JP2008066438A - Variable resistance element, nonvolatile memory element, variable resistance memory device, and method of writing data therein - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable resistance memory device of a write-once type which has a novel arrangement. <P>SOLUTION: The variable resistance memory device comprises a first electrode, a second electrode and a thin film formed between the first and second electrodes. The thin film contains an oxide including a transition metal. When an electric pulse having a level not lower than a first level is applied to the thin film via the first and second electrodes, electric resistance between the first and second electrodes is irreversibly varied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a resistance change element, a nonvolatile memory element, a resistance change memory device, and a data writing method for these. More specifically, the present invention relates to a resistance change element capable of write-once and rewritable writing, a nonvolatile memory element, a resistance change memory device, and a data writing method for these.

  In recent years, with the advancement of digital technology in electronic devices, there is an increasing need for nonvolatile storage devices that can store a large amount of data such as images and moving images with the power turned off.

As a conventional nonvolatile memory device, a resistance variable element disclosed in Patent Document 1 is known. In the variable resistance element of Patent Document 1, a perovskite material (for example, Pr _1-X Ca _X MnO ₃ (PCMO), LaSrMnO ₃ (LSMO), GdBaCo _X O _Y (GBCO), etc.) is used as the variable resistance material. The resistance value of the variable resistance material increases or decreases when a predetermined electric pulse is applied. The changed resistance value is stably stored even when the power is turned off. By associating the resistance value with the data, the variable resistance element can be used as a (rewritable) nonvolatile memory element that can be written a plurality of times.

As another nonvolatile memory device, there is an antifuse-type memory element disclosed in Patent Document 2. The memory element of Patent Document 2 uses a SiO ₂ thin film as an antifuse for a part of the memory element. When a predetermined electric pulse is applied to the memory element, the electric resistance is irreversibly lowered. Such changes are preserved even when the power is turned off. Also, the high resistance value in the initial state is stored for a long time with the power off. Therefore, the memory element can be used as a non-volatile memory element that can be recorded only once (write-once type). The write-once nonvolatile storage device is expected to be useful for encryption technology, unauthorized copy prevention technology, and the like.
US Pat. No. 6,204,139 US Pat. No. 6,034,882

  In the conventional configuration, the write-once nonvolatile memory device has a problem that the recording speed is low. In addition, there are limited choices of configurations that can be used as a write-once nonvolatile memory device.

  There are also devices that need to perform both write-once and rewritable storage. In the case of manufacturing such a device, in the conventional configuration, it is necessary to manufacture a write-once nonvolatile memory device and a rewritable nonvolatile memory device by separate processes. For this reason, when such an apparatus is manufactured based on the prior art, there is a problem that the manufacturing process is complicated, the manufacturing time is increased, and the manufacturing cost is increased.

  An object of the present invention is to provide a write-once nonvolatile memory device capable of high-speed recording. Another object of the present invention is to provide a write-once nonvolatile memory device having a novel configuration. Still another object of the present invention is to make it possible to manufacture a device capable of executing both a write-once type nonvolatile memory and a rewritable type nonvolatile memory with a simple process and at a low cost in a short time. .

  The present inventor has discovered that when a large voltage is applied to a resistance variable element using a resistance variable film containing an oxide, breakdown occurs, and the resistance value irreversibly decreases (see Examples). By utilizing such a property, it becomes possible to use a resistance change type storage device that has been used only as a rewritable type as a write-once type non-volatile storage device. Therefore, a write-once nonvolatile memory device having a novel configuration can be provided.

  A conventional write-once nonvolatile memory device, which is an antifuse memory device, has a writing speed per cell of about 1 μs (IEEE Electron Device Letters, Vol. 25, No. 5 (2005) p. 5). 271-p.273). On the other hand, when the variable resistance element using the variable resistance film containing the oxide of the present invention is used for a write-once nonvolatile memory, the writing speed per cell is about 100 ns (see the examples). . According to the resistance variable element of the present invention, it is possible to realize a write-once nonvolatile memory device in which the writing speed is dramatically improved.

  The present inventor has also found that even a resistance variable element manufactured by the same method can be used for reversible memory or irreversible memory by changing an applied electric pulse. (See Examples). By utilizing this property, both functions can be realized by an apparatus manufactured by the same process, and manufacturing time and manufacturing cost can be reduced.

  Therefore, a variable resistance element according to the present invention includes a first electrode, a second electrode, and a variable resistance film formed between the first electrode and the second electrode, The resistance change film contains an oxide containing a transition metal, and a first electric pulse, which is an electric pulse of a first level or higher, is applied to the resistance change film via the first electrode and the second electrode. In this case, the variable resistance element for irreversible storage performs irreversible storage of data corresponding to the first electrical pulse by irreversibly changing the electrical resistance of the resistance change film.

  In such a configuration, it is possible to use, for irreversible memory, a resistance variable element that uses a transition metal oxide, which has been used only for reversible memory, as a resistance variable film. Therefore, a write-once nonvolatile memory device having a novel configuration can be provided. In addition, a write-once nonvolatile memory device with dramatically improved write speed can be realized.

  In the resistance variable element, the oxide may be an oxide containing at least one transition metal selected from the group consisting of iron, copper, nickel, titanium, vanadium, chromium, and manganese.

  In such a configuration, a specific oxide can be used as the material of the resistance change film.

  In the resistance variable element, the first electrode and the second electrode are made of at least one material selected from the group consisting of platinum, ruthenium, iridium, silver, gold, ruthenium oxide, and iridium oxide. May be included.

  In such a configuration, a specific metal or metal oxide can be used as the electrode material.

  The resistance change memory device according to the present invention further includes a plurality of the resistance change elements, and further applies the first electric pulse to the resistance change film via the first electrode and the second electrode. This is a write-once variable resistance storage device including a writing device that causes the variable resistance element to perform irreversible storage of data corresponding to the first electric pulse.

  In such a configuration, a write-once resistance change type storage device can be configured using a resistance change type element that has been used only for reversible storage.

  In the resistance variable element, the second electric pulse or the third electric pulse which is smaller than the first level electric pulse and is different from each other may be applied to the first electrode and the second electric pulse. When applied to the variable resistance film via an electrode, the electrical resistance of the variable resistance film changes reversibly, thereby reversibly storing data corresponding to the second electric pulse or the third electric pulse. You may go.

  In such a configuration, the same resistance variable element can be used for both irreversible storage and reversible storage. For this reason, the write-once storage device and the rewritable storage device can be manufactured in substantially one process. Therefore, a nonvolatile memory device having both irreversible memory and reversible memory functions can be manufactured in a short time and at low cost.

  In the resistance variable element, the fourth electric pulse, which is an electric pulse smaller than the first level, is applied until the electric resistance between the first electrode and the second electrode does not change. Forming treatment applied to the variable resistance film via the second electrode and the second electrode may be performed.

  In such a configuration, the electrical resistance of the variable resistance film can be adjusted to an appropriate level before use by forming processing.

  The resistance change type storage device of the present invention is a resistance change type storage device comprising a plurality of the resistance change type elements on the same substrate, wherein the resistance change type elements belonging to the first group store the irreversible memory. The resistance variable element belonging to the second group may perform the reversible storage. Alternatively, the resistance change type storage device includes a writing device, and the writing device causes the resistance change type element belonging to the first group to perform the irreversible storage, and the resistance change belonging to the second group. The mold element may perform the reversible storage. Alternatively, the resistance change storage device includes: a first writing device that causes the resistance change element belonging to the first group to perform the irreversible storage; and a resistance change element that belongs to the second group. A second writing device that performs reversible storage may be provided.

  With this configuration, the write-once storage device and the rewritable storage device can be manufactured in substantially one process. Therefore, it is possible to manufacture a nonvolatile storage device having both irreversible storage and reversible storage functions in a short time and at low cost.

  The data writing method to the resistance variable element according to the present invention includes a first electrode, a second electrode, a resistance change film formed between the first electrode and the second electrode, And the resistance change film includes an oxide containing a transition metal, wherein the resistance change film is a data writing method to the resistance change element, wherein the first electric pulse that is an electric pulse of a first level or higher is applied to the first electric pulse. The electrical resistance of the variable resistance film is irreversibly changed by applying to the variable resistance film via the second electrode and the second electrode, thereby irreversibly storing data corresponding to the first electrical pulse. It is what makes you do.

  In such a configuration, it is possible to use, for irreversible memory, a resistance variable element that uses a transition metal oxide, which has been used only for reversible memory, as a resistance variable film. Therefore, a write-once nonvolatile memory device having a novel configuration can be provided. In addition, a write-once nonvolatile memory device with dramatically improved write speed can be realized.

  The data writing method to the nonvolatile memory element of the present invention includes a first electrode, a second electrode, a resistance change film formed between the first electrode and the second electrode, And the resistance change film includes an oxide containing a transition metal, wherein the resistance change film is a data writing method to the resistance change element, wherein the first electric pulse that is an electric pulse of a first level or higher is applied to the first electric pulse. The electrical resistance of the variable resistance film is irreversibly changed by applying to the variable resistance film via the second electrode and the second electrode, thereby irreversibly storing data corresponding to the first electrical pulse. And applying a second electric pulse or a third electric pulse that is smaller than the first level and different from each other to the resistance change film via the first electrode and the second electrode. Of the variable resistance film Reversibly changing the air resistance is thereby intended to perform a reversible storage of data corresponding to the second electrical pulse or the third electrical pulses.

  In such a configuration, the resistance variable element manufactured by substantially one process can be used for both reversible memory and irreversible memory. Therefore, both the functions of irreversible storage and reversible storage can be realized by a nonvolatile storage device manufactured inexpensively in a short time.

  The data writing method to the resistance variable element according to the present invention includes a first electrode, a second electrode, and a resistance change film formed between the first electrode and the second electrode. The variable resistance film includes an oxide containing a transition metal, and is a data writing method to a plurality of variable resistance elements formed on the same substrate, the variable resistance element belonging to the first group Applies irreversible electrical resistance of the resistance change film by applying a first electrical pulse, which is an electrical pulse of a first level or higher, to the resistance change film via the first electrode and the second electrode. Thus, irreversible storage of data corresponding to the first electric pulse is performed, and the resistance variable element belonging to the second group has an electric pulse smaller than the first level. Different second electrical pulses or A third electric pulse is applied to the variable resistance film through the first electrode and the second electrode, thereby reversibly changing the electric resistance of the variable resistance film, and thereby the second electric pulse. Alternatively, irreversible storage of data corresponding to the third electric pulse is performed.

  In such a configuration, the resistance variable element manufactured by substantially one process can be used for both reversible memory and irreversible memory. Therefore, both the functions of irreversible storage and reversible storage can be realized by a nonvolatile storage device manufactured inexpensively in a short time.

  In the above-described data writing method to the resistance variable element, the oxide includes an oxide containing at least one transition metal selected from the group consisting of iron, copper, nickel, titanium, vanadium, chromium, and manganese. It may be.

  In such a configuration, a specific oxide can be used as the material of the resistance change film.

  In the data writing method to the resistance variable element, the first electrode and the second electrode are at least selected from the group consisting of platinum, ruthenium, iridium, silver, gold, ruthenium oxide, and iridium oxide. One or more materials may be included.

  In such a configuration, a specific metal or metal oxide can be used as the electrode material.

  The present invention has the above-described configuration and has the following effects. That is, a write-once nonvolatile memory device capable of high-speed recording can be provided. In addition, a write-once nonvolatile memory device having a novel structure can be provided. Furthermore, a device capable of performing both a write-once type memory and a rewritable type memory can be manufactured at a low cost in a short time by a simple process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
[Configuration of resistance variable element]
FIG. 1 is a conceptual diagram showing an example of the configuration of the resistance variable element according to Embodiment 1 of the present invention. Hereinafter, the resistance variable element of this embodiment will be described with reference to FIG.

As shown in FIG. 1, the variable resistance element 10 according to the present embodiment has a structure in which a lower electrode 12, a resistance change film 13 (resistance change layer), and an upper electrode 14 are sequentially stacked on a substrate 11. It has. For example, a silicon substrate is used as the substrate 11. For the lower electrode 12 and the upper electrode 14, for example, Pt (platinum), Ru (ruthenium), Ir (iridium), Ag (silver), Au (gold), RuO ₂ (ruthenium oxide), IrO ₂ (iridium oxide) Etc. are preferably used. When the substrate 11 is heated when the resistance change film 13 is formed, it is preferable that the material of the lower electrode 12 be stable at the heating temperature. For the resistance change film 13, for example, an oxide containing at least a transition metal is preferably used. Examples of the oxide containing a transition metal include Fe (iron), Cu (copper), Ni (nickel), Ti (titanium), V (vanadium), Cr (chromium), and Mn (manganese). And an oxide (PrCaMnO) containing plural kinds of metals. The lower electrode 12, the resistance change film 13, and the upper electrode 14 can be formed by a known film formation technique such as sputtering. The size of the electrode and the resistance change film can be appropriately set according to the degree of integration of elements.
[Writing and reading of variable resistance element]
When the resistance variable element 10 is used, a power source 15 is electrically connected to the upper electrode 14 and the lower electrode 12. Since the electric resistances of the upper electrode 14 and the lower electrode 12 are substantially zero, the electric resistance between the upper electrode 14 and the lower electrode 12 is substantially equal to the electric resistance of the resistance change film 13. Hereinafter, the electrical resistance between the upper electrode 14 and the lower electrode 12 (the electrical resistance of the resistance change film 13) is defined as the resistance value R of the resistance change element 10. When an electric pulse is applied between the upper electrode 14 and the lower electrode 12 by the power supply 15, R changes. Hereinafter, the voltage of the applied electric pulse is V. The width of the electric pulse can be set as appropriate, but may be a value between 100 ns and 1 ms, for example.

  Let Rini be the value of R in a state (initial state) in which an electrical pulse enough to change R has not been applied after manufacture. When an electric pulse (first electric pulse) having a voltage Vw0 whose absolute value exceeds a predetermined value Vth1 (first level) is applied to the resistance variable element 10 in the initial state, R becomes Rlow0 or lower. Once R becomes equal to or lower than Rlow0, the value of R does not substantially change even if an electric pulse having an absolute voltage value exceeding Vth1 is applied thereafter. That is, when an electric pulse of the voltage Vw0 is applied, the resistance value R of the resistance variable element 10 changes irreversibly from Rini to Rlow0. By setting Rini to the high resistance state (hereinafter, the resistance value R in this state is Rhigh0), Rlow0 to the low resistance state, and assigning 1 and 0 to each state, 1-bit data is assigned to the resistance variable element 10. (Binary data here) can be stored irreversibly. Rhigh0 may correspond to 0 and Rlow0 may correspond to 1. In the present invention, irreversible storage means so-called write-once storage, and data once written cannot be rewritten thereafter. The written data is read by applying the voltage Vr between the upper electrode 14 and the lower electrode 12 and detecting the flowing current. By making the absolute value of Vr sufficiently lower than Vth1, it is possible to prevent the resistance value R from changing due to the read operation. According to such a configuration, a resistance variable element using an oxide as a resistance variable film can be used as a resistance variable element for irreversible memory.

  When an electric pulse (fourth electric pulse) of voltage Vf is applied a plurality of times, R may gradually change and converge to a constant value. Hereinafter, such processing is referred to as forming. After forming, by applying an electric pulse (second electric pulse) of the voltage Vw1 such that the absolute value of the voltage does not exceed Vth2 (second level: Vth2 <Vth1), R becomes Rlow1. Further, by applying an electric pulse (third electric pulse) having a voltage Vw2 whose absolute value does not exceed Vth2, R becomes Rhigh1 (> Rlow1). The second electric pulse and the third electric pulse are different from each other. However, either the voltage or the pulse width may be equal. Further, Vw1 and Vw2 may have the same polarity or different polarities. In order not to cause an unintended irreversible change, the difference between Vth2 and Vth1 is preferably 1 V or more. By setting Rhigh1 to a high resistance state and Rlow1 to a low resistance state and assigning 1 and 0 to each state, 1-bit data can be stored reversibly in the resistance variable element 10. Rhigh1 may correspond to 0 and Rlow1 may correspond to 1. In the present invention, reversible storage refers to so-called rewritable storage, and data can be written again to an element in which data has been written once. The written data is read by applying the voltage Vr between the upper electrode 14 and the lower electrode 12 and detecting the flowing current. By making the absolute value of Vr sufficiently lower than Vth2, it is possible to prevent the resistance value R from changing due to the read operation. According to such a configuration, the resistance variable element for irreversible memory can be used as a resistance variable element for reversible memory.

  In the above description, irreversible memory is stored in the resistance variable element before forming. Depending on the selection of the material and the like, an irreversible change may occur even when an electric pulse of voltage Vw0 is applied to the resistance variable element after forming. In such a case, all of the plurality of variable resistance elements formed may be formed and a part may be used for irreversible storage and a part for reversible storage. Further, when the resistance value of the resistance variable element before forming is low, the resistance value may be increased by forming to form a write-once or rewritable resistance variable memory device.

Depending on the material used for the resistance change film, the film forming method, etc., forming may not be necessary. In such a case, the variable resistance element that has not been formed can be used for irreversible storage as well as for reversible storage.
[Configuration of Resistance Change Memory Device]
FIG. 2 is a plan view showing an example of the configuration of the resistance variable memory apparatus according to the first embodiment of the present invention. Hereinafter, the resistance change type storage device of this embodiment will be described with reference to FIG.

  As shown in FIG. 2, the resistance change storage device 100 according to the present embodiment includes a control device 120, a first column decoder 121, a first row decoder 123, a write-once memory cell array 125 on a substrate 111. A second column decoder 131, a second row decoder 133, and a rewritable memory cell array 135 are formed. Although not shown in FIG. 2, the control device 120 includes a power supply 15 and is configured to be able to apply electric pulses having a plurality of different voltages and widths.

  The write-once memory cell array 125 includes a plurality of memory cells arranged in a matrix. Each memory cell includes a resistance variable element 10. The configuration of the resistance variable element 10 is the same as that shown in FIG. As the write-once memory cell array 125, for example, a known 1T1R type memory cell array (a configuration in which one memory cell includes one transistor and one resistance change element) can be used. Each column of memory cells corresponds to the first bit line 122. Each row of memory cells corresponds to the first word line 124.

The rewritable memory cell array 135 includes a plurality of memory cells arranged in a matrix. Each memory cell includes a resistance variable element 10. The configuration of the resistance variable element 10 is the same as that shown in FIG. As the rewritable memory cell array 135, for example, a known 1T1R type memory cell array (a structure in which one memory cell includes one transistor and one resistance change element) can be used. Each column of memory cells corresponds to the first bit line 122. Each row of memory cells corresponds to the first word line 124. The resistance change element 10 of the rewritable memory cell array 135 is subjected to the forming process described above during manufacturing.
[Writing and reading of resistance change type memory device]
Hereinafter, writing and reading operations of the resistance change memory device 100 will be described. In the following description, it is assumed that 1 is assigned to Rhigh0 and Rhigh1, and 0 is assigned to Rlow0 and Rlow0. However, the correspondence between the resistance state and the written data is not limited to such a mode.

  First, the write operation will be described. When the data received from the system (not shown) is to be stored irreversibly, the control device 120 writes the received data into the write-once memory cell array 125. The control device 120 controls the first column decoder 121 based on the address of the memory cell to be written to select a specific first bit line 122. Further, the control device 120 controls the first row decoder 123 based on the address of the memory cell to be written to select a specific first word line 124. The control device 120 applies an electric pulse to the resistance variable element 10 of the address via the selected first bit line 122 and first word line 124. When the value to be written is 0, the voltage of the electric pulse is Vw0, and when the value to be written is 1, the voltage of the electric pulse is 0 (no electric pulse is applied). The resistance value R of the resistance variable element 10 to which the electric pulse of the voltage Vw0 is applied is Rlow0. The resistance value R of the resistance variable element 10 to which no electric pulse is applied remains Rhigh0 and does not change. With this operation, irreversible writing is performed on the write-once memory cell array 125.

  The resistance variable element 10 to which no electric pulse is applied is still in a state in which the resistance value changes when the electric pulse is applied. On the other hand, the resistance value of the other variable resistance element 10 changes to Rlow0. As described above, the resistance value once changed to Rlow0 does not change even when an electric pulse is applied again. Even if the writing is attempted again, the memory cells whose values are already 0 remain as they are, and some of the memory cells whose values are 1 are rewritten to 0. As described above, the value of the memory cell can be rewritten only in one direction from 1 to 0. As a result, even if writing is performed again, the data held in the memory cell does not substantially make sense. With this configuration, the resistance change storage device 100 functions as a write-once storage device.

  When the data received from the system (not shown) is to be stored reversibly, the control device 120 writes the received data into the rewritable memory cell array 135. The control device 120 controls the second column decoder 131 based on the address of the memory cell to be written to select a specific second bit line 132. Further, the control device 120 controls the second row decoder 133 based on the address of the memory cell to be written to select a specific second word line 134. The control device 120 applies an electric pulse to the resistance variable element 10 of the address via the selected second bit line 132 and second word line 134. When the value to be written is 0, the voltage of the electric pulse is Vw1, and when the value to be written is 1, the voltage of the electric pulse is Vw2. When the electric pulse of the voltage Vw1 is applied, the resistance value R of the resistance variable element 10 corresponding to the address is Rlow1. When the electric pulse of the voltage Vw2 is applied, the resistance value R of the resistance variable element 10 corresponding to the address is Rhigh1. Reversible writing is performed by applying electrical pulses of voltage Vw1 and voltage Vw2. With this configuration, the resistance change storage device 100 functions as a rewritable storage device.

Next, the reading operation will be described. The controller 120 receives the address of the memory cell to be read from the system (not shown). Based on the received address, the control device 120 determines whether the address corresponds to a memory cell of the write-once memory cell array 125 or a memory cell of the rewritable memory cell array 135. Based on the determination result, a predetermined bit line and word line are selected by the same method as at the time of writing. The control device 120 transmits the resistance variable element 10 of the address via the selected first bit line 122 and the first word line 124 or via the second bit line 132 and the second word line 134. A voltage Vr is applied to. Based on the magnitude of the current flowing through the resistance variable element 10 at the address, the value written in the memory cell is read out. The voltage Vr is lower than any of Vw0, Vw1, and Vw2, and the resistance value R does not change by the read operation.
[Main features and effects]
According to the resistance variable element and the data writing method of this embodiment, when an electric pulse having a voltage Vw0 whose absolute value exceeds Vth1 (first level) is applied, the resistance value R changes irreversibly to Rlow0. The characteristic (first characteristic) of the resistance variable element is used. By utilizing the first characteristic, a resistance variable element that has been used only in a conventional rewritable memory device can be used as a write-once memory element.

  Further, in the resistance variable element and the data writing method of the present embodiment, when an electric pulse having a voltage Vw1 and a voltage Vw2 whose absolute values are smaller than Vth1 (first level) is applied, the resistance value R becomes Rlow1 and Rhigh1. The characteristic (second characteristic) of the variable resistance element that reversibly changes between the two is utilized. By combining the first characteristic and the second characteristic, the resistance change type storage device that has been conventionally used as a rewritable type storage device can be used as a rewritable type or a write-once type.

  In the resistance change storage device of this embodiment, a plurality of resistance change elements are formed on the same substrate, and then the resistance change elements are divided into two groups. Irreversible storage is performed for one group (write-once memory cell array), and reversible storage is performed for the other group (rewritable memory cell array). When one device is manufactured by combining a conventional irreversible storage device using an antifuse memory and a conventional resistance change storage device that performs reversible storage, both devices are manufactured in separate processes. This requires a long manufacturing time and high cost. In the resistance change memory device of this embodiment, the resistance change element manufactured by the same process can be used for both a write-once memory device and a rewritable memory device. An apparatus having both functions is useful as a rewritable storage device in which information for preventing unauthorized copying is provided in a write-once portion, for example. According to this configuration, the write-once storage device and the rewritable storage device can be manufactured in substantially one process. Therefore, a nonvolatile memory device having both irreversible memory and reversible memory functions can be manufactured in a short time and at low cost.

The resistance change type storage device of the present embodiment includes two types of writing devices. The first writing device performs irreversible writing to the write-once memory cell array (first group), and the second writing device is reversible to the rewritable memory cell array (second group). Write. In the description of FIG. 2, the first writing device and the second writing device are composed of a single control device, two types of column decoders, and two types of row decoders, but the control devices are also separated. Thus, the two writing devices may be configured as completely independent devices. By providing two types of writing devices, both irreversible memory and reversible memory functions can be realized within a single resistance change memory device.
[Modification]
In the above description, the irreversible storage and the reversible storage are selectively executed by changing the voltage (absolute value) of the electric pulse. However, the width of the electric pulse may be changed. Furthermore, both the voltage and the width of the electric pulse may be changed. By changing the level of energy input by the electric pulse, irreversible storage and reversible storage can be selectively performed. That is, the “level” of the electric pulse may be the level of the absolute value of the voltage, the level of the pulse width, or a combination of both the absolute value of the voltage and the pulse width (for example, the product of the voltage and the pulse width). )

  In the above description, the write-once memory cell array and the rewritable memory cell array are described as being formed on the same substrate (chip), but both may be formed on the same wafer and then separated. Even in such a configuration, if the separated memory cell array is incorporated in the same device, a nonvolatile memory device having both irreversible memory and reversible memory functions can be manufactured in a short time and at low cost.

  It is not always necessary to perform both irreversible storage and reversible storage, and it may be configured as a resistance change element or resistance change storage device that performs only irreversible storage. By providing a plurality of variable resistance elements using oxides as variable resistance films, a novel write-once nonvolatile memory device can be realized.

  The material of the resistance change film is not necessarily limited to the metal oxide, but may be other materials. The resistance change film may be a phase change film. A nonvolatile memory element having a resistance change film changes its resistance value when a stimulus such as heat or electricity is applied to the resistance change film. Data is stored in association with the change in resistance value. In the conventional nonvolatile memory element, the level of the stimulus (second stimulus) is set so that the resistance value reversibly changes. It can be easily analogized that the resistance value changes irreversibly when a stimulus of higher level (first stimulus) than before is applied. Therefore, it is expected that other nonvolatile memory elements such as phase change memory elements (PRAM) can selectively generate irreversible and reversible changes by varying the level of stimulation applied. . For example, in the case of a phase change memory element, increasing the heating level (first heating) causes an irreversible change in the electrical resistance of the resistance change film, and lowering the heating level (second heating, third heating). It is expected that the electrical resistance of the resistance change film can be reversibly changed by heating (a). That is, the present invention can be applied to other nonvolatile memory elements including a phase change type memory element and having a resistance change film. According to this configuration, the write-once storage device and the rewritable storage device can be manufactured in substantially one process. Therefore, a nonvolatile memory device having both irreversible memory and reversible memory functions can be manufactured in a short time and at low cost.

  In the present invention, a part of one memory cell array may be used for irreversible storage and the rest of the memory array may be used for reversible storage. FIG. 3 is a plan view showing a configuration of a resistance variable memory apparatus according to a modification of the present invention. As shown in FIG. 3, the resistance change type storage device 200 of this modification includes a control device 120, a column decoder 141, a bit line 142, a row decoder 143, a word line 144, and a memory cell array 145. ing. A part of the memory cell array 145 constitutes a write-once area 146 and the rest constitutes a rewritable area 147. The control device 120 performs irreversible writing on the write-once area 146 and reversible writing on the rewritable area 147. Even in such a configuration, the same effect as the resistance change storage device 100 can be obtained.

In the above description, it is configured as a binary memory. For example, by causing the resistance variable element 10 to take an intermediate resistance value between the high resistance state and the low resistance state, information of 1 bit or more per element can be stored. Also good. That is, a multi-value memory that can store three or more values may be configured.
(Example 1)
In this example, first, a lower electrode (thickness: 200 nm) made of Pt (platinum) was formed on a silicon substrate by sputtering using a Pt (platinum) target. On the lower electrode, a variable resistance film (thickness: about 100 nm) made of an oxide containing Fe (iron) as a transition metal was formed by sputtering using a Fe—O (iron oxide) target. The temperature of the substrate during sputtering was 300 ° C. Further, an upper electrode (thickness: 100 nm) made of Pt (platinum) was formed on the variable resistance film by sputtering using a Pt (platinum) target. The area of the portion where the upper electrode and the resistance change film are in contact, that is, the size of the electrode was approximately 1 μm × 1 μm to 5 μm × 5 μm.
By this method, a resistance variable element in which a lower electrode, a resistance change film, and an upper electrode were sequentially laminated on a silicon substrate was obtained.

  A read voltage is applied between the upper electrode and the lower electrode of the resistance variable element with the lower electrode as a reference (0 V) (the same applies hereinafter), and immediately after formation (initial state), between the upper electrode and the lower electrode. The resistance value (initial resistance value) of was measured. Note that the read voltage of the resistance value was +50 mV. (Hereinafter, the resistance value measurement method is the same for all examples). The obtained initial resistance value was 2.5 MΩ.

  Next, when an electric pulse (first electric pulse) of +5 V and 100 μs was applied to the resistance variable element, the resistance value changed to 50Ω. In this state, even if an electric pulse with an absolute value of 5 V or more (± 6 V, ± 7 V, etc.) and a pulse width of 100 μs is applied, the resistance value varies only within the measurement error range (± 10 Ω) and is approximately 50 Ω. It remained. Therefore, it was found that an irreversible change (change in resistance value) occurs in the resistance change film by applying an electrical pulse of +5 V and 100 μs. That is, in this embodiment, when the pulse width is 100 μs, Vth1 (first level) can be set to 5V.

  When a + 3V or + 4V electric pulse (pulse width 100 μs) is applied to the resistance variable element in the initial state obtained by the above method, the resistance value does not necessarily decrease to 50Ω, and the initial resistance value In some cases, it remained (2.5 MΩ). On the other hand, when an electric pulse of +5 V (pulse width 100 μs) was applied, the resistance value decreased to about 50Ω with a probability of 100%. Naturally, even when a read voltage (+50 mV, 100 ns) was applied, no change in resistance value was observed. From the above results, it was found that the resistance variable element obtained by the above-described method can be used for a write-once resistance variable memory device.

On the other hand, an electric pulse (fourth electric pulse) of +2 V, 100 μs was applied a plurality of times between the upper electrode and the lower electrode of the resistance variable element in the initial state obtained by the above method. As a result, the resistance value gradually decreased, and when the electric pulse was applied about 100 times, the resistance value was stabilized at a substantially constant value (100 kΩ) (forming). When an electric pulse (second electric pulse) of −2 V and 100 ns was applied in this state, the resistance value was 10 kΩ. Further, when an electric pulse (third electric pulse) of +2 V and 100 ns was applied, the resistance value returned to 100 kΩ. Thereafter, the same change was repeated. That is, it was found that by applying an electric pulse of ± 2 V and 100 ns, the resistance value repeatedly reversibly changes between a high resistance state (100 kΩ) and a low resistance state (10 kΩ). In order to prevent an irreversible change, it was found that the absolute value of the voltage is preferably 3 V or less when the pulse width is 100 ns. That is, when the pulse width is 100 ns, Vth2 (second level) can be 3V. From the above results, it was found that the resistance variable element formed by the above-described method and formed can be used for a rewritable resistance variable memory device.
(Example 2)
In this example, first, a lower electrode (thickness: 200 nm) made of Pt (platinum) was formed on a silicon substrate by sputtering using a Pt (platinum) target. A resistance change film (thickness) made of an oxide containing Cu (copper) as a transition metal by sputtering using a Cu (copper) target on the lower electrode in an atmosphere in which oxygen gas is introduced into Ar gas. About 50 nm). The temperature of the substrate during sputtering was 200 ° C. Further, an upper electrode (thickness: 100 nm) made of Pt (platinum) was formed on the variable resistance film by sputtering using a Pt (platinum) target. The area of the portion where the upper electrode and the resistance change film are in contact, that is, the size of the electrode was approximately 1 μm × 1 μm to 5 μm × 5 μm. By this method, a resistance variable element in which a lower electrode, a resistance change film, and an upper electrode were sequentially laminated on a silicon substrate was obtained.

  The resistance value (initial resistance value) between the upper electrode and the lower electrode immediately after formation (initial state) was measured. The obtained initial resistance value was 5 MΩ.

  Next, when an electric pulse (first electric pulse) of +4 V and 1 ms was applied to the resistance variable element, the resistance value changed to 30Ω. In this state, even if an electrical pulse with a pulse width of 1 ms is applied with a voltage of 5 V or more (± 6 V, ± 7 V, etc.), the resistance value will only fluctuate within the measurement error range (± 10 Ω), approximately 30 Ω. It remained. Therefore, it was found that an irreversible change (change in resistance value) occurs in the resistance change film by applying an electric pulse of +4 V and 100 μs. That is, in this embodiment, when the pulse width is 100 μs, Vth1 (first level) can be set to 4V.

  When a + 2V or + 3V electric pulse (pulse width 100 μs) is applied to the resistance variable element in the initial state obtained by the above method, the resistance value does not necessarily decrease to 30Ω, and the initial resistance value In some cases, it remained (2.5 MΩ). On the other hand, when an electric pulse of +4 V (pulse width 100 μs) was applied, the resistance value decreased to about 30Ω with a probability of 100%. Naturally, even when a read voltage (+50 mV, 100 ns) was applied, no change in resistance value was observed. From the above results, it was found that the resistance variable element obtained by the above-described method can be used for a write-once resistance variable memory device.

On the other hand, an electric pulse (fourth electric pulse) of +2 V, 100 μs was applied a plurality of times between the upper electrode and the lower electrode of the resistance variable element in the initial state obtained by the above method. As a result, the resistance value gradually decreased, and when the electric pulse was applied about 50 times, the resistance value was stabilized at a substantially constant value (10 kΩ) (forming). In this state, when an electric pulse (second electric pulse) of +2.5 V and 100 ns was applied, the resistance value was 100 kΩ. Further, when an electric pulse (third electric pulse) of +1.5 V and 1 μs was applied, the resistance value was 10 kΩ. Thereafter, the same change was repeated. That is, by applying an electrical pulse of +2.5 V, 100 ns and an electrical pulse of +1.5 V, 1 μs, the resistance value reversibly changes between a high resistance state (100 kΩ) and a low resistance state (10 kΩ). It turns out that it repeats. In order to prevent an irreversible change, the absolute value of the voltage is 3 V or less when the pulse width is 100 ns, and the absolute value of the voltage is 2 V or less when the pulse width is 1 μs. It turned out to be preferable. That is, when the pulse width is 100 ns, Vth2 (second level) can be 3V. When the pulse width is 1 μs, Vth2 (second level) can be 2V. From the above results, it was found that the resistance variable element formed by the above-described method and formed can be used for a rewritable resistance variable memory device.
(Example 3)
In this example, first, a lower electrode (thickness: 200 nm) made of Pt (platinum) was formed on a silicon substrate by sputtering using a Pt (platinum) target. In an atmosphere in which oxygen gas is introduced into Ar gas, a resistance change film (thickness) made of an oxide containing Ni (nickel) as a transition metal is formed on the lower electrode by sputtering using a Ni (nickel) target. About 30 nm). The temperature of the substrate during sputtering was 300 ° C. Further, an upper electrode (thickness: 100 nm) made of Pt (platinum) was formed on the variable resistance film by sputtering using a Pt (platinum) target. The area of the portion where the upper electrode and the resistance change film are in contact, that is, the size of the electrode was approximately 1 μm × 1 μm to 5 μm × 5 μm. By this method, a resistance variable element in which a lower electrode, a resistance change film, and an upper electrode were sequentially laminated on a silicon substrate was obtained.

  The resistance value (initial resistance value) between the upper electrode and the lower electrode immediately after formation (initial state) was measured. The obtained initial resistance value was 5 MΩ.

  Next, when an electric pulse (first electric pulse) of +5 V and 100 μs was applied to the resistance variable element, the resistance value changed to 50Ω. In this state, even if an electric pulse with an absolute value of 5 V or more (± 6 V, ± 7 V, etc.) and a pulse width of 100 μs is applied, the resistance value varies only within the measurement error range (± 10 Ω) and is approximately 50 Ω. It remained. Therefore, it was found that an irreversible change (change in resistance value) occurs in the resistance change film by applying an electrical pulse of +5 V and 100 μs. That is, in this embodiment, when the pulse width is 100 μs, Vth1 (first level) can be set to 5V.

  When a + 3V or + 4V electric pulse (pulse width 100 μs) is applied to the resistance variable element in the initial state obtained by the above method, the resistance value does not necessarily decrease to 50Ω, and the initial resistance value In some cases, it remained (2.5 MΩ). On the other hand, when an electric pulse of +5 V (pulse width 100 μs) was applied, the resistance value decreased to about 100Ω with a probability of 100%. Naturally, even when a read voltage (50 mV, pulse width 100 ns) was applied, no change in resistance value was observed. From the above results, it was found that the resistance variable element obtained by the above-described method can be used for a write-once resistance variable memory device.

On the other hand, a +2 V, 100 ms electric pulse (fourth electric pulse) was applied a plurality of times between the upper electrode and the lower electrode of the resistance variable element in the initial state obtained by the above method. As a result, the resistance value gradually decreased, and when the electric pulse was applied about 50 times, the resistance value was stabilized at a substantially constant value (10 kΩ) (forming). In this state, when an electric pulse (second electric pulse) of +3 V and 100 ns was applied, the resistance value was 100 kΩ. Further, when an electric pulse (third electric pulse) of +2 V and 1 μs was applied, the resistance value returned to 10 kΩ. Thereafter, the same change was repeated. That is, it was found that by applying +3 V, 100 ns electric pulse and +2 V, 1 μs electric pulse, the resistance value changed in a similar manner (reversible change in resistance value. In addition, an irreversible change was caused. In order to avoid this, it has been found that the absolute value of the voltage is preferably 4 V or less when the pulse width is 100 ns, and the absolute value of the voltage is preferably 3 V or less when the pulse width is 1 μs. That is, when the pulse width is 100 ns, Vth2 (second level) can be 4 V. When the pulse width is 1 μs, Vth2 (second level) can be 3 V. From the results, it was found that the variable resistance element formed by the above-described method and formed can be used for a rewritable variable resistance memory device.
Example 4
In this example, first, a lower electrode (thickness: 200 nm) made of Pt (platinum) was formed on a silicon substrate by sputtering using a Pt (platinum) target. On the lower electrode, a variable resistance film (thickness: about 100 nm) made of an oxide containing Fe (iron) as a transition metal was formed by sputtering using a Fe—O (iron oxide) target. The temperature of the substrate during sputtering was 300 ° C. Further, an upper electrode (thickness: 200 nm) made of Ag (silver) was formed on the resistance change film by sputtering using an Ag (silver) target. The area of the portion where the upper electrode and the resistance change film are in contact, that is, the size of the electrode was approximately 1 μm × 1 μm to 5 μm × 5 μm. By this method, a resistance variable element in which a lower electrode, a resistance change film, and an upper electrode were sequentially laminated on a silicon substrate was obtained.

  A read voltage is applied between the upper electrode and the lower electrode of the resistance variable element with the lower electrode as a reference (0 V) (the same applies hereinafter), and immediately after formation (initial state), between the upper electrode and the lower electrode. The resistance value (initial resistance value) of was measured. Note that the read voltage of the resistance value was +50 mV. (Hereinafter, the resistance value measurement method is the same for all examples). The obtained initial resistance value was 3 MΩ.

  Next, when an electric pulse (first electric pulse) of +7 V and 100 ns was applied to the resistance variable element, the resistance value changed to 50Ω. In this state, even if an electrical pulse with a pulse width of 100 ns is applied at a voltage of 5 V or more (± 8 V, ± 9 V, etc.), the resistance value varies only within the measurement error range (± 10 Ω), and is approximately 50 Ω. It remained. Therefore, it was found that an irreversible change (change in resistance value) occurs in the resistance change film by applying an electric pulse of +7 V and 100 ns. That is, in this embodiment, when the pulse width is 100 ns, Vth1 (first level) can be set to 7V.

  When an electric pulse (pulse width 100 ns) of +5 V or +6 V is applied to the resistance variable element in the initial state obtained by the above method, the resistance value does not necessarily decrease to 50Ω, and the initial resistance value In some cases, the change was small from (3 MΩ). On the other hand, when an electric pulse of +7 V (pulse width 100 ns) was applied, the resistance value decreased to about 50Ω with a probability of 100%. Naturally, even when a read voltage (+50 mV, 100 ns) was applied, no change in resistance value was observed. From the above results, it was found that the resistance variable element obtained by the above-described method can be used for a write-once resistance variable memory device.

On the other hand, an electric pulse (fourth electric pulse) of +1.5 V and 100 μs was applied a plurality of times between the upper electrode and the lower electrode of the resistance variable element in the initial state obtained by the above method. As a result, the resistance value gradually decreases. When an electric pulse is applied about 100 times, the resistance value becomes a substantially constant value (1 kΩ), and when an electric pulse of −1.5 V and 100 μs is further applied about 100 times, the resistance value becomes substantially constant ( 10 kΩ) (forming). In this state, when ± 2V, 100 ns electrical pulses (second electrical pulse) are alternately applied about 100 times, when a + 2V, 100 ns electrical pulse is applied, the resistance value becomes 1 kΩ, and further −2V, 100 ns. When the electric pulse (third electric pulse) was applied, the resistance value returned to 10 kΩ. Thereafter, the same change was repeated. That is, it was found that by applying an electric pulse of ± 2 V and 100 ns, the resistance value repeatedly reversibly changes between a high resistance state (10 kΩ) and a low resistance state (1 kΩ). In order to prevent an irreversible change, it was found that the absolute value of the voltage is preferably 3 V or less when the pulse width is 100 ns. That is, when the pulse width is 100 ns, Vth2 (second level) can be 3V. From the above results, it was found that the resistance variable element formed by the above-described method and formed can be used for a rewritable resistance variable memory device.
(Example 5)
Although detailed data is omitted, the same results as in Examples 1 to 4 were obtained even when PrCaMnO was used as the material of the resistance change film.

  The nonvolatile memory device according to the present invention is useful as a write-once nonvolatile memory device having a novel configuration.

It is a conceptual diagram which shows an example of a structure of the resistance variable element of 1st Embodiment of this invention. It is a top view which shows an example of a structure of the resistance change memory | storage device of 1st Embodiment of this invention. It is a top view which shows the structure of the resistance change memory | storage device of the modification of this invention Sakae.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Resistance change element 11 Substrate 12 Lower electrode 13 Resistance change film 14 Upper electrode 15 Power supply 100 Resistance change memory device 111 Substrate 120 Control device 121 First column decoder 122 First bit line 123 First row decoder 124 First word line 125 Write-once memory cell array 131 Second column decoder 132 Second bit line 133 Second row decoder 134 Second word line 135 Rewritable memory cell array 141 Column decoder 142 Bit line 143 Row decoder 144 Word line 145 Memory cell array 146 Write once area 147 Rewritable Region 200 resistance change memory device

Claims (14)

A first electrode;
A second electrode;
A variable resistance film formed between the first electrode and the second electrode;
The resistance change film contains an oxide containing a transition metal,
When a first electric pulse, which is an electric pulse of a first level or higher, is applied to the variable resistance film through the first electrode and the second electrode, the electric resistance of the variable resistance film changes irreversibly. To perform irreversible storage of data corresponding to the first electrical pulse,
A variable resistance element for irreversible memory.   2. The variable resistance element according to claim 1, wherein the oxide is an oxide containing at least one transition metal selected from the group consisting of iron, copper, nickel, titanium, vanadium, chromium, and manganese.   2. The resistor according to claim 1, wherein the first electrode and the second electrode include at least one material selected from the group consisting of platinum, ruthenium, iridium, silver, gold, ruthenium oxide, and iridium oxide. Variable element. A plurality of variable resistance elements according to claim 1,
Further, by applying the first electric pulse to the variable resistance film via the first electrode and the second electrode, the data corresponding to the first electric pulse is irreversibly applied to the variable resistance element. Equipped with a writing device for performing
A write-once variable resistance memory device. Further, a second electric pulse or a third electric pulse that is smaller than the first level electric pulse and is different from each other is applied to the resistance change film via the first electrode and the second electrode. When added, reversible storage of data corresponding to the second electric pulse or the third electric pulse is performed by reversibly changing the electric resistance of the variable resistance film.
The resistance variable element according to claim 1. A fourth electric pulse, which is an electric pulse smaller than the first level, is applied to the first electrode and the second electrode until the electric resistance between the first electrode and the second electrode does not change. Forming treatment applied to the resistance change film through
The resistance variable element according to claim 1. A variable resistance storage device comprising a plurality of variable resistance elements according to claim 5 on the same substrate,
The variable resistance element belonging to the first group performs the irreversible memory,
The variable resistance element belonging to the second group performs the reversible memory.
Resistance change type memory device. With a writing device,
The writing device causes the variable resistance element belonging to the first group to perform the irreversible storage, and causes the variable resistance element belonging to the second group to perform the reversible storage;
The resistance change storage device according to claim 7. A first writing device for causing the resistance variable element belonging to the first group to perform the irreversible storage;
A second writing device that causes the resistance variable element belonging to the second group to perform the reversible storage;
The resistance change storage device according to claim 7. A first electrode; a second electrode; and a resistance change film formed between the first electrode and the second electrode, the resistance change film including an oxide containing a transition metal A method of writing data to the resistance variable element,
An electrical resistance of the resistance change film is irreversibly changed by applying a first electrical pulse, which is an electrical pulse of a first level or higher, to the resistance change film via the first electrode and the second electrode. A method for writing data to the resistance variable element, wherein the data corresponding to the first electric pulse is irreversibly stored. A first electrode; a second electrode; and a resistance change film formed between the first electrode and the second electrode, the resistance change film including an oxide containing a transition metal A method of writing data to the resistance variable element,
An electrical resistance of the resistance change film is irreversibly changed by applying a first electrical pulse, which is an electrical pulse of a first level or higher, to the resistance change film via the first electrode and the second electrode. Thereby causing irreversible storage of data corresponding to the first electrical pulse,
A second electric pulse or a third electric pulse, which is smaller than the first level and different from each other, is applied to the variable resistance film through the first electrode and the second electrode, and the resistance change is performed. Reversibly changing the electrical resistance of the membrane, thereby causing reversible storage of data corresponding to the second or third electrical pulse,
A method for writing data to a resistance variable element. A first electrode; a second electrode; and a resistance change film formed between the first electrode and the second electrode, wherein the resistance change film contains an oxide containing a transition metal. A method of writing data to a plurality of resistance variable elements formed on the same substrate,
For a resistance variable element belonging to the first group, a first electric pulse, which is an electric pulse of a first level or higher, is applied to the variable resistance film via the first electrode and the second electrode. Irreversibly changes the electrical resistance of the resistance change film, thereby causing irreversible storage of data corresponding to the first electrical pulse,
For the resistance variable element belonging to the second group, an electric pulse smaller than the first level and different from the second electric pulse or the third electric pulse is applied to the first electrode and the second electrode. The resistance change film is reversibly changed by applying to the resistance change film through the first and second electric pulses, thereby irreversibly storing data corresponding to the second electric pulse or the third electric pulse. To do,
A method for writing data to a resistance variable element.   The resistance according to any one of claims 10 to 12, wherein the oxide is an oxide containing at least one transition metal selected from the group consisting of iron, copper, nickel, titanium, vanadium, chromium, and manganese. A method of writing data to the variable element.   The first electrode and the second electrode include at least one material selected from the group consisting of platinum, ruthenium, iridium, silver, gold, ruthenium oxide, and iridium oxide. A method of writing data to the resistance variable element according to claim 1.

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