CN102683581B - A voltage-adjustable magnetoresistive random access memory unit and its random access memory - Google Patents

Abstract

The invention provides a voltage-adjustable reluctance-variable random memory cell which comprises a bottom electrode layer, a ferroelectric oxide layer formed on the bottom electrode layer and a magnetic layer formed on the ferroelectric oxide layer, wherein the magnetic layer and the bottom electrode layer are respectively used as the upper and lower electrodes of the ferroelectric oxide layer to apply voltage on the ferroelectric oxide layer, the voltage direction is perpendicular to the ferroelectric oxide layer, and the ferroelectric oxide layer can adjust and control the arrangement of magnetic moment in the magnetic layer under the action of the voltage, so that the resistance of the magnetic layer in the set measuring direction changes. The invention also provides a memory with the reluctance-variable random memory cell. According to the invention, information data can be written by the voltage, and the voltage-adjustable reluctance-variable random memory cell has the advantages of nonvolatility, low writing power consumption, high storage density and the like.

Description

A voltage-adjustable magnetoresistive random access memory unit and its random access memory

technical field

The invention relates to the technical field of random storage, in particular to a magnetoresistive variable random storage unit with adjustable voltage and a random storage unit with the storage unit.

Background technique

Magneto-resistive random access memory (MRAM) is considered to be one of the most promising next-generation embedded memories to be widely used because of its good durability and non-volatile storage characteristics. Its core working component is a stacked magnetoresistive random memory unit with a sandwich structure of "magnetic free layer/oxide tunneling insulating layer/magnetic pinned layer". Its working principle is that the ampere current passing through the bit line and the data line is used to generate a magnetic field, and the magnetization vector in the magnetic free layer is rotated through the magnetic field, so that the angle between the magnetization direction between the magnetic free layer and the magnetic pinned layer changes, thereby Two resistance states, high and low, are generated in the memory cell, corresponding to the two states of "0" and "1" of the data. The problem with MRRAM is that as the size of the memory cell shrinks, it will become increasingly difficult to generate a magnetic field through a current within the specified memory cell while ensuring that it does not have a large impact on the storage state of adjacent memory cells. The more difficult it is, this restricts the improvement of the recording density of the memory. In addition, the ampere current density per unit volume will also increase sharply, resulting in more heat loss and deteriorating device performance.

In order to solve these two problems, the current technical route is to use the magnetoresistive random access memory (STT-RAM) based on spin torque transfer, which uses the spin current to directly change the direction of the magnetization vector of the magnetic free layer in the storage unit. Regulation to complete the state writing, and does not need to use the magnetic field generated by the ampere current as an indirect means. The spin current density required by this kind of memory does not increase significantly as the volume of the memory cell decreases, which can alleviate the problems of difficulty in increasing the recording density and excessive power consumption in traditional magnetoresistive random access memory to a certain extent. However, since the state is still written in the current mode, the predictable power consumption of the memory will still be higher than that of the state written in the pure voltage mode, such as flash memory (FLASH) based on semiconductor CMOS elements, ferroelectric random access memory (FeRAM) and other embedded RAM. In addition, the direction of the write current and the read current in the spin torque transfer based magnetoresistive random access memory are both perpendicular to the stacked memory cell, which increases the risk of dielectric breakdown in the tunneling insulating layer in the memory cell , thereby affecting the durability of the storage device.

On the other hand, although the flash memory and the ferroelectric random access memory have low power consumption, they also have their own shortcomings. Wherein, the flash memory utilizes the charging and discharging of the semiconductor capacitive element to realize data recording, and the writing time is relatively long; the ferroelectric RAM utilizes the ferroelectric polarization direction of the ferroelectric material to realize data storage, although the writing speed is relatively fast, However, the reading method is destructive, that is, the stored data cannot be retained after the data is read. Moreover, as time goes on, the remnant polarization intensity of the ferroelectric film in the memory gradually decreases, which will cause the memory to be unable to correctly distinguish the two polarization states of "0" and "1" and thus fail. Table 1 compares the several different non-volatile embedded random access memories.

Table 1. Comparison of several different non-volatile embedded RAMs

Contents of the invention

The object of the present invention is to at least solve one of the above-mentioned technical defects such as low storage density, high power consumption, and slow writing speed.

Therefore, the first object of the present invention is to provide a voltage-adjustable magnetoresistive random access memory unit, which utilizes the principle of the magnetoelectric effect to control the magnetic layer by applying a voltage perpendicular to the direction of the ferroelectric oxide layer. The direction of the magnetic moment, so that its resistance in the set measurement direction changes.

The second object of the present invention is to provide a random access memory having the voltage-adjustable magnetoresistive random access memory unit.

In order to achieve the above object, the embodiment of the first aspect of the present invention proposes a voltage-adjustable magnetoresistive random access memory unit, comprising: a bottom electrode layer; a ferroelectric oxide layer formed on the bottom electrode layer; The magnetic layer on the ferroelectric oxide layer; the magnetic layer and the bottom electrode layer are respectively used as the upper and lower electrodes of the ferroelectric oxide layer to apply voltage to the ferroelectric oxide layer, wherein the The direction of the voltage is perpendicular to the ferroelectric oxide layer, and the ferroelectric oxide layer controls the rotation of the magnetic moment in the magnetic layer through magnetoelectric coupling under the action of the voltage so that the magnetic layer is set to The resistance changes in the direction of measurement.

In one embodiment of the present invention, the ferroelectric oxide layer comprises any one of the following materials: barium titanate with (001), (011) or (111) orientation, lead zirconate titanate, ferrite Bismuth, bismuth titanate-lead titanate, lead magnesium niobate-lead titanate, and lead niobate zincate-lead titanate.

In one embodiment of the present invention, the magnetic layer includes one or more of the following materials: iron, nickel, cobalt, nickel-iron alloy, cobalt-iron alloy, nickel-iron-cobalt alloy, cobalt-iron-boron alloy and other materials containing iron, An alloy of cobalt and nickel.

The embodiment of the second aspect of the present invention proposes a voltage-adjustable magnetoresistive random access memory, including: a random memory cell array, including a plurality of voltage-adjustable magnetoresistive random access memory cells according to the embodiment of the first aspect of the present invention a plurality of access transistors, each of which is connected to the bottom electrode layer of each of the random memory cells, and each of the access transistors has a source, a gate and a drain; a plurality of word lines, each The word line is connected to the gate of each of the access transistors, and is used to control the on-off between the source and the drain of the access transistor; a plurality of plate lines, and the plate lines are perpendicular to the word lines , and each of the plate lines is connected to the bottom electrode layer of each of the magnetoelectric random access memory cells; a plurality of first bit lines, the first bit lines are parallel to the word lines, and each of the first bit lines A bit line is connected to the magnetic layer of each of the random memory cells; a plurality of second bit lines, the second bit lines are perpendicular to the word line, and each of the second bit lines is connected to each of the The source of the access transistor is connected; and a plurality of interconnection lines, one end of each interconnection line is connected with the drain of each access transistor, and the other end of each interconnection line is connected with each random memory unit The magnetic layer is connected.

In one embodiment of the present invention, when a write operation is performed, the word line controls the source and drain of the corresponding access transistor to be turned on, and applies a voltage between the corresponding second bit line and the plate line so as to Magnetoelectric coupling occurs between the ferroelectric oxide layer and the magnetic layer to control the direction of the magnetic moment of the magnetic layer to deflect.

In one embodiment of the present invention, when performing a read operation, the stored information of the random memory unit is read through the second bit line and the first bit line.

In one embodiment of the present invention, the voltage-adjustable magnetoresistive random access memory further includes: a bit line selection circuit connected to the plurality of word lines, for selecting random memory cells in the random access memory .

The embodiment of the present invention adopts the multiferroic magnetoelectric composite film structure as the main part of the voltage-adjustable magnetoresistive variable random storage device, and utilizes the magnetoelectric coupling effect between the ferroelectric oxide layer and the magnetic layer, through the voltage to the magnetic The alignment direction of the magnetic moment in the layer is modulated to realize the writing of information data with voltage. Compared with the current-driven magnetoresistive random access memory, the writing power consumption is significantly reduced. Memory cells generate interference, which can reduce the distance between memory cells and increase storage density. The voltage-adjustable MRRAM proposed by the embodiments of the present invention has the characteristics of non-volatility, high storage density, low writing power consumption, and fast working speed. In addition, the embodiment of the present invention uses the magnetic layer and the bottom electrode layer as the upper and lower electrodes of the ferroelectric oxide layer to apply a vertical voltage, the layout is reasonable, the space is saved, and the number of interconnection lines used in the RAM is reduced.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and easy to understand from the following description of the embodiments in conjunction with the accompanying drawings, wherein:

Fig. 1 is a schematic structural diagram of a voltage-adjustable magnetoresistive random access memory unit and a random access memory with the unit according to an embodiment of the present invention;

2 is a schematic cross-sectional view of a voltage-adjustable magnetoresistive random access memory unit according to an embodiment of the present invention;

3 is a circuit diagram of a voltage-adjustable MRRAM according to an embodiment of the present invention;

FIG. 4 is a graph showing the variation of the resistance value of the voltage-adjustable magnetoresistive random access memory cell under the action of voltage in one embodiment of the present invention.

Explanation of reference signs:

1-Voltage-adjustable magnetoresistive random access memory unit 2-Bottom electrode layer

3-Ferroelectric oxide layer 4-Magnetic layer

5-word line 6-board line

7-The first bit line 8-The second bit line

9-Interconnect wire 10-Access transistor

11-Source 12-Gate

13-drain

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

In the description of the present invention, the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right" etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention. There is no requirement that the invention be constructed and operated in a particular orientation, and thus no limitation should be construed.

The structures and methods according to the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The present invention mainly adjusts the magnetic moment arrangement direction of the magnetic layer through voltage. Based on the anisotropic magnetoresistance effect, the change of the magnetic moment arrangement direction will cause the resistance state of the magnetic layer in the set measurement direction to change, thereby completing the data writing. Enter operation. This way of writing through voltage can overcome the problems of excessive power consumption caused by writing current in the existing MRRAM and the interference of the spatial magnetic field generated by the current on adjacent cells. In the present invention, the regulation of voltage on the magnetic moment arrangement direction of the magnetic layer is realized through the magnetoelectric coupling effect between the magnetic layer and the ferroelectric oxide layer. This laminated composite film of magnetic layer and ferroelectric oxide layer is also called multiferroic magnetoelectric composite film, which can be prepared by various physical methods such as pulsed laser deposition, magnetron sputtering and sol-gel Preparation methods such as chemical preparation methods. In 2009, J.-M.Hu of Tsinghua University, etc. used thermodynamic calculations to confirm that in the multiferroic magnetoelectric laminated composite film in which the lower layer is a ferroelectric oxide and the upper layer is a magnetic alloy film, by applying The voltage can also cause the magnetic moment alignment direction of the magnetic layer to deflect in the film plane. In January 2011, Wu Tao et al. from the University of California, Los Angeles observed in the Ni/[011]-PMN-PT single crystal system that as the voltage is applied to the PMN-PT in the direction perpendicular to the surface of the single crystal, the magnetic moment of Ni The alignment direction is deflected in the plane of the Ni film, which is a typical experimental example of voltage-regulated magnetic moment alignment of the magnetic film based on the magnetoelectric coupling effect.

According to an embodiment of the present invention, the present invention provides a voltage-adjustable magnetoresistive random access memory unit 1 and a random access memory with the unit, as shown in FIG. 1 . The voltage-adjustable magnetoresistive random access memory unit 1 adopts the structural type of a multilayer composite film. In this embodiment, the multilayer composite film structure includes a bottom electrode layer 2, a ferroelectric oxide layer 3, The magnetic layer 4 is shown in FIG. 2 .

The bottom electrode layer 2 and the magnetic layer 4 are used as the lower and upper electrodes of the ferroelectric oxide layer 3 to apply voltage to the ferroelectric oxide layer 3, and the direction of the applied voltage is perpendicular to the plane of the multilayer composite film. The ferroelectric oxide layer 3 controls the arrangement of magnetic moments in the magnetic layer 4 to deflect through magnetoelectric coupling under the action of a voltage, and different deflection directions correspond to different writing voltage information. The deflection of the alignment direction of the magnetic moments in the magnetic layer 4 can cause the resistance between any fixed and non-overlapping points in the magnetic layer to change. The first bit line 7 and the interconnection line 9 communicate with the magnetic layer 4 respectively, and the connection points are fixed and do not overlap. Therefore, changing the alignment direction of the magnetic moments in the magnetic layer 4 can lead to a change in the resistance between the first bit line 7 and the interconnection line 9 .

The present invention adopts the multiferroic magnetoelectric composite film as the main part of the voltage-adjustable magnetoresistive variable random storage unit 1, and utilizes the magnetoelectric coupling effect between the ferroelectric oxide layer 3 and the magnetic layer 4 to control the ferromagnetism by the electric field. The arrangement of the magnetic moments in the free layer 4 is modulated, realizing the writing of information data with the electric field. Compared with the magnetoresistive random access memory in the prior art, it has the characteristics of high storage density, low writing power consumption and fast working speed.

According to an embodiment of the present invention, the ferroelectric oxide layer 3 is preferably, but not limited to, barium titanate, lead zirconate titanate, bismuth ferrite, bismuth titanate-titanate with (011) or (111) orientation Lead, lead magnesium niobate-lead titanate and lead niobate zincate-lead titanate and other materials to form.

According to an embodiment of the present invention, the magnetic layer 4 is preferably but not limited to iron (Fe), nickel (Ni), cobalt (Co), nickel-iron alloy (NiFe), cobalt-iron alloy (CoFe), nickel-iron-cobalt alloy ( NiFeCo), cobalt-iron-boron alloy (CoFeB), or other alloys containing Fe, Co, and Ni.

In addition, the bottom electrode layer 2 can be formed using metal or oxide materials known in the art.

The circuit structure of the random access memory with the voltage-adjustable magnetoresistive random access memory unit 1 is shown in Fig. word line 5, a plurality of plate lines 6 perpendicular to the word line 5, a plurality of first bit lines 7 parallel to the word line 5, and a plurality of second bit lines 8 perpendicular to the word line 5, A plurality of interconnection lines 9 and a plurality of access transistors 10 .

More specifically, the word line 5 is connected to the gate 12 of the access transistor 10 for controlling the on-off between the source 11 and the drain 13 of the access transistor 10; the second bit line 8 is connected to the source 11 of the access transistor 10 connected; one end of the interconnection line 9 is connected to the drain 13 of the access transistor 10, and the other end is connected to the magnetic layer 4 of the voltage-adjustable magnetoresistive variable random memory unit 1; when the word line 5 has a high-level signal, The voltage signal between the second bit line 8 and the plate line 6 can directly act on the ferroelectric oxide layer 3 of the voltage-adjustable magnetoresistive random memory cell 1; wherein, the high level on the word line 5 The signal refers to a signal exceeding a threshold voltage required to conduct the source 11 and the drain 13 of the access transistor 10 to each other.

The first bit line 7 of the voltage-adjustable MRRAM is connected to the magnetic layer 4 of the voltage-adjustable MRRAM unit 1, and the first bit line 7 is connected to the magnetic layer 4 of the interconnection line 9. The change of moment arrangement can cause the resistance between the first bit line 7 and the interconnection line 9 to change. When a high-level signal is passed on the word line 5, the resistance can be detected through the first bit line 7 and the second bit line 8. Variety.

The voltage signal written into the voltage-adjustable magnetoresistive variable random memory cell 1 is applied through the second bit line 8 and the plate line 6; the circuit for reading the memory resistance change signal is connected to the second bit line 8 and the first bit line 7 on.

In one embodiment of the present invention, it also includes a circuit for selecting storage cells in the memory, and a circuit for selecting different voltage-adjustable magnetoresistive random access memory cells 1 in the voltage-adjustable magnetoresistive random access memory. The decoder is connected to the plate line 6, and the column decoder is connected to the word line 5, and different voltage-adjustable magnetoresistive random memory cells can be selected and operated through the row and column decoders.

The voltage-adjustable magnetoresistive random access memory mentioned in the embodiments of the present invention can be deposited and prepared by processes and methods known in the art that are compatible with the semiconductor industry, such as physical vapor deposition (PVD), chemical vapor deposition (CVD) ), photolithography and other film preparation, etching and wiring, etc. Of course, the voltage-adjustable magnetoresistive random access memory device can also be deposited and prepared by other physical or chemical film preparation methods.

The structure of the magnetoelectric random access memory unit of the present invention will be further described below by way of embodiments.

The ferroelectric oxide layer 3 is prepared as lead magnesium niobate-lead titanate (PMN-PT) with (001) orientation, and a 5nm thick polycrystalline nickel (Ni) film 4 is deposited on it as a magnetic layer. The magnetic layer 4 obtained by the etching technique has a length of 64 nm and a width of 64 nm. Apply a voltage perpendicular to the thickness direction of the film in the ferroelectric oxide layer 3. Figure 4 shows the variation of the resistance change rate of the magnetic film layer with the voltage applied to the ferroelectric oxide layer 3. In this system, the critical switching voltage V ^cr about 0.28V.

As shown in Figure 1, when the sample of the embodiment is first applied with a negative voltage (the voltage of the plate line 6 is higher than V ^cr , and the voltage of the second bit line 8 is 0), the sample resistance occurs from a low-resistance state at a place exceeding the critical voltage A sudden change to a high-resistance state; continue to increase the voltage in this direction, and the resistance state remains unchanged. The sample remained in a high-resistance state when the voltage was reduced to zero. When a voltage is applied to the second bit line 8 and the plate line 6 remains at 0, after the critical switching voltage is exceeded, the resistance state of the sample changes from the original high resistance state to a low resistance state, and the low resistance state is maintained when the voltage continues to increase . When the voltage is reduced to zero, the sample remains in a low-resistance state, because the resistance state of the sample in the example can be maintained after the voltage is withdrawn no matter under the action of forward or reverse voltage, which shows that the random memory cell 1 is non-volatile with storage.

The embodiment of the present invention adopts the "magnetic/ferroelectric" laminated composite thin film structure as the main part of the voltage-adjustable magnetoresistive random storage device, and utilizes the magnetoelectric coupling between the ferroelectric oxide layer and the magnetic layer and the magnetic thin film The anisotropic magnetoresistance effect, through the electric field to modulate the direction of the magnetic moments in the magnetic layer, realizes the writing of information data with voltage, compared with the commercial magnetoresistive RAM, it reduces the power consumption of writing, and because There is no interference of the spatial magnetic field generated by the writing current on the adjacent memory cells, which can reduce the distance between the memory cells and increase the storage density. The voltage-adjustable MRRAM proposed by the embodiments of the present invention has the characteristics of non-volatility, low writing power consumption, and high storage density. In addition, the embodiment of the present invention uses the magnetic layer and the bottom electrode layer as the upper and lower electrodes of the ferroelectric oxide layer to apply a vertical voltage, which has a reasonable layout, saves space, and reduces the number of connection lines used in the random access memory.

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications and substitutions can be made to these embodiments without departing from the principle and spirit of the present invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (5)

1. A voltage-adjustable magnetoresistive random access memory unit, characterized in that, comprising: bottom electrode layer; a ferroelectric oxide layer formed over the bottom electrode layer; and a magnetic layer formed over the ferroelectric oxide layer; Wherein, the magnetic layer and the bottom electrode layer respectively act as upper and lower electrodes of the ferroelectric oxide layer to apply a voltage to the ferroelectric oxide layer, wherein the direction of the voltage is perpendicular to the direction of the ferroelectric oxide layer. layer, the ferroelectric oxide layer can regulate the arrangement of magnetic moments in the magnetic layer under the action of the voltage, so that the resistance of the magnetic layer in the set measurement direction changes; The ferroelectric oxide layer includes any one of the following materials: barium titanate, lead zirconate titanate, bismuth ferrite, bismuth titanate-lead titanate with (001), (011) or (111) orientation , lead magnesium niobate-lead titanate and lead niobate zincate-lead titanate; The magnetic layer includes one or more of the following materials: Fe, Ni, Co, NiFe, CoFe, NiFeCo, CoFeB or alloy materials containing Fe, CO, Ni. 2. A magnetoresistive random access memory, characterized in that, comprising: An array of magnetoresistive random memory cells, the array of magnetoresistive random memory cells comprising a plurality of voltage-adjustable magnetoresistive random memory cells according to claim 1; A plurality of access transistors, each of the access transistors is connected to the magnetic layer of each of the voltage-adjustable magnetoresistive random memory cells, and each of the access transistors has a source, a gate, and a drain; a plurality of word lines, each of which is connected to the gate of each of the access transistors, and is used to control the on-off between the source and drain of the access transistors; a plurality of plate lines, the plate lines are perpendicular to the word lines, and each of the plate lines is connected to the bottom electrode layer of each voltage-adjustable magnetoresistive random memory unit; a plurality of first bit lines, the first bit lines are parallel to the word lines, and each of the first bit lines is connected to the magnetic layer of each voltage-adjustable magnetoresistive random memory unit; a plurality of second bit lines, the second bit lines are perpendicular to the word line, and each of the second bit lines is connected to the source of each of the access transistors; and A plurality of interconnection lines, one end of each interconnection line is connected to the drain of each access transistor, and the other end of each interconnection line is connected to each voltage-adjustable magnetoresistive variable random memory unit The magnetic layer is connected, wherein the connection point between the interconnection line and the magnetic layer does not coincide with the connection point between the first bit line and the magnetic layer, and the interconnection line and the first bit line can be connected to each other. The change in in-plane resistance of the magnetic layer is measured. 3. The magnetoresistive variable random access memory according to claim 2, characterized in that, when performing a write operation, the word line controls the source and drain of the corresponding access transistor to be turned on, and the corresponding second bit line A voltage is applied between the wire and the plate wire, so that the ferroelectric oxide layer controls the arrangement of magnetic moments in the magnetic layer to change. 4. The magnetoresistive random access memory according to claim 2, wherein, when performing a read operation, the magnetoresistive random access memory unit is read through the second bit line and the first bit line store information. 5. The MRRAM according to claim 2, further comprising: The column decoder connected to the plurality of word lines, and the row decoder connected to the plurality of plate lines are used to select the voltage-adjustable magnetoresistive random access memory unit in the magnetoresistive random access memory.