KR100772797B1 - Magnetoresistive RAM, cell and array thereof - Google Patents

Abstract

The present invention provides at least one magnetoresistive RAM (MRAM), which reads and writes data by providing a magnetic tunnel junction (MTJ) between a gate metal electrode and a subchannel. The above-described MRAM cells relate to an MRAM cell array configured on a bit line and a word line, and an MRAM cell storing at least two or more data. Therefore, the MRAM cell can be configured with a simple structure, and thus the cell array and the structure of the MRAM can be improved, thereby improving the process therefor, and reducing the cell size of the MRAM and improving the sensing margin.

Description

Magnetoresistive RAM and its cell and array

1 shows a conventional MRAM cell array.

2A and 2B are schematic diagrams of a typical MTJ.

3A and 3B are cross-sectional views showing the structure of an MRAM cell according to the present invention.

4 is an exemplary diagram of an MRAM device according to the present invention.

5 is a graph showing voltage versus current characteristics of an MRAM device according to the present invention.

6 is a circuit diagram illustrating an embodiment of an MRAM cell array in accordance with the present invention.

7 is an operation timing diagram of an MRAM cell array according to the present invention.

8 is a timing diagram of an operation during writing of an MRAM cell array according to the present invention.

9 is a circuit diagram illustrating another embodiment of a cell array using MRAM cells according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetoresistive random access memory (MRAM). In particular, the present invention provides an MTJ (Magnetic Tunnel Junction, MTJ) between a gate metal electrode and a subchannel. A read / write MRAM, an MRAM cell array in which at least one of the MRAM cells is configured on a bit line and a word line, and an MRAM cell storing at least two or more data.

Most semiconductor memory manufacturers are developing MRAM using ferromagnetic materials as one of the next generation memory devices.

MRAM is a type of memory that stores a magnetic polarization state in a thin film of magnetic material. The write and read operation is performed by changing or detecting a magnetic polarization state by a magnetic field generated by a combination of bit line current and word line current. This is done.

Such MRAM is generally composed of various cell types such as Giant Magneto Resistance (GMR) and Magnetic Tunnel Junction (MTJ).

In other words, MRAM implements a memory device by using a large magnetoresistance (GMR) phenomenon or spin polarization magnetic permeation phenomenon, which occurs because spin has a great influence on electron transfer.

First, an MRAM using a giant magnetoresistance (GMR) phenomenon is implemented using a phenomenon in which the resistance in the case where the spin directions are different in the two magnetic layers having a nonmagnetic layer between them is significantly different.

In addition, the MRAM using the spin polarization magnetic permeation phenomenon is implemented by using the phenomenon that current transmission occurs much better than the case where the spin direction is the same in the two magnetic layers having the insulating layer interposed therebetween.

This conventional MRAM has a 1T + 1MTJ structure having one switching element and one MTJ as shown in FIG. 1.

Specifically, the MRAM cell includes a plurality of word lines WL1 to WL4, a plurality of bit lines BL1 and BL2, and a cell 1 selected by them, and sense amplifiers SA1 and SA2 connected to the plurality of bit lines BL1 and BL2. It is provided.

The MTJ is operated in the same structure as in FIGS. 2A and 2B.

Specifically, the MTJ is formed by stacking a free ferromagnetic layer 2, a tunnel junction layer 3, and a fixed ferromagnetic layer 4. Here, the free ferromagnetic layer 2 and the fixed ferromagnetic layer 4 usually have a material such as NiFeCo / CoFe, and the tunnel junction layer 3 has a material such as Al ₂ O ₃ .

In addition, the free ferromagnetic layer 2 and the fixed ferromagnetic layer 4 have different thicknesses, and thus the fixed ferromagnetic layer 4 has a changed magnetic polarization state in a strong magnetic field, and the free ferromagnetic layer 2 has a weak magnetic field. The magnetic polarization state changes at.

In FIG. 2A, the free ferromagnetic layer 2 and the fixed ferromagnetic layer 4 have the same magnetization direction, in which case the sensing current increases. In addition, in FIG. 2B, the free ferromagnetic layer 2 and the fixed ferromagnetic layer 4 have a small sensing current because the magnetization directions are opposite.

Here, the magnetization direction of the free ferromagnetic layer 2 is changed by an external magnetic field, and information of "0" or "1" is stored in accordance with the magnetization direction of the free ferromagnetic layer 2.                         

Therefore, at the time of writing, the fixed ferromagnetic layer 4 does not change the magnetic polarization state, but only the free ferromagnetic layer 2 generates a magnetic field in which the magnetic polarization state is changed.

However, the conventional MRAM cell operated as described above has a 1T + 1MTJ structure, which makes the cell structure complicated. Therefore, a process for implementing a cell of a complicated structure is difficult. In addition, conventional MRAM cells are also disadvantageous in terms of cell size due to their structural problems.

The present invention has been made to solve the above problems, and an object of the present invention is to implement an MRAM cell having a simple structure for storing two or more data by coupling an MTJ element to a gate of a switching element, and having a small cell size burden. In implementing MRAM.

Another object of the present invention is to implement an MRAM cell array and an MRAM using a bipolar type MRAM cell employing MTJ.

MRAM according to the present invention for achieving the above object is a plurality of word lines and bit lines, a plurality of sense amplifiers and each word line and each connected to each bit line to sense the current supplied to the bit line and outputs the data It is configured to correspond to the bit line unit, the MTJ is coupled to the gate connected to the word line, the data is written according to the polarity of the current between the drain and the small source, the current corresponding to the data according to the magnetization direction of the MTJ An MRAM cell is outputted to read data.

It is preferred here that either the drain or the source is connected to the cell plate.

In addition, the MRAM according to the present invention is commonly connected to each of a plurality of word lines, a plurality of bit lines and a plurality of bit line bars, a pair of each bit line and a bit line bar, and supplied to a plurality of bit lines and a plurality of bit line bars. A plurality of sense amplifiers configured to sense a current to be output as data, a first MTJ configured at a first gate, corresponding to each word line and each bit line unit, and configured to read and write data; A second MTJ is configured at a second gate, and has a second MRAM cell configured to correspond to each word line and each bit line bar, and read and write data opposite to data stored in the first MRAM cell. It has a memory cell.

In this case, one of the source and the drain is preferably connected to the cell plate.

In the MRAM cell of the present invention, the MTJ magnetization state is determined according to the polarity of the current between the source and the gate because an MTJ for data write and read is formed between the gate contact region formed on the insulating film and the word line thereon. The data is written, and the amount of current flowing from the drain to the source is determined by the tunneling current generated differently according to the magnetization state of the MTJ at a constant trigger voltage, thereby reading the data.

In the MRAM cell array according to the present invention, an MRAM cell including an MTJ including data reads and writes according to a change in magnetization state is connected to one bit line and one word line in a gate connected to a word line. The plurality of memory cells are repeatedly connected to rows and columns, and either one of a source and a drain is connected to a cell plate.

In addition, in the MRAM cell array according to the present invention, a first MRAM cell in which a first MTJ in which data reads and writes are performed according to a change in magnetization state is formed in a first gate connected to a word line, wherein one bit line and one word are used. A second MRAM cell connected to a line and having a second MTJ configured to read and write data according to a change in magnetization state at a second gate connected to a word line is connected to one bit line bar and a word line to form a memory cell. The plurality of memory cells are repeatedly connected to the row and the column, and either the source or the drain is connected to the cell plate.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention.

The present invention employs an MTJ in a gate of a switching element configured to form an MRAM cell, and constitutes an MTJ between a gate metal electrode and a subchannel, and allows a different amount of current to flow depending on the magnetization direction of the MTJ 15. By controlling the current between the drain and the source of the switching element, an MRAM cell for storing two or more data is constructed.

3A and 3B, an MRAM cell according to the present invention includes an N + region and a gate contact region for forming a source contact region 31 and a drain contact region 32 on an insulating layer 34, which is a substrate. A contact layer 35 having a P + region for forming 33 is formed.

The barrier film 20 is formed on the gate contact region 33, and the MTJ (free ferromagnetic layer 11, the tunnel junction layer 12, and the fixed ferromagnetic layer 13) is formed on the barrier film 20. 15 is stacked and a gate metal electrode 10 connected to a word line is formed on the MTJ 15. The gate metal electrode 10 is connected to the word line as described above, and the source contact region 31 is connected to the bit line.

The MRAM cell of FIGS. 3A and 3B has a structure in which the MTJ 15 is coupled to the gate of a MOS transistor which is a switching element.

An MRAM cell according to the present invention having such a structure may be represented by a symbol as shown in FIG. 4.

Meanwhile, the MRAM cells of FIGS. 3A and 3B store data of logic "1" or logic "0" according to the magnetization direction of the free ferromagnetic layer 11 of the MTJ 15, and FIG. 3A stores logic "1". The magnetization state of storing is illustrated, and FIG. 3B illustrates the magnetization state of storing logic "0".

The write operation of the MRAM cell is performed by applying a voltage of a predetermined level for generating a write current through the gate metal electrode 10 while a constant trigger voltage is applied to the source contact region 31.

At this time, the magnetization polarity direction of the free ferromagnetic layer 11 of the MTJ 15 is determined according to the polarity of the generated write current according to the level of the voltage applied to the gate metal electrode 10. As a result, the MRAM cell having the structure shown in FIGS. 3A and 3B stores the logic "0" and the logic "1" according to the polarity of the current supplied to the gate metal 10.

The read operation of the MRAM cell is performed by sensing the amount of current regulated according to the magnetization polarity direction of the free ferromagnetic layer 11 of the MTJ 15.

Specifically, the amount of I1 flowing between the metal electrode 10 of the gate of the switching element and the subchannel (source contact region 32) varies depending on the magnetization polarity direction of the MTJ 15, and accordingly, the drain contact region The amount of current I2 flowing into the source contact region 32 at 31 varies.

That is, when a constant trigger voltage is applied to the gate metal electrode 10 and a constant sensing voltage is applied to the source contact region 31, a tunneling current (current I1) flows to the MTJ 15. At this time, if the magnetization directions of the fixed ferromagnetic layer 13 and the free ferromagnetic layer 11 are the same as in FIG. In the opposite case, the amount of current I1 is small. Accordingly, the magnetization direction of the free ferromagnetic layer 11 is sensed by detecting a large amount and a small amount of the current I2 flowing from the drain contact region 32 to the source contact region 31, and the stored information is sensed.

For reference, FIG. 5 is a graph illustrating a change in the magnitude of the current I2 according to the magnetization directions of the switching elements illustrated in FIGS. 3A and 3B.

If a large amount of current I2 is output in a state where a constant trigger voltage is applied to the word line voltage, that is, the gate metal electrode 10, the data is stored as logic "1". If the current I2 is less output, data is stored as logic "0". .

6 illustrates an example in which an MRAM cell having the structures of FIGS. 3A and 3B are configured in an array and an example in which a semiconductor memory device is implemented.

6 shows a plurality of word lines WL1, WL2... And a plurality of bit lines BL1, BL2... And a plurality of bit lines BL1, BL2... Respectively include sense amplifiers SA1 and SA2. And each memory cell formed one at each intersection where each word line and bit line cross each other in a matrix form is composed of one MRAM cell 100.

The plurality of MRAM cell arrays corresponding to one row share the same word line, and the plurality of MRAM cell arrays corresponding to one column share the same bit line. Here, the drain of each MRAM cell is connected to the cell plate CP, and the source of each MRAM cell is connected to the corresponding bit line. Accordingly, the word line signal or the bit line signal is shared per row unit or bit unit. One sense amplifier corresponds to each column.

The operation of the embodiment of the MRAM employing the MRAM cell array having the structure as described above will be described with reference to FIGS.

Referring to FIG. 7, the operation of the MRAM cell array in the read mode is divided into an initial section t0, a memory cell selection section t1, a sense amplifier enable section t2, and a read end section t3.

In the initial period t0, the low-level voltage that does not read or write data is maintained in the bit lines and the word lines, and the sense amplifier is in a disabled state.

Then, in the memory cell selection period t1, in order to read the data stored in the MRAM cell, the word line WL (represented on behalf of WL1, WL2...) And the bit line BL (BL1,) connected to the MRAM cell corresponding to the address where the data is stored. Is referred to as BL2 ...).

The predetermined trigger voltage is applied to the selected word line in the memory cell selection period t1, and the ground voltage is applied to the unselected word lines. In addition, a sensing voltage of a constant level is applied to the selected bit line.

In this case, data of the MRAM cell 100 corresponding to the memory cell selected as the sense amplifier SA connected to the bit line BL is output.

That is, as described with reference to FIGS. 3A and 3B, the trigger voltage is applied to the gate through the word line WL, and the strength of the current I1 is determined according to the magnetization direction of the MTJ 15. As a result, when logic "1", a large amount of current I2 is output to the corresponding bitline BL through the source of the MRAM cell 100, and when logic "0", a small amount of current I2 is the source of the MRAM cell 100. Through the corresponding bit line BL is output.

As such, a current corresponding to the data stored in the corresponding MRAM cell 100 is output to the bit line BL, and when a sufficient current is output to the sensed bit line BL, the current enters the sense amplifier enable period t2.

In the sense amplifier enable period t2, the enable signal SEN is applied to the sense amplifier SA at a predetermined level. Then, the sense amplifier SA senses a signal carried on the bit line BL and outputs the sensed data SA_OUT as read data.

As a result, if the amount of current supplied to the bit line BL is large, the sense amplifier SA senses the logic "1". If the amount of current supplied to the bit line BL is small, the sense amplifier SA senses the logic "0".                     

The enable signal SEN is applied to the sense amplifier SA as a trigger signal having a constant output time and enters the end section t3 when the set output time is exceeded.

In the end section t3, the signal for selecting the word line WL and the bit line BL and the signal SEN for enabling the sense amplifier are returned to the initial section t0. Therefore, the current corresponding to the data stored in the MRAM cell 100 is stopped from being output to the corresponding bit line BL, and the output of the sensed data SA_OUT is also stopped.

In contrast, referring to FIG. 8, the operation in the write mode of the MRAM cell array is divided into an initial section t0, a memory cell selection section t1, and a write end section t2.

The ground voltage is equally applied to the word line WL selected in the initial period t0 and the word line WL not selected, and a voltage for sensing a constant write current is applied to the selected word line WL as it enters the write period t1.

The trigger voltage is applied to the selected word line in the write period t1, and a voltage for generating a constant current is applied to the cell plate CP and the bit line WL.

The magnetization polarity of the free ferromagnetic layer 11 is determined by the strength of the current flowing between the cell plate CP and the bit line WL, so that data is stored in the MRAM cell with logic "0" or logic "1".

In contrast, by controlling the amount of current between the cell plate CP and the bit line BL, the magnetization polarity direction of the free ferromagnetic layer 11 formed in the MRAM is slightly adjusted so that two or more data can be stored.                     

Therefore, the time for storing data in the MRAM cell is guaranteed to the write period t1, and then the ground voltage is applied to the word line in the write end period t2.

Meanwhile, the MRAM cell array and the MRAM employing the same include a plurality of word lines WL1 and WL2 and a plurality of bit line BL and BL_B pairs as shown in FIG. 9. Each bit line BL and BL_B is connected to the same sense amplifier SA. MRAM cells 100a and 100b formed at the intersections of the same word line WL and bit lines BL and BL_B form one memory cell. The drains of these MRAM cells 100a and 100b are commonly connected to the cell plate CP.

Accordingly, the memory cell is composed of a word line WL and a pair of MRAM cells 100a and 100b connected to a pair of bit lines BL and BL_B.

The MRAM cells 100a and 100b of FIG. 9 store data opposite to each other, and the values stored in the memory cells are sensed by the sense amplifier SA by these data. Accordingly, there is no need for a reference cell to be configured in the sense amplifier SA connected to the bit lines BL and BL_B.

In the above-described embodiment of FIG. 9, read and write operations are performed as in FIGS. 7 and 8.

That is, the read mode is divided into an initial section t0, a memory cell selection section t1, a sense amplifier enable section t2, and a read end section t3.

The word line WL, the bit lines BL and BL_B are selected while entering the memory cell selection section t1 in the initial period t0, and a predetermined trigger voltage is applied to the selected word line WL. In addition, a sensing voltage having a constant level is applied to the selected bit line BL. In this case, opposite data corresponding to the memory cell selected by the sense amplifier SA connected to the bit lines BL and BL_B is output.

As shown in FIGS. 3A and 3B, the trigger voltage is applied to the gates of the MRAM cells 100a and 100b through the word line WL, and the intensity of the current I1 is determined according to the magnetization direction of each MTJ 15. And the MRAM cells 100a and 100b output the controlled current I2 to the current I1.

If the logic "1" is stored in the MRAM cell 100a connected to the bit line BL, a current corresponding to "1" is output to the bit line BL, and a current corresponding to "0" to the corresponding bit line BL_B. Is output.

As described above, when a current corresponding to the data stored in the corresponding MRAM cells 100a and 100b is output to the bit lines BL and BL_B and a sufficient amount of current is output to the bit lines BL and BL_B, the sense amplifier enable period. It enters t2.

In the sense amplifier enable period t2, the current output to each of the bit lines BL and BL_B is sensed by the sense amplifier SA to which the enable signal SEN is applied. As a result, the sensed data SA_OUT outputs read data of logic "1". . After a constant output time for which the enable signal SEN is maintained, it enters the end section t3.

Meanwhile, in the write mode, the ground voltage is equally applied to the word line selected in the initial period t0 and the word line not selected, and the trigger voltage is applied to the selected word line while entering the write period t1.

The trigger voltage is applied to the selected word line in the write period t1, and a voltage for generating a constant current is applied to the cell plate CP and the bit line WL.

The magnetization polarity of the free ferromagnetic layer 11 is determined by the strength of the current flowing between the cell plate CP and the bit line WL, so that data is stored in the MRAM cell with logic "0" or logic "1".

In this state, the magnetization direction of the free ferromagnetic layer 11 formed in the MRAM is slightly adjusted by additionally adjusting the magnitudes of the currents of the word line WL and the bit line BL, thereby allowing two or more data to be stored.

In contrast, by adjusting the amount of write current, the magnetization direction of the free ferromagnetic layer 11 formed in the MRAM is slightly different, so that two or more data can be stored.

As described above, the source and the drain of the MRAM cell may be interchanged. In this case, as described above, the cell plate is connected to the source and the drain is connected to the bit line.

As described above, according to the present invention, the MRAM cell can be configured in a simple structure, so that the cell array and the structure of the MRAM can be improved, thereby improving the process therefor.

In addition, the structure improved by the present invention has the effect of reducing the cell size of the MRAM and improving the sensing margin.

Claims (21)

A plurality of word lines and bit lines; A plurality of sense amplifiers connected to each bit line to sense current supplied to the bit line and output the data; And Each word line and each bit line unit is configured to correspond to an MTJ coupled to a gate connected to the word line, and data is written according to a polarity of a current between a drain and a source, and according to the magnetization direction of the MTJ. And an MRAM cell for outputting a current corresponding to data to the bit line to read the data. The method of claim 1, The drain of the MRAM cell is connected to a cell plate and the source is connected to a bit line. The method of claim 1, The source of the MRAM cell is connected to a cell plate and the drain is connected to a bit line. The method of claim 1, And storing at least two pieces of data in the MTJ by adjusting the magnitudes of the currents of the word line and the bit line. A plurality of word lines; A plurality of bit lines and a plurality of bit line bars; A plurality of sense amplifiers connected in common to each pair of bit lines and each bit line bar to sense current supplied to the plurality of bit lines and the plurality of bit line bars and output the data as data; A first MTJ is configured at a first gate, a first MRAM cell configured to correspond to each word line and each bit line unit to read and write data, and a second MTJ is configured at a second gate. And a memory cell having a second MRAM cell configured to correspond to each word line and each bit line bar unit, and to read and write data opposite to data stored in the first MRAM cell. The method of claim 5, Each drain of the first and second MRAM cells is commonly connected to a cell plate, and each source is connected to the bit line and the bit line bar. The method of claim 5, Wherein each source of the first and second MRAM cells is commonly connected to a cell plate, and each drain is connected to the bit line and the bit line bar. The data read of the first MRAM cell, The selected word line and the bit line are selected, and a current whose amount is controlled according to the magnetization state of the first MTJ is supplied to the bit line by a trigger voltage applied to the word line, and the sense amplifier supplies the current. Is made by sensing The data lead of the second MRAM cell is The specified word line and the bit line bar are selected, and a current whose amount is controlled in accordance with the magnetization state of the second MTJ by a trigger voltage applied to the word line is supplied to the bit line bar, and the sense amplifier supplies the current. MRAM, characterized in that made by sensing. The method of claim 5, wherein the data write of the first MRAM cell and the second MRAM cell, The magnetization state of the first MTJ and the second MTJ is determined according to the polarity of the current between the source and the drain, and the corresponding data is stored. The method of claim 5, And storing at least two pieces of data in the first MTJ and the second MTJ by adjusting magnitudes of the currents of the word line, the bit line, and the bit line bar. Since the MTJ for data writing and reading is formed between the gate contact region formed in the upper film of the insulating film and the word line thereon, the MTJ magnetization state is determined according to the polarity of the current between the source and the gate to write the data. MRAM cell, characterized in that the amount of current flowing from the drain to the source is determined by the tunneling current generated differently according to the magnetization state of the MTJ under a constant trigger voltage state. The method of claim 11, And said drain is connected to a cell plate and said source is connected to a bit line. The method of claim 11, MRAM cell, characterized in that the source is connected to the cell plate and the drain is connected to the bit line. The method of claim 11, And storing at least two pieces of data in the MTJ by adjusting the magnitudes of the currents of the word line and the bit line. An MRAM cell including an MTJ in which data reads and writes are made in response to a change in magnetization state at a gate connected to a word line is connected to one bit line and one word line to form a memory cell. An MRAM cell array, characterized in that a plurality of repetitive connections. The method of claim 15, MRAM cell array, characterized in that the source of the MRAM cell is connected to the bit line, the drain is connected to the cell plate. The method of claim 15, And the drain of the MRAM cell is connected to the bit line and the source is connected to a cell plate. A first MRAM cell including a first MTJ configured to read and write data according to a change in magnetization state in a first gate connected to a word line is connected to one bit line and one word line, and is connected to the word line. A second MRAM cell including a second MTJ configured to read and write data according to a change in magnetization state in a second gate is connected to one bit line bar and the word line to form a memory cell, and the memory cell is connected to a row and a column. An MRAM cell array, characterized in that a plurality of repetitive connections. The method of claim 18, And drains of the first and second MRAM cells are connected to a cell plate and a source is connected to the bit line and the bit line bar. The method of claim 18, MRAM cell array, characterized in that the source of the first and second MRAM cells is connected to a cell plate and the drain is connected to the bit line and the bit line bar. The method of claim 18, And storing at least two pieces of data in the first MTJ and the second MTJ by adjusting magnitudes of currents of the word line, the bit line, and the bit line bar.

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