TWI650887B - Resistive random access memory - Google Patents

Abstract

A resistive random access memory comprising: a memory unit disposed between an intersection of a first wire and a second wire. The memory unit includes: a selector structure, a first current limiter structure, and a resistance structure. The first current limiter structure is disposed between the selector structure and the first wire. The resistor structure is disposed between the selector structure and the second wire or between the first current limiter structure and the first wire.

Description

Resistive random access memory

This invention relates to a non-volatile memory, and more particularly to a resistive random access memory.

Resistive random access memory (RRAM) is a type of non-volatile memory. Resistive random access memory is widely studied because of its simple structure, low operating voltage, fast operation time, multi-bit memory, low cost and good durability. The basic structure commonly used in resistive random access memory is composed of a transistor plus a resistor (1T1R). The resistance value of the resistor is changed by changing the applied bias voltage, so that the component is in a high resistance state or a low resistance state, and thereby 0 or 1 of the bit signal is judged.

The present invention provides a resistive random access memory capable of reducing the size of a resistive random access memory device and improving component accumulation.

A resistive random access memory of the present invention, comprising: a memory single The element is disposed between the intersection of the first wire and the second wire. The memory unit includes three elements in series connected in any order: a selector structure, a first current limiter structure, and a resistance structure.

In an embodiment of the invention, the resistive random access memory, wherein the selector structure comprises a first conductive layer, a selected material layer and a second conductive layer in sequence.

In an embodiment of the present invention, the resistive random access memory, wherein the first current limiter structure sequentially includes a third conductive layer, a first metal layer, a first current limiting material layer, and a fourth conductive layer. .

In an embodiment of the invention, the resistive random access memory, wherein the resistor structure sequentially includes a fifth conductive layer, a variable resistance layer, and a sixth conductive layer.

In an embodiment of the invention, the resistive random access memory, wherein one of the fifth conductive layer or the sixth conductive layer has an oxygen affinity higher than that of the other one.

In an embodiment of the invention, the resistive random access memory, wherein the memory unit further comprises a second current limiter structure in series with the three elements.

In an embodiment of the invention, the resistive random access memory, wherein the second current limiter structure further comprises a seventh conductive layer, a second current limiting material layer and an eighth conductive layer.

In an embodiment of the invention, the resistive random access memory, wherein the materials of the first conductive layer and the second conductive layer comprise titanium nitride, tantalum nitride, Titanium, tantalum or indium tin oxide.

In an embodiment of the invention, the resistive random access memory, wherein the material of the selected material layer comprises tantalum or titanium dioxide or an amorphous chalcogen compound.

In an embodiment of the invention, the resistive random access memory, wherein the materials of the third conductive layer and the fourth conductive layer comprise titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide.

In an embodiment of the invention, the resistive random access memory, wherein the material of the first current limiting material layer comprises tantalum or titanium dioxide.

In an embodiment of the invention, the resistive random access memory, wherein the materials of the fifth conductive layer and the sixth conductive layer comprise titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. One of the fifth conductive layer or the sixth conductive layer has an oxygen affinity higher than that of the other one.

In an embodiment of the invention, the resistive random access memory, wherein the material of the variable resistance layer comprises a transition metal oxide.

In an embodiment of the invention, the resistive random access memory, wherein the material of the variable resistance layer comprises aluminum, titanium, tantalum, copper, silver or nickel.

In an embodiment of the invention, the resistive random access memory, wherein the materials of the seventh conductive layer and the eighth conductive layer comprise titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide.

In an embodiment of the invention, the resistive random access memory, wherein the material of the second current limiting material layer comprises tantalum or titanium dioxide.

Based on the above, the resistive random access memory structure of the present invention replaces the conventional resistive random access memory structure by a resistor structure connecting the selector structure and the first current limiter structure (ie, the structure of the 1R1D1S or 1D1S1R). (A transistor is connected to a resistor structure, that is, the structure of 1T1R), which can reduce the size of the resistive random access memory device and improve the component accumulation.

The resistive random access memory of the present invention has a selector structure. In an embodiment, the selector structure forms a Schottky barrier between the conductive layer and the selected material layer, and can be used as a switch for controlling the memory unit circuit. For this Schottky barrier to maintain sufficient nonlinearity, a key requirement is that the Schottky barrier can be narrowed by high electric fields. In another embodiment, the material is selected to be a chalcogenide that operates below its crystallization temperature, but undergoes a transition above a threshold valtage.

The resistive random access memory of the present invention has a first current limiter structure, and a Schottky barrier that is not narrowed by an electric field is formed between the current limiting material layer and the current limiting material layer by using a conductive layer or a metal layer. The current limiter that controls the current amount of the memory unit circuit can also control the current flowing through the resistor structure to be lower than a saturation current value, which can prevent the resistor structure from changing resistance during the SET operation. Irreversible damage.

The above described features and advantages of the invention will be apparent from the following description.

100‧‧‧Resistive random access memory

110‧‧‧ memory unit

120‧‧‧Select material layer

122, 128‧‧‧Limited material layer

124, 130‧‧‧ metal layer

126‧‧‧Variable Resistance Layer

140, 142, 144, 146, 148, 150, 152, 154, 156, 158‧‧‧ conductive layers

WL, WL1, WL2, WL3, WL4, WL5, WL6‧‧‧ character lines

BL, BL1, BL2, BL3‧‧‧ bit line

R‧‧‧Resistor structure

D1, D2‧‧‧ current limiter structure

S‧‧‧ selector structure

1A is a top plan view of a resistive random access memory of the present invention.

1B is a side elevational view of a resistive random access memory of the present invention.

2A is a schematic diagram showing the connection of the respective structures of the memory cells of the resistive random access memory according to the first embodiment of the present invention.

2B is a cross-sectional view showing each structure of a memory cell of the resistive random access memory according to the first embodiment of the present invention.

3A is a schematic diagram showing the connection of the respective structures of the memory cell of the resistive random access memory according to the second embodiment of the present invention.

3B is a cross-sectional view showing the structure of a memory cell of the resistive random access memory according to the second embodiment of the present invention.

4A is a schematic diagram showing the connection of the respective structures of the memory cell of the resistive random access memory according to the third embodiment of the present invention.

4B is a cross-sectional view showing the structure of a memory cell of a resistive random access memory according to a third embodiment of the present invention.

FIG. 5A is a schematic diagram showing the connection of the respective components of the memory cell of the resistive random access memory according to the fourth embodiment of the present invention.

5B is a cross-sectional view showing the structure of a memory cell of the resistive random access memory according to the fourth embodiment of the present invention.

Referring to FIG. 1A and FIG. 1B, the resistive random access memory 100 has The plurality of bit lines BL and the plurality of word lines WL are disposed in parallel with each other, and the plurality of word lines WL are disposed in parallel with each other and perpendicular to the bit lines BL. A memory unit 110 is provided between the intersection of each bit line BL and the word line WL. In other words, the memory unit 110 is disposed, for example, between intersections of two wires WL/BL crossing each other, one of which serves as a word line and the other of which serves as a bit line.

Referring to FIG. 2A and FIG. 2B, the memory unit 110 includes a selector structure S, a current limiter structure D1 and a resistance structure R, wherein the current limiter structure D1 is disposed between the selector structure S and the wires WL/BL, and the resistance structure R is disposed between the current limiter structure D1 and the wires WL/BL.

The selector structure S sequentially includes a conductive layer 142, a selection material layer 120, and a conductive layer 140. The selector structure S is, for example, a bipolar selector. The selector structure S can form a Schottky barrier between the conductive layer 142, the conductive layer 140 and the selective material layer 120. For this Schottky barrier to maintain sufficient nonlinearity, a key requirement is that the Schottky barrier can be narrowed by high electric fields. The requirement for the above conditions to occur is that the material layer 120 must be sufficiently thin. In addition, the chalcogenide compound is highly insulating when it is lower than a threshold voltage Vth, but becomes highly conductive when it is higher than the threshold voltage Vth. The material of the conductive layer 142 and the conductive layer 140 is, for example, a conductive material, such as titanium nitride (TiN), tantalum nitride (TaN), titanium (Ti), tantalum (Ta) or indium tin oxide (ITO, Indium Tin Oxide). . The material of the material layer 120 is selected, for example, as a semiconductor material such as bismuth (Si) or titanium dioxide (TiO ₂ ) or an amorphous chalcogen compound such as carbon doped GeTe.

The current limiter structure D1 sequentially includes a conductive layer 144, a metal layer 124, and a current limiting Material layer 122 and conductive layer 142. The current limiter structure D1 can be used as a control memory unit circuit by forming a Schottky barrier between the conductive layer 144 or the metal layer 124, the current limiting material layer 122 and the conductive layer 142, which is thick enough and not narrowed by an electric field. The current limiter of the current amount can also control the current flowing through the resistor structure below a saturation current value to avoid irreversible damage of the resistor structure during the SET operation. The material of the conductive layer 144 and the conductive layer 142 is, for example, a conductive material such as titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. The material of the metal layer 124 is, for example, a metal such as titanium. The material of the current limiting material layer 122 is, for example, a semiconductor material such as tantalum or titanium dioxide.

The resistor structure R sequentially includes a conductive layer 146, a variable resistance layer 126, and a conductive layer 144. The material of the conductive layer 144 and the conductive layer 146 is, for example, a conductive material such as titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. The oxygen affinity of the conductive layer 144 is higher than the oxygen affinity of the conductive layer 146. The variable resistance layer 126 may be a single layer structure or a multilayer structure. When the variable resistance layer 126 is a single layer structure, the material thereof is, for example, a transition metal oxide such as nickel oxide (NiO), hafnium oxide (HfO), or HbO ₂ , ZrO, ZrO ₂ , Ta ₂ O ₅ , Zinc Oxide (ZnO), T ₃ (WO ₃ ), Cobalt Oxide (CoO) And bismuth pentoxide (Nb ₂ O ₅ ). When the variable resistance layer 126 is a multi-layer structure, a metal layer (not shown) and a variable resistance material layer may be included. The metal layer may serve as an oxygen exchange layer. The oxygen affinity of the metal layer is, for example, greater than the conductive layer 144 and the conductive layer 146. Oxygen affinity. The material of the metal layer is, for example, a metal material such as titanium, tantalum, niobium, zirconium, platinum or aluminum; and the material of the variable resistance material layer is, for example, a transition metal oxide such as nickel oxide (NiO) or hafnium oxide (HfO). , cerium oxide (HfO ₂ ), zirconium oxide (ZrO), zirconium dioxide (ZrO ₂ ), tantalum pentoxide (Ta ₂ O ₅ ), zinc oxide (ZnO), tungsten trioxide (WO ₃ ), cobalt oxide (CoO) and bismuth pentoxide (Nb ₂ O ₅ ).

In the memory unit 110 of this embodiment, the conductive layer 142 serves as both the upper electrode of the selector structure S and the lower electrode of the current limiter structure D1, and the conductive layer 144 serves as both the upper electrode of the current limiter structure D1 and the resistance structure. The lower electrode of R. The conductive layer 142 and the conductive layer 144 may be a single layer material or a multi-layer material. When it is a multi-layer material, each layer may be used as an upper electrode or a lower electrode of each of the above structures, wherein the layers may be the same or different.

In the memory unit 110 of this embodiment, the conductive layer 146 serves as the upper electrode of the memory unit 110, and the conductive layer 140 serves as the lower electrode of the memory unit 110. The conductive layer 146 as the upper electrode may also be the same layer as the bit line or the word line, and the conductive layer 140 as the lower electrode may be the same layer as the bit line or the word line. For example, when the conductive layer 140 and the bit line are the same layer, the conductive layer 146 and the word line are the same layer, or when the conductive layer 140 and the word line are the same layer, the conductive layer 146 and the bit line are the same layer.

Referring to FIG. 3A and FIG. 3B, the memory unit 110 includes a selector structure S, a current limiter structure D1 and a resistor structure R, wherein the current limiter structure D1 is disposed between the selector structure S and the wires WL/BL, and the resistor The structure R is disposed between the selector structure S and the wires BL/WL.

The selector structure S sequentially includes a conductive layer 154, a selection material layer 120, and a conductive layer 152. The selector structure S is, for example, a bipolar selector. The selector structure S can form a Schottky barrier between the conductive layer 154, the conductive layer 152 and the selective material layer 120, can be used as a switch for controlling the memory unit circuit, or the selected material layer is amorphous with a threshold voltage Vth. A chalcogen compound that keeps the circuit open when the bias voltage V is less than Vth (ie, 0<|V|<|Vth|), and turns off the circuit when the bias voltage V exceeds Vth (ie, |V|>|Vth|) . The material of the conductive layer 154 and the conductive layer 152 is, for example, a conductive material, such as titanium nitride (TiN), tantalum nitride (TaN), titanium (Ti), tantalum (Ta) or indium tin oxide (ITO, Indium Tin Oxide). . The material of the material layer 120 is selected, for example, as a semiconductor material such as bismuth (Si) or titanium dioxide (TiO ₂ ).

The current limiter structure D1 sequentially includes a conductive layer 156, a metal layer 124, a current limiting material layer 122, and a conductive layer 154. The current limiter structure D1 forms a Schottky barrier between the current limiting material layer 122 and the conductive layer 154, and can be used as a current limiter for controlling the current amount of the memory unit circuit, and can also control the current flowing through the resistor structure. Below a saturation current value, it can be avoided that the resistance structure can cause irreversible damage during the SET operation. The material of the conductive layer 156 and the conductive layer 154 is, for example, a conductive material such as titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. The material of the metal layer 124 is, for example, a metal such as titanium. The material of the current limiting material layer 122 is, for example, a semiconductor material such as tantalum or titanium dioxide.

The resistor structure R sequentially includes a conductive layer 152, a variable resistance layer 126, and a conductive layer 150. The material of the conductive layer 152 and the conductive layer 150 is, for example, a conductive material such as titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. The variable resistance layer 126 may be a single layer structure or a multilayer structure. When the variable resistance layer 126 is a single layer structure, the material thereof is, for example, a transition metal oxide such as nickel oxide (NiO), hafnium oxide (HfO), or HbO ₂ , ZrO, ZrO ₂ , Ta ₂ O ₅ , Zinc Oxide (ZnO), T ₃ (WO ₃ ), Cobalt Oxide (CoO) And bismuth pentoxide (Nb ₂ O ₅ ). When the variable resistance layer 126 is a multi-layer structure, a metal layer (not shown) and a variable resistance material layer may be included. The metal layer may serve as an oxygen exchange layer. The oxygen affinity of the metal layer is, for example, greater than the conductive layer 152 and the conductive layer 150. Oxygen affinity. The material of the metal layer is, for example, a metal material such as titanium, tantalum, niobium, zirconium, platinum or aluminum; and the material of the variable resistance material layer is, for example, a transition metal oxide such as nickel oxide (NiO) or hafnium oxide (HfO). , cerium oxide (HfO ₂ ), zirconium oxide (ZrO), zirconium dioxide (ZrO ₂ ), tantalum pentoxide (Ta ₂ O ₅ ), zinc oxide (ZnO), tungsten trioxide (WO ₃ ), cobalt oxide (CoO) and bismuth pentoxide (Nb ₂ O ₅ ).

In the memory unit 110 of this embodiment, the conductive layer 154 serves as both the upper electrode of the selector structure S and the lower electrode of the current limiter structure D1, and the conductive layer 152 serves as both the upper electrode of the resistance structure R and the selector structure S. Lower electrode. The conductive layer 154 and the conductive layer 152 may be a single layer material or a multi-layer material. When it is a multi-layer material, each layer may be used as an upper electrode or a lower electrode of each of the above structures, wherein the layers may be the same or different.

In the memory unit 110 of this embodiment, the conductive layer 156 serves as the upper electrode of the memory unit 110, and the conductive layer 150 serves as the lower electrode of the memory unit 110. The conductive layer 156 as the upper electrode may also be the same layer as the bit line or the word line, and the conductive layer 150 as the lower electrode may be the same layer as the bit line or the word line. For example, when the conductive layer 156 and the bit line are the same layer, the conductive layer 150 and the word line are the same layer, or when the conductive layer 156 and the word line are the same layer, the conductive layer 150 and the bit line are the same layer.

4A and 4B, the memory unit 110 includes a selector structure. S, the current limiter structure D1, the current limiter structure D2 and the resistance structure R, wherein the current limiter structure D1 is disposed between the selector structure S and the wire WL/BL, and the resistance structure R is disposed in the current limiter structure D1 and Between the wires WL/BL, the current limiter structure D2 is disposed between the resistor structure R and the wires WL/BL. The layer of the selector structure S, the current limiter structure D1 and the resistor structure R and the material of each layer are the same as those of the first embodiment, and are not described herein again.

The current limiter structure D2 sequentially includes a conductive layer 148, a metal layer 130, a current limiting material layer 128, and a conductive layer 146. The material of the conductive layer 148 and the conductive layer 146 is, for example, a conductive material such as titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. The material of the metal layer 130 is, for example, a metal such as titanium. The material of the current limiting material layer 128 is, for example, a semiconductor material such as tantalum or titanium dioxide.

In the memory unit 110 of this embodiment, the conductive layer 146 serves as both the upper electrode of the resistor structure R and the lower electrode of the current limiter structure D2, and the conductive layer 144 serves as both the upper electrode of the current limiter structure D1 and the resistor structure R. The lower electrode, while the conductive layer 142 serves as both the upper electrode of the selector structure S and the lower electrode of the current limiter structure D1. The conductive layer 146, the conductive layer 144 and the conductive layer 142 may be a single layer material or a multi-layer material. When it is a multi-layer material, each layer may be used as an upper electrode or a lower electrode of each of the above structures, wherein each layer material may be the same or different.

In the memory unit 110 of this embodiment, the conductive layer 148 serves as the upper electrode of the memory unit 110, and the conductive layer 140 serves as the lower electrode of the memory unit 110. The conductive layer 148 as the upper electrode may also be the same layer as the bit line or the word line, and the conductive layer 140 as the lower electrode may be the same layer as the bit line or the word line. For example, when When the electrical layer 148 is in the same layer as the bit line, the conductive layer 140 and the word line are the same layer, or when the conductive layer 148 and the word line are the same layer, the conductive layer 140 and the bit line are the same layer.

5A and 5B, the memory unit 110 includes a selector structure S, a current limiter structure D1, a current limiter structure D2, and a resistance structure R, wherein the current limiter structure D1 is disposed on the selector structure S and the wire WL. Between /BL, the resistor structure R is disposed between the selector structure S and the wires BL/WL, and the current limiter structure D2 is disposed between the resistor structure R and the wires BL/WL. The layer of the selector structure S, the current limiter structure D1 and the resistor structure R and the material of each layer are the same as those of the second embodiment, and are not described herein again.

The current limiter structure D2 sequentially includes a conductive layer 150, a metal layer 130, a current limiting material layer 128, and a conductive layer 158. The material of the conductive layer 150 and the conductive layer 158 is, for example, a conductive material such as titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. The material of the metal layer 130 is, for example, a metal such as titanium. The material of the current limiting material layer 128 is, for example, a semiconductor material such as tantalum or titanium dioxide. The purpose of the current limiter structure D2 is to limit the current, the direction of which is opposite to the direction in which the current limiter structure D1 acts, since the Schottky energy barrier acts primarily in a preferred direction.

In the memory unit 110 of this embodiment, the conductive layer 154 serves as both the upper electrode of the selector structure S and the lower electrode of the current limiter structure D1, and the conductive layer 152 serves as both the upper electrode of the resistive structure R and the selector structure S. The lower electrode, while the conductive layer 150 serves as both the upper electrode of the current limiter structure D2 and the lower electrode of the resistance structure R. The conductive layer 154, the conductive layer 152 and the conductive layer 150 may be a single layer material or a multi-layer material. When it is a multi-layer material, each layer may be respectively used as the above structure. The electrode or the lower electrode, wherein the materials of the layers may be the same or different.

In the memory unit 110 of this embodiment, the conductive layer 156 serves as the upper electrode of the memory unit 110, and the conductive layer 158 serves as the lower electrode of the memory unit 110. The conductive layer 156 as the upper electrode may also be the same layer as the bit line or the word line, and the conductive layer 158 as the lower electrode may be the same layer as the bit line or the word line. For example, when the conductive layer 156 and the bit line are the same layer, the conductive layer 158 and the word line are the same layer, or when the conductive layer 156 and the word line are the same layer, the conductive layer 158 and the bit line are the same layer.

In summary, the resistive random access memory of the present invention has a selector structure, a first current limiter structure and a resistor structure, and the resistor structure is coupled to the selector structure and the current limiting structure (ie, the structure of the 1R1D1S or the 1D1S1R). ), instead of the traditional resistive random access memory structure (a transistor connected to a resistor structure, that is, the structure of 1T1R), the component accumulation can be improved.

The resistive random access memory of the present invention has a selector structure. The selector structure can form a Schottky barrier between the conductive layer and the selected material layer, can be used as a switch for controlling the memory unit circuit, or select a material layer. It is an amorphous chalcogen compound having a threshold voltage Vth, which maintains the circuit open when the bias voltage V does not reach Vth (ie, 0<|V|<|Vth|), and the bias voltage V exceeds Vth (ie, |V|> When |Vth|) turns off the circuit.

The resistive random access memory of the present invention has a first current limiter structure, which can form a Schottky barrier between the current limiting material layer and the adjacent conductive layer, and thus is lower than a reverse bias In this case, the energy barrier is wide enough to limit the current, and the current flowing through the resistor structure can be controlled to be lower than a saturation current value, which can prevent irreversible damage of the resistor structure during the SET operation.

The resistive random access memory of the present invention further has a second current limiter structure disposed on the other side of the resistor structure adjacent to the first current limiter structure or the selector structure, when the memory unit is in another polarity In operation, it can be used as a current limiter for controlling the current amount of the memory unit circuit, and can also control the current flowing through the resistor structure to be lower than a saturation current value, thereby avoiding irreversible damage of the resistor structure during the SET operation. .

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

Claims (16)

A resistive random access memory, comprising: a memory unit disposed between intersections of a first wire and a second wire, the memory unit comprising three elements connected in series in any order: a selector structure; Current limiter structure; and resistance structure. The resistive random access memory of claim 1, wherein the selector structure comprises a first conductive layer, a selection material layer and a second conductive layer in sequence. The resistive random access memory of claim 1, wherein the first current limiter structure comprises a third conductive layer, a first metal layer, a first current limiting material layer and a fourth conductive layer in sequence. Floor. The resistive random access memory of claim 1, wherein the resistive structure comprises a fifth conductive layer, a variable resistance layer and a sixth conductive layer in sequence. The resistive random access memory of claim 4, wherein one of the fifth conductive layer or the sixth conductive layer has an oxygen affinity higher than that of the other one. The resistive random access memory of claim 1, wherein the memory unit further comprises a second current limiter structure in series with the three elements. The resistive random access memory of claim 6, wherein the second current limiter structure further comprises a seventh conductive layer, a second current limiting material layer and an eighth conductive layer. The resistive random access memory according to claim 2, wherein the material of the first conductive layer and the second conductive layer comprises titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. . The resistive random access memory according to claim 2, wherein the material of the material selection layer comprises ruthenium or titanium dioxide or an amorphous chalcogen compound. The resistive random access memory according to claim 3, wherein the material of the third conductive layer and the fourth conductive layer comprises titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. . The resistive random access memory of claim 3, wherein the material of the first current limiting material layer comprises tantalum or titanium dioxide. The resistive random access memory according to claim 4, wherein the material of the fifth conductive layer and the sixth conductive layer comprises titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. . The resistive random access memory of claim 4, wherein the material of the variable resistance layer comprises a transition metal oxide. The resistive random access memory of claim 4, wherein the material of the variable resistance layer comprises aluminum, titanium, tantalum, copper, silver or nickel. The resistive random access memory according to claim 7, wherein the material of the seventh conductive layer and the eighth conductive layer comprises titanium nitride, tantalum nitride, titanium, tantalum or indium tin oxide. . The resistive random access memory of claim 7, wherein the material of the second current limiting material layer comprises tantalum or titanium dioxide.