JP2008244373A - Two-layer structure provided by directly depositing manganese oxide on amorphous substrate or amorphous film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching element or a memory element of a manganese oxide operating at room temperature and at a low temperature. <P>SOLUTION: By manufacturing a two-layer structure provided by depositing the manganese oxide on an amorphous substrate or an amorphous film, the switching element or the memory element, having the characteristics of reversibly changing from a high resistance condition to a low resistance condition, or from a low resistance condition to a high resistance condition by applying specific current threshold or voltage threshold. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a manganese oxide switching element or memory element.

Perovskite-type manganese oxides represented by the chemical formula Pr1-xCaxMnO3 (0.3 ≦ x <0.75; PCMO) undergo charge-alignment (CO) in which Mn3 + and Mn4 + are arranged alternately due to Yarn-Teller deformation at low temperatures (~ 240 K) Happens. Furthermore, it is a substance that aligns with spin at low temperatures and becomes an antiferromagnetic insulator. There has been a report that the PCMO CO decay occurs by applying external perturbation to the COMO PCMO due to the electric field, and the physical properties of the PCMO are transferred from the insulator to the metal. In Patent 3030333, when a voltage is applied to PCMO (x = 0.3) that is CO at T = 20 K, the resistance of PCMO suddenly decreases from high to low at a specific voltage threshold (around 700 V). It shows a reversible change from low resistance to high resistance at around 250 V when the voltage changes to the resistance state and decreases. This effect is thought to occur only at low temperatures because CO occurs only at low temperatures. In fact, according to FIG. 1 used in Japanese Patent No. 3030333, the change in resistance is shown only at about 110 K or less.
(Patent Document 1)

  In addition, changes in electrical resistance due to the application of PCMO voltage have been confirmed even in laminated junctions using PCMO (x = 0.5) films [J. Sakai et al., J. Appl. Phys. 90, 1410 (2001). )]. Here, it can be seen that at T = 30 K, the voltage changes from the high resistance state to the low resistance state at a voltage of 4.7 V, and returns to the high resistance state at 1.3 V. However, in this case as well, when measuring at a slightly high temperature T = 75 K, a change in resistance is no longer observed. In addition, a change in resistance was observed in a ramp edge type junction using a PCMO (x = 0.5) film, but the change was also observed only at low temperatures from around T = 160 K [T. Murakami et al., J. Appl. Phys. 94, 6549 (2003)]. (Non-Patent Documents 1 and 2)

  In addition to the CO phenomenon, a high-resistance, low-resistance state is switched by applying a voltage pulse to PCMO at room temperature [SQ Liu et al., Appl. Phys. Lett. 76, 2749 (2000)] Phenomenon that voltage-current characteristics become figure-eight (a phenomenon that changes from high resistance to low resistance at a positive voltage and from low resistance to high resistance at a negative voltage) [A. Odagawa et. Al., Thin Solid Films 486, 75 (2005)] has been reported. All of these phenomena that occur at room temperature have non-volatile characteristics. In other words, even if the applied voltage is returned to 0 V, the high resistance or low resistance state is maintained, so unlike the characteristics due to CO described above, this phenomenon occurs at the interface between the metal electrode and PCMO. Some think that there is. Currently, the application of memory elements using this phenomenon has begun. (Non-Patent Documents 3 and 4)

Insulator-metal transition caused by the collapse of conventional PCMO CO occurs only at low temperatures and cannot be used as a switching element at room temperature. In addition, a nonvolatile resistance change element that is considered to use an interface phenomenon that operates at room temperature is suitable for use as a memory element, but for use as a switching element, the previous resistance is maintained even when the voltage is returned to 0 V. Since the state is maintained, an operation for releasing the resistance state is necessary.
Patent registration 3030333 J. Sakai et al., J. Appl. Phys. 90, 1410 (2001) T. Murakami et al., J. Appl. Phys. 94, 6549 (2003) SQ Liu et al., Appl. Phys. Lett. 76, 2749 (2000). A. Odagawa et al., Thin Solid Films 486, 75 (2005).

  The problem to be solved is that manganese oxide cannot be easily used as a switching element that is controlled by current or voltage from room temperature (around 300 K) to low temperature (around 150 K).

  By controlling the current or voltage at room temperature or low temperature by creating a two-layer structure obtained by heating the amorphous substrate or film and depositing manganese oxide directly on the amorphous substrate or film. A switching element or a memory element that can be obtained is obtained.

  It is desirable that the amorphous substrate has a softening point at a temperature required for crystallization of manganese oxide, 800 ° C. or more. In particular, synthetic quartz glass having a high softening point of 1600 degrees is desirable as an amorphous substrate.

The manganese oxide is preferably a perovskite type manganese oxide represented by the chemical formula R1-xAxMnO3 (where R is a rare earth ion and A is an alkaline earth ion), and in particular, the rare earth ion is praseodymium and the alkaline earth ion is calcium. desirable.

  The manganese oxide deposited directly on the amorphous substrate or the amorphous film according to the present invention exhibits a sudden change in resistance value at room temperature or low temperature by application of current or voltage. It can be used as a memory element (for example, a switching element in which the high resistance state is 0 and the low resistance state is 1). In addition, since an amorphous substrate such as a synthetic quartz substrate is used as the substrate, it can be manufactured at low cost and can be configured with a simple structure including only a film and an electrode terminal. In addition, coexistence with oxide electronic devices such as memory resistance change elements that have already begun to be applied is facilitated.

  The present inventor has found that a two-layer structure of manganese oxide deposited directly on an amorphous substrate has a higher resistivity than that of the single crystal of manganese oxide at room temperature, measured voltage-current characteristics, and identified When the current threshold or the voltage threshold is added, the high resistance is changed to the low resistance state, and when the current or voltage is lowered, the low resistance is switched to the high resistance state.

  This two-layer structure is manufactured as follows. First, an amorphous substrate is mounted on a heating apparatus and inserted into a chamber of a film forming apparatus. Examples of the amorphous substrate include fused silica glass, synthetic quartz glass, and amorphous metal.

  Instead of an amorphous substrate, an oxide single crystal substrate or a metal polycrystalline substrate may be used, and an amorphous film deposited thereon may be used. Examples of the amorphous film include a SiO2 film.

  Examples of the film forming apparatus include a pulse laser deposition apparatus and a sputtering apparatus. After the chamber is evacuated, the amorphous substrate is heated. Oxygen is introduced into the chamber. Thereafter, manganese oxide is deposited to obtain a two-layer structure. Here, the order of heating the amorphous substrate and introducing oxygen into the chamber may be reversed. Alternatively, manganese oxide may be preliminarily deposited on an amorphous substrate that has not been heated by a film forming apparatus, and then the two-layer structure may be heated to crystallize the manganese oxide.

  Examples of the two-layer structure manganese oxide include a perovskite-type manganese oxide material represented by the chemical formula R1-xAxMnO3 (where R is a rare earth ion and A is an alkaline earth ion). Examples of rare earth ions include praseodymium and neodymium, and examples of alkaline earth ions include calcium and strontium.

  Examples of the present invention will be shown below to clarify the present invention more specifically, but it goes without saying that the present invention is not limited by the description of such examples. There is no place. In addition to the following examples, in addition to the description in the embodiment of the present invention described above, the present invention is based on the knowledge of those skilled in the art unless it departs from the spirit of the present invention. It should be understood that various changes, modifications, improvements and the like can be made.

  A perovskite-type manganese oxide PCMO (x = 0.5) film was deposited on a synthetic quartz (amorphous SiO2) substrate using a pulsed laser deposition (PLD) method (KrF excimer laser). The softening point of the synthetic quartz substrate used in this example is about 1600 ° C. First, a synthetic quartz substrate was bonded to a heater using a silver paste. The heater was inserted into the chamber of the PLD apparatus, and the inside of the chamber was set to a high vacuum (10-6 Torr order).

  Thereafter, an electric current was passed through the heater to set the synthetic quartz substrate temperature to 760 ° C. The substrate temperature is preferably 700 ° C. or more to promote crystallization of PCMO, and is preferably 800 ° C. or less to avoid extreme aggregation of PCMO crystals.

  Oxygen was introduced into the chamber and the partial pressure of oxygen was 300 mTorr. The distance between the synthetic quartz substrate and the PCMO polycrystalline target was adjusted to 29 mm. The laser frequency was set to 4 Hz, the energy density was set to 1 J / cm2, the laser was irradiated to the PCMO polycrystalline target for 14 minutes, and the ablation plasma generated therefrom was deposited on the synthetic quartz substrate. At this time, the film thickness of PCMO was about 200 nm.

  After the PCMO deposition, the oxygen partial pressure was set to 10 Torr, the synthetic quartz substrate temperature was lowered to 550 ° C., and annealing was performed for 1 hour. Thus, a two-layer structure of the manganese oxide PCMO and the synthetic quartz substrate shown in FIG. 1 was obtained.

  After the substrate on which the PCMO film was deposited was taken out of the chamber, electrode terminals for voltage-current measurement were formed. When forming an electrode pattern having an interelectrode distance of 1 μm, electron beam exposure was used as a photosensitive means for organic resist. Ti and Au were deposited on the patterned resist by vacuum evaporation, and electrodes were formed by lift-off.

  The voltage application current measurement was performed with the circuit shown in FIG. 2 at room temperature (298 K) using a R6243 voltage current source monitor manufactured by Advantest Corporation. The current limit was set to 10 mA to protect the PCMO film.

  Fig. 3 shows the voltage-current characteristics. This figure shows that the voltage applied to the two-layer structure is increased from 0 V to 4 V in increments of 0.1 V, then decreased from 4 V to -4 V, and then returned from -4 V to 0 V. It is the graph which read and plotted the electric current value. The inset in FIG. 3 is expressed in logarithmic display.

  Looking at this graph in detail, when the applied voltage is 0.1 V, the resistance of the PCMO film is about 30 kΩ (resistivity is about 180 Ωcm), and the resistivity of the PCMO single crystal is 1800 to 1 It can be seen that it is 18000 times larger.

  As the voltage is increased, the current value that was 4 mA from 3.3 V to 3.5 V is 10 mA or more, showing a rapid change of about twice or more, and the resistance of the two-layer structure is reduced from high resistance to low. It changes to a resistance state and it can confirm that it is switching. Next, when the applied voltage is lowered, the current becomes smaller than 10 mA from around 2.4 V, and it can be seen that the original high resistance state is restored around 1 V. The same characteristics can be confirmed even when the applied voltage is negative, and the current that was -3 mA at -3.3 V has suddenly changed to -10 mA or less at -3.4 V. When the voltage is returned to 0 V, -1.5 V It turns out that it has returned to the high resistance state near V.

  When a voltage is applied in this way, when a certain voltage threshold or current threshold is exceeded, the state changes from a high resistance state to a low resistance state, and when the voltage is returned, a reversible change returns from the low resistance state to the high resistance state. Show. Although it resembles the characteristics at the time of CO decay, which had been seen only at low temperatures in PCMO single crystals and PCMO laminated junctions in the past, the results in Fig. 3 were obtained at room temperature (298 K).

Figure 4 shows the results of voltage-current characteristics of the same sample measured at low temperature (150 K). As the voltage is increased, the current value that was 0.5 mA from 5.2 V to 5.4 V is 10 mA or more, indicating a rapid change of approximately 20 times or more, and switching from a high resistance to a low resistance state. I can confirm that. After that, when the applied voltage is lowered, it can be seen that the high resistance state is restored at around 2.5 V. Similar characteristics can be confirmed even if the applied voltage is negative.

  Thus, the resistance changes at both room temperature and low temperature, and can be used as a switching element.

  Further, it can be used as a memory by the following method. As can be seen from the voltage-current characteristics in FIG. 3, after the high resistance state is changed to the low resistance state, hysteresis is shown and the state returns to the high resistance state. By fixing the voltage applied to the two-layer structure to a voltage within the hysteresis range, a binary resistance state can be present. For example, in FIG. 3, the applied voltage is fixed at 3 V. In the high resistance state, a current of 2.9 mA flows, and in the low resistance state, a current of 10 mA or more flows.

  Rewriting from a high resistance state to a low resistance state can be performed by increasing the voltage applied to the two-layer structure, switching to a low resistance state, and lowering the voltage to 3 V again.

  Conversely, rewriting from low resistance to high resistance can be done by lowering the applied voltage, switching to high resistance, and then returning to 3V again. In this way, switching between two values is possible, and a high resistance or low resistance state can be maintained, so that it can be used as a memory.

  The manganese oxide switching element or memory element of the present invention can be expected for application to oxide devices.

A two-layer structure in which manganese oxide is deposited on the amorphous substrate of the present invention. It is the figure which showed the measuring method. Example 1 It is the figure which showed the current-voltage characteristic in room temperature (298K). Example 1 It is the figure which showed the electric current-voltage characteristic in low temperature (150K). Example 1

Claims (12)

A two-layer structure in which manganese oxide is deposited directly on an amorphous substrate or film.

2. The two-layer structure according to claim 1, wherein the amorphous substrate has a softening point of 800 ° C. or higher at a temperature higher than that required for crystallization of manganese oxide.

3. The two-layer structure according to claim 2, wherein the amorphous substrate is synthetic quartz glass.

2. The two-layer structure according to claim 1, wherein the manganese oxide is a perovskite-type manganese oxide represented by the chemical formula R1-xAxMnO3 (R is a rare earth ion and A is an alkaline earth ion).

2. The two-layer structure according to claim 1, wherein the manganese oxide is a perovskite-type manganese oxide represented by a chemical formula Pr1-xCaxMnO3.

A switching element with a two-layer structure in which manganese oxide is deposited directly on an amorphous substrate or film.

A memory device with a two-layer structure in which manganese oxide is deposited directly on an amorphous substrate or film.

7. The switching element according to claim 6, wherein the electrical resistance of the manganese oxide changes by a factor of 2 or more depending on the voltage or current.

8. The memory element according to claim 7, wherein the electrical resistance of the manganese oxide changes by a factor of 2 or more depending on voltage or current.

A method for manufacturing a two-layer structure manufactured by heating an amorphous substrate or film and depositing manganese oxide directly on the amorphous substrate or film.

A manufacturing method comprising a step of producing a two-layer structure by depositing manganese oxide directly on an amorphous substrate or an amorphous film, and a step of heating the two-layer structure.

12. The method for producing a two-layer structure according to claim 10 or 11, wherein heating is performed at a temperature required for crystallizing the manganese oxide between 700 and 800 degrees.

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