WO2004086407A1 - 磁気メモリデバイスおよびセンスアンプ回路、ならびに磁気メモリデバイスの読出方法 - Google Patents
磁気メモリデバイスおよびセンスアンプ回路、ならびに磁気メモリデバイスの読出方法 Download PDFInfo
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- WO2004086407A1 WO2004086407A1 PCT/JP2004/003973 JP2004003973W WO2004086407A1 WO 2004086407 A1 WO2004086407 A1 WO 2004086407A1 JP 2004003973 W JP2004003973 W JP 2004003973W WO 2004086407 A1 WO2004086407 A1 WO 2004086407A1
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B61/00—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
- H10B61/20—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices comprising components having three or more electrodes, e.g. transistors
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
- G11C11/14—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements
- G11C11/15—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements using multiple magnetic layers
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B61/00—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
- H10B61/10—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices comprising components having two electrodes, e.g. diodes or MIM elements
Definitions
- the present invention relates to a magnetic memory device configured using a magnetoresistive element, a sense amplifier circuit applied to reading information from a magnetic memory device, and a method of reading information in a magnetic memory device.
- volatile memories such as DRAMs and SRAMs have been used as general-purpose memories used in information processing devices such as computers and mobile communication devices.
- Volatile memory loses all information unless it is constantly powered. Therefore, a non-volatile memory must be provided separately for information storage, and flash EEPROMs and hard disk drives are used.
- flash EEPROMs and hard disk drives are used for these non-volatile memories.
- increasing the speed of information processing has become an important issue.
- up-computing computing there is a strong demand for the development of high-speed nonvolatile memory as a key device.
- MRAM Magnetic Random Access Memory
- MRAM Magnetic Random Access Memory
- GMR Giant Magneto-Resistive
- GMR refers to a laminated body in which two ferromagnetic layers are stacked with their easy axes of magnetization aligned with each other. The resistance of the stacked body is such that the magnetization direction of each ferromagnetic layer is along the easy axis of magnetization. It is a phenomenon that is minimum when parallel and maximum when antiparallel.
- the two ferromagnetic layers consist of a fixed layer whose magnetization direction is fixed and a free layer (magnetic layer) whose magnetization direction can be changed by an external magnetic field. Stacked through I have.
- Each memory cell stores information by associating these two states with binary information of “0” and “1”, and detects a difference in resistance corresponding to the information as a change in current or voltage. It is a mechanism to read information.
- TMR Transmission Magneto-Resistive
- GMR Global Magnetic elements using the TMR (Tunneling Magneto-Resistive) can greatly increase the rate of change in resistance compared to GMR elements.
- TMR refers to the magnetization directions of two ferromagnetic layers (a fixed layer with a fixed magnetization direction and a free layer whose magnetization direction can be changed) stacked with an extremely thin insulating layer interposed between them. This is a phenomenon in which the value of the tunnel current flowing through the insulating layer changes depending on the relative angle of. That is, when the magnetization directions are parallel, the tunnel current is maximum (the element resistance is minimum), and when the magnetization directions are antiparallel, the tunnel current is minimum (the element resistance is maximum).
- TMR-MRAM stored information is written in the same way as GMR-MRAM, and information is read out by passing a current perpendicular to the insulating layer in the layer plane and the relative magnetization direction between the ferromagnetic layers. (Parallel or antiparallel) is detected as a difference between the output current value and the cell resistance value.
- TMR element As a specific example of the TMR element, a laminated structure of C0FeZA1 oxide / CoFe is known, but its resistance change rate is over 40%.
- TMR elements have a high resistance and are said to be easy to match with semiconductor devices such as MOS field-effect transistors (MOS FETs). Because of these advantages, TMR-MRAM is easier to achieve higher output than GMR-MRAM, and is expected to have improved storage capacity and access speed.
- MOS FETs MOS field-effect transistors
- the structure that has the best characteristics in terms of power consumption efficiency during readout is a structure in which a selection semiconductor element is arranged for each TMR element.
- the noise caused by the variations can be ignored. Absent.
- the S / N ratio of the output voltage of the memory cell is only a few dB. there is a possibility.
- a commonly used method is to compare the output voltage V of one selected memory cell with a reference voltage Vref and differentially amplify the difference voltage Vsig.
- the purpose of differential amplification is firstly to remove noise generated in the data line pair to which the storage cell is connected, and secondly, to reduce the output due to the characteristic variation of the semiconductor element for driving the sense line or selecting the cell. It is to remove the voltage offset.
- the circuit that generates the reference voltage Vref is realized by a circuit using a dummy cell or semiconductor element, and since there is element variation between this circuit and the memory cell, it is necessary to completely remove the offset of the output voltage. Is in principle impossible
- a storage cell is constituted by a pair of TMR elements and the outputs from the elements forming the pair are differentially amplified.
- writing is performed such that the magnetization directions of the magneto-sensitive layers of the paired TMR elements are always antiparallel to each other. That is, in one element, writing is performed complementarily so that the magnetization of the free layer and the magnetization of the fixed layer are parallel to each other, and the magnetization of both layers is antiparallel to each other, and the output of the two elements is compared.
- dynamic amplification and reading out common-mode noise is removed and the S / N ratio is improved.
- Such a differential amplification type circuit configuration is disclosed in Japanese Patent Application Laid-Open No. 2001-236781, Japanese Patent Application Laid-Open No. 201-266656, ISSCC 2000 Digest paper TA7.2, and the like. .
- the first TMR element and the second TMR element constituting a storage cell are One end is separately connected to the pair of first and second data lines, and the other end is connected to the bit line via the same cell selecting semiconductor element.
- the word line is connected to the cell selection semiconductor element.
- the information is read from the bit line and the first and second data lines while maintaining the first data line and the second data line at the same potential. This is performed by giving a potential difference between each of the data lines and outputting the difference value of the amount of current flowing through the first and second data lines.
- the resistance variation between the TMR elements connected to the first and second data lines and the characteristic variation between the selection semiconductor elements Needs to be sufficiently suppressed.
- the first data line and the second data line are configured to give an equal potential voltage difference, the read current fluctuates according to the variation.
- this configuration does not allow the above-mentioned variations to be suppressed in principle, and there is a problem that it is extremely difficult to take a thorough measure against noise due to these variations.
- the present invention has been made in view of the above problems, and has as its object to provide a magnetic memory device and a sense amplifier circuit capable of obtaining a read signal output with a high SZN ratio and reducing power consumption and circuit space. , And a method of reading a magnetic memory device.
- a magnetic memory device includes a plurality of magnetoresistive elements each having a magneto-sensitive layer whose magnetization direction changes according to an external magnetic field, and one storage cell includes a pair of magnetic sensors.
- a magnetic memory device configured to include a resistance effect element, comprising: a read line pair for supplying a read current to the pair of magnetoresistive elements; and a read current flowing through the read line pair.
- a sense amplifier circuit for reading information from the memory cell, wherein the sense amplifier circuit includes a differential switch pair provided for each read line pair, and a bias resistor provided between each differential switch pair and a power supply. And a constant current circuit provided in common for the plurality of differential switch pairs and for stabilizing the sum of a pair of read currents flowing through each of the differential switch pairs.
- connection refers to at least a state of being electrically connected, and is not necessarily a condition of being physically directly connected.
- the “power supply” is a current or voltage supply source necessary for circuit operation, and means an internal power supply line of the magnetic memory device.
- a “differential switch pair” refers to a differential operation that has a completely on-off relationship, for example, a current of 160 A flows through one switch element and no current flows through the other switch element.
- there are two relative states that occur during operation for example, 110 iA flows through one switch element and 50 A current flows through the other switch element. It also means that the differential operation is performed in an intermediate state where the current flows and the other current can flow less.
- a pair of read currents whose sum is always constant is supplied to each of a pair of magnetoresistive elements constituting the storage cell, and the storage cell outputs the read current based on a difference between the read currents.
- the information is read.
- the read current is differentially output, noise generated in each of the read lines and offset components included in the output value of each magnetoresistive element are canceled.
- the difference between the read currents is differentially amplified as a voltage difference by the sense amplifier circuit.
- a plurality of sense amplifier circuits are provided for each read line pair in a portion including a differential switch pair and a bias resistor pair, but since a constant current circuit for stabilizing the total read current is shared, a constant amplifier circuit is provided. Variations in the sense amplifier output due to variations in the characteristics of the current circuit can be suppressed.
- the magnetic memory device includes a current-voltage conversion resistor pair between the read line pair and the power supply, and a terminal of the current-voltage conversion resistor pair on a side opposite to the power supply side includes: It is preferable to be connected to a differential switch pair of the sense amplifier circuit. A read current supplied from the power supply to each of the pair of read lines is extracted as a voltage output due to a voltage drop in the current-voltage conversion resistor pair, and is input to the sense amplifier circuit.
- the current-voltage conversion resistor desirably has a resistance value larger than the resistance value of the magnetoresistive element.
- a first switch for selecting any one of the plurality of differential switch pairs, a power supply and a readout are provided between each of the plurality of differential switch pairs and the constant current circuit.
- a pair of second switches are provided between the pair of lines and select whether or not to supply a read current to the pair of read lines. That is, only the sense amplifier circuit selected by the first switch conducts between the differential switch element constant current circuits and becomes operable, and the read current only flows to the read line pair selected by the pair of second switches. Is supplied.
- the first and second switches When the first and second switches are controlled to be opened and closed based on a first selection signal for selecting one of a plurality of differential switch pairs, the first and second switches include a memory cell to be read.
- the bit string is selected, and the sense amplifier circuit corresponding to the selected bit string is selected as an operation target. Further, the first switch opens and closes based on a first selection signal for selecting one of the plurality of differential switch pairs and a second selection signal indicating the read mode. If the second switch is controlled to be opened and closed based on the first selection signal, the information is controlled so as to be outputted only in the read mode and not outputted in the write mode.
- the constant current circuit can be configured using a band gap reference.
- a current control transistor a diode connected between the base of the current control transistor and ground, and an emitter of the current control transistor can be configured. It can be configured to include a current control resistor connected between the evening and the ground.
- a constant current circuit having such a configuration, when the base of the transistor is connected to a constant current circuit control terminal to which a control signal of a voltage level capable of shutting off the transistor is input, the base is input to the constant current circuit control terminal.
- the standby state does not completely stop the operation of the circuit system, but means a temporary stop state in which the circuit does not operate until it is selected next time.
- a bias resistor pair can also be provided in common for a plurality of differential switch pairs, and in this case, it is preferable because the influence of the characteristic variation of the bias resistor pair is eliminated from the sense amplifier output.
- the pair of second switches, the pair of current-voltage conversion resistors, and the pair of differential switches are integrated and arranged in the same region. That is, a pair of second switches and a pair of current-voltage conversion resistors are formed in a region where the sense amplifier circuit is formed. As a result, the elements forming a pair are arranged close to each other, so that the temperature changes during driving are substantially equal, and it is possible to prevent the characteristic values from being shifted from each other.
- these pair of second switches, current-voltage conversion resistor pairs, and differential switch pairs form symmetrical circuits, appropriate differential outputs can be obtained. Preferred.
- “symmetric” means that among the elements constituting the circuit, the electrical characteristics of the paired elements are substantially equal.
- Such a magnetic memory device includes a plurality of first write lines and a plurality of second write lines extending so as to intersect the plurality of first write lines, respectively.
- an annular magnetic layer configured to be penetrated by the first and second write lines.
- the “circular” of the “circular magnetic layer” means that when at least viewed from the first and second write lines that penetrate the inside, the surroundings are completely and continuously surrounded magnetically and electrically.
- the cross section in the direction crossing the first or second write line indicates a closed state. Therefore, the annular magnetic layer allows the insulator to be contained as long as it is magnetically and electrically continuous. It is a matter of course that an oxide film generated in the manufacturing process may be included.
- the “axial direction” refers to the opening direction when focusing on the annular magnetic layer alone, that is, the extending direction of the first and second write lines penetrating the inside.
- the one side of the laminate is arranged .
- the annular magnetic layer is The purpose is to include a case where the annular magnetic layer is provided so as to include a part of the multilayer body, in addition to a case where the annular magnetic layer is provided separately from the multilayer body on one side of the multilayer body.
- each of the magnetoresistive elements information is written by a magnetic field generated by a current flowing through both the first and second write lines passing through the annular magnetic layer.
- a closed magnetic path is formed in the annular magnetic layer by passing a current through the write line, the magnetization reversal of the magneto-sensitive layer is performed efficiently, and information is reliably written. From the information thus written, a larger signal output can be obtained at the time of reading.
- the read current flowing through the free layer flows through the ring-shaped magnetic layer to the read line.
- the write line can be arranged close to the magneto-sensitive layer. In such a case, the magnitude of the write current flowing through the write line can be reduced, and writing can be performed efficiently.
- the magnetization directions of the magneto-sensitive layers in the pair of magnetoresistive elements are antiparallel to each other by a magnetic field induced by a current flowing through both the first and second write lines. It is preferable that the information be stored in the storage cell. At this time, the magnetoresistive element forming a pair always has the other in a high resistance state if one is in a low resistance state, and binary information corresponds to such two states. The stored information is read from the storage cell based on the difference between the read currents flowing through each of the pair of magnetoresistive elements.
- the magnetizations are antiparallel to each other means that the magnetization directions of each other, that is, the angle formed by the average magnetization in the magnetic layer is strictly 180 degrees, This also includes the case where the angle between the magnetizations deviates from 180 degrees by a predetermined angle due to an error or the like that occurs because the axis is not uniaxial.
- the sense amplifier circuit of the present invention includes a plurality of magnetoresistive elements each having a magneto-sensitive layer whose magnetization direction changes by an external magnetic field, and a pair of read lines for supplying a read current to a pair of magnetoresistive elements.
- the difference between the read currents is differentially amplified as a voltage difference, and in that case, the sum of the read currents is made constant in a constant current circuit shared by a plurality of sense amplifiers. Therefore, variation in output due to variation in the constant current circuit is suppressed.
- the read method of the magnetic memory device of the present invention includes a plurality of magnetoresistive elements each having a magneto-sensitive layer whose magnetization direction changes by an external magnetic field, and a read line pair for supplying a read current to a pair of magnetoresistive elements.
- a magnetic memory device configured so that one storage cell includes a pair of magnetoresistive elements, wherein a differential switch pair is provided for each read line pair.
- a pair of bias resistors is provided between the differential switch pair and the power supply, a constant current circuit is provided in common for a plurality of differential switch pairs, and a memory cell is provided based on a difference between a pair of read currents flowing through the read line pair. It reads information.
- the read method of the magnetic memory device of the present invention reads information from the magnetic memory device of the present invention.
- the read current is differentially output, and noise generated in each of the read lines and the output value of each magnetoresistive element are output. Is removed.
- the difference between the read currents is differentially amplified as a voltage difference by the differential switch pair, and the sum of the read currents is made uniform by using a constant current circuit shared by a plurality of differential switch pairs. Thus, variation in output due to variation in characteristics of the constant current circuit is suppressed.
- FIG. 1 is a block diagram showing an overall configuration of a magnetic memory device according to a first embodiment of the present invention.
- FIG. 2 is a diagram showing a configuration of a storage cell and a read circuit of the magnetic memory device shown in FIG.
- FIG. 3 is a circuit diagram for explaining the configuration of the entire sense amplifier in the read circuit shown in FIG.
- FIG. 4 shows the mounting of the memory cell group shown in Fig. 1 around the Y-direction drive circuit.
- FIG. 5 is a diagram showing the actual circuit arrangement of the Y-direction drive circuit section shown in FIG. 4.
- FIG. 6 is a diagram showing the pattern of the sense amplifier circuit area in the unit drive circuit shown in FIG.
- FIG. 1 A first figure.
- FIG. 7 is a cross-sectional view showing a specific configuration of the memory cell shown in FIG.
- FIG. 8 is a diagram showing a storage cell of the magnetic memory device shown in FIG. 1 and a wiring structure for writing the same.
- FIG. 9 is a diagram showing an equivalent circuit of the storage cell shown in FIG.
- FIG. 10A and FIG. 10B are diagrams for explaining a method of storing information in the storage cell shown in FIG.
- FIG. 11 is a diagram for explaining a method of writing information in the storage cell shown in FIG.
- FIG. 12 is a diagram for explaining the principle of reading operation from a storage cell in the magnetic memory device shown in FIG.
- FIG. 13 is a circuit diagram for explaining a comparative example of the read circuit shown in FIG.
- FIG. 14 is a diagram showing a rectifying element according to a modification of the backflow prevention diode in the readout circuit shown in FIG. 2 and an arrangement thereof.
- FIG. 15 is a diagram showing a rectifying element according to a modification of the backflow prevention diode in the readout circuit shown in FIG. 2 and its arrangement.
- FIG. 16 is a diagram showing an arrangement according to a modification of the backflow prevention diode in the read circuit shown in FIG.
- FIG. 17 is a diagram showing a rectifying element according to a modification of the backflow prevention diode in the readout circuit shown in FIG. 2 and an arrangement thereof.
- FIG. 18 is a diagram showing a rectifying element according to a modification of the backflow prevention diode in the readout circuit shown in FIG. 2 and an arrangement thereof.
- FIG. 19 is a configuration diagram of a sense amplifier according to the second embodiment of the present invention.
- FIG. 20 is a diagram showing a specific example of the switch shown in FIG.
- FIG. 21 shows the relationship between the input control signal and the operating state in the switch shown in FIG. It is a figure showing correspondence.
- FIG. 22 is a diagram showing a modification of the switch shown in FIG.
- FIG. 23 is a diagram of a read circuit according to an embodiment of the magnetic memory device of the present invention.
- FIG. 24 is a diagram showing the relationship between the bit decode voltage in the read circuit shown in FIG. 19 and the measured current values at the measurement points P1 to P4.
- FIG. 25 is a diagram showing the relationship between the bit decode voltage in the read circuit shown in FIG. 19 and the measured current values at the measurement points P1 to P9.
- FIG. 26 is a diagram showing the relationship between the resistance change and the output voltage of each storage cell of the magnetic storage element in the read circuit shown in FIG.
- FIG. 27 is an equivalent circuit diagram for explaining a read circuit of a comparative example with respect to the embodiment shown in FIG.
- FIG. 28 is a diagram showing the relationship between the resistance fluctuation between the paired magnetic storage elements and the output voltage in the read circuit shown in FIG. BEST MODE FOR CARRYING OUT THE INVENTION
- the read circuit system adopts a differential read method
- each of the sense amplifier circuits for differentially amplifying the read current is part of a constant current.
- the configuration is that the circuit is shared. Therefore, in the first embodiment, the configuration of a basic readout circuit system having the feature (1) will be described. In this section, we will discuss various ways to improve the SZN ratio of read signals. Next, the feature (2) in the second embodiment will be described.
- FIG. 1 is a diagram showing an overall configuration of a magnetic memory device according to a first embodiment of the present invention.
- This magnetic memory device is an MRAM embodied as a so-called semiconductor memory chip, and includes an address buffer 101, a data buffer 102, a control logic unit 103, a memory cell group 104, a Y-direction.
- the driving circuit section 106 and the X-direction driving circuit section 108 are main components.
- the memory device has a memory cell group 104 arranged in a large area in the center of the silicon chip, and circuit parts and wiring such as the drive circuit sections 106, 108 mounted in a small area around it. I have.
- the storage cell group 104 has a large number of storage cells 12 arranged in a word line direction (X direction) and a bit line direction (Y direction) so as to form a matrix as a whole.
- Each memory cell 12 is a minimum unit for storing data, and stores "1" and "0" bit data.
- each column of the storage cells 12 in the storage cell group 104 is referred to as a word column Xn, and each row is referred to as a bit column Yn.
- the ⁇ -direction drive circuit unit 106 includes a ⁇ -direction address decoder 106 ⁇ , a sense amplifier 106 ⁇ ⁇ ⁇ ⁇ for reading, and a ⁇ -direction current drive 106 C for writing, each of which is a memory cell group 104.
- a ⁇ -direction address decoder 106 ⁇ a sense amplifier 106 ⁇ ⁇ ⁇ ⁇ for reading
- a ⁇ -direction current drive 106 C for writing, each of which is a memory cell group 104.
- Yn Y1, Y2,
- the X-direction drive circuit section 108 is composed of an X-direction address decoder 108 A, a constant current circuit 108 B for reading, and an X-direction current drive 108 for writing, each of which has a memory cell group 1. 04 is connected to each word string Xn (X 1, X 2,...) Of the memory cell 12. Therefore, for example, as shown in the figure, one storage cell 12 stores address (Xn, Yn) in the code direction and bit direction input from the X-direction address decoder 108A and the Y-direction address decoder 106A. Is uniquely selected by
- the address buffer 101 has external address input terminals AO to A20 and is connected to a Y-direction address decoder 106A and an X-direction address decoder 108A via address lines 105 and 107. I have.
- the address buffer 101 captures a selection signal for selecting the memory cell 12 from the external address input terminals AO to A20, and amplifies the internal buffer amplifier to the voltage level required by the address decoders 106A and 108A. It has the function to do.
- the amplified selection signal is sent to the memory cell 12 in two directions: word column direction (X direction) and bit column direction (Y direction). And input to each of the address decoders 106A and 108A.
- the address buffer 101 stores one storage cell from the plurality of storage cell groups 104.
- An address signal for selecting the group 104 is also input.
- the data buffer 102 includes external data terminals DO to D7 for exchanging digital data signals with the outside, and is connected to the control logic unit 103 by a control signal line 113.
- the data buffer 102 includes an input buffer 102A and an output buffer 102B, each of which operates according to a control signal from the control logic unit 103.
- the input buffer 102 is connected to the Y-direction current drive 106 C and the X-direction current drive 108 C via the write data buses 110, 111, respectively, so that external data can be written during memory writing.
- the output buffer 102B is connected to the sense amplifier 106B via the read data bus 112, and by using the internal buffer amplifier, the read input from the sense amplifier 106B at the time of memory reading is performed. It has a function to output data signals to external data terminals DO to D7 with low impedance.
- the control logic section 103 includes an input terminal CS and an input terminal WE, and is connected to the data buffer 102 via a control signal line 113.
- the control logic unit 103 controls the operation of the memory cell group 104. From the input terminal CS, a signal (chip select; CS) indicating whether to make the write / read operation of the magnetic memory device active or not. ) Is entered. Also, a write enable signal (write enable; WE) for switching between write and read is input from the input terminal WE.
- the control logic section 103 has a function of amplifying a signal voltage taken from the input terminal CS and the input terminal WE to a voltage level required in the drive circuit sections 106 and 108 by an internal buffer amplifier.
- FIG. 2 is a configuration diagram of a circuit system including a memory cell group and a read circuit thereof.
- This readout circuit system is a differential amplification type in which a memory cell 12 is composed of a pair of magnetoresistive elements 12A and 12B. Here, the reading of information from each memory cell 12 is performed by magnetic resistance. Sensing current flowing to each of the anti-effect elements 12A and 12B (flows from the sense bit decode lines 21A and 21B to the magnetoresistive elements 12A and 12B, respectively, and the common sense decode line 3 1 The difference value of the current flowing out of the device is output as an output.
- bit direction unit read circuit 80 which is a repeat unit of the read circuit. , 80 ⁇ , 8 ⁇ + 1, ⁇ ), which are arranged in parallel in the bit string direction.
- Each of the bit direction unit read circuits 80 (:..., 80 ⁇ , 8 ⁇ + 1, ⁇ ') is connected to the ⁇ direction address decoder 106 at the bit decode line 20 ( ⁇ , 20 ⁇ , 2 ⁇ + 1, ..), And connected to the output buffer 102 # via the read data bus 112. It should be noted that since the figure does not have enough space to draw the entire bit direction unit readout circuit 80, it is represented by two columns. Similarly, the memory cell group 104 is represented by two columns of bit strings Yn and Yn + 1.
- the magnetoresistive elements 12A and 12B of each memory cell 12 are magnetoresistive elements using GMR or TMR.
- GMR magnetic resonance
- TMR magnetic resonance
- the memory cell group 104 includes sense code decode lines 31 (hereinafter abbreviated as sense word lines) arranged in the X direction and a pair of sense bit decode lines 21 1 arranged in the direction. , 21 ⁇ (hereinafter abbreviated as sense bit lines) to form a matrix wiring.
- the individual memory cells 12 are arranged at these intersections, and the memory cells 12 connected in parallel to the common sense bit lines 21A, 21 1 form a bit string Yn, and The memory cells 12 connected in cascade to the word line 31 constitute a word string Xn.
- one end of each of a pair of magnetoresistive elements 12A and 12B is connected to sense bit lines 21A and 21B, and the other end of each is connected to sense bit lines 21A and 21B.
- sense bit lines 21A and 21B are connected to a common sense word line 31 via a pair of backflow prevention diodes 13A and 13B.
- the individual magnetoresistive elements 12 A The current path of the sensing current to 12 B is from the node between the conductor from each element and the sense bit lines 21 A and 21 B to the node between the conductor from each element and the sense lead 31. Route.
- the sense bit lines 21 A and 21 B correspond to the “read line pair” of the present invention.
- the sense bit lines 21 A and 21 B are arranged in pairs for each bit string Yn (Yl, ⁇ 2,%) Of the memory cell 12. These sense bit lines 21 # and 21 # extend in the direction ⁇ so as to penetrate the memory cell group 104, and one end is connected to the power supply Vcc. On one end side of the sense bit lines 21 A and 21 B (power supply Vcc side), current-voltage conversion resistors 23 A and 23 B and collector-emitters of transistors 22 A and 22 B, respectively. Are connected in series. Further, the plurality of storage cells 12 forming the bit string Yn are connected to both the sense bit line 21A and the sense bit line 21B. Specifically, one end of the magnetoresistive element 12A in the memory cell 12 is connected to the sense bit line 21A, and one end of the magnetoresistive element 12B is connected to the sense bit line 21B. I have.
- a bit decode line 20 is connected to the base side of the transistors 22A and 22B.
- the bit decode line 20 is connected to the Y-direction address decoder 106A.
- the Y-direction address decoder 106A selectively selects the bit string Yn to which the storage cell 12 to be written / read belongs.
- the output selection signal is input. That is, the bit decode lines 20 (... 20 ⁇ , 2 ⁇ + 1,...) Are provided corresponding to each bit string Yn of the memory cell 12, and receive the selection signal from the Y-direction address decoder 106 A. It has the function of sending to the bit string Yn to be operated.
- the transistors 22A and 22B have a function as a pair of second semiconductor switches that open and close according to the value of a selection signal (bit decode value) input from the bit decode line 20.
- bit decode line 20 and the sense bit lines 21A and 21B have the same decoding function as described above, they are clearly distinguished in operation. That is, the bit decode line 20 is a signal line for transmitting the selected cell from the Y-direction address decoder 106 A, and its value is a binary digital signal of “High” and “Low”.
- the sense bit lines 21A and 21B are analog signal lines for detecting a weak current flowing into the magnetoresistive elements 12A and 12B. The same applies to the word decod line 30 and the sense line 31.
- the sense amplifier input lines 4 OA, 4 OBs (hereinafter, input lines 40A and 4 OBs) are derived.
- the current-voltage conversion resistors 23A and 23B function as bias resistors for the sense amplifier 106B. That is, it is installed to convert a sensing current flowing from the power supply Vcc through the sense pit lines 23A and 23B into a voltage due to its own voltage drop, and to lead it to the sense amplifier 106B from the input lines 40A and 40B. .
- the current-voltage conversion resistors 23A and 23B also have the function of generating an intermediate voltage level that is lower by one ⁇ than the supply voltage of the power supply Vcc.
- the current-voltage conversion resistors 23A and 23B have a high resistance value of, for example, about 100, and at least the resistance values of the magnetoresistive elements 12A and 12B. It is desirable to have a large resistance value.
- Each of the sense word lines 31 is connected to storage cells 12 arranged in the same word string Xn (XI, X2,).
- backflow prevention diodes 13A and 13B as rectifying elements are arranged between the memory cell 12 and the sense line 31.
- the backflow preventing diodes 13A and 13B correspond to the magnetoresistive elements 12A and 12B, respectively, and are individually connected.
- the magnetoresistive element 12A and the backflow preventing diode 13A, and the magnetoresistive element 12B and the backflow preventing diode 13B are insulated from each other.
- the backflow preventing diode 13 is provided as a one-way element for preventing current from flowing back from the sense word line 31 to each of the magnetoresistive elements 12A and 12B.
- Examples of the backflow prevention diode 13 include a pn junction diode and a diode.
- a short-circuit between the base and collector of a bipolar junction transistor (BJT: Bipolar Junction Transistor) or a diode, or a short-circuit between the gate and drain of an M ⁇ S FET Diodes and the like can be used.
- the ground side of the sense word line 31 is connected between the collector and the emitter of the transistor 33, and the base side of the transistor 33 is connected to the word decode line 30 defined Corresponding to the word string Xn. , 30 ⁇ , 3 ⁇ + 1, ⁇ ).
- the code decode line 30 is connected to the X-direction address decoder 108, and receives a selection signal for selecting the row Xn from the X-direction address decoder 108 A, and outputs the selection signal to the transistor 330.
- the c- transistor 33 having a function of transmitting the signal to the base of the sense word line 31 1 functions as a first semiconductor switch that opens and closes according to the value of a selection signal (bit decode value) input to the base. It controls the continuity and interruption of the power supply.
- a BJT or M ⁇ S FET can be used.
- a current limiting resistor 34 is provided on the emitter side of the transistor 33.
- a constant current circuit 108 B is further provided on the ground side of sense word line 31.
- the constant current circuit 108 B has a function of making the current flowing through the sense word line 31 constant, and is composed of a constant voltage generating diode 32, a transistor 33 and a current limiting resistor 34. Therefore, the transistor 33 has a function of flowing a constant current between the collector and the emitter in addition to the function as the semiconductor switch for word decoding, and the base side thereof is also connected to the anode of the diode 32. ing.
- the diode 32 is, in this case, one in which two diodes are connected in series.
- One sense amplifier 106B is provided in the bit-direction unit readout circuit 80, and in each bit-direction unit readout circuit 80, takes in the p potential difference between a pair of sense bit lines 21A and 21B, and this potential difference Has the function of amplifying
- the sense amplifier 106 B of the read circuit 80 in each bit direction is connected to the corresponding sense bit lines 21 A and 21 B by input lines 4 OA and 40 B, respectively, and all are connected to a common cell. It is connected to the sense amplifier output lines 51 A and 5 IB (hereinafter, output lines 51 A and 5 IB), and finally connected to the output buffer 102 B by the read data bus 112.
- the sense amplifier 106 B itself is configured as a so-called differential amplifier, and includes an amplification stage including transistors 41 A and 41 B, and bias resistors 42 A and 42 B that are bias resistors for extracting a voltage output. It has a diode 43 for voltage drop, a transistor 44 having a current control function and a selection switch function, and a resistor 45 for voltage drop.
- FIG. 3 shows a portion of the sense amplifier 106B extracted from the entire readout circuit.
- the sense amplifier 106B provided in each bit direction unit read circuit 80 is cascaded to the output lines 51A and 51B.
- the bias resistors 42A and 42B are shared by all the cascaded sense amplifiers 106B. Note that the output lines 51 ⁇ and .51 ⁇ ⁇ ⁇ ⁇ are replaced by the read data bus 112 at the final stage of the output and are connected to the output buffer 102 ⁇ .
- Transistors 41 A and 41 ⁇ have input lines 40 A and 40 ⁇ connected to the base side, and bias resistors 42 ⁇ and 42 ⁇ connected to the collector side via output lines 51 ⁇ and 51 ⁇ . I have. Further, the collector side of the transistor 44 is commonly connected to the emitter side of the transistors 41 ⁇ and 41 B.
- the transistor 44 has both a current limiting function and a function as a semiconductor switch that opens and closes according to the bit decode value from the bit decode line 20, and the bit decode line 20 is connected to the base side via the diode 43.
- the emitter side is grounded via resistor 45.
- the diode 43 uses the bandgap reference to create an intermediate voltage level that is ⁇ lower than the voltage level of the bit decode line 20, and is used to set this voltage value as the base-side input voltage of the transistor 44. ing.
- bias resistors 42 ⁇ and 42 ⁇ whose resistance values are precisely aligned. It is important that the characteristics of the transistors 41 A and 41 ⁇ be well aligned with each other. Also, diode 43, transistor 44 and resistor 45 Are required to be equal among the sense amplifiers 106B. Since the bit decode value, which is a constant voltage, is base-input to the transistor 44, the current flowing into the resistor 45 through the collector and the emitter of the transistor 44 is limited to a constant value. Therefore, the sum of the currents flowing through the transistors 41A and 41B becomes constant, and the differential output is directly normalized. Therefore, it is desirable to equalize the above-described characteristics in order to make the current specification values for each sense amplifier 106B uniform and to suppress variations in output signal values.
- FIG. 4 shows a state of mounting around the Y-direction drive circuit unit of the memory cell group
- FIG. 5 shows an actual circuit arrangement of the Y-direction drive circuit unit.
- the Y-direction drive circuit section 106 is formed on one side of the memory cell group 104, and a bonding pad 122 is provided above the Y-direction drive circuit section.
- each of the Y-direction address decoder 106A, the sense amplifier 106B, and the Y-direction current drive 106C is provided with each bit string Yn (Yl, ⁇ 2, ⁇ ) is realized as one configuration unit.
- a unit driving circuit DUn (DU1, DU2,...) Combines one structural unit of these circuits 106 6 to 106C for each corresponding bit string Yn (Y1, Y2, etc ...), and the unit drive circuit DUn is formed so that its width is within the width W of the memory cell 12 so that it is arranged exactly at the end of the corresponding bit string Yn. I have.
- FIG. 5 shows one unit drive circuit.
- the circuit area of the Y-direction address decoder 106A is formed between the power supply line 122 (Vcc), the power supply line 123 (Vm) of the intermediate potential, and the ground line 124 (GND).
- the power supply line 123 at the intermediate potential is a voltage source that supplies a voltage corresponding to the band gap + 2 ⁇ to a current limiting transistor and a constant current circuit 108B in the X direction. Further, an address line 105 extends so as to cross this circuit area, and an address decoder 106A of the unit drive circuit DUn is connected to the address line 105.
- the circuit area of the sense amplifier 106B is composed of a power supply line 125 and a power supply of intermediate potential. It is formed between line 123 and ground line 124. In this area, the output lines 51A and 51B extend so as to cross, and the sense amplifier 106B of each unit drive circuit D Un is wired so as to be cascaded.
- the circuit area of the c- direction current drive 106C in which the power supply line 125 is provided is formed between the power supply line 125, the power supply line 126 of the intermediate potential, and the ground line 127.
- FIG. 6 specifically shows a circuit pattern arrangement of only a sense amplifier among the unit drive circuits.
- the sense amplifier 106 B is not only associated with each bit string Yn (Yl, ⁇ 2,...), But also sense bit lines 21 1, 2 Connected to the power supply Vcc side of 1 1. Therefore, here, the transistors 22A and 22B and the current-voltage conversion resistors 23A and 23B are integrated with the sense amplifier 106B in the circuit area of the sense amplifier 106B. I have.
- the transistors 22 A and 22 B, the current voltage and the voltage inside the pair of transistors 41 A and 41 B in the sense amplifier 106 B are shown. It can be seen that the conversion resistors 23 A and 23 B are arranged exactly in pairs. Here, via pads 128A and 128B are connected to sense bit lines 21A and 21B, respectively. Also, although not shown in FIG. 6, the bit decode line 20 passes through the ground line 124 and is connected to the Y-direction address decoder 106A. In order to facilitate such understanding, in FIG. 6, the power supply line 125 is intentionally placed above and the ground line 124 is placed below, so that they correspond to FIGS. 2 and 3 instead of FIG. .
- the pair of the transistors 22A and 22B, the pair of the current-voltage conversion resistors 23A and 23B, and the sense amplifier 106B are all differential pairs, and their characteristics are different from those of the pair. It is important for operation that they are aligned. Therefore, it is a matter of course to equalize the characteristics in advance, but still the output characteristics may be different when the temperature conditions at the installation location of each circuit element are different.
- the paired circuit elements are arranged close to each other, since both receive the same temperature change, their characteristics change similarly, and there is almost no difference. Thereby, the change in the output value caused by the temperature change can be reduced. (Structure of memory cell)
- FIG. 7 is a cross-sectional view illustrating a configuration of a storage cell.
- the memory cell 12 has a pair of left and right magnetoresistive elements 12 A and 12 B mounted on the substrate 10.
- Each of these magnetoresistive elements 12 A and 12 B has a laminated body in which a first magnetic layer 1, a non-magnetic layer 2, and a second magnetic layer 3 are laminated, and one side of the laminated body. It is arranged so that the direction along the lamination plane is the axial direction, and is penetrated by the write bit line 6a and write lead line 6b (first and second write lines). And the formed annular magnetic layer 5.
- the second magnetic layer 3 and the annular magnetic layer 5 are joined via the nonmagnetic conductive layer 4 and are electrically connected.
- each of the magnetoresistive elements 12 A and 12 B is provided with a read sensing conductor 11 on the upper surface of the laminated body (the surface opposite to the annular magnetic layer 5), and is directed toward the substrate 10.
- a current can flow through the stacked body in a direction perpendicular to the stacked surface.
- the first magnetic layer 1 is a ferromagnetic layer having a fixed magnetization direction
- the second magnetic layer 3 is a ferromagnetic layer (magnetic sensing layer) whose magnetization direction is changed by an external magnetic field.
- These are laminated with a few nanometers (10 A) and a very thin nonmagnetic layer 2 interposed therebetween.
- a tunnel current flows to the first magnetic layer 1. That is, the nonmagnetic layer 2 here is a tunnel barrier layer.
- This tunnel current changes depending on the relative angle between the spin of the first magnetic layer 1 and the spin of the second magnetic layer 3 at the interface with the nonmagnetic layer 2. That is, when the spin of the first magnetic layer 1 and the spin of the second magnetic layer 3 are parallel to each other, the resistance value of the magnetoresistive element 12A (12B) is minimum and antiparallel. Is the largest.
- the magnetization of the second magnetic layer 3 is changed by a magnetic field induced by the write bit line 6a and the write word line 6b.
- the magnetization of the second magnetic layer 3 is reversed by the induced magnetic field, whereby the relative angle with respect to the magnetization of the first magnetic layer 1 is reversed. I'm going to do it.
- the memory cell 12 to be written is selected by a so-called matrix drive method, current is supplied to not only one of the write bit line 6a and the write word line 6b but also to both of them.
- the magnetic properties and dimensions of the second magnetic layer 3 are set so that the magnetization reversal is possible only when the magnetic flux flows in the same direction. This is the basic structure of the magnetoresistive element 12A (12B) as a TMR element.
- the annular magnetic layer 5 has a cylindrical shape having an axis perpendicular to the plane of FIG. 7 and is parallel to the write bit line 6a and the write word line 6b. Part is included. That is, the axial direction of the annular magnetic layer 5 is the direction in which the write bit line 6a and the write word line 6b extend, and has a closed annular shape in a cross-sectional direction crossing the axial direction.
- the annular magnetic layer 5 is made of a high-permeability magnetic material. By confining the magnetic flux generated by the current of the included write bit line 6a and write lead line 6b in the layer, It has a function of efficiently changing the magnetization direction of the magnetic layer 3.
- the annular magnetic layer 5 has a closed loop in cross section as shown in the figure, and the generated induction magnetic field flows through the layer along a plane parallel to the cross section.
- the annular magnetic layer 5 has an electromagnetic shielding effect that does not generate a leakage magnetic flux to the outside.
- the second magnetic layer 3 since the second magnetic layer 3 is configured so as to be in contact with the entire surface of the second magnetic layer 3, it is easy to transmit a magnetic field to the second magnetic layer 3, and the second magnetic layer 3 having a high magnetic flux density has a high magnetic flux density. The magnetization direction can be changed more efficiently.
- FIG. 8 shows the wiring structure of the write bit line 6a and the write word line 6b.
- the magnetic memory device of the present embodiment has a plurality of write bit lines 6a and a plurality of write code lines 6b extending so as to intersect with the write bit lines 6a, respectively. And although they extend so as to intersect, they extend partially in parallel in the intersecting region, and the magnetoresistive elements 12 A and 12 B are formed in the parallel portions.
- the term “parallel” as used herein includes a manufacturing error range of ⁇ 10 °
- the combined magnetic field of the parallel write bit line 6 a and write word line 6 b is The magnetization of the second magnetic layer 3 is reversed by using this, but the magnitude of the induced magnetic field is larger than the combined magnetic field when each wiring crosses. Thus, the writing operation can be performed efficiently.
- each layer of the laminate except the nonmagnetic layer 2 through which a tunnel current flows, and the nonmagnetic conductive layer 4 and the annular magnetic layer 5 are all made of a material having conductivity.
- a cobalt iron alloy (CoFe) is used, and other simple cobalt (Co), a cobalt platinum alloy (CoPt), Nickel iron cobalt alloy (NiFeCo) or the like can be used.
- the first magnetic layer 1 and the second magnetic layer 3 are desirably set so that their easy axes of magnetization are parallel to each other in order to stabilize the magnetization direction in a state of being parallel or antiparallel to each other.
- the thickness of the nonmagnetic layer 2 is determined based on tunnel resistance and the like. Generally, in a magnetic memory element using a TMR element, a tunnel resistance of about several tens (xm) 2 is appropriate in order to match a semiconductor device such as a transistor. However, in order to increase the density and speed of operation of the magnetic memory device, the tunnel resistance is preferably 101 ⁇ ⁇ (zm) 2 or less, more preferably lk Q ⁇ (m) 2 or less. .
- the thickness of the nonmagnetic layer (tunnel barrier layer) 2 is preferably 2 nm or less, more preferably 1.5 nm or less.
- the tunnel resistance can be reduced, but a leak current due to the unevenness of the junction interface between the first magnetic layer 1 and the second magnetic layer 3 occurs.
- the MR ratio may decrease.
- the thickness of the nonmagnetic layer 2 needs to have a thickness that does not allow a leak current to flow, and specifically, it is desirable that the thickness be 0.3 nm or more.
- the nonmagnetic conductive layer 4 functions to provide antiferromagnetic coupling between the second magnetic layer 3 and the annular magnetic layer 5, and for example, ruthenium (Ru), copper (Cu), or the like is used.
- ruthenium (Ru), copper (Cu), or the like is used for the annular magnetic layer 5.
- iron (Fe), nickel iron alloy (NiFe), Co, CoFe, NiFeCo, or the like can be used for the annular magnetic layer 5.
- the magnetic permeability of the annular magnetic layer 5 is preferably as large as possible. Than Preferably it is 6000 or more.
- Each of the write bit line 6a and the write word line 6b has a structure in which titanium (Ti), titanium nitride (TiN), and aluminum (A1) are sequentially stacked. It is electrically insulated from each other by the rim.
- the write bit line 6a and the write word line 6b may be made of, for example, at least one of aluminum (A 1), copper (Cu), and tantalum (W).
- An epitaxial layer 9 is formed on a substrate 10 on which the magnetoresistive elements 12A and 12B are formed, and a conductive layer 8 and an insulating layer 7 are further formed thereon. Is composed of conductive layers 8 A and 8 B insulated from each other via an insulating layer 7. The magnetoresistive elements 12 A and 12 B are formed on the upper surfaces of the conductive layer 8 and the insulating layer 7. Positioned to overlap. Therefore, the magnetoresistive element 12A and the magnetoresistive element 12B are individually joined to the separately insulated conductive layers 8A and 8B, respectively, and are electrically insulated from each other. That is, here, the wiring is made such that the magnetoresistive element 12A and the magnetoresistive element 12B are electrically non-conductive.
- the substrate 10 is an n-type silicon wafer.
- an n-type silicon wafer is subjected to impurity diffusion of P (phosphorus), and a substrate 10 which is n-type due to high-concentration diffusion of P (phosphorus) is used.
- the epitaxial layer 9 is made to be n-type by diffusing P (phosphorus) at a low concentration, and a metal is used for the conductive layer 8. At this time, the epitaxial layer which is an n-type semiconductor is used.
- a band gap is generated to form a Schottky diode, which is the backflow prevention diodes 13A and 13B in the present embodiment.
- the backflow prevention diodes 13A and 13B as a Schottky diode in this way requires a silicon layer with an epitaxial layer to be easily available, low in size, and a simple forming process. There are advantages.
- the Schottky diode has a leakage current more than several hundred times larger than that of the PN junction diode, and the leakage current increases with a rise in temperature.
- This magnetic memory device If the device is a MRAM semiconductor memory chip and several thousand Schottky diodes are connected in parallel for each of the 12 memory cells, the S / N ratio of the read output will increase because the leakage current will increase considerably. It may be the cause of lowering.
- the backflow prevention diode 13 is replaced with a PN junction diode, base ⁇ It can also be formed by a BJT with a short circuit between the collectors or an M ⁇ S FET with a short circuit between the gate and drain.
- FIG. 9 is a circuit diagram of the storage cell.
- the magnetoresistive element 12A (12B) has a low-resistance state in which the current density of the tunnel current that can flow is high and a 3 ⁇ 4-resistance state in which the current density is low.
- information is stored with one of the magnetoresistive elements 12A and 12B having a low resistance and the other having a high resistance.
- the two magnetoresistive elements 12 A and 12 B are differentially amplified and read. Therefore, the two magnetoresistive elements 12 A and 12 B forming a pair need to be manufactured so that the resistance value, the magnetoresistance change rate, and the magnitude of the reversal magnetic field of the second magnetic layer 3 are equal. There is.
- FIGS. 1OA and 10B show the memory cells in the same manner as FIG. 9, and show the first magnetic layers 1 and 2 of the magnetoresistive elements 12A and 12B, respectively.
- the white arrow indicates the magnetization of the first magnetic layer 1, and the magnetization is fixed to the right in both the magnetoresistive elements 12A and 12B.
- the black arrows indicate the magnetization of the second magnetic layer 3, and are magnetized in directions antiparallel to each other in the magnetoresistive elements 12A and 12B.
- the magnetization directions of the second magnetic layers 3 of the pair of magnetoresistive elements 12A and 12B are opposite to each other. Information is stored in rows.
- the combination of the magnetization directions of the first magnetic layer 1 and the second magnetic layer 3 is always (parallel, antiparallel) Or the second state of (anti-parallel, parallel). Therefore, by associating binary information “0” and “1” with these two states, one bit of information is stored in one storage cell 12.
- the magnetoresistive element 12 A (12 B) if the magnetization directions of the first magnetic layer 1 and the second magnetic layer 3 are parallel, a large tunnel current flows and the resistance is low, and the anti-parallel state occurs. In this case, a high resistance state where only a small tunnel current flows flows.
- the magnetoresistive element 12 A and the magnetoresistive element 12 B forming a pair always store information with one of the low resistance and the other of the high resistance.
- FIG. 11 shows the direction of the write current when writing the “1” bit shown in FIG. 10 to the storage cell 12.
- the induction magnetic field is confined inside the annular magnetic layer 5
- the effective magnetic field strength contributing to the magnetization reversal of the second magnetic layer becomes larger than before.
- the magnetization of the second magnetic layer 3 can be reversed with a necessary and sufficient magnetic field strength, and an efficient write operation can be performed.
- the magnetization of the second magnetic layer 3 is aligned so as to be sufficiently large in a predetermined direction. You. Therefore, the possibility that the magnetization direction of the second magnetic layer 3 is disturbed by the external disturbance magnetic field can be reduced, and the information once written can be prevented from being unexpectedly erased or rewritten. That is, information can be written reliably.
- the address buffer 101 captures the signal voltage of the external data terminals AO-A20, amplifies it with the internal buffer, and
- the data buffer 102 takes in the signal voltages of the external data terminals DO to D7, amplifies them with the internal buffer, and writes data buses 110, 1 1
- the address decoders 106 A and 108 A select the write bit line 6 a and the write word line 6 b having the corresponding decoded value according to the selection signal.
- the current flowing through the write bit line 6a and the write word line 6b is determined by the current drive 106C and 108C.
- the storage cell 12 in which current flows through both the write bit line 6a and the write word line 6b is intentionally selected, and predetermined bit data is written therein.
- the directions of the currents of the write bit line 6a and the write word line 6b are indicated by arrows, and a state in which the storage cell 12 is selected is shown.
- the magnetic memory device reads information written in each storage cell 12 as follows.
- FIG. 12 shows the basic configuration of a memory cell.
- Each storage cell 12 is in a state where the magnetoresistive effect elements 12A and 12B have the magnetization directions as shown in the drawing to store information.
- the storage cell 12 from which information is read is selected by inputting a selection signal to the bit decode line 2 o in the Y direction and to the word decode line 30 in the X direction in accordance with the address. For example, if the storage cell 12 to be selected is in the Yn column, ⁇ row, the Yn-th bit decode line 2 On and the Xn + 1-th word decode line 30 A signal is input to n + 1.
- the transistors 22 A and 22 B are turned on, and the Yn-th column-directional block of the memory cell 12 (bit string Yn) , The sensing current flows.
- the sensing current flows down the sense bit lines 21 A and 21 B from the power supply Vcc side to the opposite side.
- the sensing current flows from the Yn-th sense bit lines 21 A and 21 B to the magnetoresistive element 12 A and the backflow prevention diode 13 A and the magnetoresistive element 12 B and the backflow prevention Both pass through the diode 13 B and flow into the Xn + 1th sense line 31, and further pass through the collector-emitter of the transistor 33 forming the constant current circuit 108 B, and ground from the resistor 34. Get out.
- the storage cell 12 in the Yn column and the Xn + 1th row is selected by flowing the sensing current to the magnetoresistive elements 12A and 12B in the Yn column and the Xn + 1th row.
- Reading of information is performed by detecting the difference between the current values flowing through the magnetoresistive elements 12A and 12B of the memory cell 12.
- the current flowing through them is substantially equal to the sensing current flowing through the sense bit lines 21A and 21B.
- a voltage drop due to the sensing current occurs in the current-voltage conversion resistor 23 A (23 B) connected in series with the sense bit line 21 A (21 B).
- the voltage drop Va is determined by Equation 1 when the magnitude of the sensing current is I sense and the resistance value of the current-voltage conversion resistor 23 A (23 B) is Ra.
- Va (Volt) I sense (A) XRa ( ⁇ )
- Equation 1 the values of the current-voltage conversion resistor 23 A and the current-voltage conversion resistor 23 B are good, and if they are the same, the sensing current I sense is converted to voltage by the voltage drop Va and detected. You can see that Therefore, the voltage drops of the current-voltage conversion resistor 23 A and the current-voltage conversion resistor 23 B are input as readout output signals here.
- the power lines 4 OA and 4 OB are taken out and the difference is detected. As described above, by using the two magnetoresistive elements 12 A and 12 B and extracting the difference between the respective output values, a large output value from which noise has been removed can be obtained as the memory cell 12.
- the magnitude of the sensing current flowing through the selected storage cell 12 is adjusted by the current limiting resistor 34 provided on the ground side of the sense word line 31.
- the current limiting resistor 34 has the effect of limiting the amount of current by itself.
- a constant current circuit 1 08 B composed of a combination of the current limiting resistor 34 and the transistor 33 and the diode 32 is also provided. Operate to keep the current within a certain range.
- the two diodes 32 connected in series fix the intermediate voltage level + 2 ⁇ higher than ground by the diode band gap reference. To produce. Therefore, an intermediate voltage level is applied to the base terminal of the transistor 34, and the transistor 34 is turned on. At this time, the magnitude I sense of the sensing current flowing from the sense word line 31 is obtained by Expression 2 when the resistance value of the current limiting resistor 34 is Rc. ⁇ 2)
- I sense (A) (2 ⁇ '— ") (Volt) / Rc ( ⁇ )
- Equation 2 is the forward voltage of the two diodes 32 connected in series, and ⁇ ′′ is the forward voltage between the base and the emitter of the transistor 33. Since these are values specific to the semiconductor device, Equation 2 is This shows that the sensing current I sense takes a constant value if the resistance value Rc is determined, and that the sensing current I sense can be uniquely determined using the resistance value Rc as a parameter.
- the sensing current I sense is a current flowing through the sense word line 31 and is sense bit line 21 A and sense bit line 21 B, or magnetoresistive element 12 A and magnetoresistive element 12 B Is the sum of the currents flowing through both.
- the current limiting resistor 34 is 50 k ⁇ and a diode 32 and a transistor 33 are a silicon diode and a silicon transistor, the sensing current I sense by the constant current circuit 108 will be approximately 1 5 Become A.
- the current flowing through both elements may be different.
- the sum is always approximately equal to 15 / XA.
- the variation in the resistance value of the magnetoresistive element 12A (12B) due to manufacturing reasons means that the nonmagnetic layer 2 has a thickness of only a few atomic units of several nm (tens A). In addition, it means that the resistance value changes due to slight disturbance of the thickness and atomic arrangement. Therefore, great care is taken to form the non-magnetic layer 2 with a uniform thickness, but in reality, the resistance of the magnetoresistive element 12 A (12 B) is 15 to 50%. When the conditions such as the degree and the production equipment are bad, more variation occurs.
- Variations in the resistance values of the magnetoresistive elements 12A and 12B can be considered in two cases for each factor.
- the first case is that the resistance values of the magnetoresistive elements 12A and 12B at the time of low resistance and at the time of high resistance are different between the memory cells 12 due to variations in the thickness of the nonmagnetic layer 2 and the like. It is. In general, when the thickness of the nonmagnetic layer 2 increases, the resistance of the pair of magnetoresistive elements 12A and 12B takes a large value both at low resistance and at high resistance.
- the second is that, due to the unevenness of the junction interface, the difference in the thickness of the non-magnetic layer 2, and other factors, the magnetoresistive elements 12A and 12B forming a pair in each memory cell 12 In this case, the ratio between the resistance value when a large tunnel current flows and the resistance value when only a small tunnel current flows, that is, the MR ratio varies.
- each current value flowing through the sense bit lines 21A and 21B is obtained by distributing a certain standardized current amount according to the resistance ratio. Therefore, the deviation of each current value is smaller than the degree of variation of the resistance value.
- the difference between the current values of the sense bit lines 21A and 2IB is always kept within a certain range. Therefore, the difference between the voltage drops of the current-voltage conversion resistors 23 A and 23 B is also kept within a certain range, and a stable differential output can be obtained, and the SZN ratio of the read signal can be improved. .
- the backflow prevention diodes 13 A, 13 B provided on the current path on the sense word line 31 side of each of the magnetoresistive elements 12 A, 12 B are: Current is prevented from flowing back from the sense word line 31 to the magnetoresistive elements 12A and 12B.
- the magnetoresistive elements 1 2 ⁇ and 1 2 ⁇ of the bit string Yn and the word string ⁇ are connected to a common sense bit line 2 1 A, 2 1 ⁇ and a common sense word line 3 1.
- part of the sensing current deviates from the normal path, flows out to another path via the magnetoresistive element 12 A, 12 ⁇ ⁇ that is not a read target, and then flows to the ground as it is or again.
- the reason why such a wiring structure is adopted is to simplify the wiring by sharing the selection switch of the memory cell 12 with a single switch for each column in both the bit direction and the directional direction. This is to share the constant current circuit 108 08 for each column.
- FIG. 13 shows, as a comparative example with respect to the present embodiment, the leakage current when the backflow prevention diodes 13A and 13B are not on the current paths of the magnetoresistive elements 12A and 12B.
- This shows the route (i) and the wraparound routes (ii) and (iii).
- the storage cell 12 of the pit string Yn and the word string ⁇ + 1 is the cell from which information is just read. That is, the normal current path is shown by the solid line.
- a part of the sensing current flows backward from the sense line 31 to the magnetoresistive elements 12A and 12B adjacent in the word column direction, for example, as shown in a path (i), and furthermore, the sense bit Line 2 flows to On + 1.
- the same leakage also occurs in a large number of magnetoresistive elements 12 A and 12 B (not shown) commonly connected to the same sense word line 31.
- the paths are illustrated with the magnetoresistive effect element 12 A being the lower resistance side in all the memory cells 12.
- the storage is further down the sense bit line 21 A, adjacent in the bit column direction, passing through the low-resistance magnetoresistive element 12 A, and further adjacent through the sense word line 31 in the word column direction. The current flows back to the magnetoresistive element 12 A on the low resistance side of the cell 12.
- the sense bit line 21 A which is different from the normal path, is moved up to the magnetoresistive element 12 A (adjacent in the bit string direction in the figure) connected to the selected sense word line 31, and It flows into the low-resistance magnetoresistive element 12 A, and finally flows into the selected sense word line 31.
- a similar wraparound occurs when a number of magnetoresistive elements 12 A (not shown) connected to the same sense bit line 21 A and a sense word line 31 connected to those magnetoresistive elements 12 A are connected. The same also occurs for many magnetoresistive elements 12A and 12B (not shown). When the magnetoresistive effect element 12B has a low resistance, wraparound also occurs.
- Route (iii) is another example of wraparound.
- backflow prevention diodes 13A and 13B are provided on the current paths of the magnetoresistive elements 12A and 12B as in the present embodiment. It can be cut off by installing. In this way, it is possible to reduce the fluctuation of the sensing current caused by the current leaking or sneaking through the magnetoresistive elements 12A and 12B, that is, the noise to the signal. Even when the current paths of the magnetoresistive elements 12A and 12B of each memory cell 12 are connected to one diode, the paths (i) and (ii) can be cut off. Yes, it is expected to have a certain effect on leakage and sneak current.
- the magnetoresistive elements 12 A and 12 B in the memory cell 12 are made non-conductive as in the present embodiment, and the backflow is prevented independently of each other. Need to be applied. (Modified example of backflow prevention diode)
- the backflow prevention diodes 13A and 13B of the present embodiment can be replaced by transistors that are also elements having a rectifying action.
- FIG. 14 shows a modified example in which transistors 63 A and 63 B for preventing reverse current are provided between the magnetoresistive elements 12 A and 12 B and the sense word line 31. ing.
- the backflow prevention transistors 63 A and 63 B are connected to the sense bit lines 21 A and 2 IB or the sense word line 31. Conduction can be performed in conjunction with it. In such a case, the transistors 22A and 22B need not be provided.
- the backflow prevention transistors 63A and 63B also function as unidirectional elements.
- the advantage of using the backflow prevention transistors 63A and 63B is that the voltage at the time of conduction is considerably lower than the forward voltage of the diode.
- Transistor The collector-emitter voltage when conducting in the evening is very low (about 0.2 V), but the diode has a band gap ⁇ (0.65 V to 0.75 V) as a forward voltage. Voltage is applied.
- the current path is connected in series from the power supply Vcc to the ground, and the current-voltage conversion resistor 23 A (23 B) and the transistor 2
- the backflow prevention transistors 63A and 63B must be operated at a power supply voltage as low as 0.5V as compared with the backflow prevention diodes 13A and 13B. Can be. In addition, by distributing the surplus of this voltage, the circuit can be raised from five stages to several stages, and even more complicated control operations can be performed.
- the backflow prevention diodes 13A and 13B can be replaced by backflow prevention M ⁇ S FET 73A and 73B.
- the drain-source voltage during conduction is as low as about 0.1 IV, and the operation and effect are almost the same as those of the backflow prevention transistors 63A and 63B.
- These rectifying elements are provided between the sense bit lines 21A and 21B and the magnetoresistive elements 12A and 12B, respectively, as shown in FIGS. 16 to 18. It may be.
- a large number of sense amplifiers 106 B of each bit direction unit readout circuit 80 (..., 8 On, 80 nil,...) Are cascaded to the output lines 51 A and 51 B on the collector side.
- the transistor 44 is turned on at the same time, so that the corresponding one sense amplifier 106B becomes active, and only its collector output is output line 51A. , 51 1B.
- the bias resistors 42A and 42B are shared, the path of the current supplied from the power supply (Vcc) to each sense amplifier 106B is unified. This contributes to equalizing the amount of current flowing through the transistors 41A and 41B for each sense amplifier 106B, and acts to stabilize the offset amount with respect to the output value. Further, since the transistors 22A and 22B, the current-voltage conversion resistors 23A and 23B, and the sense amplifier 106B are integrated in the same width W region as the memory cell 12, these transistors Among them, the elements forming a differential pair also have almost the same temperature change during operation. This suppresses fluctuations in the output value caused by temperature changes.
- the output of the sense amplifier 106B is finally input to the output buffer 102B via the output lines 51A and 51B and the read data bus 112.
- the output buffer 102B amplifies the input signal voltage and outputs it from the external data terminals DO to D7 as a binary voltage signal.
- the magnetoresistive elements 12A and 12B are provided with the annular magnetic layer 5, so that the writing can be performed efficiently and the second magnetic layer 3 Information can be reliably written with the magnetization directions aligned sufficiently.
- the magnetoresistive effect element 12 A may be used depending on the relative magnetization direction with the first magnetic layer 1.
- the tunnel current value at (12B) also clearly shows a binary state, and an output value with a high SZN ratio can be obtained.
- the memory cell 12 is composed of a pair of magnetoresistive elements 12A and 12B, and the current flowing through both is differentially output, so that the sense bit lines 21A and 21B are connected. The combined noise is removed.
- a constant current circuit 108B is provided on the ground side of the sense word line 31 so that the total sum of the sensing currents flowing through the readout circuit is kept constant. The difference between the current values of the bit lines 21 A and 2 IB is always kept within a certain range. Normalizing the total current value to a constant value in this way means that the variation of the resistance between the pair of magnetoresistive elements 12A and 12B can be reduced even if the sense bit lines 21A and 21B This has the effect of suppressing fluctuations in the current value.
- the transistor 33 of the constant current circuit 108B also functions as a semiconductor switch of the word decode line 30, the transistor 33 can be manufactured relatively easily and is advantageous in circuit design.
- Backflow prevention diodes 13 A and 13 B are provided as direction elements, so that current is prevented from flowing back from sense word line 31 to magnetoresistive elements 12 A and 12 B. .
- the storage cells 12 connected to the common sense bit lines 21 A, 2 IB or the common sense word line 31 and the magnetoresistive element 1 2 in one storage cell 12 A current path is prevented from being formed between A and the magnetoresistive element 12B, and leakage and sneak of the sensing current are blocked, so that noise can be reduced.
- the sense amplifier 106 B is cascaded to the output lines 51 A and 51 B, and the bias resistors 42 A and 42 B are used in common.
- the amount of current flowing through 1 A and 41 B is made uniform, and the offset amount with respect to the output value of each sense amplifier 106 B can be kept constant. Also, by reducing the number of resistive components, power consumption due to leakage current (a current that constantly flows in parts other than the operation target due to the circuit configuration) can be reduced. Further, by reducing the number of components and unifying the output line of each sense amplifier 106B into a pair of output lines 51A and 51B, circuit space can be saved.
- the transistors 22A and 22B and the current-voltage conversion resistors 23A and 23B are integrated with the sense amplifier 106B. Therefore, a differential amplifier circuit is configured together with the sense amplifier 106B, and a pair of circuit elements are formed at positions close to each other. Therefore, since these circuit elements are driven under the same temperature condition, characteristic variations due to temperature changes are suppressed, and noise in the differential amplifier circuit can be prevented.
- noise due to variation in characteristics of each storage cell 12 and resistance between the pair of magnetoresistive elements 12 A and 12 B In addition to reducing noise due to variations, noise coupled to the data lines, noise due to variations in the characteristics of the sense amplifier 106B and other differential pairs, and noise from peripheral circuits wrapping around from the power supply circuit were reduced.
- the SZN ratio of the read signal output can be greatly improved and improved. Therefore, this magnetic memory device can perform a stable operation with little reading error. Also, a large signal output value can be obtained by improving the S / N ratio. Sufficient output can be obtained even when the memory cell 12 is highly integrated, and on the other hand, low current and low voltage driving can be realized.
- the magnetic memory device in order to prevent dielectric breakdown of an ultra-thin tunnel barrier layer, it is necessary to set an appropriate voltage to a magnetic memory element when a tunnel current is applied to the element.
- the magnetic memory device according to the present embodiment includes the constant current circuit 108 B to reduce the tunnel current and reduce the voltage applied to the tunnel barrier layer 2 to a voltage sufficiently lower than the electrical withstand voltage. It can be driven.
- the read circuit of the present embodiment has a current path in series from the power supply Vcc to the ground, a current-voltage conversion resistor 23 A (23 B), a transistor 22 A (22 B), a magnetoresistive effect.
- FIG. 19 is a diagram showing a configuration of a sense amplifier according to the second embodiment.
- the circuit portion including the diode 43, the transistor 44, and the resistor 45 of the first embodiment is grouped as a constant current circuit 50, and is shared by the sense amplifiers 106B.
- the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will not be repeated.
- transistors 41 A and 41 B are connected to switches 46 (..., 46 ⁇ , 46n + l,...) Are commonly connected to one constant current circuit 50. That is, one sense amplifier 106 # is selected by the switch 46, and the constant current circuit 50 operates as a part of the selected sense amplifier 106 #.
- each of the switches 46 ( ⁇ , 46 ⁇ , 46 ⁇ + 1, ⁇ ) has a corresponding bit decode line 20 (..., 20 ⁇ , 2 ⁇ + 1, ⁇ ) and a read selection signal.
- Line 90 is connected.
- a read / write signal for selecting whether the magnetic memory device performs a read operation or a write operation is transmitted from the read select signal line 90, and the switch 46 sets a bit decode value and a read / write signal. It opens and closes in response to both.
- a read / write signal is input to the control logic unit 103, a chip select signal (CS) for controlling whether or not to activate a magnetic memory device, and a write enable signal for switching between read and write.
- CS chip select signal
- WE write enable signal
- the readout circuit system reads out information only when the readout operation is instructed, and furthermore, when reading out the information, the sense circuit corresponding to the selected bit string Yn.
- Amplifier 106 ⁇ is selected as the operation target.
- the switch 46 is configured as follows, for example.
- FIG. 20 shows the configuration
- FIG. 21 shows the operation state of the switch corresponding to the input signal.
- the switch 46 includes a transistor 461 having a base terminal connected to a read selection signal line 90, and a transistor 462 having a base terminal connected to a bit decode line 20.
- the collector and emitter of the transistor 462 are connected between the emitter terminals of the transistors 41 ⁇ and 41 ⁇ and the transistor 48 of the constant current circuit 50.
- transistor 46 1 ? The collector terminal is connected to the power supply (Vcc), and the emitter terminal is connected to the emitter side of the transistor 462.
- the voltage value VI (the voltage of the read / write select signal) when the base input voltage of the transistor 461 is "High” Voltage value
- the voltage value V 2 (the voltage value of the pit decode value) when the base input voltage of the transistor 462 is “H igh” is in a relationship of VI—V 2> 0.3 (Volt).
- the potential at the connection point P (the common emitter voltage of the transistors 461 and 462) is a value obtained by subtracting the forward voltage between the base and the emitter of the transistor 461 from V1.
- the voltage applied between the base emitter of the transistor 462 becomes lower than the forward voltage of the transistor 462 by 0.3 V, and the current does not easily flow through the transistor 462.
- the switch 46 conducts only when "Low” is input to the transistor 461 and "High” is input to the transistor 462. Therefore, the read Z write signal in this case is set to “Low” when instructing a read, and to "High” when instructing a write.
- the switch 46 is connected to the transistors 41 A and 41 B of the sense amplifier 106 B and the constant current circuit 50. This is for interrupting the conduction between the two, and does not limit the operation of the constant current circuit 50 itself.
- the constant current circuit 50 is composed of a diode 47, a transistor 48, and a resistor 49, and uses the band gap reference of the diode 47 to generate a constant current.
- This constant current circuit 50 operates in the same manner as the constant current circuit 108 B described in the first embodiment, and calculates the total amount of current flowing through both the transistors 41 A and 41 B. It is stipulated. That is, it works so as to keep the differential output value of the sense amplifier 106 B within a certain range.
- the transistor 48 functions as a switch whose base terminal is connected to the constant current circuit control terminal 91.
- the constant current circuit control terminal 91 receives a control signal of a voltage level that can turn off the transistor 48.
- the sense amplifier circuit 1 that shares the constant current circuit 50 according to the control signal. Everything in 06B can be controlled to either the active state or the standby state.
- the circuit portion including the diode 43, the transistor 44, and the resistor 45 has a constant current function, and the transistor 44 is individually opened and closed according to the bit decode value. It is controlled whether or not to activate the sense amplifier 106B.
- the constant current circuit 50 is responsible for the constant current function
- the switch 46 is responsible for the switching operation for selecting the sense amplifier 106 B according to the bit decode value. It has become.
- the switch 46 corresponds to the “first switch” of the present invention
- the transistors 22 A and 22 B correspond to the “pair of second switches” of the present invention. I have.
- Such a sense amplifier 106B operates as follows.
- a read / write signal is input to the read selection signal line 90. If the signal voltage value is "High”, a write operation is instructed, and the switch 46 is not turned on. If this signal value is "Low”, a read operation is instructed, and each of the switches 46 is opened and closed by the input bit decode value.
- the bit decode line 20 and the word decode line 30 corresponding to the address of the memory cell 12 are selected. This allows the transistor 22 A, 22 B and the transistor 33 are turned on, and the sense bit lines 21 A, 21 B pass through the magnetoresistive elements 12 A, 12 B to be read, and the sense line 3 The sensing current flows to 1.
- the bit decode value from the bit decode line 20 is input to one switch 46.
- the sense amplifier 106 B to be activated becomes operable. That is, only the sense amplifier 106B corresponding to the bit string selected by the bit decode value is selectively activated only when the read operation is instructed by the read / write signal.
- the sense amplifier 106B selected in this way differentially amplifies the potential difference taken out from the input lines 40A and 40B and sends it to the output lines 51A and 51B. At this time, since each of the sense amplifiers 106 B has the same constant current circuit 50 as a constituent element, variation in output values between the sense amplifiers 106 B in each bit string is suppressed. .
- the number of components can be significantly reduced.
- the sense amplifier 106B selected by the bit decode value becomes active and consumes power. Therefore, sharing a constant current circuit can reduce unnecessary power consumption that occurs in conventional multiple constant current circuits. Further, the path of the current flowing from the power supply (V cc) to the ground is formed only at the time of reading, and is always narrowed down to only one path passing through the sense amplifier 106 B to be read. Unnecessary power consumption in a portion other than the circuit portion that performs the read operation can be reduced.
- a switch 46 is provided to connect one of the transistors 41 A and 41 B to the constant current circuit 50, and this switch 46 is not only ORed with the read / write signal but also with the bit decode value. Therefore, the read circuit can operate only when there is a read command, and only the circuit corresponding to the selected bit string Y n operates. Thus, by inputting the read / write signal to the switch 46, the entire read circuit system can be operated according to the read / write signal.
- a sense amplifier that shares the constant current circuit 50 by opening and closing the transistor 48 All states of 106 6 can be controlled at once. For example, when the transistor 48 is turned off, current consumption in the constant current circuit 50 is reduced, which can contribute to power consumption reduction.
- the read circuit system operates with three control commands including the read / write signal, the bit decode value, and the control signal of the constant current circuit control terminal 91. Operation is not possible unless all the conditions of the three control signals are satisfied. Therefore, the circuits other than the necessary circuits are placed in the standby state as much as possible, and the power consumption due to the leakage current can be greatly reduced.
- FIG. 22 shows a configuration of a switch according to a modification of the second embodiment.
- the switches 46 are provided corresponding to the respective sense amplifiers 106, but in this modified example, the functions of the switches 46 are combined into one switch. ing. Only one transistor 4 6 1 connected to the read select signal line 9 0 is provided, but each of them is a bit decode line 2 0 (..., 2 On, 2 ⁇ ⁇ + 1,. ) Connected to each sense amplifier 106 0 are provided in a plurality of transistors 462 (..., 462 ⁇ , 462 ⁇ + 1, so .
- transistors 46 1 and 46 2 are configured such that all the emitter sides are commonly connected and are arranged in a row, and a plurality of transistors 4 62 (..., 46 2 ⁇ , 46 2 ⁇ + 1, ⁇ ') share the transistor 4 6 1.
- Transistor 4 6 When “Low” (read command) is input to 1 and a bit decode value is input to any of the transistors 462 (..., 462 ⁇ , 462 ⁇ + 1,...), The selected transistor 462 is activated. Conduct. For example, when the bit decode value Yn is input from the bit decode line 2 On, only the transistor 462 ⁇ is turned on, and the sense amplifier 106 corresponding to the bit string ⁇ is activated. When "High” (write command) is input to the transistor 461, none of the transistors 462 remains off even if a bit decode value is input. [Verification of amplification degree by sense amplifier]
- the current value at each measurement point was measured using a current probe while the information was being read.
- the measurement points are nine points P1 to P9 shown in FIG.
- FIG. 24 shows the measurement results of the measurement points P1 to P4.
- the current flowing through the sense bit line 21 A on the side connected to the magnetic resistance erectile element 12 A is the emitter current of the transistor 22 A, that is, the collector current and the base current of the transistor 22 A.
- the collector current at measurement point P1 is It can be seen that the base current of P3 is large enough to be ignored. Therefore, it can be seen that the currents flowing through the collector and the emitter of the transistor 22A are almost equal.
- the relationship between the collector current at the measurement point P2 for the transistor 22B and the base current at the measurement point P4 is the same, and it can be seen that the currents flowing at the collector end and the emitter end of the transistor 22B are almost equal.
- FIG. 25 shows the measurement results of measurement points P 1 to P 9 (the scale of the current value on the vertical axis is different from that of FIG. 20).
- the current flowing through the current-to-voltage conversion resistors 23 A and 23 B is branched, and the transistors 22 A and 22 A, which are bit string selection switches,
- the collector terminal of 22 B and the base terminal of the transistor 41 A, 41 B which is the differential pair of the sense amplifier 106 B. Furthermore, the sum of the collector currents and base currents of the transistors 41 A and 4 IB is the respective emitter current, and the emitter currents are combined on a common wiring and flow into the collector terminal of the transistor 44. .
- the collector current of the transistors 41 A and 41 B is the base current (measurement point P 7,
- the difference between the collector current of transistor 41A at measurement point P5 and the collector current of transistor 41B at measurement point P6 is the difference between the original output of sense bit lines 21A and 21B. It can be seen that it is extremely large compared to the current difference. The ratio of the current difference is about 200 times in the case of the measurement data shown. Therefore, it can be seen that in this magnetic memory device, a very large output can be obtained by amplifying the read signal with such a sense amplifier 106B.
- the measurement results show that the transistors 41A, 41A at the measurement points P7, P8
- the magnetoresistive element 12 A (12 The variation of the read signal (voltage) with respect to the resistance variation in B) was examined separately for two cases.
- FIG. 26 shows the measurement results.
- the horizontal axis shows the resistance value R TMK1 of the magnetoresistive effect element
- the vertical axis shows the output voltage value normalized by the power supply voltage Vcc.
- the open circles indicate the output voltage value from the magnetoresistive element 12 A (1 2 B) taking the resistance value R H when the resistance is high
- the X mark indicates the resistance value RL when the resistance is low.
- the measured values are connected by solid lines, and the dotted lines show the results of a comparative example in which a current flows through a pair of magnetic storage elements and the voltage drop of the magnetic storage elements is directly sensed. .
- FIG. 27 shows an equivalent circuit diagram of the comparative example.
- This reading circuit is composed of a pair of magnetic storage elements (variable resistance R 1, R2), and each pair of magnetic storage elements is connected in series to a current source and a cell-selecting semiconductor switch. These series wirings are independent of each other. .
- the voltage drop of the magnetic storage element is directly read as S and ZS, the current-voltage conversion resistor is not used.
- the measurement result is shown by a dotted line in FIG.
- the output value greatly changes in proportion to the resistance of the magnetic storage element. Therefore, the degree of resistance variation of the magnetic storage element immediately affects the output value as a change.
- the MR ratio of each memory cell 12 was changed by fixing the resistance value R H and changing the resistance value Ri_, and each output voltage was measured.
- Figure 28 shows the measurement results.
- the horizontal axis shows the MR ratio (%), and the vertical axis shows the output voltage value normalized by the power supply voltage Vcc.
- the open circle indicates the output voltage value from the magnetoresistive element 12 A (1 2 B) having the resistance value R H
- the X mark indicates the magnetoresistive element 1 2 having the resistance value RL.
- the output voltage value from B (1 2 A) is shown.
- the measured values are connected by a solid line, and the dotted line is the offset reference value due to the constant current effect for each of the resistance values R H and R L.
- the output voltage from the resistance value RL and the output voltage from the resistance value RH tend to approach each other as the MR ratio decreases. That is, if the MR ratio varies for each of the memory cells 12, the effect appears in the voltage output in this manner. Nevertheless, the output voltage on the resistance value R side and the output voltage on the resistance value RH side are each within a certain range with respect to the reference value. In this case, if the MR ratio is about 15% or more, the difference between the two is sufficient as an output. It is running low.
- the present invention is not limited to the above embodiment and examples, and various modifications can be made.
- the sense amplifier 106B, the constant current circuit 108B, and the switching elements such as the transistors 22A and 22B are configured using bipolar transistors.
- CMOS complementary metal-oxide-semiconductor
- a switch such as the switch 46 having two or more control commands may be constituted by a MOS FET, but may be constituted by a logic gate.
- the circuit system of the sense amplifier 106B is configured to be controlled by two control signals input to the switch 46 and one control signal input to the transistor 48.
- the switch 46 may have a circuit configuration in which the switch 46 is replaced with a switch of three control commands that operates according to these three control signals.
- the magnetoresistive elements 12A and 12B are described as being TMR elements.
- two magnetoresistive elements in the magnetic memory device of the present invention store one unit of information. Any type may be used as long as the configuration is adopted.
- it can also be replaced by a CPP (Current Perpendicular to the Plane) — GMR element, which also has a structure in which current flows perpendicular to the magnetic layer stacking plane.
- the element structure in that case can be the same as that of the above-described magnetoresistive element 12A (12B) except that the nonmagnetic layer 2 is changed from an insulating layer to a nonmagnetic metal layer.
- the pair of magneto-resistance effect elements may be a magneto-resistance effect element (CIP (Current flows In the Plane) -GMR) including a stacked body in which current flows in a direction parallel to the stacking plane.
- CIP Current flows In the Plane
- GMR magneto-resistance effect element
- a pair of read lines supplying a read current to a pair of magnetoresistive elements, and a pair of read currents flowing through the pair of read lines are provided.
- a sense amplifier circuit for reading information from the storage cell based on the difference between the differential switch pair and a differential switch pair provided for each read line pair, and between the differential switch pair and the power supply.
- a constant current circuit provided in common for the plurality of differential switch pairs and for stabilizing the sum of a pair of read currents flowing through each of the differential switch pairs. Characteristics are unified, and the variation of the current amplification factor for each differential switch pair is suppressed.
- a stable differential output can be obtained from the sense amplifier circuit, and the SZN ratio of the read signal output can be improved.
- the number of components can be reduced, and unnecessary power consumption due to current flowing to circuit parts that are not the target of operation can be reduced. Can be avoided.
- the sense amplifier circuit since the sense amplifier circuit has such a configuration, in the readout circuit system, the current path flowing from the power supply to the ground can be limited to only one path passing through one sense amplifier circuit. Power consumption can be reduced.
- a first switch is provided between each of the plurality of differential switch pairs and the constant current circuit, and selects any one of the plurality of differential switch pairs; a power supply and a read line pair; And a pair of second switches for selecting whether or not to supply a read current to the read line pair, according to the open / close state of the first switch.
- Conduction between the pair and the constant current circuit can be interrupted, and only the sense amplifier circuit selected by the control signal input to the first switch can be operated. Therefore, it is possible to perform various operation controls on the circuit system including the sense amplifier circuit in accordance with the control signal input to the first switch. Also, when the sense amplifier circuit is not an operation target, if the first switch is controlled so as to be cut off so that current does not flow through the sense amplifier circuit, unnecessary power consumption may occur there. It is avoided and power consumption can be reduced.
- the bias resistor pair is also provided in common for a plurality of differential switch pairs, the characteristics of these bias resistor pairs are also standardized, and the offset amount with respect to the output value of each sense amplifier circuit Of the differential switch This contributes to the equalization of the amount of current in the switch pair. Therefore, it is possible to improve the S ratio of the read signal output. Also, the number of resistance components can be reduced, and unnecessary power consumption can be avoided.
- each of the paired elements will be close to each other. This arrangement ensures that the environmental temperatures are almost equal, prevents the characteristic values from deviating from each other due to temperature changes during driving, and ensures that these circuits perform proper differential operation. Therefore, it is possible to prevent the occurrence of signal noise.
- the differential switch pair provided for each read line pair, the bias resistor pair provided between each differential switch pair and the power supply, and a plurality of differential switches are provided.
- a constant current circuit is provided commonly for the dynamic switch pair, and information is read from the memory cell based on the difference between a pair of read currents flowing through the read line pair, so that the characteristics of the constant current circuit are uniform.
- the variation of the current amplification factor for each differential switch pair can be suppressed. This makes it possible to stably obtain the differential output for each read line pair from any line pair, and to improve the SZN ratio of the read signal output.
- the constant current circuits provided corresponding to the differential switch pairs are integrated, the number of components can be reduced and unnecessary power consumption can be avoided. Furthermore, in the magnetic memory device to which this sense amplifier circuit is applied, the current path from the power supply to the ground in the driving readout circuit system can be limited to only one path passing through one sense amplifier circuit. It is possible to reduce unnecessary power consumption.
- a differential switch pair is provided for each read line pair, a bias resistor pair is provided between each differential switch pair and a power supply, and a plurality of differential switches are provided.
- a constant current circuit is provided in common for the pair, and information is read from the memory cell based on the difference between the pair of read currents flowing through the read line pair.Therefore, the read current is differentially output, and the noise generated in each of the read lines And the offset component included in the output value of each magnetoresistive element is removed.
- the sense amplifier circuit that differentially amplifies the difference between the read currents as a voltage difference can share the constant current circuit by sharing the constant current circuit. Variations in the sense amplifier output due to variations in the characteristics of the current circuit are suppressed. Therefore, a stable differential output can be obtained, and the SZN ratio of the read signal output can be improved.
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Abstract
Description
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US10/550,105 US7277320B2 (en) | 2003-03-24 | 2004-03-23 | Magnetic memory device, sense amplifier circuit and method of reading from magnetic memory device |
EP04722698A EP1610340A1 (en) | 2003-03-24 | 2004-03-23 | Magnetic memory device, sense amplifier circuit, and reading method of magnetic memory device |
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US7206221B2 (en) * | 2005-09-09 | 2007-04-17 | Northern Lights Semiconductor Corp. | Upside-down magnetoresistive random access memory |
US7355886B1 (en) * | 2006-12-05 | 2008-04-08 | Spansion Llc | Method of programming, erasing and reading memory cells in a resistive memory array |
US7673195B2 (en) * | 2007-10-03 | 2010-03-02 | International Business Machines Corporation | Circuits and methods for characterizing device variation in electronic memory circuits |
US8310314B2 (en) * | 2010-09-06 | 2012-11-13 | Mediatek Inc. | Signal amplification circuits for receiving/transmitting signals according to input signal |
US8923041B2 (en) | 2012-04-11 | 2014-12-30 | Everspin Technologies, Inc. | Self-referenced sense amplifier for spin torque MRAM |
US9530469B2 (en) * | 2013-03-15 | 2016-12-27 | Sony Semiconductor Solutions Corporation | Integrated circuit system with non-volatile memory stress suppression and method of manufacture thereof |
US10726895B1 (en) | 2019-01-07 | 2020-07-28 | International Business Machines Corporation | Circuit methodology for differential weight reading in resistive processing unit devices |
CN110277490B (zh) * | 2019-06-24 | 2023-06-09 | 中国科学院微电子研究所 | Stt-mram参考单元及其制备方法及包含该参考单元的芯片 |
CN112259152B (zh) * | 2019-07-22 | 2022-06-24 | 中电海康集团有限公司 | Mram阵列的测试电路 |
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US5281873A (en) | 1989-11-21 | 1994-01-25 | Fujitsu Limited | Sense amplifier control circuit |
US6188615B1 (en) * | 1999-10-29 | 2001-02-13 | Hewlett-Packard Company | MRAM device including digital sense amplifiers |
JP3868699B2 (ja) | 2000-03-17 | 2007-01-17 | 株式会社東芝 | 磁気メモリ装置 |
US6473336B2 (en) | 1999-12-16 | 2002-10-29 | Kabushiki Kaisha Toshiba | Magnetic memory device |
US6396733B1 (en) * | 2000-07-17 | 2002-05-28 | Micron Technology, Inc. | Magneto-resistive memory having sense amplifier with offset control |
TW584976B (en) | 2000-11-09 | 2004-04-21 | Sanyo Electric Co | Magnetic memory device |
US6600690B1 (en) * | 2002-06-28 | 2003-07-29 | Motorola, Inc. | Sense amplifier for a memory having at least two distinct resistance states |
US6621729B1 (en) * | 2002-06-28 | 2003-09-16 | Motorola, Inc. | Sense amplifier incorporating a symmetric midpoint reference |
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2003
- 2003-03-24 JP JP2003081251A patent/JP4365604B2/ja not_active Expired - Fee Related
-
2004
- 2004-03-23 US US10/550,105 patent/US7277320B2/en not_active Expired - Fee Related
- 2004-03-23 EP EP04722698A patent/EP1610340A1/en not_active Withdrawn
- 2004-03-23 WO PCT/JP2004/003973 patent/WO2004086407A1/ja active Application Filing
- 2004-03-24 TW TW093107873A patent/TWI237263B/zh not_active IP Right Cessation
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WO1991007757A1 (en) * | 1989-11-21 | 1991-05-30 | Fujitsu Limited | Sense amplifier control circuit |
JP2001236781A (ja) * | 1999-12-16 | 2001-08-31 | Toshiba Corp | 磁気メモリ装置 |
JP2001273759A (ja) * | 2000-03-27 | 2001-10-05 | Sharp Corp | 磁気メモリセルと磁気メモリ装置 |
JP2002260377A (ja) * | 2000-11-09 | 2002-09-13 | Sanyo Electric Co Ltd | 磁気メモリ装置 |
JP2002170374A (ja) * | 2000-11-28 | 2002-06-14 | Canon Inc | 強磁性体不揮発性記憶素子およびその情報再生方法ならびにそれを用いたメモリチップおよび携帯型情報処理装置 |
JP2002298572A (ja) * | 2001-03-28 | 2002-10-11 | Toshiba Corp | 半導体記憶装置 |
JP2003030976A (ja) * | 2001-04-02 | 2003-01-31 | Hewlett Packard Co <Hp> | オンザフライでピン留めされる軟らかいリファレンス層のためのクラッディングされた読出し導体 |
JP2002353415A (ja) * | 2001-05-23 | 2002-12-06 | Internatl Business Mach Corp <Ibm> | 記憶素子、メモリセル及び記憶回路ブロック |
JP2004119638A (ja) * | 2002-09-25 | 2004-04-15 | Tdk Corp | 磁気メモリデバイス、並びに磁気メモリデバイスの書込方法および読出方法 |
Also Published As
Publication number | Publication date |
---|---|
TW200501161A (en) | 2005-01-01 |
US20060120146A1 (en) | 2006-06-08 |
EP1610340A1 (en) | 2005-12-28 |
TWI237263B (en) | 2005-08-01 |
US7277320B2 (en) | 2007-10-02 |
JP4365604B2 (ja) | 2009-11-18 |
JP2004348775A (ja) | 2004-12-09 |
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