Magnetic field sensing element based on tunnel magnetoresistance technology and preparation method

Abstract

The invention discloses a magnetic field sensing element based on a tunnel magnetoresistance technology and a preparation method, and relates to the technical field of sensors, and the magnetic field sensing element based on the tunnel magnetoresistance technology comprises a bottom electrode which comprises a buffer layer, a pinning layer and a reference layer; a junction region including a barrier layer, a free layer, and an anti-magnet layer; and a top electrode. A magnetron sputtering method is adopted, required materials grow layer by layer based on a silicon substrate, and photoetching patterning and magnetic shielding layer design are carried out after growth is completed. The magnetic field sensing element with high sensitivity and high stability is realized through materials, a preparation process and a magnetic multilayer film; the sensing element has the advantages of wide measurement range, strong anti-interference capability, miniaturization, integration, low power consumption and the like. Due to the advantages, the tunnel magnetic resistance technology has wide application prospects in the fields of magnetic field detection, magnetic recording, magnetic navigation, magnetic induction and the like.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, in particular to a magnetic field sensing element based on tunnel magnetoresistance technology and a preparation method thereof. Background Art

[0002] Traditional magnetic field sensors such as Hall elements and magnetoresistive elements have low sensitivity and a relatively narrow measurement range. At the same time, the magnetoresistive change of traditional magnetic field sensing elements is often nonlinear with the magnetic field strength, requiring complex correction. The present invention proposes a preparation method and structure of a magnetic field sensing element based on tunnel magnetoresistive technology, which uses advanced micro-nano processing to achieve miniaturization and low power consumption. In contrast, traditional magnetic field sensing elements are large in size, have high power consumption, and are easily interfered by the surrounding electromagnetic field. Summary of the invention

[0003] In view of the above problems existing in the magnetic field sensor element based on the tunnel magnetoresistance technology, the present invention is proposed.

[0004] Therefore, the problem to be solved by the present invention is the deficiency of power consumption of the traditional magnetic field sensor element.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a magnetic field sensing element based on tunnel magnetoresistance technology, comprising a bottom electrode, a buffer layer, a pinning layer and a reference layer stacked from bottom to top; a junction region, a barrier layer, a free layer and an anti-magnetic layer stacked from bottom to top, and the junction region is arranged on the upper side of the bottom electrode; and a top electrode is arranged on the upper side of the junction region.

[0006] As a preferred solution of the magnetic field sensor element based on tunnel magnetoresistance technology described in the present invention, a soft magnetic layer is also provided on the upper side of the free layer to weaken the antiferromagnetic coupling effect of the antiferromagnetic magnet layer, and the soft magnetic layer is a NiFe soft magnetic film.

[0007] As a preferred solution of the magnetic field sensor element based on tunnel magnetoresistance technology described in the present invention, the buffer layer is a multilayer film of alternating Ta and Ru, and the pinning layer is PtMn.

[0008] As a preferred solution of the magnetic field sensing element based on tunnel magnetoresistance technology described in the present invention, the barrier layer is made of MgO to obtain a higher magnetoresistance, the free layer is made of CoFeB, and the anti-magnetic layer is made of IrMn to guide the magnetization direction of the free layer to be perpendicular to the reference layer.

[0009] As a preferred solution of the magnetic field sensor element based on tunnel magnetoresistance technology described in the present invention, wherein: the top electrode is Ru / Ta / Ti from bottom to top, and the top electrode is used to prevent the ferromagnetic layer from being oxidized.

[0010] In order to solve the above technical problems, the present invention also provides the following technical solutions: a method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology, the method comprising: using a magnetron sputtering preparation process to grow a bottom electrode, a barrier layer and a free layer layer by layer based on a silicon substrate; after the growth is completed, performing photolithography patterning and magnetic shielding layer design.

[0011] As a preferred solution of the method for preparing the magnetic field sensor element based on the tunnel magnetoresistance technology of the present invention, the method comprises: spin coating AZ5214 photoresist on the magnetic multilayer film; performing a pre-baking treatment at 95°C for 90s; performing ultraviolet photolithography and development using a mask; performing ion beam etching to etch the bottom electrode to the Si bottom;

[0012] Use plasma to apply glue and strip off the residual photoresist to complete the preparation of the bottom electrode.

[0013] As a preferred solution of the method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology described in the present invention, wherein: an MTJ device of a certain shape is prepared by micro-nano processing techniques such as photolithography, etching, and stripping; and the junction area is etched to the bottom electrode at an etching angle of 30°.

[0014] As a preferred solution of the preparation method of the magnetic field sensor element based on the tunnel magnetoresistance technology described in the present invention, wherein: SiO2 is deposited by the ICP-CVD process to achieve mutual insulation between the junction area, the bottom electrode and the subsequently deposited top electrode; SiO2 etching in the junction area and the bottom electrode area is achieved through photolithography and RIE etching to expose the electrode surface and realize a conductive channel.

[0015] As a preferred solution of the method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology described in the present invention, the method comprises: performing photolithography and development; preparing a top electrode by using an electron beam evaporation method for Au; completing the stripping of the photoresist and the Au film thereon to complete the preparation of the top electrode.

[0016] The beneficial effects of the present invention are as follows: the present invention adopts the magnetron sputtering method to grow the required materials layer by layer based on the silicon substrate, and after the growth is completed, photolithography patterning and magnetic shielding layer design are performed. The magnetic field sensor element with high sensitivity and high stability is realized through materials, preparation processes, and magnetic multilayer films; this sensor element has the advantages of wide measurement range, strong anti-interference ability, miniaturization and integration, and low power consumption. These advantages make the tunnel magnetoresistance technology have broad application prospects in the fields of magnetic field detection, magnetic recording, magnetic navigation, magnetic induction, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 Schematic diagram of the structure of a magnetic field sensing element based on tunnel magnetoresistance technology.

[0019] Figure 2 This is a flow chart for the preparation of magnetic field sensing elements based on tunnel magnetoresistance technology.

[0020] Figure 3 This is the chip layout of the magnetic field sensing element based on tunnel magnetoresistance technology.

[0021] Figure 4 Schematic diagram of the simulation processing of magnetic field sensing elements based on tunnel magnetoresistance technology.

[0022] Figure 5 The present invention is a preparation process of the bottom electrode of the magnetic field sensing element based on the tunnel magnetoresistance technology.

[0023] Figure 6 The present invention is a preparation process of the junction region of a magnetic field sensing element based on tunnel magnetoresistance technology.

[0024] Figure 7 The present invention is a preparation process of the insulating layer of the magnetic field sensing element based on the tunnel magnetoresistance technology.

[0025] Figure 8 The present invention is a preparation process of the top electrode of the magnetic field sensing element based on the tunnel magnetoresistance technology. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0027] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it an embodiment that is mutually exclusive with other embodiments, either individually or selectively.

[0029] Example 1

[0030] Reference Figure 1 and Figure 2 , which is the first embodiment of the present invention, provides a magnetic field sensing element based on tunnel magnetoresistance technology.

[0031] Specifically, the bottom electrode 100 includes a buffer layer 101, a pinned layer 102 and a reference layer 103, the pinned layer 102 is arranged on the upper side of the buffer layer 101, and the buffer layer 101 is arranged on the upper side of the buffer layer 101; the junction region 200 includes a barrier layer 201, a free layer 202 and an anti-magnetic layer 203, the free layer 202 is arranged on the upper side of the barrier layer 201, and the anti-magnetic layer 203 is arranged on the upper side of the free layer 202; the top electrode 300.

[0032] Furthermore, a NiFe soft magnetic film is also provided on the upper side of the free layer 202 to weaken the antiferromagnetic coupling effect of the anti-magnetic layer 203. The buffer layer 101 is a multilayer film of alternating Ta and Ru, which can increase the thickness of the bottom electrode and reduce the influence of the bottom electrode resistance on the magnetoresistance. The pinned layer 102 is made of PtMn, and the reference layer 103 is made of CoFe / Ru / CoFeB as an artificial antiferromagnetic layer. The two ferromagnetic layers are antiferromagnetically coupled by controlling the thickness of the non-magnetic layer.

[0033] The barrier layer 201 is made of MgO, which has a spin filtering effect, that is, it has a selective filtering effect on spin-polarized electrons, so that a higher magnetoresistance rate can be obtained, which can reach up to 180%. The growth quality of the barrier layer 201 directly determines the size of the magnetoresistance effect. The free layer 202 is made of CoFeB, and the anti-magnetic layer 203 is made of IrMn to guide the magnetization direction of the free layer 202 to be perpendicular to the reference layer 103.

[0034] Among them, since the magnetic moment of the reference layer 103 is pinned, the change of the magnetoresistance resistance is mainly determined by the rotation of the magnetic moment of the free layer 202. Therefore, on the basis of controlling the magnetization direction of the free layer 202 to be perpendicular to the reference layer 103, the pinning effect on the free layer 202 should be weakened as much as possible, and the NiFe soft magnetic film is grown between the antiferromagnetic layer 203 and the free layer 202 to weaken the antiferromagnetic coupling of IrMn. In the free layer 202 area, CoFeB / FeNi / IrMn / Ru / Ta / Ti are grown in sequence from bottom to top. The Ru / Ta / Ti capping layer located at the top can prevent the ferromagnetic layer from being oxidized, and mainly plays a protective role.

[0035] The bottom electrode 100 is composed of a Ta, Ru buffer layer 101, a PtMn pinning layer 102, and a CoFe / Ru / CoFeB artificial antiferromagnetic layer; the junction region 200 is composed of a MgO barrier layer 201, a CoFeB free layer 202, a NiFe soft magnetic layer 204, and an IrMn antiferromagnetic layer 203; and the top electrode 300 is a Ru / Ta / Ti covering layer.

[0036] Example 2

[0037] Reference Figure 3 and Figure 4 , which is the second embodiment of the present invention, is based on the previous embodiment and provides a method for preparing a tunneling magnetoresistive film stack.

[0038] Specifically, when preparing the bottom electrode 100, the bottom substrate is a silicon wafer, and a plurality of layers of Ta and Ru alternating multilayer films are grown on the substrate as a buffer layer 100. The function of the buffer layer 100 is to enhance the bonding force between the magnetic film and the substrate. In addition, since the buffer layer 100 itself has a regular lattice sequence, it is easy to induce the formation of a specific orientation of the magnetic layer, thereby obtaining a larger magnetoresistance effect and laying a foundation for the formation of an exchange bias. Above the buffer layer 100, PtMn is selected as the pinning layer 102, which can form an exchange coupling with the adjacent magnetic layer, realize an exchange bias, and pin the magnetic moment orientation of the magnetic layer in a fixed direction. The reason for selecting PtMn as the pinning layer 102 at the bottom layer here is that its Neel temperature is higher than IrMn, which is convenient for secondary annealing to form double pinning. Above the pinned layer 102, the reference layer 103 uses CoFe / Ru / CoFeB to form a synthetic antiferromagnetic layer (SAF). By controlling the thickness of the intermediate non-magnetic layer, the two ferromagnetic layers can form an antiferromagnetic coupling. The SAF structure is convenient for increasing the exchange bias of the pinned layer 102 and improving the thermal / magnetic stability of the magnetic moment of the pinned layer 102. In addition, the Ru in the SAF structure also has the function of absorbing the diffused B ions in the upper layer CoFeB to prevent the B ions from diffusing upward and affecting the crystal quality of the barrier layer.

[0039] Furthermore, when preparing the barrier layer 201, a magnetron sputtering method is used to sputter and grow an MgO film, and a high-purity MgO target with a copper backplane is used to make the insulating barrier layer. The growth conditions of MgO, the sputtering method and the sputtering time are experimentally studied to control the overall resistance of the MTJ.

[0040] When preparing the free layer 202, in order to make a single MTJ produce a linear magnetoresistance response to an external magnetic field, the magnetization directions of the free layer 202 and the reference layer 103 are often required to be perpendicular to each other. There are many ways to guide the magnetization direction of the free layer 202, such as introducing a built-in or external magnetic field, inducing magnetic anisotropy by controlling the shape of the MTJ, etc. This operation inevitably reduces the detection range while achieving a good linear response. This report introduces MFC (magnetic flux concentrator) to increase the MTJ detection range on the basis of controlling the linear response, and uses a double pinning method to induce the magnetization direction of the free layer 202 to be perpendicular to the reference layer 103. Since the magnetic moment of the reference layer 103 is strongly pinned, the change in the magnetoresistance value is mainly determined by the rotation of the magnetic moment of the free layer 202.

[0041] By formula

[0042]

[0043] It can be seen that based on the selected materials of the ferromagnetic layer and the barrier layer 201, the sensitivity of the MTJ depends on the anisotropy field H of the free layer 202. k , H k The size of H is related to the thickness of the free layer 202. The smaller the thickness, the k The smaller the free layer thickness is, the smaller it is. However, the nonlinearity of the MTJ magnetoresistance response is positively correlated with the sensitivity. Therefore, on the basis of controlling the magnetization direction of the free layer 202 to be perpendicular to the reference layer 103, the pinning effect on the free layer 202 should be weakened as much as possible. Therefore, the SAF structure is not used and the NiFe soft magnetic film is grown between the antiferromagnetic layer 203 and the free layer 202 to weaken the antiferromagnetic coupling of IrMn. IrMn is selected as the antiferromagnetic layer here because its Neel temperature is lower than PtMn, which is convenient for secondary annealing and guides the magnetization direction of the free layer to be perpendicular to the reference layer.

[0044] It should be noted that the thickness of MgO needs to be as thin as possible.

[0045] Example 3

[0046] Reference Figures 5 to 8 , which is the third embodiment of the present invention, is based on the first two embodiments and provides a method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology.

[0047] Specifically, the grown magnetic multilayer film needs to be prepared into a MTJ device of a certain shape through micro-nano processing such as photolithography, etching, and stripping. The processing process can be roughly divided into four parts: bottom electrode 100 preparation, junction area 200 preparation, insulating layer 400 covering, and top electrode 300 preparation. Each part consists of several steps. The specific preparation process is as follows:

[0048] First, the bottom electrode 100 is prepared, and AZ5214 photoresist is spin-coated on the magnetic multilayer film. Figure 5 As shown, a pre-bake treatment is then performed at 95°C for 90s, and UV lithography and development are performed using a mask so that the shape of the bottom electrode is retained on the photoresist. Next, IBE parameters are set for ion beam etching, and then plasma is used for gluing. The sample is immersed in acetone for ultrasonic treatment to remove residual photoresist, thereby completing the preparation of the bottom electrode 100.

[0049] After the bottom electrode 100 is prepared, the junction region 200 is prepared. The preparation process of the junction region 200 is basically similar to the etching of the bottom electrode 100. The difference lies in the different masks used during exposure. Figure 6 The figure shows the schematic diagram of the junction region 200 after the mask pattern is successfully transferred to the photoresist after photoresist coating, photolithography and development. Since the thickness of the tunnel junction barrier layer 201 is relatively thin, it is very easy for the bottom electrode conductive particles to be deposited on the barrier layer again during the etching process, thus causing the magnetic tunnel junction to short-circuit. In order to solve this problem, the etching angle of the junction region 200 is optimized, and it is found through experiments that when the etching angle of the junction region 200 is 30°, the success rate of sample preparation can be greatly improved.

[0050] Then, the insulating layer 400 is prepared, such as Figure 7 As shown, SiO2 insulation treatment is required: first, SiO2 is deposited by ICP-CVD process to achieve mutual insulation between the junction area 200, the bottom electrode 100 and the subsequently deposited top electrode 300; on this basis, SiO2 etching is achieved in the junction area 200 and the bottom electrode 100 through photolithography, photolithography and RIE etching to expose the electrode surface and realize a conductive channel.

[0051] Finally, the top electrode 300 is prepared, such as Figure 8 As shown, first, photolithography and development are performed. In this step, the photoresist is used as a negative photoresist. Next, Au is used to prepare the top electrode 300 by electron beam evaporation. Finally, the photoresist and the Au film thereon are stripped off to complete the preparation of the top electrode 300.

[0052] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A magnetic field sensing element based on tunnel magnetoresistance technology, characterized in that: include, A bottom electrode (100) having a buffer layer (101), a pinning layer (102) and a reference layer (103) stacked from bottom to top; A junction region (200) having a barrier layer (201), a free layer (202) and an anti-magnetic layer (203) stacked from bottom to top, wherein the junction region (200) is arranged on the upper side of the bottom electrode (100); The top electrode (300) is disposed on the upper side of the junction region (200).

2. The magnetic field sensor element based on tunnel magnetoresistance technology according to claim 1, characterized in that: A soft magnetic layer (204) is also provided on the upper side of the free layer (202) to weaken the antiferromagnetic coupling effect of the antiferromagnetic magnet layer (203), and the soft magnetic layer (204) is a NiFe soft magnetic film.

3. The magnetic field sensor element based on tunnel magnetoresistance technology as claimed in claim 2, characterized in that: The buffer layer (101) is a multilayer film of alternating Ta and Ru, and the pinning layer (102) is made of PtMn.

4. The magnetic field sensor element based on tunnel magnetoresistance technology as claimed in claim 3, characterized in that: The barrier layer (201) is made of MgO to obtain a higher magnetoresistance, the free layer (202) is made of CoFeB, and the anti-magnetic layer (203) is made of IrMn to guide the magnetization direction of the free layer (202) to be perpendicular to the reference layer (103).

5. The magnetic field sensor element based on tunnel magnetoresistance technology as claimed in claim 4, characterized in that: The top electrode (300) is Ru / Ta / Ti from bottom to top, and the top electrode (300) is used to prevent the ferromagnetic layer from being oxidized.

6. A method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology, characterized in that: The method is applicable to the magnetic field sensing element based on tunnel magnetoresistance technology as described in claims 1 to 5, and comprises: The magnetron sputtering process is used to grow the bottom electrode, barrier layer and free layer layer by layer on the silicon substrate. After the growth is completed, photolithography patterning and magnetic shielding layer design are carried out.

7. The method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology according to claim 3, characterized in that: The specific preparation method of the bottom electrode includes: Spin coating AZ5214 photoresist on the magnetic multilayer film; Carry out pre-baking at 95°C for 90 seconds; UV photolithography and development using a mask; Perform ion beam etching to etch the bottom electrode to the Si bottom; Use plasma to apply glue and strip off the residual photoresist to complete the preparation of the bottom electrode.

8. The method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology according to claim 4, characterized in that: The specific preparation method of the junction region includes: Through micro-nano processing techniques such as photolithography, etching, and stripping, MTJ devices with certain shapes are prepared; The junction region to the bottom electrode is etched at an etching angle of 30°.

9. The method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology according to claim 4, characterized in that: The specific preparation method of the insulating layer includes: SiO2 is deposited by ICP-CVD process to achieve mutual insulation between the junction area, the bottom electrode and the subsequently deposited top electrode; Through photolithography, RIE etching, SiO2 etching in the junction area and bottom electrode area is achieved to expose the electrode surface and realize a conductive channel.

10. The method for preparing a magnetic field sensor element based on tunnel magnetoresistance technology according to claim 4, characterized in that: The specific preparation method of the top electrode includes: Perform photolithography and development; The top electrode is prepared by electron beam evaporation method using Au; The photoresist and the Au film thereon are stripped off, and the preparation of the top electrode is completed.

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