Electricity-free activated ni-fe2o4 resistive random access memory and preparation method thereof
By designing the oxygen vacancy distribution of the SrRuO3/SrTiO3 structure in the NiFe2O4 resistive switching memory, a NiFe2O4 thin film with a mixture of amorphous and crystalline states was formed, which solved the problems of high electro-activation voltage and high power consumption, and realized a resistive switching memory with low resistance, no electro-activation and low power consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2022-12-07
- Publication Date
- 2026-04-14
AI Technical Summary
Existing NiFe2O4 resistive switching memory devices suffer from problems such as excessively high electrical activation voltage (>10V) and high operating power consumption.
The structure employs a bottom-up approach, consisting of a lower electrode layer, a resistive switching layer, and a top electrode layer. The lower electrode layer is a SrRuO3 thin film, and the resistive switching layer is a NiFe2O4 thin film. By controlling the oxygen vacancy concentration, the NiFe2O4 thin film has a high oxygen vacancy rate on the side closer to the SrRuO3 thin film and a low oxygen vacancy rate on the side farther from the top electrode, forming a mixed amorphous and crystalline structure with a low initial resistance. This avoids the electro-activation process and reduces operating power consumption.
A NiFe2O4 resistive switching memory without electrical activation process was realized. The device has a simple structure, simple fabrication process, low power consumption, low initial resistance, and stable performance.
Smart Images
Figure CN115802881B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of memory technology, and more specifically, relates to an electrically activated NiFe2O4 resistive switching memory and its preparation method. Background Technology
[0002] Traditional CMOS-based Dynamic Random Access Memory (DRAM) and Flash Memory (FLASH) both face the dual challenges of limited cell size reduction and high power consumption. Among newly proposed non-volatile memories, Resistive Random Access Memory (ReRAM) is gradually showing a trend of replacing traditional memories due to its advantages such as fast read / write speeds, high storage density, and low power consumption. Information storage in ReRAM is based on the memristor effect, which enables switching between 0 and 1. Common memristor effects include metal ion effects, oxygen ion effects, electronic effects, and thermal effects. Through these effects, the memory can switch between high and low resistance states.
[0003] Nickel ferrite (NiFe2O4) thin films possess abundant optical, electrical, and magnetic physicochemical properties, and have broad application prospects in photocatalysis, microwave, magnetic recording, and resistive switching memory. However, existing NiFe2O4 resistive switching memory devices suffer from problems such as excessively high electroforming voltage (>10V) and high operating power consumption. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to provide an electrically activated NiFe2O4 resistive switching memory and its fabrication method, thereby solving the technical problems of excessively high electro-forming voltage (>10V) and high operating power consumption in existing NiFe2O4 resistive switching memory devices.
[0005] To achieve the above objectives, the present invention provides an electrically activated NiFe2O4 resistive switching memory, comprising a lower electrode layer, a resistive switching layer, and a top electrode layer disposed from bottom to top; wherein:
[0006] The lower electrode layer is a SrRuO3 thin film layer;
[0007] The resistive switching layer is a NiFe2O4 thin film layer;
[0008] The oxygen vacancy concentration in the NiFe2O4 thin film layer gradually decreases from the side closer to the SrRuO3 thin film layer to the side closer to the top electrode, making the initial resistance of the resistive switching memory low-resistance state, eliminating the need for an electrical activation process and reducing operating power consumption.
[0009] Preferably, the thickness of the NiFe2O4 thin film layer is 10-40 nm.
[0010] More preferably, the thickness of the NiFe2O4 thin film layer is 15-25 nm.
[0011] Preferably, the thickness of the SrRuO3 thin film layer is 40-60 nm.
[0012] Preferably, the top electrode layer is Pt, Au, or TiN.
[0013] According to another aspect of the present invention, a method for fabricating the aforementioned resistive switching memory is provided, comprising the following steps:
[0014] (1) A lower electrode layer SrRuO3 thin film was deposited on the substrate;
[0015] (2) A resistive switching layer NiFe2O4 thin film is deposited on the SrRuO3 thin film layer;
[0016] (3) The NiFe2O4 thin film layer is photolithographically developed, and a top electrode is deposited on the developed NiFe2O4 thin film layer.
[0017] Preferably, step (1) involves depositing a lower electrode layer (SrRuO3) thin film on the substrate using pulsed laser deposition. The deposition conditions include: a temperature of 650–700°C, an oxygen atmosphere in the cavity, a pressure of 10–15 Pa, a laser energy of 250–450 mJ, a laser frequency of 1–8 Hz, and a base vacuum of 1 × 10⁻⁶ mJ. -6 ~1×10 -5 Pa, the distance between the surface to be deposited and the target is 40-60 mm.
[0018] Preferably, the oxygen pressure used in step (1) when depositing the lower electrode layer SrRuO3 thin film is greater than the oxygen pressure used in step (2) when depositing the resistive switching layer NiFe2O4 thin film.
[0019] Preferably, step (2) involves depositing a resistive switching layer NiFe2O4 thin film on the SrRuO3 thin film using pulsed laser deposition. The deposition process conditions include: a temperature of 600–700°C, an oxygen atmosphere in the cavity, a pressure of 3–10 Pa, a more preferably 630–670°C, a more preferably 8–10 Pa, a laser energy of 250–450 mJ, a laser frequency of 1–8 Hz, and a base vacuum of 1 × 10⁻⁶ mJ. -6 ~1×10 -5 Pa, the distance between the surface to be deposited and the target is 40-60 mm.
[0020] Preferably, in step (3), the photolithography development includes pre-baking at 97°C for 2-3 minutes, pre-exposure time of 1.2-2 seconds, post-exposure at 115°C for 2-3 minutes, and post-exposure time of 1-12 seconds.
[0021] Preferably, step (3) involves depositing the top electrode on the NiFe2O4 thin film using magnetron sputtering. The magnetron sputtering process conditions include: a temperature of room temperature and a deposition rate of [missing information]. The deposition time is 1500–2000 s.
[0022] Preferably, the substrate is SrTiO3, LaAlO3, DyScO3, KTaO3 or (La,Sr)(Al,Ta)O3.
[0023] In summary, compared with the prior art, the above-described technical solutions conceived by this invention have the following advantages:
[0024] Beneficial effects:
[0025] (1) The present invention provides an electrically activated NiFe2O4 resistive switching memory, comprising a lower electrode layer, a resistive switching layer, and a top electrode layer arranged from bottom to top; wherein: the lower electrode layer is a SrRuO3 thin film layer; and the resistive switching layer is a NiFe2O4 thin film layer. In the present invention, the oxygen vacancy concentration in the crystal structure of the NiFe2O4 thin film layer near the SrRuO3 thin film layer is higher than that near the top electrode of the NiFe2O4 thin film layer, and shows a gradually decreasing trend, so that the NiFe2O4 resistive switching memory device does not require an electrical activation process and has low operating power consumption during use.
[0026] (2) The NiFe2O4 resistive switching memory provided by this invention has a simple structure and a simple fabrication process. On the one hand, by controlling the lower electrode SrRuO3 thin film layer and the process conditions during the fabrication of the NiFe2O4 thin film layer, including oxygen pressure and temperature, the NiFe2O4 thin film near the lower electrode has a large number of oxygen vacancy defects and has an amorphous structure, while the NiFe2O4 thin film far from the lower electrode has a relatively low oxygen vacancy content and still has a crystalline structure. This results in poor crystallinity and high oxygen vacancy concentration at the bottom of the NiFe2O4 thin film in the resistive switching memory of this invention. At the same time, electrical tests show that the resistivity of the amorphous NiFe2O4 thin film is even lower, resulting in a high overall oxygen vacancy content in the NiFe2O4 resistive switching layer. The initial resistive state is a low-resistivity state, thus the NiFe2O4 resistive switching memory device of this invention does not require an electrical activation process during operation and has low operating power consumption. Attached Figure Description
[0027] Figure 1 This is a schematic cross-sectional view of the NiFe2O4 resistive switching memory device provided by the present invention.
[0028] Figure 2 This is a schematic diagram of the conductive channel of the NiFe2O4 resistive switching memory in this invention when no operating voltage is applied.
[0029] Figure 3 This is a schematic diagram of the conductive path of the NiFe2O4 resistive switching memory of the present invention after a positive Reset voltage is applied in the initial state.
[0030] Figure 4 This is a high-resolution transmission electron microscope image of the NiFe2O4 resistive switching memory in Example 1.
[0031] Figure 5 This is the surface X-ray photoelectron spectrum of the resistive switching layer thin film obtained in Embodiment 1 of the present invention.
[0032] Figure 6 This is the X-ray photoelectron spectrum of the resistive switching layer thin film obtained in Example 1 of the present invention after etching for 100 s.
[0033] Figure 7 This is the X-ray photoelectron spectrum of the resistive switching layer thin film obtained in Example 1 of the present invention after etching for 200 s.
[0034] Figure 8 This is the X-ray photoelectron spectrum of the resistive switching layer thin film obtained in Example 1 of the present invention after etching for 300 s.
[0035] Figure 9 This is the forming curve of the NiFe2O4 resistive switching memory prepared in Example 1 after the first reset when a negative voltage is applied.
[0036] Figure 10 This is a DC cycling characteristic curve of the NiFe2O4 resistive switching memory in Embodiment 1 of the present invention.
[0037] Figure 11 This is a retention characteristic curve of the NiFe2O4 resistive switching memory in Embodiment 1 of the present invention.
[0038] Figure 12 This is a pulse cycle characteristic diagram of the NiFe2O4 resistive switching memory in Embodiment 1 of the present invention.
[0039] Figure 13 This is a DC cycling curve of the NiFe2O4 resistive switching memory in Embodiment 2 of the present invention. Detailed Implementation
[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0041] Industry standards for NiFe2O4 resistive switching memory devices suffer from problems such as excessively high electroforming voltage (>10V) and high operating power consumption. This invention, through experiments, reveals that the growth quality of NiFe2O4 thin films is significantly affected by oxygen vacancy defects and lattice mismatch with the substrate material. Different substrate materials and oxygen pressures can be used to prepare NiFe2O4 thin films with varying microstructures and resistive switching properties. This invention provides an electro-activated NiFe2O4 resistive switching memory, comprising a lower electrode layer, a resistive switching layer, and a top electrode layer arranged from bottom to top; wherein: the lower electrode layer is a SrRuO3 thin film layer; and the resistive switching layer is a NiFe2O4 thin film layer. The NiFe2O4 thin film layer has a high oxygen vacancy concentration on the side near the SrRuO3 thin film layer, making it amorphous. The NiFe2O4 thin film layer has a lower oxygen vacancy concentration on the side near the top electrode, making it crystalline. The resistive switching layer as a whole contains a large number of oxygen vacancies, resulting in a low initial resistance state for the device. It does not require an electrical activation process and has low operating power consumption.
[0042] Experiments have shown that the aforementioned oxygen vacancy concentration distribution in the NiFe2O4 thin film layer on this device helps reduce the electrical activation voltage and operating power consumption of the resistive switching memory device using NiFe2O4 thin film as the resistive switching layer. Through extensive experimental research, this invention has discovered that SrRuO3 itself readily exhibits oxygen vacancies on its surface during deposition, absorbing some of the oxygen from the NiFe2O4 thin film layer. This results in a further deficiency of oxygen ions in the low-oxygen-pressure deposited NiFe2O4 film, leading to a higher number of oxygen vacancies. As the thickness of the NiFe2O4 film increases, the oxygen absorption effect of SrRuO3 weakens, and the crystallinity of the NiFe2O4 film increases. In some embodiments of this invention, by controlling the process conditions of the lower electrode SrRuO3 thin film layer and the NiFe2O4 thin film layer during fabrication—for example, the lower electrode SrRuO3 thin film layer is prepared under a relatively high oxygen pressure environment, while the NiFe2O4 thin film layer is prepared under a relatively low oxygen pressure environment—the NiFe2O4 film near the lower electrode has a large number of oxygen vacancy defects, resulting in a generally high number of oxygen vacancies in the NiFe2O4 film. This invention's experiments revealed that a large number of oxygen vacancy defects lead to a near-amorphous structure in NiFe2O4, while on the other side, the NiFe2O4 film farther from the lower electrode has a relatively lower oxygen vacancy concentration and still exhibits a crystalline structure. Furthermore, comparative testing showed that the resistivity of crystalline NiFe2O4 is higher than that of amorphous NiFe2O4. Additionally, the NiFe2O4 crystal structure is an inverse spinel type, with a lattice constant of [missing value]. The crystal structure of SrRuO3 is perovskite type, with a lattice constant of . The severe lattice mismatch between the crystal structures of NiFe2O4 and SrRuO3 makes it difficult for NiFe2O4 near the SrRuO3 thin film layer to crystallize, resulting in an amorphous structure. These factors may explain why the NiFe2O4 resistive switching memory device provided by this invention has a low initial resistance, enabling it to operate with low power consumption without an electrical activation process.
[0043] This invention achieves a NiFe2O4 resistive switching memory device with low power consumption and no electrical activation process by controlling the oxygen vacancy distribution and crystallinity of the NiFe2O4 thin film. The invention uses SrRuO3 as the lower electrode material, requiring no special treatment. In a preferred embodiment, a mixed amorphous and crystalline NiFe2O4 resistive switching film is prepared on a SrRuO3 substrate using a pulsed laser deposition process with low oxygen pressure. The oxygen vacancy concentration in this film gradually decreases from the lower electrode to the upper electrode, resulting in a high overall oxygen vacancy content. Electrical performance test results show that, compared to other NiFe2O4 resistive switching memory devices, this invention achieves low initial resistance, enabling electrical activation-free operation and significantly reducing operating power consumption.
[0044] The following is an example:
[0045] Example 1
[0046] (1) Clean the SrTiO3 substrate with acetone, ethanol and deionized water for 15 min each.
[0047] (2) A SrRuO3 lower electrode was fabricated on the substrate described in step (1) using pulsed laser deposition. The process conditions were as follows: temperature 680℃, cavity atmosphere oxygen, pressure 15Pa, laser energy 250mJ, laser frequency 4Hz, and base vacuum 5×10⁻⁶. -6 Pa, the distance between the substrate and the target is 55 mm; the thickness of the SrRuO3 film is 50 nm.
[0048] (3) A NiFe2O4 thin film was prepared on the lower electrode described in step (2) using pulsed laser deposition. The process conditions were as follows: temperature 650℃, cavity atmosphere oxygen, pressure 10Pa, laser energy 250mJ, laser frequency 5Hz, and base vacuum 5×10⁻⁶. -6 Pa, the distance between the lower electrode and the target is 55 mm; the NiFe2O4 film thickness is 20 nm.
[0049] (4) A Pt top electrode was fabricated on the NiFe2O4 thin film prepared in step (3) using magnetron sputtering and a mask. The process conditions were: room temperature, deposition rate of [missing information]. A deposition time of 2000 s yielded a NiFe2O4 resistive switching memory with a Pt / NFO(NiFe2O4) / SRO(SrRuO3) / STO(SrTiO3) structure, as shown in the schematic diagram below. Figure 1 As shown.
[0050] Figure 2 This is a schematic diagram of the conductive channel in the initial state of the NiFe2O4 resistive switching memory in this example. There are many oxygen vacancies at the bottom and few oxygen vacancies at the top. At this time, the conductive channel is completely connected, so the initial resistance of the device is low, and no electrical activation process is required. Figure 3 This is a schematic diagram of the conductive channel after a positive Reset voltage is applied. The oxygen vacancy is driven downward by the electric field, the conductive channel is broken in the upper layer, and the device switches to a high-resistivity state.
[0051] Figure 4 This is a high-resolution transmission electron microscope image of the NiFe2O4 resistive switching memory in this embodiment. It can be seen that the bottom is mainly amorphous and the upper layer is mainly crystalline.
[0052] Figure 5 , Figure 6 , Figure 7 and Figure 8 The images show X-ray photoelectron spectra obtained from the surface of the resistive switching layer film obtained in this embodiment, and from etching downwards from the surface for 100s, 200s, and 300s, respectively. It can be seen that the oxygen vacancy percentage in the resistive switching layer gradually increases from the surface to the bottom, with the percentages being 41%, 52%, 56%, and 57% respectively. This indicates that the NiFe2O4 resistive switching memory prepared in this embodiment has a high overall oxygen vacancy content in its resistive switching film layer, and the oxygen vacancy percentage gradually decreases from the side near the bottom electrode to the side near the top electrode. This suggests that the device is in a low-resistance state from the outset and does not require an electro-activation process.
[0053] Figure 9 This is the forming curve of the NiFe2O4 resistive switching memory prepared in this embodiment after the first reset with a negative voltage applied. It can be seen that the voltage at which the resistance value switches is approximately -1.6V, which is consistent with... Figure 10 Since the Set voltage values are consistent, it can be determined that the NiFe2O4 resistive switching memory in this example does not require an electrical activation process.
[0054] Figure 10 This is a DC cycling characteristic curve of the NiFe2O4 resistive switching memory in this embodiment. It can be seen that the device's on / off ratio can reach 10. 2 It also exhibits good cycle stability; Figure 11 This is a retention characteristic curve of the NiFe2O4 resistive switching memory. It can be seen that the device has excellent retention characteristics at 10... 4 There was no significant decay within s. Figure 12 This is the pulse cycle characteristic diagram of the NiFe2O4 resistive switching memory. According to Joule's law, the power consumption is 15.6pJ, which is lower than that of similar NiFe2O4 resistive switching memory devices.
[0055] Example 2
[0056] (1) Clean the SrTiO3 substrate with acetone, ethanol and deionized water for 15 min each.
[0057] (2) A SrRuO3 lower electrode was fabricated on the substrate described in step (1) using pulsed laser deposition. The process conditions were as follows: temperature 680℃, cavity atmosphere oxygen, pressure 15Pa, laser energy 250mJ, laser frequency 4Hz, and base vacuum 5×10⁻⁶. -6 Pa, the distance between the substrate and the target is 55 mm; the thickness of the SrRuO3 film is 50 nm.
[0058] (3) A NiFe2O4 thin film was prepared on the lower electrode described in step (2) using pulsed laser deposition. The process conditions were as follows: temperature 700℃, cavity atmosphere oxygen, pressure 10Pa, laser energy 250mJ, laser frequency 5Hz, and background vacuum of 5×10⁻⁶ mJ. -6 Pa, the distance between the lower electrode and the target is 55 mm; the NiFe2O4 film thickness is 20 nm.
[0059] (4) A Pt top electrode was fabricated on the NiFe2O4 thin film prepared in step (3) using magnetron sputtering and a mask. The process conditions were: room temperature, deposition rate of [missing information]. A NiFe2O4 resistive switching memory device with a deposition time of 2000 s was obtained with a Pt / NFO(NiFe2O4) / SRO(SrRuO3) / STO(SrTiO3) structure.
[0060] Figure 13 This is a DC cycling curve of the NiFe2O4 resistive switching memory prepared in Example 2. The device exhibits good cycling stability. Figure 13 and Figure 10 In comparison, the switching window of the device prepared in this embodiment is weaker than that of the device prepared in Example 1.
[0061] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A NiFe2O4 resistive switching memory that requires no electrical activation, characterized in that, It includes a bottom electrode layer, a resistive switching layer, and a top electrode layer arranged from bottom to top; wherein: The lower electrode layer is a SrRuO3 thin film layer; the thickness of the SrRuO3 thin film layer is 40-60 nm. The resistive switching layer is a NiFe2O4 thin film layer; the thickness of the NiFe2O4 thin film layer is 10-40 nm; The top electrode layer is Pt, Au, or TiN; The method for fabricating the resistive random access memory includes the following steps: (1) A lower electrode layer SrRuO3 thin film is deposited on the substrate; the deposition process conditions include: a temperature of 650-700 °C. o C, The cavity atmosphere is oxygen, and the pressure is 10-15 Pa; (2) A resistive switching layer NiFe2O4 thin film is deposited on the SrRuO3 thin film layer; the deposition process conditions include: a temperature of 600-700 °C. o C, The cavity atmosphere is oxygen, and the pressure is 3-10 Pa; (3) Photolithography is performed on the NiFe2O4 thin film layer to deposit a top electrode on the developed NiFe2O4 thin film layer; The NiFe2O4 thin film layer has a high oxygen vacancy concentration on the side near the SrRuO3 thin film layer, making it amorphous. Conversely, the NiFe2O4 thin film layer has a lower oxygen vacancy concentration on the side near the top electrode, making it crystalline. The oxygen vacancy concentration in the NiFe2O4 thin film layer gradually decreases from the side near the SrRuO3 thin film layer to the side near the top electrode, resulting in a low initial resistance for the resistive switching memory. This eliminates the need for an electrical activation process during use and reduces operating power consumption.
2. The resistive random access memory as described in claim 1, characterized in that, The thickness of the NiFe2O4 thin film is 15-25 nm.
3. The method for fabricating a resistive switching memory as described in claim 1 or 2, characterized in that, Includes the following steps: (1) A lower electrode layer SrRuO3 thin film is deposited on the substrate; the deposition process conditions include: a temperature of 650-700 °C. o C, The cavity atmosphere is oxygen, and the pressure is 10-15 Pa; (2) A resistive switching layer NiFe2O4 thin film is deposited on the SrRuO3 thin film layer; the deposition process conditions include: a temperature of 600-700 °C. o C, The cavity atmosphere is oxygen, and the pressure is 3-10 Pa; (3) Photolithography is performed on the NiFe2O4 thin film layer to deposit a top electrode on the developed NiFe2O4 thin film layer.
4. The preparation method according to claim 3, characterized in that, Step (1) involves depositing a lower electrode layer (SrRuO3) thin film on the substrate using pulsed laser deposition. The deposition process conditions include: laser energy of 250–450 mJ, laser frequency of 1–8 Hz, and a base vacuum of 1 × 10⁻⁶ mJ. -6 ~1×10 -5 Pa, the distance between the surface to be deposited and the target is 40-60 mm.
5. The preparation method according to claim 3, characterized in that, Step (2) involves depositing a resistive switching layer, NiFe2O4, onto the SrRuO3 thin film using pulsed laser deposition. The deposition process conditions include: laser energy of 250–450 mJ, laser frequency of 1–8 Hz, and a base vacuum of 1 × 10⁻⁶ mJ. -6 ~1×10 -5 Pa, the distance between the surface to be deposited and the target is 40-60 mm.
6. The preparation method according to claim 3, characterized in that, Step (3) The top electrode is prepared by magnetron sputtering on the NiFe2O4 thin film. The magnetron sputtering process conditions include: room temperature, deposition rate of 0.3~0.6 Å / s, and deposition time of 1500~2000 s.