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CN-122028644-A - Tunneling magnetoresistance enhancement method of magnetic tunnel junction and magnetic tunnel junction

CN122028644ACN 122028644 ACN122028644 ACN 122028644ACN-122028644-A

Abstract

The invention discloses a tunneling magnetoresistance enhancement method of a magnetic tunnel junction and the magnetic tunnel junction, and belongs to the technical fields of functional material preparation and spintronics. The method comprises the steps of S1, sequentially depositing a buffer layer and a pinning layer comprising a first coupling layer on a substrate, S2, carrying out pre-annealing treatment on the pinning layer before depositing an MgO barrier layer, S3, sequentially depositing a second coupling layer, a reference layer, the MgO barrier layer, a free layer and a protective layer on the pre-annealed pinning layer to form a full-film stack structure, and S4, carrying out sectional gradient annealing treatment on the full-film stack, wherein the treatment comprises four stages of low-temperature interface restoration, medium-temperature lattice optimization, high Wen Zixuan strengthening and gradient cooling which are sequentially carried out. The invention also provides a magnetic tunnel junction prepared by the method. Through the synergistic effect of the pre-annealing and the sectional gradient annealing, the invention eliminates interface defects, optimizes MgO crystal structure and strengthens spin orbit coupling, thereby remarkably improving tunneling magnetoresistance efficiency.

Inventors

  • DU YINCHANG
  • MENG DEQUAN
  • CHEN LEI
  • LI YUTING

Assignees

  • 致真精密设备(杭州)有限公司

Dates

Publication Date
20260512
Application Date
20260116

Claims (10)

  1. 1. A method for enhancing tunneling magnetoresistance of a magnetic tunnel junction, comprising the steps of: S1, sequentially depositing a buffer layer and a pinning layer comprising a first coupling layer on a substrate, wherein the pinning layer comprises a composite multilayer film structure of alternately deposited platinum layers and cobalt layers; S2, before the MgO barrier is deposited, pre-annealing the pinning layer deposited in the step S1; S3, sequentially depositing a second coupling layer, a reference layer, an MgO barrier layer, a free layer and a protective layer on the pinning layer subjected to pre-annealing treatment to form a full film stack structure, wherein the reference layer and the free layer both comprise CoFeB alloy layers; And S4, carrying out sectional gradient annealing treatment on the full membrane stack structure, wherein the sectional gradient annealing treatment comprises four stages which are sequentially carried out, namely, carrying out low-temperature interface repair in the first stage, carrying out medium-temperature lattice optimization in the second stage, carrying out high Wen Zixuan reinforcement in the third stage and carrying out gradient cooling in the fourth stage.
  2. 2. The method according to claim 1, wherein the pre-annealing treatment in step S2 is performed by heating the sample deposited with the buffer layer and the pinning layer to 250-350 ℃ at a temperature rising rate of 5-15 ℃ per minute in a vacuum environment, maintaining the temperature for 20-40 minutes, and then cooling to room temperature.
  3. 3. The method according to claim 2, wherein the pre-annealing treatment has a temperature rise rate of 10 ℃ per minute, a soak temperature of 300 ℃ and a soak time of 30 minutes.
  4. 4. The method according to claim 1, wherein the parameters of each stage of the step S4 of the step-wise gradient annealing process are: the first stage, heating the sample to 150-190 ℃ at a temperature rising rate of 3-7 ℃ per minute, and preserving heat for 20-30 minutes; a second stage, namely continuously heating the sample from the temperature of the first stage to 250-290 ℃ at a heating rate of 2-5 ℃ per minute, and preserving heat for 35-55 minutes; a third stage, namely continuously heating the sample from the temperature of the second stage to 310-330 ℃ at a heating rate of 1-3 ℃ per minute, and preserving heat for 15-25 minutes; and a fourth stage, namely reducing the temperature of the sample from the third stage to below 100 ℃ at a cooling rate of 3-5 ℃ per minute, and then naturally cooling the sample to room temperature.
  5. 5. The method of claim 4, wherein the step of determining the position of the first electrode is performed, The first stage is heated to 180 ℃ at a rate of 5 ℃ per minute and is kept for 25 minutes; The second stage is heated to 270 ℃ at a rate of 3 ℃ per minute and is kept for 45 minutes; the third stage is heated to 320 ℃ at a rate of 2 ℃ per minute and kept for 18 minutes; the fourth stage is cooled to below 100 ℃ at a rate of 4 ℃ per minute.
  6. 6. The method of claim 1, wherein the MgO barrier layer is deposited in step S3 by using a radio frequency magnetron sputtering process, the sputtering power is 50-80W, the working gas pressure is 0.17-0.25Pa, and the target base distance is 8-12cm.
  7. 7. The method of claim 6, wherein the process parameters for depositing the MgO barrier are a radio frequency power of 50W, an operating gas pressure of 0.18Pa, and a target base distance of 10cm.
  8. 8. The method of claim 1, wherein the structure of the pinning layer, in order from the buffer layer side, is: a platinum layer with a thickness of 1.8-2.2 nm; a first periodic structure comprising p periods of cobalt/platinum bilayer units, wherein each of said cobalt/platinum bilayer units comprises a cobalt layer having a thickness of 0.3-0.5nm and a platinum layer having a thickness of 0.5-0.7nm, p being an integer from 3 to 5; A cobalt layer with a thickness of 0.3-0.5nm located over the first periodic structure; The first coupling layer is positioned on the cobalt layer and is a ruthenium layer with the thickness of 0.7-1.0 nm; A cobalt layer with a thickness of 0.3-0.5nm on the first coupling layer; a second periodic structure comprising q periods of platinum/cobalt bilayer units, wherein each of said platinum/cobalt bilayer units comprises a platinum layer having a thickness of 0.5-0.7nm and a cobalt layer having a thickness of 0.3-0.5nm, q being an integer from 2 to 4.
  9. 9. The method of claim 1, wherein the reference layer has a thickness of 0.9-1.1nm, the free layer has a thickness of 1.5-1.7nm, the MgO barrier layer has a thickness of 1.2-1.4nm, and the second coupling layer has a tantalum layer having a thickness of 0.7-0.9 nm.
  10. 10. A magnetic tunnel junction, characterized in that it is produced by the method of any one of claims 1 to 9.

Description

Tunneling magnetoresistance enhancement method of magnetic tunnel junction and magnetic tunnel junction Technical Field The invention belongs to the technical field of functional material preparation and spintronics, and particularly relates to a tunneling magnetoresistance enhancement method of a magnetic tunnel junction and the magnetic tunnel junction. Background A magnetic tunnel junction (Magnetic Tunnel Junction, MTJ) is a nanoscale heterostructure consisting of two ferromagnetic layers and an insulating tunneling barrier layer sandwiched therebetween, the working principle of which is based on Spin-dependent tunneling effect (Spin-DEPENDENT TUNNELING, SDT). When the magnetization directions of the two ferromagnetic layers are parallel, the tunneling resistance is small, and when the magnetization directions are antiparallel, the tunneling resistance is increased, which phenomenon is called tunneling magnetoresistance (Tunneling Magnetoresistance, TMR). Because of its excellent spintronics and wide application prospect, the magnetic tunnel junction has become a hot spot for research and development in the field of spintronics, and has wide application value in the fields of magnetic random access memories (Magnetic Random Access Memory, MRAM), magnetic sensors, spin logic devices and the like. The size of the tunneling magnetoresistance is closely related to a number of factors, where the material selection, thickness, interface quality, and crystal structure of the insulating tunneling barrier layer play a critical role in TMR performance. Researches show that MgO is used as an insulating tunneling barrier layer material, and the tunneling magnetoresistance performance of the magnetic tunnel junction can be remarkably improved due to the unique crystal structure and electronic characteristics of the MgO. MgO has a face-centered cubic crystal structure, and the (001) crystal face of the MgO is matched with the lattice constant of the traditional ferromagnetic metal (such as Fe, co, ni and the like), so that a highly crystallized interface can be formed, thereby reducing the interface scattering effect and enhancing the tunneling probability of spin polarized electrons. In addition, mgO tunneling barrier has a band-selective tunneling effect (Spin-DEPENDENT FILTER EFFECT), i.e., allows the passage of electron states of a particular symmetry, which further increases the size of the tunneling magnetoresistance. Amorphous Al 2O3 is often used as a tunneling barrier in conventional magnetic tunnel junctions. Although Al 2O3 has high resistivity and good electrical insulation properties, its amorphous structure has difficulty in providing band-selective tunneling effect, resulting in limited performance of tunneling magnetoresistance. In contrast, the MgO tunnel barrier layer can realize high-quality monocrystalline film growth through the magnetron sputtering combined annealing process, and the ordering and crystal matching of the ferromagnetic layer and the tunnel barrier interface are greatly improved, so that the tunnel magnetoresistance effect is remarkably enhanced. This performance boost makes MgO tunnel barrier-based magnetic tunnel junctions an important research focus in the field of spintronics. However, the preparation process of the MgO tunnel barrier layer has a significant effect on the performance of the magnetic tunnel junction. First, an appropriate annealing treatment may promote the crystallization process of the MgO layer, which is converted from an amorphous or polycrystalline state to a highly crystallized single crystal structure. Secondly, the preparation quality of the MgO layer directly determines the scattering degree of spin polarized electrons in the tunneling process. In actual preparation, the sputtering power and the sputtering air pressure of the MgO layer can have great influence on the preparation quality of the MgO layer. Therefore, how to control the interface quality and the crystal orientation of the MgO tunnel barrier by optimizing the preparation process becomes a key technical problem for improving the TMR performance of the magnetic tunnel junction. Currently, the prior art (e.g., CN 201610898458.2) proposes to repair interface damage and improve TMR by using a process of "plasma treatment + single-stage annealing" after deposition of the reference layer. However, the annealing process of the method is relatively simple (such as the heat preservation temperature is 120-400 ℃ and the heating rate is 0.1-1 ℃ per second), the effect is mainly limited to repairing shallow layer defects introduced by plasma treatment, and the effect on systematically optimizing the flatness of a bottom layer film, accurately regulating and controlling the MgO crystallization process, strengthening deep problems such as spin orbit coupling and the like is limited. In particular, for high-end MTJ devices employing complex multilayer film structures (e.g., pt/Co) as the pinning layer and