JP5467241B2 - MEMORY ELEMENT, MANUFACTURING METHOD THEREOF, AND STORAGE DEVICE PROVIDED WITH MEMORY ELEMENT - Google Patents

Description

  The present invention relates to a memory element, a manufacturing method thereof, and a storage device including the memory element.

  Conventionally, in a computer, a storage device called a so-called DRAM (Dynamic Random Access Memory) is generally used.

  This DRAM is composed of a capacitor and a transistor formed on a semiconductor substrate, and stores data of one bit of “0” or “1” by controlling the amount of charge accumulated in the capacitor by the transistor. .

  In the DRAM, since the charge accumulated in the capacitor decreases with time, it is necessary to perform a refresh process in which the capacitor is recharged at regular intervals and the stored data is held.

  Recently, a so-called MRAM (Magnetroresistive Random Access Memory) that can store data for a long time without performing a refresh process like a DRAM has been used.

  In an MRAM, a ferromagnetic tunnel junction element is formed by laminating a free magnetic layer that can be magnetized in a free direction and a fixed magnetic layer that is magnetized in a fixed direction. One bit of data “0” or “1” is stored.

  That is, in the ferromagnetic tunnel junction device, the magnitude of the electric resistance is different depending on whether the magnetization direction of the free magnetic layer and the magnetization direction of the fixed magnetic layer are parallel or antiparallel. Are different from each other, and data of 1 bit is stored using the state of the different electric resistance (see, for example, Patent Document 1).

Therefore, in the MRAM, data can be written by magnetizing the free magnetic layer in a predetermined direction.
Japanese Patent Laid-Open No. 11-097766

  However, in the MRAM, in order to magnetize the free magnetic layer in a predetermined direction, a predetermined current is passed based on Ampere's law, and a magnetic field of a predetermined threshold value or more must be applied to the free magnetic layer. Therefore, there is a problem that a relatively large current needs to flow and power consumption is large.

  Even in the case of DRAM, since power is consumed in the refresh process, it has been difficult to reduce power consumption.

  The inventors of the present invention have studied the compound having a layered triangular lattice structure containing a rare earth element, and have come to realize that a memory element with low power consumption can be provided by utilizing the dielectric properties of the compound. It is made.

The memory element of the present invention is a memory element having a resistor whose electrical resistance changes when a voltage is applied and a voltage application electrode for applying a predetermined voltage to the resistor. The body is composed of a compound having a layered triangular lattice structure having a W layer and containing a rare earth element, and a region having a role of positive charge and a region having a role of negative charge in the W layer by applying an electric field from the outside. To control the state of the electric dipole, and to generate different electric resistances depending on the state of the electric dipole, the resistor being R, Sc, Y, Dy, Ho, Er, At least one element selected from Tm, Yb, Lu, Ce, Ma and Mb, at least one element selected from Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, Cd with duplication allowed elements, n an integer of 1 or more, m an integer of 0 or more, the [delta] as a real number of 0 to 0.2, and _{m (RMbO 3-δ) n} (MaO) The compound having a layered triangular lattice structure represented by the above formula, or a compound in which a part of R of the compound is substituted with an element having a positive divalent value or less .

Furthermore, the memory element of the present invention is also characterized by the following points. That is,
(1) Power coining with the electrodes for pressurizing provided so as to face each other across the resistor as two pair, and also used as electrodes for voltage detection to detect the electrical resistance of the electrode resistor for voltage application That.
( 2 ) The voltage application electrodes are provided separately in the c-axis direction of the compound constituting the resistor.

Further, in the method for manufacturing a memory element according to the present invention, a memory element having a resistor whose electrical resistance is changed by applying a voltage and an electrode for applying a voltage for applying a predetermined voltage to the resistor is manufactured. The resistor is composed of a compound having a layered triangular lattice structure having a W layer and containing a rare earth element, and a region having a role of positive charge in the W layer by applying an electric field from outside. A region having a role of negative charge is generated to control the state of the electric dipole, and different electric resistances are generated according to the state of the electric dipole. The resistor is represented by R, Sc, Y , Dy, Ho, Er, Tm, Yb, Lu, Ce, at least one element selected from Ma, Mb, and Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, Cd At least one element selected by allowing, n is an integer of 1 or more, m is an integer of 0 or more, δ is a real number of 0 or more and 0.2 or less Te, further comprising the step of forming a compound obtained by substituting a positive divalent following elements a part of R of the compound, or a compound having a layered triangular lattice structure, expressed as _{(RMbO 3-δ) n (} MaO) m It was.

In addition, the memory device of the present invention includes a plurality of memory elements each including a resistor whose electrical resistance changes when a voltage is applied and a voltage application electrode for applying a predetermined voltage to the resistor. The resistor is made of a compound having a layered triangular lattice structure having a W layer and containing a rare earth element, and acts as a positive charge in the W layer by applying an electric field from the outside. A region having a role of negative charge and a region having a negative charge to control a state of the electric dipole, and generating a different electric resistance according to the state of the electric dipole, and the resistor, R, At least one element selected from Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, and Ce, Ma and Mb, Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, Cd At least one element selected with duplication allowed, n is an integer of 1 or more, m is an integer of 0 or more, and δ is 0 or more of 0 Consists of a compound having a layered triangular lattice structure represented by (RMbO _{3 -δ} ) _n (MaO) _m as a real number of .2 or less , or a compound in which a part of R of the compound is substituted with an element less than positive divalent It was decided to.

  According to the present invention, a memory element that stores predetermined data using different resistance values of a resistor, a manufacturing method thereof, and a memory device including the memory element, the layered triangular lattice containing the rare earth element as the resistor By comprising a compound having a structure, data can be stored by changing the electrical resistance by applying a predetermined voltage to the resistor.

  In addition, the memory element formed using this resistor can reduce power consumption by eliminating the need for a refresh process, and can further reduce the power consumption due to miniaturization of the resistor. Can also be reduced.

FIG. 1 is a schematic explanatory diagram of the arrangement of each element in a plan view of a compound having a layered triangular lattice structure. FIG. 2 is a schematic explanatory diagram of the arrangement of each element in a side view of a compound having a layered triangular lattice structure. FIG. 3 is a schematic diagram of a memory element according to the embodiment of the present invention. FIG. 4 is a schematic diagram of a memory device according to another embodiment. FIG. 5 is a schematic diagram of a memory device according to another embodiment. FIG. 6 is a schematic diagram of a memory element according to another embodiment. FIG. 7 is a schematic diagram of a memory device according to another embodiment. FIG. 8 is a schematic diagram of a memory device according to another embodiment. FIG. 9 is a schematic diagram of a storage device according to an embodiment of the present invention.

10,40,70 Insulating substrate
21,21 ", 51,81 1st electrode
22,22 ', 22 ", 52,82 Second electrode
30,30 ', 30 ", 60,90 resistor

  In the memory element, the manufacturing method thereof, and the memory device including the memory element of the present invention, the memory element is configured by using a resistor whose electric resistance is changed by applying a voltage.

  In particular, the resistor is composed of a compound having a layered triangular lattice structure containing a rare earth element.

Specifically, the R, S c, Y, Dy , Ho, Er, Tm, Yb, Lu, at least one element selected Ce or et al., Ma and Mb, Ti, Mn, Fe, Co, Cu , Ga, Zn, Al, Mg, Cd, at least one element selected by allowing duplication, n is an integer greater than or equal to 1, m is an integer greater than or equal to 0, δ is a real number greater than or equal to 0 and less than or equal to 0.2 (RMbO ₃ A compound represented as _-δ ) _n (MaO) _m or a compound in which a part of R of the compound is substituted with an element less than or equal to positive divalent.

Hereinafter, a compound having a layered triangular lattice structure will be described with LuFe ₂ O _{4 in} which R is Lu and Ma and Mb are Fe as representative examples.

LuFe ₂ O ₄ can be produced by the following procedure.
(1) Lutetium oxide (Lu ₂ O ₃ ) and iron (III) oxide (Fe ₂ O ₃ ) are mixed at a ratio of 1: 2 and mixed with a ball mill for about 1 hour to form a mixture.
(2) The mixture is formed into a predetermined shape and heated to 800 ° C. for 24 hours in an oxygen atmosphere to form a pre-fired body.
(3) The temporary fired body is fired by the FZ (Floating Zone) method to obtain single crystal LuFe ₂ O ₄ . At this time, crystals are grown in an atmosphere of a CO—CO ₂ mixed gas that is a mixed gas of carbon monoxide and carbon dioxide.

In the main firing for producing a single crystal, a CO ₂ —H ₂ mixed gas may be used instead of the CO—CO ₂ mixed gas, and the amount of oxygen is obtained by firing while controlling the oxygen partial pressure in a reducing atmosphere. Is adjusted.

The crystal structure of single crystal LuFe ₂ O ₄ will be described with reference to FIGS. For convenience of explanation, the crystal structure of LuFe ₂ O ₄ is in a state before so-called charge ordering, in which the ordered structure of Fe ³⁺ and Fe ²⁺ does not appear in Fe ions in the crystal.

  FIG. 1 is a schematic explanatory diagram of the arrangement of each element in plan view, and shows the positional relationship between the triangular lattice of element A, the triangular lattice of element B, and the triangular lattice of element C. In the following, the position of the lattice point in the triangular lattice of element A is “A position”, the position of the lattice point in the triangular lattice of element B is “B position”, and the position of the lattice point in the triangular lattice of element C is “C position”. I will call it.

FIG. 2 is a schematic explanatory diagram of the arrangement of each element in a side view, and each element is located at a predetermined position in the following order from the uppermost layer downward.
Lu-B position
OC position
Fe-C position
O-B position
OC position
Fe-B position
O-B position
Lu-C position
O-A position
Fe-A position ○
O-C position ○
O-A position ○
Fe-C position
OC position
Lu-A position
O-B position
Fe-B position
O-A position
O-B position
Fe-A position
O-A position
Lu-B position

Among these, a portion composed of four layers marked with a circle is called a W layer (W-Layer), and having this W layer is a characteristic point of LuFe ₂ O ₄ .

Further, it is known that a W layer is also formed in a compound having a layered triangular lattice structure other than LuFe ₂ O ₄ .

The W layer has a triangular lattice laminated structure, and the presence of the same number of Fe ²⁺ and Fe ³⁺ in LuFe ₂ O ₄ causes frustration of charges.

As a result, in LuFe ₂ O ₄ , the region rich in Fe ³⁺ has a role of positive charge in the W layer, while the region rich in Fe ²⁺ has a role of negative charge. (Electrical polarization) appears.

Moreover, in LuFe ₂ O ₄ , the state of the electric dipole can be controlled by applying an electric field from the outside, and LuFe ₂ O ₄ has different electric resistances depending on the state of the electric dipole.

  As described above, a compound having a layered triangular lattice structure containing a rare earth element has a W layer and can control the charge order structure in the W layer by an electric field applied from the outside to generate different states of electrical resistance. Therefore, a memory element can be configured.

  That is, as shown in FIG. 3, the memory element of the present invention is formed by sequentially laminating a first electrode 21, a resistor 30, and a second electrode 22 on a predetermined insulating substrate 10 from below. The electric resistance of the resistor 30 can be changed by applying an electric field to the resistor 30 with the first electrode 21 and the second electrode 22 set to a predetermined potential.

  A voltage application device (not shown) is connected to the first electrode 21 and the second electrode 22 so that a predetermined electric field acts on the resistor 30 between the first electrode 21 and the second electrode 22.

  That is, in the voltage application device, the first electrode 21 acts on the resistor 30 depending on whether the first electrode 21 has a higher potential than the second electrode 22 or the second electrode 22 has a higher potential than the first electrode 21. The direction of the electric field to be adjusted is adjusted so that the resistor 30 can be changed to two states having different electric resistances. However, in order to change the electrical resistance of the resistor 30, it is necessary to apply an electric field of a predetermined threshold value or more to the resistor 30.

  The first electrode 21 and the second electrode 22 are made of a highly conductive metal such as Au or Cu.

The resistor 20 is LuFe ₂ O ₄ in this embodiment. The resistor 20 is not limited to LuFe ₂ O ₄ , and R is selected from In, Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ti, Ca, Sr, Ce, Sn, and Hf. At least one element selected, Ma and Mb, at least one element selected from Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, and Cd with duplication allowed, n is one or more A compound having a layered triangular lattice structure represented by (RMbO _{3 -δ} ) _n (MaO) _m , wherein R is an integer, m is an integer of 0 or more, δ is a real number of 0 to 0.2, or a part of R of the compound A compound in which is substituted with an element having a positive divalent value or less can be used. Hereinafter, the resistor 20 will be described as LuFe ₂ O ₄ .

  The memory element described above can be formed as follows.

  First, a first metal layer is formed on the insulating substrate 10 by sputtering or the like.

Next, fine particles of LuFe ₂ O ₄ are formed on the first metal layer by CVD (Chemical Vapor Deposition), sputtering, MBE (Molecular Beam Epitaxy), or aerosol deposition. A resistor layer is formed.

  Next, a second metal layer is formed on the resistor layer by sputtering or the like.

Thereafter, an etching mask is formed on the upper surface of the second metal layer, and the second metal layer, the resistor layer, and the first metal layer are sequentially etched by etching or electron beam lithography to thereby form the first electrode. 21, a resistor 30 and a second electrode 22 are formed. The resistor layer is preferably a single crystal of LuFe ₂ O ₄ , but may be polycrystalline.

When the resistor layer is formed, the c-axis direction of LuFe ₂ O ₄ is made to coincide with the opposing direction of the first electrode 21 and the second electrode 22. Note that the c-axis direction of LuFe ₂ O ₄ is not necessarily completely coincident with the opposing direction of the first electrode 21 and the second electrode 22, and at least the c-axis direction of LuFe ₂ O ₄ is the first electrode. It does not have to be orthogonal to the facing direction of 21 and the second electrode 22.

  In this manner, by using a compound having a layered triangular lattice structure containing a rare earth element as a resistor, the electric resistance of the resistor can be easily switched, so that a memory element with low power consumption can be obtained.

  In particular, by providing a pair of first electrode 21 and second electrode 22 for applying a predetermined voltage to the resistor, spaced apart in the c-axis direction of the compound, the first electrode 21 and the second electrode 22 The electric resistance of the resistor 30 can be effectively changed by the formed electric field, and the power consumption can be further reduced.

  In the memory element shown in FIG. 1, the first electrode 21, the second electrode 22, and the resistor 30 have the same width. For example, as shown in FIG. The width may be smaller than that of the electrode 21 and the resistor 30.

  Furthermore, as shown in FIG. 5, the second electrode 22 ′ may have a smaller width than the resistor 30 ′, and the resistor 30 ′ may have a smaller width than the first electrode 21.

  Alternatively, as shown in FIG. 6, the width dimension of the first electrode 21 "and the second electrode 22" may be smaller than the width dimension of the resistor 30 ".

  In addition, the first electrode 21 and the second electrode 22 are not only formed apart in the vertical direction, but, for example, as shown in FIG. 7, the first electrode 21 is separated by a predetermined dimension in the surface direction of the insulating substrate 40. 51 and a second electrode 52 may be provided, and a resistor 60 made of a compound having a layered triangular lattice structure containing a rare earth element may be provided between the first electrode 51 and the second electrode 52.

In this case, a resistor layer is formed in advance on the insulating substrate 40 using fine particles of LuFe ₂ O ₄ by a CVD method, a sputtering method, an MBE method, an aerosol deposition method, or the like. The resistor 60 is formed into a predetermined cell shape by electron beam lithography or the like.

  Thereafter, a metal layer is formed on the insulating substrate 40 by sputtering or the like to cover the resistor 60, and a first mask for etching for forming the first electrode 51 and the second electrode 52 is formed. By etching the metal layer, the first electrode 51, the resistor 60, and the second electrode 52 are arranged in the surface direction of the insulating substrate 40. Instead of forming the resistor 60 before the first electrode 51 and the second electrode 52, the first electrode 51 and the second electrode 52 may be formed before the resistor 60.

  Here, when the first electrode 51, the resistor 60, and the second electrode 52 are disposed in the plane direction of the insulating substrate 40 as shown in FIG. 7, the c-axis direction of the compound constituting the resistor 60 Is the surface direction of the insulating substrate 40.

That is, by forming the resistor 60 using the insulating substrate 40 whose surface crystal plane is adjusted, the c-axis direction of the compound constituting the resistor 60 can be the plane direction of the insulating substrate 10. In this embodiment, ScAlMgO ₄ is used for the insulating substrate 40.

  In the above-described embodiment, the direction of the electric field applied to the resistors 30 and 60 by the first electrodes 21 and 51 and the second electrodes 22 and 52 is either the vertical direction of the insulating substrate 10 or the surface direction of the insulating substrate 40. However, in some cases, as shown in FIG. 8, the second electrode 82 is provided obliquely above the first electrode 81 provided on the upper surface of the insulating substrate 70 with the resistor 90 interposed therebetween. Also good.

  A memory device can be formed using the memory element described above. In the storage device, as shown in FIG. 9, the number of memory elements m corresponding to the storage capacity is arranged in a matrix.

  The first wiring 101 is connected to the first electrode of the memory element m, and the second wiring 102 is connected to the second electrode of the memory element m via the control transistor t.

  In the memory device of this embodiment, the memory elements m arranged in the vertical direction in FIG. 9 share one first wiring 101, and the memory elements m arranged in the horizontal direction in FIG. The second wiring 102 is shared.

  The first wiring 101 is connected to the first driver circuit 103, the second wiring 102 is the second driver circuit 104, and the first wiring 101 and the second wiring 102 are connected by the first driver circuit 103 and the second driver circuit 104. A predetermined electric field is applied to the memory element m.

  The first driver circuit 103 and the second driver circuit 104 are controlled by control signals input from a main control unit (not shown).

  A control signal line 105 is connected to each gate of the control transistor t. The control signal line 105 is connected to the third driver circuit 106 and output from the third driver circuit 106 to the control signal line 105. The control transistor t performs on / off switching control of the control transistor t.

  In FIG. 9, the control transistors t arranged in the horizontal direction share one control signal line 105. The third driver circuit 106 is also controlled by a control signal input from a main control unit (not shown).

  When storing predetermined data in the storage device configured as described above, the first wiring 101 connected to the memory element m storing the predetermined data in the first driver circuit 103 is set to the first potential, and the second driver The second wiring 102 connected to the memory element m that stores predetermined data in the circuit 104 is set to the second potential, and the third transistor circuit 106 turns on the control transistor t connected to the memory element m that stores predetermined data. A signal is being input.

  Therefore, a predetermined electric field can be applied to the resistor of the memory element m by the first electrode having the first potential and the second electrode having the second potential, and the electric resistance of the resistor can be set to a predetermined value. The electrical resistance is.

  In addition, since the control transistors t arranged in the horizontal direction in FIG. 9 share one control signal line 105, not only the control transistor t connected to the memory element m that stores predetermined data, All the control transistors t arranged in the horizontal direction are in the on state.

  At this time, the first driver circuit 103 and the second driver circuit 104 cause the first electrode and the second electrode of each memory element m to have the same potential in the memory elements m other than the memory element m that stores predetermined data. This prevents meaningless data from being written in the memory element m.

  On the other hand, when data is read from the predetermined memory element m, an ON signal is input to the control transistor t connected to the memory element m from which the third driver circuit 106 reads data, and the first driver circuit 103 and the second driver A predetermined read current is supplied to the memory element m from which data is read by the circuit 104 via the first wiring 101 and the second wiring 102.

  Then, the value of the current for reading is detected by the first driver circuit 103 or the second driver circuit 104, and the resistance value of the memory element m is detected by comparing this current value with a predetermined threshold value. Reading data.

  When data is read from the memory element m, it is stored in the memory element m as the data is read as a state where an electric field smaller than the electric field whose resistance state changes in the resistor in the memory element m acts. Data is not overwritten.

  As described above, in the memory element m, when writing data and when reading data, the first electrode and the second electrode are shared, and the first electrode and the second electrode are used for detecting the electrical resistance of the resistor. By using it as an electrode for voltage detection, the structure of the memory element m can be prevented from becoming complicated, and the memory element m can be formed very easily.

  According to the present invention, a memory device with low power consumption can be provided.

Claims (5)

A resistor whose electrical resistance changes by applying a voltage;
A memory element having a voltage application electrode for applying a predetermined voltage to the resistor,
The resistor is composed of a compound having a layered triangular lattice structure having a W layer and containing a rare earth element. By applying an electric field from the outside, a region having a role of positive charge and a role of negative charge are formed in the W layer. A region having an electric dipole is generated, and an electric resistance different depending on the state of the electric dipole is generated.
The resistor is R, at least one element selected from Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ce;
Ma and Mb are at least one element selected from Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, and Cd with duplication allowed,
n is an integer of 1 or more,
m is an integer greater than or equal to 0,
A compound having a layered triangular lattice structure represented by (RMbO _{3 -δ} ) _n (MaO) _m or a part of R of the compound was substituted with an element less than positive divalent, where δ is a real number between 0 and 0.2 . A memory device composed of a compound. The voltage application electrodes are provided as a pair so as to face each other with the resistor interposed therebetween, and the voltage application electrode is also used as a voltage detection electrode for detecting the electrical resistance of the resistor. The memory device according to claim 1 . The memory element according to claim 2, wherein the voltage application electrode is provided to be separated in a c-axis direction of the compound constituting the resistor. A resistor whose electrical resistance changes by applying a voltage;
A method of manufacturing a memory element having a voltage application electrode for applying a predetermined voltage to the resistor,
The resistor is composed of a compound having a layered triangular lattice structure having a W layer and containing a rare earth element. By applying an electric field from the outside, a region having a role of positive charge and a role of negative charge are formed in the W layer. A region having an electric dipole is generated, and an electric resistance different depending on the state of the electric dipole is generated.
The resistor is R, at least one element selected from Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ce;
Ma and Mb, at least one element selected from Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, and Cd, allowing duplication,
n is an integer of 1 or more,
m is an integer greater than or equal to 0,
A compound having a layered triangular lattice structure represented by (RMbO _{3 -δ} ) _n (MaO) _m or a part of R of the compound was substituted with an element less than positive divalent, where δ is a real number between 0 and 0.2 . A method for manufacturing a memory element, comprising a step of forming a compound. A resistor whose electrical resistance changes by applying a voltage;
A storage device comprising a plurality of memory elements each having a voltage application electrode for applying a predetermined voltage to the resistor,
The resistor is composed of a compound having a W layer and a layered triangular lattice structure containing a rare earth element, and a region having a role of positive charge and a role of negative charge in the W layer by applying an electric field from the outside. To produce a region having a control of the state of the electric dipole, and to produce a different electrical resistance depending on the state of the electric dipole,
The resistor is R, at least one element selected from Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ce;
Ma and Mb, at least one element selected from Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, and Cd, allowing duplication,
n is an integer of 1 or more,
m is an integer greater than or equal to 0,
A compound having a layered triangular lattice structure represented by (RMbO _{3 -δ} ) _n (MaO) _m or a part of R of the compound was substituted with an element less than positive divalent, where δ is a real number between 0 and 0.2 . Memory device composed of compounds.

Images