CN105938872A - Magnetic tunnel junction structure and tunnel magnetoresistive element - Google Patents

Abstract

The invention discloses a magnetic tunnel junction structure, which belongs to the technical field of magnetoelectronics. The magnetic tunnel junction structure of the present invention includes the following improvements: introducing an ultra-thin metal Mg layer to form an insulating barrier layer of a Mg/MgO/Mg sandwich superlattice structure; utilizing two ferromagnetic material layers with opposite magnetostrictive properties The formed superlattice structure serves as the free layer of the pinned TMR structure; an additional pinning layer that can realize the pinning effect on the edge micro magnetic domains in the free layer is introduced on the side wall of the free layer. The invention also discloses a tunnel magneto-resistance element, a tunnel magneto-resistance head, a tunnel magneto-resistance sensor and a magnetic storage unit using the tunnel magneto-resistance element. Compared with the prior art, the invention can effectively reduce the electromagnetic noise in the MTJ element and greatly improve the sensitivity of the TMR sensor.

Description

Magnetic tunnel junction structure, tunnel magnetoresistive element

technical field

The invention relates to a magnetic tunnel junction structure, belonging to the technical field of magnetoelectronics.

Background technique

Biomolecular recognition has a wide range of applications in RNA strand recognition, gene detection, bacterial diagnosis, new drug discovery, DNA defects and lethal agents in biological warfare, food safety, and early diagnosis and detection of major diseases represented by malignant tumors. Magnetic biomolecular recognition, detection and monitoring is a new type of biomolecular measurement technology developed in recent years. The basic principle of magnetic nanoparticle molecular recognition is to use high-performance magnetic field sensors to measure the fringe field of magnetic nanoparticles labeled biomolecules under magnetization. The fringing field emanating from a single magnetic nanoparticle is about 2 Oe, which is on the order of magnitude similar to the geomagnetic field of 0.5 Oe. Considering the distance between the magnetic particle and the magnetically sensitive layer in the measurement, for the detection of a single magnetic particle, the sensor must have the ability to measure the magnetic field strength below 0.05Oe, which requires an ultra-sensitive sensing system. Although magnetic nanoparticles with large magnetic moments can help obtain large magnetic fringe fields, the key to solving the bottleneck of magnetic molecular recognition technology still depends on the breakthrough of sensor technology. Current sensing systems for small magnetic field measurements include magnetic anisotropy (AMR), Hall effect, based on superconducting quantum interference devices (SQUID) and spin electron resonance (SER) and other technologies. The low sensitivity of AMR and Hall effect limit their application in biomolecular detection. SQUID and SER have high sensitivity. However, the large size of SQUID and SER prevents them from being used in portable and economical biomolecular detection of diseases and early diagnosis of diseases.

The TMR (Tunneling Magneto Resistance, tunneling magnetoresistance) element developed based on the spin electron tunneling transmission effect, also known as the MTJ (Magnetic Tunnel Junctions, magnetic tunnel junction) element, has a resistance value change rate of up to 180% at room temperature (RA～1.00), almost 3 orders of magnitude higher than traditional magnetic sensors. Different from the principle of GMR, the magnetic tunnel junction (TMR) is composed of magnetic metal/non-magnetic insulator/magnetic metal (FM/I/FM). In this structure, if the magnetization directions of the two ferromagnetic layers are parallel, an iron The electrons of the majority-spin subband in the magnetic layer will enter the vacant state of the majority-spin subband in the other electrode, and the electrons of the minority-spin subband will also enter the vacancy of the minority-spin subband of the other electrode from one electrode. State, the coercive force of the ferromagnetic layer overcome by the magnetic field can make their magnetization direction turn to the magnetic field direction and tend to be consistent, at this time TMR is a minimum value; if the magnetization directions of the two electrodes are antiparallel, then the magnetization direction of one electrode The spin of the majority subband is parallel to the spin of the electrons in the minority subband of the other electrode, so that the electrons in the majority subband of one electrode must search for the spin of the minority subband in the other electrode during the tunnel conduction process. Empty state, TMR is the maximum value. Since only a simple ferromagnetic layer needs to be reversed, only a very small external field is needed to achieve the maximum value of TMR, so its magnetic field sensitivity is extremely high, and at the same time, the junction resistance with high TMR is easy to obtain a large electrical signal output. Making TMR-based sensors one of the very few magnetic field sensors with ultra-high sensitivity. At the same time, the characteristics of the electrical signal output of the TMR sensor are easily integrated with modern semiconductor circuits to achieve the goals of miniaturization, digitization, networking, portability and economy.

Existing TMR structures can be further divided into two categories: a pinned TMR structure with a pinning layer and a TMR structure without a pinning layer. Figure 1 shows a TMR structure without a pinning layer. Between the substrate and the protective layer is a traditional magnetic metal/nonmagnetic insulator/magnetic metal sandwich structure, where the nonmagnetic insulator is also called an insulating barrier layer. The pinned TMR adds an antiferromagnetic (AF) pinning layer to the traditional magnetic metal/nonmagnetic insulator/magnetic metal sandwich structure. As shown in Figure 2, the ferromagnetic layer close to the pinning layer is called The pinned layer, and another ferromagnetic layer is called the free layer.

In the existing TMR sensor structure, MgO is usually chosen as the insulating barrier layer because it has extremely small crystal dislocations with the magnetic metal alloy in the ferromagnetic layer, thereby reducing the spin-dependent electron transfer between the insulating layer and the magnetic layer. Interfacial electron scattering improves signal output. However, the high insulating properties of a single MgO layer lead to high junction resistance, power consumption, and electrical noise, which adversely affect the sensitivity enhancement of TMR sensors.

In addition, due to the high spin polarizability of CoFe materials, existing TMR sensors often use a single CoFe magnetic layer as the free layer, which can enhance the dR/R index of the sensor. However, the CoFe magnetic layer has positive magnetostriction, which will bring magnetic noise, which is not conducive to the further improvement of the sensitivity of the TMR sensor.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a magnetic tunnel junction structure, which can effectively reduce the electromagnetic noise in the MTJ element and greatly improve the sensitivity of the TMR sensor.

The present invention specifically adopts the following technical solutions to solve the above technical problems:

A magnetic tunnel junction structure comprising a first ferromagnetic layer, a second ferromagnetic layer, and an insulating barrier layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer; the insulating barrier layer includes an MgO layer , between the MgO layer and the first ferromagnetic layer and between the MgO layer and the second ferromagnetic layer, a metal Mg thin film with a thickness smaller than that of the MgO layer is arranged respectively.

Preferably, the magnetic tunnel junction structure further includes a pinning layer disposed outside the second ferromagnetic layer for magnetically pinning the second ferromagnetic layer.

Further, the first ferromagnetic layer is a composite layer including a first magnetic layer and a second magnetic layer, and the first magnetic layer and the second magnetic layer have opposite magnetostrictive properties.

Furthermore, a discontinuous Ta metal layer is disposed between the first magnetic layer and the second magnetic layer.

In order to suppress the magnetic noise generated by the rotation of tiny magnetic domains at the edge of the free layer of the pinned TMR structure, the present invention further provides an additional pinning layer around the sidewall of the first ferromagnetic layer, and the additional pinning layer can A magnetic dipole field for pinning the marginal magnetic domains in the first ferromagnetic layer is generated.

Preferably, the second ferromagnetic layer is a superlattice antiferromagnetic layer of CoFe/Ru/CoFe structure.

According to the same inventive idea, the following technical solutions can be obtained:

A tunnel magnetoresistive element, comprising a substrate and the magnetic tunnel junction structure as described in any one of the above technical solutions arranged on the substrate.

Further, the tunnel magnetoresistive element further includes a buffer layer disposed between the substrate and the magnetic tunnel junction structure, and a protective layer disposed on the magnetic tunnel junction structure.

The tunnel magnetoresistive element of the present invention can be widely used in magnetic storage, magnetoresistive sensors, magnetic readout heads, magnetic biomolecular detection, etc. The following are several specific applications:

A tunnel magneto-resistive magnetic head, comprising the tunnel magneto-resistive element described in any one of the above technical solutions.

A tunnel magneto-resistive sensor, comprising the tunnel magneto-resistive element described in any one of the above technical solutions.

A magnetic storage unit, comprising a tunnel magnetoresistive element as described in any one of the above technical solutions.

A magnetic biomolecule detection unit, comprising a tunnel magneto-resistance element as described in any one of the above technical solutions.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

The present invention improves the existing TMR structure using a single MgO layer as an insulating barrier layer, introduces ultra-thin metal Mg layers on both sides of the MgO layer, thereby forming an insulating barrier layer of a Mg/MgO/Mg sandwich superlattice structure, It can effectively reduce the junction resistance (RA value) of the TMR structure, form a sudden interface MgO, and prevent the diffusion of MgO in the ferromagnetic layer during deposition and annealing, thereby effectively suppressing magnetic noise and improving the signal-to-noise ratio and sensitivity.

The present invention further utilizes a composite layer composed of two ferromagnetic material layers with opposite magnetostrictive properties as the free layer of the pinned TMR structure, thereby comprehensively adjusting the magnetostriction and dR/R of the TMR structure, and further through The interface layer of the two ferromagnetic material layers is inserted into a discontinuous Ta metal layer to maintain the magnetic coupling of the two ferromagnetic material layers, and can obtain soft magnetostriction and large dR/R.

The present invention further arranges an additional pinning layer around the sidewall of the free layer, and the additional pinning layer can generate a magnetic dipole field that pins the tiny magnetic domains at the edge of the free layer, and can suppress the pinning type TMR structure free layer. The magnetic noise generated by the rotation of tiny magnetic domains at the edge further improves the signal-to-noise ratio and sensitivity of the TMR element. The TMR sensor of the present invention can obtain dR/R ~ 80%, RA ~ 0.45 and Q factor ~ 80 representing the signal-to-noise ratio at room temperature, thus making it possible to measure single biomolecules.

While greatly improving the signal-to-noise ratio and sensitivity of the TMR element, the invention does not need to introduce an expensive and complicated preparation process, and can be realized by using the existing preparation process technology of the TMR element, which is beneficial to large-scale production.

Description of drawings

FIG. 1 is a schematic diagram of an existing TMR structure without a pinning layer;

FIG. 2 is a schematic structural diagram of an existing pinned TMR;

Fig. 3 is the first embodiment of the TMR element of the present invention;

Fig. 4 is the second embodiment of the TMR element of the present invention;

Fig. 5 is a third embodiment of the TMR element of the present invention.

detailed description

The technical scheme of the present invention is described in detail below in conjunction with accompanying drawing:

In order to improve the sensitivity of the existing TMR device, the idea of the present invention is realized by effectively suppressing the magnetic noise existing in the TMR structure. The present invention improves specifically through the following aspects:

1. Introduce an ultra-thin metal Mg layer to form an insulating barrier layer of the Mg/MgO/Mg sandwich superlattice structure:

The existing TMR structure chooses MgO as the insulating barrier layer because it has extremely small crystal dislocations with magnetic transition metal alloys (such as FeCo), thereby reducing spin-dependent electron scattering and electron scattering at the interface between the insulating layer and the magnetic layer. Extend the mean free shell of spin-dependent electrons. Another reason is that electrons can only tunnel through the spin-up energy band ∆1 because of the special electronic band structure of MgO. In this way, MgO acts as a spin filter layer, which can improve the spin polarizability and dR/R of electrons. Electrical noise in MTJ sensors, especially at high frequencies, mainly originates from the insulating barrier layer in the sensor. Reducing the RA value of the MTJ can effectively reduce electrical noise. In the present invention, an ultra-thin Mg layer (thickness smaller than that of the MgO layer) is respectively inserted between the two ferromagnetic layers and the MgO layer. This method can effectively reduce the junction resistance (RA value) of the TMR structure, and at the same time form an abrupt interfacial MgO, which prevents the diffusion of MgO in the ferromagnetic layer during deposition and annealing.

Fig. 3 has shown the first embodiment of TMR element of the present invention, as shown in the figure, on substrate, be formed with: buffer layer, pinning layer, pinned layer, insulation barrier layer, free layer, protection layer, wherein the insulating barrier layer includes a MgO layer, and a metal Mg thin film with a thickness smaller than that of the MgO layer is respectively arranged between the MgO layer and the free layer and between the MgO layer and the pinned layer. Figure 3 uses a pinned TMR structure as an example. In fact, for a non-pinned TMR structure, the insulating barrier layer of this Mg/MgO/Mg sandwich superlattice structure can also be used. In addition to the above insulating barrier layer, other parts of the TMR element can use various existing or future materials and structures, for example, the free layer can use CoFe or NiFe, the pinned layer can use CoFe, antiferromagnetic pinning Layer can use IrMn or Pt/Mn. This new TMR structure can effectively suppress noise and improve signal-to-noise ratio and sensitivity.

2. Using a superlattice structure composed of two ferromagnetic material layers with opposite magnetostrictive properties as the free layer of the pinned TMR structure:

Due to the high spin polarizability of CoFe materials, the existing TMR sensors often use a single CoFe magnetic layer as the free layer, which can enhance the dR/R index of the sensor, but the CoFe magnetic layer has positive magnetostriction, which will bring to magnetic noise. To this end, a ferromagnetic material layer with opposite magnetostrictive properties can be introduced to form a superlattice structure with CoFe to replace the existing single CoFe free layer. For example, the NiFe magnetic layer has good magnetostriction but low spin polarizability and dR/R; thus a free layer combining CoFe and NiFe can comprehensively tune the magnetostriction and dR/R. In particular, by further inserting a discontinuous Ta metal layer in the CoFe/NiFe interface layer, the CoFe/NiFe magnetic coupling can be maintained, and soft magnetostriction and large dR/R can be obtained.

Fig. 4 shows the second embodiment of the TMR element of the present invention, as shown in the figure, on the substrate, be formed with: buffer layer, pinning layer, pinned layer, insulation barrier layer, free layer, protection layer; wherein the insulating barrier layer includes a MgO layer, and a metal Mg film with a thickness smaller than the thickness of the MgO layer is respectively arranged between the MgO layer and the free layer and between the MgO layer and the pinned layer; the free layer is composed of CoFe magnetic A composite layer of a NiFe magnetic layer and a CoFe magnetic layer, a discontinuous Ta metal layer is inserted between the CoFe magnetic layer and the NiFe magnetic layer, so that part of the CoFe magnetic layer is in contact with the NiFe magnetic layer, while the other part is separated by the Ta metal layer .

3. Introduce an additional pinning layer on the side wall of the free layer that can pin the tiny magnetic domains at the edge of the free layer:

The magnetic noise mainly originates from the switching action of the magnetic layer in the TMR structure under the external field. Therefore, suppressing the rotation and jumping of the magnetic domains of the magnetic layer under the external field becomes the key to suppressing the noise. TMR sensors have two main magnetic layers: one is a magnetically free layer and the other is a pinned layer. For the magnetic free layer, due to the shrinkage of the device size, the magnetic coercive force becomes larger, and there are many tiny magnetic domains at the edge of the magnetic free layer. The rotation of these tiny magnetic domains under the external field is the main source of magnetic noise in the magnetic free layer, so an additional pinning layer composed of hard magnetic materials can be introduced at the edge of the free layer. After the magnetic field annealing treatment, the magnetic dipoles of the hard magnetic material are arranged along the magnetic field direction to form a large static magnetic dipole field, which can effectively pin the tiny magnetic domains to become magneto-dead layers, without Then jump with the external magnetic field, thereby suppressing the magnetic noise.

Fig. 5 has shown the 3rd embodiment of TMR element of the present invention, as shown in the figure, be formed with in sequence on substrate: buffer layer, pinning layer, pinned layer, insulation barrier layer, free layer, protection layer; wherein the insulating barrier layer includes a MgO layer, and a metal Mg film with a thickness smaller than the thickness of the MgO layer is respectively arranged between the MgO layer and the free layer and between the MgO layer and the pinned layer; the free layer is composed of CoFe magnetic A composite layer of a NiFe magnetic layer and a CoFe magnetic layer, a discontinuous Ta metal layer is inserted between the CoFe magnetic layer and the NiFe magnetic layer, so that part of the CoFe magnetic layer is in contact with the NiFe magnetic layer, while the other part is separated by the Ta metal layer ; An additional pinning layer is arranged on both sides of the free layer and the insulating barrier layer, and the additional pinning layer can generate a magnetic dipole field for pinning the edge micro magnetic domains in the free layer. The material of the additional pinning layer can be the material used for the pinning layer, such as IrMn or Pt/Mn.

In addition, in order to suppress the rotation of the magnetic domains of the pinned layer under the external field, the artificially synthesized superlattice pinned layer can be considered. This superlattice pinned layer is composed of CoFe/Ru/CoFe. The upper and lower layers of CoFe establish extremely strong ferromagnetic coupling through the Ru layer, so that the magnetic domains of the pinned layer are difficult to rotate under the external field, thereby suppressing the magnetic noise.

The TMR structure of the present invention can be prepared by using the existing process technology, which does not increase the difficulty of production and facilitates large-scale mass production. Taking the TMR element shown in Figure 5 as an example, the following process can be used for preparation:

Step 1, depositing a pinning layer and a CoFe/Ru/CoF pinning layer sequentially on the substrate by using a thin film vacuum deposition method;

Step 2, depositing a Mg/MgO/Mg insulating barrier layer thin film structure by a thin film vacuum deposition method;

The 3rd step, utilize thin film vacuum deposition method to make CoFe/NiFe free layer thin film;

Step 4, depositing a protective layer using a thin film vacuum deposition method;

Step 5, photolithographic protective layer film;

Step 6, manufacturing additional pinning layer structure by ion beam etching;

Step 7, using thin film vacuum deposition method to deposit additional pinning layer material;

Step 8, annealing at 210°C and 370°C.

The TMR sensor prepared by the above method can obtain a sensitivity of up to 120% dR/R at room temperature, making it possible to measure single biomolecules. The TMR element of the invention can be widely used in magnetic storage, magnetoresistive sensors, magnetic readout heads, etc., and has good application prospects.

Claims (13)

1. A magnetic tunnel junction structure comprising a first ferromagnetic layer, a second ferromagnetic layer and an insulating barrier layer sandwiched between the first ferromagnetic layer and the second ferromagnetic layer; it is characterized in that the insulating The potential barrier layer includes a MgO layer, and a metal Mg thin film with a thickness smaller than that of the MgO layer is arranged between the MgO layer and the first ferromagnetic layer and between the MgO layer and the second ferromagnetic layer. 2 . The magnetic tunnel junction structure according to claim 1 , further comprising a pinning layer disposed outside the second ferromagnetic layer for magnetically pinning the second ferromagnetic layer. 3 . 3. The magnetic tunnel junction structure according to claim 2, wherein the first ferromagnetic layer is a composite layer comprising a first magnetic layer and a second magnetic layer, and the magnetic layer of the first magnetic layer and the second magnetic layer The stretching properties are opposite. 4. The magnetic tunnel junction structure according to claim 3, wherein a discontinuous Ta metal layer is disposed between the first magnetic layer and the second magnetic layer. 5. The magnetic tunnel junction structure according to claim 3, wherein the first magnetic layer is a CoFe magnetic layer, and the second magnetic layer is a NiFe magnetic layer. 6. The magnetic tunnel junction structure according to any one of claims 1 to 5, wherein an additional pinning layer is provided around the sidewall of the first ferromagnetic layer, and the additional pinning layer can generate The magnetic dipole field of the pinning effect is realized by the marginal magnetic domains in the first ferromagnetic layer. 7. The magnetic tunnel junction structure according to claim 6, wherein the second ferromagnetic layer is a superlattice ferromagnetic layer of CoFe/Ru/CoFe structure. 8 . A tunnel magnetoresistive element, characterized by comprising a substrate and the magnetic tunnel junction structure according to any one of claims 1 to 7 arranged on the substrate. 9 . The tunnel magnetoresistive element according to claim 8 , further comprising a buffer layer disposed between the substrate and the magnetic tunnel junction structure, and a protective layer disposed on the magnetic tunnel junction structure. 10. A tunnel magneto-resistive magnetic head, characterized in that it comprises the tunnel magneto-resistive element as claimed in claim 8 or 9. 11. A tunnel magneto-resistive sensor, characterized in that it comprises the tunnel magneto-resistive element as claimed in claim 8 or 9. 12. A magnetic memory unit, comprising the tunnel magnetoresistive element as claimed in claim 8 or 9. 13. A magnetic biomolecule detection unit, comprising the tunnel magneto-resistance element according to claim 8 or 9.