JP2009071206A - Resistance memory device and switching circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain certainly switching characteristics from a low resistance state to a high resistance state which can stably obtain a high resistance change rate in a resistance memory device having an element body consisting of a titanium based composite oxide of a polycrystal. <P>SOLUTION: The voltage of polarization 14 inverse to the polarization 16 in which switching to a high resistance state from a low resistance state generates is applied to the element body 2, and thereby electroforming treatment is carried out. At this time, a resistance memory device 1 becomes to be in a low resistance state. In addition, when switching voltage is applied by the polarization 16, the resistance memory device 1 is made to be in high resistance. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a resistance memory element and a switching circuit, and more particularly to a resistance memory element including an element body made of a semiconductor ceramic as a polycrystalline body and a switching circuit configured using the same.

  The resistance memory element includes an element body having a resistance memory function, and this element body exhibits, for example, a relatively high resistance in an initial state, but changes to a low resistance state when a voltage of a predetermined value or more is applied, Even if the voltage is removed, this low resistance state is retained (stored). On the other hand, if a voltage higher than the specified value is applied to the element body in the low resistance state in the reverse direction, it returns to the high resistance state and this voltage is removed. Even so, the high resistance state is maintained (stored).

  Such a resistance memory element can be switched between a low resistance state and a high resistance state by applying a voltage equal to or higher than a predetermined value in each of the forward direction and the reverse direction. Can be stored. By utilizing such a resistance switch effect, the resistance memory element can be used not only as a so-called memory element but also as a switching element.

For example, Non-Patent Document 1 describes a resistive memory element that is of interest to the present invention. In Non-Patent Document 1, the above-described resistance memory characteristic is expressed at the interface between different materials, more specifically, at the junction interface between the SrTiO ₃ single crystal substrate and the SrRuO ₃ thin film (single crystal thin film). An element is described. In this resistance memory element, the switching voltage that can change the resistance state is about 3 V at the maximum, and switching is performed at a relatively low voltage.

  There are relatively many circuits to which a rated voltage of 3 V or more is applied among the circuits in which the resistance memory element is to be used. Therefore, when the resistance memory element described in Non-Patent Document 1 is to be used as a switching element in a relatively high driving voltage environment as described above, the switching voltage needs to be higher than the rated voltage.

  However, the resistance memory element described in Non-Patent Document 1 has a relatively low switching voltage of about 3 V at the maximum, and there is a possibility that the driving voltage itself may cause inadvertent switching. There is a problem that you can not.

Therefore, for realizing a switching element that switches at a high voltage of, for example, 30 V or more, it is necessary to insert another resistor in series. In this case, although the switching voltage can be increased, the inserted resistor As a result, the power consumption is increased, and the rate of change in resistance switched for this resistor is reduced.
T. Fujii, et al., “Hysteretic current-voltage characteristics and resistance switching at an epitaxial oxide Schottky Junction SrRuO3 / SrTi0 / SrTi0.99Nb0.01O3 .99Nb0.01O3) ", APPLIED PHYSICS LETTERS 86, 012107 (2005)

  In view of the above-mentioned problems, the present inventor has developed a novel semiconductor ceramic as in the following (1) and (2), more specifically, a resistor comprising an element body made of a polycrystalline titanium-based composite oxide. A memory element was proposed.

(1) General formula: (Sr _1-x A _x ) _v (Ti _1-y B _y ) _w O ₃ (where A is at least one element selected from Y and rare earth elements, and B is Nb and / or Ta), and 0.001 ≦ x + y ≦ 0.02 (where 0 ≦ x ≦ 0.02 and 0 ≦ y ≦ 0.02), and 0 Those satisfying the condition of 87 ≦ v / w ≦ 1.030.

(2) General _{formula: {(Sr 1-x M} x) 1-y A y} (Ti 1-z B z) O 3 ( however, M is at least one of Ba and Ca, A is, Y And at least one element selected from rare earth elements, and B is at least one of Nb and Ta.) And 0 <x ≦ 0.5, 0.001 ≦ y + z ≦ 0 0.02 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02), and when 0.5 <x ≦ 0.8, 0.003 ≦ y + z ≦ 0.02 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02), and 0.8 <x ≦ 1.0, 0.005 ≦ y + z ≦ 0.01 (where 0 ≦ y ≦ 0.02, Satisfying the condition of 0 ≦ z ≦ 0.02).

  According to the resistance memory element including the element body made of the novel semiconductor ceramic described above, the switching voltage can be increased and the resistance change rate can be increased as compared with the element described in Non-Patent Document 1. Further, the switching voltage can be controlled by controlling the number and thickness of the grain boundaries of the semiconductor ceramic existing between a pair of electrodes for applying the switching voltage.

FIG. 7 shows, for example, a typical current-voltage characteristic (IV characteristic) of a resistance memory element including an element body made of a semiconductor ceramic having the above composition (1). In the resistance memory element having the IV characteristics shown in FIG. 7, the titanium-based composite oxide constituting the element body has a composition of Sr _0.992 La _0.008 TiO ₃ . In order to obtain the IV characteristics shown in FIG. 7, a voltage pulse with a pulse width of 0.1 sec was applied in increments of 1 V, and the flowing current was measured.

  Referring to FIG. 7, first, when a voltage is applied from 0 V to 100 V [1], the current reaches 100 mA (current limit) at about 60 V [2]. Thereafter, when the voltage is lowered from 100 V to 0 V, the current becomes smaller than 100 mA at about 20 V [3], and does not show the same IV characteristic on the way back and forth [4], and changes from the high resistance state to the low resistance state. .

  Next, when the voltage is applied from 0V to -100V [5], the current limit is reached once at about -30V, the current starts to decrease from about -40V [6], and the current gradually decreases to -100V. (In other words, resistance increases) [7]. Thereafter, when a voltage is applied from −100 V to 0 V, the same IV characteristics are not shown on the way back and forth as in the case described above [8], and the current decreases while maintaining the high resistance state.

  As described above, according to the resistance memory element shown in FIG. 7, a switching voltage appears at around 50 V in absolute value, and switching with a high resistance change rate is applied regardless of whether a forward or reverse voltage is applied. The characteristics are stably obtained.

  The resistance memory element including the element body made of the novel semiconductor ceramic described above has been developed in an attempt to realize a higher switching voltage than that described in Non-Patent Document 1. However, on the other hand, from the viewpoint of power consumption and the like, depending on the application, it may not be as low as that described in Non-Patent Document 1, but a lower switching voltage may be desired.

  Therefore, in the resistance memory element including the element body made of the novel semiconductor ceramic described above, the switching voltage is lowered by reducing the distance between the electrodes to which the switching voltage is applied, that is, the thickness of the semiconductor ceramic located between the electrodes. As shown in FIG. 6, for example, the polarity switching from the low resistance to the high resistance state stably shows a high resistance change rate, but the resistance changing rate is the polarity switching from the high resistance to the low resistance state. In some cases, the sample was extremely small. FIG. 6 is a diagram showing the IV characteristics of the sample 11 having the same composition as the sample having the IV characteristics shown in FIG. 7 and prepared in an experimental example described later.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a resistance memory element capable of stably obtaining a high resistance change rate with a wide range of switching voltages.

  Another object of the present invention is to provide a switching circuit capable of stably obtaining a switching operation for controlling a current flow in the circuit.

  The IV characteristic shown in FIG. 7 described above is evaluated for a sample that has been subjected to electroforming by applying a pulse voltage of 100 to 200 V and a pulse width of 100 msec 10 to 50 times in each of the forward and reverse directions. It is a thing. In this way, in the case of a sample subjected to electroforming treatment alternately several times in each of the forward direction and the reverse direction, even if the same composition and the same switching voltage are applied, the low resistance ⇒ high resistance between the individual samples It was found that there was a difference in switching characteristics between the high resistance state and the low resistance state. That is, it was found that stable switching characteristics can be obtained in the low resistance → high resistance state, but individual switching voltages are likely to vary in the high resistance → low resistance state. Furthermore, it was found that when the thickness between the electrodes was reduced, the above tendency was prominent, and a high resistance change rate was obtained only in the low resistance → high resistance state.

  From this, it can be seen that if only switching from the low resistance to the high resistance state can be used, a resistance memory element that stably exhibits a high resistance change rate can be realized even with a relatively low switching voltage.

  Thus, as a result of extensive research by the present inventors, it has been found that there is a certain relationship between the polarity of the voltage applied as electroforming and the switching characteristics. And, if the electroforming process is applied only to one polarity and a switching voltage having a polarity opposite to that applied with the electroforming process is applied, a stable switching from a low resistance to a high resistance state is surely generated. Found that it can be.

  Under such a background, the present invention includes an element body made of a polycrystalline titanium-based composite oxide. When a switching voltage in the first direction is applied to the element body, the element body is changed from a low resistance state to a high resistance state. In order to solve the technical problem described above, the element body is first switched to the element body in a direction opposite to the first direction. The electroforming process is performed by applying a voltage in two directions.

The polycrystalline titanium complex oxide constituting the element body is
General _{formula: {(Sr 1-x M} x) 1-y A y} (Ti 1-z B z) O 3 ( however, M is at least one of Ba and Ca, A is, Y and rare earth elements And B is at least one of Nb and Ta), and
When 0 ≦ x ≦ 0.5, 0.001 ≦ y + z ≦ 0.02 (however, 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02),
When 0.5 <x ≦ 0.8, 0.003 ≦ y + z ≦ 0.02 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02), and 0.8 <x ≦ When 1.0, it is preferably a semiconductor ceramic that satisfies the condition of 0.005 ≦ y + z ≦ 0.01 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02).

  It is preferable that the maximum current flowing in the element body during the electroforming process is limited to 10 to 500 mA.

  The resistance memory element according to the present invention preferably further includes a pair of electrodes opposed via at least a part of the element body, and these electrodes are made of a material having a work function larger than that of the titanium-based composite oxide. Is preferred.

  The present invention is also directed to a switching circuit in which a switching element for controlling the flow of current in the circuit is inserted. In the switching circuit according to the present invention, the resistance memory element according to the present invention is used as the switching element, and the voltage for the electroforming process is applied in the direction opposite to the direction of the current flowing in the switching circuit. A switching element is inserted so that the second direction is directed.

  According to the present invention, since the polarity for switching from the low resistance to the high resistance state is always used, the resistance having a stable high resistance change rate even at a relatively low switching voltage of about 10 to 40 V, for example. A memory element can be obtained.

In the present invention, as described above, the polycrystalline titanium-based composite oxide constituting the element body has the general formula: {(Sr _1-x M _x ) _1-y A _y } (Ti _1-z B _z ) When represented by O ₃ , a higher resistance change rate can be obtained.

  In this invention, when the maximum current flowing in the element body during electroforming is limited to 10 to 500 mA, it is possible to reliably obtain a high resistance change rate and to ensure that irreversible resistance deterioration occurs. Can be prevented.

  When a pair of electrodes facing each other through at least a part of the element body are both made of a material having a work function larger than that of the titanium-based composite oxide, a Schottky barrier is formed between the element body and the electrode, so that low resistance ⇒ It is impossible to distinguish the polarity (the direction in which the switching voltage should be applied) for switching to the high resistance state by the electrode. However, according to the present invention, such distinction is unnecessary, and therefore, when the pair of electrodes are both made of a material having a work function larger than that of the titanium-based composite oxide, the significance of the present invention is more remarkable. It becomes.

In Non-Patent Document 1, resistance memory characteristics are expressed at the junction interface between the SrTiO ₃ single crystal substrate and the SrRuO ₃ thin film (single crystal thin film), and one electrode is Schottky using Pt. Since the barrier is used and ohmic property is used using Ag in the other electrode, the polarity at which the switching characteristics are expressed is specified. Therefore, the technique described in Non-Patent Document 1 cannot encounter the above-described problem that the present invention intends to solve.

  According to the switching circuit of the present invention, even if the switching voltage is about 10 to 40 V, for example, the resistance memory element having high switching characteristics is incorporated as the switching element, so that an excellent switching action can be exhibited. Can do.

  FIG. 1 is a sectional view showing a resistance memory element 1 according to an embodiment of the present invention.

The resistance memory element 1 includes an element body 2 made of a polycrystalline titanium-based composite oxide. The titanium-based composite oxide is preferably represented by the general formula: {(Sr _1-x M _x ) _1-y A _y } (Ti _1-z B _z ) O ₃ (where M represents Ba and Ca). At least one of them, A is at least one element selected from Y and rare earth elements, and B is at least one of Nb and Ta).

  In the above general formula, when 0 ≦ x ≦ 0.5, 0.001 ≦ y + z ≦ 0.02 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02), and 0.5 < When x ≦ 0.8, 0.003 ≦ y + z ≦ 0.02 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02), and 0.8 <x ≦ 1.0 The composition ratio is selected so as to satisfy the condition of 0.005 ≦ y + z ≦ 0.01 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02).

  The resistance memory element 1 also includes at least one pair of counter electrodes 3 and 4 that face each other with at least a part of the element body 2 interposed therebetween. In this embodiment, the element body 2 has a laminated structure, and the counter electrodes 3 and 4 are positioned so as to sandwich at least a part of the element body 2 while being positioned inside the element body 2. It is formed by firing at the same time as firing for obtaining the element body 2. By performing such simultaneous firing at a relatively high temperature, the interface between the counter electrodes 3 and 4 and the element body 2 can be made strong, and the withstand voltage characteristics of the resistance memory element 1 can be improved. .

  The counter electrodes 3 and 4 preferably form a Schottky barrier with the element body 2. That is, the work function of the counter electrodes 3 and 4 is preferably higher than the work function of the element body 2. Specifically, one type of metal selected from Pd, Pt, Ag—Pd, Au, Ru, and Ir is opposed. It is preferably used as a material for the electrodes 3 and 4.

  The resistance memory element 1 further includes terminal electrodes 5 and 6. Terminal electrodes 5 and 6 are formed on each end of element body 2 and are electrically connected to counter electrodes 3 and 4, respectively. Terminal electrodes 5 and 6 are formed, for example, by baking a conductive paste containing silver.

  In such a resistance memory element 1, when a switching voltage in the first direction is applied between the counter electrodes 3 and 4 via the terminal electrodes 5 and 6, a portion of the element body 2 sandwiched between the counter electrodes 3 and 4. After that, even if the switching voltage in the first direction is removed, the low resistance state of the element body 2 is maintained. On the other hand, a second direction opposite to the first direction is provided between the counter electrodes 3 and 4. When the switching voltage is applied, the resistance of the portion of the element body 2 sandwiched between the counter electrodes 3 and 4 becomes high, and even if the switching voltage in the second direction is removed, Is retained.

  In the resistance memory element 1 according to the present invention, the above-described switching voltage becomes high, for example, 5 V or higher, and a high resistance change rate, for example, 5000% or higher can be realized.

  When the polycrystalline titanium complex oxide as the semiconductor ceramic constituting the element body 2 is 0 ≦ x ≦ 0.5 in the above general formula, 0.005 ≦ y + z ≦ 0.01 (however, , 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02), a higher resistance change rate can be realized, for example, 10000% or more. it can.

  The mechanism by which the characteristics of the resistance memory element 1 as described above are manifested has not been completely elucidated. In general, a resistance switching effect appears at the interface between a semiconductor and a metal, and the resistance change itself is considered to be caused by the semiconductor side. In this invention, since the ceramic itself is made into a semiconductor by using a polycrystalline titanium-based composite oxide as a semiconductor ceramic, its resistance is low, but the grain boundary is high, and the switching phenomenon The voltage applied to the electrodes 3 and 4 is caused to disperse at the electrode interface and the grain interface, and the effective voltage applied to each interface is reduced, so that a higher switching voltage than that described in Non-Patent Document 1 is obtained. It is thought that it has been realized.

  In a polycrystalline titanium-based composite oxide as a semiconductor ceramic, the reason why the grain boundary is increased in resistance is simply that conduction electrons are scattered at the grain boundary and mobility is lowered, resulting in high resistance. In addition, it is presumed that shallow grain boundary levels are naturally generated, which become traps of electrons and that a low grain boundary barrier is formed.

That is, as described above, assuming that the resistance is simply increased due to scattering of conduction electrons at the grain boundary, it seems that a resistor is connected in series to the resistance memory element described in Non-Patent Document 1. The rate of resistance change is
Resistance change rate = {(series resistance component + element resistance in high resistance state) − (series resistance component + element resistance in low resistance state)} / (series resistance component + element resistance in low resistance state)
It is expressed by the following formula.

  Also in this element, assuming that only the resistance at the electrode interface changes and resistance switching occurs, in the above formula, the resistance of the element corresponds to the resistance of the grain boundary, and the series resistance component corresponds to the ceramic itself. However, since the resistance of the ceramic itself is high, the rate of change in resistance should also decrease. For example, if the series resistance component is 1 MΩ and this does not change, even if the resistance of the element is 6 ohms, such as 1 Ω in the low resistance state and 1 MΩ in the high resistance state, there is a series resistance component. The resistance changes only approximately twice, such as 1 MΩ + 1Ω in the resistance state and 1 MΩ + 1 MΩ in the high resistance state. From this, it can be explained that the resistance memory element 1 according to the present invention is not only high resistance because conduction electrons are scattered at the grain boundary and mobility is lowered.

  As described above, according to the resistance memory element 1 according to the present invention, resistance switching can be performed at a relatively high voltage, and a resistance change rate equal to or higher than that of the non-patent document 1 can be realized. It can be considered that the low grain boundary barrier formed at the grain boundary has a great influence. That is, it is speculated that the application of the switching voltage also changes the height of the grain boundary barrier, which may lead to a high rate of resistance change. This is because, as described above, when the resistance at the grain boundary is simply increased and the voltage applied to the interface with the electrodes 3 and 4 is lowered to cause the resistance switching phenomenon, the resistance change rate is explained to be high. This is because it cannot be done.

  The polycrystalline titanium-based composite oxide as a semiconductor ceramic constituting the element body 2 has a characteristic in which the switching voltage described above changes depending on the number of grain boundaries existing in a portion sandwiched between the counter electrodes 3 and 4. . Therefore, the switching voltage can be controlled by controlling the number of grain boundaries existing in the portion sandwiched between the counter electrodes 3 and 4, that is, the interval between the counter electrodes 3 and 4.

  Therefore, when the interval between the counter electrodes 3 and 4 is narrowed and the switching voltage is lowered, as described above, the forming voltage is applied multiple times in each of the forward direction and the reverse direction, and the electroforming process is performed. In the sample we performed, there is a difference in switching characteristics between low resistance ⇒ high resistance state and high resistance ⇒ low resistance state, and stable high switching characteristics can be obtained in the low resistance ⇒ high resistance state. It was found that the individual switching voltages are likely to vary in the low resistance state.

  On the other hand, if the electroforming process is applied to only one polarity and a switching voltage having a polarity opposite to that applied with the electroforming process is applied, a switching from a low resistance to a high resistance state is necessarily generated. Can be.

  This will be described with reference to FIG. FIG. 2 is a diagram showing a switching circuit 11 in which the resistance memory element 1 shown in FIG. 1 is used as a switching element for controlling the flow of current in the circuit.

  Referring to FIG. 2, resistance memory element 1 as a switching element is inserted in switching circuit 11. A power source 12 for applying a forming voltage or a switching voltage thereto is connected to the resistance memory element 1 via an on / off control switch 13.

  First, as shown in FIG. 2A, the switch 13 is turned on, and the voltage is applied from the power supply 12 to the resistance memory element 1 with the polarity in the direction indicated by the arrow 14, thereby completing the electroforming process. The direction indicated by the arrow 14 is opposite to the current 15 or 17 (see FIG. 2B or FIG. 2D) flowing in the switching circuit 11.

  After the electroforming process as described above, the switch 13 is turned off as shown in FIG. In addition, the resistance memory element 1 subjected to the electroforming process is in a low resistance state. Therefore, as shown in FIG. 2B, in the switching circuit 11, the flow of current is allowed and a large current can flow as shown by the arrow 15.

  In the state of FIG. 2B, the switch 13 is turned on, and the switching voltage from the power source 12 has the polarity in the direction indicated by the arrow 16 (that is, the direction opposite to the arrow 14 in FIG. 2A). When the resistance is increased and the resistance is increased (see FIG. 2C), the resistance memory element 1 is in a high resistance state (see FIG. 2D). As a result, the flow of current in the switching circuit 11 is limited by the resistance memory element 1, and the flowing current becomes small as shown by the arrow 17 (see FIG. 2D). In FIG. 2, the magnitude of the current is represented by changing the thickness of each of the arrow 15 and the arrow 17.

  In order to lower the resistance of the resistance memory element 1 again, as shown in FIG. 2A, the switch 13 is turned on, and the switching voltage is applied from the power source 12 to the resistance memory element 1 with the polarity in the direction indicated by the arrow 14. That's fine.

  As described above, when the thickness between the electrodes 3 and 4 is reduced, the electroforming process is applied only to one polarity, and a switching voltage having a polarity opposite to the polarity subjected to the electroforming process is applied. It is speculated that the reason why the low resistance ⇒ high resistance state switching can surely occur is because the grain boundary barrier of the polycrystalline titanium-based composite oxide has some involvement in the switching characteristics. Is done. That is, it is assumed that the reason why the good switching characteristics are exhibited only in one polarity is related to the decrease in the number of grain boundaries. In the case where both the electrodes 3 and 4 use a Schottky barrier, one of the Schottky barriers is deteriorated by the electroforming process, and this may be involved.

  Next, the electroforming process of the resistance memory element 1 according to the present invention and the resistance switching characteristic after the electroforming process will be described more specifically.

FIG. 3 shows a typical current-voltage characteristic (IV characteristic) of the resistance memory element 1 according to the present invention. Note that the resistance memory element 1 having the IV characteristics shown in FIG. 3 is an example in which the semiconductor ceramic constituting the element body has a composition of Sr _0.992 La _0.008 TiO ₃ and will be described later. It was produced in.

  First, as shown in FIG. 3, as an electroforming process, a current limit was set to 30 mA, and a voltage pulse with a pulse width of 0.1 sec was applied from 0 V to 100 V on the plus side in increments of 1V. After this electroforming process, the IV characteristics were evaluated.

  In the evaluation of the IV characteristics, the voltage was swept in the order of 0V → predetermined voltage (plus side) → 0V → predetermined voltage (minus side) → 0V. At this time, the voltage was applied by a voltage pulse having a pulse width of 0.1 sec. As shown in Fig. 3, switching from high resistance to low resistance occurs in the same polarity (positive direction) as the one subjected to electroforming, and low resistance to high resistance in reverse polarity (negative direction). It can be seen that switching occurs. And it turns out that the high resistance change rate is stably implement | achieved in the reverse polarity which performed the switching which switched from the low ⇒ high resistance state.

  FIG. 4 is a diagram corresponding to FIG. 3 and shows a case where the electroforming process is performed with the polarity opposite to that in FIG. 4 is different from the case of FIG. 3 in that the current limit is set to 30 mA.

  In the case shown in FIG. 4, first, as an electroforming process, a voltage pulse with a pulse width of 0.1 sec was applied from 0 V to −80 V in the negative direction in increments of 1 V. After this electroforming process, the IV characteristics were evaluated.

  In the evaluation of the IV characteristics, the voltage was swept in the order of 0V → predetermined voltage (plus side) → 0V → predetermined voltage (minus side) → 0V. At this time, the voltage was applied by a voltage pulse having a pulse width of 0.1 sec. As shown in FIG. 4, switching from a low resistance to a high resistance state occurs in the polarity opposite to the polarity subjected to electroforming (positive direction), and in the same polarity (negative direction), the high resistance is set to low resistance. It can be seen that state switching occurs. And it turns out that the high resistance change rate is stably implement | achieved in the reverse polarity which performed the switching which switched from the low ⇒ high resistance state.

  Next, a voltage of 50 V is applied to the resistance memory element 1 according to the present invention having the IV characteristics shown in FIG. 3 while changing the pulse width to 1 msec, 10 msec, 100 msec, and the resistance change. As a result of investigating the pulse width dependence, the resistance did not change even when a pulse voltage with a pulse width of 1 msec or a pulse voltage with a pulse width of 10 msec was applied, and the resistance was not applied until a pulse voltage with a pulse width of 100 msec was applied. Has been confirmed to change. On the other hand, in the resistance memory element described in Non-Patent Document 1, when a voltage of 5V is applied, the resistance is increased at a pulse width of 1 msec (current value decreases), and a voltage of 5V is applied with a longer pulse width of 10 msec. It has been confirmed that when applied, the resistance is further increased.

  For this reason, in the resistance memory element 1 according to the present invention, in order to cause the resistance switching phenomenon, it is necessary to apply a voltage of a certain value or more. Further, in the resistance memory element described in Non-Patent Document 1, In comparison, it can be seen that it is necessary to apply a voltage having a longer pulse width.

  Therefore, when the element according to the present invention is used as a switching element such as a signal circuit or a power supply circuit, the resistance state is very stable against spike noise (voltage or current pulse noise) existing in the circuit. Therefore, even if spike noise in the circuit enters the element, the resistance state of the element does not change, and malfunction of the circuit hardly occurs.

In resistive memory element 1 according to the present invention, as the titanium-based composite oxide of the polycrystalline body constituting the element body, the above-mentioned general _{formula: {(Sr 1-x M} x) 1-y A y} (Ti 1- _z B _{z) O 3} (however, M is at least one of Ba and Ca, a is at least one element selected from Y and rare earth elements, B is at least one of Nb and Ta )), For example, a general formula: (Sr _1-x A _x ) _v (Ti _1-y B _y ) _w O ₃ (where A is at least one selected from Y and rare earth elements) B is at least one of Nb and Ta.) And 0.001 ≦ x + y ≦ 0.02 (where 0 ≦ x ≦ 0.02 and 0 ≦ y ≦ 0) .02) and 0.87 ≦ v / Conditions of ≦ 1.030 may be achieved, thereby satisfying is used.

  In the case of the latter titanium-based composite oxide, in the above general formula, the condition of 0.005 ≦ x + y ≦ 0.01 is further satisfied, or the condition of 0.950 ≦ v / w ≦ 1.010 is further satisfied. By doing so, the resistance change rate can be further increased, and for example, a resistance change rate of 10,000% or more can be realized.

  In the resistance memory element 1 shown in FIG. 1, the counter electrodes 3 and 4 that form a pair are arranged at the central portion in the thickness direction of the element body 2, but are arranged at a position biased toward one end side in the thickness direction. In an extreme case, one of the counter electrodes 3 and 4 may be formed on the outer surface of the element body 2. Further, the pair of counter electrodes 3 and 4 may both be arranged on the outer surface of the element body 2 so as to be arranged at a predetermined interval, and may be opposed to each other at their edges. Further, the pair of counter electrodes 3 and 4 may be arranged side by side on the same surface in the element body 2 so as to face each other at their edges.

  Note that, as described above, the counter electrodes 3 and 4 are arranged inside the element body 2, and the portion sandwiched between the counter electrodes 3 and 4 forming a pair is a very small part of the element body 2. This is to ensure a mechanical strength of a predetermined level or more in the element body 2 while reducing the distance between 3 and 4. Therefore, if it is not necessary to consider the problem of mechanical strength, a counter electrode may be formed on each main surface of the thin plate-shaped element body.

  The counter electrodes 3 and 4 forming a pair are not only used for applying a forming voltage and a switching voltage but also used for current measurement (for resistance measurement). An electrode for current measurement may be provided separately for application. In this case, typically, the first, second and third electrodes are formed in this order so as to face each other. For example, the first and second electrodes are used while sharing the first electrode. Current measurement and applying a voltage using the first and third electrodes, or applying a voltage using the first and second electrodes and using the first and third electrodes Can be measured.

  Next, an experimental example in which a phenomenon that motivates the present invention has been found, and an experimental example carried out in order to confirm the effect of the present invention or to obtain a preferable range of the present invention will be described.

[Experimental Example 1]
A phenomenon that is a motivation for completing the present invention can be found from this experimental example 1.

As starting materials for the polycrystalline titanium-based composite oxide constituting the element, strontium carbonate (SrCO ₃ ) and titanium oxide (TiO ₂ ), and lanthanum oxide (La ₂ O ₃ ) as a donor were used. Using. Then, after the _firing, so that the composition of Sr _{0.992 La} 0.008 TiO _3, were weighed the starting material.

  Next, the starting material weighed as described above was added to pure water together with a dispersant, and wet mixing and pulverization was performed using PSZ balls having a diameter of 2 mm for 24 hours. After mixing and pulverizing, the obtained slurry was dried and granulated, and calcined in the atmosphere at a temperature of 1200 ° C. for 2 hours. After granulating the obtained calcined powder, it is added to pure water together with a dispersant, pulverized for 24 hours using a PSZ ball having a diameter of 5 mm, and then added with an acrylic binder, a plasticizer, an antifoaming agent, etc. The mixture was mixed for 12 hours to obtain a green sheet forming slurry.

  Next, a doctor blade method was applied to the resulting slurry to form a sheet, thereby obtaining a green sheet. The thickness of this green sheet was adjusted to be about 25 μm and about 80 μm, respectively. Next, the green sheet was cut into strips, and a conductive paste containing Pd was screen-printed to form a counter electrode.

  Thereafter, a plurality of green sheets including a green sheet on which a conductive paste film to be a counter electrode is formed are stacked, pressed, and cut to have a size of 2.0 mm × 1.2 mm × 1.2 mm. Got green chips.

Next, the green chip was degreased at a temperature of 550 ° C. in the air, and then fired at a temperature of 1300 to 1400 ° C. for 2 hours in the air. The chip after baking was polished, the counter electrode was exposed, and the counter area of the counter electrode was calculated from the size, and it was about 0.5 mm ² .

  In order to form a terminal electrode on the fired body obtained as described above, a conductive paste containing Ag was applied, and baked at a temperature of 750 ° C. in the atmosphere. did.

  For each sample thus obtained, a pulse voltage of 100 to 200 V and a pulse width of 100 msec was applied 10 to 50 times in each of the forward direction and the reverse direction to perform electroforming, and then IV The characteristics were evaluated.

  For evaluation of the IV characteristics, an “ADVANTEST R6246 pulse source meter” was used, and the voltage was swept from 0 V → predetermined voltage (plus side) → 0 V → predetermined voltage (minus side) → 0V. At this time, the voltage was applied by a voltage pulse, and measurement was performed with a pulse width of 0.1 sec.

Based on the IV characteristics obtained as described above, the maximum resistance change rate was obtained. The maximum resistance change rate is a low resistance state and a high resistance state at a voltage higher than +10 V or a voltage lower than −10 V in a polarity (both positive side and negative side can be changed) from a low resistance state to a high resistance state. The resistance change rate is calculated at a voltage at which the difference between the resistance and the resistance is the largest. The resistance change rate [%] =% when the resistance ρ _H is in the high resistance state and ρ _L is the resistance in the low resistance state. It is obtained from the equation (ρ _H −ρ _L ) / ρ _L × 100. The reason for obtaining the maximum resistance change rate in this way is that the resistance of the resistance memory element has voltage dependency.

  In Table 1, “element thickness: 50 μm” and “element thickness: 20 μm” indicate that the thickness between the counter electrodes of the element body is 50 μm and 20 μm, respectively, and the thickness of the green sheet is about 80 μm and It corresponds to about 25 μm.

  Samples 1 to 10 and Samples 11 to 20 in Table 1 have the same composition, and the maximum resistance change rate when the same switching voltage is applied is the column of “resistance change rate” in Table 1. Is shown in Variation occurs between the samples 1 to 10 and between the samples 11 to 20.

  In Table 1, “+ direction” and “− direction” indicate the application direction of the switching voltage. “Switching” indicates the mode of switching when a switching voltage is applied, “Low → High” indicates switching from low resistance to high resistance, and “High → Low” indicates switching from high resistance to low resistance. It indicates that switching has occurred. For example, the polarity in which “low to high” occurs varies depending on the sample, but this is only because the “+ direction” and the “− direction” were provisionally determined when the switching voltage was applied.

  For example, sample 1 and sample 11 correspond to each other, but if the applied voltages are the same as each other, there is a risk that the sample 11 may be damaged due to excessive voltage applied. The measurement was made slightly lower.

  From Table 1, in Samples 1 to 10 where the element thickness is as thick as 50 μm (that is, the switching voltage is high), the polarity in which switching occurs in the low resistance → high resistance state and the polarity in which switching occurs in the high resistance → low resistance state. Even in this case, while the high resistance change rate of 5000% or more, more specifically 29000% or more, can be realized, in the samples 11 to 20 where the element thickness is as thin as 20 μm (that is, the switching voltage is low), A high resistance change rate of 5000% or more, more specifically 31000% or more is realized in polarity switching from low resistance to high resistance state, but 1000% in polarity switching from high resistance to low resistance state. There are many samples that do not satisfy this, and the variation in resistance change rate is large.

  Of the samples shown in Table 1, typical IV characteristics of Samples 1 and 11 are shown in FIGS. 5 and 6, respectively.

  As apparent from FIGS. 5 and 6, the device is thicker than the sample 1 (FIG. 5), which has a large device thickness, a high switching voltage, and can achieve a resistance change rate of 5000% or more in any polarity. In sample 11 (FIG. 6), which has a low thickness, a low switching voltage, and a low resistance change rate in the polarity in which switching between a high resistance and a low resistance state occurs, the hysteresis is small and the element thickness is large in the IV characteristics. Compared with the sample 1, the resistance change rate is low.

  Note that even with the latter sample with a thin element thickness, a resistance change rate of 5000% or more can be realized in the polarity where switching from a low resistance to a high resistance state occurs. Also, as shown in Table 1, it is small and stable.

  From Experimental Example 1 above, when the element thickness is controlled and a small switching voltage is realized, it is necessary to select the polarity at which switching from the low resistance to the high resistance state occurs when using the resistance memory element. Recognize.

  In addition, even if the element thickness is large and a sufficiently large resistance change rate can be obtained regardless of whether switching is from low resistance to high resistance or high resistance to low resistance, switching from low resistance to high resistance is possible. Focusing on the variation in the resistance change rate in the case and the variation in the resistance change rate in the case of switching from the high resistance to the low resistance state, in the samples 1 to 10 shown in Table 1, in the low resistance to the high resistance state, While the standard deviation of the rate of change in resistance is 3289, the standard deviation is 12598 in the state of high resistance → low resistance. Therefore, it can be seen that in order to stably use a large rate of change in resistance, it is preferable to use a polarity that causes switching from a low resistance to a high resistance state.

[Experimental example 2]
Experimental example 2 was carried out in order to confirm the effect of the present invention.

  About the sample for evaluation produced in Experimental Example 1, as an electroforming process, the current limit was set to 100 mA, the voltage was applied from 0 V to 100 V, and then the IV characteristics were evaluated.

  From the above IV characteristics, the rate of resistance change at the higher of −10 V and +10 V is obtained, and low resistance in each of the + direction (the same polarity as the forming) and the − direction (the opposite polarity to the forming) ⇒ We investigated whether switching to a high resistance state occurred or whether switching from a high resistance to a low resistance state occurred. The results are shown in Table 2.

  As can be seen from Table 2, when a switching voltage is applied with the same polarity (+ direction) as the one subjected to electroforming, switching from high resistance to low resistance occurs, and switching is performed with reverse polarity (-direction). When voltage is applied, switching from low resistance to high resistance occurs. As for the rate of change in resistance, the resistance change is stable at 5000% or more, more specifically 38000% or more in the polarity switching from low resistance to high resistance, that is, the polarity opposite to that of forming. It can be seen that the rate is achieved.

[Experiment 3]
Experimental Example 3 was carried out in order to obtain a preferable range for the current limitation during the electroforming process.

  From Experimental Examples 1 and 2, in order to achieve a stable high resistance change rate with a desired polarity, the electroforming process is opposite to the polarity that causes switching from a low resistance to a high resistance state while providing a current limit. It became clear that it should be applied with the polarity.

  Therefore, the electroforming process was performed on the evaluation sample manufactured in Experimental Example 1 while changing the current limit value. And about the obtained resistance memory element, the resistance change rate in the polarity which switches from a low resistance ⇒ high resistance state was calculated | required.

  In addition, 20 obtained samples for evaluation were prepared, each current amount was limited and a forming process was performed once, and then the probability of obtaining a resistance switching phenomenon (forming success probability) was evaluated.

  The results are shown in Table 3. In Table 3, the rate of change in resistance is the rate of change in resistance that was the lowest among the samples in which the resistance switching phenomenon was obtained.

  When the current limit is made larger than 500 mA as in the sample 37, the resistance change rate is shown in Table 3 as 13000%, but the probability of obtaining the resistance switching phenomenon is as low as 45%, and the resistance deterioration occurs. There was a thing. This is presumed that the electric barrier presumed to be formed at the grain boundaries and electrode interfaces was destroyed because an excessive current flowed during the electroforming process.

  On the other hand, when the current limit was made lower than 25 mA as in Sample 31, a large resistance change rate of 11500% was obtained, but it was found that the resistance memory effect was also unstable.

  From the above, it can be seen that in order to obtain a stable high resistance change rate, it is important not only to pay attention to the polarity of the electroforming process, but also to set the current limiting amount within an appropriate range.

It is sectional drawing which shows the resistance memory element 1 by one Embodiment of this invention. 1 is a diagram showing a switching circuit 11 in which the resistance memory element 1 shown in FIG. 1 is used as a switching element for controlling the flow of current in the circuit, in which an electroforming process and a low resistance and a high resistance are shown. It is for demonstrating the switching voltage application process for conversion. It is a figure which shows the typical current-voltage characteristic of the resistance memory element based on this invention, Comprising: The case where the electroforming process is carried out by the polarity of the plus side is shown. FIG. 4 is a diagram corresponding to FIG. 3, showing a case where the electroforming process is performed with a negative polarity opposite to that in FIG. 3. It is a figure which shows the current-voltage characteristic of the resistance memory element which concerns on the sample 1 produced in Experimental example 1. FIG. It is a figure which shows the current-voltage characteristic of the resistive memory element which concerns on the sample 11 produced in Experimental example 1. FIG. It is a figure which shows the electric current-voltage characteristic of the resistive memory element provided with the element | base_body which has the composition similar to the samples 1 and 11 produced in Experimental example 1, and performed the same electroforming process, but a switching voltage is comparatively high The case is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Resistance memory element 2 Element body 3, 4 Counter electrode 5, 6 Terminal electrode 11 Switching circuit 12 Power supply

Claims (5)

It has a switching element in which an element body made of a polycrystalline titanium-based composite oxide is provided, and when the switching voltage in the first direction is applied to the element body, the element body switches from a low resistance state to a high resistance state. A resistance memory element,
The resistance memory element according to claim 1, wherein the element body is subjected to an electroforming process by applying a voltage to the element body in a second direction opposite to the first direction. The polycrystalline titanium complex oxide constituting the element body is:
General _{formula: {(Sr 1-x M} x) 1-y A y} (Ti 1-z B z) O 3 ( however, M is at least one of Ba and Ca, A is, Y and rare earth elements And B is at least one of Nb and Ta), and
When 0 ≦ x ≦ 0.5, 0.001 ≦ y + z ≦ 0.02 (however, 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02),
When 0.5 <x ≦ 0.8, 0.003 ≦ y + z ≦ 0.02 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02), and 0.8 <x ≦ 1.0 is a semiconductor ceramic that satisfies the condition of 0.005 ≦ y + z ≦ 0.01 (where 0 ≦ y ≦ 0.02, 0 ≦ z ≦ 0.02), The resistance memory element according to claim 1.   The resistance memory element according to claim 2, wherein a maximum current flowing in the element body during the electroforming process is limited to 10 to 500 mA.   The electrode according to claim 1, further comprising a pair of electrodes facing each other through at least a part of the element body, wherein the electrodes are made of a material having a work function larger than that of the titanium-based composite oxide. The resistance memory element according to any one of the above. A switching circuit in which a switching element for controlling the flow of current in the circuit is inserted,
The resistance memory element according to any one of claims 1 to 4 is used as the switching element, and a voltage for the electroforming process is applied in a direction opposite to a direction of a current flowing in the switching circuit. The switching circuit, wherein the switching element is inserted so that the second direction is directed.

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