Tantalum-doped hafnium dioxide ferroelectric film, preparation method and application thereof

Abstract

The present invention discloses a tantalum-doped hafnium dioxide ferroelectric film, its preparation method and application. Ta metal target and HfO2 ceramic target are used in a multi-target co-magnetron sputtering device. By controlling the sputtering power, Ta:HfO2 films with different Ta doping ratios are obtained. In addition, by adjusting the sputtering power and the working gas Ar:O2 ratio, the residual polarization intensity P of the Ta:HfO2 film can be adjusted. r Can reach 100 μC / cm 2 , a 4-10-fold improvement compared to data reported in the literature. This method, applied to biomimetic synaptic devices, achieved the ability to switch between long-term potentiation and inhibition by controlling the oxygen flow during functional layer growth, adjusting the width of electrical pulses during synaptic testing, and varying the value of an external series resistor. This invention broadens the range of materials available for the dielectric layer of biomimetic synaptic devices, and the proposed synaptic device structure is simple and stable, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the field of ferroelectric film preparation and design, and in particular relates to a tantalum-doped hafnium dioxide ferroelectric film, a preparation method and application thereof. Background Art

[0002] Ferroelectric memory is one of the strong contenders for the next generation of non-volatile memory due to its advantages such as non-volatility, low power consumption, and fast read and write speed. To date, large-scale ferroelectric memories are based on traditional ferroelectric thin film materials. However, the poor compatibility of traditional ferroelectric materials with standard CMOS processes, environmental pollution, and difficulty in miniaturization have restricted the development of ferroelectric devices. In 2011, the advent of Si-doped HfO2 ferroelectric thin films ushered in a new era of HfO2 ferroelectric research. Compared with traditional ferroelectric materials, HfO2-based ferroelectric thin films have the following advantages: (1) simple composition and no toxic elements; (2) nanometer-sized (1-10nm) HfO2 thin films still have good electrical properties, thermal stability and ferroelectric properties; (3) compatible with advanced CMOS semiconductor processes; (4) large coercive field and high Curie temperature. It can be seen that the excellent ferroelectric properties of HfO2 thin films will be widely used in integrated electronic devices and other aspects. Therefore, it is of great significance to study this new type of HfO2 ferroelectric material.

[0003] From the HfO2 phase diagram, we can see that it has three stable crystal structures: monoclinic phase, tetragonal phase and cubic phase. At room temperature and pressure, HfO2 often exists in the monoclinic phase (P21 / c). When the temperature rises to above 1700 °C, the monoclinic phase transforms into the tetragonal phase, and when it rises to above 2600 °C, the tetragonal phase transforms into the cubic phase. The above three crystal phases are all centrosymmetric and do not have macroscopic ferroelectric properties. The ferroelectricity of HfO2 material mainly comes from a metastable crystal structure with non-centrosymmetry-the orthorhombic phase, with a space group of Pca21. The ferroelectric performance of HfO2 is best only when it obtains a specific orthorhombic phase. At present, HfO2 ferroelectric thin films are generally obtained by doping 2+ / 3+ elements, such as La, Y, Sc, Gd, Sr, Al, Ga, etc., and low-valence elements (acceptors) replace Hf 4+This leads to valence imbalance, which in turn reduces charge loss by increasing the oxygen vacancy concentration. While increasing the oxygen vacancy concentration increases the proportion of the orthorhombic phase and enhances ferroelectric properties, it also compromises the stability of ferroelectric devices. Therefore, for the long-term development of HfO2-based ferroelectric thin films, selecting appropriate high-valence element doping methods to achieve stable ferroelectric properties while reducing the oxygen vacancy concentration is essential. Furthermore, the preparation of HfO2-based ferroelectric thin films has a significant disadvantage: high-temperature annealing. Currently reported annealing temperatures are generally between 700 and 1000°C. Ferroelectric capacitors in semiconductor chips are not suitable for high-temperature annealing, with a typical thermal budget in the range of 400 to 600°C. Therefore, finding a suitable preparation method that fundamentally reduces the thermal budget is key to expanding the application range of HfO2.

[0004] As the scale of integrated circuits approaches physical limits, further improvements in computer performance inevitably require new computer architectures. Brain-inspired computing is a key area of integrated circuit development in the post-Moore era. Developing artificial synaptic devices that mimic ideal synaptic behavior is key to building brain-inspired computing chips with neuron-synapse-neuron connections.

[0005] Ferroelectric synaptic devices have two typical structures: two-terminal and three-terminal. In addition to effectively mimicking the functions of biological synapses, ferroelectric synaptic devices also offer advantages such as zero loss, low power consumption, and high operating speed. At the application level, research on neural networks based on ferroelectric synapses has made a series of advances in image recognition. Furthermore, ferroelectric synapses have also been applied to tactile and visual bionics. Therefore, research on ferroelectric synaptic devices is key to building low-energy and efficient brain-inspired intelligent networks and improving computer performance. Although research on ferroelectric synapses has made rich and instructive progress, the ferroelectric materials used in synaptic devices are mainly traditional ferroelectric materials. HfO2 ferroelectric synaptic devices are still in the experimental verification stage, and research on optimizing doping elements and regulating synaptic performance presents significant challenges, which is also the focus of future research on HfO2 ferroelectric synapses. Summary of the Invention

[0006] HfO2 ferroelectric thin films offer advantages over traditional ferroelectric materials and offer enormous potential for application. However, the stabilization and improvement of their ferroelectric properties, combined with the reduction of their thermal budget, have been bottlenecks restricting their application. As a new material in the ferroelectric research field that has only recently gained attention, HfO2 research is still underdeveloped, and more effort is needed to further develop its fundamental research. To address these issues, the present invention provides a tantalum-doped hafnium dioxide ferroelectric thin film and a method for preparing the same. This method utilizes a multi-target co-magnetron sputtering system to introduce Ta doping, thereby improving ferroelectric performance while reducing the thermal budget.

[0007] Specifically, the present invention adopts the following technical solutions:

[0008] A method for preparing a tantalum-doped hafnium dioxide (Ta:HfO2) ferroelectric thin film comprises the following steps:

[0009] (1) Prepare the substrate and clean and dry it;

[0010] (2) sputtering or evaporating a Ti layer on the substrate, and then sputtering or evaporating a Pt bottom electrode on the Ti layer;

[0011] (3) Preparation of Ta:HfO2 on Pt bottom electrode by co-magnetron sputtering: Place the substrate and target (Ta metal target, HfO2 ceramic target) into a vacuum chamber;

[0012] (4) Evacuate to the target vacuum degree and heat the substrate to the target temperature;

[0013] (5) Adjust the flow of working gases Ar and O2 and control the vacuum valve to achieve the working pressure;

[0014] (6) Set the sputtering power of the two targets respectively;

[0015] (7) Start co-sputtering.

[0016] Furthermore, the sputtering process parameters of the present invention are as follows: the back vacuum of the vacuum chamber is less than 10 -4 Pa, substrate heating temperature 300 ~ 500 ℃, Ar gas flow rate is 50 ~ 120sccm, O2 gas flow rate is 0sccm ~ 30sccm, HfO2 target RF sputtering power is 50 ~ 100W, Ta target DC sputtering power is 4W ~ 10W, Ar gas and O2 gas mixed gas working pressure is 0.8 ~ 1.2Pa, by controlling the sputtering time, the thickness of the Ta:HfO2 film is obtained to be 20 ~ 100nm.

[0017] Furthermore, by adjusting the sputtering power and changing the molar percentage of Ta doping, a Ta:HfO2 film with an orthorhombic phase is obtained.

[0018] Furthermore, based on the growth parameters of the orthorhombic phase Ta:HfO2 film, the Ar:O2 ratio of the working gas in the sputtering deposition process is regulated. The Ar gas flow rate can be fixed and the O2 flow rate can be changed to achieve the purpose of controlling the oxygen-related defects in the Ta:HfO2 ferroelectric film and improving the ferroelectric properties.

[0019] According to another aspect of the present invention, there is provided an application of a Ta:HfO2 ferroelectric thin film in the preparation of a biomimetic synaptic device, wherein the capacitor structure comprises, from bottom to top, a substrate - a bottom electrode - a ferroelectric thin film - a top electrode, wherein the bottom electrode is a Pt metal layer obtained by thermal evaporation or sputtering, the ferroelectric thin film functional layer is Ta:HfO2 prepared by the above process, the top electrode Pt is obtained by sputtering, and the top electrode is preferably a dot electrode.

[0020] Furthermore, the top electrode of the present invention adopts radio frequency sputtering, the target material is Pt, the deposition temperature is room temperature, the working gas is Ar gas, the flow rate is 50sccm~120sccm, the sputtering power is 40W~100W, the top electrode style and size are controlled by the mask, the thickness is controlled by the sputtering time, and the top electrode thickness is 30~60nm.

[0021] Furthermore, by controlling the O2 flow during the growth of the functional layer, adjusting the width of the electrical pulse in the synaptic test, and changing the resistance value of the external series resistor, the transition regulation of long-term potentiation and inhibition of the synaptic device can be achieved.

[0022] The control method specifically includes:

[0023] During the process of preparing the functional layer, the ratio of Ar gas to O2 gas in the magnetron sputtering working gas is controlled. For example, the Ar flux is fixed at 100 sccm, and the O2 flux is changed. When the O2 flux is small (5 sccm or 10 sccm), the synaptic device prepared based on the functional layer has long-term inhibition properties. Conversely, when the oxygen flux is large (20 sccm), the synaptic device prepared based on the functional layer has long-term potentiation properties.

[0024] Furthermore, the control method further comprises:

[0025] An electrical excitation method is adopted, specifically: by grounding the bottom electrode of the neural synaptic device based on Ta:HfO2 ferroelectric film, and adjusting the width of the top electrode input pulse (1µs or 1ms), the controllability of the long-term inhibition or long-term enhancement of the synaptic device is simulated.

[0026] Furthermore, the control method further comprises:

[0027] By changing the size of the series resistance of the external circuit of the synaptic device, when the external resistance is small (10kΩ), the Ta:HfO2 ferroelectric thin film synaptic device exhibits long-term depression plasticity. On the contrary, when the external resistance is large (39kΩ or 100kΩ), the synaptic device exhibits long-term enhancement properties.

[0028] The beneficial effects that can be achieved by the present invention are:

[0029] The present invention utilizes a multi-target co-sputtering system to produce HfO2-based ferroelectric thin films with excellent ferroelectric properties, expanding the range of doping elements. Furthermore, through further improvements to the preparation method, the film's remnant polarization strength can be significantly increased, reversing the technical prejudice that multiphase HfO2-based ferroelectric films have low remnant polarization strength. The ferroelectric thin films of the present invention can be produced over large areas without requiring subsequent high-temperature annealing, reversing the perception that HfO2-based ferroelectric films require high-temperature rapid annealing and providing a solution to the high thermal budget issues encountered in practical applications.

[0030] Building on the structure of traditional biomimetic neural synaptic devices, this invention innovatively proposes a Ta:HfO2-based functional layer for synaptic devices, broadening the range of options for ferroelectric synaptic device functional layers. Furthermore, by regulating the oxygen flow rate during functional layer growth, the width of the electrical excitation pulses used in synaptic simulation testing, and an external series resistor, the present invention achieves controllable transitions between long-term inhibition and enhancement properties in the synaptic device. The functional layer is produced via magnetron sputtering, resulting in a simple preparation process, high reliability, and the potential for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of Ta:HfO2-based ferroelectric thin film deposition in the present invention;

[0032] Figure 2 Schematic diagram of the structure of Ta:HfO2-based ferroelectric thin film capacitor;

[0033] Figure 3 XRD curves of Ta:HfO2 thin films at different Ta target sputtering powers provided by the examples of the present invention;

[0034] Figure 4 PV curves of Ta:HfO2 thin films with different oxygen flow rates provided by the examples of the present invention;

[0035] Figure 5 Schematic diagram of the effect of changes in oxygen flux in a functional layer on a synaptic device according to a specific embodiment of the present invention;

[0036] Figure 6 This is a test result of the effect of pulse width change on a synaptic device provided by a specific embodiment of the present invention;

[0037] Figure 7 Schematic diagram of the effect of an external resistor on a synaptic device according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0038] The following provides a further detailed description of the present invention in conjunction with the accompanying drawings. The scientific terms used in the description have the meanings commonly understood in the relevant disciplines. The substrate in the following embodiments is a dry-oxidized Si wafer, wherein the Si wafer is B-doped (1.2-1.5 mol%), p-type conductive single crystal, has a crystal orientation of (100), a resistivity of 2-4 Ω.cm, and an oxide layer SiO2 thickness of 300 nm. Specific embodiments are as follows:

[0039] Example 1

[0040] A Ti layer with a thickness of about 20 nm is sputtered or evaporated on the substrate (oxidized Si wafer), and then a bottom electrode Pt is sputtered or evaporated on the Ti layer. The Pt thickness is 50 nm. The deposition process is as follows: Figure 1 As shown in the figure, Ta:HfO2 thin films were deposited using a multi-target co-magnetron sputtering system. The specific steps were as follows: placing the substrate and targets (Ta target, HfO2 target) into a vacuum chamber; evacuating the chamber to a target vacuum degree of 5.0×10 -5 Pa, then heat the substrate to the target temperature of 500℃; adjust the working gas Ar gas flow rate to 100sccm, the O2 gas flow rate to 5sccm, and control the working gas pressure in the chamber to be constant at 1.0Pa by adjusting the vacuum valve; adjust the Ta target DC sputtering power to 4W, and the HfO2 RF sputtering power to 70W; start co-sputtering, control the sputtering time, and obtain a Ta:HfO2 film with a thickness of 70nm. The crystal structure of the obtained film was characterized, and the XRD test results are shown as follows Figure 3 .

[0041] Example 2

[0042] A Ti layer with a thickness of approximately 20 nm was sputtered or evaporated on the substrate (oxidized Si wafer), and then a bottom electrode Pt was sputtered or evaporated on the Ti layer. The Pt thickness was 50 nm. Ta:HfO2 thin films were deposited using a multi-target co-magnetron sputtering system. The specific steps were as follows: the substrate and targets (Ta target, HfO2 target) were placed in a vacuum chamber; the vacuum was evacuated to a target vacuum of 5.0×10 -5 Pa, then heat the substrate to the target temperature of 500℃; adjust the working gas Ar gas flow rate to 100sccm, the O2 gas flow rate to 5sccm, and control the working pressure in the chamber to be constant at 1.0Pa by adjusting the vacuum valve; adjust the Ta target DC sputtering power to 10W, and the HfO2 RF sputtering power to 70W; start co-sputtering, control the sputtering time, and obtain a Ta:HfO2 film with a thickness of 70nm. The obtained film was characterized for crystal structure, and the XRD test results are shown as follows Figure 3 .

[0043] Example 3

[0044] A Ti layer with a thickness of approximately 20 nm was sputtered or evaporated on the substrate (oxidized Si wafer), and then a bottom electrode Pt was sputtered or evaporated on the Ti layer. The Pt thickness was 50 nm. Ta:HfO2 thin films were deposited using a multi-target co-magnetron sputtering system. The specific steps were as follows: the substrate and targets (Ta target, HfO2 target) were placed in a vacuum chamber; the vacuum was evacuated to a target vacuum of 5.0×10 -5 Pa, then heat the substrate to the target temperature of 500℃; adjust the working gas Ar gas flow rate to 100sccm, the O2 gas flow rate to 5sccm, and control the working pressure in the chamber to be constant at 1.0Pa by adjusting the vacuum valve; adjust the Ta target DC sputtering power to 6W, and the HfO2 RF sputtering power to 70W; start co-sputtering, control the sputtering time, and obtain a Ta:HfO2 film with a thickness of 70nm. The crystal structure of the obtained film was characterized, and the XRD test results are shown as follows Figure 3 In order to obtain the macroscopic ferroelectric properties of Ta:HfO2, this embodiment uses radio frequency sputtering deposition combined with an electrode mask to prepare a Pt top electrode. The target material is Pt, the deposition temperature is room temperature, the working gas is Ar gas, the flow rate is 100 sccm, the sputtering power is 50W, the electrode diameter is 100µm, and the thickness is 50nm. The ferroelectric test performance at different voltages is obtained using a macroscopic ferroelectric tester. The test results are shown in the figure. Figure 4 .

[0045] Example 4

[0046] A Ti layer with a thickness of approximately 20 nm was sputtered or evaporated on the substrate (oxidized Si wafer), and then a bottom electrode Pt was sputtered or evaporated on the Ti layer. The Pt thickness was 50 nm. Ta:HfO2 thin films were deposited using a multi-target co-magnetron sputtering system. The specific steps were as follows: the substrate and targets (Ta target, HfO2 target) were placed in a vacuum chamber; the vacuum was evacuated to a target vacuum of 5.0×10 -5 Pa, and then heat the substrate to the target temperature of 500 ° C; adjust the working gas Ar gas flow rate to 100 sccm, the O2 gas flow rate to 0 sccm, and control the working gas pressure in the chamber to be constant at 1.0 Pa by adjusting the vacuum valve; adjust the Ta target DC sputtering power to 6W, and the HfO2 RF sputtering power to 70W; start co-sputtering, control the sputtering time, and obtain a Ta:HfO2 film with a thickness of 70nm. In order to obtain the macroscopic ferroelectric properties of Ta:HfO2, this embodiment uses RF sputtering deposition and combines it with an electrode mask to prepare a Pt top electrode, the target material is Pt, the deposition temperature is room temperature, the working gas Ar gas, the flow rate is 100 sccm, the sputtering power is 50W, the electrode diameter is 100µm, and the thickness is 50nm. The ferroelectric test performance under different voltages is obtained using a macroscopic ferroelectric tester, and the test results are as follows: Figure 4 .

[0047] Example 5

[0048] A Ti layer with a thickness of approximately 20 nm was sputtered or evaporated on the substrate (oxidized Si wafer), and then a bottom electrode Pt was sputtered or evaporated on the Ti layer. The Pt thickness was 50 nm. Ta:HfO2 thin films were deposited using a multi-target co-magnetron sputtering system. The specific steps were as follows: the substrate and targets (Ta target, HfO2 target) were placed in a vacuum chamber; the vacuum was evacuated to a target vacuum of 5.0×10 -5 Pa, and then heat the substrate to the target temperature of 500 ° C; adjust the working gas Ar gas flow rate to 100 sccm, the O2 gas flow rate to 10 sccm, and control the working gas pressure in the chamber to be constant at 1.0 Pa by adjusting the vacuum valve; adjust the Ta target DC sputtering power to 6W, and the HfO2 RF sputtering power to 70W; start co-sputtering, control the sputtering time, and obtain a Ta:HfO2 film with a thickness of 70nm. In order to obtain the macroscopic ferroelectric properties of Ta:HfO2, this embodiment uses RF sputtering deposition and combines it with an electrode mask to prepare a Pt top electrode, the target material is Pt, the deposition temperature is room temperature, the working gas Ar gas, the flow rate is 100 sccm, the sputtering power is 50W, the electrode diameter is 100µm, and the thickness is 50nm. The ferroelectric test performance under different voltages is obtained using a macroscopic ferroelectric tester, and the test results are as follows: Figure 4 .

[0049] Example 6

[0050] A Ti layer with a thickness of approximately 20 nm was sputtered or evaporated on the substrate (oxidized Si wafer), and then a bottom electrode Pt was sputtered or evaporated on the Ti layer. The Pt thickness was 50 nm. Ta:HfO2 thin films were deposited using a multi-target co-magnetron sputtering system. The specific steps were as follows: the substrate and targets (Ta target, HfO2 target) were placed in a vacuum chamber; the vacuum was evacuated to a target vacuum of 5.0×10 -5 Pa, and then heat the substrate to the target temperature of 500 ° C; adjust the working gas Ar gas flow rate to 100 sccm, the O2 gas flow rate to 15 sccm, and control the working gas pressure in the chamber to be constant at 1.0 Pa by adjusting the vacuum valve; adjust the Ta target DC sputtering power to 6W, and the HfO2 RF sputtering power to 70W; start co-sputtering, control the sputtering time, and obtain a Ta:HfO2 film with a thickness of 70nm. In order to obtain the macroscopic ferroelectric properties of Ta:HfO2, this embodiment uses RF sputtering deposition and combines it with an electrode mask to prepare a Pt top electrode, the target material is Pt, the deposition temperature is room temperature, the working gas Ar gas, the flow rate is 100 sccm, the sputtering power is 50W, the electrode diameter is 100µm, and the thickness is 50nm. The ferroelectric test performance under different voltages is obtained using a macroscopic ferroelectric tester, and the test results are as follows: Figure 4 .

[0051] Example 7

[0052] A Ti layer with a thickness of approximately 20 nm was sputtered or evaporated on the substrate (oxidized Si wafer), and then a bottom electrode Pt was sputtered or evaporated on the Ti layer. The Pt thickness was 50 nm. Ta:HfO2 thin films were deposited using a multi-target co-magnetron sputtering system. The specific steps were as follows: the substrate and targets (Ta target, HfO2 target) were placed in a vacuum chamber; the vacuum was evacuated to a target vacuum of 5.0×10 -5 Pa, and then heat the substrate to the target temperature of 500 ° C; adjust the working gas Ar gas flow rate to 100 sccm, the O2 gas flow rate to 20 sccm, and control the working gas pressure in the chamber to be constant at 1.0 Pa by adjusting the vacuum valve; adjust the Ta target DC sputtering power to 6W, and the HfO2 RF sputtering power to 70W; start co-sputtering, control the sputtering time, and obtain a Ta:HfO2 film with a thickness of 70nm. In order to obtain the macroscopic ferroelectric properties of Ta:HfO2, this embodiment uses RF sputtering deposition and combines it with an electrode mask to prepare a Pt top electrode. The target material is Pt, the deposition temperature is room temperature, the working gas Ar gas, the flow rate is 100 sccm, the sputtering power is 50W, and a circular top electrode 4 is prepared using a mask. The electrode diameter is 100µm and the thickness is 50nm. The ferroelectric test performance under different voltages is obtained using a macroscopic ferroelectric tester. The test results are as follows: Figure 4 Table 1 Parameter information of tantalum-doped hafnium dioxide film

[0053]

[0054] Effect of Ta target sputtering power (or Ta doping atomic percentage) on HfO2 crystal structure:

[0055] During the growth of Ta:HfO2 thin films, the RF sputtering power of the HfO2 target is fixed, and the change of the DC sputtering power of the Ta target directly reflects the doping percentage of the Ta element. Figure 3 As shown, different Ta sputtering powers have a decisive influence on the crystal structure. At a Ta sputtering power of 4 W (Example 1), the crystal structure is monoclinic, which lacks ferroelectric properties. At a Ta sputtering power of 10 W (Example 2), excessive Ta doping causes disorder in the crystal structure. At a Ta sputtering power of 6 W (Example 3), the XRD diffraction peak position indicates the presence of orthorhombic HfO2 as the primary phase. The appearance and enhancement of the orthorhombic phase indirectly demonstrate the ferroelectric properties of the resulting HfO2 film. Therefore, to further investigate the effect of oxygen flow rate on ferroelectric properties during growth, a Ta target DC sputtering power of 6 W was selected for the growth of the Ta:HfO2 films in Examples 4, 5, 6, and 7 of the present invention.

[0056] Effect of oxygen flow rate on macroscopic ferroelectric properties during the growth of Ta:HfO2 thin films:

[0057] The oxygen content (oxygen vacancies) in ferroelectric films has an important influence on ferroelectric properties. In order to verify and optimize the ferroelectric properties of the orthorhombic phase Ta:HfO2 film, the present invention optimizes the oxygen flow rate during the magnetron sputtering deposition process. Generally speaking, the greater the oxygen flow rate, the lower the oxygen vacancy concentration. Figure 4 As shown in the PV curves of samples with different oxygen flow rates, when the oxygen flux is 0 sccm, the Ta:HfO2 film has almost no ferroelectric properties. As the oxygen flux increases, the ferroelectric properties show a trend of first increasing and then decreasing. Among them, the remnant polarization strength of the Ta:HfO2 film with an oxygen flux of 10 sccm can reach ~100µC / cm 2 .

[0058] As shown in the examples of the present invention, the Ta doping concentration and the oxygen flux during magnetron sputtering can significantly affect the ferroelectric properties of Ta:HfO2 thin films. By controlling the experimental process, the remanent polarization strength has been significantly improved. For example, the remanent polarization strength of the sample in Example 5 reached ~100µC / cm 2 This paper proposes a method for depositing HfO2-based ferroelectric thin films and details how controlling growth parameters (sputtering power and oxygen flux) significantly improves the film's ferroelectric properties. The inventors hope this article will provide experimental insights and dispel the common misconception that HfO2-based ferroelectric films exhibit low remnant polarization.

[0059] This embodiment also provides a biomimetic ferroelectric synaptic device structure, such as Figure 2 As shown, a biomimetic synaptic device structure based on a tantalum-doped hafnium dioxide ferroelectric thin film comprises, from bottom to top, a substrate 1, a bottom electrode 2, a Ta:HfO2 ferroelectric thin film 3, and a top electrode 4. The top electrode 4 is a metal electrode, such as conventional Al, Pd, Au, Pt, etc., preferably Pt material, with a thickness of 30nm to 60nm, preferably 50nm. The Ta:HfO2 ferroelectric thin film 3, which exhibits significant room-temperature ferroelectric properties, has a thickness greater than 20nm, preferably 70nm. The bottom electrode 2 is a metal material, preferably Pt material, but can also be substituted with other materials. The substrate 1 is a Si wafer with an oxide layer, but can also be substituted with other substrates. The operating mechanism of the synaptic device of the present invention is based on the potential barrier at the interface between the ferroelectric oxide and the electrode. The barrier height is regulated by the ferroelectric polarization and the applied voltage. Therefore, the synaptic device can exhibit bidirectional analog resistive switching behavior, and the conductance can be continuously and gradually controlled. In addition, the transformation of long-term plasticity enhancement and inhibition provides an important theoretical basis for further clarifying the patterns of learning and memory and the pathogenesis of related neuropsychiatric diseases.

[0060] Example 8:

[0061] This embodiment achieves the regulation of the long-term plasticity of the Ta:HfO2 ferroelectric synaptic device by changing the oxygen content of the functional layer, and adopts the capacitor devices prepared in Examples 3, 5 and 7.

[0062] The synaptic performance of the three ferroelectric synaptic devices with Ta:HfO2 functional layers and different oxygen flow rates was tested. The bottom electrode 2 was grounded, and multiple positive pulses of the same amplitude were input to the top electrode 4. The pulse amplitude was 6V, the pulse width was 5µs, and the pulse interval was 100ns. A 100kΩ series resistor was connected to the test circuit. Figure 5 As shown, oxygen flow rates of 5 sccm and 10 sccm in the functional layer simulated long-term inhibition. Conversely, when the functional layer was grown at an oxygen flow rate of 20 sccm, the current and conductance of the entire device gradually increased, simulating the long-term potentiation performance of a synaptic device. Therefore, under the same synaptic device simulation parameters, changing the oxygen content in the functional layer can induce a shift in the long-term plasticity of the Ta:HfO2 synaptic device.

[0063] Example 9:

[0064] This embodiment achieves the regulation of the long-term plasticity of the Ta:HfO2 ferroelectric synaptic device by changing the width of the simulated electrical excitation pulse, and uses the device prepared in Example 7.

[0065] Based on the ferroelectric synaptic device with Ta:HfO2 functional layer in this embodiment, the synaptic performance was tested. The bottom electrode 2 was grounded, and multiple positive pulses with the same amplitude were input to the top electrode 4. The pulse amplitude was 7V, the pulse width was 1µs or 1ms, and the pulse interval was 100ns. A 10kΩ series resistor was connected to the test circuit. The effect of pulse width on the Ta:HfO2-based synaptic device is shown in Figure 2. Figure 6 As shown, with 1ms pulse width electrical pulse stimulation, the current and reactance gradually increase with increasing pulse number, indicating long-term potentiation. With 1µs pulse width electrical pulse stimulation, the current and reactance gradually decrease with increasing pulse number, indicating long-term inhibition. Thus, while maintaining the same functional layers, varying the pulse width can shift the long-term plasticity of Ta:HfO2 synaptic devices.

[0066] Example 10:

[0067] This embodiment achieves the regulation of the long-term plasticity of the Ta:HfO2 ferroelectric synaptic device by changing the external resistor, and uses the device prepared in Example 7.

[0068] Based on the ferroelectric synaptic device with Ta:HfO2 functional layer in this embodiment, the synaptic performance was tested. The bottom electrode 2 was grounded, and multiple positive pulses with the same amplitude were input to the top electrode 4. The pulse amplitude was 6V, the pulse width was 5µs, and the pulse interval was 100ns. The test circuit was connected to an external series resistor of 10kΩ, 39kΩ, or 100kΩ. The effect of the external resistor on the Ta:HfO2-based synaptic device is shown in Figure 2. Figure 7 As shown, when the external series resistance is 10 kΩ, the current and reactance of the synaptic device gradually decrease with increasing pulse number, indicating long-term inhibition. When the external series resistance is 39 kΩ or 100 kΩ, the current and reactance gradually increase with increasing pulse number, indicating long-term inhibition. Thus, under the same functional layer and pulse parameters, changing the external series resistance can shift the long-term plasticity of the Ta:HfO2 synaptic device.

[0069] The present invention has been described in detail above with reference to specific examples. The above description is merely illustrative and non-restrictive. The embodiments of the present invention include but are not limited to the above-mentioned specific embodiments. For those skilled in the art, any modifications and replacements made to the above-mentioned technical solutions should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a tantalum-doped hafnium dioxide ferroelectric thin film, characterized in that: The preparation method specifically comprises the following steps: (1) Prepare the substrate and clean and dry it; (2) sputtering or evaporating a Ti layer on the substrate, and then sputtering or evaporating a Pt bottom electrode on the Ti layer; (3) Ta:HfO2 was prepared on the Pt bottom electrode by co-magnetron sputtering: the targets used were HfO2 ceramic target and Ta metal target; the back vacuum of the vacuum chamber was less than 10 -4 Pa, the substrate is heated to 500 ℃, and the working atmosphere is a mixture of Ar and O2; the AC sputtering power of the HfO2 ceramic target is 70W, the DC sputtering power of the Ta metal target is 6W, the Ar gas flow rate is 100sccm, and the O2 flow rate is 10sccm; co-sputtering begins, and the thickness of the Ta:HfO2 film is determined by the sputtering time; the working pressure of the Ar gas and O2 gas mixture is 1.0Pa, and the thickness of the Ta:HfO2 film is obtained by controlling the sputtering time to be 20~100nm.

2. The method for preparing a tantalum-doped hafnium dioxide ferroelectric thin film according to claim 1, wherein: The substrate is an n-type single crystal silicon wafer, or an n-type polycrystalline silicon wafer, or a p-type single crystal silicon wafer, or a p-type polycrystalline silicon wafer, the Ti layer thickness is 15-30nm, and the Pt bottom electrode thickness is 30-70nm.

3. Tantalum-doped hafnium dioxide ferroelectric thin film prepared by the preparation method according to claim 1 or 2.

4. Use of the tantalum-doped hafnium dioxide ferroelectric thin film according to claim 3 in the preparation of a biomimetic synaptic device.

5. The use according to claim 4, characterized in that The device consists of a substrate, a bottom electrode, a Ta:HfO2 film and a top electrode.

6. The use according to claim 4, characterized in that The top electrode is deposited by RF sputtering, the target material is Pt, the deposition temperature is room temperature, the working gas is Ar gas, the flow rate is 50sccm-120sccm, the sputtering power is 40W~100W, the top electrode style and size are controlled by the mask, and the top electrode thickness is 30~60nm.

7. The use according to claim 4, characterized in that By controlling the O2 flow during the growth of the functional layer, adjusting the width of the electrical pulse in the synaptic test, and changing the resistance value of the external series resistor, the transition regulation of long-term potentiation and inhibition of the synaptic device can be achieved.

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