Preparation method of nitrogen-vacancy assisted high-durability wurtzite ferroelectric material

Abstract

This invention discloses a nitrogen vacancy-assisted method for preparing a high-durability wurtzite ferroelectric material, comprising the following steps: Step 1: Selecting a suitable growth substrate and depositing a bottom electrode on the substrate; Step 2: Depositing a wurtzite ferroelectric thin film on the bottom electrode using magnetron sputtering under controlled atmosphere and temperature; Step 3: Sputtering and depositing a top electrode on the wurtzite ferroelectric thin film, followed by photolithography and etching to obtain a ferroelectric memory; Step 4: Introducing controllable nitrogen vacancies in the post-growth treatment of the ferroelectric memory, ultimately obtaining the high-durability wurtzite ferroelectric material. This invention effectively reduces the coercive field by rationally introducing nitrogen vacancies, thereby improving... E bd / E c The ratio is reduced and the operating voltage is lowered, improving the stability and durability of the material during long-term operation, thus meeting the requirements of the next generation of non-volatile memory for low power consumption and high reliability.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor memory device technology, specifically relating to a method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material. Background Technology

[0002] Wurtzite ferroelectric memories are a potential choice for in-memory computing non-volatile memories due to their large storage window, multi-level storage capacity, and low thermal budget. However, wurtzite ferroelectric materials still face a key bottleneck in practical applications: their coercive electric field (… E c The electric breakdown field strength is usually large, resulting in a high electrical breakdown field strength. E bd ) and coercive electric field ( E c The ratio of ) E bd / E c The small polarization threshold (SLT) makes the material prone to approaching breakdown conditions during polarization reversal, resulting in reliability and durability far below the levels required for large-scale commercial applications. While existing methods such as strain modulation, ion doping, or heterojunction engineering have improved ferroelectric properties to some extent, their overall impact on reducing ferroelectricity is limited. E c and improvement E bd / E c The ratio has limited effect and cannot fundamentally solve the problem of high... E c The resulting durability defects.

[0003] To address the issue of large coercive electric fields in wurtzite ferroelectric materials, researchers have proposed various modification methods, such as a high-durability superlattice wurtzite ferroelectric material and its preparation and application, as disclosed in publication number CN119876899A. By using epitaxial strain to modulate lattice distortion and polarization behavior, employing ion doping to adjust the local electric field to improve ferroelectric properties, or using heterostructure design to stabilize polarization through interfacial coupling effects, these methods can optimize ferroelectric performance to some extent and enhance the material's application potential.

[0004] Despite some progress made by existing methods, there are still challenges in reducing the coercive electric field and significantly improving its efficiency. E bd / E c These approaches offer limited benefits and fail to fundamentally address the issues of electrical breakdown and insufficient durability during polarization reversal. Furthermore, these solutions often come with limitations such as stringent processing conditions, complex fabrication processes, and difficulties in large-scale scaling, making their application in practical applications like non-volatile memory still challenging.

[0005] Therefore, a new control strategy is urgently needed to effectively reduce the coercive electric field and improve the polarization performance of wurtzite ferroelectric materials while maintaining their excellent polarization characteristics. E bd / E c The ratio is adjusted to improve the stability and durability of the device, meeting the needs of next-generation high-performance non-volatile memory applications. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, the present invention aims to provide a nitrogen-vacancy-assisted method for preparing high-durability wurtzite ferroelectric materials, thereby solving the problem of excessively large coercive electric fields in existing wurtzite ferroelectric materials. E bd / E c The problem of low ratio, easy device breakdown, and insufficient durability was addressed. By appropriately introducing nitrogen vacancies, the coercive electric field was effectively reduced, thereby improving... E bd / E c The ratio is reduced and the operating voltage is lowered, improving the stability and durability of the material during long-term operation, thus meeting the requirements of the next generation of non-volatile memory for low power consumption and high reliability.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material includes the following steps; Step 1: Deposit and fabricate the bottom electrode on the substrate; Step 2: A wurtzite ferroelectric thin film is deposited on the bottom electrode using magnetron sputtering under nitrogen-deficient atmosphere conditions. This is the first process step that can actively introduce nitrogen vacancies.

[0008] Step 3: Deposit a top electrode using magnetron sputtering on the wurtzite ferroelectric thin film, and perform photolithography and etching to obtain the ferroelectric memory; Step 4: Apply an electric field stimulation treatment and / or perform heat treatment on the ferroelectric memory to regulate the nitrogen vacancy concentration in the wurtzite ferroelectric thin film; The electric field stimulation treatment includes applying a periodic pulsed voltage or an alternating electric field to cause the ferroelectric thin film to undergo polarization reversal cycles; the heat treatment is carried out in a vacuum, inert atmosphere or reducing atmosphere to promote the migration of nitrogen atoms and form a controllable nitrogen vacancy structure, thereby obtaining a wurtzite ferroelectric material with high durability.

[0009] Both steps 2 and 4 can be used to select different treatments to ultimately prepare high-durability wurtzite ferroelectric materials.

[0010] The introduction of nitrogen vacancies in steps 2 and 4 is achieved through various means, including the introduction and uniform distribution of nitrogen vacancies in wurtzite ferroelectric materials through reasonable process control or electrical activation, thereby regulating the lattice environment and polarization behavior and reducing the coercive electric field. E c ), in the limited breakdown field strength ( E bd (Upgrade) E bd / E c The ratio is adjusted, and the operating voltage of the device is reduced.

[0011] Specifically, including but not limited to: Step 4 involves the electric field inducing nitrogen vacancy formation. By applying a cyclic electric field under certain temperature and bias conditions, the migration and escape of nitrogen elements in the crystal lattice are promoted, forming local nitrogen vacancies. By controlling the electric injection voltage and time, the controllable generation of nitrogen vacancies can be achieved without destroying the overall crystal lattice structure.

[0012] A cyclic electric field with a strength of 4.5-5.5 MV / cm and a frequency of 10-100kHz is applied across the ferroelectric memory, and the number of cycles is approximately 10. 5 Second-rate.

[0013] When a cyclic electric field is applied across the two ends of the ferroelectric memory, the electric field drives some nitrogen atoms to migrate and escape along the lattice channels, forming nitrogen vacancies locally. Under the action of the electric field, the nitrogen vacancies continue to migrate and eventually become uniformly distributed in the lattice without producing obvious local agglomeration. The uniformly distributed nitrogen vacancies assist in the reversal of ferroelectric polarization, reduce the reversal barrier of wurtzite ferroelectricity, and enable wurtzite ferroelectric activation to operate at a lower voltage, greatly improving durability.

[0014] The condition where the atmosphere is a nitrogen atmosphere is insufficient is: During the thin film deposition process, by reducing the nitrogen partial pressure or introducing a vacuum / reducing atmosphere, the nitrogen plasma is not allowed to completely occupy all the crystal lattices, and nitrogen vacancies are uniformly doped into the crystal lattice, forming uniformly distributed nitrogen vacancies in the wurtzite ferroelectric thin film material.

[0015] If nitrogen vacancies are introduced during the material growth stage under nitrogen-deficient atmosphere conditions, when thin film growth is carried out under these conditions to introduce nitrogen vacancies, the volumetric flow rate ratio of nitrogen to argon is (1~4):1, and preferably greater than 3:1; and during the deposition process, the partial pressure of nitrogen is controlled to be 10% to 50% of the total reactive gas pressure. Within this range, by adjusting the flow rate ratio of nitrogen to argon and / or the partial pressure of nitrogen, the deposition environment is made to be in a state of nitrogen deficiency, so as to form a controllable nitrogen vacancy structure.

[0016] The insufficient nitrogen atmosphere conditions also include at least one of the following: (1): Reduce nitrogen flow rate and increase the proportion of inert gas; (2): Introduce vacuum dilution conditions into the deposition atmosphere to make the substrate a low-nitriding-activity environment; (3): Introduce a reducing atmosphere of hydrogen or argon-hydrogen mixture to suppress nitrogen plasma activity.

[0017] For specific parameter ranges, please refer to: nitrogen flow rate to argon flow rate ratio between 1:4 and 4:1, RF power greater than 120W, deposition temperature between 25℃ and 300℃, and vacuum degree below 10℃ before gas filling. -3 The vacuum level should be 0.1-1 Pa, and the lower the better. During deposition with reactive gas, the overall vacuum level should be 0.1-1 Pa. The nitrogen plasma in the atmosphere is insufficient to completely occupy all the crystal lattices, thus forming uniformly distributed nitrogen vacancies in the material.

[0018] In step 3, the top electrode is a Pt circular top electrode.

[0019] Step 4, the method for introducing controllable nitrogen vacancies, is as follows: Applying a periodic alternating electric field to the ferroelectric memory promotes the migration and dissipation of nitrogen elements in the lattice, forming local nitrogen vacancies. By controlling the electric injection voltage and time, the controllable generation of nitrogen vacancies can be achieved without destroying the overall lattice structure.

[0020] The applied periodic alternating electric field has waveforms including triangular waves, rectangular waves, sine waves, and their superpositions. The electric field strength is slightly greater than that of the coercive electric field, approximately 4.5-6 MV / cm, with a frequency of 30-500 kHz and a cycle number of approximately 10. 5 The specific parameters can be fine-tuned based on the implementation effect of the specific materials.

[0021] When a cyclic electric field is applied across the two ends of the ferroelectric memory, the electric field drives some nitrogen atoms to migrate and escape along the lattice channels, forming nitrogen vacancies locally. Under the action of the electric field, the nitrogen vacancies continue to migrate and eventually become uniformly distributed in the lattice without producing obvious local agglomeration. The uniformly distributed nitrogen vacancies assist in the reversal of ferroelectric polarization and reduce the reversal barrier of wurtzite ferroelectricity.

[0022] The wurtzite ferroelectric material is used in ferroelectric memory.

[0023] A top electrode is sputtered onto a wurtzite ferroelectric thin film, followed by photolithography and etching to obtain a ferroelectric memory.

[0024] The beneficial effects of this invention are: This invention introduces nitrogen vacancies, an intrinsic point defect, into wurtzite ferroelectric materials, thereby altering the coordination environment and electronic structure of the atoms surrounding the defect. When some nitrogen atoms are missing, the binding effect on neighboring cations (such as Al, Ga, Sc, etc.) is weakened, inducing local lattice distortion reconstruction, which reduces the free energy difference and flipping barrier between polarized and antipolarized states, and significantly reduces the coercive electric field.

[0025] Furthermore, since nitrogen vacancies primarily function in the polarization reversal process, their impact on the intrinsic breakdown field strength of the material is limited. E bd The impact is relatively small. E c Significantly decreased E bd Under stable conditions, the material E bd / E c The significantly improved ratio provides a greater breakdown safety margin when the device reaches polarization reversal conditions. This not only allows the device to perform reliable read and write operations at lower voltages, but also effectively suppresses charge injection, defect accumulation, and dielectric degradation caused by high electric field stress, thereby improving the stability and durability of the device.

[0026] Compared to traditional strain modulation, impurity doping, or heterostructure design, this invention optimizes performance by controlling the nitrogen vacancy concentration in wurtzite ferroelectric materials. Nitrogen vacancies, as intrinsic defects within the material, can be directly controlled through growth and post-processing, eliminating the need for additional heterogeneous components or complex structural designs, thus simplifying the fabrication process. Since this method primarily operates on the intrinsic lattice structure of the material and does not depend on specific interfacial couplings or strain states, it can achieve stable control in wurtzite ferroelectric materials of varying compositions, thicknesses, and morphologies, including thin films and bulk materials, demonstrating good process compatibility and promising prospects for large-scale applications. This invention provides a new and effective approach to improving the electrical performance of wurtzite ferroelectric materials and extending device lifetime, and is particularly suitable for next-generation non-volatile memories and high-performance electronic devices. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the first-principles calculation of the flipping barrier with and without nitrogen vacancies in this invention.

[0028] Figure 2 The polarization hysteresis curves before and after introducing nitrogen vacancies in this invention are shown.

[0029] Figure 3 The graph shows the change in durability performance before and after the introduction of nitrogen vacancies in this invention. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings.

[0031] like Figures 1-3 As shown, this invention provides a nitrogen vacancy-assisted method for preparing high-durability wurtzite ferroelectric materials. By rationally controlling the process or electrically activating the material, nitrogen vacancies are introduced and uniformly distributed in the wurtzite ferroelectric material, thereby regulating the lattice environment and polarization behavior, and reducing the coercive electric field. E c ), in the limited breakdown field strength ( E bd (Upgrade) E bd / E c This ratio, along with reducing the device's operating voltage, ultimately significantly improves the material's durability and reliability.

[0032] Example 1: Deposition of wurtzite ferroelectric materials under nitrogen-deficient atmosphere conditions: Step 1: Select a suitable growth substrate and deposit the bottom electrode on the substrate; Step 2: During the deposition process, the nitrogen / argon flow ratio is controlled at 3:7, which is lower than the nitrogen partial pressure required by conventional processes (greater than 5:5), resulting in a partial nitrogen deficiency during film growth.

[0033] Step 3: Sputter metal (Pt) is deposited on the wurtzite ferroelectric thin film, followed by photolithography and etching to obtain the ferroelectric memory; Under conditions of insufficient nitrogen partial pressure, some lattice sites fail to be fully occupied by nitrogen atoms, leading to the spontaneous formation of nitrogen vacancies in the material. Due to controlled deposition conditions, nitrogen vacancies are not concentrated at grain boundaries or surfaces, but are uniformly doped throughout the lattice. The moderate formation of nitrogen vacancies alters the local electric field environment and atomic coordination states, lowering the energy barrier during polarization reversal.

[0034] In summary, by comparing the electrical performance of samples prepared under conventional nitrogen-supply conditions with those prepared under conventional conditions, the method of this embodiment demonstrates superior coercive electric field, breakdown performance, and cycle durability.

[0035] Example 2: Electric field-assisted activation to form nitrogen vacancies in wurtzite ferroelectric materials: refer to Figure 3 As shown, this invention introduces and stably distributes nitrogen vacancies in the wurtzite structure through an electric field-induced method, thereby achieving control over the coercive electric field (…). E c ( ) Regulation and durability improvement.

[0036] Step 1: Select a suitable growth substrate and deposit the bottom electrode on the substrate; Step 2: Deposit a wurtzite ferroelectric thin film on the bottom electrode using a conventional wurtzite ferroelectric growth process via magnetron sputtering; Step 3: Sputter and deposit the top electrode on the wurtzite ferroelectric thin film, and perform photolithography and etching to obtain the ferroelectric memory; Step 4: Apply a periodic alternating electric field across the capacitor. The waveform is a triangular wave with an electric field strength of 5.7 MV / cm, a frequency of 100 kHz, and a cycle count of 4.1e5. Under these conditions, the electric field drives some nitrogen atoms to migrate and escape along the lattice channels, forming nitrogen vacancies locally. These nitrogen vacancies continuously migrate under the influence of the electric field, eventually distributing uniformly within the lattice without significant local aggregation. This uniform distribution of nitrogen vacancies assists in the reversal of ferroelectric polarization, lowering the reversal barrier of wurtzite ferroelectricity. This allows wurtzite ferroelectric activation to operate at a lower voltage, significantly improving durability.

[0037] Step 5: Mechanism of nitrogen vacancy formation: like Figure 2 As shown, the formation of nitrogen vacancies mainly originates from ion migration driven by an electric field.

[0038] In the wurtzite structure, nitrogen atoms are located at octahedral positions coordinated with Al / Sc atoms, exhibiting high polarization sensitivity. Under the influence of an applied electric field and thermodynamics, some nitrogen atoms escape to the surface or interface, leaving stable vacancy sites. Due to the cyclic effect of the electric field, the distribution of nitrogen vacancies tends to be uniform, preventing concentration at local grain boundaries or electrode interfaces, thus avoiding excessive leakage current caused by defect aggregation.

[0039] Step 6: Performance Characterization and Results Ferroelectric loop tests revealed that, as Figure 2 As shown, the coercive electric field of the AlScN thin film after electric field activation treatment is... E c It is reduced by about 30%, which greatly reduces the operating voltage and significantly improves durability.

[0040] In summary, this embodiment demonstrates that introducing nitrogen vacancies through electric field-assisted activation can effectively improve the electrical properties and durability of wurtzite ferroelectric materials, providing a new technical approach for non-volatile memory applications.

[0041] The nitrogen-vacancy-assisted wurtzite ferroelectric material preparation method proposed in this invention can effectively reduce the coercive electric field by uniformly introducing and controlling nitrogen vacancies in the material. This not only improves the electric field performance under limited breakdown field strength... E bd / E cThis method improves the ratio of high stress to low stress, reduces the operating voltage of the device, and mitigates the damage to the material caused by long-term high field stress, thereby significantly improving durability and reliability. Compared with traditional doping or strain control methods, this method has a simpler process and can be achieved through various means such as nitrogen atmosphere control, electric injection, and nitrogen plasma treatment, showing good scalability and application prospects.

Claims

1. A method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material, characterized in that, Includes the following steps; Step 1: Deposit and fabricate the bottom electrode on the substrate; Step 2: Deposit a wurtzite ferroelectric thin film on the bottom electrode using magnetron sputtering under nitrogen-deficient atmosphere conditions; Step 3: Deposit a top electrode using magnetron sputtering on the wurtzite ferroelectric thin film, and perform photolithography and etching to obtain the ferroelectric memory; Step 4: Apply an electric field stimulation treatment and / or perform heat treatment on the ferroelectric memory to regulate the nitrogen vacancy concentration in the wurtzite ferroelectric thin film; The electric field stimulation treatment includes applying a periodic pulsed voltage or an alternating electric field to cause the ferroelectric thin film to undergo polarization reversal cycles; the heat treatment is carried out in a vacuum, inert atmosphere or reducing atmosphere to promote the migration of nitrogen atoms and form a controllable nitrogen vacancy structure to obtain wurtzite ferroelectric material.

2. The method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material according to claim 1, characterized in that, The insufficient nitrogen atmosphere condition is as follows: during the thin film deposition process, by reducing the nitrogen partial pressure or introducing a vacuum / reducing atmosphere, the nitrogen plasma is insufficient to completely occupy all the crystal lattices, and nitrogen vacancies are uniformly doped into the crystal lattice, forming uniformly distributed nitrogen vacancies in the wurtzite ferroelectric thin film material.

3. The method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material according to claim 2, characterized in that, If nitrogen vacancies are introduced during the material growth stage under nitrogen-deficient atmosphere conditions, when thin film growth is carried out under these conditions to introduce nitrogen vacancies, the volumetric flow rate ratio of nitrogen to argon is (1~4):1, and the partial pressure of nitrogen is controlled to be 10%~50% of the total reaction gas pressure during deposition. Within this range, by adjusting the flow rate ratio of nitrogen to argon and / or the partial pressure of nitrogen, the deposition environment is made to be in a state of nitrogen deficiency, so as to form a controllable nitrogen vacancy structure.

4. The method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material according to claim 3, characterized in that, The insufficient nitrogen atmosphere conditions also include at least one of the following: (1): Reduce nitrogen flow rate and increase the proportion of inert gas; (2): Introduce vacuum dilution conditions into the deposition atmosphere to make the substrate a low-nitriding-activity environment; (3): Introduce a reducing atmosphere of hydrogen or argon-hydrogen mixture to suppress nitrogen plasma activity.

5. The method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material according to claim 1, characterized in that, In step 2, the parameters for magnetron sputtering deposition of wurtzite ferroelectric thin films are as follows: RF power greater than 120W, deposition temperature 25℃-300℃, vacuum degree less than 10 before gas filling. -3 The vacuum level should be 0.1-1 Pa, and the lower the better. When the reactive gas is filled for deposition, the overall vacuum level should be 0.1-1 Pa.

6. The method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material according to claim 2, characterized in that, In step 3, the top electrode is a Pt circular top electrode.

7. The method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material according to claim 1, characterized in that, Step 4, the method for introducing controllable nitrogen vacancies, is as follows: Applying a periodic alternating electric field to the ferroelectric memory promotes the migration and dissipation of nitrogen elements in the lattice, forming local nitrogen vacancies. By controlling the electric injection voltage and time, the controllable generation of nitrogen vacancies can be achieved without destroying the overall lattice structure.

8. The method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material according to claim 7, characterized in that, The applied periodic alternating electric field has waveforms of triangular waves, rectangular waves, sine waves, and their superpositions. The electric field strength is greater than that of the coercive electric field, 4.5-6 MV / cm, with a frequency of 30-500 kHz and approximately 10 cycles. 5 indivual.

9. The method for preparing a nitrogen-vacancy-assisted high-durability wurtzite ferroelectric material according to claim 8, characterized in that, When a cyclic electric field is applied across the two ends of the ferroelectric memory, the electric field drives some nitrogen atoms to migrate and escape along the lattice channels, forming nitrogen vacancies locally. Under the action of the electric field, the nitrogen vacancies continue to migrate and eventually become uniformly distributed in the lattice without producing obvious local agglomeration. The uniformly distributed nitrogen vacancies assist in the reversal of ferroelectric polarization and reduce the reversal barrier of wurtzite ferroelectricity.

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