Hafnium oxide-based RRAM with niobium oxide thermal enhancement layer and application of hafnium oxide-based RRAM

Abstract

The invention discloses a hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer and application, and belongs to the field of semiconductor memory devices. The hafnium oxide-based RRAM with the niobium oxide thermal enhancement layer sequentially comprises a top electrode, a niobium oxide layer, an HfO2 layer, an HfOx layer and a bottom electrode from top to bottom, and the niobium oxide thermal enhancement layer is inserted into the hafnium oxide-based RRAM, so that the forming voltage and the working temperature can be reduced, a storage window is also enlarged, and in the forming process, the storage temperature of the storage window can be increased. The growth direction of the conductive filament is effectively controlled; and the breaking point of the conductive filament can be effectively regulated and controlled in the reset process.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor memory devices, and particularly relates to a hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer and its applications. Background Art

[0002] The resistive random access memory (RRAM) has the advantages of small size, high operating speed, high durability, easy three-dimensional integration, etc. Therefore, RRAM has the greatest potential to replace the mainstream flash memory. After more than a decade of rapid development, RRAM has great development prospects. In recent years, resistive random access memories based on oxide resistive layers have been widely used in 3D integrated cross-point arrays, high-performance memory SCM, and analog components in disruptive technology architectures. Although hafnium oxide-based RRAM has good scalability and easy manufacturability, there are actually many problems, such as: the forming (soft breakdown of the dielectric layer by applying a high voltage to form a conductive filament and convert the device from the initial high-resistance state to an operable low-resistance state) voltage is too high, resulting in excessive power consumption, bringing additional complexity and cost to circuit design; the device stability is insufficient, and the performance of the device will degrade under high-temperature environments and long-term operation; the ability to maintain and precisely control different resistance levels is weak, thus greatly narrowing the application range; the durability is insufficient, and performance degradation may occur after a large number of write / erase cycles.

[0003] Therefore, a hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer is proposed. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer and its applications, and solve the problems in the prior art.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer includes, from top to bottom: a top electrode, a niobium oxide layer, an HfO2 layer, an HfO x layer, and a bottom electrode.

[0007] Further, the thicknesses of both the top electrode and the bottom electrode are 20 nm, the thickness of the HfO2 layer is 6 nm, and the thickness of the HfO x layer is 10.5 nm, and the thickness of the niobium oxide layer is 1.5 - 4.5 nm.

[0008] Further, the material of the top electrode is Pt.

[0009] Further, the material of the bottom electrode is Ti.

[0010] Furthermore, the material of the niobium oxide layer is niobium pentoxide.

[0011] A method for regulating the rupture position of the conductive filament in the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer as described above, characterized in that the thickness of the niobium oxide layer is adjusted.

[0012] The application of the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer as described above in a simulated neural synapse.

[0013] A storage device, comprising the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer as described above.

[0014] A computer, comprising the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer as described above.

[0015] A brain-like chip, comprising the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer as described above.

[0016] The beneficial effects of the present invention:

[0017] 1. By introducing a niobium oxide thermal enhancement layer into the hafnium oxide-based RRAM, the present invention significantly reduces the forming voltage. A lower forming voltage means less initial stress is applied to the material and structure, which is beneficial for reducing material damage or degradation that may be caused by high voltage, thereby improving the overall reliability and lifespan of the device. The fluctuation range of the forming voltage and the set / reset (the set process forms a conductive filament by applying a voltage to turn the device from a high-resistance state to a low-resistance state, while the reset process breaks the conductive filament by applying a reverse voltage to turn the device back from the low-resistance state to the high-resistance state) voltage values is smaller, which is more conducive to integrating stable circuits.

[0018] 2. By introducing a niobium oxide thermal enhancement layer into the hafnium oxide-based RRAM, under the oxygen vacancy conduction mechanism, the growth direction of the conductive filament and the rupture of the conductive filament during the reset process are regulated, which is beneficial for further exploring the potential of high-density storage in RRAM. By finely controlling the conductive filament, unnecessary stress and loss can be reduced, which helps to improve the service life and write / erase cycle times of the storage unit.

[0019] 3. The storage window of the RRAM of the present invention is increased; this means that the difference between the high and low resistance states is more obvious, making it easier to distinguish between these two states when reading data, thereby improving the accuracy and reliability of data reading. A larger storage window can provide better anti-noise performance. Even if there is a certain amount of noise or interference, due to the large difference between the two states, the storage state can still be accurately identified without error, reducing the possibility of misreading. The sensitivity requirements for the reading circuit can be appropriately reduced because it is not necessary to detect very precise voltages or currents to distinguish different storage states, and thus the corresponding circuit design can also be simplified, reducing the overall power consumption and cost.

[0020] 4. The operating temperature of the RRAM device of the present invention is greatly reduced. A lower operating temperature can reduce the risk of aging and damage of materials due to thermal stress. As the operating temperature decreases, the wear rate of the internal components of the RRAM device will also slow down, including not only the formation and breakage process of the conductive filaments, but also other physical properties that may be affected by temperature. The insertion of the niobium oxide thermal enhancement layer significantly reduces the energy loss caused by Joule heat, which means that more input energy is effectively used for the processes of data writing, reading, and erasing, rather than being converted into useless heat, thereby improving the energy efficiency ratio and reducing the overall power consumption. For electronic devices with increasing integration, effective heat dissipation is an important design consideration. Therefore, the reduction of the operating temperature of the RRAM device can reduce the requirements for the heat dissipation system, reduce the cost and volume of the heat dissipation system, and also increase the application range of the device.

[0021] 5. The improved hafnium oxide-based RRAM proposed by the present invention has fast read and write speeds and low latency characteristics, and can be widely applied to high-performance computing applications; in embedded systems, RRAM can be used to replace traditional flash memory, providing faster read and write speeds, higher reliability, and longer service life; with its superior low-power consumption characteristics, it can be applied in mobile devices; in neuromorphic applications, because of its adjustable conductivity, it can be used to simulate neural synapses, providing a hardware foundation for the continuous development of AI algorithms. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 (a) is a schematic diagram of the overall structure of the hafnium oxide-based RRAM of the present invention;

[0024] Figure 1(b) is a schematic diagram of the material composition of the device of the present invention;

[0025] Figure 2 They are respectively the pre-factor σ0 of the conductivity exponent and the activation energy E of electron conduction of the Nb2O5 thin film during the simulation process of the present invention ac And the relationship with the oxygen vacancy concentration in the thin film;

[0026] Figure 3 It is the thermal conductivity k of the Nb2O5 thin film th And the relationship with the oxygen vacancy concentration of the thin film;

[0027] Figure 4 It is a graph showing the test results of the forming voltage of the RRAM and the improved RRAM of the present invention;

[0028] Figure 5 It is a graph showing the test results of the operating temperature of the RRAM and the improved RRAM of the present invention;

[0029] Figure 6 It is a graph showing the test results of the storage window of the RRAM and the improved RRAM of the present invention;

[0030] Figure 7 It is a graph showing the control results of the growth direction of the conductive filament during the forming process of the RRAM and the improved RRAM of the present invention;

[0031] Figure 8 They are two devices Pt / HfO2 / HfO x / Ti and Pt / Nb2O5 / HfO2 / HfO x / Ti after 100 set and reset cycles of the voltage distribution box plot;

[0032] Figure 9 It is a graph showing the influence results of the rupture position of the conductive filament during the reset process of the improved RRAM with different thicknesses of the niobium oxide insertion layer of the present invention. Detailed implementation manners

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0034] Embodiment 1

[0035] Such as Figure 1As shown in (a) of x , the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer includes, from top to bottom: a top electrode (TE), a Nb2O5 layer, a HfO2 layer, a HfO x layer, and a bottom electrode (BE); wherein, the thicknesses of the top electrode and the bottom electrode are both 20 nm, the thickness of the niobium oxide layer is 1.5 nm, the thickness of the HfO2 layer is 6 nm, and the thickness of the HfO

[0036] layer is 10.5 nm; the material of the top electrode is Pt, and the material of the bottom electrode is Ti. Figure 1 As shown in (b) of

[0037] , niobium oxide (Nb2O5) with a high concentration of oxygen vacancies is inserted between the top electrode and hafnium oxide with a low concentration of oxygen vacancies (HfO2); in order to eliminate the influence of device area and size on the conductive filament, the areas of all devices and the thicknesses of the upper and lower electrodes are fixed. It can be seen from previous studies that the conductive filaments in the LRS exhibit weak metal behavior, which is due to the metal subbands formed by the high concentration of oxygen vacancies. Similarly, the conductive filaments in the LRS in this model correspond to the regions with a higher concentration of oxygen vacancies, thus locally conducting electricity to the metal electrodes. A bias voltage is applied to the top electrode (TE) of the device, while the bottom electrode (BE) is always grounded. In addition, the ambient temperature of all devices is set to room temperature.

[0038] In this embodiment, niobium oxide is specifically selected as niobium pentoxide (Nb2O5), while in other embodiments, niobium oxide can also be selected as NbO, NbO2, Nb2O3.

[0039] The present invention analyzes the model resistance mechanism using the Oxygen Vacancy Conductive Filament Model, which generally refers to the oxygen vacancy exchange between the high-resistance layer and the low-resistance layer - the oxygen vacancy redistribution in the oxynitride RRAM device. The occurrence of oxygen vacancy migration is affected by local density, temperature gradient, and local electric field. That is, a positive triangular wave is applied to the upper electrode of the RRAM. Due to the influence of various physical fields such as electric field and thermal field, oxygen vacancies will be attracted from the high-concentration oxide layer to the low-concentration oxide layer, and conductive filaments will be generated in a very short time. When the conductive filaments connect the top electrode and the high-oxygen-vacancy-concentration oxide layer, the device can switch from the OFF state to the ON state.

[0040]

[0041] In the formula, P is the atomic density, ρ is the material density, m mol is the molar mass, and N A is the Avogadro constant.

[0042] The molar mass of hafnium oxide is 210.49 g / mol -1 , so the atomic density P is 2.77×10 22 cm -3 , and the maximum doping concentration is 4.3% of the atomic density. Therefore, the maximum concentration of oxygen vacancies in the simulation is 1.2×10 21 cm -3 . Similarly, the maximum concentration of oxygen vacancies in niobium oxide in the simulation is 4.5×10 21 cm -3 .

[0043] The conductivity of the oxide layer is related to the changes in the oxygen vacancy concentration, temperature (T), electric field (E), and conductivity (σ):

[0044] σ = σ0(n D )exp(-E ac (n D ) / kT)+σ PF (E,T) (2)

[0045] where σ0 represents a factor before the conductivity exponent, and E ac represents the activation energy of electron conduction; σ PF (E,T) represents the Poole–Frenkel conduction term:

[0046]

[0047] The pre-exponential factor and the conductivity activation energy are functions of the oxygen vacancy concentration (Nb2O5). Figure 2 In (a), it is a function of the pre-exponential factor and the oxygen vacancy concentration. It can be seen that when the oxygen vacancy concentration is 0 cm -3 , σ0 is 0 S / m; when the oxygen vacancy concentration is 4.5×10 21 cm -3 , σ0 is 5×10 5 S / m; Figure 2 In (b), it is a function of the conductivity activation energy and the oxygen vacancy concentration. It can be seen that when the oxygen vacancy concentration is 0 cm -3 , E ac is 0.048 eV; when the oxygen vacancy concentration is 1.5×10 21 cm -3 , E ac is 0.01 eV; when the oxygen vacancy concentration is 4.5×10 21 cm -3 , E ac is 0.01 eV.

[0048] Based on the oxygen vacancy transport drift-diffusion equation, the electrical transport current continuity equation, and the Fourier equation for Joule heating, by coupling the above three components and self-consistently solving the above three partial differential equations (PDEs), a complete oxide-based switching process can be obtained.

[0049] ① Oxygen vacancy migration equation

[0050]

[0051] where and v nD represent the diffusion flux and drift flux terms. represents the Soret diffusion flux, where S represents the Soret coefficient (S = -E a / kT 2 ). Since the diffusion constant varies at different temperatures, Soret diffusion can be used to explain the movement of particles along the temperature gradient. Due to the increase in the oxygen ion diffusivity at higher temperatures, this part of the simulation illustrates the tendency of oxygen vacancies to flow towards the region with higher temperature. The generation and recombination rates of oxygen vacancies are represented by G and R respectively:

[0052]

[0053] The diffusion coefficient (D) of ions is temperature-dependent and satisfies the Arrhenius equation:

[0054]

[0055] v also satisfies the Arrhenius equation:

[0056]

[0057] where E b is the activation energy for oxygen vacancy hopping, b is the minimum lattice size at splitting, E c is the relaxation energy during the recombination process, a is the effective jump distance, f is the attempt escape frequency, E a is the diffusion barrier, k is the Boltzmann constant, T is the temperature, and q is the elementary charge.

[0058] ② Electrical transport current continuity equation

[0059]

[0060] where σ is the electrical conductivity, defined as: where σ0 is the pre-exponential factor, ψ is the electric potential, and E ac is the activation energy.

[0061] ③ Fourier equation for Joule heating

[0062]

[0063] Among them, k th is the thermal conductivity, J is the current density, and E is the electric field. The relationship between the thermal conductivity of Nb2O5 and the oxygen vacancy concentration is as Figure 3 shown. It can be seen from Figure 3 that when the oxygen vacancy concentration is 0 cm -3 , k th is 0.12 W m -1 k -1 ; when the oxygen vacancy concentration is 4.5×10 21 cm -3 , k th is 53.7 W m -1 k -1 . Among them, the dielectric and electrode material parameters are shown in Table 1:

[0064] Table 1 Material parameters used in the model

[0065]

[0066] Example 2

[0067] In this example, the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer in Example 1 is experimentally tested;

[0068] Among them, the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer in Example 1 is used as the improved RRAM; the RRAM without a niobium oxide layer is used as the original RRAM. The original RRAM includes, from top to bottom: a top electrode (20 nm), a HfO2 layer (6 nm), a HfO x layer (12 nm), and a bottom electrode (20 nm), and the top electrode material is Pt, and the bottom electrode material is Ti.

[0069] 1) Conduct a comparative test on the forming voltage of the improved RRAM;

[0070] The test process is as follows: Apply triangular wave voltages with different amplitudes from small to large to the top electrode until the RRAM completes the forming process.

[0071] The test results are as Figure 4 shown. It can be seen that the forming voltage of the original RRAM is 6.7 V. After inserting the niobium oxide (Nb2O5) layer, the forming voltage of the device is reduced to 4.2 V; it can be concluded from this that the addition of the niobium oxide thermal enhancement layer can reduce the forming voltage of the RRAM device.

[0072] 2) Conduct a comparative test on the operating temperature of the improved RRAM;

[0073] The testing process is as follows: Apply a triangular wave scanning voltage with an amplitude of 4.2 V and a period of 20 ms to the Pt top electrode.

[0074] The test results are as Figure 5 shown. It can be seen that the inserted niobium oxide acts as a thermal enhancement layer. Compared with hafnium oxide, niobium oxide has a lower thermal conductivity, which can effectively prevent heat loss during the forming process. The improved RRAM device is more likely to obtain sufficient heat, thus greatly reducing the forming voltage. The maximum forming temperature of the improved RRAM device is about 1000 K lower than that of the original RRAM device.

[0075] 3) Conduct a comparative test on the storage window of the improved RRAM;

[0076] The testing process is as follows: Apply a triangular wave with an amplitude of 1.1 V and a period of 3 ms to the Ti bottom electrode to make the device complete the reset process; after the reset process is completed, continue to apply a triangular wave with an amplitude of -1.15 V and a period of 3 ms to the Ti bottom electrode to make the device complete the set process;

[0077] The test results are as Figure 6 shown. It can be seen that the HRS (high resistance state caused by the breakage of the conductive filament) of the two devices is approximately (≈10^7 Ω). For the LRS (low resistance state caused by the formation of the conductive filament), the original RRAM device is ≈10^5 Ω, and the improved RRAM device is ≈10^2 Ω. It is analyzed that the improved RRAM has a larger storage window, further improving the accuracy of device application.

[0078] 4) Test the control of the growth direction of the conductive filament during the forming process of the improved RRAM;

[0079] The testing process is as follows: At the initial high resistance state of the devices Pt / HfO2 / HfO x / Ti and Pt / Nb2O5 / HfO2 / HfO x / Ti, apply the corresponding forming voltage to make the devices complete the forming process. During the simulation process, solve the three partial differential equations described above, and the formation state diagram of each transient of the conductive filament during the forming process can be drawn according to the calculation results.

[0080] Figure 7 (a)-(d) in demonstrates the dynamic process of the oxygen vacancy concentration distribution during the formation of the conductive filament in the device Pt / HfO2 / HfO x / Ti during the forming process; it can be seen that in the switching layer of the original hafnium oxide RRAM device, the conductive filament starts from the high oxygen vacancy concentration region (HfOx ) It grows unidirectionally towards the region with a low oxygen vacancy concentration (HfO2). As the voltage increases, oxygen vacancies continuously accumulate, and finally a conical conductive filament is formed to connect the top electrode and the bottom electrode, and the device switches to the conductive state.

[0081] Figure 7 (e)-(h) in it demonstrate the dynamic process of the oxygen vacancy concentration distribution during the formation of the conductive filament in the device Pt / Nb2O5 / HfO2 / HfO x / Ti; It can be seen that in the improved RRAM device, as the applied voltage increases, oxygen vacancies diffuse from the bilateral high-concentration regions (Nb2O5 and HfO x ) to the low-concentration region (HfO2) respectively, and connect in the HfO2 region to make the device in the LRS. Finally, a conductive filament with a hourglass shape is formed in the switching layer.

[0082] In summary, it can be concluded that the improved RRAM device can effectively control the growth direction of the conductive filament during the forming process.

[0083] 5) During the set / reset process of the improved RRAM, the stability of the device is tested;

[0084] The test process is as follows: After the device Pt / Nb2O5 / HfO2 / HfO x / Ti completes the forming process, triangular wave voltages with different polarities are continuously applied to the bottom electrode to make the device complete 100 reset / set cycles, and the reset and set voltages for 100 times are respectively counted. The device Pt / HfO2 / HfO x / Ti also performs the above operations as a control experiment.

[0085] The test results are as Figure 8 shown, Figure 8 (a) in it is the box plot of the set voltage distribution in 100 set and reset cycles of the two devices Pt / HfO2 / HfO x / Ti and Pt / Nb2O5 / HfO2 / HfO x / Ti. Figure 8 (b) in it is the box plot of the reset voltage distribution in 100 set and reset cycles of the two devices Pt / HfO2 / HfO x / Ti and Pt / Nb2O5 / HfO2 / HfO x / Ti.

[0086] Figure 8 In it, D1 represents Pt / HfO2 / HfO x / Ti, D2 represents Pt / Nb2O5 / HfO2 / HfO x / Ti. The box plots of the voltage distributions during 100 set and reset cycles of the two devices are respectively shown in the figure. It can be seen that: after 100 cycles, the average reset voltage of the improved device D2 is 1.00 V, and the average reset voltage of device D1 is 1.36 V; correspondingly, the average set voltage of device D2 is -1.1 V, and the average set voltage of device D is -1.5 V; the fluctuation ranges of both the set voltage and the reset voltage of device D2 are smaller than those of device D1. Therefore, the improved device has better stability.

[0087] 6) Conduct experimental research on the influence of different thicknesses of niobium oxide layers on RRAM devices;

[0088] As Figure 9 shown, in order to study the influence of the thickness of the inserted niobium oxide layer on the device, while keeping other parameters of the device unchanged, the thickness of the Nb2O5 thin film was changed, and a variable experiment was carried out (where the thicknesses of the Nb2O5 thin film were respectively selected as 1.5 nm, 2.5 nm, 3.5 nm, and 4.5 nm). Voltages were respectively applied to make each device complete the forming and reset processes, and the fracture positions of the conductive filaments during the reset process were analyzed.

[0089] It can be seen that during the reset process, it can be found that as the thickness of the inserted layer increases, the initial fracture point of the conductive filament gets closer and closer to the Nb2O5 / HfO2 interface, and the distance between the initial fracture point and the interface gets smaller and smaller, as Figure 9 shown. The Nb2O5 TEL layer concentrates heat in a tiny area near the Nb2O5 / HfO2 interface layer to break the conductive filament. Therefore, the fracture position of the conductive filament can be regulated by changing the thickness of the inserted niobium oxide layer.

[0090] In the description of this specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0091] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer, characterized in that, From top to bottom, it successively includes: a top electrode, a niobium oxide layer, a HfO2 layer, a HfO x layer, and a bottom electrode.

2. The hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to claim 1, characterized in that, The thicknesses of both the top electrode and the bottom electrode are 20 nm, the thickness of the HfO2 layer is 6 nm, and the thickness of the HfO x layer is 10.5 nm. The thickness of the niobium oxide layer is 1.5 - 4.5 nm.

3. The hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to claim 1, wherein The material of the top electrode is Pt.

4. The hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to claim 1, characterized in that, The material of the bottom electrode is Ti.

5. The hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to claim 1, wherein The material of the niobium oxide layer is niobium pentoxide.

6. A method for regulating the rupture position of the conductive filament of the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to any one of claims 1-5, characterized in that, Adjust the thickness of the niobium oxide layer.

7. Application of the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to any one of claims 1-5 in a simulated neural synapse.

8. A storage device, characterized in that, Comprising the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to any one of claims 1-5.

9. A computer, characterized in that, Comprising the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to any one of claims 1-5.

10. A brain-like chip, characterized in that, Comprising the hafnium oxide-based RRAM with a niobium oxide thermal enhancement layer according to any one of claims 1-5.

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