Patent Application
20150070980
Embodiments relates to a magnetic memory device utilizing magnetic domain wall motion.
Memory devices using magnetic thin wires with multiple magnetic domains along the directions in which the lines extend are known.
According to one embodiment, a magnetic memory device comprises a magnetic thin wire comprising magnetic domains along a direction in which the magnetic thin wire extends. Magnetization directions of the magnetic domains are variable. A magnetic tunnel junction (MTJ) structure comprises a pinned layer with a fixed magnetization direction and an insulator, and make a MTJ comprising the pinned layer, the insulator and a magnetic domain in the magnetic thin wire in a first position to sandwich the insulator with the pinned layer. First and second electrodes are at both ends of the magnetic thin wire. At least one third electrode is coupled to the magnetic thin wire between the first and second electrodes.
Embodiments will now be described with reference to the figures. The embodiments are not exclusive to each other and can be combined unless they are obviously exclusive to each other. Therefore, description for a particular embodiment is applicable to another embodiment.
Components with substantially the same functionalities and configurations will be referred to with the same reference number and duplicate descriptions will be made only when required. The embodiments only used to illustrate devices and methods to implement the technical idea thereof, and the technical idea does not limit materials, dimensions, structures, and arrangements of components to the following ones. The figures are merely schematic, and in order to illustrate a particular feature clearly, the feature may be different in scale among figures.
Relative dimensions of components illustrated in a particular figure may be different from actual ones in order to, for example, emphasize the feature.
A selected magnetic thin wire ML has its magnetic domain walls moved to a particular direction to have a write or read (or, access) target magnetic domain moved to a position of the write mechanism (or, write position) or a position of a read mechanism (or, read position). For moving the magnetic domain walls, current source/sinks to conduct current are coupled at the both ends of a magnetic thin wire ML, for example. For example, current source/sinks SC are provided in the both sides of a cell array CA, and current source/sinks SC at the both sides of a particular cell array CA make a pair. Each pair of current source/sinks SC cooperates to conduct current through a particular magnetic thin wire ML in a selected one of two directions along the thin line. This current moves the magnetic domain walls and hence the magnetic domains of the magnetic thin wire ML. Alternatively, the magnetic domain walls are moved by an electric field from interconnects around the magnetic thin wires. The motion of the magnetic domains can be performed by any mechanism.
A row decoder (or, word line controller) RD selects a row in accordance with a received address (or, row address) signal. Specifically, it electrically couples specified magnetic thin wires ML to a related component. A column decoder (or, bit line controller) CD selects a column in accordance with a received address (or, column address) signal. Specifically, it electrically couples selected magnetic thin wires ML to a related a component. Each sense amplifier SA senses data from a corresponding cell array CA. A latch TL temporarily stores data to and from the magnetic thin wires ML.
A sequencer SQ manages operation of the whole magnetic memory device MD in accordance with a lookup table LUT, a command latch CL, and an address latch AL. The lookup table LUT stores information including various types of parameters. The command latch CL, address latch AL, and data latch DL0 respectively receive command CMD, address signal ADD, and data DAT from outside the magnetic memory device MD through an input receiver IR and a demultiplexer DMU. The data latch DL0 supplies received data to the column decoders CD and the latch TL. The input receiver IR controls the input of signals. A data latch DL1 receives data from the latch TL. The data latch TL and a status register SR output data DATA and status information STATUS outside the magnetic memory device MD through a multiplexer MUX and an output driver OD, respectively. A power-on sequencer PNS and a power-off sequencer PFS control power on and off of the sequencer SQ, respectively.
The magnetic memory device MD receives power potential Vdd and a common (or, ground) potential Vss (GND) from the outside. A voltage and current generator VG generates various voltages and currents for operation of the magnetic memory device MD in accordance with the power received from the outside and control by the sequencer SQ.
In order to move the magnetic domain walls by current, a voltage is applied to the both ends of a particular magnetic thin wire. The applied voltage V for moving is V=I×a×ρ×l/a=i×ρ×l, where ρ, l, a, and i are the resistivity, length, cross sectional area of a magnetic thin wire, and the current density required for moving the magnetic domain walls. That is, the longer the magnetic thin wire, the larger the required current for moving the magnetic domains and hence the required voltage. The length of the magnetic thin wire is proportional to the number of magnetic domains, or the storage capacity of the magnetic thin wire. Therefore, increasing the storage capacity of the magnetic thin wire requires a larger voltage to be applied to the magnetic thin wire for moving the magnetic domain walls.
A voltage is generated between two electrodes which sandwich another electrode. For example, during the period A, the electrode EA is set to a potential V2 (or, applied with a voltage V2), and the electrodes E0 to E8 are set to a potential V1 (or, applied with a voltage V1), and the electrode E9 between electrodes E8 and EA is made to electrically float (or, not controlled to a fixed voltage). As a result of such voltage application, all the magnetic domains between electrodes E8 and EA move rightward. The magnetic domains on the left-hand side of the electrode E8 do not move. Also, in other periods B to I, the voltage V2 is applied to the left-hand-side one of an electrode pair with another electrode interposed therebetween as well as all the electrodes at its left-hand side, the voltage V1 is applied to the right-hand-side one of the electrode pair as well as all the electrodes at its right-hand side, and the intervening electrode E is made to electrically float. In other words, a potential difference is generated only between an electrode pair which defines an area targeted for the magnetic domain wall motion, and no potential difference is generated among the remaining electrodes. This moves the magnetic domains between the electrode pair rightward.
In order to move the magnetic domains leftward, a combination of voltages opposite to the voltages applied as in
The voltages may be as shown in
Such voltage application to only a part of the magnetic thin wire ML is contrastive to applying voltages to the both ends of the magnetic thin wire ML to move all the magnetic domains therein. Furthermore, voltages are applied to only a part of the magnetic thin wire ML, and therefore the magnitude thereof is smaller than that applied to the both ends of the magnetic thin wire ML.
The application of voltages as in
In each of the drivers E0D to EAD, the transistor TP1 (TP1_0 to TP1_A) and TN1 (TN1_0 to TN1_A) are coupled in series between the power node and ground node. In the drivers E0D, E1D, E9D, and EAD, the transistor TP1 (TP1_0, TP1_1, TP1_9, or TP1_A) receives the output of the inverter IV1 (IV_0, IV_1, IV_9, or IV_A). In the drivers E2D to E8D, the transistors TP1 and TN1 receive the outputs of NOR gate NOR1 (NOR1_2 to NOR1_8) and OR gate OR1 (OR1_2 to OR1_8), respectively.
A signal E02L is input to the gate of the transistor TN1_0 and the NOR gate NOR1_2. A signal E02R is input to the inverter IV1_0 and OR gate OR1_2. A signal E13L is input to the gate of the transistor TN1_1 and the NOR gate NOR1_3. A signal E13R is input to the inverter IV1_4 and OR gate OR1_3. A signal E24L is input to the OR gate OR1_2 and NOR gate NOR1_4. A signal E24R is input to the NOR gate NOR1_2 and OR gate OR1_4. A signal E35L is input to the OR gate OR1_3 and NOR gate NOR1_5. A signal E35R is input to the NOR gate NOR1_3 and OR gate OR1_5. A signal E46L is input to the OR gate OR1_4 and NOR gate NOR1_6. A signal E46R is input to the NOR gate NOR1_4 and OR gate OR1_6. A signal E57L is input to the OR gate OR1_5 and NOR gate NOR1_7. A signal E57R is input to the NOR gate NOR1_5 and OR gate OR1_7. A signal E68L is input to the OR gate OR1_6 and NOR gate NOR1_8. A signal E68R is input to the NOR gate NOR1_6 and OR gate OR1_8. A signal E79L is input to the OR gate OR1_7 and inverter IV1_9. A signal E79R is input to the NOR gate NOR1_7 and the gate of the transistor TN1_9. A signal E8AL is input to the OR gate OR1_8 and the gate of the inverter IV1_A. A signal E8AR is input to the NOR gate NOR1_8 and the gate of the transistor TN1_A. The signals in
The application of voltages as in
According to the first embodiment, the magnetic thin wire ML is coupled to electrodes E at the both ends, and is also coupled to at least one electrode E between the ends. Forming a potential difference between a pair of electrodes E moves the magnetic domains only between the electrode pair. Such a partial magnetic domain wall motion can make the voltage for the magnetic domain wall motion smaller than that for an example of the voltage application to the ends of the magnetic thin wire ML, and eliminates the necessity of a high voltage for moving the magnetic domain walls even in a long thin line ML. Use of a high voltage is unnecessary, and therefore no circuit for generating and applying a high voltage is necessary. This prevents an increase of the chip area of the magnetic memory device, and eliminates the necessity of a dedicated process for forming transistors for the high voltage.
Moreover, the voltage for moving the magnetic domain walls is not proportional to the length of the magnetic thin wire ML, and therefore a long ferromagnetic thin wire ML can be implemented. Extension of the magnetic thin wires ML can reduce the number of accompanying mechanism for reads or writes for each magnetic thin wire ML, such as the MTJ structure and a selection circuit, and therefore can reduce the chip size of the magnetic memory device MD. Such extension of the magnetic thin wire ML and removal of the necessity for the high voltage can realize a magnetic memory device MD with a high capacity and high density.
In the second embodiment, the first embodiment is applied to multiple magnetic thin wires.
The arrangement of the components as shown in
Electrodes E0 to EY extend perpendicularly. The electrodes E0 to EY are in a line horizontally. The electrodes E have intervals along the direction in which the electrodes E (E0 to EY) extend, and are in contact with the contacts SC at their sides. Each contact SC extends in a direction which penetrates the figure, and is in contact with a particular magnetic thin wire ML. The combination of coupled electrodes E and magnetic thin wires ML via the contacts SC is different among
Specifically, in the
In the
In the
A structure of ends of the magnetic thin wires ML and the vicinity thereof is as shown in
In step S2, a layer for the lowest magnetic thin wires ML (or, the magnetic thin wires ML0 in the
In step S4, the stack of the films and layers obtained by the steps so far is patterned by a lithography step and an etching to be formed into stripes in the plane shape thereof (see,
In step S8, the interlayer dielectrics and pinned layers PL are repeatedly patterned by a photolithography process and an etching to form a stair structure of the set of pinned layers PL at the ends thereof. Specifically, the end of each pinned layer PL is removed one by one by an etching so that a higher pinned layer PL is shorter than a lower pinned layer PL. In step S9, the ends of the magnetic thin wires ML, where the stair structure of the pinned layers PL are positioned, are selectively etched back. In step S10, an interlayer dielectric (not shown) such as SiO2 is formed over the entire surface of the structure obtained by the steps so far to bury the stair-structure part of the pinned layers PL. The upper surface of this interlayer dielectric is then planarized.
In step S11, holes for the contacts C0 which reach respective tops of pinned layers PL are formed in the interlayer dielectric by a lithography step and an etching. The contact holes are then buried with a conductive material to form the contacts C0, whose tops are then planarized. In step S12, contact holes which reach the contacts SC are formed by a lithography step and an etching in the interlayer dielectric. In step S13, the contact holes are buried by a conductive material to form the contacts C3, whose tops are then planarized. In step S14, interconnects LY0 are formed by a lithography step, an etching, and planarization. In step S15, holes for the contacts C1 are formed by a lithography step and an etching in the interlayer dielectric. In step S16, the contact holes are buried with a conductive material to form the contacts C1, whose tops are then planarized. In step S17, the interconnects LY1 are formed by a lithography step, an etching, and planarization.
The MTJ structures MTJ may be formed at different sides of the different magnetic thin wires ML instead of the same side. For example, every two magnetic thin wires ML form the MTJ structures MTJ at a particular end, and every other two magnetic thin wires ML form the MTJ structures MTJ at the other end. This example is illustrated in
The second embodiment is based on the first embodiment, and therefore the same advantages as the first embodiment can be obtained according to the second embodiment. Moreover, according to the second embodiment, the magnetic domain walls of multiple magnetic thin wires ML are moved simultaneously. This results in driver circuits fewer than an example of magnetic domain wall motion in units of magnetic thin wire ML, and can reduce the area of the chip of the magnetic memory device MD and the manufacturing cost of the chips. Furthermore, the magnetic thin wires ML are provided along (or, in parallel) with the substrate sub, and therefore complementary MOS (CMOS) circuits (or, their transistors) for various periphery circuits can be formed on the substrate sub below the magnetic thin wires ML. This further reduces the chip area and increase an integration of the magnetic memory device MD.
The third embodiment relates to an example of magnetic domain wall motion with an electric field.
Each of the electrodes VE1 and VE2 is coupled to a corresponding electrode E via a contact C2. For example, the electrodes VE1 from the left side of
As described above and shown in
After step S26, steps S8 to S11 are executed. In step S28 after step S11, holes for the contacts C2 and C3 are formed by a lithography step and an etching. In step S29, the contact holes are buried with a conductive material to form the contacts C2 and C3, whose tops are then planarized. After step S29, steps S14 to S17 are executed.
According to the third embodiment, even with an example of magnetic domain walls being moved with the electric field, the magnetic thin wires ML can be provided along (or, in parallel) with the substrate sub as in the second embodiment, which produces the same advantages as the second embodiment.
The fourth embodiment relates to an example of the magnetic thin wires being formed along a direction perpendicular to the substrate.
Electrodes HE for magnetic domain wall motion with a plate shape are provided along the surface of the substrate sub. The electrodes HE are in a line along the direction perpendicular to the surface of the substrate sub at intervals. The electrodes HE receive voltages to generate electric fields for moving the magnetic domain walls. An electrode HE at a higher level is shorter than an electrode HE at a lower level, and therefore a set of the electrodes HE form a stair at the end. Each electrode HE is coupled at the end at the top to a contact C5. The contacts C5 are coupled at the tops to the interconnects LY2. A plane view of the ends of the electrodes HE is illustrated in
For reads and/or writes, MTJ structures and transistors for selecting such structures are necessary. However, providing structures and elements for respective magnetic thin wires also involves provision of a control and/or drive circuit for the MTJ structures and elements and interconnects. This consumes a large area of a chip of a magnetic memory device utilizing magnetic domain wall motion. The stacked magnetic thin wires ML as in the
Between the power supply node and one end (or, node N_0) of the magnetic thin wire ML_0 which is not commonly coupled, p-type MOSFETs TP11_0 and TP12_0, and an n-type MOSFETs TN11_0 are coupled in series. The transistor TP11_0 is coupled to a node IS20 at the gate. The transistor TP12_0 receives the inverted signal of a signal E0R from the sequencer SQ at the gate. The transistor TN11_0 receives a signal E0L from the sequencer SQ at the gate. Similarly, between the power supply node and one end (or, node N_Z) of the magnetic thin wire ML_Z which is not commonly coupled, p-type MOSFETs TP11_Z and TP12_Z, and an n-type MOSFET TN11_Z are coupled in series, where Z=1, 2, 3, 4, or 5. The transistor TP11_Z is coupled to a node IS20 at the gate. The transistor TP12_Z receives the inverted signal of a signal EZR from the sequencer SQ at the gate. The transistor TN11_Z receives a signal EZL from the sequencer SQ at the gate. The node IS20 is supplied with a constant current from a current source IS2. The current source IS2 is enabled by a signal SFT.
Between the power supply node and ground node, p-type MOSFETs TP14 and TP15, and an n-type MOSFET TN13 are coupled in series. The transistor TP14 is coupled to the node IS20 at the gate. The connection node between the transistors TP15 and TN13 is coupled to one end (node N_6) of the magnetic thin wire ML_6. The transistor TP15 receives the output of a NOR gate NOR11 at the gate. The transistor TP15 receives signals E0L, E1L, E2L, E3L, E4L, and ESL. The transistor TN13 receives the output of an OR gate OR11 at the gate. The transistor TN13 receives signals E0R, E1R, E2R, E3R, E4R, and E5R.
With the signals SFT and EOL made high and remaining signals EXL (X=1, 2, 3, 4, and 5) and signals NYR (Y=0, 1, 2, 3, 4, and 5) made low, a current flows from the node N_6 to the node N_0, and this current moves the magnetic domain walls in the magnetic thin wire ML_0 from the node N_0 to the node N_6. This transfers the data in the moved magnetic domains to the magnetic thin wire ML_6.
With the signals SFT and E2L made high and the remaining signals EXL (X=0, 1, 3, 4, and 5) and signals NYR (Y=0, 1, 2, 3, 4, and 5) made low, a current flows from the node N_6 to the N_2, and this current moves the magnetic domain walls in the magnetic thin wire ML_2 from the node N_2 to the node N_6. This transfers the data in the moved magnetic domains to the magnetic thin wire ML_6.
Similarly, with the signals SFT and EZL made high and the remaining signals EXL (X=0 to 5 excluding Z) and the signal NYR (Y=0, 1, 2, 3, 4, and 5) made low, a current flows from the node N_6 to N_Z, and this current moves the magnetic domain walls in the magnetic thin wire ML_Z from node N_Z to the node N_6. This transfers the data in the moved magnetic domains to the magnetic thin wire ML_6.
Thus, a magnetic thin wire is utilized which has magnetic domain walls moved only in a part between two electrodes between which a potential difference is present, and no current flows (or, is made to flow) in other parts to result in no magnetic domain wall motion. Specifically, a potential difference is generated only between one of the nodes E_0 to E_5 and the node E_6, and the magnetic domains in one of the magnetic thin wires ML_0 to ML_5 move.
Thus, the motion of the magnetic domains are caused in one of the magnetic thin wires ML_0 to ML_5, and the data in the magnetic domains to be accessed is transferred to the magnetic thin wire ML_5. The to-be-accessed magnetic domain is further moved through the magnetic thin wire ML_6 until it enters the MTJ structure MTJ, where a read or write is executed. The motion of the magnetic domains in the magnetic thin wire ML_6 are possible by generating a potential difference between the node N_6 and the other end.
In the
Similarly, a p-type MOSFET TP17_Z is coupled between the node of potential VA and a node N_Z (Z=1, 2, 3, or 4). The transistor TP17_Z receives the output of an OR gate OR13_Z at the gate. The OR gate OR13_Z receives, among all the signals E0L, E1L, E2L, E3L, and E4L, all signals except for the corresponding signal EZL.
According to the fifth embodiment, the magnetic thin wires for data storage ML_0 to ML_5, and magnetic thin wire for data transmission (or, passage) ML_6 are provided. A voltage application to non-ends of a magnetic thin wire is used to carry out motion only in a voltage-applied part to transfer to-be-accessed data in the magnetic thin wires for data storage ML_0 to ML_5 to the magnetic thin wire for transmission ML_6. The to-be-accessed data is further transferred in the magnetic thin wire ML_6 to the MTJ structure MTJ. Such arrangement allows a single MTJ structure MTJ to be shared by multiple magnetic thin wires ML. This can decrease the number of control elements which accompany the MTJ structures MTJ, and reduces the area of the chip of the magnetic memory device.
The sixth embodiment relates to a structure of the fifth embodiment.
Above the transistors T, magnetic thin wires ML 11 to ML1_14 are formed in different layers along (or, in parallel) with the substrate sub. The magnetic thin wires ML_11 to ML14 have the same features as the magnetic thin wire ML of the embodiments described so far, and store data. The magnetic thin wire MLs (ML_11 to ML_14) are coupled at the bottoms to source/drain areas SD via contacts C11 on source/drain areas SD, interconnects LY11 on the contacts C11 and contacts C12 on the interconnects LY11. A section of each magnetic thin wire ML including a section connected to a contact C12 is included in a data transfer area DTA0, and is used to transfer data. A section of each magnetic thin wire ML other than the data transfer area DTA0 is included in the memory area DSA, and is used to store data.
Non-lowest magnetic thin wires ML_12 to ML_14 are coupled, at ends at the side of the data transfer area DTA0, to a magnetic thin wire MLV. The magnetic thin wire MLV has the same features as other magnetic thin wires ML, extends along the direction perpendicular to the surface of the substrate sub, and is included in the data transfer area DTA1. The magnetic thin wire MLV is used to transfer data as the magnetic thin wire ML_6 of the fifth embodiment. The lowest magnetic thin wire MLV is coupled at the bottom to the lowest magnetic thin wire ML_11. The magnetic thin wire ML_11 sandwiches at the bottom a tunnel insulating film (not shown) with a pinned layer PL, and makes an MTJ structure MTJ for reads/writes. The pinned layer PL is also coupled to a source/drain area SD via the contacts C11, C12, and interconnect LY11.
The structure illustrated in
The section where the magnetic thin wires ML and contacts C13 are connected is illustrated in
According to the sixth embodiment, the structure of the fifth embodiment can be implemented to obtain the same advantages as the fifth embodiment.
The seventh embodiment relates to the combination of the second and sixth embodiments.
According to the seventh embodiment, the advantages of the second and sixth embodiments can be obtained.
The eighth embodiment relates to the combination of the third and sixth embodiments.
According to the eighth embodiment, the advantages of the third and sixth embodiments can be obtained.
The ninth embodiment relates to a structure of a magnetic thin wire.
Magnetic domain walls need to stay stably if there is no external force for moving the magnetic domain walls, such as force by current or voltage, applied to the magnetic thin wire. The magnetic domain walls, however, may vibrate slightly due to, for example, thermal energy to result in unintentional motion. In order to prevent such migration, it is proposed forming a pinning site in a magnetic thin wire (see, for example, U.S. Pat. No. 7,551,469). The pinning site can be implemented by narrowing the magnetic thin wire in a part than other parts, or forming constriction. Therefore, a pinning site has a cross section smaller than other parts.
The magnetic thin wire 110 has pinning sites PS102, PS103, and PS104 at equally-spaced nodes N102, N103, and N104, respectively. Each area between a pair of the end nodes N101 and N105 and pinning sites PS10 (PS102, PS103, and PS104) of the magnetic thin wire 110 defines a magnetic domain, i.e., has a single magnetization direction, and stores 1-bit information. Specifically, at time to, magnetic domains A to D are formed between the nodes N101 and N102, nodes N102 and N103, nodes N103 and N104, and nodes N104 and N105, respectively. The boundaries of magnetic domains are located at the pinning sites PS102 to PS104. The node N105 is coupled to the power supply node, and the node N101 is coupled to the current sink ISN11.
At time t0, with a current conducted from the node N105 to the node N101 in the magnetic thin wire 110 while an enable signal EN for the current sink ISN11 is high, magnetic domain walls move in a direction of the current, i.e., to the node N105. In other words, with an electron flow passed from the node N101 to node N105, the magnetic domain walls move to the same direction as the electron flow. If the current larger than a threshold flows, the magnetic domain walls move.
Because of an RC delay of the magnetic thin wire 110, a time for the current to reach the threshold for moving the magnetic domain walls from the start of the flow of the current depends on the position of the nodes as illustrated in
A current pulse illustrated as the potential of the node N101 is applied from time t0 to t1. A delay at the node N102 is small, and therefore after the current pulse rises at time t0, the potential of the node N102 exceeds the threshold promptly. As a result, the magnetic domain walls between the magnetic domains A and B move to the node N105 to reach the next pinning site PS103 at the time t2, and stabilize there.
In contrast, the potential of the node N103 rises slowly, and therefore at time t1 the move has not progress sufficiently yet and the magnetic domain walls between the magnetic domains B and C have not reached the node N104.
For this reason, the magnetic domain walls between the magnetic domains B and C are pushed back to the node N103 by the magnetic domain C by the time t2, and the magnetic domain B disappears.
To address such a phenomenon, the magnetic thin wire ML of the ninth embodiment is configured as shown in
The magnetic thin wire ML is coupled to a current sink (or, an electron source) S1, and a power supply node (or, an electron sink) at both end nodes Na and Ne, respectively. The magnetic thin wire ML has nodes Nb, Nc, and Nd in the mentioned order from the end node Na to the node Ne. The nodes Nb, Nc, and Nd are in unequally-spaced positions between the end nodes Na and Ne. Specifically, a further adjacent-node-pair from the current sink ISN11 (or, the node Na) has a shorter distance between the pair. More specifically, the distance becomes smaller in order of the distance between nodes Na and Nb, between the nodes Nb and Nc, between the nodes Nc and Nd, and between the nodes Nd and Ne. The magnetic thin wires ML have pinning sites PSb, PSc, and PSd at the nodes Nb, Nc, and Nd, respectively. Therefore, a pinning-site-pair farther from the current sink has a smaller distance between the pair.
With a current pulse as illustrated in
At time t0, magnetic domains A to D are formed between the nodes Na and Nb, nodes Nb and Nc, nodes Nc and Nd, and nodes Nd and Ne, respectively. The boundaries of the magnetic domains are located in the pinning sites PSb, PSc, and PSd.
When the current pulse rises at time t0, a current at the node Nb exceeds a threshold immediately, and the magnetic domain walls between the magnetic domains A and B move toward the node Ne. The magnetic domain wall between the magnetic domains A and B starts to move earliest from the start of the application of the current pulse, and therefore a time spent for the motion needs to be long. To this end, the interval between the nodes Na and Nb is made longer than that between the nodes Nb and Nc. For this reason, the magnetic domain wall between the magnetic domains A and B has not reached the node C at time T0 yet, and finally reaches it at time t2.
When the value of a current at the node Nc reaches the threshold after the value of the current at the node Nb reaches the threshold, the magnetic domain wall between the magnetic domains B and C moves toward the node Ne. The magnetic domain wall between the magnetic domains B and C starts to move with a delay from the start of the application of the current pulse, and therefore takes longer than the time spent for the magnetic domain wall between the magnetic domains A and B to move. Therefore, the distance between the node Nc and the next node Nd in the moving direction is made shorter than that between the nodes Nb and Nc. This enables the magnetic domain wall between the magnetic domains B and C to reach the node Nd at time t2.
Similarly, when the value of a current at the node Nd reaches the threshold after the value of the current at the node Nc reaches the threshold, the magnetic domain wall between the magnetic domains C and D moves toward the node Ne. The magnetic domain wall between the magnetic domains C and D starts to move with a larger delay from the start of the application of the current pulse, and therefore takes longer than the time spent for the magnetic domain wall between the magnetic domains B and C to move. Therefore, the distance between the node Nd and the next node Ne in the moving direction is made shorter than that between the nodes Nc and Nd. This enables the magnetic domain wall between the magnetic domains C and D to reach the node Ne at time t2.
Thus, a data loss is prevented even with a waveform as in
The description so far relates to the example of the magnetic domain wall motion by current application. The present embodiment is, however, also applicable to an example of magnetic domain wall motion by electric field application. Further, in the example of the magnetic domain wall motion by electric field application, the magnitude of field varies depending on the position in the magnetic thin wire ML due to the RC delay. For this reason, the data loss can be prevented also in the example of the magnetic domain wall motion in the magnetic thin wire which has pinning sites at irregular intervals due to electric field application.
The description so far relates to the example of the magnetic thin wire ML with four magnetic domains. A magnetic thin wire ML with less or more magnetic domains can, however, be implemented in accordance with the principle described above.
According to the ninth embodiment, the magnetic thin wire ML has multiple pinning sites PS (PSb to PSd) with intervals which become shorter along the direction in which magnetic domain walls move. For this reason, a pinning-site interval nearer to where the electron flow is applied is longer, and it also takes more time for the magnetic domain wall to reach the next magnetic domain wall position. Therefore, times for the magnetic domain walls to reach the respective next magnetic domain wall positions are substantially the same, and each magnetic domain wall can reach the next magnetic domain wall position successfully. This serves for prevention of a particular magnetic domain wall from failing to reach the next magnetic domain wall position and the resultant loss of the data in the magnetic domain just before the magnetic domain wall along the moving direction. Therefore, even with a long magnetic thin wire ML, stable (or, without no data loss) magnetic domain wall motion is possible, and a magnetic memory device MD with a large capacity can be implemented.
The tenth embodiment relates to reads of data.
As described above, a magnetic thin wire ML is accompanied by at least one MTJ structure MTJ for reads or for both reads and writes. A bias current for the MTJ structure MTJ is set as the median between a current through the MTJ structure MTJ in the high resistance state, and that in the low resistance state. Upon such bias current application, the MTJ structure MTJ in the high resistance state exhibits a high voltage across the structure, and the MTJ structure MTJ in the low resistance state exhibits a low voltage across the structure. The magnitude of such terminal voltage is detected to determine the data.
The magnetoresistance ratio (MR) of the MTJ structure MTJ is now about 100% in magnitude with MgO used for its tunnel insulating film TIL. However, if the tunnel resistance of the MTJ structure MTJ deviates by 100% due to unintended process variation of the tunnel insulating films TIL, the change in resistance of the MTJ structure MTJ cannot be detected. Specifically, if the resistance of the MTJ structure MTJ is more than twice the intended value, the MTJ structure MTJ always exhibits the high terminal voltage in response to application of a fixed bias current, i.e., the MTJ structure MTJ is always determined to be in the high resistance state. Similarly, if the resistance of the MTJ structure MTJ is less than half the intended value, the MTJ structure MTJ always exhibits the low terminal voltage in response to application of a fixed bias current, i.e., the MTJ structure MTJ is always determined to be in the low resistance state. This results in impossibility of distinguishing values of data.
To address the phenomenon described above, a magnetic memory device MD in the tenth embodiment is configured as follows.
As illustrated in
In the tenth embodiment, the magnetic thin wire ML of any form can be used, and a structure of
Each magnetic thin wire ML is accompanied by an MTJ structure MTJ. Each MTJ structure MTJ is used to read data from a corresponding magnetic thin wire ML, and optionally to write data to that magnetic thin wire ML. Each MTJ structure MTJ is coupled at a first end to a corresponding row select transistor RST. The select transistor RST is made of an n-type MOSFET. Transistors RST of the 0th column are coupled to a word line WL0 at the gates. Similarly, transistors RST of the Vth column are coupled to a word line WLV at the gates. Transistors RST of the 0th row are coupled at the second ends to a bit line BL0. Similarly, transistors RST of the Wth (W=0 to m) row are coupled at the second ends to a bit line BLW. The word lines WL (WL0 to WLn) and signal lines SFL (SFL0 to SFLn) and SFR (SFR0 to SFRn) are controlled by a row decoder RD and current source/sink SC.
The row decoder RD and current source/sink SC include OR gates OR21, OR22, OR23, OR24, and OR25, AND gates AND11, AND12, and AND13, and NAND gates NAND11, and NAND12 for a single column. The figure only illustrates features for the word line WL0.
The OR gate OR21 receives signals RD, WR1, and SFTR from the sequencer SQ, and supplies the output to the AND gate AND11. The OR gate OR22 receives signals WR0 and SFTL from the sequencer SQ, and supplies the output to the NAND gate NAND11. The OR gate OR23 receives the signal RD and a signal WR from the sequencer SQ, and supplies the output to the AND gate AND13. The OR gate OR24 receives the signals RD, WR0, and SFTL from the sequencer SQ, and supplies the output to the AND gate AND12. The OR gate OR25 receives the signals WR1 and SFTR from the sequencer SQ, and supplies the output to the NAND gate NAND12.
The AND gates AND11, AND12 and AND13, and the NAND gate NAND11 and NAND12 further receive row adds RowAdd. The output of the AND gate AND13 is supplied to the corresponding word line WL0. The AND gate AND11 and NAND gate NAND11 supply respective outputs to respective gates of an n-type MOSFET TN21 and p-type MOSFET TP21, respectively. The transistors TP21 and TN21 are coupled in series between the power node and ground node, and the connection node is coupled to the signal line SFL0. The AND gate AND12 and NAND gate NAND12 supply respective outputs to respective gates of an n-type MOSFET TN22 and p-type MOSFET TP22, respectively. The transistors TP22 and TN22 are coupled in series between the power node and ground node, and the connection node is coupled to the signal line SFR0.
The signal RowAdd is made high when the corresponding row is selected. The signal RD is made high during a data read. The signal WR is made high during a write, and further, while 0-data and 1-data writes are executed, signals WR0 and WR1 are respectively made high to respectively instruct a write of 0-data and that of 1-data in a write-target cell (or, write-target magnetic domain in the MTJ element MTJ). The signals SFTR and SFTL are made high to move the magnetic domain walls in the magnetic thin wire ML rightward and leftward in
The set of the OR gates OR21, OR22, OR23, OR24, and OR25, AND gates AND11, AND12, and AND13, and NAND gates NAND11, and NAND12 is also provided for word lines WL other than the word line WL0.
The sense node SN is coupled to the inverting input end of an operational amplifier OP2. The operational amplifier OP2 is enabled with signal RD received, receives a reference potential VREF at the non-inverting input, and outputs a sense amplifier output SAO. The magnitude of the reference potential VREF is determined in accordance with a principle, which will be described later.
The sense node SN further includes a feedback loop FB. The feedback loop FE includes an operational amplifier OP3, p-type MOSFETs TP32 and TP33, an n-type MOSFET TN32, and a capacitor CP. The sense node SN is coupled to the non-inverting input end of the operational amplifier OP3. The operational amplifier OP3 is enabled while it is receiving the signal PS, and receives a potential VSET of a particular magnitude at the inverting input. The output of the operational amplifier OP3 is coupled to one end of each of transistors TN32 and TP32. The transistors TN32 and TP32 receive at respective gates a signal PS and its inverted signal bPS, respectively. The other end of each of transistors TN32 and TP32 is grounded through the capacitor CP and coupled to the gate of the transistor TP33. The transistor TP33 is coupled between the power node and sense node SN. The transistor TP33 adjusts and supplies a bias current to the sense node SN.
The operation of the magnetic memory device of the tenth embodiment will now be described with reference to
First, a magnetic field is applied to the pinned layer PL as described above to improve the MR ratio while at least one of magnetic domains (to be referred to a reference section RF) in the unused area US1 is located in the MTJ structure MTJ before the shipment. The position of the reference section RF (as illustrated in
As illustrated in
In step S33, the sequencer SQ determines the current bias. Specifically, the sequencer SQ makes the signals PS and bPS low and high level, respectively, and disconnects the feedback loop FB from the sense node SN (or, disables the feedback loop FB). This results in the voltage at the gate of the transistor TP33 stored in the capacitor CP. This in turn forms a state where the voltage of the automatically-determined magnitude keeps biasing the gate of the transistor TP33.
In step S34, the sequencer SQ makes the signal SFT high from time t11 to t12. The transitioned high signal SFT makes components involved in the magnetic domain wall motion, such as the logical gates in the row decoder RD and current source/sink SC in
With the magnetization direction of the read-target magnetic domain parallel with that of the pinned layer PL, the sense node SN has the same potential as the potential VSET. This is because the bias current by the transistor TP33 is adjusted through the adjusted gate potential of the transistor TP33 to equalize the sense node SN to the potential VSET during the read of the data from the magnetic domain with the magnetization direction parallel to that of the pinned layer PL. In contrast, the magnetization direction of the read-target magnetic domain antiparallel with that of the pinned layer PL results in the high resistance of the MTJ structure MTJ, which in turn results in the higher potential of the sense node SN than the potential VSET. Then, the reference potential VREF is set higher than the potential VSET and lower than the potential of the sense node SN upon the read of the data from a magnetic domain with the magnetization direction antiparallel to that of the pinned layer PL. The potential of the sense node SN upon the read of the data from the magnetic domain with the antiparallel magnetization direction can be calculated from a theoretical value. This is because the resistances of the tunnel insulating films of the MTJ structures may greatly vary by the variation in property whereas the MR ratios of MTJ structures agree well with the theoretical values. Thus determined reference potential VREF can distinguish the parallel state and antiparallel state of the MTJ structure MTJ. Specifically, the reference potential VREF is 0.8 times the potential VSET.
Thus, for each MTJ structure MTJ, the bias current for a read which involves that MTJ structure MTJ is determined. The determined bias current is then used to execute a read. This means that variations in the properties of the MTJ structures MTJ due to variations in the properties of tunnel insulating films TIL are corrected.
In step S36, the sequencer SQ determines whether all read-target data in the magnetic thin wire ML has been read. For example, with the whole of the header HD, data area DT, and footer FT in a particular magnetic thin wire ML to be read, the determination of step S36 corresponds to whether the last piece of data in the footer FT has been read. With unread data, the flow returns to step S34.
When the determination at step S36 is Yes, the flow shifts to step S37. In step S37, the sequencer SQ controls related components to return the read position to the reference section RF in the magnetic thin wire ML. Specifically, the sequencer SQ moves the reference section RF back into the MTJ structure MTJ. The sequencer SQ moves the reference section RF back into the MTJ structure MTJ whenever a read or write in the magnetic thin wire ML is completed.
According to the tenth embodiment, the read from the magnetic domain with known stored-data is used to determine, for each MTJ structure MTJ, a bias current for a read involving that MTJ structure MTJ. The determined bias current is then used to execute the read. This results in correction of property variations in the MTJ structures MTJ due to property variations in the tunnel insulating films TIL during reads. This can in turn implement the magnetic memory device MD in which reads are possible even with property variations among components.
The eleventh embodiment relates to the arrangement of a cell array and related components based thereon.
A row controller RC and a column controller CC operates for a cell array CA in the same circuit set. The row controller RC controls and selects one or more rows in the corresponding cell array CA in accordance with an address signal. The column controller CC controls and selects columns in the corresponding cell array CA in accordance with the address signal, outputs read data from the cell array CA, and supplies write data to the cell array CA. The circuit sets including the row controller RC, column controller CC, and domain wall motion driver SG are arranged in a matrix.
Each pair of circuit sets adjacent in the same column is provided with a single preamplifier and write circuit PAW. A preamplifier and write circuit PAW is located between two corresponding circuit sets, and is coupled to the column controllers CC of these two circuit sets. The preamplifier and write circuit PAW receives from the coupled column controllers CC read current (or, data) from the corresponding cell arrays CA, and amplifies the received the read current with a preamplifier (or, preamplifier unit). In the illustrated example, each preamplifier and write circuit PAW is coupled to a single data line DTL through a cell array select transistor CST. The preamplifier and write circuits PAW of the same column are coupled to the same data line DTL via respective cell array select transistors CST. However, different preamplifier units and write circuit units in a preamplifier and write circuit PAW may be coupled to different data lines DTL through respective cell array select transistors CST. The data lines DTL are coupled to a sense amplifier SA and latch TL. The magnetic memory device MD includes components (or, functional blocks) illustrated in
The cell array CA further includes two kinds of electrodes RDL and LDL for moving the magnetic domain walls. Receiving voltage alternately, the electrodes RDL and LDL move the magnetic domains of the magnetic thin wire ML therebetween as described for other embodiments. The structure and arrangement of the magnetic thin wires ML and electrodes RDL and LDL are illustrated in
As illustrated in
A set of (or, all) the row select transistors RST belonging to the 0th column are coupled to a bit line BL_0 at the side opposite the MTJ structure MTJ. Similarly, a set of (or, all) the row select transistors RST belonging to the Qth (0≦Q≦2M−1) column are coupled to a bit line BL_Q at the side opposite the MTJ structure MTJ.
A set of (or, all) the magnetic thin wires ML belonging to the 0th column is also coupled to a bit line BL′_0 at the tops (or, the side opposite the MTJ structure MTJ). Similarly, the set of (or, all) the magnetic thin wires ML belonging to the Qth row are also coupled to a bit line BL′_Q at the side opposite the MTJ structure MTJ. The bit lines BL_0 and BL′_0 make a pair. Similarly, the bit line BL_Q and BL′_Q make a pair.
A set of (or, all) the row select transistors RST belonging to the 0th row is coupled to a word line WL_0 at the gates. Similarly, a set of (or, all) select-transistors MLST belonging to the Rth (0≦R≦QN−1) row is coupled to a word line WL_R at the gates.
The block BLK_0 is provided with two types of electrode sets, i.e., a set of electrodes LDL_0, and a set of electrodes RDL_0. Similarly, a block MB_S (0≦S≦2N-n−1) is provided with two types of electrode sets, i.e., a set of electrodes RDL_S and a set of electrodes LDL_S.
The electrodes LDL (LDL_0 to LDL_2N-n−1) extend along the x-axis, and are in a line along the z-axis direction. All electrodes LDL belonging to the same block BLK are mutually coupled at a position, such as an end of that block BLK in the x-axis direction, by a connection pattern extending in the z-direction. Therefore, all electrodes LDL belonging to the same block BLK are driven to the same potential.
Similarly, electrodes RDL (RDL_0 to RDL_2N-n−1) extend along the x-axis, and are in a line along the z-axis direction. All electrodes RDL belonging to the same block BLK are mutually coupled at a position, such as an end of that block ELK in the x-axis direction, by a connection pattern extending in the z-direction. Therefore, all electrodes RDL belonging to the same block BLK are driven to the same potential.
Furthermore, each interval between magnetic-thin-wire sets MLS is provided with a set of electrodes LDL along the z-axis or a set of electrodes RDL along z-axis. The sets of electrodes LDL in a line along the z-axis and the sets of electrodes RDL in a line along the z-axis are alternately located in a line along the y-axis. Therefore, any magnetic thin wire set MLS is provided with a set of electrodes RDL at a side along the y-axis and a set of electrodes LDL at the other side. Therefore, each magnetic thin wire ML is provided with an array of the electrodes LDL at a side, and an array of the electrodes RDL at the other side as described in other embodiments. However, the positions of the electrodes RDL on the z-axis and those of the electrode LDL on the z-axis do not match, and only a part of an electrode RDL and a part of an electrode LDL which face overlap along the z-axis.
With such arrangement of the magnetic thin wires ML and electrodes LDL and RDL, for any magnetic thin wire ML, an associated set of the electrodes LDL and an associated set of the electrodes LDL have the same relative positions to that magnetic thin wire ML as illustrated in
The row controller RC includes a block-decoder/row-decoder BRD. The row controller RC selects a single block BLK and a single word line WL in a cell array CA in accordance with the received row address signals Specifically, for example, the row controller RC includes buffers IV21 coupled to respective word lines WL_0 to WL_2N−1. The block-decoder/row-decoder BRD supplies a high-level signal to a particular word line WL selected in accordance with the row address signals via the corresponding buffer IV21.
The block-decoder/row-decoder BRD also outputs block select signals BSL_0 to BSL_2N-n−1. In order to select a block BLK specified by the row address signals, the block-decoder/row-decoder BRD supplies a selected one of the block BLK_0 to BLK_2N-n−1 with a corresponding one of block select signals BSL_0 to BSL_2N-n−1 via the corresponding buffer IV22. The block select signals BSL_0 to BSL_2N-n−1 are supplied to AND gates AND 31_0 to AND31_2N-n−1, respectively. The AND gates AND31_0 to AND31_2N-n−1 further receive the signal SFT, and output signals SFTE_0 to SFTE_2N-n 1, respectively. The signal SFTE_0 is supplied to respective gates of gate transistors TTL_0 and TTR_0. Similarly, the signal SFTE_S is supplied to respective gates of gate transistors TTL_S and TTR_S. The gate transistors TTL_0 to TTL_2N-n−1, and TTR_0 to TTR_2N-n−1 are each made of an n-type MOSFET, for example.
The signal SFT is supplied from the domain wall motion driver SG, and is generated from signals DSFT and USFT supplied from the sequencer SQ as will be described. The signals DSFT and USFT are supplied from the sequencer SQ. The signal DSFT instructs moving of the magnetic domain walls of the magnetic thin wires ML to the direction toward the substrate (or, downward along the z-axis), and the signal USFT to the direction away from the substrate (or, upward along the z-axis). Therefore, when the AND gate AND31_0 receives the block select signal BSL_0 and signal SFT, the transistors TTL_0 and TTR_0 turn on, which respectively couples the nodes SP0 and SP1 to the electrodes LDL_0 and RDL_0, which enables the magnetic domain walls to be moved in the block BLK_0. Similarly, when the AND gate AND31_S receives the block select signal BSL_S and signal SFT, the transistors TTL_S and TTR_S turn on, which respectively couples the nodes SP0 and SP1 to the electrodes LDL_S and RDL_S, which enables the magnetic domain walls to be moved in the block BLKS.
The bit lines BL— 0 to BL— 2M−1 are coupled to a read and write circuit RWC via column select transistors BLST_0 to BLST_2M−1, respectively. The bit lines BL′_0 to BL′_2M−1 are coupled to the read and write circuit RWC via column select transistors BLST′_0 to BLST′_2M−1, respectively. The transistors BLST_0 to BLST_2M−1, and BLST′_0 to BLST′_2M−1 are included in the column controller CC, for example, and each made of an n-type MOSFET. The transistors BLST_0 and BLST′_0 receive a column select signals CSL_0 at the gates. Similarly, the transistors BLST_Q and BLST′_Q receive a column select signal CSL_Q at the gates. The column select signals CSL_0 to CSL_2M−1 are supplied from a column decoder CD via inverters IV23_0 to IV23_2M−1, respectively. The column decoder CD is included in the column controller CC.
The bit lines BL′_0 to BL′_2M−1 are also coupled to an output node SP2 of the domain wall motion driver SG via transistors BLFST_0 to BLFST_2M−1, respectively. The transistors BLFST_0 to BLFST_2M−1 are each made of an n-type MOSFETs, for example, and receive the signal SFT at the gates.
Magnetic domain wall motion (or, data shifts) will now be described with reference to
The signal SFT is also supplied to the inverter IV41 via a delay element DE1. The delay element DE1 delays the input signal by the unit delay time td. The output n0 of the inverter IV41 is supplied to a NAND gate NAND22. The NAND gate NAND22 further receives the signal SFT directly and supplies the output to an inverter IV42. The output node of the inverter IV42 is coupled to the node SP0 via an n-type MOSFET TN41 and to the node SP1 via an n-type MOSFET TN42. The nodes SP0 and SP1 output signal SP0 and SP1 described above. The transistors TN41 and TN42 receive the signals DSFT and USFT at the gates, respectively.
The output of the inverter IV41 is also supplied to a NAND gate NAND23 via a delay element DE2 and an inverter IV43. The delay element DE2 delays the input signal by the unit delay time td. The output n1 of the inverter IV43 is supplied to a NAND gate NAND23. The output of the inverter IV43 is further supplied to a NAND gate NAND23 via a delay element DE3 and an inverter IV44. The NAND gate NAND23 supplies the output to an inverter IV45. The output of the inverter IV45 is supplied to the node SP1 via an n-type MOSFET TN43 and to the node SP0 via an n-type MOSFET TN44. The transistors TN43 and TN44 receive the signals DSFT and USFT at the gates, respectively.
The output n2 of the inverter IV44 is also supplied to a NAND gate NAND24. The NAND gate NAND24 further receives the signal SFT. The output of the NAND gate NAND24 is supplied to an inverter IV46. The output node of the inverter IV46 outputs a signal SP2.
The domain wall motion driver of
The signals DSFT and USFT are low before the operation as illustrated in
With the signals SFT, n0, n1, and n2 thus transitioning, the signal SP0 remains high (or, voltage VSFT) from time t20 to t21, the signal SP1 remains high (or, voltage VSFT) from time t22 to t23, and the signal SP2 remains high (or, voltage VSFT) from time t20 to t23. In other words, the signal SP1 remains high after the maintaining of high by the signal SP0. With such voltage changes, the magnetic domain walls of the selected magnetic thin wire ML move in the direction toward the substrate by a single magnetic domain.
In contrast, with the magnetic thin wire ML selected, the signal USFT is made high at time t30 as illustrated in
Reads and writes in the magnetic memory device MD of the eleventh embodiment will now be described. The magnetic thin wires ML belonging to the same row make a magnetic thin wire set MLS as described above. Moreover, electrodes LDL for motion are shared by multiple columns in a block BLK, and the electrodes RDL are also shared by columns. For this reason, the motion of magnetic domain walls is executed in units of blocks. In accordance with this, reads and writes are executed as in
One or three or more bit lines BL, however, may share a preamplifier unit PA. The preamplifier unit PA is included in the preamplifier and write circuit PAW, and is further coupled to the sense amplifier SA.
A set of magnetic domains on the same xy-plane in the selected block BLKS, which will be referred to as a magnetic domain array DA, is located in the MTJ structures MTJ, and this magnetic domain array DA is the current target for the read. A read-target magnetic domain array DA will be referred to as a selected magnetic domain array DA. First, the sequencer SQ selects the first word line WL_2nS in the selected block BLK_S. This results in the magnetic thin wires ML in the magnetic thin wire set MLS of the 2nS row coupled to the bit lines BL_0 to BL_2M−1, respectively. In this state, the sequencer SQ selects the column select signals CSL_0 to CSL_2M−1 one after another (see,
The sequencer SQ selects the next word line WL in the selected block BLK_S. The order of selection of word lines WL in the selected block BLK_S is arbitrary.
The above description is for an operation for an example with a single preamplifier unit PA provided for bit lines BL_0 to BL_2M−1. With the bit lines BL_0 to BL_2M−1 divided into groups, the magnetic memory device MD can be configured to read or write in parallel in units of groups. In such an example, preamplifier units PA in the preamplifier and write circuit PAW are coupled to respective data lines DTL via respective cell array select transistors CST, and the preamplifier units PA operate in parallel. For example, the bit lines BL_0 to BL_2M−1 are divided into a group of bit lines BL_0 to BL_2P−1, and a group of bit lines BL_2M−2P to BL_2M−1, and reads and writes are executed in parallel in units of groups. The parallel reads and writes will be described in the description of read and write sequences in detail later.
The sequencer SQ then moves the magnetic domain walls to locate the next magnetic domain array DA in the corresponding MTJ structures MTJ, or moves them to the position for read. Then, the sequencer repeats the same operation as that described above for selected magnetic domain array DA for the currently-selected magnetic domain array DA, and completes the read of the currently-selected magnetic domain array DA.
The sequencer SQ executes the operation for a single magnetic domain array DA to all the read-target magnetic domain arrays DA in the selected block BLK. For example, the sequencer SQ executes reads from all magnetic domain arrays DA in the selected block BLK_S. Thus, the read from the selected block BLK_S completes.
Referring to
The transistor TP42 and p-type MOSFET TP44 are coupled in series between the node of the potential VDDR and node n12. The gate of the transistor TP42 is coupled to the connection node between the transistors TP41 and TN51. The transistor TP44 receives an array select signal at the gate. With the cell array CA for which the preamplifier unit PA serves selected, that preamplifier unit PA receives a low-level array select signal, which turns on the transistor TP44.
Current through the cell MTJ, i.e., the node n11, is mirrored by the preamplifier unit PA, and the mirrored current flows into the sense amplifier SA from the node n12. In the sense amplifier, the node n12 is grounded via an n-type MOSFET TN53, coupled to the gate of a transistor TN53, and coupled to an inverter IV51. The output of the inverter IV51 is the output of the sense amplifier SA, and is supplied to the latch TL. With the current through the node n11, i.e., the current based on the current through the node n12, the potential of the node n12 varies. This potential is translated into the digital value of “0” or “1” by the inverter IV51, and then taken into the latch TL.
As described above, the magnetic memory device MD can have the bit lines BL_0 to BL_2M−1 divided into groups and be configured to read in parallel in units of groups.
At time t41, the sequencer SQ makes the first word line WL_0 high for selection thereof. While the word line WL_0 is selected, the sequencer SQ makes the column select signals CSL_0 to CSL_2P−1 high one after another in order to select columns. In parallel to this, the sequencer SQ makes column select signals CSL_2M-2P to CSL_2M−1 high one after another.
The sequencer SQ then maintains the column select signals CSL_1 and CSL_2M-2P+1 high from time t44 to t45 as in from time t42 to t43. As a result, the bit lines BL_1 and BL_2P+1 are applied with the voltage Vcell from time t44 to time t45 by the same operation as described for the column select signals CSL_0 and CSL_2M-2P. Thus, a current based on the MTJ structure MTJ including the magnetic domain at the intersection of the word line WL_0 and bit line BL_1 within the selected magnetic domain array DA is supplied to the preamplifier unit PA coupled to the bit line BL_1. Moreover, a current based on the MTJ structure MTJ including the magnetic domain at the intersection of the word line WL_0 and bit line BL_2M-2P+1 within the selected magnetic domain array DA is supplied to the preamplifier unit PA coupled to the bit line BL_2M-2P+1. Similarly, the sequencer SQ makes multiple or, for example, all column select signals CSL in a single block BLK high at least once by time t48 while the word line WL_0 is high. Specifically, the sequencer SQ makes the column select signals CSL_0 to CSL_2P−1 high one after another, and column select signals CSL_2M-2P to CSL_2M−1 high one after another. As a result, the data of the magnetic domain at each intersection between the word line WL_0 and bit lines BL_0 to BL_2M−1 within the selected magnetic domain array DA in total is read sequentially.
A parallel read from three or more groups can also be implemented by executing the two-group parallel read described so far to the three or more groups. In contrast, in an example with the magnetic memory device MD not supporting parallel reads of bit-line groups, the column select signals CSL_0 to CSL_2M−1 in a single block BLK are made high one after another while the word line WL_0 is high.
After time t48, the sequencer SQ makes the word line WL_0 low at time t49.
The sequencer SQ repeats the operation for a single word line WL from time t41 to t49 for the remaining word lines WL in the block BLK_0 from time t51 to t55. Thus, the read from a single selected magnetic domain array completes.
The sequencer SQ maintains all bit lines BL′_0 to BL′_2M−1, all electrodes LDL_0 to LDL_2N-n−1, all electrodes RDL_0 to RDL_2N-n−1, the signals DSFT and USFT, all word lines WL in unselected blocks, and all block select signals BSL_0 to BSL_2N-n−1 low from time t41 to t55.
The sequencer SQ then selects the next magnetic domain array DA in the selected block.
The column select signals CSL_0 to CSL_2M−1 are low due to wall motion, and therefore the column select transistors BLST′_0 to BLST′_2M−1 are off. Because of the high signal SFT, the transistors BLFST_0 to BLFST_2M−1 are on to result in the voltage VSFT applied to the bit lines BL′_0 to BL′_2M−1 via the transistors BLFST_0 to BLFST_2M−1. The purpose of such application is to accommodate a case where application of a negative electric field to the magnetic thin wires ML of the selected block BLK_0 from the electrodes LDL_0 and RDL_0 moves the magnetic domain wall to allow a negative electric field to be applied to the magnetic thin wire ML from the electrodes LDL and RDL without generating a negative voltage lower than the voltage VSS.
Referring to
The write circuit unit WCU has a section WCU0 for 0-data write, and a section WCU1 for 1-data write. These sections each include a current mirror circuit, and conduct respective currents for the 0-data write and 1-data write to the node nW. The 1-data write section WCU1 includes a p-type MOSFET TP51 and an n-type MOSFET TN64 coupled in series between the supply node of a potential VDDW and the node nW, and a p-type MOSFET TP52 and a current source ISW1. The potential VDDW is higher than the intermediate potential Vm and high enough to allow the transistors TP51, TP52, TN67, and TN68 to execute the pentode operation. The transistor TN64 receives the signal WR1 at the gate. The transistor TP52 and current source ISW1 are coupled in series between the supply node of potential VDDW and ground node. The transistor TP52 has the gate coupled to its own drain and the gate of the transistor TP51. The current source ISW1 conducts the current for writing 1-data. A high signal WR1 enables the 1-data-write section WCU1, and the signal WR1 is maintained to be high while the 1-data-write current is being supplied to the bit lines BL.
The 0-data-write section WCU0 includes n-type MOSFETs TN66 and TN67 coupled in series between the node nW and ground node, an n-type MOSFET TN68, and a current source ISW0. The transistor TN66 receives the signal WR0 at the gate. The current source ISW1 and transistor TN68 is coupled in series between the supply node of potential VDDW and the ground node. The transistor TN68 has the gate coupled to its own drain and the gate of the transistor TN67. The current source ISW0 conducts the current for writing 0-data. A high signal WR0 enables the 0-data-write section WCU0, and the signal WR0 is maintained to be high while the 0-data-write current is being supplied to the bit lines BL.
As described above, the magnetic memory device MD can have the bit lines BL_0 to BL_2M−1 divided into groups and be configured to write in parallel in units of groups.
First of all, the signal WRT (not shown) remains high during the write including the period of
At time t72, the sequencer SQ makes the first word line WL_0 high for selection thereof. While the word line WL_0 is selected, the sequencer SQ makes the column select signals CSL_0 to CSL_2W−1 high one after another in order to select columns. In parallel with this, the sequencer SQ makes the column select signals CSL_2M-2W to CSL_2M−1 high one after another.
The sequencer SQ then maintains the column select signals CSL_1 and CSL_2M-2W+1 high from time t75 to t77 as in from time t73 to t74. As a result, bit line BL_1 is coupled to the node nW of the write circuit unit WCU, and bit lines BL_2M-2W+1 to the node nW of another write circuit unit WCU as illustrated in
A parallel write to three or more groups can also be implemented by executing the two-group parallel write described so far to the three or more groups. In contrast, in an example with the magnetic memory device MD not supporting parallel writes of bit-line groups, the column select signals CSL_0 to CSL_2M−1 in a single block BLK are made high one after another while the word line WL_0 is high.
The sequencer SQ makes the word line WL_0 low at time t80 after time t79.
The sequencer SQ repeats the operation for a single word line WL from time t72 to t80 for the remaining word lines WL in the block BLK_0 until time t81. Thus, the write to a single selected magnetic domain array DA completes.
The sequencer SQ maintains all electrodes LDL_0 to LDL_2N-n−1, all electrodes RDL_0 to RDL_2N-n−1, signals DSFT and USFT, all word lines WL in the unselected blocks, and all block select signals BSL_0 to BSL_2N-n−1 low from time t71 to t80.
Following the completion of the write to the selected magnetic domain array DA, the sequencer SQ makes all column select signals CSL_0 to CSL_2M−1 high to turn on the column select transistors BLST_0 to BLST_2M−1 from time t82 to t83. This discharges the bit line BL_0 to BL_2M−1 to the potential VSS.
The sequencer SQ then selects the next magnetic domain array DA in the selected block. The selection of the next magnetic domain array DA is the same as described with reference to
According to the eleventh embodiment, multiple rows (or, multiple magnetic thin wire sets MLS) have the magnetic domains moved together. This makes many magnetic thin wires ML targeted for a read, and accommodating this by providing the sense amplifier SA in an area with packed cell arrays CA would require a large area. This is because sense amplifiers generally have large areas. To address this, preamplifiers, which have small areas, are provided in the area with packed cell arrays CA, and in addition, a single preamplifier and write circuit PAW is shared by adjacent cell arrays CA (or, circuit sets). This allows for magnetic domain motion and data reads and writes in units of blocks with suppression of an increase of the area.
The twelfth embodiment relates to modification of the eleventh embodiment.
According to the twelfth embodiment, multiple rows have the magnetic domains moved together, and preamplifiers, which have small areas, are provided in the area with packed cell arrays CA, and in addition a single preamplifier and write circuit PAW is shared by adjacent cell arrays CA (or, circuit sets). This can produce the same advantages as the eleventh embodiment. Moreover, according to the twelfth embodiment, bit lines BL′ are coupled between the MTJ structures MTJ and magnetic thin wires ML. This avoids generation of a potential difference between the opposite ends of the respective magnetic thin wires ML during reads and writes, and therefore current does not flow through the magnetic thin wires ML. This in turn prevents unintentional motion of the magnetic domain walls due to currents through the magnetic thin wires ML during reads or writes.
The thirteenth embodiment relates to a modification of the eleventh embodiment.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
This application claims the benefit of U.S. Provisional Application No. 61/875,461, filed Sep. 9, 2013, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61875461 | Sep 2013 | US |
