A potassium niobate-based material usable for ferroelectric random access memory and a method of preparation

Abstract

This invention discloses a potassium niobate-based material and its preparation method for use in ferroelectric random access memory (RAM). The chemical composition is (1-x)(0.998KNbO3-0.002Fe)-xMnO2, where 0.0001≤x≤0.003. The preparation process includes: weighing K2CO3, Nb2O5, Fe, and MnO2 according to the stoichiometric ratio; grinding, pre-calcining, ball milling, and sieving the raw materials; pressing them into thin sheets; and heating at 1020~1040 °C. o Sintering at C for 2 hours yielded a potassium niobate-based material modified with iron and manganese. The preparation steps of this invention are simple, environmentally friendly, and highly reproducible. This material exhibits a high hysteresis loop rectangularity of 1.98 and a density of 34.61 μC / cm². 2 With its moderate remanent polarization and low coercive electric field of 32.94 kV / cm, it is an inorganic material with promising applications in ferroelectric random access memory.

Description

Technical Field

[0001] This invention relates to the field of storage materials, and more specifically to a potassium niobate-based material and its preparation method that can be used in ferroelectric random access memory. Background Technology

[0002] Ferroelectricity is an indispensable characteristic for the fabrication of novel ferroelectric random access memory (FeRAM). Ferroelectric RAM offers read / write speeds comparable to dynamic random access memory (DRAM), and features data retention after power failure, low power consumption, long lifespan, and ease of integration, making it promising for applications in aerospace, artificial intelligence, and other fields. Existing ferroelectric RAM materials mainly include lead zirconate titanate (PZT)-based, strontium titanate (SrTiO3)-based, and hafnium oxide (HfO2)-based materials. PZT has advantages such as high hysteresis loop rectangularity, large remanent polarization, and low coercivity, but its fabrication and application are limited by the toxicity of lead. SrTiO3 has relatively low hysteresis loop rectangularity and remanent polarization, which is unfavorable for data storage. While HfO2 has relatively high hysteresis loop rectangularity and large remanent polarization, its excessively high coercivity is detrimental to polarization reversal. Therefore, the preparation of ferroelectric materials that are environmentally friendly, have high hysteresis loop rectangularity, moderate remanent polarization, and low coercive electric field is an urgent research topic to be solved in the field of ferroelectric random access memory.

[0003] Potassium niobate (KNbO3) is due to its Nb content. 5+ KNbO3 exhibits spontaneous polarization due to its deviation from the octahedral symmetry center of NbO6. The theoretical spontaneous polarization intensity of KNbO3 at room temperature is as high as 43.3 μC / cm. 2 KNbO3 is a promising ferroelectric memory material. However, pure KNbO3 ferroelectric materials exhibit spontaneous domain flipping and domain wall displacement after the removal of the external electric field, leading to a significant decrease in hysteresis loop rectangularity and remanent polarization. To achieve high hysteresis loop rectangularity and remanent polarization, it is necessary to increase the pinning effect of KNbO3 domain orientation and domain wall displacement. For example, doping with Mn can introduce point defects, pinning the domains and domain walls, thereby increasing the dielectric constant and improving thermal stability. Therefore, a new formulation and supporting improvement method are needed to achieve high hysteresis loop rectangularity, moderate remanent polarization intensity, and low coercive electric field intensity, which can meet the application environment and performance requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a potassium niobate-based material and its preparation method that can be used in ferroelectric random access memory, so as to improve the hysteresis loop rectangularity and remanent polarization intensity of potassium niobate-based inorganic materials.

[0005] To achieve the above objectives, the present invention provides a potassium niobate-based material that can be used in ferroelectric random access memory, with the chemical formula: (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2, 0.0001≤x≤0.003; The preparation method of the above potassium niobate-based material is as follows: (1) Ingredients According to the stoichiometric ratio of (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2 (x = 0.0001, 0.0005, 0.001, 0.002), K2CO3, Nb2O5, Fe and MnO2 raw materials were weighed separately using a high-precision electronic balance.

[0006] (2) Grinding The accurately weighed mixture was ground in an agate mortar and pestle for 4 hours.

[0007] (3) Preheating The ground mixture was transferred into an alumina crucible and placed in a muffle furnace. The furnace was then heated at room temperature for 5 seconds. o Heating rate increased to 100 °C / min o Hold at 3°C ​​for 30 minutes, then increase the temperature to 270°C at the same rate. o Hold at 720°C for 120 minutes, then increase the temperature to 720°C. o After holding at temperature C for 180 minutes, allow it to cool naturally to room temperature.

[0008] (4) Ball milling and drying The pre-calcined powder was transferred into a ball mill jar and milled for 8 hours using agate ball milling balls with anhydrous ethanol as the medium. The slurry was then poured into a porcelain pan and allowed to air dry before being heated to 100°C. o Keep warm at C for 1 hour.

[0009] (5) Grinding The dried powder was ground in an agate mortar for 2 hours.

[0010] (6) Add glue Add 5 wt.% PVA adhesive to the powder.

[0011] (7) Grinding After adding the glue, continue grinding the powder for 1 hour.

[0012] (8) Preloading After the powder is placed in a sealed bag, it is compacted under a uniaxial pressure of 8 MPa for 1 min.

[0013] (9) Grinding After compaction, the powder was ground in an agate mortar and pestle for 2 hours.

[0014] (10) Sieving Use a 300-mesh sieve to sift the powder.

[0015] (11) Tableting The sieved powder is pressed into a disc with a diameter of 10 mm and a thickness of about 1 mm under a single-shaft pressure of 8 MPa.

[0016] (12) De-glue Place the disc into the crucible and put it into the muffle furnace, starting at room temperature and increasing the pressure by 2... o Heating at a rate of C / min, the temperature reaches 100 o C, 150 o C, 200 o C, 300 o C, 400 o C, 500 o C or 600 o The temperature was maintained at 700°C for 30 minutes. o Keep warm at C for 2 hours.

[0017] (13) Sintering Place the disc inside the muffle furnace, starting at room temperature and increasing the temperature by 5 degrees Celsius. o Heating at a rate of C / min, when the temperature reaches 100 o C or 700 o The temperature was maintained at C for 30 minutes to reach 1020~1040°C. o Keep warm at C for 2 hours.

[0018] (14) Grinding disc After sintering, the discs are polished to a thickness of 0.11~0.15mm using 600, 1200 and 2000 grit sandpaper, then polished with metallographic sandpaper and wiped clean with alcohol. Attached Figure Description

[0019] Figure 1 This is a room temperature SEM image of Embodiment 1 of the present invention.

[0020] Figure 2 This is a room temperature SEM image of Embodiment 2 of the present invention.

[0021] Figure 3 This is a room temperature SEM image of Embodiment 3 of the present invention.

[0022] Figure 4 This is a room temperature SEM image of Embodiment 4 of the present invention.

[0023] Figure 5 This is the room temperature hysteresis curve of Embodiment 1 of the present invention.

[0024] Figure 6This is the room temperature hysteresis curve of Embodiment 2 of the present invention.

[0025] Figure 7 This is the room temperature hysteresis curve of Example 3 of the present invention.

[0026] Figure 8 This is the room temperature hysteresis curve of Example 4 of the present invention. Detailed Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments.

[0028] Example 1: The chemical formula of the material in this example is (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2, where x = 0.0001. Its preparation steps include: (1) Ingredients According to the stoichiometric ratio (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2 (x = 0.0001), K2CO3 (purity 99.00%), Nb2O5 (purity 99.00%), Fe (purity 98.35%) and MnO2 (purity 99.00%) raw materials were weighed using a high-precision electronic balance.

[0029] (2) Grinding The accurately weighed mixture was ground in an agate mortar and pestle for 4 hours.

[0030] (3) Preheating The ground mixture was transferred into an alumina crucible and placed in a muffle furnace. The furnace was then heated at room temperature for 5 seconds. o Heating rate increased to 100 °C / min o Hold at 3°C ​​for 30 minutes, then increase the temperature to 270°C at the same rate. o Hold at 720°C for 120 minutes, then increase the temperature to 720°C. o After holding at temperature C for 180 minutes, allow it to cool naturally to room temperature.

[0031] (4) Ball milling and drying The pre-calcined powder was transferred into a ball mill jar and milled for 8 hours using agate ball milling balls with anhydrous ethanol as the medium. The slurry was then poured into a porcelain pan and allowed to air dry before being heated to 100°C. o Keep warm at C for 1 hour.

[0032] (5) Grinding The dried powder was ground in an agate mortar for 2 hours.

[0033] (6) Add glue Add 5 wt.% PVA adhesive to the powder.

[0034] (7) Grinding After adding the glue, continue grinding the powder for 1 hour.

[0035] (8) Preloading After the powder is placed in a sealed bag, it is compacted under a uniaxial pressure of 8 MPa for 1 min.

[0036] (9) Grinding After compaction, the powder was ground in an agate mortar and pestle for 2 hours.

[0037] (10) Sieving Use a 300-mesh sieve to sift the powder.

[0038] (11) Tableting The sieved powder is pressed into a disc with a diameter of 10 mm and a thickness of about 1 mm under a single-shaft pressure of 8 MPa.

[0039] (12) De-glue Place the disc into the crucible and put it into the muffle furnace, starting at room temperature and increasing the pressure by 2... o Heating at a rate of C / min, the temperature reaches 100 o C, 150 o C, 200 o C, 300 o C, 400 o C, 500 o C or 600 o The temperature was maintained at 700°C for 30 minutes. o Keep warm at C for 2 hours.

[0040] (13) Sintering Place the disc inside the muffle furnace, starting at room temperature and increasing the temperature by 5 degrees Celsius. o Heating at a rate of C / min, when the temperature reaches 100 o C or 700 o The temperature was maintained at C for 30 minutes to reach 1020~1040°C. o Keep warm at C for 2 hours.

[0041] (14) Grinding disc After sintering, the discs are polished to a thickness of 0.11~0.15mm using 600, 1200 and 2000 grit sandpaper, then polished with metallographic sandpaper and wiped clean with alcohol.

[0042] After polishing, the upper and lower surfaces of the potassium niobate-based material are coated with silver paste and placed in a vacuum drying oven at 100°C. o The temperature was maintained at C for 2 hours. Its hysteresis loop was measured under the conditions of room temperature, 10 Hz, and 120 kV / cm. Figure 2As shown in Table 1, the hysteresis loop rectangularity, remanent polarization, and coercive field of the ferroelectric material in this embodiment at room temperature are also shown.

[0043] Example 2: The chemical composition of the material in this example is (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2, where x = 0.0005. Its preparation method is the same as in Example 1. The room-temperature hysteresis loop characterization method for the ferroelectric material in this example is the same as in Example 1, such as... Figure 2 As shown in Table 1, the hysteresis loop rectangularity, remanent polarization, and coercive field of the ferroelectric material in this embodiment at room temperature are also shown.

[0044] Example 3: The chemical composition of the material in this example is (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2, where x = 0.001. Its preparation method is the same as in Example 1. The surface SEM image was characterized using high-resolution field emission scanning electron microscopy, as shown below. Figure 1 As shown; the room temperature hysteresis loop characterization method for the ferroelectric material in this embodiment is the same as that in Example 1, such as... Figure 2 As shown in Table 1, the hysteresis loop rectangularity, remanent polarization, and coercive field of the ferroelectric material in this embodiment at room temperature are also shown.

[0045] Example 4: The chemical composition of the material in this example is (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2, where x = 0.003. Its preparation method is the same as in Example 1. The surface SEM image was characterized using high-resolution field emission scanning electron microscopy, as shown below. Figure 1 As shown; the room temperature hysteresis loop characterization method for the ferroelectric material in this embodiment is the same as that in Example 1, such as... Figure 2 As shown in Table 1, the hysteresis loop rectangularity, remanent polarization, and coercive field of the ferroelectric material in this embodiment at room temperature are also shown.

[0046] After preparation using the above method, the hysteresis loop rectangularity, remanent polarization intensity, and coercive field of the ferroelectric materials in four different embodiments are shown in Table 1: Table 1. Hysteresis loop rectangularity, remanent polarization, and coercive field of ferroelectric materials in each embodiment.

[0047] As shown in Table 1, with the increase of manganese doping, the hysteresis loop rectangularity of the material of the present invention is consistently high; the remanent polarization is moderate; and the coercive electric field strength continuously increases. The hysteresis loop rectangularity of each embodiment is higher than 1.96, and the remanent polarization of Example 3 is as high as 34.61 μC / cm. 2Furthermore, it maintains a low coercive field of 32.94 kV / cm, which meets the requirements of ferroelectric random access memory for high hysteresis loop rectangularity, moderate remanent polarization, and low coercive field in ferroelectric materials. This indicates that (1-x)(0.998KNbO3 - 0.002Fe)-xMnO2 is a promising inorganic material for ferroelectric memory applications.

[0048] Depend on Figure 2 It is evident that the ferroelectric materials in each embodiment exhibit high hysteresis loop rectangularity and moderate remanent polarization intensity under the action of an external electric field, overcoming the problems of hysteresis loop rectangularity and remanent polarization intensity in pure potassium niobate ferroelectric materials.

[0049] The above descriptions are several preferred embodiments of the present invention. Although they cannot be construed as limiting the scope of the present invention, equivalent variations made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A potassium niobate-based material for use in ferroelectric random access memory, characterized in that: The chemical composition is (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2, where 0.0001≤x≤0.

003.

2. A method for preparing a potassium niobate-based material for use in ferroelectric random access memory according to claim 1, characterized in that... It consists of the following steps: (1) Ingredients According to the stoichiometric ratio of (1-x)(0.998KNbO3 - 0.002Fe) - xMnO2, K2CO3, Nb2O5, Fe and MnO2 raw materials were weighed separately using a high-precision electronic balance; (2) Grinding The accurately weighed mixture was ground in an agate mortar and pestle for 4 hours. (3) Preheating The ground mixture was transferred into an alumina crucible and placed in a muffle furnace. The furnace was then heated at room temperature for 5 seconds. o Heating rate increased to 100 °C / min o Hold at 3°C ​​for 30 minutes, then increase the temperature to 270°C at the same rate. o Hold at 720°C for 120 minutes, then increase the temperature to 720°C. o After holding at temperature C for 180 minutes, allow it to cool naturally to room temperature. (4) Ball milling and drying The pre-calcined powder was transferred into a ball mill jar and milled for 8 hours using agate ball milling balls with anhydrous ethanol as the medium. The slurry was then poured into a porcelain pan and allowed to air dry before being heated to 100°C. o Keep warm at C for 1 hour; (5) Grinding The dried powder was ground in an agate mortar for 2 hours. (6) Add glue Add 5 wt.% PVA adhesive to the powder; (7) Grinding After adding the glue, continue grinding the powder for 1 hour; (8) Preloading After the powder is placed in a sealed bag, it is compacted under a single-axis pressure of 8 MPa for 1 min. (9) Grinding After compaction, the powder was ground in an agate mortar and pestle for 2 hours. (10) Sieving Use a 300-mesh sieve to sift the powder. (11) Tableting The sieved powder is pressed into a disc with a diameter of 10 mm and a thickness of about 1 mm under a single-shaft pressure of 8 MPa. (12) De-glue Place the disc into the crucible and put it into the muffle furnace, starting at room temperature and increasing the pressure by 2... o Heating at a rate of C / min, the temperature reaches 100 o C, 150 o C, 200 o C, 300 o C, 400 o C, 500 o C or 600 o The temperature was maintained at 700°C for 30 minutes. o Keep warm at C for 2 hours; (13) Sintering Place the disc inside the muffle furnace, starting at room temperature and increasing the temperature by 5 degrees Celsius. o Heating at a rate of C / min, when the temperature reaches 100 o C or 700 o The temperature was maintained at C for 30 minutes to reach 1020~1040°C. o Keep warm at C for 2 hours; (14) Grinding disc After sintering, the discs are polished to a thickness of 0.11~0.15mm using 600, 1200 and 2000 grit sandpaper, then polished with metallographic sandpaper and wiped clean with alcohol.

3. The method for preparing a potassium niobate-based material for use in ferroelectric random access memory according to claim 2, characterized in that: In step (1), the raw materials used and their purity are K2CO3 (99.00%), Nb2O5 (99.00%), Fe (98.35%) and MnO2 (99.00%).

4. The method for preparing a potassium niobate-based material for use in ferroelectric random access memory according to claim 2, characterized in that: In steps (3) and (13), the heating rate is 5. o C / min.

5. The method for preparing a potassium niobate-based material for use in ferroelectric random access memory according to claim 2, characterized in that: In step (14), when the thickness of the disc is greater than 0.30 mm, use 600 grit sandpaper to polish it; when the thickness is between 0.20 and 0.30 mm, use 1200 grit sandpaper to polish it; when the thickness is between 0.11 and 0.20 mm, use 2000 grit sandpaper to polish it, and finally use metallographic sandpaper for polishing.

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