Perovskite vertical ferrimagnetic tunnel junctions and methods of making and using the same

Abstract

This invention belongs to the field of semiconductor device technology and discloses an all-oxide vertical ferrimagnetic tunnel junction, its fabrication method, and its applications. The all-oxide vertical ferrimagnetic tunnel junction comprises NiCo layers sequentially stacked on a substrate. 2‑y Fe y O4 layer, MgAl2O4 layer, NiCo 2‑x Fe x O4 layer, and NiCo 2‑y Fe y O4 layer, MgAl2O4 layer, NiCo 2‑x Fe x The O4 layer is ring-shaped, where 0 ≤ y ≤ x ≤ 0.2; the substrate composition is MgAl2O4. This all-oxide vertical ferrimagnetic tunnel junction exhibits a significant tunneling magnetoresistance signal when a 1 μA current is applied under magnetic field assistance, corresponding to a current density less than 1 A / cm². 2 High conductivity results in low overall resistance of the tunnel junction, reducing energy consumption. Furthermore, the lower current density helps reduce transistor size, enabling denser storage.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, and specifically relates to all-oxide vertical ferrimagnetic tunnel junctions, their preparation methods, and applications. Background Technology

[0002] With the rapid development of big data and artificial intelligence, the demands on data storage technologies are increasing. Magnetic Random Access Memory (MRAM) has attracted widespread attention due to its advantages such as non-volatility, fast read / write speeds, scalability, and simple writing mechanisms. MRAM is a non-volatile, lossless read-out memory. Its basic unit has a transistor and a magnetoresistive element, where the high and low resistance states of the magnetoresistive element (such as a tunnel junction) determine the "1" and "0" states. Dynamic RAMs (DRAMs) based on semiconductor technology face many limitations in maintaining significant growth rates. For example, charge leakage as device size shrinks leads to increased power consumption. Compared to DRAMs, MRAM has lower static power consumption. Furthermore, the mismatch between the operating speed of memory and processor in computers is a significant factor hindering the development of the electronics industry. CPUs process at nanosecond speeds, while hard disks read / write speeds are around 100 microseconds, but MRAM operates at speeds close to traditional static random access memory (SRAM). In the early 1990s, star-shaped and Toggle designs based on current-induced Oersted fields were developed. Between 2005 and 2015, STT-MRAM with spin-transfer torque (STT) dominated the market.

[0003] Furthermore, by integrating new technologies such as spin orbital moment (SOT) into MRAM devices, read / write speed, stability, and energy efficiency are constantly improving, but SOT-MRAM is still in the research and development stage. Through the study of the anisotropy of the interface in the Ta / CoFeB / MgO system, a magnetic tunnel junction (p-MTJ) with vertical anisotropy (PMA) was discovered and successfully commercialized. As the core structure of magnetic random access memory, p-MTJ has the following advantages: (1) It can maintain the magnetization state in a small size, and can store more data bits in the same area; (2) Compared with planar magnetic tunnel junction MTJ, the intrinsic switching current is smaller, which can achieve lower power consumption; (3) It has good thermal stability, which is conducive to maintaining data integrity and stability at higher temperatures; (4) It has strong resistance to external magnetic fields and radiation; (5) It can simplify the structural design of storage devices.

[0004] The exploration of new materials and structures is in full swing, aiming to further improve the performance and reduce the cost of p-MTJs. Currently, the commercialization of p-MTJs not only brings new opportunities to the storage technology field but also opens up new possibilities for future data storage and processing technologies.

[0005] Currently, the core structure of commercial MRAM relies on p-MTJs with CoFeB / heavy metals and PMA, but its disadvantages are also obvious: (1) The manufacturing process of CoFeB / heavy metal tunnel junctions requires precisely controlled deposition technology and complex multilayer structures, which may lead to increased production costs; (2) Scalability reaches its limit, and it is impossible to manufacture devices smaller than 20nm while maintaining data storage capacity; (3) Interface and compatibility issues between CoFeB / heavy metal tunnel junctions and other materials may affect overall performance, especially when integrated with semiconductor materials; (4) Although CoFeB / heavy metal tunnel junctions have PMA, they are still sensitive to external magnetic fields, and the PMA originates from the magnetic anisotropy of the interface, which means that the thickness must be precisely controlled. As transistor size approaches its physical limit, the method of increasing storage density simply by shrinking the size becomes increasingly difficult and expensive, which leads to a slowdown in the growth rate of Moore's Law. Researchers and companies are developing new storage technologies, such as ReRAM (Resistive Random Access Memory) and PCM (Phase Change Memory). These technologies aim to provide higher storage density, faster read and write speeds, and lower power consumption. At the same time, memory hierarchy optimization and system integration technologies are also being developed.

[0006] Therefore, there is an urgent need to provide a tunnel junction device with lower energy consumption. Summary of the Invention

[0007] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes an all-oxide vertical ferrimagnetic tunnel junction, its fabrication method, and its applications. The all-oxide vertical ferrimagnetic tunnel junction of this invention, which utilizes the all-oxide vertical ferrimagnetic tunnel structure to fabricate an MRAM (Magnetic Random Access Memory), has an all-oxide vertical ferrimagnetic tunnel junction as its basic storage unit. This MRAM possesses advantages such as non-volatility, low power consumption, high-density integration, good thermal stability, fast and stable read / write speeds, good compatibility with CMOS technology, and low manufacturing cost.

[0008] The all-oxide vertical ferrimagnetic tunnel junction of this invention can detect a significant tunneling magnetoresistance signal with an applied current of 1 μA under magnetic field assistance, corresponding to a current density of less than 1 A / cm². 2 High conductivity results in low overall resistance of the tunnel junction, reducing energy consumption. Furthermore, the lower current density helps reduce transistor size, enabling denser storage.

[0009] A first aspect of the present invention provides an all-oxide vertical ferrimagnetic tunnel junction.

[0010] Specifically, the all-oxide vertical ferrimagnetic tunnel junction includes NiCo layers sequentially stacked on a substrate. 2- x Fex O4 layer, MgAl2O4 layer, NiCo 2-y Fe y O4 layer, and the NiCo 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y The O4 layer is ring-shaped, wherein 0≤y≤x≤0.2; the substrate is composed of MgAl2O4.

[0011] The NiCo 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y The ring-shaped O4 layer refers to the three layers of NiCo. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y The "sandwich structure" composed of O4 layers is ring-shaped with holes inside, similar to a tunnel.

[0012] NiCo 2-x Fe x O4 layer, NiCo 2-y Fe y The O4 layer is called the magnetic layer, and the MgAl2O4 layer is called the barrier layer.

[0013] Preferably, the range of values ​​for x and y is 0 ≤ y. <x≤0.2。

[0014] Preferred, NiCo all-oxide vertical ferrimagnetic tunnel junction 2-y Fe y The O4 layer is also covered by a metal layer.

[0015] Preferably, the metal layer comprises any one of platinum (Pt), silver, copper or gold, and more preferably platinum (Pt).

[0016] Preferably, the NiCo 2-y Fe y The O4 layer consists of a ring-shaped metal layer and a top electrode layer. The top electrode layer has the same composition as the metal layer.

[0017] Preferably, the surface of the all-oxide vertical ferrimagnetic tunnel junction is covered by a silicon dioxide layer, leaving only a portion of NiCo exposed. 2-x Fe x The O4 layer is not covered, NiCo 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe yThe O4 layer is ring-shaped, and the pores inside are also filled with silica.

[0018] Preferably, the NiCo 2-x Fe x The thickness of the O4 layer is 5-15 nm, and more preferably 10-15 nm.

[0019] Preferably, the thickness of the MgAl2O4 layer is 1-3 nm, and more preferably 2-3 nm.

[0020] Preferably, the NiCo 2-y Fe y The thickness of the O4 layer is 5-15 nm, and more preferably 10-15 nm.

[0021] Preferably, the thickness of the metal layer is 15-25 nm, and more preferably 20-22 nm.

[0022] Preferably, the thickness of the top electrode layer is 40-60 nm, and more preferably 50-60 nm.

[0023] A second aspect of the present invention provides a method for preparing an all-oxide vertical ferrimagnetic tunnel junction.

[0024] Specifically, the preparation method of the all-oxide vertical ferrimagnetic tunnel junction includes the following steps:

[0025] Take a substrate and deposit NiCo sequentially on the substrate. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y O4 layer, metal layer.

[0026] A preferred method for preparing a fully oxide vertical ferrimagnetic tunnel junction includes the following steps:

[0027] (1) Take a substrate and deposit NiCo sequentially on the substrate. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y O4 layer, metal layer;

[0028] (2) Based on step (1), NiCo is etched away using ultraviolet lithography and ICP plasma. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y The O4 layer and metal layer expose the substrate.

[0029] (3) Based on step (2), further etching of NiCo is performed using ultraviolet lithography and ICP plasma. 2-y Fe y The O4 layer and MgAl2O4 layer partially make NiCo 2-x Fe x Part of the O4 layer is exposed;

[0030] (4) Based on step (3), NiCo is etched using ultraviolet lithography and ICP plasma etching. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y A through-hole is formed in the center of the O4 layer and the metal layer, but the substrate is not etched.

[0031] (5) Based on step (4), a silica layer is further deposited (to prevent leakage of the tunnel junction and to isolate the external environment);

[0032] (6) A pattern is formed using ultraviolet lithography, and a top electrode layer is deposited on the metal layer.

[0033] Preferably, the NiCo 2-x Fe x The O4 layer utilizes NiCo. 2-x Fe x O4 target material is obtained by laser pulse deposition.

[0034] Preferred, NiCo 2-x Fe x The preparation process of O4 target material includes the following steps: NiO, Co3O4 and Fe2O3 powders are mixed, pre-sintered at 1050-1100℃ for 3-4.5 hours, and then sintered at 1180-1200℃ for 5.5-6 hours.

[0035] Preferably, the NiCo 2-y Fe x The O4 layer utilizes NiCo. 2-y Fe y O4 target material is obtained by laser pulse deposition.

[0036] Preferred, NiCo 2-y Fe y The preparation process of O4 target material includes the following steps: NiO, Co3O4 and Fe2O3 powders are mixed, pre-sintered at 1050-1100℃ for 3-4.5 hours, and then sintered at 1180-1200℃ for 5.5-6 hours.

[0037] To satisfy the condition that x and y take values ​​in the range of 0 ≤ y ≤ x ≤ 0.2, during the preparation of NiCo... 2-xFe x O4 sputtering target, NiCo 2-y Fe y The amounts of NiO, Co3O4, and Fe2O3 powders can be adjusted as needed during the O4 target process.

[0038] MgAl2O4 targets are available for direct purchase from the market.

[0039] Preferably, NiCo is deposited using a laser pulse method. 2-x Fe x O4 layer, NiCo 2-y Fe y During the O4 layer deposition process, the deposition temperature is 280-350℃, the oxygen pressure is 15-26 Pa, the pulse frequency is 6-10 Hz, and the laser energy is 55-67 mJ; more preferably, NiCo is deposited using a laser pulse method. 2-x Fe x O4 layer, NiCo 2-y Fe y During the O4 layer deposition process, the deposition temperature is 300-350℃, the oxygen pressure is 20-26Pa, the pulse frequency is 8-10Hz, and the laser energy is 60-67mJ.

[0040] Preferably, during the deposition of the MgAl2O4 layer using laser pulses, the deposition temperature is 300-350℃, the oxygen pressure is 0.5-1Pa, the pulse frequency is 4-7Hz, the laser energy is 60-67mJ, and after the MgAl2O4 layer is deposited, it is kept at this temperature for 5-10 minutes.

[0041] Preferably, the deposition rate during the metal layer deposition process is 0.1-0.3 nm / s. The purpose of depositing the metal layer is to avoid the impact of subsequent photolithography etching on the tunnel junction NiCo. 2-y Fe y The O4 layer structure is modified or destroyed, while simultaneously connecting to the subsequently deposited top electrode.

[0042] Preferably, the photoresist used in steps (2) and (3) of ultraviolet lithography is positive photoresist, with an exposure time of 10-12 seconds, a development time of 20-30 seconds, and a fixing time of 10-15 seconds. The purpose of ultraviolet lithography is to obtain a specific pattern (the pattern corresponds to a diameter of 12-18 μm) so that NiCo with a specific structural shape can be obtained during ICP plasma etching. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y O4 layer, metal layer.

[0043] Preferably, the photoresist used in step (4) of ultraviolet lithography is a negative photoresist, the exposure time of the negative photoresist is 10-12s, the development time is 10-12s, and the fixing time is 10-15s. The diameter of the perforation is 4-6μm.

[0044] A third aspect of the invention provides the application of an all-oxide vertical ferrimagnetic tunnel junction.

[0045] A memory comprising the aforementioned all-oxide vertical ferrimagnetic tunnel junction.

[0046] Preferably, the memory includes a p-MTJ magnetic random access memory.

[0047] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0048] (1) MRAM containing all-oxide vertical ferrimagnetic tunnel junction has advantages such as non-volatility, low power consumption, high density integration, good thermal stability, fast and stable read and write, good compatibility with CMOS technology and low manufacturing cost.

[0049] (2) The all-oxide vertical ferrimagnetic tunnel junction of the present invention can detect a significant tunneling magnetoresistance signal when a current of 1 μA is applied under magnetic field assistance, corresponding to a current density of less than 1 A / cm2. It has high conductivity, low overall resistance of the tunnel junction, and reduced energy consumption. Moreover, the smaller current density is beneficial to reducing transistor size and achieving denser storage.

[0050] (3) The magnetic random access memory of p-MTJ including the above-mentioned all-oxide vertical ferrimagnetic tunnel junction has the following advantages: (1) The operating speed is at the nanosecond level, which matches the operating speed of CMOS devices. (2) The stored data information is non-volatile, and the magnetic transition temperature of the above-mentioned all-oxide vertical ferrimagnetic tunnel junction is above room temperature, which can realize the long-term reliability of data storage and read / write operations at room temperature and above. (3) The high conductivity of the vertical tunnel junction structure and magnetic layer can effectively reduce the intrinsic current density, reduce energy consumption, and obtain higher integration density. (4) The above-mentioned all-oxide vertical ferrimagnetic tunnel junction is composed entirely of oxides, which has low manufacturing cost and simple process, and can be compatible with other functional materials (such as III-V group optoelectronic materials) and existing CMOS technology. (5) It simultaneously meets the read rate of DRAM and (or higher) the storage density of flash memory, and can directly supply data to the CPU for logical operations, thereby improving the operating efficiency of the computer. Attached Figure Description

[0051] Figure 1 This is a schematic cross-sectional view of the all-oxide vertical ferrimagnetic tunnel junction prepared in Example 1 of the present invention.

[0052] Figure 2This is a schematic diagram of the process for preparing the all-oxide vertical ferrimagnetic tunnel junction in Example 1 of the present invention;

[0053] Figure 3 This is a schematic diagram illustrating the working principle of the all-oxide vertical ferrimagnetic tunnel junction prepared in Example 1 of the present invention. Detailed Implementation

[0054] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0055] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0056] A schematic diagram of the working principle of the all-oxide vertical ferrimagnetic tunnel junction prepared in Example 1 is shown below. Figure 3 ( Figure 3 In the diagram, "H" represents the coercive field, "M" represents the magnetic moment, and "T" represents the temperature. (NiCo) 2-x Fe x O4, NiCo 2-y Fe y O4 possesses excellent physical properties, including half-metallicity, robust perpendicular magnetic anisotropy, high electrical conductivity, ultrafast spin dynamics, and easily tunable magnetic ground state, making it an ideal material for constructing room-temperature perpendicular tunnel junctions. NiCo, with a higher Fe doping concentration... 2-x Fe x The O4 layer has a large coercive field and can be used as a magnetic reference layer (referred to as the reference layer). NiCo with a lower Fe doping concentration... 2-y Fe y The O4 layer serves as a magnetic free layer (or simply free layer). The tunnel junction principle is derived from NiCo. 2-x Fe x The spin electrons of the O4 layer tunnel through the intermediate insulating layer MgAl2O4 to reach the NiCo on the other side. 2- y Fe y The unfilled electronic states of the O4 layer and the exchange of spin subbands between the two electrodes lead to corresponding changes in conductance. Magnetoresistance depends on the NiCo layers on both sides. 2-x Fe x O4 layer, NiCo 2-y Fe y The population of electrons allowed to participate in tunneling in the O4 layer and the intermediate insulating layer. When NiCo 2-x Fe x When the magnetic moment of the O4 layer is parallel, more electrons pass through the potential barrier, corresponding to a low-resistivity state. When NiCo... 2-x Fe xWhen the magnetic moments of the O4 layers are antiparallel, the tunneling probability of the carriers decreases, corresponding to the high-resistance state. This corresponds to "0" and "1" in computer programming languages. Therefore, the resistance state change can be adjusted by a magnetic field as Figure 3 shown. The two NiCo 2-x Fe x O4 layers (corresponding to the coercive field HFM1), the coercive fields of the NiCo 2-y Fe y O4 layers (corresponding to the coercive field HFM2) (assuming HFM1 > HFM2) are of different magnitudes. This is the necessary and sufficient condition for realizing the MTJ based on NCFO (i.e., NiCo 2-x Fe x O4, NiCo 2-y Fe y O4). When the magnetic field H > HFM1 or H < HFM2, the magnetic moment directions of the two are the same, corresponding to the low-resistance state. When the magnetic field HFM1 > H > HFM2, the magnetic moment directions of the two are opposite, corresponding to the high-resistance state. By adjusting the magnitude of the magnetic field to control the magnetic moment direction of the magnetic layer, the data writing process is realized; by applying a current at both ends of the free layer and the reference layer and measuring the voltage to read the resistance, the data reading process is realized. Changing the magnetization direction of the free layer requires crossing a relatively high energy barrier, which prevents the magnetic moment from spontaneously flipping without external intervention, thus ensuring the non-volatility of the data.

[0057] Example 1

[0058] All-oxide perpendicular ferrimagnetic tunnel junction, the structure of which is as Figure 1 shown, where "100" represents the substrate (the substrate composition is MgAl2O4), "200" represents the NiCo 2-y Fe y O4 layer, "300" represents the MgAl2O4 layer, "400" represents the NiCo 2-x Fe x O4 layer, "500" represents the metal layer (the metal layer composition is Pt), "600" represents the silica layer, "700" represents the top electrode layer (the top electrode layer composition is Pt), x = 0.2, y = 0.1;

[0059] The NiCo 2-y Fe y O4 layer, MgAl2O4 layer, NiCo 2-x Fe x O4 layer are sequentially stacked on the substrate, the metal layer is placed on the NiCo 2-x Fe x O4 layer, and the NiCo 2-y Fe y O4 layer, MgAl2O4 layer, NiCo 2-x Fe xThe O4 layer and the metal layer are ring-shaped, forming pores (5 μm in diameter) filled with silicon dioxide, where 0 ≤ y ≤ x ≤ 0.2; the substrate composition is MgAl2O4. The top electrode layer is disposed on the metal layer.

[0060] The surface of the all-oxide vertical ferrimagnetic tunnel junction is covered by a silicon dioxide layer, leaving only a portion of NiCo exposed. 2-x Fe y The O4 layer is not covered, NiCo 2-y Fe y O4 layer, MgAl2O4 layer, NiCo 2-x Fe x The O4 layer is ring-shaped, and the pores inside are also filled with silica.

[0061] The preparation method of the all-oxide vertical ferrimagnetic tunnel junction includes the following steps:

[0062] (1) Take a substrate and deposit NiCo on the substrate sequentially using laser pulses. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y The structure obtained after deposition of the O4 layer is as follows: Figure 2 As shown in ①;

[0063] NiCo 2-x Fe x The preparation process of O4 (x=0.2) target material includes the following steps: NiO, Co3O4 and Fe2O3 powders (NiO 4.7646g, Co3O4 9.2167g, Fe2O3 1.0187g, the purity of the powders is 99.99% by mass) are mixed, pre-sintered at 1100℃ for 4 hours, and then sintered at 1200℃ for 6 hours to obtain the target material.

[0064] NiCo 2-y Fe y The preparation process of O4 (y=0.1) target material includes the following steps: NiO, Co3O4 and Fe2O3 powders (NiO 4.7638g, Co3O4 9.7270g, Fe2O3 0.5093g, the purity of the powders is 99.99% by mass) are mixed, pre-sintered at 1100℃ for 4 hours, and then sintered at 1200℃ for 6 hours to obtain the target material.

[0065] NiCo was deposited on a MgAl2O4(001) substrate using a laser pulse method. 2-x Fe x O4 (15nm) layer, MgAl2O4 (3nm) layer, NiCo 2-y Fe yO4 (15nm) layer structure, NiCo 2-x Fe x O4 (15nm) and NiCo 2-y Fe y The deposition conditions for the O4 (15nm) layer were: temperature 350℃, oxygen pressure 26Pa (cavity inlet flow rate 25L / min), pulse frequency 10Hz, and laser energy 67mJ; the deposition conditions for the MgAl2O4 layer were: temperature 350℃, oxygen pressure 1Pa (cavity inlet flow rate 1L / min), pulse frequency 7Hz, and laser energy 67mJ. After the MgAl2O4 layer was grown, it was kept at 350℃ and oxygen pressure 1Pa for 10 minutes.

[0066] Pt (20 nm) was deposited on a three-layer structure using magnetron sputtering at room temperature and a deposition rate of 0.1 nm / s. This was done to avoid the impact of subsequent photolithography etching on the tunnel junction NiCo. 2-y Fe y The O4 layer structure is modified or disrupted, while simultaneously connecting with the subsequently deposited top electrode layer, resulting in a structure as follows: Figure 2 As shown in ②;

[0067] (2) Using ultraviolet lithography, the geometrically shaped integral tunnel junction unit pattern is transferred onto the structure obtained in step (1). The photoresist is exposed for 12 seconds, developed for 30 seconds, and fixed for 15 seconds. Then, ICP plasma etching removes the remaining parts to the substrate (substrate over-etched by 2 nm). The gas used for ICP etching is Ar (the same below), NiCo... 2-x Fe x O4 layer, NiCo 2-y Fe y The etching rates for the O4 and MgAl2O4 layers were both 0.18 nm / s, and the Pt etching rate was 0.24 nm / s. The resulting structure is as follows: Figure 2 As shown in ③;

[0068] (3) Using ultraviolet lithography, a geometrically shaped integral junction pattern (15 μm in diameter) is transferred onto the tunnel junction. The mixture is exposed to positive photoresist for 12 seconds, developed for 30 seconds, fixed for 15 seconds, and then subjected to ICP plasma etching to remove the remaining portions down to the lowest NiCo layer. 2- x Fe x The structure obtained at the top of the O4 layer is as follows: Figure 2 As shown in ④ (the junction region in ④ consists of a Pt layer and a NiCo layer), 2-y Fe y O4 layer, MgAl2O4 layer, NiCo 2-x Fe x (composed of O4 layers);

[0069] (4) Using ultraviolet lithography, the geometrically shaped perforated area pattern (with a hole diameter of 5 μm) is transferred onto the junction structure obtained in step (3). The negative photoresist is exposed for 12 s, developed for 12 s, and fixed for 15 s. Then, ICP plasma etching is used to remove the perforated area not covered by the negative photoresist to NiCo. 2-x Fe x O4 layer, NiCo 2-x Fe x The O4 layer also forms perforations, resulting in a structure such as Figure 2 As shown in ⑤;

[0070] (5) A SiO2 insulating layer was deposited using plasma-enhanced chemical vapor deposition to prevent leakage current in the tunnel junction and isolate it from the external environment. Then, excess SiO2 was etched away using ICP plasma etching. The ICP etching gas was Ar, and the etching rate was 0.37 nm / s. The resulting structure is shown below. Figure 2 As shown in ⑥;

[0071] (6) A geometrically shaped top electrode pattern was transferred onto the junction region using ultraviolet lithography, ensuring the top electrode pattern covered the junction region. The negative photoresist was exposed for 12 seconds, developed for 12 seconds, and fixed for 15 seconds. A top electrode layer of Pt (60 nm) was deposited at room temperature at a deposition rate of 0.1 nm / s. The Pt outside the top electrode was then removed using acetone. The resulting structure is shown below. Figure 2 As shown in ⑦.

[0072] The testing method utilizes a comprehensive physical property measurement system (manufactured by QuantumDesign, the comprehensive physical property measurement system PPMS) to apply a constant current and measure the voltage. During the test, the current direction is as follows: Figure 2 As shown in ⑧.

[0073] Comparative Example 1

[0074] Compared with Example 1, the only difference in Comparative Example 1 is that Fe3O4 layers of the same thickness and shape are used instead of NiCo in Example 1. 2-y Fe y O4 layer, MgAl2O4 layer, NiCo 2-x Fe x The O4 layer (i.e., in the process of preparing the all-oxide vertical ferrimagnetic tunnel junction, Fe3O4 target material is used instead of NiCo) 2-x Fe x O4 (x = 0.2) target material, NiCo 2-y Fe yO4 (y=0.1) target material). The Fe3O4 layer has a high deposition temperature (deposition temperature is 550℃), a large lattice constant mismatch with the MgAl2O4 layer, and a poor interface with the barrier layer. The product obtained in Comparative Example 1 has a poor tunneling effect.

[0075] Comparative Example 2

[0076] Compared to Example 1, Comparative Example 2 differs only in that it uses an Al2O3 layer of the same thickness and shape instead of the MgAl2O4 layer in Example 1. The lattice constant of Al2O3 is similar to that of NiCo. 2-y Fe y Due to significant O4 mismatch, NiCo was grown using Al2O3 as the top layer of the barrier. 2- y Fe y The O4 layer is non-magnetic.

[0077] Comparative Example 3

[0078] Compared to Example 1, Comparative Example 3 differs only in that it uses an MgO layer of the same thickness and shape instead of the MgAl2O4 layer in Example 1. The lattice constant of MgO and NiCo... 2-y Fe y O4 mismatch is significant, and NiCo is grown using MgO as the top layer of the barrier. 2-y Fe y O4 may exhibit superparamagnetic behavior.

[0079] Comparative Example 4

[0080] Compared to Example 1, Comparative Example 4 differs only in that a NiO layer of the same thickness and shape is used instead of the MgAl2O4 layer in Example 1. The NiO lattice constant and NiCo... 2-y Fe y The O4 mismatch is significant, resulting in the growth of NiCo. 2-x Fe x The O4 layer exhibits deteriorated magnetism and lacks perpendicular anisotropy.

[0081] In addition, the deposition temperatures during the preparation of Al2O3, MgO, and NiO layers in Comparative Examples 2-4 were all greater than 400℃.

[0082] Comparative Example 5

[0083] Compared with Example 1, the only difference in Comparative Example 4 is that single-crystal silicon is used instead of the MgAl2O4 substrate in Example 1.

[0084] Comparative Example 6

[0085] Compared with Example 1, the only difference in Comparative Example 6 is the removal of NiCo. 2-y Fe y O4 layer and NiCo2-x Fe x The location of layer O4.

[0086] Comparative Example 7

[0087] A commercially available vertical magnetic tunnel junction using Ta / CoFeB heavy metals as the magnetic layer and MgO as the barrier layer.

[0088] Product effectiveness test

[0089] The products prepared in the above examples and comparative examples were subjected to performance testing.

[0090] The performance testing process is as follows: First, the test pucks of Example 1, the comparative tunnel junction, and the PPMS system (i.e., the comprehensive physical property measurement system) are connected with aluminum wire using an ultrasonic aluminum wire bonding machine. Then, the test pucks are placed into the test chamber of the PPMS system, a vacuum is drawn to 8 Torr, the resistance mode of the PPMS system is activated, and the test is carried out at 50K. The magnetic field sweep range is 1T, and the sweep rate is 20Oe / s. The test results are as follows:

[0091] Example 1: A significant tunneling magnetoresistance signal can be measured in the all-oxide vertical ferrimagnetic tunnel junction under magnetic field assistance with an applied current of 1 μA, corresponding to a current density of 0.6 μA / cm. 2 .

[0092] When a 1 μA current was applied to the tunnel junctions prepared in Comparative Examples 1-6 with magnetic field assistance, no tunneling magnetoresistance signal could be detected.

[0093] In Comparative Example 7, when a 1 μA current is applied to the vertical magnetic tunnel junction with magnetic field assistance, no tunneling magnetoresistance signal can be detected. Only when a 10 μA current is applied with magnetic field assistance can a tunneling magnetoresistance signal be detected, and the corresponding current density is 10 μA / cm². 2 .

[0094] It can be seen that the components or substrate of each layer of the all-oxide vertical ferrimagnetic tunnel junction of the present invention are not easily replaced. Furthermore, compared with the commercially available vertical magnetic tunnel junction of Comparative Example 7, the all-oxide vertical ferrimagnetic tunnel junction of Embodiment 1 of the present invention has higher conductivity, lower overall resistance, and reduced energy consumption. Moreover, the lower current density is beneficial for reducing transistor size and achieving denser storage.

[0095] Based on Example 1, by adjusting the process parameters in the preparation of the all-oxide vertical ferrimagnetic tunnel junction, a similar all-oxide vertical ferrimagnetic tunnel junction with the same effect as in Example 1 can also be obtained.

Claims

1. A fully oxide vertical ferrimagnetic tunnel junction, characterized in that, Including NiCo layers stacked sequentially on the substrate 2- x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y O4 layer, and the NiCo 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y The O4 layer is ring-shaped, wherein 0 ≤ y ≤ x ≤ 0.2; the substrate is composed of MgAl2O4; The NiCo 2-y Fe y The O4 layer includes, in sequence, a ring-shaped metal layer and a top electrode layer; The NiCo 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y The O4 layer is ring-shaped with pores inside filled with silica.

2. The all-oxide vertical ferrimagnetic tunnel junction according to claim 1, characterized in that, The NiCo 2-x Fe x The thickness of the O4 layer is 5-15 nm; And / or, the thickness of the MgAl2O4 layer is 1-3 nm; And / or, the NiCo 2-y Fe y The thickness of the O4 layer is 5-15 nm; And / or, the thickness of the metal layer is 15-25 nm; And / or, the thickness of the top electrode layer is 40-60 nm.

3. The method for preparing the all-oxide vertical ferrimagnetic tunnel junction according to any one of claims 1-2, characterized in that, Includes the following steps: Take a substrate and deposit NiCo sequentially on the substrate. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y O4 layer, metal layer.

4. The preparation method according to claim 3, characterized in that, Includes the following steps: (1) Take a substrate and deposit NiCo sequentially on the substrate. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y O4 layer, metal layer; (2) Based on step (1), NiCo is etched away using ultraviolet lithography and ICP plasma. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y The O4 layer and metal layer expose the substrate. (3) Based on step (2), NiCo is further etched away using ultraviolet lithography and ICP plasma. 2-y Fe y The O4 layer and MgAl2O4 layer partially make NiCo 2-x Fe x Part of the O4 layer is exposed; (4) Based on step (3), NiCo is etched using ultraviolet lithography and ICP plasma etching. 2-x Fe x O4 layer, MgAl2O4 layer, NiCo 2-y Fe y A through-hole is formed in the center of the O4 layer and the metal layer, but the substrate is not etched. (5) Further deposit a silicon dioxide layer based on step (4); (6) A pattern is formed using ultraviolet lithography, and a top electrode layer is deposited on the metal layer.

5. The preparation method according to claim 3 or 4, characterized in that, The NiCo 2-x Fe x The O4 layer utilizes NiCo. 2- x Fe x O4 target material was obtained by laser pulse deposition; And / or, the NiCo 2-x Fe x The preparation process of O4 target material includes the following steps: NiO, Co3O4 and Fe2O3 powders are mixed, pre-sintered at 1050-1100℃ for 3-4.5 hours, and then sintered at 1180-1200℃ for 5.5-6 hours to obtain the target material; And / or, the NiCo 2-y Fe y The O4 layer utilizes NiCo. 2-y Fe y O4 target material was obtained by laser pulse deposition; And / or, the NiCo 2-y Fe y The preparation process of O4 target material includes the following steps: NiO, Co3O4 and Fe2O3 powders are mixed, pre-sintered at 1050-1100℃ for 3-4.5 hours, and then sintered at 1180-1200℃ for 5.5-6 hours to obtain the target material; To satisfy the condition that x and y take values ​​in the range of 0 ≤ y ≤ x ≤ 0.2, during the preparation of NiCo... 2-x Fe x O4 sputtering target, NiCo 2-y Fe y The amounts of NiO, Co3O4, and Fe2O3 powders can be adjusted as needed during the O4 target process.

6. The preparation method according to claim 3 or 4, characterized in that, NiCo was deposited using laser pulses. 2- x Fe x O4 layer, NiCo 2-y Fe y During the O4 layer deposition process, the deposition temperature is 280-350℃, the oxygen pressure is 15-26Pa, the pulse frequency is 6-10Hz, and the laser energy is 55-67mJ. And / or, during the deposition of the MgAl2O4 layer using laser pulses, the deposition temperature is 300-350℃, the oxygen pressure is 0.5-1Pa, the pulse frequency is 4-7Hz, the laser energy is 60-67mJ, and after the MgAl2O4 layer is deposited, it is kept at this temperature for 5-10 minutes.

7. A memory, characterized in that, Includes the all-oxide vertical ferrimagnetic tunnel junction as described in any one of claims 1-2.

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