JP5311375B2 - Switching element - Google Patents

Description

  The present invention relates to a switching element capable of switching between two states.

  In the technical field of nonvolatile memory, ReRAM (resistive RAM) has attracted attention. The ReRAM is a switching element capable of switching between two states having different resistance states. Generally, the ReRAM is switched between a high resistance state and a low resistance state according to a voltage applied between the pair of electrodes and the electrode pair. And a recording film that can be selectively switched. In ReRAM, information can be recorded or rewritten using selective switching of the resistance state of the recording film. Such ReRAMs or switching elements are described, for example, in Patent Documents 1 to 4 below.

JP 2004-273615 A JP 2004-281913 A JP-A-2005-123361 JP 2005-203463 A

  ReRAM is roughly classified into bipolar and unipolar types from the viewpoint of electrical characteristics. In the bipolar type ReRAM, the voltage application direction between the electrode pair for changing the recording film from the high resistance state to the low resistance state, and between the electrode pair for changing the recording film from the low resistance state to the high resistance state. The direction of voltage application is different. That is, in the bipolar type ReRAM, voltages having different polarities are used in two kinds of resistance state changes or switching. On the other hand, in the unipolar type ReRAM, the voltage application direction between the electrode pair for changing the recording film from the high resistance state to the low resistance state, and the electrode for changing the recording film from the low resistance state to the high resistance state. The direction of voltage application between the pair is the same. That is, in the unipolar ReRAM, voltages having the same polarity are used in two types of resistance state changes.

Bipolar type ReRAM can generally operate at higher speed than unipolar type ReRAM. As the bipolar ReRAM, for example, a predetermined ReRAM having a recording film made of PrCaMnO ₃ and a predetermined ReRAM having a recording film made of SrZrO ₃ to which Cr is added have been reported. However, for these ReRAMs, the fact that bipolar operation is possible is known, but the operating principle such as how switching between two states with different resistance states occurs is not specified. There is. For switching elements such as ReRAM, if the operating principle is unknown, optimization guidelines such as material selection and design dimensions for each part of the element cannot be determined, and optimization in element design is difficult.

  The present invention has been conceived under the circumstances as described above, and it is an object of the present invention to provide a switching element capable of bipolar state switching operation on a predetermined operating principle.

  According to a first aspect of the present invention, a switching element is provided. The switching element includes a first electrode, a second electrode, a switching metal portion, a first oxide portion located between the first electrode and the switching metal portion and having P-type semiconductivity, and a second electrode. And a second oxide part located between the switching metal parts and having P-type semiconductivity. The switching metal part is a part made of a pure metal or a part made of a material exhibiting metallic conductivity.

  About this switching element which has such a structure, the polarization direction in a switching metal part can be switched selectively.

  When a voltage is applied between the first and second electrodes of the switching element as a positive electrode and a negative electrode, respectively, a partial pressure is applied to the first oxide portion using the first electrode and the switching metal portion as a positive electrode and a negative electrode, respectively. The second oxide part is subjected to partial pressure with the second electrode and the switching metal part as the negative electrode and the positive electrode, respectively. Then, the first and second electrodes are respectively used as a positive electrode and a negative electrode, a predetermined voltage is applied between the electrodes for a predetermined time, oxygen ions are generated in the first oxide portion by electric field action, and the oxygen ions are The first electrode partially oxidizes and takes in the oxygen ions. At this time, oxygen ions emit electrons. At the same time, oxygen vacancies with positive charges are generated and accumulated in the first oxide portion that releases constituent oxygen as oxygen ions to the first electrode, and a predetermined internal electric field is formed. This internal electric field prevents the supply of holes (carriers) from the first electrode to the P-type semiconducting first oxide part and the movement of holes in the first oxide part. Therefore, the resistance value of the first oxide portion increases due to the formation of the internal electric field, and the first oxide portion reaches a high resistance state (high resistance of the first oxide portion).

  On the other hand, a current flows between the first electrode from which electrons are released from oxygen ions and the switching metal part via the second electrode and the second oxide part. Specifically, electrons flow as carriers from the first electrode through the external power supply circuit to the second electrode, and exchange of electrons and holes at the interface between the second electrode and the P-type semiconducting second oxide portion. The holes flow as carriers in the second oxide part, and exchange of holes and electrons occurs at the interface between the second oxide part and the switching metal part. The electrons move to the first oxide part side (that is, toward the junction interface between the switching metal part and the first oxide part) in the switching metal part, but the switching metal part and the P-type semiconductor At the interface with the first oxide portion, the exchange of electrons and holes does not occur sufficiently. Since the first oxide part is in a high resistance state as described above in which hole movement and hole supply from the first electrode are suppressed, holes supplied to the interface between the switching metal part and the first oxide part This is because there is considerably less.

  Therefore, electrons are accumulated in the vicinity of the interface with the first oxide portion in the switching metal portion (the accumulated electrons and the above-described oxygen vacancies existing in the first oxide portion with a positive charge). In the meantime, electrostatic attraction occurs). As a result, the electron density distribution is biased in the switching metal part. In this way, polarization in a predetermined direction is induced in the switching metal part (first switching state of the switching metal part). Even if the applied voltage between the first and second electrodes is extinguished, the above-described high resistance state of the first oxide portion is maintained, and the above-described oxygen vacancy existing in the first oxide portion with a positive charge It attracts the above-mentioned stored electrons in the switching metal part, and therefore the first polarization state of the switching metal part is maintained.

  In this switching element, by applying a predetermined voltage between the first and second electrodes in a direction opposite to the voltage application direction for realizing the first polarization state, the polarization direction of the switching metal portion is as follows. Can be reversed.

  When a voltage is applied between the first and second electrodes of the switching element in which the first oxide portion is in a high resistance state and the switching metal portion is in the first polarization state as the negative electrode and the positive electrode, Part pressure is applied with the first electrode and the switching metal part as the negative electrode and the positive electrode, respectively, and the second oxide part is applied with partial pressure with the second electrode and the switching metal part as the positive electrode and the negative electrode, respectively. Then, the first and second electrodes are respectively used as a negative electrode and a positive electrode, a predetermined voltage is applied between the electrodes for a predetermined time, and by the electric field action, oxygen ions are generated in the partial oxidation region in the first electrode, and When the oxygen ions are moved to the first oxide portion, the oxygen vacancies with positive charges are electrically neutralized in the first oxide portion that has received the oxygen ions, and the presence of the oxygen vacancies. The internal electric field due to the disappearance. As a result, the resistance value of the first oxide portion decreases, and the first oxide portion reaches a low resistance state (lower resistance of the first oxide portion). Holes are easily supplied from the first electrode and the switching metal portion to the P-type semiconducting first oxide portion in the low resistance state, and the holes are likely to move in the first oxide portion.

  On the other hand, the first and second electrodes are used as the negative electrode and the positive electrode, respectively, and a predetermined voltage is applied between the electrodes for a predetermined time to generate oxygen ions in the second oxide portion by electric field action and When moved to the second electrode, the second electrode is partially oxidized and takes up the oxygen ions. At this time, oxygen ions emit electrons. At the same time, oxygen vacancies with positive charges are generated and accumulated in the second oxide portion that releases constituent oxygen as oxygen ions to the second electrode, and a predetermined internal electric field is formed. This internal electric field hinders the supply of holes (carriers) from the second electrode to the P-type semiconducting second oxide part and the movement of holes in the second oxide part. Therefore, the formation of the internal electric field increases the resistance value of the second oxide part, and the second oxide part reaches a high resistance state (high resistance of the second oxide part).

  On the other hand, a current flows between the second electrode from which electrons are released from oxygen ions and the switching metal part via the first electrode and the first oxide part. Specifically, electrons flow as carriers from the second electrode through the external power supply circuit to the first electrode, and exchange of electrons and holes at the interface between the first electrode and the P-type semiconducting first oxide portion. The holes flow as carriers in the first oxide portion, and exchange of holes and electrons occurs at the interface between the first oxide portion and the switching metal portion. The electrons move toward the second oxide part in the switching metal part (that is, toward the junction interface between the switching metal part and the second oxide part). At the interface with the second oxide portion, the exchange of electrons and holes does not occur sufficiently. Since the second oxide portion is in a high resistance state as described above in which hole movement and hole supply from the second electrode are suppressed, holes supplied to the interface between the switching metal portion and the second oxide portion. This is because there is considerably less.

  Therefore, electrons are accumulated in the vicinity of the interface with the second oxide portion in the switching metal portion (the accumulated electrons and the above-described oxygen vacancies existing in the second oxide portion with a positive charge). In the meantime, electrostatic attraction occurs). As a result, the electron density distribution is biased in the switching metal part. In this way, polarization in a direction different from the first polarization state described above is induced in the switching metal part (the second polarization state of the switching metal part). Even if the applied voltage between the first and second electrodes is extinguished, the above-described high resistance state of the second oxide portion is maintained, and the above-described oxygen vacancy existing in the second oxide portion with a positive charge It attracts the above-mentioned stored electrons in the switching metal part, and therefore the second polarization state of the switching metal part is maintained.

  For the switching metal part in the second polarization state, a predetermined voltage is applied between the first and second electrodes in the direction opposite to the voltage application direction for realizing the second polarization state, and the second It is possible to switch to a single polarization state. Specifically, the resistance of the first oxide portion is increased again, and the resistance of the second oxide portion is decreased in the same manner as when the resistance of the first oxide portion is decreased during the second polarization state. By doing so, it is possible to switch the switching metal part to the first polarization state again.

  As described above, this switching element can selectively switch between the first state in which the switching metal part is in the first polarization state and the second state in which the switching metal part is in the second polarization state. It is.

  In this switching element, the voltage application direction between the electrode pair for changing from the first state to the second state is different from the voltage application direction between the electrode pair for changing from the second state to the first state. . In other words, this device can switch between two states by bipolar operation. In addition, the present switching element can be used as a non-volatile memory element that performs recording or rewriting of information using such state switching.

  Preferably, the first and second oxide portions are included in a single oxide layer located between the first and second electrodes and the switching metal portion. According to such a configuration, it is not necessary to form the first and second oxide parts separately.

  Preferably, the first and second electrodes are made of a material that is more easily oxidized than the switching metal portion. Such a configuration is preferable for properly oxidizing the first and second electrodes in the process of the state switching operation described above. The first electrode and / or the second electrode preferably comprises a metal selected from Ti, Ta, and Al.

  Preferably, the switching metal part includes a metal selected from Pt, Au, and Pd. Such a configuration is suitable for avoiding the oxidation of the switching metal portion in the process of the state switching operation described above.

Preferably, the switching metal part is made of a magnetic metal or a magnetic semiconductor. The switching metal part is made of a half metal. This half metal is, for example, LaNiMnO ₃ (for example, LaNi _0.5 Mn _0.5 O ₃ ), LaSrMnO ₃ (for example, La _0.7 Sr _0.3 MnO ₃ ), Fe ₃ O ₄ , or SrRuO ₃ . These configurations are suitable for causing switching of the magnetic state as well as switching of the polarization state in the switching metal part. When the magnetic state of the switching metal part can be switched, between the first magnetic state generated in the switching metal part in the first polarization state described above and the second magnetic state generated in the switching metal part in the second polarization state described above. This element can be used as a nonvolatile memory element by utilizing state switching.

Preferably, the first oxide portion and / or the second oxide portion is made of PrCaMnO ₃ (eg, Pr _0.7 Ca _0.3 MnO ₃ ) or LaSrCoO ₃ (eg, La _0.7 Sr _0.3 CoO ₃ ).

  FIG. 1 is a cross-sectional view of a switching element X1 according to the first embodiment of the present invention. The switching element X1 includes a substrate S, a pair of electrodes 1 and 2, a metal layer 3, and an oxide layer 4, and is configured so that the polarization direction in the metal layer 3 can be selectively switched. ing.

The substrate S is, for example, a silicon substrate or an oxide substrate. A thermal oxide film may be formed on the surface of the silicon substrate. Examples of the oxide substrate include an MgO substrate, a SrTiO ₃ (STO) substrate, an Al ₂ O ₃ substrate, a quartz substrate, and a glass substrate.

  The electrodes 1 and 2 are made of an oxidizable conductive material that is easily oxidized, and preferably made of a material that is more easily oxidized than the metal layer 3. As a constituent material of the electrodes 1 and 2, a metal selected from the group consisting of Ti, Ta, Al, Fe, Co, and Ni, or an alloy containing the metal can be employed. The electrodes 1 and 2 may be made of the same material or different materials. The thickness of the electrodes 1 and 2 is, for example, 20 to 200 nm.

  The metal layer 3 is a switching metal part in the present invention, and is made of a non-oxidizing conductive material that is not easily oxidized. As a constituent material of the metal layer 3, Pt, Au, Pd, or an alloy containing a metal selected from these can be used. The thickness of the metal layer 3 is, for example, 5 to 30 nm.

The oxide layer 4 includes oxide portions 4a and 4b and is made of an oxide having P-type semiconductivity. The oxide portion 4 a is a portion that is substantially interposed between the metal layer 3 and the electrode 1 in the oxide layer 4. The oxide portion 4 b is a portion that is substantially interposed between the metal layer 3 and the electrode 2 in the oxide layer 4. Such an oxide layer 4 includes, for example, a perovskite structure type oxide, a spinel structure type oxide, a fluorite structure type oxide, a pyrochlore structure type oxide, a tungsten bronze structure type oxide, or a brown mirrorite structure type oxide. It consists of things. As the perovskite structure type oxide, PrCaMnO ₃ (for example, Pr _0.7 Ca _0.3 MnO ₃ ) and LaSrCoO ₃ (for example, La _0.7 Sr _0.3 CoO ₃ ) can be employed. An alkaline earth element or the like is added to these materials as necessary. The thickness of the oxide layer 4 is, for example, 20 to 200 nm.

  In the production of the switching element X1 having such a structure, for example, first, on the substrate S, the material for forming the metal layer 3, the material for forming the oxide layer 4, and the electrodes 1, 2 The material for constituting the film is sequentially formed. As a film forming method, for example, a sputtering method, a vacuum evaporation method, a CVD method, or a PLD (Pulsed Laser Deposition) method can be employed. Next, these material films are sequentially patterned by etching. For example, the switching element X1 can be manufactured in this way.

  FIG. 2 shows the operating principle of the switching element X1. As shown in FIG. 2A, when a voltage is applied between the electrodes 1 and 2 with the electrode 1 of the switching element X1 as the positive electrode and the electrode 2 as the negative electrode, the electrode 1 is used as the positive electrode and the metal layer is formed in the oxide portion 4a. 3 is applied as a negative electrode, and the oxide part 4b is applied with the electrode 2 as a negative electrode and the metal layer 3 as a positive electrode. Then, when a predetermined voltage is applied between the electrodes 1 and 2 with the electrodes 1 and 2 as the positive electrode and the negative electrode for a predetermined time, oxygen ions 5 are generated in the oxide portion 4a of the oxide layer 4 due to the electric field action. Oxygen ions 5 move to electrode 1. Then, the electrode 1 is partially oxidized and takes in the oxygen ions 5 (that is, a partially oxidized region 1a is generated in the electrode 1). At this time, the oxygen ions 5 emit electrons. At the same time, oxygen vacancies 6 accompanied by positive charges are generated and accumulated in the oxide portion 4a that releases constituent oxygen as oxygen ions 5 to the electrode 1, and a predetermined internal electric field is formed. This internal electric field hinders supply of holes (carriers) from the electrode 1 to the P-type semiconductive oxide portion 4a and movement of holes in the oxide portion 4a. Therefore, the resistance value of the oxide part 4a increases due to the formation of the internal electric field, and the oxide part 4a reaches a high resistance state (high resistance of the oxide part 4a).

  On the other hand, a current flows between the electrode 1 from which electrons are emitted from the oxygen ions 5 and the metal layer 3 through the electrode 2 and the oxide portion 4b. Specifically, electrons flow as a carrier from the electrode 1 to the electrode 2 through an external power supply circuit, and exchange of electrons and holes occurs at the interface between the electrode 2 and the P-type semiconductive oxide portion 4b. Flows in the oxide portion 4b as carriers, and exchange of holes and electrons occurs at the interface between the oxide portion 4b and the metal layer 3. The electrons move to the oxide portion 4a side in the metal layer 3 (that is, toward the bonding interface between the metal layer 3 and the oxide portion 4a), but the metal layer 3 and the P-type semiconductor oxide At the interface with the portion 4a, the exchange of electrons and holes does not occur sufficiently. Since the oxide portion 4a is in a high resistance state as described above in which hole movement and hole supply from the electrode 1 are suppressed, a considerable amount of holes are supplied to the interface between the metal layer 3 and the oxide portion 4a. Because there are few.

  Therefore, as shown in FIG. 2A, electrons 7 are accumulated in the vicinity of the interface with the oxide portion 4a in the metal layer 3 (the accumulated electrons 7 and the oxide portion 4a with a positive charge are contained in the oxide portion 4a). An electrostatic attractive force is generated between the oxygen vacancy 6 and the oxygen vacancy 6. As a result, the electron density distribution is biased in the metal layer 3. In this way, polarization in a predetermined direction is induced in the metal layer 3 (the first polarization state of the metal layer 3). Even if the applied voltage between the electrodes 1 and 2 is extinguished, the above-described high resistance state of the oxide portion 4a is maintained, and the oxygen vacancies 6 and the metal layer 3 present in the oxide portion 4a with positive charges are maintained. Therefore, the first polarization state shown in FIG. 2A of the metal layer 3 is maintained. In this first polarization state, an induced voltage V1 is generated between the portion 3a on the oxide layer 4a side in the metal layer 3 and the portion 3b on the oxide portion 4b side in the metal layer 3. By detecting this induced voltage V1, the first polarization state of the metal layer 3 can be detected.

  In the switching element X1, by applying a predetermined voltage between the electrodes 1 and 2 in the direction opposite to the voltage application direction for realizing the first polarization state, the polarization direction of the metal layer 3 is reversed as follows. be able to.

  As shown in FIG. 2B, the electrode 1 of the switching element X1 in which the oxide portion 4a is in the high resistance state and the metal layer 3 is in the first polarization state is the negative electrode and the electrode 2 is the positive electrode. When a voltage is applied to the oxide portion 4a, a partial pressure is applied to the oxide portion 4a with the electrode 1 as the negative electrode and the metal layer 3 as the positive electrode, and to the oxide portion 4b, the electrode 2 as the positive electrode and the metal layer 3 as the negative electrode. Pressure is applied. When a predetermined voltage is applied between the electrodes 1 and 2 using the electrodes 1 and 2 as a negative electrode and a positive electrode for a predetermined time, oxygen ions 5 are generated in the partial oxidation region 1a in the electrode 1 by the electric field action, and the oxygen ions 5 moves to the oxide part 4a. Then, in the oxide part 4a that has received the oxygen ions 5, the oxygen vacancies 6 accompanied by positive charges are electrically neutralized, the internal electric field due to the presence of the oxygen vacancies 6 is attenuated, and finally disappears. . Thereby, the resistance value of the oxide part 4a falls, and the oxide part 4a reaches a low resistance state (low resistance of the oxide part 4a). Holes are easily supplied from the electrode 1 and the metal layer 3 to the P-type semiconducting oxide portion 4a in a low resistance state, and the holes easily move in the oxide portion 4a.

  On the other hand, when a predetermined voltage is applied between the electrodes 1 and 2 with the electrode 1 as the negative electrode and the electrode 2 as the positive electrode over a predetermined time, oxygen ions 5 are generated in the oxide portion 4b by the electric field action, and the oxygen ions 5 moves to the electrode 2. Then, the electrode 2 is partially oxidized and takes in the oxygen ions 5. Thereby, a partially oxidized region 2 a is generated in the electrode 2. At this time, the oxygen ions 5 emit electrons. At the same time, oxygen vacancies 6 accompanied by positive charges are generated and accumulated in the oxide portion 4b that releases constituent oxygen as oxygen ions 5 to the electrode 2, and a predetermined internal electric field is formed. This internal electric field hinders the supply of holes (carriers) from the electrode 2 to the P-type semiconductive oxide part 4b and the movement of holes in the oxide part 4b. Therefore, the resistance value of the oxide portion 4b increases due to the formation of the internal electric field, and the oxide portion 4b reaches a high resistance state (high resistance of the oxide portion 4b).

  On the other hand, a current flows between the electrode 2 from which electrons are released from the oxygen ions 5 and the metal layer 3 via the electrode 1 and the oxide portion 4a. Specifically, electrons flow as a carrier from the electrode 2 to the electrode 1 through an external power supply circuit, and exchange of electrons and holes occurs at the interface between the electrode 1 and the P-type semiconductive oxide portion 4a. Flows in the oxide portion 4a as carriers, and exchange of holes and electrons occurs at the interface between the oxide portion 4a and the metal layer 3. The electrons move to the oxide portion 4b side in the metal layer 3 (that is, toward the bonding interface between the metal layer 3 and the oxide portion 4b), but the metal layer 3 and the P-type semiconductor oxide At the interface with the part 4b, the exchange of electrons and holes does not occur sufficiently. Since the oxide portion 4b is in a high resistance state as described above in which hole movement and hole supply from the electrode 2 are suppressed, a considerable amount of holes are supplied to the interface between the metal layer 3 and the oxide portion 4b. Because there are few.

  Therefore, electrons 7 are accumulated in the vicinity of the interface with the oxide portion 4b in the metal layer 3 (between the accumulated electrons 7 and the oxygen vacancies 6 existing in the oxide portion 4b with a positive charge). Causes electrostatic attraction). As a result, the electron density distribution is biased in the metal layer 3. In this way, polarization in a direction different from the first polarization state described above is induced in the metal layer 3 (the second polarization state of the metal layer 3). Even if the applied voltage between the electrodes 1 and 2 is extinguished, the above-described high resistance state of the oxide portion 4b is maintained, and the oxygen vacancy 6 and the metal layer 3 present in the oxide portion 4b with a positive charge are maintained. Therefore, the second polarization state shown in FIG. 2B of the metal layer 3 is maintained. In the second polarization state, an induced voltage V2 is generated between the portion 3a on the oxide layer 4a side in the metal layer 3 and the portion 3b on the oxide portion 4b side in the metal layer 3. By detecting this induced voltage V2, the second polarization state of the metal layer 3 can be detected.

  For the metal layer 3 in the second polarization state, a predetermined voltage is applied between the electrodes 1 and 2 in the direction opposite to the voltage application direction for realizing the second polarization state, and the first polarization state is again applied. It is possible to switch to. Specifically, the resistance of the oxide portion 4a is increased again, and the resistance of the oxide portion 4b is decreased in the same manner as the resistance of the oxide portion 4a is decreased during the second polarization state. The metal layer 3 can be switched to the first polarization state again.

  As described above, the switching element X1 can selectively switch between the first state in which the metal layer 3 is in the first polarization state and the second state in which the metal layer 3 is in the second polarization state. It is.

  In the switching element X1, the voltage application direction between the electrodes 1 and 2 for changing from the first state to the second state, and the voltage application between the electrodes 1 and 2 for changing from the second state to the first state Different from direction. In other words, this device can switch between two states by bipolar operation. Further, the switching element X1 can be used as a nonvolatile memory element that performs recording or rewriting of information using such state switching.

  In the switching element X1 of the present embodiment, the oxide parts 4a and 4b are included in the single oxide layer 4, but the oxide parts 4a and 4b may be separated on the metal layer 3.

  FIG. 3 is a cross-sectional view of the switching element X2 according to the second embodiment of the present invention. The switching element X2 includes a substrate S, a pair of electrodes 1 and 2, a conductive magnetic layer 8, and an oxide layer 4, and is configured so that the magnetic state in the conductive magnetic layer 8 can be selectively switched. Has been. The switching element X2 is different from the switching element X1 in that the conductive magnetic layer 8 is provided instead of the metal layer 3.

The conductive magnetic layer 8 includes portions 8a and 8b, and is made of a magnetic metal or a semiconductor whose magnetic properties such as the Curie temperature, the magnetic anisotropy, and the magnetization direction change according to the change in electron density. The portion 8 a is a region facing the oxide portion 4 a of the oxide layer 4 in the conductive magnetic layer 8, and the portion 8 b is a region facing the oxide portion 4 b of the oxide layer 4 in the conductive magnetic layer 8. An example of a magnetic material whose magnetism changes with a change in electron density is half metal. In the present invention, LaNiMnO ₃ (for example, LaNi _0.5 Mn _0.5 O ₃ ), LaSrMnO ₃ (for example, La _0.7 Sr _0.3 MnO ₃ ), Fe ₃ O ₄ (spinel magnetite), or SrRuO ₃ is used as the half metal. be able to. In half metal, electrons at the Fermi energy level occupy only one spin band (either up-spin band or down-spin band), and the density of electrons that occupy only one spin band changes. The magnetism is easy to change.

  FIG. 4 shows the operating principle of the switching element X2. When a voltage is applied between the electrodes 1 and 2 with the electrode 1 of the switching element X2 as the positive electrode and the electrode 2 as the negative electrode as shown in FIG. A partial pressure is applied using the layer 8 as a negative electrode, and a partial pressure is applied to the oxide portion 4b using the electrode 2 as a negative electrode and the conductive magnetic layer 8 as a positive electrode. Then, when a predetermined voltage is applied between the electrodes 1 and 2 with the electrodes 1 and 2 as the positive electrode and the negative electrode for a predetermined time, oxygen ions 5 are generated in the oxide portion 4a of the oxide layer 4 due to the electric field action. Oxygen ions 5 move to electrode 1. Then, the electrode 1 is partially oxidized and takes in the oxygen ions 5 (that is, a partially oxidized region 1a is generated in the electrode 1). At this time, the oxygen ions 5 emit electrons. At the same time, oxygen vacancies 6 accompanied by positive charges are generated and accumulated in the oxide portion 4a that releases constituent oxygen as oxygen ions 5 to the electrode 1, and a predetermined internal electric field is formed. This internal electric field hinders supply of holes (carriers) from the electrode 1 to the P-type semiconductive oxide portion 4a and movement of holes in the oxide portion 4a. Therefore, the resistance value of the oxide part 4a increases due to the formation of the internal electric field, and the oxide part 4a reaches a high resistance state (high resistance of the oxide part 4a).

  On the other hand, a current flows between the electrode 1 from which electrons are released from the oxygen ions 5 and the conductive magnetic layer 8 via the electrode 2 and the oxide portion 4b. Specifically, electrons flow as a carrier from the electrode 1 to the electrode 2 through an external power supply circuit, and exchange of electrons and holes occurs at the interface between the electrode 2 and the P-type semiconductive oxide portion 4b. Flows in the oxide part 4b as carriers, and exchange of holes and electrons occurs at the interface between the oxide part 4b and the conductive magnetic layer 8. The electrons move to the oxide portion 4a side in the conductive magnetic layer 8 (that is, toward the bonding interface between the conductive magnetic layer 8 and the oxide portion 4a). At the interface with the oxide portion 4a, the exchange of electrons and holes does not occur sufficiently. Since the oxide portion 4a is in a high resistance state as described above in which hole movement and supply of holes from the electrode 1 are suppressed, holes supplied to the interface between the conductive magnetic layer 8 and the oxide portion 4a are considerable. This is because there are few.

  Therefore, as shown in FIG. 4A, electrons 7 are accumulated in the vicinity of the interface with the oxide portion 4a in the conductive magnetic layer 8, that is, in the region 8a (the accumulated electrons 7 and oxidized with a positive charge). An electrostatic attractive force is generated between the oxygen vacancies 6 in the object part 4a). As a result, the electron density distribution is biased in the conductive magnetic layer 8. Based on such a deviation in electron density, a deviation occurs in the magnetic state in the conductive magnetic layer 8. In this way, a predetermined magnetic state is induced in the conductive magnetic layer 8 (the first magnetic state of the conductive magnetic layer 8). In addition, polarization in a predetermined direction is also induced in the conductive magnetic layer 8 (the first polarization state of the conductive magnetic layer 8). Even if the applied voltage between the electrodes 1 and 2 is extinguished, the above-described high resistance state of the oxide portion 4a is maintained, and oxygen vacancies 6 and the conductive magnetic layer 8 present in the oxide portion 4a with positive charges are maintained. Therefore, the first magnetic state shown in FIG. 4A of the conductive magnetic layer 8 is maintained (the first polarization state is also maintained). This first magnetic state is obtained by measuring an induced voltage or current between the oxide portion 4a side or the portion 8a side in the conductive magnetic layer 8 and the oxide portion 4b side or the portion 8b side in the conductive magnetic layer 8. , Can be detected. Further, after adopting a transparent substrate as the substrate S, as shown in FIG. 5, the portions 8a and 8b of the conductive magnetic layer 8 are irradiated with laser light L from the substrate S side, and the Kerr rotation angle of the reflected light is measured. Thus, it is also possible to detect the first magnetic state of the conductive magnetic layer 8 based on the difference in Kerr rotation angle between the portions 8a and 8b.

  In the switching element X2, by applying a predetermined voltage between the electrodes 1 and 2 in the direction opposite to the voltage application direction for realizing the first magnetic state, the magnetic state of the conductive magnetic layer 8 is changed as follows. Can be made.

  4B, the electrode 1 of the switching element X1 in which the oxide portion 4a is in the high resistance state and the conductive magnetic layer 8 is in the first magnetic state is the negative electrode and the electrode 2 is the positive electrode. When the voltage is applied, the oxide part 4a is divided by the electrode 1 as the negative electrode and the conductive magnetic layer 8 as the positive electrode, and the oxide part 4b is applied with the electrode 2 as the positive electrode and the conductive magnetic layer 8 as the positive electrode. Partial pressure is applied as the negative electrode. When a predetermined voltage is applied between the electrodes 1 and 2 using the electrodes 1 and 2 as a negative electrode and a positive electrode for a predetermined time, oxygen ions 5 are generated in the partial oxidation region 1a in the electrode 1 by the electric field action, and the oxygen ions 5 moves to the oxide part 4a. Then, in the oxide portion 4 a that has received the oxygen ions 5, the oxygen vacancies 6 with positive charges are electrically neutralized, and the internal electric field due to the presence of the oxygen vacancies 6 disappears. Thereby, the resistance value of the oxide part 4a falls, and the oxide part 4a reaches a low resistance state (low resistance of the oxide part 4a). Holes are easily supplied from the electrode 1 and the conductive magnetic layer 8 to the P-type semiconductive oxide portion 4a in the low resistance state, and the holes easily move in the oxide portion 4a.

  On the other hand, when a predetermined voltage is applied between the electrodes 1 and 2 with the electrode 1 as the negative electrode and the electrode 2 as the positive electrode over a predetermined time, oxygen ions 5 are generated in the oxide portion 4b by the electric field action, and the oxygen ions 5 moves to the electrode 2. Then, the electrode 2 is partially oxidized and takes in the oxygen ions 5. Thereby, a partially oxidized region 2 a is generated in the electrode 2. At this time, the oxygen ions 5 emit electrons. At the same time, oxygen vacancies 6 accompanied by positive charges are generated and accumulated in the oxide portion 4b that releases constituent oxygen as oxygen ions 5 to the electrode 2, and a predetermined internal electric field is formed. This internal electric field hinders the supply of holes (carriers) from the electrode 2 to the P-type semiconductive oxide part 4b and the movement of holes in the oxide part 4b. Therefore, the resistance value of the oxide portion 4b increases due to the formation of the internal electric field, and the oxide portion 4b reaches a high resistance state (high resistance of the oxide portion 4b).

  On the other hand, a current flows between the electrode 2 from which electrons are released from the oxygen ions 5 and the conductive magnetic layer 8 via the electrode 1 and the oxide portion 4a. Specifically, electrons flow as a carrier from the electrode 2 to the electrode 1 through an external power supply circuit, and exchange of electrons and holes occurs at the interface between the electrode 1 and the P-type semiconductive oxide portion 4a. Flows in the oxide part 4a as carriers, and exchange of holes and electrons occurs at the interface between the oxide part 4a and the conductive magnetic layer 8. The electrons move to the oxide portion 4b side in the conductive magnetic layer 8 (that is, toward the junction interface between the conductive magnetic layer 8 and the oxide portion 4b). At the interface with the conductive oxide portion 4b, exchange of electrons and holes does not occur sufficiently. Since the oxide portion 4b is in the high resistance state as described above in which hole movement and hole supply from the electrode 2 are suppressed, the holes supplied to the interface between the conductive magnetic layer 8 and the oxide portion 4b are considerable. This is because there are few.

  Therefore, electrons 7 are accumulated in the vicinity of the interface with the oxide portion 4b in the conductive magnetic layer 8 (the accumulated electrons 7 and the oxygen vacancies 6 existing in the oxide portion 4b with a positive charge). In the meantime, electrostatic attraction occurs). As a result, the electron density distribution is biased in the conductive magnetic layer 8. In this way, a magnetic state different from the first magnetic state described above is induced in the conductive magnetic layer 8 (the conductive magnetic layer 8 is changed to the second magnetic state). In the conductive magnetic layer 8, polarization in the direction opposite to the first polarization state is also induced (second polarization state of the conductive magnetic layer 8). Even when the applied voltage between the electrodes 1 and 2 is extinguished, the above-described high resistance state of the oxide portion 4b is maintained, and oxygen vacancies 6 and the conductive magnetic layer 8 existing in the oxide portion 4b with positive charges are maintained. Therefore, the second magnetic state shown in FIG. 4B of the conductive magnetic layer 8 is maintained (the second polarization state is also maintained). This second magnetic state is obtained by measuring the induced voltage or current between the oxide portion 4a side or the portion 8a side in the conductive magnetic layer 8 and the oxide portion 4b side or the portion 8b side in the conductive magnetic layer 8. , Can be detected. Further, as described above, after adopting a transparent substrate as the substrate S, as shown in FIG. 5, the portions 8a and 8b of the conductive magnetic layer 8 are irradiated with the laser light L from the substrate S side, and the reflected light is curled. By measuring the rotation angle, it is also possible to detect the second magnetic state of the conductive magnetic layer 8 based on the difference in Kerr rotation angle between the portions 8a and 8b.

  For the conductive magnetic layer 8 in the second polarization state, a predetermined voltage is applied between the electrodes 1 and 2 in the direction opposite to the voltage application direction for realizing the second magnetic state, and the first polarization is again performed. It is possible to switch to a state. Specifically, the resistance of the oxide portion 4a is increased again, and the resistance of the oxide portion 4b is decreased in the same manner as the resistance of the oxide portion 4a is decreased during the second polarization state. The conductive magnetic layer 8 can be switched to the first polarization state again.

  As described above, the switching element X2 selectively switches between the first state in which the conductive magnetic layer 8 is in the first magnetic state and the second state in which the conductive magnetic layer 8 is in the second magnetic state. Is possible.

  In the switching element X2, the voltage application direction between the electrodes 1 and 2 for changing from the first state to the second state and the voltage application between the electrodes 1 and 2 for changing from the second state to the first state Different from direction. In other words, this device can switch between two states by bipolar operation. In addition, the switching element X2 can be used as a nonvolatile memory element that performs recording or rewriting of information using such state switching.

  In the switching element X2 of the present embodiment, the oxide portions 4a and 4b are included in the single oxide layer 4, but the oxide portions 4a and 4b may be separated on the conductive magnetic layer 8. .

  A sample element having the configuration shown in FIG. 6 was produced as an example of the switching element X1 described above.

  In the production of this sample element, first, Pt was deposited to a thickness of 30 nm on the MgO substrate by sputtering. In this sputtering, Ar gas (0.5 Pa) was used as the sputtering gas, a Pt target was used, DC discharge was performed, the input power was 1.0 kW, and the temperature condition was 400 ° C.

Next, PrCaMnO ₃ (Pr _0.7 Ca _0.3 MnO ₃ ) was formed to a thickness of 200 nm on the Pt film by sputtering. In this sputtering, a mixed gas of Ar and O ₂ (0.5 Pa, oxygen concentration 15 vol%) is used as a sputtering gas, a Pr _0.7 Ca _0.3 MnO ₃ target is used, RF discharge is performed, the input power is 1.0 kW, The condition was 400 ° C.

Next, Ti was formed to a thickness of 200 nm on the PrCaMnO ₃ film by sputtering. In this sputtering, Ar gas (0.5 Pa) was used as the sputtering gas, a Ti target was used, DC discharge was performed, the input power was 1.0 kW, and the temperature condition was room temperature.

  Next, patterning was performed on each of the material films using a photolithography technique. The diameter of the electrodes 1 and 2 was 200 μm. The distance between the electrodes 1 and 2 was 1 mm. The sample element of this example was produced as described above.

  About this sample element, the presence or absence of state switching was investigated. Specifically, the voltage application under the first condition and the subsequent voltage application under the second condition are repeated a plurality of times for this sample element, and after each voltage application, between the portions 3a and 3b at both ends of the metal layer 3 The induced voltage was measured. Under the first condition, the electrode 1 is a positive electrode, the electrode 2 is a negative electrode, and the applied voltage between the electrodes 1 and 2 is a DC voltage swept with a maximum value of 5V. Under the second condition, the electrode 1 is a negative electrode, the electrode 2 is a positive electrode, and the applied voltage between the electrodes 1 and 2 is a DC voltage swept with a maximum value of 5V. After each voltage application under the first condition, an induced voltage of about 0.1 mV was detected with the part 3b as positive and the part 3a as negative (detection of the first polarization state). Further, after each voltage application under the second condition, an induced voltage of about 0.1 mV was detected with the part 3a being positive and the part 3b being negative (detection of the second polarization state). As described above, the present sample element can be selectively switched between the first state in which the metal layer 3 is in the first polarization state and the second state in which the metal layer 3 is in the second polarization state. It was.

  A sample element having the configuration shown in FIG. 7 was produced as an example of the switching element X2.

In the production of this sample element, first, LaNi _0.5 Mn _0.5 O ₃ (LNMO) is formed on a (100) surface of a transparent SrTiO ₃ (STO) substrate at a substrate temperature of 700 ° C. by a PLD (Pulsed Laser Deposition) method. Was deposited to a thickness of 30 nm. Since STO as a substrate constituent material has a perovskite structure like LNMO, LNMO can be appropriately epitaxially grown on the STO substrate in this step.

Next, PrCaMnO ₃ (Pr _0.7 Ca _0.3 MnO ₃ ) was formed to a thickness of 200 nm on the LNMO film by sputtering. In this sputtering, a mixed gas of Ar and O ₂ (0.5 Pa, oxygen concentration 15 vol%) is used as a sputtering gas, a Pr _0.7 Ca _0.3 MnO ₃ target is used, RF discharge is performed, the input power is 1.0 kW, The condition was 400 ° C.

Next, Ti was formed in a thickness of 200 nm on a PrCaMnO ₃ (Pr _0.7 Ca _0.3 MnO ₃ ) film by sputtering. In this sputtering, Ar gas (0.5 Pa) was used as the sputtering gas, a Ti target was used, DC discharge was performed, the input power was 1.0 kW, and the temperature condition was room temperature.

  Next, patterning was performed on each of the material films using a photolithography technique. The diameter of the electrodes 1 and 2 was 200 μm. The distance between the electrodes 1 and 2 was 1 mm. The sample element of this example was produced as described above. The conductive magnetic layer 8 in the sample element thus fabricated is made of LNMO, which is a magnetic half metal, and its Curie temperature is about 280 K (7 ° C.). Therefore, in the state before the voltage application described below, at the room temperature (296K, 23 ° C.), the conductive magnetic layer 8 of this sample element exhibits paramagnetism throughout.

  About this sample element, the presence or absence of state switching was investigated. Specifically, voltage application under the first condition and subsequent voltage application under the second condition are repeated a plurality of times for this sample element, and each of the portions 8a and 8b of the conductive magnetic layer 8 is magnetically applied after each voltage application. Kerr effect measurement was performed. Under the first condition, the electrode 1 is a positive electrode, the electrode 2 is a negative electrode, and the applied voltage between the electrodes 1 and 2 is a DC voltage swept with a maximum value of 5V. Under the second condition, the electrode 1 is a negative electrode, the electrode 2 is a positive electrode, and the applied voltage between the electrodes 1 and 2 is a DC voltage swept with a maximum value of 5V. In the magnetic Kerr effect measurement, at a room temperature (296K, 23 ° C.), a magnetic field is applied in a direction perpendicular to the conductive magnetic layer 8 and the magnetic field is swept within a range of ± 10 kOe, while the measurement control points (parts 8a and 8b) are measured. Was irradiated with laser light (wavelength 633 nm, beam diameter 100 μm) from the substrate S side, and the Kerr rotation angle of the reflected light was measured. After applying each voltage under the first condition, a magnetic hysteresis loop was observed for the Kerr rotation angle in the magnetic Kerr effect measurement of the part 8a, whereas in the magnetic Kerr effect measurement of the part 8b, the magnetic hysteresis loop was determined for the Kerr rotation angle. Not observed. That is, after each voltage application under the first condition, a state was detected in which the portion 8a exhibited ferromagnetism and the portion 8b exhibited paramagnetism in the conductive magnetic layer 8 of the sample element (detection of the first magnetic state). ). On the other hand, after applying each voltage under the second condition, no magnetic hysteresis loop was observed for the Kerr rotation angle in the magnetic Kerr effect measurement of the part 8a, whereas in the Kerr rotation measurement of the part 8b, the Kerr rotation angle was magnetic. A hysteresis loop was observed. That is, after each voltage application under the second condition, a state in which the portion 8a exhibits paramagnetism and the portion 8b exhibits ferromagnetism is detected in the conductive magnetic layer 8 of the sample element (detection of the second magnetic state). ). By repeating the voltage application under the first condition and the subsequent voltage application under the second condition, the part 8a is switched between ferromagnetism and paramagnetism, and the part 8b is switched between paramagnetism and ferromagnetism. The magnetism has been switched. As described above, the sample element can be selectively switched between the first state in which the conductive magnetic layer 8 is in the first magnetic state and the second state in which the conductive magnetic layer 8 is in the second magnetic state. did it.

  As a summary of the above, the configurations of the present invention and variations thereof are listed below as supplementary notes.

(Appendix 1) a first electrode and a second electrode;
A switching metal part,
A first oxide part located between the first electrode and the switching metal part and having P-type semiconductivity;
A switching element comprising: a second oxide part located between the second electrode and the switching metal part and having P-type semiconductivity.
(Supplementary note 2) The switching according to supplementary note 1, wherein the first and second oxide parts are included in a single oxide layer located between the first and second electrodes and the switching metal part. element.
(Supplementary note 3) The switching element according to supplementary note 1 or 2, wherein the first and second electrodes are made of a material that is more easily oxidized than the switching metal portion.
(Supplementary Note 4) The switching element according to any one of Supplementary Notes 1 to 3, wherein the first electrode and / or the second electrode includes a metal selected from Ti, Ta, and Al.
(Supplementary Note 5) The switching element according to any one of Supplementary Notes 1 to 4, wherein the switching metal portion includes a metal selected from Pt, Au, and Pd.
(Supplementary note 6) The switching element according to any one of supplementary notes 1 to 5, wherein the switching metal portion is made of a magnetic metal or a magnetic semiconductor.
(Supplementary note 7) The switching element according to any one of supplementary notes 1 to 5, wherein the switching metal portion is made of a half metal.
(Supplementary note 8) The switching element according to supplementary note ₇ , wherein the half metal is LaNiMnO ₃ , LaSrMnO ₃ , Fe ₃ O ₄ , or SrRuO ₃ .
(Supplementary note 9) The switching element according to any one of supplementary notes 1 to 8, wherein the first oxide part and / or the second oxide part is made of PrCaMnO ₃ or SrRuO ₃ .

FIG. 1 is a cross-sectional view of a switching element according to the first embodiment of the present invention. FIG. 2 shows an operation principle of the switching element shown in FIG. FIG. 3 is a cross-sectional view of a switching element according to the second embodiment of the present invention. FIG. 4 shows the operation principle of the switching element shown in FIG. FIG. 5 shows a method using the Kerr effect as an example of a magnetic change detection method. FIG. 6 shows the configuration of the sample element of Example 1. FIG. 7 shows the configuration of the sample element of Example 2.

X1, X2 switching element S substrate 1, 2 electrode 1a, 2a partial oxidation region 3 metal layer 4 oxide layer 4a, 4b oxide part 5 oxide ion 6 oxygen vacancy 7 electron 8 conductive magnetic layer

Claims (5)

A first electrode and a second electrode;
A switching metal part,
A first oxide part located between the first electrode and the switching metal part and having P-type semiconductivity;
A second oxide part located between the second electrode and the switching metal part and having P-type semiconductivity ,
When a voltage is applied to the first electrode and the second electrode in the first voltage application direction, polarization is induced in the first polarization state in the switching metal portion, and the first electrode and the second electrode are A switching element in which polarization is induced in a second polarization state in a direction different from the first polarization state in the switching metal portion by applying a voltage in a second voltage application direction opposite to the first voltage application direction .   2. The switching element according to claim 1, wherein the first and second oxide parts are included in a single oxide layer located between the first and second electrodes and the switching metal part.   The switching element according to claim 1, wherein the first and second electrodes are made of a material that is more easily oxidized than the switching metal portion.   The switching element according to any one of claims 1 to 3, wherein the switching metal portion includes a metal selected from Pt, Au, and Pd.   The switching element according to claim 1, wherein the switching metal portion is made of a magnetic metal or a magnetic semiconductor.

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