JP2013197561A - Resistance change type memory element using aluminum oxide layer as resistance change layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that although a method of forming a part of a conductive path by adding a conductive material for forming-less constitution of a resistance change type memory is designed, there is a problem, associated with element stability such as a leak of a current, in the method since there is a place where a distance between a conductive additive material and an upper metal electrode or lower metal electrode layer is too short because of the addition of the conductive material.SOLUTION: There is provided a resistance change type memory element whose resistance change layer has oxygen deficiency and also has a structure comprising a charge storage layer formed of an aluminum oxide layer to which a conductive material is added, and an aluminum oxide layer arranged having the charge storage layer sandwiched above and below and having oxygen deficiency. With this constitution, the resistance change type memory element is provided which has higher stability, reliability, and durability by two effects of high suppression on a leak and high stability of a filament in spite of foaming-less and low-voltage configurations.

Description

The present invention relates to a resistance random access memory device (ReRAM).
More specifically, a conductive material is added to a pair of electrodes composed of a lower metal electrode layer and an upper metal electrode, and an aluminum oxide layer and an aluminum oxide layer sandwiched between the lower metal electrode layer and the upper metal electrode. The present invention relates to a resistance change type memory element having a resistance change layer composed of a charge storage layer.

The resistance change type memory element is attracting attention as a memory having both high-speed response of DRAM and non-volatility of flash memory as a next generation type memory element. Furthermore, the structure is also a relatively simple structure with a metal / insulator (resistance change layer, oxide layer) / metal three-layer structure. It is an element expected as a memory element.

Usually, a perovskite type ternary oxide and a binary transition metal oxide are used for the insulator. However, binary transition metal oxides are typically used because of compatibility issues with conventional silicon (Si) processes. In order to use this element as a memory, a high voltage called a forming process is applied before use to form a conductive path in the insulator (soft breakdown). Since the voltage required for the forming process is higher than the operating voltage range of the semiconductor element to be incorporated (5 V or more), there is a possibility that other elements may be destroyed during the forming process. It becomes a barrier.

As shown in FIG. 1, an operation process of this variable resistance element is as follows. First, a high voltage is applied under a current limit, and when a certain threshold value is reached, an ON process (sometimes referred to as a SET process) that transitions from a high resistance state to a low resistance state. Then, the current limit is removed, and an OFF process (sometimes referred to as a RESET process) in which a current is applied to make a transition from a low resistance state to a high resistance state. Usually, since the metal oxide which is an insulator is used for the resistance change layer, the forming voltage and the ON voltage tend to increase with the increase of the film thickness. For this reason, thinning is currently in progress.

However, by making the film thinner, dielectric breakdown (breakdown) is likely to occur in the insulating layer, causing a problem in reliability. Therefore, the problem is usually solved by reducing the ON / OFF voltage by concentrating the electric field by miniaturizing the element. However, it is known that in this miniaturization, depending on the OFF mechanism, damage due to a high current at the time of OFF also occurs, causing a problem in reliability.

In recent years, many attempts have been made to search for a metal oxide film functioning as a resistance change layer and an electrode metal suitable for the metal oxide film (Non-Patent Document 2), and a technique for improving switching characteristics by further laminating an insulating film. (Non-patent Document 3) and the like are performed. However, in any case, some limited metals such as platinum (Pt) are used for the electrodes, and there is a problem that a high voltage forming process is still required for the operation of the element. Recently, there is an example of trying to reduce the power consumption by forming one element by forming one of the electrode layers from semiconductor Si or the like, but in this method, one of the electrode materials is specified. In particular, there is a drawback that the degree of freedom is unavoidable in the circuit formation or manufacturing process combined with other elements.

  Further, in a conventional resistance change layer, a metal oxide layer containing oxygen deficiency or metal deficiency is generally used. This method requires a forming process in which an electric field is applied to form a conductive path in a metal oxide layer that is an insulator by electron injection into oxygen vacancies. At this time, the resistance change layer transitions from a high resistance state as an insulator to a low resistance state. The conductive path formed by this forming is called a filament for convenience because it behaves like a metal in a low resistance state. This process requires a voltage higher than the operating voltage, and it is necessary to form a conductive path rather than a current leak by stopping before the breakdown (breakdown) called soft breakdown. Therefore, there is a practical problem that it is necessary to put an appropriate limit current (compliance) in transition from the high resistance state to the low resistance state.

  As a similar structure, Song et al. Devised a method of stabilizing operation by inserting a metal aluminum layer into an aluminum oxide layer as an insulating layer in order to control the formation of a conductive path. (Non-Patent Document 1) However, in this method, since a layered structure of a metal and a metal oxide is created, there is a problem in that the effects of current leakage, interface roughness, interdiffusion, etc. cannot be eliminated in the manufacturing method. .

In recent years, attempts have been reported to stabilize resistance change by inserting another metal oxide layer such as alumina in a resistance change element using Ta and Hf. However, in this element, the oxygen amount of Ta or Hf and the metal electrode layer, or the transfer of oxygen ions between the Ta or Hf oxide layer and the inserted oxide layer are controlled, and charge injection / release is performed. This is a different philosophy from this mechanism for control purposes. (Non-Patent Documents 2 and 4)

  We also devised a method to add a conductive material such as transition metals, alloys, metal oxides and nitrides to the aluminum oxide layer used for the resistance change layer in order to stabilize the resistance change of the device. It is carried out. In this method, the base point (prefilament) of the conductive path is previously formed in the layer, so that both the element driving voltage and the power consumption are compared with the conventional metal layer-resistance change layer-metal layer (MIM) structure. There is a merit that it is possible to fabricate a resistance change type memory element that is low and has high stability, high reliability, and high durability. (Non-patent document 5) However, in this method, the position of the additive material in the aluminum oxide layer is random, and the distance between the additive material and the metal electrode is short, depending on the amount of additive material added. In some cases, the stability of the device may be hindered, such as when the voltage is low or when the insulation resistance is apparently low, causing current leakage.

JP 2009-141225 A

Jahoon Song et al., Applied Physics Express, 3 (2010), 091101 Z.Wei et al. IEDM (2008) “Highly Reliable TaOx ReRAM and Direct Evidence of Redox Reaction Mechanism” Natsuki Fukuda et al., 72nd JSAP academic lecture (2011) 31p-ZK12 M.-J. Lee et al., Nature Materials 10 (2010) pp.625 “A fast, high-endurance and scalable non-volatile memory device made from asymmetric Ta2O5-x / TaO2-xbilayer structures.” Yoshiyuki Harada et al., The 72nd Conference on Applied Physics (2011) 31p-ZK-5

In order to solve the above problems, a charge storage layer made of an aluminum oxide layer having an oxygen vacancy and to which a conductive material is added, and an aluminum having an oxygen vacancy arranged with the charge storage layer sandwiched therebetween An aluminum oxide layer type variable resistance layer characterized by having a structure composed of an oxide layer has been devised. This variable resistance layer has the above structure as a basic structure, and the number of charge storage layers N is a numerical value of 1 or more and 100 or less. As a result, the resistance change is applied to the resistance change type memory element having the MIM type element structure of the upper metal electrode / single composition metal oxide layer (resistance change layer) / lower metal electrode layer or the layer having the prefilament, which is a conventional technique. The distance between the electrode and additive material (in the charge storage layer) is more stable by inserting an oxygen-deficient aluminum oxide layer between the upper metal electrode and the lower metal electrode layer than the resistance change memory element as a layer. An object of the present invention is to manufacture a resistance-change memory element with improved stability, reliability, and durability with reduced current leakage.

  In order to solve the above-mentioned problem, a first aspect of the present invention is a resistance change type memory element comprising an upper metal electrode / aluminum oxide layer (resistance change layer) / lower metal electrode layer, wherein the resistance change layer has an oxygen deficiency. Two types of aluminum oxide layers: a charge storage layer made of an aluminum oxide layer having a conductive material added thereto, and an oxygen-deficient aluminum oxide layer disposed so as to sandwich the charge storage layer vertically There is provided a resistance change type memory element characterized by having a structure constituted by:

  According to a second aspect of the present invention, there is provided a resistance change type memory element characterized in that the composition range of the aluminum oxide layer AlOx having oxygen vacancies of the first aspect is x <1.5.

  According to a third aspect of the present invention, there is provided a resistance change type memory element characterized in that the number N of charge storage layers in the resistance change layer of the first invention is in the range of 1 to 100.

  According to a fourth aspect of the present invention, there is provided a resistance change type memory element, wherein the conductive material of the first aspect is a metal and a semiconductor, or an oxide or a nitride of a metal and a semiconductor.

Embodiments of the present invention will be described with reference to the drawings. FIG. 2 shows an example of a resistance change memory element. The basic structure of the element includes a substrate 6, a pair of electrodes including a lower metal electrode layer 3 and an upper metal electrode 1, and a resistance change layer 8 sandwiched between the lower metal electrode layer and the upper metal electrode. The variable resistance layer has a modulated composition 2 of a charge storage layer 2 composed of an aluminum oxide layer to which oxygen vacancies and a conductive element are added, and an oxygen vacancy type aluminum oxide layer 7 arranged on the upper and lower interfaces so as to sandwich it. It is composed of various types of aluminum oxide layers. The number N of charge storage layers is in the range of 1 to 100. The lower metal electrode layer, the resistance change layer, and the upper metal electrode are arranged on the substrate in the above order so as to be in contact with each other as a multilayer structure.

As shown in FIG. 1, the element has two or more states having different electric resistance values between the lower metal electrode layer and the upper metal electrode. By applying a driving voltage or current to the memory element, specifically between the lower metal electrode layer and the upper metal electrode, the element changes from one state selected from the two or more states to another state. And change. Specifically, when there are two states (high resistance state and low resistance state) having different electrical resistance values in the element, the memory element is changed from the high resistance state A to the low resistance state B by applying a driving voltage or current. Alternatively, the low resistance state B changes to the high resistance state A.

The substrate may be, for example, a Si substrate. In this case, the surface of the substrate that is in contact with the lower metal electrode layer may be oxidized. When the substrate is made of Si, the combination of the variable resistance element and the semiconductor element of the present invention becomes easy. Note that a processed wafer in which a transistor or the like is formed on the substrate can also be included in the substrate. Therefore, the substrate may be a resin such as glass or PET film, or a single crystal metal oxide substrate such as sapphire (Al ₂ O ₃ ) or magnesium oxide (MgO).

The lower metal electrode layer and the upper metal electrode may basically have conductivity, for example, gold (Au), platinum (Pt), ruthenium (Ru), iridium (Ir), aluminum (Al), tin Examples thereof include additive indium oxide (ITO), Si, and the like, alloys thereof, oxides, nitrides, and the like.

Further, an adhesion layer may be inserted between the lower metal electrode layer and the substrate for the purpose of improving the adhesion. In particular, when the substrate surface is oxidized, it is desirable to use a 3d transition metal such as titanium (Ti) or chromium (Cr). In addition, alloys, oxides, nitrides, fluorides, carbides, borides, and the like having a lattice constant and crystal structure close to each other between the substrate and the lower metal electrode layer can be used.
The adhesion layer is formed when the lower metal electrode layer is formed by a lithography method, depending on an electrode material such as Al, by a process using an alkaline solution used for development, or when a variable resistance layer or an upper metal electrode is formed. This is to prevent peeling by the plasma utilization process.

At this time, since the resistance change layer is provided with the effect of a metal such as oxygen deficiency or added aluminum, mixing of different elements into the oxygen deficient portion, oxidation of the added metal, and the like greatly affect the device characteristics. Therefore, it is desirable to form the film in an environment with a high degree of vacuum (1 × 10 ⁻⁴ Pa or more).

Further, when a lift-off process is used when forming the electrode layer, oxygen residue of 100 W in an oxygen atmosphere with a flow rate of 100 cm ³ / min is deposited before the deposition of resist residue and organic substance contamination remaining on the substrate surface. It is desirable to perform cleaning by generating plasma for 10 seconds to 10 minutes, preferably 30 seconds to 1 minute. This process is called ashing treatment. If this process is not used, residues and contamination remain between the upper metal electrode and the resistance change layer or between the lower metal electrode layer and the resistance change layer, and a good bond is not formed. Deterioration of device characteristics is caused.

  The variable resistance layer has an oxygen deficiency and is sandwiched between a charge storage layer made of an aluminum oxide layer (AlOx: M, x <1.5, where M is a conductive material) to which a conductive material is added and above and below. The aluminum oxide layer (AlOx, x <1.5) having oxygen vacancies arranged in (2) is composed of two types of aluminum oxide layers. The aluminum oxide layer is amorphous or polycrystalline.

The additive material M may basically have conductivity, for example, gold (Au), platinum (Pt), Ru ruthenium (Ru), iridium (Ir), aluminum (Al), titanium (Ti). Any metal such as cobalt (Co), nickel (Ni), or an alloy thereof, or a substance exhibiting electrical conductivity may be nitride. Alternatively, a conductive oxide such as titanium dioxide (TiO ₂ ), tin-added indium oxide (ITO), or zinc oxide (ZnO), or a semiconductor oxide may be used. Further, the same effect can be obtained by introducing nitrogen (N ₂ ) gas during film formation using the same alumina target and adding nitrogen into the film.

The charge storage layer made of an aluminum oxide layer to which a conductive material is added is composed of an alumina target (RF sputtering) and a metal (DC sputtering) target such as aluminum, or an alumina target (RF sputtering) and conductive oxidation such as TiO ₂ or ZnO. It is also possible to form a film by a simultaneous sputtering method using an object (RF sputtering) target, a simultaneous deposition method in which alumina and aluminum are deposited by resistance heating or electron beam, and a pulsed laser deposition method.

In order to form a resistance change layer exhibiting a memory effect and a charge storage layer that forms the memory effect in the co-evaporation method, the added material has conductivity and needs to be incorporated into the film. In order to form this structure, it is necessary to control the gas in the forming chamber. In the presence of residual gas, particularly oxygen gas, vapor deposition atoms may be oxidized by the plasma of this gas and added in a non-conductive state. Further, depending on the hydrogen gas, when the hydrogen is mixed into the film, the structure and composition of the film change, and the current-voltage characteristics change. Therefore, it is necessary to produce the resistance change layer in a high vacuum atmosphere. Considering the influence of residual gas in particular, it is necessary to form it at a degree of vacuum higher than the 10 ⁻⁴ Pa level, and it is desirable that the vacuum is higher than the 10 ⁻⁵ Pa level. In a film manufactured by such a manufacturing method, the conductive material added in the film becomes the base point of the conductive path when a voltage is applied, so that the filament (conductive film) is not formed without forming a high voltage. Sex path) can be formed.

  In the element of the present invention, the resistance change operates in the charge storage layer close to the upper metal electrode and the aluminum oxide layer between the electrodes. , Can reduce the current. This has an effect of reducing the power consumption compared with the conventional similar element.

  With this operation mechanism, in this element, the filament is not completely cut in the entire resistance change layer, and many of the filaments are present up to the uppermost charge storage layer (a state where charges are injected and stored). As a result, even when charges are extracted more than necessary in the transition to the OFF state, forming is not necessary unlike other elements, and the one with the lowest resistance value in a part of the filament in the uppermost layer is brought into a conducting state. Since the effect is reproduced just by returning, its stability is greatly increased.

  In the element according to the present invention, since the electric resistance value can be held until a driving voltage or current is applied, a bit is assigned to each of the above states in the element (for example, a high resistance state (OFF state) is “0”, By setting the low resistance state (ON state) to “1”), a nonvolatile resistance change memory (memory element or a memory array in which two or more memory elements are arranged) can be constructed. Further, in the element, such a change in state can be repeated at least twice, and a nonvolatile random access memory can be constructed. In addition, it is also possible to apply the element as a switching element by assigning ON or OFF to each of the above states.

  The electric resistance value of the element may be detected by applying a voltage (read voltage) that does not change the state of the element to the element and detecting the current value flowing through the element at that time. As the reading voltage, it is preferable to apply a pulsed voltage in order to further reduce the power consumption of the element.

In order to construct a resistance change type memory using the resistance change element of the present invention, the element of the present invention is a semiconductor element, for example, a diode or a metal / oxide / silicon (MOS) type transistor. What is necessary is just to combine with transistors, such as. This makes it possible to construct 1D1R (1 diode, 1 ReRAM) and 1T1R (1 transistor, 1 ReRAM), which are the minimum components of the memory element.

  The resistance change element of the present invention can be formed by a general thin film forming process and a fine processing process by applying a semiconductor manufacturing process. For example, RF and DC, ECR (electron cyclotron resonance), helicon, inductively coupled plasma (ICP), various sputtering methods such as facing target, PLD (pulse laser deposition), IBD (ion beam deposition) ), MBE (molecular beam epitaxial method) or the like, an ion plating method, or the like may be used. In addition to these PVD methods, a CVD (chemical vapor deposition) method, a MOCVD (organic metal CVD) method, a plating method, a sol-gel method, or the like may be used. However, the formation of the variable resistance layer using the DC / RF co-sputtering method is desirable because it is easy to control the addition amount and the composition while maintaining the conductivity of the conductive material in the film.

For microfabrication of each layer, physical or chemical etching methods such as ion milling, RIE (reactive ion etching), and FIB (focused ion beam) used in semiconductor processes can be used. In particular, since aluminum oxide and aluminum are used as semiconductor wiring and interlayer insulating films, the RIE method using chlorine (Cl) -based gas (for example, chlorine (Cl ₂ ), boron trichloride (BCl ₃ ), etc.). Semiconductor manufacturing technology by has already been established.

In addition, photolithographic methods for forming fine patterns, methods using ultraviolet light such as steppers and contact mask aligners, methods using electron beams such as electron beam (EB) lithography, and laser processing techniques are combined. It is possible to do. For planarization of the surface of each layer, for example, CMP (chemical mechanical polishing), cluster ion beam etching, or the like may be used.

  On the other hand, in the charge storage layer in the variable resistance layer according to the present invention, a conductive material such as metal, alloy, oxide, or nitride is introduced into the metal oxide film at the time of film formation. In particular, it becomes possible to introduce a metal target by argon plasma by DC sputtering, nitride by nitrogen plasma, and oxide by oxygen in alumina or oxygen plasma. By adding a conductive material to the aluminum oxide film of the insulating film, the overall apparent resistance can be reduced. In addition, since the charge is injected, accumulated, and held by the presence of the metal and the metal nitride in the layer, the metal oxide which is originally an insulator can be electrically conducted. Forming a filament (conductive path) at a low voltage similar to the ON voltage without having a forming process by inserting the charge storage layer to which such a metal and a conductive material are added into the change layer. Is possible. This can also be expected to have a significant effect on power consumption.

  In order to use the memory element as a resistance change type memory (ReRAM), a high voltage forming process for transitioning the resistance change layer from the insulating state to the conductive state is omitted. Yes, it is a great merit for practical use by saving power and eliminating restrictions on use.

In addition, a conductive layer may be used for the lower metal electrode layer, and it is not necessary to select the upper and lower electrode materials as in the conventional ReRAM element, particularly when the semiconductor is used as an electrode. It is easy to form a junction with a semiconductor element, a substrate, and a circuit, and there is an advantage that it can be directly manufactured on an existing semiconductor element.

In the aluminum oxide ReRAM and the co-deposited film, it is clear from the experimental results so far that there is no dependency on the electrode size, and the memory element operates with a filament type mechanism.
The co-evaporated layer (aluminum oxide layer to which a conductive material is added) has a feature that the same operation is performed without using a high voltage forming process such as that of aluminum oxide and filament type. This is due to the fact that the prefilament that is the basis of the filament has already been formed at the time of film formation. However, in the resistance state where the amount of conductive element added by co-evaporation is low (5% or less), the resistance value in the initial state is clearly much higher than the high resistance state in the operating state, and is added for non-forming. The amount needs to be increased. Therefore, if the additive amount is increased to reduce forming, the apparent distance between the electrode and the additive material may become too short, resulting in a decrease in insulation and a cause of current leakage. This causes a decrease in the yield of the element. However, in this device, since an aluminum oxide layer is always inserted between the charge storage layer and the electrode, it always has a certain distance or more and there is little fear of current leakage.

Previously, other materials had limitations on the electrode, such as the need to use one of the Schottky-type electrode materials, but this device does not have a clear limitation, so it matches with other semiconductor devices and circuits. There is an advantage that it is easy to take. In addition, since the charge storage layer is formed in the resistance change layer of this element, the ON voltage (voltage for transition from the high resistance state to the low resistance state) is 5.0 V or less (mostly 2. 0V to 3.0V) and OFF voltage can be driven at a low voltage of 1.0V or less (mostly between 0.3V and 0.5V). This can be expected to save power during operation.

4 shows IV characteristics of a typical resistance change type memory device according to the present invention. 1 shows a resistance variable memory element structure according to the present invention. The IV (memory) characteristics of a 56 μm square, three-layer structure type memory device. Change in resistance between a high resistance (OFF) state and a low resistance (ON) state during an operation cycle of a 56 μm square three-layer structure type memory device. A histogram of the ON / OFF operating voltage of a 56 μm square three-layer structure type memory device. The IV (memory) characteristics of a 56 μm square, five-layer structure type memory device. Change in resistance of high resistance (OFF) state / low resistance (ON) state during an operation cycle of a 56 μm square, five-layer structure type memory device. 56 μm square, 5-layer structure type ON / OFF operating voltage histogram.

<Example 1>
Al ₂ O ₃ / Al (20 W): Al ₂ O ₃ (Al DC 20 W, Al ₂ O ₃ RF 200 W co-deposited film) / Al ₂ O ₃ three-layer structure variable resistance layer silicon oxide SiO ₂ layer (200 nm) An aluminum (Al) lower wiring layer is formed on an attached silicon Si (100) surface substrate by an electron beam evaporation method at a growth rate of 20 nm and 1 to 3 nm / min. The film is formed at a growth rate of / min. Thereafter, a variable resistance layer is formed on the lower metal electrode layer by using a DC / RF simultaneous sputtering method. A charge storage layer made of an aluminum oxide layer to which a conductive element is added is formed simultaneously by 60 nm of Al by DC sputtering and Al ₂ O ₃ by RF sputtering. The aluminum oxide layer is formed by depositing Al ₂ O ₃ with a thickness of 15 nm on the front and back sides by RF sputtering.

Under this condition, Al is mixed in the change layer by about 6 to 9% and exhibits a charge injection effect. The sample after film formation was coated with a photoresist AZ5214 (manufactured by AZ Electronic Materials) by 1.4 μm by spin coating, and the solution (solvent) in the photoresist was vaporized at 90 ° C. for 2 minutes to solidify the resist (soft Bake). After that, the electrode pattern was exposed for 1.5 seconds using a contact mask aligner (mercury lamp with a wavelength of 350 nm). After exposure, the substrate is subjected to reversal baking (pattern reversal from a negative pattern to a positive pattern) for 30 seconds at 120 ° C., and then an upper metal electrode pattern is exposed and formed by irradiating a Hg lamp with a mask aligner once again. In the exposed pattern, the resist in the electrode forming portion is developed and removed by a developer NMD-3 (manufactured by Tokyo Ohka Co., Ltd.) resist for the lift-off process. An upper metal electrode is formed using this resist pattern. The upper metal electrode is formed by using an electron beam vapor deposition or vacuum vapor deposition apparatus, depositing a 200 nm Al film, and processing and forming necessary portions in a lift-off process.

  FIG. 3 shows IV (memory) characteristics of the variable resistance element formed by this method. This is an IV characteristic of a device having a 56 μm square upper metal electrode. Transition from high resistance state (OFF state) to low resistance state (ON state) at 2.0 to 3.0 V, and transition from low resistance state (ON state) to high resistance state (OFF state) at −0.5 V or less. You can see how it happens.

Subsequently, changes in resistance values in the high resistance state (OFF state) and the low resistance state (ON state) when 100 cycles of operation are performed on the element of the aluminum-added aluminum oxide film having the upper metal electrode of 56 μm square are summarized. This is shown in FIG. The number of operation cycles is plotted on the horizontal axis, and the resistance values in the high resistance state and low resistance state at that time are plotted on the vertical axis. It can be seen that in the resistance change of 100 times, the same 10 ¹ Ω level (low resistance state, ON state) and 10 ² Ω level (high resistance state, OFF state) are repeatedly operated. Therefore, the resistance change value between the high resistance state and the low resistance state is 10 times or more, and the switching is also good.

FIG. 5 shows a histogram that summarizes the ON voltage and OFF voltage of each element when an operation cycle is performed in order to evaluate the variation in the operating voltage of the three-layer structure type memory element. The horizontal axis represents voltage, and the vertical axis represents the number of elements operating at that voltage. Normally, the resistance change memory element does not operate at the same voltage, but operates with a certain degree of variation. It can be said that the smaller the variation or variation in voltage between elements and between operations, the more stable the operation and the higher the reliability.

In this element, it can be seen that the ON voltage operates from 1.0 V to 5.0 V centering on 2.0 V. Further, it can be seen that the OFF voltage is operating at 1.0 V or less, particularly 0.5 V or less. This operation is a result of continuous resistance change cycles. Since the ON / OFF voltages operate without overlapping, it is possible to operate the element by applying a voltage in pulses.

From all the above experimental results, the present element is concentrated in a certain region for both the ON / OFF voltage, and ON and OFF can be clearly distinguished even in the operating voltage. Further, since the voltage is 5.0 V or less and within the operating voltage of the semiconductor element, it can be said that the element is highly reliable and suitable for practical use.

<Example 2>
Al ₂ O ₃ / Al (20 W): Al ₂ O ₃ (Al DC 20 W, Al ₂ O ₃ RF 200 W co-deposited film) / Al ₂ O ₃ / Al (20 W): Al ₂ O ₃ / Al ₂ O ₃ 5 The lower metal electrode layer of the layer structure type resistance change layer is formed under a high vacuum of Ti 20 nm and Al 200 nm using a lift-off process with a vacuum deposition apparatus and below 1 × 10 ⁻⁴ Pa level. Below this vacuum level, alumina mixed in the film or the surface roughness increased (Ra several nm to several tens of nm), and the Al surface changed from silver to a mixed color of silver and white. After the lift-off process, an ashing process is performed in an oxygen plasma atmosphere (oxygen flow rate 100 cm ³ / min, 100 W, 3 min) in order to remove the resist residue on the lower metal electrode layer.

The resistance change layer was formed using a lift-off process. The resistance change layer is formed only on the lower metal electrode layer by using a two-layer resist method using two types of photoresists, OFPR800 (manufactured by Tokyo Ohka) and AZ5214 (manufactured by AZ Electronic Materials). A mask aligner was used for exposure.
The variable resistance layer is formed by a charge storage layer and an interlayer insulating film layer using a DC / RF simultaneous sputtering method as in the sample of the first embodiment. In this element, films were alternately formed with a thickness of 15 nm.
After the lift-off process, ashing is performed in an oxygen plasma atmosphere (oxygen flow rate 100 cm ³ / min, 100 W, 3 minutes) in order to remove the resist residue on the resistance change layer.
As in Example 1, the upper metal electrode is formed by applying a photoresist with a thickness of 1.4 μm by spin coating and using a mask aligner with 200 nm of Al in a photolithography lift-off process.

FIG. 6 shows the IV characteristics of the variable resistance element. As in the first embodiment, the element transitions from a high resistance (OFF) state to a low resistance (ON) state in a range of 1.0 V to 3.0 V, and transitions from the OFF state to the ON state at −0.5 V or less. Indicates.

  FIG. 7 shows a change in resistance in the ON / OFF cycle of this element, and FIG. 8 shows a histogram of voltage at that time. During 100 cycles, the ON state shows a value around 10Ω, and the OFF state shows a resistance value in the kΩ range. The resistance change value is 10 times or more, and the switching characteristics are also good. The voltage distribution at that time is also a normal distribution centering on the ON voltage from 1.5V to 2.0V, and the maximum value is 4.0V. Further, since the OFF side is concentrated to −0.5 V or less and the voltage distribution is uniform, it is easy to form a peripheral circuit.

  In addition, this element has been developed by a general photolithography method, and this element is formed on an existing semiconductor element (MOS device) in a very general semiconductor manufacturing process including electron beam lithography and laser lithography. You can guess that it is possible.

  If the resistance change type memory element of the present invention is used, the structure is simple and can be miniaturized. Therefore, it is possible to reduce the size of a memory mounted on an electronic device such as a personal computer or a mobile phone. In addition, since the driving voltage and current are small, it can be expected to save energy. For this reason, it becomes possible to greatly increase the driving time of the terminal without changing the capacity of the rechargeable battery. In addition, from the non-volatile point of view, it is possible to store and hold the operation of various electronic terminals, reduce the drive time at the time of restart, and form a power-saving operation computer such as normally-off computing and a mobile terminal It becomes.

Furthermore, the elements used are mainly aluminum (Al) and oxygen (O), and the influence on the human body is harmless. Also, from the viewpoint of the number of Clarke indicating the crust content, both aluminum and oxygen are in the top ten and are relatively abundant elements on the earth. New memory devices currently being developed, and precious metals such as platinum (Pt), hafnium (Hf), nickel (Ni), tantalum (Ta) and rare earth (rare earth) that are used in memory devices currently in use From the fact that no rare metals are used, it can be said that this memory element is an elemental strategic memory element.

DESCRIPTION OF SYMBOLS 1 Upper metal electrode 2 Charge storage layer 3 Lower metal electrode layer 4 Adhesion layer 5 Silicon oxide SiO2 layer 6 Substrate 7 Aluminum oxide layer 8 Resistance change type memory element

Claims (4)

A resistance change type memory device comprising an upper metal electrode / aluminum oxide layer (resistance change layer) / lower metal electrode layer, wherein the resistance change layer has an oxygen deficiency and is doped with aluminum oxide to which a conductive substance is added. A resistance change characterized by having a structure composed of two types of aluminum oxide layers, a charge storage layer made of a physical layer and an oxygen-deficient aluminum oxide layer disposed so as to sandwich the charge storage layer vertically Type memory device. 2. The resistance change type memory element according to claim 1, wherein the composition range of oxygen deficient AlOx in the aluminum oxide layer having oxygen deficiency is x <1.5. 2. The resistance change type memory element according to claim 1, wherein the number N of charge storage layers in the resistance change layer is in the range of 1 to 100. The resistance change type memory device according to claim 1, wherein the conductive material is a metal and a semiconductor, or an oxide or a nitride of a metal and a semiconductor.