JP5846571B2 - Manganese oxide, ferroelectric memory device including manganese oxide, and ferroelectric memory device - Google Patents

Description

  The present invention relates to a novel manganese oxide exhibiting ferroelectricity and capable of controlling the magnitude of polarization by an external magnetic field, and use thereof.

  For the realization of a ubiquitous information society, there is a need for high performance and high density memory devices. In particular, the development of a memory that combines high operating speed, low power consumption, and non-volatility is regarded as most important. As memories having the above requirements, ferroelectric memories (FeRAM), magnetoresistive memories (MRAM), and resistance change memories (ReRAM) have been actively researched and developed. Among these, the ferroelectric memory is considered promising because it uses the spontaneous polarization provided in the ferroelectric as a memory carrier, and thus can save power and operate at high speed.

Displacement type ferroelectrics represented by BaTiO ₃ (barium titanate) and PbZr _x Ti _1-x O ₃ (PZT: lead zirconate titanate), which are general materials for conventional ferroelectric memories, are enormous electricity. Has polarization. For example, Patent Document 1 describes that PZT exhibits a switching charge amount of about 27 to 33 μC / cm ² .

JP 2010-278476 A (released on December 9, 2010)

T. Kimura et. Al., Magnetic control of ferroelectric polarization., Nature, 426, p.55, 2003. N. A. Hill, Why are there so few magnetic ferroelectrics ?, J. Phys. Chem. B, 104, p.6694, 2000. G. Catalan et. Al., Physics and Applications of Bismuth Ferrite., Advanced Materials, 21, p.2463, 2009.

However, the crystal structure of BaTiO ₃ is successively deformed into an orthorhombic crystal and a rhombohedral crystal in a temperature region near room temperature. When the crystal structure is deformed, the direction of spontaneous polarization is rotated, and the polarization component in the crystal c-axis direction is reduced. Furthermore, the spontaneous polarization itself becomes unstable, and the memory retention characteristic is significantly deteriorated.

PZT has a tetragonal structure even at low temperatures if the Ti concentration is 58% or more. Therefore, at present, PZT is mainly used as a ferroelectric material for industrial use. However, PZT is a harmful compound containing lead as one of the constituent elements. PZT is designated as a first-class chemical substance designated by the government as PRTR (abbreviation of Pollutant Release and Transfer Register, a substance that is obligated to register emissions and transfers as environmental pollutants) . The toxicity of PZT is A in comprehensive judgment and B in human carcinogenicity judgment (reference Kanagawa PRTR information; http://www.k-erc.pref.kanagawa.jp/prtr/). For this reason, it is an important industrial issue to develop a ferroelectric that does not contain a lead component and has a tetragonal structure that is stable in a wide temperature range. In addition, since zirconia and titanium elements are expensive elements, it is desired to develop a ferroelectric material composed of inexpensive elements.
A conventional ferroelectric memory uses spontaneous polarization inherent in a displacement type ferroelectric material as a memory carrier. In the displacement type ferroelectric substance, spontaneous charge is generated by shifting the ions carrying the charges in the crystal from the symmetrical position of the crystal structure. In the conventional displacement type ferroelectric, the spontaneous polarization value is an eigenvalue of the substance and cannot be controlled by an external parameter. For this reason, a ferroelectric memory capable of multi-value recording has not been realized.

In order to realize the multi-value recording, it is essential to control the polarization value of the ferroelectric material by an external parameter. As a method for controlling the polarization value by an external parameter, it has been proposed to use an electromagnetic effect. In recent years, it has been reported that the magnitude and direction of electric polarization can be controlled by a magnetic field in TbMnO ₃ or the like which is a magnetic order induction type ferroelectric (see Non-Patent Document 1). However, the magnitude of the spontaneous polarization of the magnetic order induced ferroelectric is about 1/1000 compared to the magnitude of the spontaneous polarization of the displacement type ferroelectric. Thus, it is difficult to apply a material with small spontaneous polarization to a ferroelectric memory. In addition, since the spontaneous polarization of the magnetic order induced ferroelectric is induced by the magnetic order, the ferroelectric transition temperature and the magnetic transition temperature are equal. Since the ferroelectric transition temperature and magnetic transition temperature of TbMnO ₃ are about 30 K, it is impossible to operate as a ferroelectric memory at room temperature.

From the viewpoint of controlling the magnitude of polarization using the electromagnetic effect, a substance that exhibits ferroelectricity due to spontaneous polarization due to the shift of magnetic ions from the symmetrical position of the crystal structure is capable of multi-value recording. It is considered to be optimal as a material constituting the ferroelectric memory to be realized. However, there is no report of such a substance until now (refer nonpatent literature 2). For example, BiFeO ₃ (see Non-Patent Document 3) is a ferroelectric substance containing magnetic ions. Ferroelectricity is caused by displacement of Bi ions, and magnetism is played by spins of Fe ions. Therefore, the electromagnetic effect obtained by applying an external magnetic field is extremely small, and a change in polarization value sufficient to realize multi-value recording in a memory cannot be obtained.

  The present invention has been made in view of the above problems, and the first of its purposes is to use a compound that does not contain harmful lead and exhibits ferroelectric properties equivalent to those of conventional displacement ferroelectrics. It is to provide a ferroelectric. The second is to provide a ferroelectric that does not contain an expensive raw material such as titanium as its main component. A third object is to provide a magnetic ferroelectric material that exhibits ferroelectric characteristics resulting from displacement of magnetic ions and that can change the ferroelectric characteristics by applying an external magnetic field, and uses thereof.

The manganese oxide according to the present invention has a perovskite structure and has the following formula (1):
Sr _1-x Ba _x MnO ₃ (1 ≧ x> 0.4) (1)
It is a substance represented by.

In the manganese oxide according to the present invention, the Mn site is replaced with at least one element A selected from the group consisting of Al (aluminum), Ga (gallium), Fe (iron), and Cr (chromium). Following formula (2)
Sr _1-x Ba _x Mn _1-y A _y O ₃ (0.5 ≧ y> 0) (2)
A substance represented by

  In the manganese oxide according to the present invention, y is more preferably in the range of 0.05 ≧ y> 0.

  More preferably, the ferroelectric memory element according to the present invention includes any one of the above-described formulas (1) and (2) as a ferroelectric.

  The ferroelectric memory element according to the present invention more preferably includes a first electrode and a second electrode provided on a surface perpendicular to the polarization direction of the manganese oxide so as to sandwich the manganese oxide.

  A ferroelectric memory device according to the present invention is electrically connected to a ferroelectric memory element array having a plurality of ferroelectric memory elements in a matrix and either the first electrode or the second electrode. A plurality of word lines that electrically connect the ferroelectric memory element in one of a row direction and a column direction, and the other of the first electrode and the second electrode. And a plurality of bit lines electrically connecting the ferroelectric memory elements in a direction different from the word line in the row direction and the column direction, and parallel and perpendicular to the polarization direction of the manganese oxide More preferably, an external magnetic field applying means for applying an external magnetic field in any one direction is provided.

  The manganese oxide according to the present invention has the effect of realizing a safe ferroelectric material that does not contain lead, which is a toxic material. Moreover, since it is comprised with an inexpensive raw material, there exists an effect of suppressing manufacturing cost. Furthermore, since the ferroelectric characteristics can be controlled by controlling the applied magnetic field strength, there is an effect of realizing a ferroelectric memory element and a ferroelectric memory device capable of multi-value recording.

It is a figure which shows a mode that the crystal structure of the manganese oxide which concerns on one Embodiment of this invention, and the spin which Mn ion has are antiferromagnetically ordered. (A) in the figure shows the Ba concentration dependence of the lattice constant in the manganese oxide according to one embodiment of the present invention, and (b) shows the Ba concentration dependence of the tetragonal degree in the manganese oxide. FIG. (A) in a figure shows the temperature dependence of the lattice constant in the manganese oxide which concerns on one Example of this invention, (b) is a figure which shows the temperature dependence of the tetragonal degree in the said manganese oxide. is there. It is a figure which shows the electric field dependence of the electric polarization in the manganese oxide which concerns on one Example of this invention. It is a figure which shows the electric field dependence of the electric polarization in the manganese oxide which added Al or Ga which concerns on the other Example of this invention. 1 is a schematic diagram showing a configuration of a ferroelectric memory element according to an embodiment of the present invention. 1 is a schematic diagram showing a configuration of a ferroelectric memory device according to an embodiment of the present invention. It is the schematic which shows the other structure of the ferroelectric memory element based on one Embodiment of this invention. It is the schematic which shows other structure of the ferroelectric memory element based on one Embodiment of this invention. It is the schematic which shows other structure of the ferroelectric memory element based on one Embodiment of this invention. It is the schematic which shows other structure of the ferroelectric memory element based on one Embodiment of this invention.

Embodiment 1
The manganese oxide Sr _1-x Ba _x MnO ₃ (1 ≧ x> 0.4) according to an embodiment of the present invention will be described with reference to FIGS.

(Crystal Structure of Magnetic Ferroelectric Sr _1-x Ba _x MnO ₃ )
Sr _1-x Ba _x MnO ₃ (1 ≧ x> 0.4) has a perovskite structure as shown in FIG. Mn ions 3 that are magnetic ions are present at the center of symmetry of the unit cell 1. The center of symmetry of the unit cell 1 is the Mn site. One of Sr ions and Ba ions is present at the eight vertices of the unit cell 1. The vertex of the unit cell 1 is defined as Sr site 2. O ions 4 are present at the center of the six faces of the unit cell 1. In addition, as shown in FIG. 1, the orthogonal coordinate which consists of a-axis, b-axis, and c-axis is defined. If herein it was expressed as _{Sr 1-x Ba x MnO 3} , unless otherwise specified means that the _{Sr 1-x} Ba x _MnO 3 having a perovskite structure (1 ≧ x> 0.4). In Sr _1-x Ba _x MnO ₃ , x represents the ratio of Sr sites substituted with Ba ions when all Sr sites are 1. However, in this specification, x is referred to as Ba concentration.

The perovskite structure of Sr _1-x Ba _x MnO ₃ causes a structural transition at a predetermined temperature (near 420K: referred to as a structural transition temperature) sufficiently higher than room temperature. The perovskite structure is cubic on the higher temperature side than the structural transition temperature, whereas the perovskite structure is tetragonal on the lower temperature side than the structural transition temperature. Along with the structural transition from cubic to tetragonal, Sr _1-x Ba _x MnO ₃ transitions from dielectric to ferroelectric. Therefore, the structural transition temperature of Sr _1-x Ba _x MnO ₃ is also a ferroelectric transition temperature.

The ion radius of Ba ions is larger than that of Sr ions. Accordingly, the lattice constant of Sr _1-x Ba _x MnO ₃ increases as the Ba concentration increases. As a result, the structural transition temperature and the ferroelectric transition temperature are considered to increase. This is thought to increase the dielectric constant near room temperature.

In a region lower than the structure transition temperature, Sr _1-x Ba _x MnO ₃ can have only a tetragonal crystal structure. That is, there is no deformation to a crystal structure such as orthorhombic and rhombohedral symmetry. It is known that the direction of spontaneous polarization in a displacement-type ferroelectric greatly depends on the crystal structure. However, when Sr _1-x Ba _x MnO ₃ is in the ferroelectric state, its crystal structure is always tetragonal. Therefore, the direction of spontaneous polarization does not rotate.

In Sr _1-x Ba _x MnO ₃ , Mn ions 3 and O ions 4 are displaced by applying an external electric field in any of the a-axis, b-axis, and c-axis directions. As a result, Sr _1-x Ba _x MnO ₃ exhibits ferroelectricity. Further, the spin 5 of the Mn ion 3 has an antiferromagnetic order. A state in which the spins 5 of the Mn ions 3 are arranged is shown in FIG. By applying an external magnetic field in the a-axis direction, the spins 5 of the Mn ions 3 are arranged parallel to the a-axis direction and antiferromagnetically even at room temperature. Thus, Sr _1-x Ba _x MnO ₃ is a magnetic ion displacement type ferroelectric, in other words, a magnetic ferroelectric. The presence of magnetic order between the spins 5 of the Mn ions 3 causes spin-lattice interactions in Sr _1-x Ba _x MnO ₃ . As a result, a tetragonal structure that exhibits ferroelectricity is firmly retained. The reason why Sr _1-x Ba _x MnO ₃ does not deform into a crystal structure other than tetragonal in the region lower than the structural transition temperature is that there is an antiferromagnetic spin order between Mn spins. As described above, in Sr _1-x Ba _x MnO ₃ , the sequential deformation from the tetragonal crystal to another structure, which has occurred in the conventional non-magnetic displacement ferroelectric, is completely suppressed.

Sr _1-x Ba _x MnO ₃ does not use the toxic element Pb contained in PZT, which is a conventional displacement ferroelectric substance. Therefore, it is a ferroelectric material that is safe for the environment and the human body. Further, Ti contained in BaTiO ₃ is not used. Ti is a relatively expensive material. Therefore, Sr _1-x Ba _x MnO ₃ is an important material not only from its physical characteristics but also from an industrial viewpoint.

(Crystal structure and ferroelectricity)
(A) and (b) of FIG. 2 show the Ba concentration dependence of the lattice constant and the tetragonal degree in Sr _1-x Ba _x MnO ₃ obtained in Example 1 described later. In the perovskite structure of Sr _1-x Ba _x MnO ₃ , it can be seen that when x = 0, that is, in the case of SrMnO ₃ , the lattice constants of the a-axis and the c-axis are equal and cubic (in FIG. 2). (See (a)). The tetragonal degree is the ratio of the lattice constant between the a-axis and the c-axis, and is defined as c-axis lattice constant / a-axis lattice constant. Therefore, when x = 0, the tetragonal degree is 1.

As the Ba concentration increases, the a-axis and c-axis lattice constants gradually increase. However, in the region of 0.4 ≧ x ≧ 0, the a-axis and c-axis lattice constants are equal and the tetragonal degree does not change from 1. When x exceeds 0.4, a difference occurs in the lattice constants of the a axis and the c axis. For example, when x = 0.45, the c-axis lattice constant is further increased compared to the case of x = 0.4. On the other hand, the lattice constant of the a axis becomes small. Therefore, the tetragonal degree increases from 1. When x = 0.5, the lattice constant of the c-axis is further increased, so that the tetragonal degree is further increased. Thus, the crystal structure of Sr _1-x Ba _x MnO ₃ is a cubic crystal in the region of 0.4 ≧ x ≧ 0 and is a tetragonal crystal in the region of x> 0.4. Sr _1-x Ba _x MnO ₃ exhibits ferroelectricity when the crystal structure is tetragonal. Therefore, in order to use Sr _1-x Ba _x MnO ₃ as a ferroelectric in the room temperature region, it is necessary that x> 0.4. When x is increased in a region where x> 0.4, there is a positive correlation between the Ba concentration and the tetragonal degree. Therefore, Sr _1-x Ba _x MnO ₃ exhibits ferroelectricity in the region of x> 0.4. Note that since Ba is completely replaced by Sr when x = 1, the range of Ba concentration in Sr _1-x Ba _x MnO ₃ is 1 ≧ x> 0.4. In consideration of the use as a ferroelectric memory element, a more preferable Ba concentration range is 1 ≧ x> 0.45 in order to ensure sufficient ferroelectricity.

FIG. 3 shows the temperature dependence of the lattice constant ((a) in the figure) and the tetragonal degree ((b) in the figure) in Sr _0.5 Ba _0.5 MnO ₃ obtained in Example 1 described later. Showing gender. The broken line shown in the vicinity of 420 K in FIG. 3 indicates the structural transition temperature at which Sr _0.5 Ba _0.5 MnO ₃ undergoes a structural transition from cubic to tetragonal. Sr _1-x Ba _x MnO ₃ exhibits ferroelectricity when the crystal structure becomes tetragonal. Therefore, the ferroelectric transition temperature coincides with the structural transition temperature. The lattice constants of the a-axis and c-axis show the temperature dependence shown in (a) in FIG. The temperature dependence of tetragonal crystallinity has a peak in the vicinity of 250K, and is substantially constant in a temperature range of about 150K or less (see (b) in FIG. 3). It can be seen that although there is a change in the tetragonal degree of Sr _0.5 Ba _0.5 MnO ₃ in the temperature range of about 420 K or less, there is no structural phase transition. Therefore, Sr _1-x Ba _x MnO ₃ realizes a stable polarization switch and retention of spontaneous polarization in the entire temperature range of about 420 K or less including room temperature.

The broken line illustrated at about 190K in FIG. 3 indicates the antiferromagnetic magnetic transition temperature of Sr _0.5 Ba _0.5 MnO ₃ . As antiferromagnetic ordering occurs between the spins 5 of the Mn ions 3, spin-lattice interaction acts between the spins 5 and the crystal lattice (see also FIG. 1). For this reason, the tetragonal crystallinity is remarkably reduced (see (b) in FIG. 3). Tetragonal crystallinity reflects the lattice strain caused by the sample being in a ferroelectric state. In the case of a displacement type ferroelectric, it is known that the tetragonal degree is proportional to the square of the spontaneous polarization. Therefore, the spontaneous polarization of Sr _1-x Ba _x MnO ₃ changes by about 8 to 9 μC / cm ² at the boundary of the magnetic transition temperature.

(Dependence of electric polarization on electric field)
FIG. 4 shows a ferroelectric polarization hysteresis curve in twin state Sr _0.5 Ba _0.5 MnO ₃ obtained in Example 1 described later. The broken line and the solid line in the figure show the ferroelectric polarization hysteresis curve in the absence of an applied magnetic field and in the presence of an applied magnetic field.

Let P _zero be the value of positive spontaneous polarization in the absence of an applied magnetic field. On the other hand, the value of positive spontaneous polarization in the case of applying an external magnetic field and P _H. As is clear from FIG. 4, it is possible to significantly increase the value of spontaneous polarization by applying an external magnetic field. The value of spontaneous polarization that increases by applying an external magnetic field is approximately the same as the value of spontaneous polarization (8 to 9 μC / cm ² ) that changes with the occurrence of antiferromagnetic magnetic order at the magnetic transition temperature. . When spins 5 are arranged antiferromagnetically by an external magnetic field, Mn ions 3 and O ions 4 are displaced in a direction in which the Mn—O—Mn bond angle deviates from 180 degrees by applying an electric field (also in FIG. 1). reference). Therefore, the electric polarization value increases.

In the temperature region higher than the magnetic transition temperature, Sr _1-x Ba _x MnO ₃ has a weak antiferromagnetic order. Due to the competition between weak antiferromagnetic order and thermal energy, the spin of Mn ions exists in an antiferromagnetic order and swayed (see also FIG. 1). The spontaneous polarization value is increased by forcing the spinning spin into an antiferromagnetic ordered state by applying an external magnetic field. Therefore, lowering the temperature and applying an external magnetic field have the same effect in the sense of bringing the spin into an antiferromagnetic ordered state. That is, by controlling the intensity of the external magnetic field, it is possible to control the spin order state. In other words, it is possible to control the spontaneous polarization value of Sr _1-x Ba _x MnO ₃ by controlling the strength of the external magnetic field.

In the conventional displacement type ferroelectric, the spontaneous polarization value is a value unique to the substance, and it is impossible to control the spontaneous polarization value by an external parameter. However, Sr _1-x Ba _x MnO ₃ has the characteristics of producing ferroelectricity by the displacement of Mn ions having spins and the characteristic of spins having antiferromagnetic order. ing. By utilizing the close relationship between dielectric properties and spin order, the spontaneous polarization value is controlled by an external magnetic field. That is, it is possible to control the spontaneous polarization value of the ferroelectric using the electromagnetic effect.

(Production method)
A method for producing Sr _1-x Ba _x MnO ₃ (1 ≧ x> 0.4) will be described below.

SrCO ₃ , BaCO ₃ and Mn ₂ O ₃ powders are used as starting materials for producing Sr _1-x Ba _x MnO ₃ . In order to obtain the desired composition ratio of Sr _1-x Ba _x MnO ₃ , the respective starting material powders are mixed in a stoichiometric ratio. The mixed powder is fired in an argon gas atmosphere or an argon gas flow. At this time, for example, the firing temperature may be 1100 ° C. and the firing time may be 24 to 36 hours. For the firing, any one of a tubular furnace and an electric furnace capable of controlling the atmosphere may be used. After the fired product is thoroughly ground, it is fired again in an argon gas atmosphere or in an argon gas flow. At this time, for example, the firing temperature may be 1200 ° C. and the firing time may be 24 to 36 hours. The fired product is ground again and pressed into a rod-like shape having a diameter of 5 mm and a length of 5 to 10 cm. By firing the rod-shaped raw material in an argon gas atmosphere or an argon gas flow, a rod _- shaped sample of Sr _1-x Ba _x MnO _3-δ is obtained. Here, δ represents the amount of oxygen deficiency. At this time, for example, the firing temperature may be 1250 ° C. and the firing time may be 24 to 36 hours.

The rod-shaped sample is melted and crystal-grown by the floating zone melting (FZ) method, thereby obtaining a high-quality single crystal of Sr _1-x Ba _x MnO ₃ . As an FZ furnace for performing the FZ method, for example, an FZ furnace commercially available from Canon Machinery Co., Ltd., Crystal System Co., Ltd., and the like can be used. The seed crystal used for making the rod-shaped sample into a high-quality single crystal may be a single crystal or polycrystal of Sr _1-x Ba _x MnO ₃ . Crystal growth by the FZ method is performed in an argon atmosphere or an argon gas flow. The crystal growth rate is 1.5 to 10 mm per hour.

Single crystal obtained here is _{Sr 1-x Ba x MnO 3} -δ having an oxygen deficiency. In order to fill the oxygen deficient portion with oxygen, oxygen annealing is performed as the final step of crystal production. A single crystal of Sr _1-x Ba _x MnO _3-δ produced by the FZ method and an oxidizing agent (KClO ₄ or NaClO ₃ ) are packed together in a gold capsule. The gold capsule is set in the high-pressure synthesizer and annealed under conditions of a pressure of 5 to 7 GPa and an annealing temperature of 400 to 600 ° C. The annealing time is about one week.

  Removal of oxygen vacancies can also be removed by annealing in an ozone atmosphere. The annealing conditions at this time are an annealing temperature of 200 to 300 ° C. and an annealing time of 1 to 2 hours.

The single crystal manufacturing method using the FZ method is a method for obtaining a high-quality single crystal. A high-quality single crystal is necessary for accurate physical property evaluation of Sr _1-x Ba _x MnO ₃ . On the other hand, for industrial use, not only the quality of crystals but also requirements such as short production time and low production cost are required. Therefore, another method for producing Sr _1-x Ba _x MnO ₃ will be described below.

The step of obtaining a fired product of Sr _1-x Ba _x MnO _3-δ by repeating firing and pulverization using powder raw materials of SrCO ₃ , BaCO ₃ and Mn ₂ O ₃ is a single crystal using FZ method. This is the same as the process in the manufacturing method. By grinding this fired product, a powder material of Sr _1-x Ba _x MnO _3-δ is obtained. After a powder material of Sr _1-x Ba _x MnO _3-δ is dispersed in an organic solvent, it is applied on a substrate using a spin coating method. Thereafter, by baking, a crystal thin film of Sr _1-x Ba _x MnO _3-δ can be obtained. Thereafter, in the oxygen gas flow, by performing oxygen annealing at an annealing temperature of 400 to 600 ° C. and an annealing time of about one week, a thin film crystal of Sr _1-x Ba _x MnO ₃ in which oxygen deficient portions are filled with oxygen is obtained. .

As still another method for producing the Sr _1-x Ba _x MnO ₃ crystal thin film, a chemical vapor deposition (CVD) method, a sputtering method, a pulse laser deposition (PLD) method, or the like may be used. The composition of the sample after the film formation is Sr _1-x Ba _x MnO _{3 -δ} , but the thin film crystal of Sr _1-x Ba _x MnO ₃ from which oxygen defects are removed by oxygen annealing in the oxygen gas flow. can get.

(Modification 1)
Sr is a modification of the _{1-x Ba x MnO 3 Sr} 1-x Ba x Mn 1-y A y O 3 (A = Al, Ga, Fe and Cr) will be described below.

_{Sr 1-x Ba x Mn 1} -y A y O 3 _is substituted for the Mn site in _{Sr 1-x Ba x MnO 3} Al, Ga, In at least one element A selected from the group consisting of Fe and Cr This is a manganese oxide having a perovskite structure. Incidentally, if the herein was expressed as _{Sr 1-x Ba x Mn 1} -y A y O 3 , unless otherwise specified in the _{Sr 1-x Ba x Mn 1} -y A y O 3 having a perovskite structure Means that.

Said y represents the ratio of the Mn site substituted by the ion of element A (a form of trivalent ion) when all Mn sites are 1, and 0.5 ≧ y> 0. In order to replace Mn, y is a number larger than 0. Even if the Mn site is replaced with any element of Al, Ga, Fe and Cr, the dielectric constant characteristics of Sr _1-x Ba _x MnO ₃ are greatly impaired if y is in the range of 0.5 or less. There is no. That is, the crystal structure does not change from the perovskite structure to another structure.

FIG. 5 shows Sr _1-x Ba _x MnO _{3 as} a base material, Sr _1-x Ba _x Mn _0.99 Al _0.01 O _{3 in} which 1% of all Mn sites are substituted with Al (see also Example 2). ) And the electric field dependence of the electric polarization of Sr _1-x Ba _x Mn _0.99 Ga _0.01 O ₃ (see also Example 2) in which 1% of all Mn sites are substituted with Ga. The squareness ratios of the saturation polarization value, spontaneous polarization value and ferroelectric polarization hysteresis curve are Sr _1-x Ba _x MnO ₃ , Sr _1-x Ba _x Mn _0.99 Al _0.01 O ₃ and Sr _1-x Ba _x. It is different for each of Mn _0.99 Ga _0.01 O ₃ . However, all samples show good ferroelectric properties.

A characteristic of Sr _1-x Ba _x MnO ₃ is that a relatively large leakage current flows. This leakage current is caused by a high carrier density in the crystal, and the carrier density increases when trivalent Mn ions are mixed in Sr _1-x Ba _x MnO ₃ . By adding trivalent metal ions such as Al, Ga, Fe and Cr, generation of trivalent Mn ions can be suppressed, and the residual carrier density in the manganese oxide can be reduced. As a result, it is possible to stabilize the switch operation in a temperature region near room temperature. In addition, since the effect of adding a trivalent metal ion appears even in a minute amount, the above y is 0.05 ≧ y> 0 from the viewpoint of maintaining various characteristics inherent in Sr _1-x Ba _x MnO _3. Is more preferable.

Hereinafter, a method for producing Sr _1-x Ba _x Mn _1-y A _y O ₃ will be described. The method for preparing the crystal sample is the same as that of Sr _1-x Ba _x MnO ₃ except that the oxide of element A to be substituted is used in addition to SrCO ₃ , BaCO ₃ , and Mn ₂ O ₃ as a starting material. For example, when substituting Mn sites 3 with Al, powders of SrCO ₃ , BaCO ₃ , Mn ₂ O ₃ and Al ₂ O ₃ may be mixed so as to obtain a desired stoichiometric ratio. The subsequent manufacturing method is the same as that of Sr _1-x Ba _x MnO _3, and is therefore omitted here.

(Modification 2)
Described below _{Sr 1-x Ba x Mn 1} -z D z O 3 is a variation of _{Sr 1-x} Ba _x MnO ₃ according to an embodiment of the present invention (D = Ti, Zr and Hf).

_{Sr 1-x Ba x Mn 1} -z D z O 3 _is be substituted with at least one element D selected from the group consisting of Mn sites in _{Sr 1-x Ba x MnO 3} Ti, from Zr and Hf Is a manganese oxide having a perovskite structure. Incidentally, if the herein was expressed as _{Sr 1-x Ba x Mn 1} -z D z O 3 , unless otherwise specified in the _{Sr 1-x Ba x Mn 1} -z D z O 3 having a perovskite structure Means that.

Said z represents the ratio of the Mn site substituted with the ion of the element D (form of a tetravalent ion) when all Mn sites are set to 1, and is 0.5> = z> 0. In order to replace Mn, z is a number greater than 0. Even if the Mn site is replaced with any element of Ti, Zr and Hf, the dielectric constant characteristics of Sr _1-x Ba _x MnO ₃ are not significantly impaired if z is in the range of 0.5 or less. . That is, the crystal structure does not change from a perovskite structure to another structure.

By replacing the Mn site of Sr _1-x Ba _x MnO ₃ with any element of Ti, Zr, and Hf, it is possible to control only the magnetic transition temperature without changing the ferroelectric transition temperature. Become. This means that when the electric polarization of manganese oxide is changed using an externally applied magnetic field, the degree of change can be controlled. In the temperature region near _300K, a magnetic field is applied to _{Sr 1-x Ba x Mn 1} -z D z O 3. In the case of a sample having a low magnetic transition temperature, the magnetic order at 300 K is weak, and as a result, the magnetic fluctuation becomes large. For this reason, the magnetic fluctuation suppressed by applying an external magnetic field increases, and the change in electric polarization also increases. On the other hand, in the case of a sample having a high magnetic transition temperature, a certain degree of magnetic order is maintained even at 300K. That is, it is considered that the magnetic fluctuation is relatively small even when no external magnetic field is applied. Therefore, the effect of suppressing magnetic fluctuation by applying an external magnetic field is relatively small, and the change in electric polarization is also small.

Hereinafter, a method for producing Sr _1-x Ba _x Mn _1-z D _z O ₃ will be described. The method for preparing the crystal sample is the same as Sr _1-x Ba _x MnO ₃ except that the oxide of element D to be substituted is used in addition to SrCO ₃ , BaCO ₃ , and Mn ₂ O ₃ as starting materials. For example, when substituting Mn with Ti, powders of SrCO ₃ , BaCO ₃ , Mn ₂ O ₃ and TiO ₂ may be mixed so as to obtain a desired stoichiometric ratio. The subsequent manufacturing method is the same as that of Sr _1-x Ba _x MnO _3, and is therefore omitted here.

[Embodiment 2]
(Ferroelectric memory device)
Nonvolatile memories using a ferroelectric material can be broadly classified into two types: a capacitor type and a field effect transistor (FET) type. Here, a ferroelectric memory element used as a capacitor type will be described.

  FIG. 6 shows a schematic diagram of the configuration of the ferroelectric memory element 10 according to an embodiment of the present invention. The ferroelectric memory element 10 includes a ferroelectric layer 11, a lower electrode (first electrode) 12, and an upper electrode (second electrode) 13. The ferroelectric layer 11 includes any one of the manganese oxides described in the first embodiment as a ferroelectric. The polarization direction of the manganese oxide is a direction perpendicular to the in-plane direction of the ferroelectric layer 11.

  The lower electrode 12 and the upper electrode 13 are provided so as to sandwich the ferroelectric layer 11 therebetween. As a material constituting the lower electrode 12 and the upper electrode 13, a highly conductive substance such as Cu, Al, Ti, Pt, and Au may be used.

  When information is recorded in the ferroelectric memory element 10, a pulse voltage is applied to the lower electrode 12 and the upper electrode 13. By applying the pulse voltage, an external electric field is generated on the surfaces of both ends of the ferroelectric layer 11 (surfaces in which the lower electrode 12 and the upper electrode 13 are in direct contact). As a result, the ferroelectric layer 11 Spontaneously polarized. The polarization direction 105 of spontaneous polarization (see FIG. 7) is determined by the polarity of the applied pulse voltage. For example, when the lower electrode 11 is a plus electrode and the upper electrode is a minus electrode (in this case, the polarity is I), the recording state is “1”. On the other hand, when the lower electrode 11 is a negative electrode and the upper electrode is a positive electrode (in this case, the polarity is II), the recording state is “0”. As a result, binary values can be recorded as in the case of using a conventional displacement type ferroelectric substance.

  Furthermore, in the ferroelectric memory element 10 according to the embodiment of the present invention, the spontaneous polarization value of the ferroelectric layer 11 can be controlled by applying an external magnetic field when recording information by applying a pulse voltage. it can. In addition to the selection of polarity I and polarity II, the value of spontaneous polarization is controlled by selecting the presence or absence of an external magnetic field. In this case, four values can be recorded in one ferroelectric memory element 10. That is, the ferroelectric memory 10 realizes multi-value recording. Specifically, the value of the spontaneous polarization with the polarity I and the presence of a magnetic field is set to the recording state “11”. The value of spontaneous polarization with polarity I and no magnetic field is assumed to be the recording state “10”. The value of the spontaneous polarization with the polarity II and the presence of a magnetic field is defined as a recording state “01”. The value of spontaneous polarization with polarity II and no magnetic field is assumed to be the recording state “00”.

  By controlling the strength of the applied magnetic field in multiple stages, the number of states that can be recorded in one ferroelectric memory element 10 can be further increased. Therefore, the ferroelectric memory element 10 according to the embodiment of the present invention can increase the density of the ferroelectric memory.

(Modification 1)
As a modification of the capacitor-type ferroelectric memory device according to one embodiment of the present invention, a schematic diagram of a configuration of a ferroelectric memory device 20 is shown in FIG. Note that members common to the ferroelectric memory element 10 are denoted by common member numbers and description thereof is omitted.

  The ferroelectric memory element 20 includes an insulator layer 21 in addition to the ferroelectric layer 11, the lower electrode 12 and the upper electrode 13. The upper electrode 12 is formed on the ferroelectric layer 11 via the insulator layer 21. By providing the ferroelectric memory element 20 with the above-described configuration, deterioration of the ferroelectric layer 11 with time can be suppressed. The insulator layer 21 only needs to be formed on one or both of the upper and lower surfaces of the ferroelectric layer 11. For the insulator layer 21, for example, an oxide such as silicon oxide can be used.

(Modification 2)
FIG. 9 shows a schematic diagram of a configuration of a ferroelectric memory element 30 as another modification of the ferroelectric memory element according to the embodiment of the present invention. Note that members common to the ferroelectric memory element 10 are denoted by common member numbers and description thereof is omitted.

  The ferroelectric memory element 30 is an FET type ferroelectric memory element. In the ferroelectric memory element 30, the ferroelectric layer 11 is formed on the upper surface of the channel region 32 formed on the surface of the silicon substrate 31. A drain region 33 and a source region 35 are provided on the surface of the silicon substrate 31 and are connected to a drain electrode 34 and a source electrode 36, respectively. An upper electrode 13 is formed on the upper surface of the ferroelectric layer 11, and the upper electrode 13 is connected to the gate electrode 37. In the ferroelectric memory element 30, the channel region 32 functions as a lower electrode (first electrode).

  Since the ferroelectric memory element 30 has the above-described configuration, it is possible to form the ferroelectric memory element on the silicon substrate without providing a capacitor structure different from the CMOS structure. Therefore, the process flow can be integrated in the manufacturing process of the ferroelectric memory element and the manufacturing process of the transistor having the CMOS structure constituting the logic circuit. As a result, the manufacturing cost can be reduced.

  When information is recorded in the ferroelectric memory element 30, a pulse voltage is applied to the source electrode 36 and the gate electrode 37. When the pulse voltage is applied, the spontaneous polarization value generated by the ferroelectric layer 11 can be controlled by controlling the strength of the external magnetic field applied to the ferroelectric memory element 30. That is, even in the channel type ferroelectric memory element 30, multilevel recording is realized by using the ferroelectric layer 11.

(Modification 3)
FIG. 10 shows a schematic diagram of a configuration of a ferroelectric memory element 40 as still another modification of the ferroelectric memory element according to the embodiment of the present invention. Note that members common to the ferroelectric memory element 30 are denoted by common member numbers and description thereof is omitted.

  The ferroelectric memory element 40 is different from the ferroelectric memory element 30 in that an insulating layer 21 is provided between the ferroelectric layer 11 and the channel region 32. As the insulator layer 21, an oxide film such as silicon oxide can be used. By providing the ferroelectric memory element 40 with the above-described configuration, deterioration of the ferroelectric layer 11 with time can be suppressed.

(Modification 4)
FIG. 11 shows a schematic diagram of a configuration of a ferroelectric memory device 50 as still another modification of the ferroelectric memory device according to the embodiment of the present invention. Members common to the ferroelectric memory elements 30 and 40 are denoted by common member numbers, and description thereof is omitted.

  The ferroelectric memory element 50 is different from the ferroelectric memory element 30 in that a metal buffer layer 51 is provided between the ferroelectric layer 11 and the channel region 32. In other words, the configuration of the ferroelectric memory element 50 is a configuration in which the insulator layer 21 included in the ferroelectric memory element 40 is replaced with a metal buffer layer 51. The drain region 34 and the source region 35 formed on the silicon substrate surface and the metal buffer layer 51 are not in direct contact with each other. By providing the ferroelectric memory element 50 with the metal buffer layer 51, deterioration of the ferroelectric layer 11 with time can be suppressed. At the same time, since it is not necessary to provide the insulator layer 21 between the ferroelectric layer 11 and the channel region 32, a decrease in the spontaneous polarization value can be suppressed. Therefore, an improvement in the reliability of the ferroelectric memory element can be expected.

[Embodiment 3]
(Ferroelectric memory device)
A ferroelectric memory device 100 according to an embodiment of the present invention will be described with reference to FIG. In addition, about the member which has the same structure as the said Embodiment 2, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The ferroelectric memory device 100 includes a ferroelectric memory element array in which ferroelectric memory elements 10 are arranged in a matrix, a plurality of word lines 101, and a plurality of bit lines 102. The word line 101 is a wiring arranged in the row direction of the ferroelectric memory element array. The word line 101 and the lower electrode 12 of the ferroelectric memory element 10 arranged in the row direction are electrically connected. The bit line 102 is a wiring arranged in the column direction of the ferroelectric memory element array. Further, the bit line 102 and the upper electrode 13 of the ferroelectric memory element 10 arranged in the column direction are electrically connected. The ferroelectric memory device 100 has a device structure in which a nonmagnetic solid material (not shown in FIG. 7) is embedded between a plurality of ferroelectric memory elements 10.

  The ferroelectric memory device 100 further includes a coil 103. The coil 103 is an external magnetic field applying unit used when information is recorded in the ferroelectric memory element 10. Specifically, the wiring is arranged so as to surround the ferroelectric memory element array. By passing a current in the direction of the arrow shown in FIG. 7 in the coil 103, an external magnetic field 104 having a substantially uniform intensity is applied to a region inside the coil. By controlling the value of the current flowing through the coil 103, the strength of the external magnetic field 104 applied to the ferroelectric memory element 10 can be controlled.

  The ferroelectric memory device 100 may be configured as a recording medium in which the coil 103 is provided on the ferroelectric memory element array substrate (see FIG. 7), but the coil 103 is connected to the ferroelectric memory element array substrate. May be provided separately.

(Outline of information recording)
One of the plurality of word lines 101 is selected. Similarly, any one of the plurality of bit lines 102 is selected. When a voltage pulse is applied to the selected word line 101 and bit line 102, an electric field is generated only in the ferroelectric memory element 10 where the selected word line 101 and bit line 102 intersect. That is, one ferroelectric memory element 10 is selected from the ferroelectric memory array by selecting one word line 101 and one bit line 102 from the plurality of word lines 101 and the plurality of bit lines 102, respectively.

In accordance with the state (spontaneous polarization value) recorded in the selected ferroelectric memory element 10, a current is passed through the coil 103 to generate the external magnetic field 104. For example, when it is desired to record the spontaneous polarization value P ₁ , the external magnetic field 104 having the intensity H ₁ corresponding to P ₁ is generated. For this purpose, the current I ₁ may be passed through the coil 103. By applying a voltage pulse to the selected word line 101 and bit line 102 in the state where an external magnetic field of intensity H ₁ is applied, the spontaneous polarization value P ₁ is recorded in the selected ferroelectric memory element 10. . Note that the polarization direction 105 can be controlled by controlling the polarity of the voltage pulse applied to the word line 101 and the bit line 102.

If you want to record in different spontaneous polarization value ferroelectric memory device 10 of P ₂ which is the P ₁ generates an external magnetic field 104 of the intensity H ₂ corresponding to P _2. For that purpose, the current I ₂ may be passed through the coil 103. By applying a voltage pulse to the selected word line 101 and bit line 102 in a state where an external magnetic field of strength H ₂ is applied, the spontaneous polarization value P ₂ is recorded in the selected ferroelectric memory element 10. .

  The external magnetic field 104 necessary for recording the desired spontaneous polarization value and the current value to be passed through the coil 103 for applying the external magnetic field 104 are determined by performing a preliminary experiment or performing a simulation in advance. You only need to know the correspondence. The correspondence relationship may be recorded as a look-up table and may be part of the configuration of the ferroelectric memory device 100.

  In the ferroelectric memory device 100 according to the embodiment of the present invention, the number of the ferroelectric memory elements 10 constituting the ferroelectric memory element array may be arbitrary. Further, the number of the ferroelectric memory elements 10 surrounded by one coil 103 may be arbitrary.

  In the present embodiment, the polarization direction of the ferroelectric memory element 10 and the direction of the external magnetic field 104 have been described as being parallel. However, the polarization direction of the ferroelectric memory element 10 and the direction of the external magnetic field 104 may be perpendicular.

(Reading information)
As in the case of information recording, the word line 101 and the bit line 102 corresponding to the ferroelectric memory element 10 from which information is to be read are selected. By specifying the voltage value resulting from the spontaneous polarization value generated between the selected word line 101 and bit line 102, the spontaneous polarization value recorded in the ferroelectric memory element 10 can be specified. That is, the recorded information can be read. As a method for specifying the voltage value resulting from the spontaneous polarization value, a conventionally used method may be used in the capacitor-type ferroelectric memory.

  Even in the case where the ferroelectric memory device includes the FET type ferroelectric memory elements 30, 40, and 50, a conventional reading method may be used in the FET type ferroelectric memory.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to this example.

[Example 1]
In accordance with the method described below, Sr _1-x Ba _x MnO ₃ crystals having a Ba concentration range of 0.5 ≧ x ≧ 0 were prepared, and the lattice constants of the a-axis and c-axis of each crystal were measured. Furthermore, the temperature dependence of lattice constant and tetragonal degree and the electric field dependence of electric polarization were measured for crystals with x = 0.5.

(Method for producing Sr _1-x Ba _x MnO ₃ )
In Sr _1-x Ba _x MnO ₃ , crystals with a Ba concentration in the range of 0.5 ≧ x ≧ 0 were produced by changing the mixing ratio of the starting materials. As the starting material, powders of SrCO ₃ , BaCO ₃ and Mn ₂ O ₃ marketed by High Purity Chemical Laboratory Co., Ltd. were used. Each raw material was weighed and mixed so as to obtain a desired stoichiometric ratio.

Then, it baked in argon atmosphere using the tubular furnace. The firing conditions were a firing temperature of 1100 ° C. and a firing time of 36 hours. After the fired product was thoroughly ground, it was fired again in an argon atmosphere using a tubular furnace. The conditions for the second firing were a firing temperature of 1200 ° C. and a firing time of 36 hours. After the fired product is ground again, pressure is applied to a rod-like shape having a diameter of about 5 mm and a length of about 7.5 cm to be hardened. At this time, the applied pressure was 10 MPa. The powder sample pressed into a rod shape was further fired in an argon atmosphere. The firing conditions at this time were a firing temperature of 1250 ° C. and a firing time of 36 hours. As a result, a rod-shaped sample of Sr _1-x Ba _x MnO _3-δ (0.5 ≧ x ≧ 0) was obtained.

The rod-shaped sample was melted and crystal-grown using the FZ method to obtain a single crystal of Sr _1-x Ba _x MnO _3-δ (0.5 ≧ x ≧ 0). When performing FZ method, the FZ furnace marketed by Canon Machinery Co., Ltd. was used. Crystal growth by the FZ method was performed in an argon gas atmosphere. The crystal growth rate was 5 mm per hour.

Single crystal obtained by the FZ method is _{Sr 1-x Ba x MnO 3} -δ having an oxygen deficiency. In order to remove oxygen vacancies, oxygen annealing was performed as the final step of crystal production. For oxygen annealing, a high-pressure synthesizer commercially available from Tri Engineering was used. A gold capsule packed together with a single crystal of Sr _1-x Ba _x MnO _3-δ and KClO ₄ acting as an oxidizing agent was set in a high-pressure synthesizer. Then, oxygen annealing was performed under conditions of a pressure of 6 GPa, an annealing temperature of 600 ° C., and an annealing time of 1 hour. As a result, a single crystal of Sr _1-x Ba _x MnO ₃ (0.5 ≧ x ≧ 0) without oxygen deficiency and completely filled with oxygen was obtained.

(Dependence of crystal structure on Ba concentration)
X-ray diffraction was measured for each sample of Sr _1-x Ba _x MnO ₃ (0.5 ≧ x ≧ 0) grown by the FZ method using a RINT-III X-ray diffractometer manufactured by Rigaku Corporation. As a result, it was confirmed that any sample of Sr _1-x Ba _x MnO ₃ (0.5 ≧ x ≧ 0) was a single crystal having a perovskite structure. The a-axis and c-axis lattice constants and tetragonal degree obtained from the result of the X-ray diffraction measurement were obtained. The measurement conditions for the X-ray diffraction measurement are as follows.
・ Sampling width: 0.02 degrees ・ Scanning speed: 2 degrees per minute ・ Divergent slit: 0.67 degrees ・ Scattering slit: 0.67 degrees ・ Reception slit: 0.3 mm
Measurement temperature: room temperature The results are as shown in FIG.

(Temperature dependence of crystal structure)
FIG. 3 shows the temperature dependence of the a-axis and c-axis lattice constants and the tetragonal degree in the Sr _1-x Ba _x MnO ₃ (x = 0.5) single crystal. The lattice constant was measured with a RINT-III X-ray diffractometer manufactured by Rigaku Corporation. The measurement conditions are as follows.
・ Sampling width: 0.02 degrees ・ Scanning speed: 2 degrees per minute ・ Divergent slit: 0.67 degrees ・ Scattering slit: 0.67 degrees ・ Reception slit: 0.3 mm
・ Measurement temperature: 4.2-450K
(Dependence of electric polarization on electric field)
FIG. 4 shows the result of measuring the electric field dependence of the electric polarization using twin state Sr _0.5 Ba _0.5 MnO ₃ . In FIG. 4, the measurement result when no external magnetic field is applied is indicated by a broken line, and the measurement result when an external magnetic field is applied is indicated by a solid line. For the electric field dependence measurement of electric polarization, a Precision Premier II apparatus manufactured by Radiant Technology was used. The frequency of the applied electric field was 1 kHz, and the application direction was the c-axis direction. The measurement temperature is room temperature.

When an external magnetic field was not applied, an electric polarization value of 8 to 9 μC / cm ² was shown at an electric field strength of 100 kV / cm. Thereafter, even when the electric field strength was 0 kV / cm, a spontaneous polarization value (P _zero ) of 4.5 μC / cm ² was exhibited. From this, it was confirmed that Sr _1-x Ba _x MnO ₃ (x = 0.5) in the twin state has ferroelectric characteristics.

When an external magnetic field was applied in the c-axis direction, an electric polarization value of ²⁰ μC / cm ² was shown at an electric field strength of 100 kV / cm. Thereafter, even when the electric field strength was 0 kV / cm, a spontaneous polarization value (P _H ) of about 13 μC / cm ² was exhibited. From this, it was confirmed that the ferroelectric characteristics can be controlled by controlling the external magnetic field to be applied in twin Sr _0.5 Ba _0.5 MnO ₃ .

In this example, twin-state Sr _1-x Ba _x MnO ₃ (x = 0.5) was used, so P _zero = 4.5 μC / cm ² . However, by using a single domain Sr _1-x Ba _x MnO ₃ single crystal, P _zero becomes 13.5 μC / cm ² . This spontaneous polarization value is comparable to that of BaTiO ₃ , which is a conventional displacement type ferroelectric substance. Therefore, it is possible to produce a magnetic ferroelectric material having ferroelectric properties equivalent to those of a conventional displacement ferroelectric material.

[Example 2]
Sr _0.5 Ba _0.5 Mn _0.99 Al _0.01 O ₃ added with 1% Al ions and Ga ions added 1% to twin Sr _0.5 Ba _0.5 MnO ₃ Sr _0.5 Ba _0.5 Mn _0.99 Ga _0.01 O ₃ was prepared, and the electric field dependence of electric polarization was measured.

_{(Sr 1-x Ba x Mn} 1-y A y O 3 (A = Al and Ga) a method for manufacturing a)
Preparation of Sr _0.5 Ba _0.5 Mn _0.99 Al _0.01 O ₃ and Sr _0.5 Ba _0.5 MnO ₃ , Sr _0.5 Ba _0.5 Mn _0.99 Ga _0.01 O ₃ The method is basically the same as the method for producing Sr _1-x Ba _x MnO ₃ described in Example 1. The difference from the method for producing Sr _1-x Ba _x MnO ₃ is that Al ₂ O ₃ and Ga ₂ O ₃ are used as main raw materials for adding Al and Ga.

In order to produce Sr _0.5 Ba _0.5 Mn _0.99 Al _0.01 O ₃ , SrCO ₃ , BaCO ₃ , Mn ₂ O ₃ and high purity chemical research institute, which are commercially available as starting materials, and Al ₂ O ₃ powder was used. Each raw material was weighed and mixed so as to have a desired stoichiometric ratio, and then Sr _0.5 Ba was used using the same method as the method for producing Sr _1-x Ba _x MnO ₃ described in Example 1. _0.5 Mn _0.99 Al _0.01 O ₃ was produced.

In order to produce Sr _0.5 Ba _0.5 Mn _0.99 Ga _0.01 O ₃ , SrCO ₃ , BaCO ₃ , Mn ₂ O ₃ and high-purity chemical research institute, which are commercially available as starting materials, and Ga ₂ O ₃ powder was used. Each raw material was weighed and mixed so as to have a desired stoichiometric ratio, and then Sr _0.5 Ba was used using the same method as the method for producing Sr _1-x Ba _x MnO ₃ described in Example 1. _0.5 Mn _0.99 Ga _0.01 O ₃ was produced.

(Electric field dependence of electric polarization value)
Electricity for Sr _0.5 Ba _0.5 MnO ₃ , Sr _0.5 Ba _0.5 Mn _0.99 Al _0.01 O ₃ and Sr _0.5 Ba _0.5 Mn _0.99 Ga _0.01 O ₃ The result of measuring the electric field dependence of polarization is shown in FIG. The electric field dependence of the electric polarization was measured using a Precision Premier II apparatus manufactured by Radiant Technology. The measurement temperature is room temperature.

By adding Al 1% and Ga 1% to Sr _0.5 Ba _0.5 MnO ₃ , an electric polarization value, a spontaneous polarization value, and a ferroelectric polarization hysteresis curve when an electric field strength of 100 kV / cm is applied. The squareness ratio has changed. However, both Sr _0.5 Ba _0.5 Mn _0.99 Al _0.01 O ₃ and Sr _0.5 Ba _0.5 Mn _0.99 Ga _0.01 O ₃ crystals have good ferroelectric properties. I confirmed that I have it.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be used as a ferroelectric substance provided in a ferroelectric memory that does not contain a lead element that is a harmful element as a main raw material and enables multi-value recording made of inexpensive elements.

1 Unit cell 2 Sr site 3 Mn ion 4 O ion 5 Spin 10 Ferroelectric memory element 11 Ferroelectric layer 12 Lower electrode (first electrode)
13 Upper electrode (second electrode)
20 Ferroelectric Memory Device 21 Insulator Layer 30 Ferroelectric Memory Device 31 Silicon Substrate 32 Channel Region (First Electrode)
33 Drain region 34 Drain electrode 35 Source region 36 Source electrode 37 Gate electrode 40 Ferroelectric memory device 50 Ferroelectric memory device 51 Metal buffer layer 100 Ferroelectric memory device 101 Word line 102 Bit line 103 Coil (external magnetic field applying means) )
104 External magnetic field 105 Polarization direction

Claims (6)

The following formula (1) having a perovskite structure
Sr _1-x Ba _x MnO ₃ (1 > x> 0.4) (1)
Manganese oxide represented by 2. The manganese oxide according to claim 1, wherein the Mn site is replaced with at least one element A selected from the group consisting of Al (aluminum), Ga (gallium), Fe (iron), and Cr (chromium). The following formula (2)
Sr _1-x Ba _x Mn _1-y A _y O ₃ (0.5 ≧ y> 0) (2)
Manganese oxide represented by   The manganese oxide according to claim 2, wherein y is in a range of 0.05 ≧ y> 0.   A ferroelectric memory device comprising the manganese oxide according to claim 1 as a ferroelectric.   The ferroelectric memory element according to claim 4, further comprising a first electrode and a second electrode provided on a surface perpendicular to the polarization direction of the manganese oxide so as to sandwich the manganese oxide. A ferroelectric memory element array comprising a plurality of the ferroelectric memory elements according to claim 5 in a matrix,
A plurality of word lines electrically connected to one of the first electrode and the second electrode, and electrically connecting the ferroelectric memory element in one of a row direction and a column direction; ,
A plurality of bits electrically connected to the other of the first electrode and the second electrode, and electrically connecting the ferroelectric memory element in a direction different from the word line in a row direction and a column direction Lines and,
A ferroelectric memory device comprising: an external magnetic field applying unit that applies an external magnetic field in either one direction parallel to or perpendicular to the polarization direction of the manganese oxide.

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