A planar hall sensor based on a magnetic thin film on a periodic corrugated substrate

Abstract

This invention discloses a planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate, belonging to the field of magnetic device technology. It comprises, from bottom to top, a periodically corrugated substrate, a buffer layer, a magnetic thin film layer, a protective layer, and a conductive metal layer. The conductive metal layer includes two conductive metal layers for detecting planar Hall signals arranged perpendicular to the corrugation direction, and two conductive metal layers for external current connection arranged parallel to the corrugation direction. This invention achieves uniaxial anisotropy induced by patterned magnetic thin films by depositing a magnetic thin film layer on the periodically corrugated substrate. Compared to traditional planar Hall sensors with shape-induced uniaxial magnetic anisotropy, this invention eliminates the need for precise etching processes; the fabrication process is more convenient and cost-effective by simply adjusting the corrugation period and amplitude of the periodically corrugated substrate. Furthermore, the performance of the planar Hall sensor is easier to control.

Description

Technical Field

[0001] This invention belongs to the field of magnetic device technology, and specifically relates to a planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate. Background Technology

[0002] With the rapid development of modern information technology, magnetoresistive sensors are widely used in many fields such as biosensors, industrial inspection, aerospace, positioning and navigation, and are developing towards miniaturization and high sensitivity. The main principle of magnetoresistive sensors is the magnetoresistance effect (MR), which mainly includes anisotropic magnetoresistance (AMR) sensors, planar Hall effect (PHE) sensors, giant magnetoresistance (GMR) sensors, and tunneling magnetoresistance (TMR) sensors. Among them, planar Hall sensors, due to their advantages of high detection accuracy, low noise, and low thermal drift, can be used to detect magnetization shifts in small magnetic fields and can also measure tiny magnetic beads at the micro-nano scale, which makes planar Hall sensors have broad application prospects in biosensors.

[0003] Planar Hall sensors are highly sensitive to disturbances in the magnetization direction of the ferromagnetic layer, requiring precise control of the magnetization direction in a zero-field state. This necessitates uniaxial anisotropy in the ferromagnetic layer. Current mainstream fabrication methods primarily induce uniaxial anisotropy by altering the shape of the magnetic thin film, such as elliptical or cross-shaped planar Hall sensors. Since the uniaxial anisotropy of the magnetic thin film significantly impacts sensor performance, this places high demands on the precise etching of patterns during fabrication. Finding alternative methods to induce uniaxial anisotropy in the magnetic thin film, thereby reducing the fabrication cost of planar Hall sensors and allowing for the control of the anisotropic field to achieve specific performance characteristics, is a pressing issue that needs to be addressed before planar Hall sensors can be practically applied. Summary of the Invention

[0004] The purpose of this invention is to address the problems in the prior art by providing a planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate, which induces uniaxial anisotropy through a patterned magnetic thin film that does not require precise etching.

[0005] The technical solution adopted in this invention is as follows:

[0006] A planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate is characterized by comprising, from bottom to top, a periodically corrugated substrate 1, a buffer layer 2, a magnetic thin film layer 3, a protective layer 4, and a conductive metal layer, wherein the conductive metal layer comprises two conductive metal layers 5 for detecting planar Hall signals arranged perpendicular to the corrugation direction, and two conductive metal layers 6 for external current connection arranged parallel to the corrugation direction.

[0007] Furthermore, the periodic corrugated substrate 1 is a sapphire substrate, obtained by annealing a planar sapphire substrate at 1100–1400°C for 2–10 hours.

[0008] Furthermore, the ripple period of the periodic corrugated substrate 1 is 10nm to 1μm, and the ripple amplitude is 10nm to 100nm.

[0009] Furthermore, by adjusting the annealing temperature and annealing time, the ripple period and ripple amplitude of the periodic corrugated substrate 1 are changed, thereby controlling the magnitude of the anisotropic field of the magnetic thin film layer 3 and realizing the performance regulation of the planar Hall sensor.

[0010] Furthermore, a thin film deposition process is used to sequentially obtain a buffer layer 2, a magnetic thin film layer 3, and a protective layer 4 on a periodically corrugated substrate 1.

[0011] Furthermore, the magnetic thin film layer 3 can be prepared using NiFe thin film, NiCo thin film, FeCo thin film, etc., by thin film deposition processes such as evaporation deposition, sputtering deposition, and molecular beam epitaxy, with a thickness of 10nm to 300nm.

[0012] Furthermore, both the buffer layer 2 and the protective layer 4 are made of Ta and are prepared using thin film deposition processes such as evaporation deposition, sputtering deposition, and molecular beam epitaxy. The thickness of the buffer layer 2 is 2 nm to 10 nm, and the thickness of the protective layer 4 is 1 nm to 5 nm.

[0013] Furthermore, the conductive metal layer is made of conductive metals such as copper and gold, and has a thickness of 50nm to 100nm.

[0014] Furthermore, by applying current to two external current-conducting metal layers 6 arranged parallel to the corrugation direction, and detecting signals by two detection plane Hall signal conductive metal layers 5 arranged perpendicular to the corrugation direction, the function of a planar Hall sensor is realized, which is used to detect changes in the magnitude and direction of the magnetic field perpendicular to the corrugation direction.

[0015] The beneficial effects of this invention are as follows:

[0016] This invention proposes a planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate. By depositing a magnetic thin film layer on a periodically corrugated substrate, a magnetic thin film with a periodically corrugated structure is obtained, realizing uniaxial anisotropy induced by patterned magnetic thin film. Compared with traditional planar Hall sensors with shape-induced uniaxial magnetic anisotropy, this invention does not require precise etching or other process requirements. The magnetic thin film can be patterned simply by adjusting the corrugation period and amplitude of the periodically corrugated substrate. Preferably, the corrugation period and amplitude can be adjusted by changing the annealing process. The fabrication process is more convenient, the manufacturing cost is lower, and the performance control of the planar Hall sensor is also easier. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate provided in Example 1; wherein, Figure 1 (a) is a schematic diagram of the overall structure; Figure 1 (b) is a schematic diagram of the back side of the periodically corrugated substrate;

[0018] Figure 2 This is a schematic diagram showing the dimensions and orientation of the planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate provided in Example 1.

[0019] Figure 3 The normalized hysteresis loop of the magnetic thin film layer with the periodic corrugated structure in Example 1;

[0020] Figure 4 The angle dependence curve of the planar Hall signal of a periodic corrugated magnetic thin film layer obtained by micromagnetic simulation in Example 1 is shown.

[0021] Figure 5 The above are field-dependent curves of planar Hall signals of magnetic thin film layers with different ripple amplitudes obtained by micromagnetic simulation in Example 1.

[0022] Figure 6 From Figure 5 The relationship between the detection range and sensitivity of the planar Hall sensor as a function of ripple amplitude is extracted from the field-dependent curve.

[0023] Figure 7 The above are field-dependent curves of planar Hall signals of magnetic thin film layers with different ripple periods obtained by micromagnetic simulation in Example 1.

[0024] Figure 8 From Figure 7 The relationship between the detection range and sensitivity of the planar Hall sensor as a function of the ripple period is extracted from the field dependence curve.

[0025] Figure 9 This illustrates the relationship between the dimensions of the periodically corrugated substrate and the annealing time in Example 1; wherein, Figure 9 (a) represents the average ripple period; Figure 9 (b) represents the average ripple amplitude;

[0026] Figure label:

[0027] 1 is a periodic corrugated substrate, 2 is a buffer layer, 3 is a magnetic thin film layer, 4 is a protective layer, 5 is a conductive metal layer for detecting Hall signals on the detection plane, 6 is a conductive metal layer for external current, 7 is perpendicular to the corrugation direction, 8 is parallel to the corrugation direction, 9 is the corrugation period, 10 is the corrugation amplitude, and 11 is the thickness of the magnetic thin film layer. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Example 1

[0030] This embodiment provides a planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate, the overall structure of which is as follows: Figure 1 As shown in (a), the structure includes, from bottom to top, a periodically corrugated substrate 1, a buffer layer 2, a magnetic thin film layer 3, a protective layer 4, and a conductive metal layer. The conductive metal layer includes two Hall signal conductive metal layers 5 arranged perpendicular to the corrugation direction 7, and two external current conductive metal layers 6 arranged parallel to the corrugation direction 8. A schematic diagram of the direction perpendicular to the corrugation direction 7 and the direction parallel to the corrugation direction 8 is shown below. Figure 2 As shown.

[0031] Among them, the periodically corrugated substrate 1 is a periodically corrugated sapphire substrate, which is obtained by annealing a planar sapphire substrate at 1400℃ to obtain the periodically corrugated structure on the surface, and the back side is as follows. Figure 1 (b) shows the planar structure; the buffer layer 2 is made of Ta and has a thickness of 5 nm; the magnetic thin film layer 3 is made of Ni. 80 Fe 20 The thin film has a thickness of 50 nm; the protective layer 4 is made of Ta and has a thickness of 2 nm; the conductive metal layer is made of Cu metal and has a thickness of 60 nm.

[0032] The method for fabricating a planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate proposed in this embodiment specifically includes the following steps:

[0033] Step 1: Anneal the m-plane sapphire substrate at a high temperature of 1400℃. By adjusting the annealing time to different lengths (2-10 hours), different dimensional parameters are formed (i.e., ...). Figure 2 The periodic corrugated substrate 1 (shown with ripple period and ripple amplitude) Figure 9 (a) shows the relationship between the average corrugation period of the periodic corrugated substrate 1 and the annealing time. Figure 9 (b) shows the relationship between the average corrugation amplitude of the periodically corrugated substrate 1 and the annealing time;

[0034] Step 2: A buffer layer 2 with a thickness of 5 nm, a magnetic thin film layer 3 with a thickness of 50 nm, and a protective layer 4 with a thickness of 2 nm are sequentially prepared on a periodically corrugated substrate 1 using DC magnetron sputtering.

[0035] Step 3: Combine a mask on the protective layer 4 and obtain a conductive metal layer with a thickness of 60nm by RF (radio frequency) sputtering.

[0036] Figure 3 The normalized hysteresis loop of the periodically corrugated magnetic thin film layer 3 is shown. The test sample was annealed for 2 hours, with a ripple period of 193 nm and a ripple amplitude of 25 nm. The test results show that the periodically corrugated magnetic thin film layer 3 exhibits good uniaxial anisotropy, with the easy axis parallel to the ripple direction and the difficult axis perpendicular to the ripple direction.

[0037] This embodiment utilizes the patterning of the magnetic thin film layer 3 to induce uniaxial anisotropy of the thin film. By applying a current parallel to the ripple direction, the function of a planar Hall sensor is realized. The principle is as follows:

[0038] The planar Hall effect differs from the traditional Hall effect in that its physics originates from anisotropic scattering caused by spin-orbit coupling, while the traditional Hall effect originates from the Lorentz force experienced by charge carriers under a magnetic field. Because the applied magnetic field, applied current, and induced voltage all lie in the same plane, this effect is called the planar Hall effect, to distinguish it from the traditional Hall effect where all three are perpendicular to each other. Macroscopically, the planar Hall effect manifests as the resistivity of the magnetic thin film layer 3 changing with the applied magnetic field. In the anisotropic magnetic thin film layer 3, assuming the resistivity parallel to and perpendicular to the magnetization direction are ρ... ∥ and ρ ⊥ The current densities parallel to and perpendicular to the magnetization direction are J, respectively. ∥ and J ⊥ According to Ohm's law, the current density J and the magnetization vector are obtained. The relationship is:

[0039]

[0040] The plane Hall voltage value V was calculated. PHE for:

[0041]

[0042] Where I is the magnitude of the applied current; t is the thickness of the magnetic thin film layer 3; and θ is the angle between the magnetization intensity and the current direction.

[0043] The planar Hall effect requires the magnetic material to have uniaxial magnetic anisotropy, and the magnetic thin film layer 3 with a periodic corrugated structure has uniaxial magnetic anisotropy along the easy axis direction parallel to the corrugation direction, so it can be used to fabricate a planar Hall sensor.

[0044] When a current parallel to the corrugation direction is applied to a planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate, due to the planar Hall effect, the resistivity of the magnetic thin film layer 3 in the direction perpendicular to the corrugation changes linearly with the change of the applied magnetic field in that direction. This change in resistivity can also be reflected as a change in voltage; therefore, the magnitude of the applied magnetic field can be detected by measuring the voltage in that direction. Thus, the magnetic thin film layer 3 deposited on the periodically corrugated substrate 1 can realize the function of a planar Hall sensor.

[0045] Based on the above formula, the relationship between the planar Hall signal and the magnitude and direction of the external magnetic field can be obtained. In this embodiment, the performance of the planar Hall sensor is verified by adjusting the magnitude of the external magnetic field, the angle between the magnetization intensity and the current direction. Specifically:

[0046] For a planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate, where the magnetic thin film layer 3 has a thickness of 50 nm, the corrugation period of the periodically corrugated substrate 1 is 100 nm, and the corrugation amplitude is 50 nm, the angle dependence curve of the planar Hall signal of the periodically corrugated magnetic thin film layer is obtained through micromagnetic simulation, as shown in the figure. Figure 4 As shown, the planar Hall signal exhibits a linear relationship near the angle between the magnetization intensity and the current direction of 0. This range, which maintains a linear relationship, is the detection range of the planar Hall sensor, and the rate of change of the external magnetic field near the 0 angle is the sensitivity of the planar Hall sensor.

[0047] For a magnetic thin film layer 3 with a thickness of 50 nm and a fixed ripple period of 100 nm for the periodically corrugated substrate 1, a set of field-dependent curves for planar Hall signals based on magnetic thin films on a periodically corrugated substrate with different ripple amplitudes were obtained through micromagnetic simulation. Figure 5 As shown, where one unit h represents 1 nm; it can be seen that the planar Hall signal exhibits a linear relationship near the external magnetic field magnitude of 0. This range, maintaining a linear relationship, is the detection range of the planar Hall sensor. The rate of change of the external magnetic field near 0 is the sensitivity of the planar Hall sensor. The relationship between the detection range and sensitivity of the planar Hall sensor with the ripple amplitude is as follows: Figure 6 As shown.

[0048] For a magnetic thin film layer 3 with a thickness of 50 nm and a fixed ripple amplitude of 50 nm on a periodically corrugated substrate 1, a set of field-dependent curves for planar Hall signals based on magnetic thin films on a periodically corrugated substrate with different ripple periods were obtained through micromagnetic simulation. Figure 7As shown, where one unit 'l' represents 2 nm; it can be seen that the planar Hall signal exhibits a linear relationship near the external magnetic field magnitude of 0. This range, maintaining a linear relationship, is the detection range of the planar Hall sensor. The rate of change of the external magnetic field near 0 is the sensitivity of the planar Hall sensor. The relationship between the detection range and sensitivity of the planar Hall sensor with the ripple period is as follows: Figure 8 As shown.

[0049] The above embodiments are only for illustrating the principles and advantages of the present invention, and are not intended to limit the present invention. They are only for helping to understand the principles of the present invention. The scope of protection of the present invention is not limited to the above configurations and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the disclosed technology without departing from the essence of the present invention, but they are still within the scope of protection of the present invention.

Claims

1. A planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate, characterized in that, The device comprises, from bottom to top, a periodically corrugated substrate (1), a buffer layer (2), a magnetic thin film layer (3), a protective layer (4), and a conductive metal layer. The conductive metal layer includes two detection plane Hall signal conductive metal layers (5) arranged perpendicular to the corrugation direction, and two external current conductive metal layers (6) arranged parallel to the corrugation direction. By applying current to the two external current conductive metal layers (6), the two detection plane Hall signal conductive metal layers (5) detect the signal, thereby realizing the function of a planar Hall sensor for detecting the magnitude and direction changes of the magnetic field perpendicular to the corrugation direction. The periodic corrugated substrate (1) has a corrugation period of 10 nm to 1 μm and a corrugation amplitude of 10 nm to 100 nm. By depositing a magnetic thin film layer (3) on a periodic corrugated substrate (1), a magnetic thin film with a periodic corrugated structure is obtained, thereby realizing the uniaxial anisotropy induced by patterned magnetic thin film; by adjusting the corrugation period and corrugation amplitude of the periodic corrugated substrate (1), the magnetic thin film can be patterned.

2. The planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate according to claim 1, characterized in that, The periodic corrugated substrate (1) is a sapphire substrate, which is obtained by annealing a planar sapphire substrate at 1100~1400℃ for 2~10 h.

3. The planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate according to claim 1, characterized in that, The magnetic thin film layer (3) is a NiFe thin film, NiCo thin film or FeCo thin film, which is prepared by evaporation coating, sputtering coating or molecular beam epitaxy process, and has a thickness of 10 nm to 300 nm.

4. The planar Hall sensor based on a magnetic thin film on a periodically corrugated substrate according to claim 1, characterized in that, The materials of the buffer layer (2) and the protective layer (4) are both Ta, and they are prepared by evaporation coating, sputtering coating or molecular beam epitaxy. The thickness of the buffer layer (2) is 2 nm to 10 nm, and the thickness of the protective layer (4) is 1 nm to 5 nm.

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