive lines 9A to 9C is set in the direction of the arrow shown in the figure. Determine that current flows. That is, when the data to be searched is 1, when the potential of the bit conductive lines 9A and 9C is set to +, a current (in this example, the current in the + direction) flows in the direction of the arrow, and when the data to be searched is 0 Indicates that the potential of the bit conductive line 9B is-, and a current (in this example, a current in the-direction) flows in the direction of the arrow shown in the figure. In this way, the magnetization direction of the soft magnetic layer 3 of each memory cell is magnetized in a direction corresponding to the magnetic field generated by the direction of current. This is referred to as transfer in the present specification. When a current is passed with the bit conductive line 9A at a positive potential, only the soft magnetic layer of the storage cell 1g inverts the magnetization direction among the storage cells 1a, 1d, and 1g corresponding to the bit conductive line 9A. As a result, the magnetization direction of the soft magnetic layer of the memory cell 1g and the magnetization direction of the hard magnetic layer do not match, and the magnetoresistance of the memory cell 1g increases by ΔR. Of the memory cells 1b, 1e, and 1f corresponding to the bit conductive line 9B, only the soft magnetic layer of the memory cell 1h reverses the magnetization direction by transfer. As a result, the magnetization direction of the soft magnetic layer of the memory cell 1g and the magnetization direction of the hard magnetic layer do not match, and the magnetoresistance of the memory cell 1g increases by ΔR. Further, among the memory cells 1c, 1f and 1i corresponding to the bit conductive line 9C, only the soft magnetic layer of the memory cell 1c reverses the magnetization direction by transfer. As a result, the magnetization direction of the soft magnetic layer of the memory cell 1c and the magnetization direction of the hard magnetic layer do not match, and the magnetoresistance of the memory cell 1c increases by ΔR. By such a transfer operation, the potentials or resistance values of the detection conductive lines (information read output lines) 11A and 11C of the memory cell array including the memory cells in which the magnetization direction of the soft magnetic layer is reversed are changed. As shown in FIG. 4, in this example, the resistance value of the detection conductive line (information readout output line) 11A increases by ΔR, and the resistance value of the detection conductive line (information readout output line) 11C increases by 2ΔR. Increase. As described above, in the present embodiment, since the memory cell in which the soft magnetic layer and the hard magnetic layer are inconsistent bits is in a high resistance state, the memory cell column in which a plurality of memory cells are connected in series has the number of inconsistent bits, That is, the resistance increase is proportional to the Hamming distance described later. The magnetic associative memory according to the present embodiment is characterized in that the stored data is non-volatile and one-to-many Hamming distance calculations can be performed simultaneously using the parallel application characteristics of the conductor current magnetic field.

  In the present specification, the voltage or resistance value of the detection conductive line (information read output line) of each memory cell column before the search, and the detection conductive line (information read output line) of each memory cell column after the search. The relative difference from the voltage or resistance value is called the Hamming distance. If this hamming distance is 0, it means that the search data and the stored data match, and the greater the hamming distance, the greater the difference between the search data and the stored data, that is, the lower the similarity. Means that. About the usage method of Hamming distance, if the well-known usage method is used, the usage form will not be limited.

Pseudo-spin valve film cell materials that can be used specifically include a soft magnetic layer formed of Fe ₂₁ Co ₇₉ (3 nm to 4 nm), a non-magnetized layer of Cu (4 nm to 5 nm), and a hard magnetized layer of Fe ₂₇ Co ₇₃ (4 nm to 5 nm) can be formed. The digit conductive line, the bit conductive line, and the detection conductive line are formed of Cu (0.4 μm to 0.6 μm), and an insulating layer (0.6 μm) formed of a heat-treated polymer film on the pseudo-spin valve film cell material. Bit conductive lines and digit conductive lines are sequentially formed in a matrix through (˜0.8 μm). In the magnetic associative memory formed using the specific pseudo spin valve film cell material created in this way, the recording information of the hard magnetic layer is recorded by flowing a current of 7 to 10 mA through the bit conductive line and the digit conductive line. It was confirmed that the reflected bipolar voltage output was obtained. Also, it was confirmed that the magnetization direction of the soft magnetic layer can be reversed by applying a current of 7 to 10 mA to the bit conductive line during the transfer.

  In the fields of image recognition technology and robotics technology, the associative memory function is craved, but in the actual application field, a wide variety of recognition functions are required and it is assumed that the battery is driven. High capacity and low power consumption are regarded as major issues. The magnetic associative memory of the present invention is a memory that can realize non-volatile characteristics and high integration characteristics that are not found in conventional associative memories. Therefore, since power is not required for memory retention, it is possible to supply power only when necessary (normally off function) and to turn on the power and start it instantly (instant on function). Expected to reduce operating power consumption. In addition, by using the parallel application characteristics of current magnetic fields, the number of parallel operations can be greatly improved compared to conventional associative memories, contributing to various fields that require comparison and association between large volumes of data. Is considered large.

It is a perspective view used in order to explain the composition of the pseudo spin valve film cell used in the magnetic associative memory of the present embodiment. It is a perspective view used in order to demonstrate the relationship between the electroconductive matrix used for writing of the magnetic content addressable memory of this Embodiment, and a memory cell. It is a perspective view used in order to demonstrate the structure to the magnetic content addressable memory of this Embodiment. It is a figure used in order to demonstrate the reading method of the data from the magnetic content addressable memory of this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Memory cell 3 Soft magnetic layer 4 Nonmagnetic layer 5 Hard magnetic layer 7 Digit conductive line 9 Bit conductive line 11A-11C Detection conductive line (information reading output line)

Claims (5)

A conductive line matrix in which a plurality of digit conductive lines arranged in the column direction and a plurality of bit conductive lines arranged in the row direction are arranged to form a matrix in a state of being electrically insulated from each other;
A plurality of pseudo spin-valve film cells each disposed at a position corresponding to the intersection of the digit conductive line and the bit conductive line in the conductive line matrix;
The pseudo spin valve film cell is composed of at least one soft magnetic layer having a small magnetization switching magnetic field and at least one hard magnetic layer having a large magnetization switching magnetic field, which are opposed to each other with a nonmagnetic layer having conductivity therebetween,
The direction of magnetization of the hard magnetic layer is determined by a magnetic field generated by passing a current through the digit conductive line and the bit conductive line,
A magnetic content addressable memory configured to determine a magnetization direction of the soft magnetic layer by a magnetic field generated by passing a current through the bit conductive line;
A plurality of pseudo-spin valve film cells arranged in the column direction are electrically connected in series by a conductive wire for detection to constitute a plurality of memory cell columns,
Each of the plurality of bit conductive lines is used as a search data input line, and the plurality of detection conductive lines are used as information read output lines.   The magnetic content addressable memory according to claim 1, wherein the soft magnetic layer is made of NiFe, the nonmagnetic layer is made of Cu, and the hard magnetic layer is made of CoFe.   The magnetic content addressable memory according to claim 1, wherein the soft magnetic layer is made of NiFe, the nonmagnetic layer is made of Cu, and the hard magnetic layer is made of NiFe.   The magnetic content addressable memory according to claim 1, wherein the soft magnetic layer is made of CoFe, the nonmagnetic layer is made of Cu, and the hard magnetic layer is made of CoFe. An information reading method from a magnetic content addressable memory for reading information stored in the plurality of memory cell columns in the magnetic content addressable memory according to any one of claims 1 to 4,
The potential of the plurality of bit conductive lines is set to a potential corresponding to a search data string, and the search data string is transferred to the soft magnetic layer of the plurality of pseudo spin valve film cells respectively constituting the plurality of memory cell strings,
A change in voltage based on a change in magnetoresistance of the plurality of pseudo-spin valve film cells included in the memory cell row that respectively appears at the output portion of the detection conductive line of the plurality of memory cell rows after the transfer, and the search data A method of reading information from a magnetic associative memory, wherein information stored in the plurality of memory cell columns is read as a Hamming distance between the column and a data column stored in the hard magnetic layer of the memory cell column.

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