A resistive random access memory with adjustable operating voltage and a preparation method thereof

Abstract

The present invention discloses a resistive random access memory (RRAM) with adjustable operating voltage and a preparation method thereof, which includes a substrate, a bottom electrode, a resistive switching layer, and a top electrode arranged in sequence from bottom to top. The resistive switching layer is a Ta2O5 thin film doped with W, with a thickness of 40 - 120 nm. The top electrode and the bottom electrode are made of metal W and Pt respectively, and the substrate material is Ti / SiO2 / Si. In the present invention, the Ta2O5 is doped with W element, and the formation energy and diffusion barrier energy of oxygen vacancies in Ta2O5 are changed by doping, so as to change the diffusion activation energy of oxygen vacancies, realize the regulation of the diffusion activation energy of oxygen vacancies, and further regulate the operating voltage of the device, so as to achieve the purpose of controlling the operating voltage of the RRAM device.

Description

Technical Field:

[0002] The present invention relates to the technical field of memories, and particularly to a resistive random access memory (RRAM) with adjustable operating voltage and a preparation method thereof. Background Art:

[0004] The human brain nerves can break through the bottleneck limitations of traditional von Neumann computers, parallelly process a large number of real-time data tasks, and show great advantages in pattern recognition, image thinking, associative memory, etc. How to be inspired by the human brain nervous system, construct a new type of electronic nerve device, and build a circuit of a human brain-like nervous system has become the primary task to be solved and the current research hotspot. At present, the research on human brain nerve simulation based on memristors is still in its initial stage. Internationally, researchers mainly use memristors with storage functions as electronic synaptic devices and realize the key function of synaptic plasticity in human brain cognition, and have made a series of groundbreaking progress.

[0005] In an RRAM, the two states of the high resistance state and the low resistance state of the device are changed by voltage, and this voltage is called the state operation voltage. The voltage that makes the RRAM change from the high resistance state to the low resistance state is called the set voltage, and the voltage that makes the low resistance state change to the high resistance state is called the reset voltage. At present, one of the important problems faced by RRAM applications is that the operating voltage is not adjustable. The non-adjustability of the operating voltage will cause a large change in the resistance state of the device, resulting in misreading of data, and further affecting the lifespan of the RRAM, causing the device to fail prematurely.

[0006] Content of the Invention Patent:

[0007] The technical problem to be solved by the present invention is: overcoming the deficiencies of the prior art, providing a method of doping W in Ta 2 O 5 thin film to form a resistive switching layer Ta 2 O 5 :W (Ta 2-x W x O 5 ), thereby changing the diffusion barrier of oxygen ions in Ta 2 O 5 and further changing the diffusion activation energy of oxygen ions, so as to change the operating voltage of the resistive random access memory, and achieving the regulation of the operating voltage of the resistive random access memory by controlling the doping amount.

[0008] To solve the above technical problem, a technical solution provided by the present invention is: a resistive random access memory with adjustable operating voltage, including a substrate, a bottom electrode, a resistive switching layer, and a top electrode sequentially arranged from bottom to top, characterized in that: the resistive switching layer is a Ta 2 O 5 thin film doped with W.

[0009] Further, the thickness of the resistive switching layer is 40 nm - 120 nm.

[0010] Further, the top electrode and the bottom electrode are made of metal W and Pt respectively. The thickness of metal W is 100 - 300 nm, and the thickness of metal Pt is 10 - 50 nm.

[0011] Further, the resistive switching layer thin film is a W-doped Ta 2 O 5 thin film prepared by sol-gel.

[0012] Further, the molar doping concentration of W in the resistive switching layer is 1% - 10%.

[0013] To solve the above technical problems, another technical solution provided by the present invention is: a method for manufacturing a resistive random access memory with adjustable operating voltage, and the steps are as follows: Step 1: Clean the Ti / SiO2 / Si substrate;

[0014] Step 2: Use electron beam evaporation to deposit a layer of Pt thin film to form the bottom electrode;

[0015] Step 3: Prepare a spin-coating solution from tantalum ethoxide, WCl 6 and 2-ethoxyethanol. Filter the solution through a 0.2 mm ultrafiltration membrane filter and let it stand for 16 hours to form a sol for thin film spin-coating. Spin-coat the sol at 3000 - 4500 rpm for 30 - 45 seconds, and then anneal it at 60 °C for 30 - 60 minutes to form the resistive switching layer;

[0016] Step 4: Use magnetron sputtering technology to deposit a layer of metal W on the resistive switching layer to form the top electrode.

[0017] Further, in the above Step 3, the preparation process of the spin-coating solution is as follows: Tantalum ethoxide is used as the precursor solution of Ta 2 O 5 , and the WCl 6 solution is used as the precursor solution of W ions for doping. Mix the three solutions of tantalum ethoxide, WCl 6 and 2-ethoxyethanol, and keep the mixed solution stirred at room temperature for 30 - 45 minutes. Then add an aqueous hydrochloric acid solution of 0.20 - 0.30 mol / L to the solution at room temperature.

[0018] Further, the tungsten chloride solution is prepared by dissolving the corresponding WO 3 in an aqueous hydrochloric acid solution of 0.2 - 0.3 mol / L, then carefully drying and dissolving it in an ethanol solution.

[0019] Further, in the mixed solution formed by mixing the three solutions, the volume ratio of 2-ethoxyethanol / tantalum ethoxide is kept at 8 - 12:1.

[0020] Further, in the fourth step, the deposition technique is radio frequency magnetron sputtering, the initial vacuum degree is 5×10-4Pa, the working gas is argon with a purity of 99.99%, the sputtering power is 160 - 220W, the working air pressure is 1.0Pa, and the W thin film is obtained by sputtering deposition for 25 - 45 minutes.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. By doping W in the Ta 2 O 5 thin film to form a resistive switching layer Ta 2-x W x O 5 thin film, the diffusion barrier of oxygen ions in Ta 2 O 5 and the operating voltage of the resistive random access memory are increased, and the purpose of regulating the operating voltage can be achieved.

[0023] 2. By doping the Ta 2 O 5 with the W element, the formation energy and diffusion barrier energy of oxygen vacancies in Ta 2 O 5 are changed by doping, and then the diffusion activation energy of oxygen vacancies is changed, so as to realize the regulation of the diffusion activation energy of oxygen vacancies, and further regulate the operating voltage of the device. The preparation process is simple and easy to operate. The obtained device has a low operating voltage and can be applied to large-scale electronic synapses. Description of the drawings:

[0025] Figure 1 Schematic structural diagram of a resistive random access memory with adjustable operating voltage;

[0026] Figure 2 Resistive random access memory with undoped resistive switching layer Ta 2 O 5 W / Ta 2 O 5 / Pt current-voltage test result graph;

[0027] Figure 3 Resistive random access memory with W-doped resistive switching layer Ta 2 O 5 W / Ta 2-x W x O 5 / Pt current-voltage test result graph;

[0028] Figure 4 Ta 2 O 5 Schematic structural diagram and oxygen vacancy diffusion path schematic diagram;

[0029] Figure 5Calculation results of the relationship between the oxygen vacancy formation energy and the W doping concentration;

[0030] Figure 6 Ta 2-x W x O 5 Calculation results of the relationship between the diffusion barrier of oxygen ions and the W doping concentration in it;

[0031] Figure 7 Curve of the average diffusion barrier size varying with the W doping concentration;

[0032] Figure 8 Ta 2-x W x O 5 Calculation results of the density of electronic states. Specific implementation manner:

[0034] Example: Refer to Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 、 Figure 7 and Figure 8 , in the figure, 1 - substrate, 2 - bottom electrode, 3 - resistive switching layer, 4 - top electrode.

[0035] A resistive switching memory with adjustable operating voltage, comprising a substrate, a bottom electrode, a resistive switching layer, and a top electrode sequentially arranged from bottom to top. The resistive switching layer is a Ta 2 O 5 thin film doped with W, with a thickness of 40 - 120 nm. The top electrode and the bottom electrode are made of metal W and Pt respectively, and the substrate material is Ti / SiO 2 / Si; by doping with W element in Ta 2 O 5 , by doping, the formation energy and diffusion barrier energy of oxygen vacancies in Ta 2 O 5 are changed, and then the diffusion activation energy of oxygen vacancies is changed to realize the regulation of the diffusion activation energy of oxygen vacancies. Realize the regulation of the formation and breaking of the conductive filament channel and the operating voltage of the device, and achieve the purpose of controllable operating voltage.

[0036] The present application will be described in detail below with reference to the accompanying drawings and examples.

[0037] Example 1:

[0038] A method for preparing a resistive switching memory with adjustable operating voltage, the steps of which are: Step 1: Cleaning the Ti / SiO2 / Si substrate 1;

[0039] Step 2: Deposit a Pt thin film by electron beam evaporation to form the bottom electrode 2. The specific deposition parameters are as follows: the vacuum degree is 5×10-4 Pa, the bombardment current is 150 mA, the substrate temperature is 180 °C, the substrate rotation speed is 6 r / s, and the electron beam voltage is 6 kV.

[0040] Step 3: Ethanol tantalum (Aldrich; 99.98%) is used as the precursor solution for Ta 2 O 5 . A WCl 6 (Aldrich 99.9%) solution is used as the W ion precursor solution for doping. This chloride solution is prepared by dissolving the corresponding WO 3 in 0.2 mol / L hydrochloric acid aqueous solution, then carefully dried and dissolved in ethanol solution. Mix the three solutions of ethanol tantalum, WCl 6 and 2-ethoxyethanol, and keep the volume ratio of 2-ethoxyethanol / ethanol tantalum at 8:1. Then, stir the mixed solution at room temperature for 30 minutes. Then add 0.20 mol / L hydrochloric acid aqueous solution to the solution at room temperature to form the final solution. Subsequently, filter the solution through a 0.2 mm ultrafiltration membrane filter and let it stand for 16 hours for spin coating of the thin film. Spin coat the sol at 3000 rpm for 45 seconds, and then anneal it at 60 °C for 30 minutes to form the resistive switching layer 3.

[0041] Step 4: Use magnetron sputtering technology to deposit a layer of metal W on the resistive switching layer 3 to form the top electrode 4. The deposition technology is radio frequency magnetron sputtering. The initial vacuum degree is 5×10-4 Pa, the working gas is argon with a purity of 99.99%, the sputtering power is 160 W, the working gas pressure is 1.0 Pa, and the W thin film is obtained by sputtering deposition for 25 minutes to form the top electrode 4.

[0042] Example 2:

[0043] A method for preparing a resistive random access memory with adjustable operating voltage, the steps are as follows: Step 1: Clean the Ti / SiO2 / Si substrate 1;

[0044] Step 2: Deposit a Pt thin film by electron beam evaporation to form the bottom electrode 2. The specific deposition parameters are as follows: the vacuum degree is 5×10-4 Pa, the bombardment current is 150 mA, the substrate temperature is 180 °C, the substrate rotation speed is 6 r / s, and the electron beam voltage is 6 kV.

[0045] Step 3: Ethanol tantalum (Aldrich; 99.98%) is used as the precursor solution for Ta 2 O 5 . A WCl 6 (Aldrich 99.9%) solution is used as the W ion precursor solution for doping. This chloride solution is prepared by dissolving the corresponding WO 3It is prepared by dissolving in 0.22 mol / L hydrochloric acid aqueous solution, then carefully dried and dissolved in ethanol solution. Mix tantalum ethoxide, WCl 6 and 2-ethoxyethanol solutions, and keep the volume ratio of 2-ethoxyethanol / tantalum ethoxide at 9:1. Then, keep the mixed solution stirring at room temperature for 36 minutes. Then add 0.25 mol / L hydrochloric acid aqueous solution to the solution at room temperature to form the final solution. Subsequently, filter the solution through a 0.2 mm ultrafiltration membrane filter and let it stand for 16 hours for spin coating of the thin film. Spin coat the sol at 3300 rpm for 42 seconds, and then anneal it at 60 °C for 40 minutes to form the resistive switching layer 3.

[0046] Step 4: Deposit a layer of metal W on the resistive switching layer 3 using magnetron sputtering technology to form the top electrode 4. The deposition technology is radio frequency magnetron sputtering, the initial vacuum degree is 5×10-4 Pa, the working gas is argon with a purity of 99.99%, the sputtering power is 170 W, the working gas pressure is 1.0 Pa, and sputter deposit for 30 minutes to obtain a W thin film to form the top electrode 4.

[0047] Example 3:

[0048] A preparation method of a resistive random access memory with adjustable operating voltage, the steps are as follows: Step 1: Clean the Ti / SiO2 / Si substrate 1;

[0049] Step 2: Evaporate a layer of Pt thin film using electron beam evaporation to form the bottom electrode 2. The specific deposition parameters are: the vacuum degree is 5×10-4 Pa, the bombardment current is 150 mA, the substrate temperature is 180 °C, the substrate rotation speed is 6 r / s, and the electron beam voltage is 6 kV.

[0050] Step 3: Tantalum ethoxide (Aldrich; 99.98%) is used as the precursor solution of Ta 2 O 5 . The WCl 6 (Aldrich 99.9%) solution is used as the W ion precursor solution for doping. The chloride solution is prepared by dissolving the corresponding WO 3 in 0.24 mol / L hydrochloric acid aqueous solution, then carefully dried and dissolved in ethanol solution. Mix tantalum ethoxide, WCl 6 and 2-ethoxyethanol solutions, and keep the volume ratio of 2-ethoxyethanol / tantalum ethoxide at 10:1. Then, keep the mixed solution stirring at room temperature for 40 minutes. Then add 0.27 mol / L hydrochloric acid aqueous solution to the solution at room temperature to form the final solution. Subsequently, filter the solution through a 0.2 mm ultrafiltration membrane filter and let it stand for 16 hours for spin coating of the thin film. Spin coat the sol at 3600 rpm for 40 seconds, and then anneal it at 60 °C for 45 minutes to form the resistive switching layer 3.

[0051] Step 4: Use magnetron sputtering technology to deposit a layer of metal W on the resistive switching layer 3 to form the top electrode 4. The deposition technology is radio frequency magnetron sputtering. The initial vacuum degree is 5×10-4 Pa, the working gas is argon with a purity of 99.99%, the sputtering power is 180 W, the working gas pressure is 1.0 Pa, and the W thin film is obtained by sputtering deposition for 35 minutes to form the top electrode 4.

[0052] Example 4:

[0053] A preparation method of a resistive random access memory with adjustable operating voltage, the steps are as follows: Step 1: Clean the Ti / SiO2 / Si substrate 1;

[0054] Step 2: Use electron beam evaporation to deposit a layer of Pt thin film to form the bottom electrode 2. The specific deposition parameters are: the vacuum degree is 5×10-4 Pa, the bombardment current is 150 mA, the substrate temperature is 180 °C, the substrate rotation speed is 6 r / s, and the electron beam voltage is 6 kV.

[0055] Step 3: Tantalum ethoxide (Aldrich; 99.98%) is used as the precursor solution for Ta 2 O 5 The precursor solution of WCl 6 (Aldrich 99.9%) solution is used as the doped W ion precursor solution. The chloride solution is prepared by dissolving the corresponding WO 3 in an aqueous solution of 0.26 mol / L hydrochloric acid, then carefully dried and dissolved in an ethanol solution. Mix the three solutions of tantalum ethoxide, WCl 6 and 2-ethoxyethanol, and keep the volume ratio of 2-ethoxyethanol / tantalum ethoxide as 11:1. Then, keep the mixed solution stirring at room temperature for 40 minutes. Then add an aqueous solution of 0.28 mol / L hydrochloric acid to the solution at room temperature to form the final solution. Subsequently, filter the solution through a 0.2 mm ultrafiltration membrane filter and let it stand for 16 hours for spin coating of the thin film. Spin coat the sol at 4000 rpm for 35 seconds, and then anneal it at 60 °C for 50 minutes to form the resistive switching layer 3.

[0056] Step 4: Use magnetron sputtering technology to deposit a layer of metal W on the resistive switching layer 3 to form the top electrode 4. The deposition technology is radio frequency magnetron sputtering. The initial vacuum degree is 5×10-4 Pa, the working gas is argon with a purity of 99.99%, the sputtering power is 190 W, the working gas pressure is 1.0 Pa, and the W thin film is obtained by sputtering deposition for 45 minutes to form the top electrode 4.

[0057] Example 5:

[0058] A preparation method of a resistive random access memory with adjustable operating voltage, the steps are as follows: Step 1: Clean the Ti / SiO2 / Si substrate 1;

[0059] Step 2: Deposit a Pt thin film using electron beam evaporation to form the bottom electrode 2. The specific deposition parameters are as follows: the vacuum degree is 5×10-4 Pa, the bombardment current is 150 mA, the substrate temperature is 180 °C, the substrate rotation speed is 6 r / s, and the electron beam voltage is 6 kV.

[0060] Step 3: Tantalum ethoxide (Aldrich; 99.98%) is used as the precursor solution for Ta 2 O 5 . The WCl 6 (Aldrich 99.9%) solution is used as the W ion precursor solution for doping. This chloride solution is prepared by dissolving the corresponding WO 3 in 0.2 mol / L hydrochloric acid aqueous solution, then carefully dried and dissolved in ethanol solution. Mix the three solutions of tantalum ethoxide, WCl 6 , and 2-ethoxyethanol, and keep the volume ratio of 2-ethoxyethanol / tantalum ethoxide at 12:1. Then, keep the mixed solution stirring at room temperature for 45 minutes. Then add 0.30 mol / L hydrochloric acid aqueous solution to the solution at room temperature to form the final solution. Subsequently, filter the solution through a 0.2 mm ultrafiltration membrane filter and let it stand for 16 hours for thin film spin coating. Spin coat the sol at 4500 rpm for 30 seconds, and then anneal it at 60 °C for 60 minutes to form the resistive switching layer 3.

[0061] Step 4: Use magnetron sputtering technology to deposit a layer of metal W on the resistive switching layer 3 to form the top electrode 4. The deposition technology is radio frequency magnetron sputtering. The initial vacuum degree is 5×10-4 Pa, the working gas is argon with a purity of 99.99%, the sputtering power is 220 W, the working gas pressure is 1.0 Pa, and the W thin film is obtained by sputtering deposition for 40 minutes to form the top electrode 4.

[0062] Next, use the preparation methods disclosed in Examples 1 to 5 to fabricate the resistive random access memories (hereinafter referred to as Resistive Random Access Memory 1 to Resistive Random Access Memory 5) with adjustable operating voltage disclosed in this application as Figure 1 shown. The structural parameters of the resistive random access memories are as follows:

[0063] Resistive Random Access Memory 1:

[0064] The substrate, bottom electrode, resistive switching layer, and top electrode are arranged in sequence from bottom to top. Among them, the resistive switching layer is a Ta 2 O 5 thin film doped with W, with a thickness of 40 nm and a molar doping concentration of W of 1%; the top electrode and the bottom electrode are metal W and Pt respectively, the thickness of the bottom electrode is 10 nm, and the thickness of the top electrode is 100 nm; the substrate material is Ti / SiO 2 / Si.

[0065] Resistive random access memory two:

[0066] The substrate, bottom electrode, resistive switching layer, and top electrode are sequentially arranged from bottom to top. Among them, the resistive switching layer is Ta doped with W 2 O 5 thin film, with a thickness of 60 nm and a molar doping concentration of W of 1.04%; the top electrode and bottom electrode are metal W and Pt respectively, the thickness of the bottom electrode is 20 nm, and the thickness of the top electrode is 150 nm; the substrate material is Ti / SiO 2 / Si.

[0067] Resistive random access memory three:

[0068] The substrate, bottom electrode, resistive switching layer, and top electrode are sequentially arranged from bottom to top. Among them, the resistive switching layer is Ta doped with W 2 O 5 thin film, with a thickness of 80 nm and a molar doping concentration of W of 2.08%; the top electrode and bottom electrode are metal W and Pt respectively, the thickness of the bottom electrode is 30 nm, and the thickness of the top electrode is 200 nm; the substrate material is Ti / SiO 2 / Si.

[0069] Resistive random access memory four:

[0070] The substrate, bottom electrode, resistive switching layer, and top electrode are sequentially arranged from bottom to top. Among them, the resistive switching layer is Ta doped with W 2 O 5 thin film, with a thickness of 100 nm and a molar doping concentration of W of 4.17%; the top electrode and bottom electrode are metal W and Pt respectively, the thickness of the bottom electrode is 40 nm, and the thickness of the top electrode is 250 nm; the substrate material is Ti / SiO 2 / Si.

[0071] Resistive random access memory five:

[0072] The substrate, bottom electrode, resistive switching layer, and top electrode are sequentially arranged from bottom to top. Among them, the resistive switching layer is Ta doped with W 2 O 5 thin film, with a thickness of 120 nm and a molar doping concentration of W of 10%; the top electrode and bottom electrode are metal W and Pt respectively, the thickness of the bottom electrode is 50 nm, and the thickness of the top electrode is 300 nm; the substrate material is Ti / SiO 2 / Si.

[0073] Adopt the manufacturing method of Example 3 and fabricate an undoped resistive random access memory according to the structural parameters of resistive random access memory three to form a comparative example of resistive random access memory three. The difference is that in the resistive random access memory of the comparative example, the resistive switching layer 3 is an undoped Ta2O5 thin film prepared by sol-gel to form an undoped resistive random access memory.

[0074] The fabricated undoped resistive random access memory (RRAM) and doped RRAM were tested, and the test results are as Figure 2 and Figure 3 shown. The test results indicate that the forward resistance transition voltage of this RRAM is about 0.8 V, and the reverse resistance transition voltage is about -2 V.

[0075] The test results show that, compared with the undoped RRAM device, after doping the resistive switching layer Ta 2 O 5 with W, the forward and reverse resistance transition voltages both increase by about 0.5 V.

[0076] The first-principles calculation of the oxygen vacancy formation energy of Ta 2-x W x O 5 was carried out. The calculation model is a 4×2×3 supercell, which contains 96 Ta atoms and a total of 240 oxygen atoms. The calculation model is as Figure 4 shown. Figure 4 The small atoms represent oxygen atoms, the large atoms represent tantalum atoms, 3f represents that there are 3 Ta atoms bonded to oxygen atoms, and 2f represents that there are 2 Ta atoms bonded to oxygen atoms.

[0077] Table 1 (unit: eV)

[0078]

[0079] Table 1 shows the calculation results of the oxygen vacancy formation energy of Ta 2 O 5 and Ta 2-x W x O 5 where the doping concentration of the W element is 1.04%. The results in Table 1 show that after introducing the dopant W, the oxygen vacancy formation energies of vo-2f, vo-3f, and vo-in increase by 0.38 eV, 1.27 eV, and 1.44 eV respectively. Similarly, the oxygen vacancy formation energies of +1 valence and +2 valence also have a similar variation law. This indicates that after doping, the difficulty of forming Vo in the active layer Ta 2-x W x O 5 increases, which is consistent with the increase in the operating voltage of the RRAM device observed in the experiment.

[0080] The present invention also studied the influence relationship of the W element doping concentration on the oxygen vacancy formation. Figure 5 is Ta 2-x W x O 5Calculation results of the formation energy of oxygen vacancies varying with dopant concentration. After W doping, the formation energy of oxygen vacancies increases by 0.2 eV compared with that without doping. For example, when the W doping concentration is equal to 1.04%, the formation energy of VO-2f changes from 5.66 eV to 5.85 eV and approaches 5.81 eV after the doping concentration increases. W has 6 valence electrons, and W has 1 more valence electron than Ta. After W replaces Ta, the matrix will have 1 more valence electron, and there are enough valence electrons to bond with lattice oxygen. Therefore, it is difficult for lattice oxygen to break away from the lattice position and become free oxygen. Therefore, after W doping, the formation energy of oxygen vacancies increases.

[0081] The conductive channel is a microscopic channel with high conductivity formed by oxygen vacancies. Before the formation of the conductive channel, oxygen vacancies are randomly distributed in the resistive switching layer. The formation of the conductive channel depends on the movement or diffusion of oxygen vacancies. The energy required for oxygen vacancies to diffuse from one lattice oxygen position to an adjacent lattice oxygen position is the diffusion activation energy. The physical basis for the resistive random access memory to store data is that the resistance state of the resistive switching layer realizes high-resistance state and low-resistance state, corresponding to binary "0" and "1" respectively. The low-resistance state corresponds to the formation of a conductive channel in the resistive random access memory, and the high-resistance state corresponds to the disconnection of the conductive channel.

[0082] We 2-x W x O 5 carried out theoretical calculations on the diffusion barrier of oxygen vacancies in Figure 6 as shown. The diffusion path of oxygen vacancies is calculated according to 3f1-3f2-2f1-3f3. Figure 6 There are 4 doping concentrations shown, which are obtained by replacing 1, 2, 3, and 4 Ta atoms in the supercell with W atoms respectively, and the corresponding doping concentrations are 1.04%, 2.08%, 3.12%, and 4.17% respectively.

[0083] From the calculation results of the doping concentration of W element and the diffusion barrier ( Figure 6 ), it can be seen that after doping one W atom, the diffusion of oxygen vacancies increases significantly, and the diffusion barrier increases by more than 1 time compared with that without doping. However, as the doping concentration increases, the diffusion barrier gradually decreases. The diffusion barrier ranges from 0.2 to 1.2 eV within the studied doping concentration range.

[0084] From Figure 5 the defect formation results of 0-valent oxygen vacancies, it can be seen that the formation energy of defects remains almost unchanged with the doping concentration. Therefore, the following analysis mainly focuses on the defect diffusion barrier. The average values of the diffusion barriers of the diffusion paths at 4 doping concentrations in Figure 6 are statistically analyzed, and the results are shown in Figure 7As can be seen from the figure, the maximum value of the diffusion barrier appears at 1.04%, and the minimum value appears at the doping concentration of 2.08%. After the doping concentration exceeds 2.08%, the diffusion barrier gradually increases, but the increasing rate slows down. It can be seen that under the regulation of the doping concentration, the average diffusion barrier changes from 1.054 eV to 0.56 eV, changing by nearly 0.5 eV, achieving an obvious change in the diffusion barrier. Based on the above analysis, when the doping concentration is 2.08%, the minimum operating voltage will be obtained, and when it is 1.04% or higher than 4.17%, a larger operating voltage will be obtained.

[0085] Because of the hybridization between W and O, a strong adsorption effect is formed between W and O, making it difficult for O ions to detach, so the diffusion barrier increases compared with that of the undoped one. The hybridization between W and O atoms can be seen from Figure 8 the Ta shown in 2-x W x O 5 the results of the electronic density of states. In Figure 8 , in the region where the horizontal axis is -0.12, -1.17 eV, there is a strong hybridization between the d-orbital electrons of W atoms and the p-orbital electrons of O.

[0086] However, as the doping concentration increases, there will be excess electrons in the matrix. To maintain electrical neutrality, this electron may transfer to Ta or W, making Ta become Ta 4+ or W 5+ , but no matter which element it transfers to, it will make the ionic radii of these two elements larger, the unit cell expands, making the migration of oxygen ions easier, resulting in a decrease in the diffusion barrier. Therefore, as the doping concentration increases, the diffusion barrier gradually decreases.

[0087] In the resistive random access memory, the operating voltage of the device is directly related to the ease of oxygen vacancy diffusion, and the degree of oxygen vacancy diffusion is directly determined by the diffusion activation energy. Therefore, by regulating the diffusion activation energy, the purpose of controlling the operating voltage of the device can be achieved. The present invention achieves the purpose of regulating the diffusion activation energy of oxygen vacancies and realizes the regulation of the operating voltage by doping the resistive layer with W element.

[0088] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a resistive random access memory with adjustable operating voltage, the steps are as follows: Step 1, cleaning the Ti / SiO2 / Si substrate; Step 2, depositing a layer of Pt thin film by electron beam evaporation to form a bottom electrode; Step 3: Prepare a spin coating solution from tantalum ethoxide, WCl 6 and 2-ethoxyethanol, filter the solution through a 0.2 mm ultrafiltration membrane filter and let it stand for 16 hours to form a sol for thin film spin coating. Spin coat the sol at 3000 - 4500 rpm for 30 - 45 seconds, and then anneal it at 60 °C for 30 - 60 minutes to form a resistive switching layer, which is a Ta 2 O 5 thin film doped with W; Step 4, using magnetron sputtering technology to deposit a layer of metal W on the resistive layer to form a top electrode.

2. A preparation method of a resistive random access memory with adjustable operating voltage according to claim 1, characterized in that: In the third step, the preparation process of the spin-coating solution is as follows: tantalum ethoxide is used as the precursor solution for Ta 2 O 5 , and the WCl 6 solution is used as the W ion precursor solution for doping. Tantalum ethoxide, WCl 6 , and 2-ethoxyethanol are mixed, and the mixed solution is stirred at room temperature for 30 to 45 minutes. Then, an aqueous hydrochloric acid solution with a concentration of 0.20 to 0.30 mol / L is added to the solution at room temperature.

3. A preparation method of a resistive random access memory with adjustable operating voltage according to claim 2, characterized in that: Tungsten chloride solution is composed of the corresponding WO 3 prepared by dissolving in an aqueous hydrochloric acid solution of 0.2 - 0.3 mol / L, and then carefully dried and dissolved in an ethanol solution.

4. A preparation method of a resistive random access memory with adjustable operating voltage according to claim 2, characterized in that: In the mixed solution formed by mixing the three solutions, the volume ratio of 2-ethoxyethanol / tantalum ethoxide is maintained at 8-12:

1.

5. A preparation method of a resistive random access memory with adjustable operating voltage according to claim 1, characterized in that: In the step 4, the deposition technology is radio frequency magnetron sputtering, the initial vacuum degree is 5×10-4Pa, the working gas is argon with a purity of 99.99%, the sputtering power is 160-220W, the working pressure is 1.0Pa, and the W thin film is obtained by sputtering deposition for 25-45 minutes.

6. A resistive random access memory with adjustable operating voltage prepared by the method according to any one of claims 1-5, including a substrate, a bottom electrode, a resistive layer and a top electrode arranged in sequence from bottom to top, characterized in that: The resistive switching layer is Ta doped with W 2 O 5 thin film.

7. A resistive random access memory with adjustable operating voltage according to claim 6, characterized in that: The thickness of the resistive layer is 40nm-120nm.

8. A resistive random access memory with adjustable operating voltage according to claim 6, characterized in that: The top electrode and the bottom electrode are metal W and Pt respectively, the thickness of metal W is 100-300nm, and the thickness of metal Pt is 10-50nm.

9. A resistive random access memory with adjustable operating voltage according to claim 6, characterized in that: The resistive switching layer thin film is a W-doped Ta 2 O 5 thin film prepared by sol-gel method.

10. A resistive random access memory with adjustable operating voltage according to claim 6, characterized in that: The molar doping concentration of W in the resistive layer is 1%-10%.

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