CN113571632B

CN113571632B - A kind of abnormal Hall element and preparation method thereof

Info

Publication number: CN113571632B
Application number: CN202111109797.5A
Authority: CN
Inventors: 程雅慧; 李岩; 张瑞; 陈菲菲; 刁凌雪; 刘晖
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 2021-09-23
Filing date: 2021-09-23
Publication date: 2021-12-10
Anticipated expiration: 2041-09-23
Also published as: CN113571632A

Abstract

The invention provides an anomalous Hall element and a preparation method thereof. The single crystal Ni thin film co-doped with Fe and Cr epitaxially grown on single crystal MgO (100) is used as the active layer material, and the shape of the active layer is "ten" The film thickness is 2 nm~30 nm, and it is grown by ion beam deposition method. The miniature anomalous Hall element of the present invention has smaller volume, larger anomalous Hall resistivity, smaller resistivity and power consumption, wider operating temperature range, and is widely used in the fields of magnetoelectric signal conversion and the like .

Description

Abnormal Hall element and preparation method thereof

Technical Field

The invention relates to an abnormal Hall element with a single crystal thin film material as an active layer and a preparation method thereof.

Background

The Abnormal Hall Effect (AHE) is a spin-dependent electrical transport phenomenon in which a magnetic material induces a hall voltage in a magnetic field, and is an important component of spintronics. Abnormal hall sensors are prepared based on this effect. The abnormal Hall sensor is a magnetoelectric converter, can output magnetic variables by corresponding change of electric signals to realize measurement of an electric field or a magnetic field, and can be used in a plurality of occasions related to magnetic field change, such as abnormal Hall sensors for spin valve magnetic detection, speed sensors on automobiles, switch type abnormal Hall effect sensors, gear rotating speed detection, automobile engine ignition timing, taximeters and the like. The element has small volume, low cost and simple preparation, can realize non-contact sensing due to interaction with a magnetic field, has higher reliability, and is widely applied to the aspects of aerospace, automobile industry, magnetic field detection and the like. At present, a magnetic sensor based on abnormal hall effect becomes one of the most potential elements, but problems still exist in hall resistivity, temperature stability, power consumption and the like, and the large-scale commercial use of the element is limited.

The abnormal hall sensor is composed of a substrate, an active layer, electrodes and a package for protecting them. Wherein the active layer is critical to the overall hall device performance. The magnetic transition metals such as iron, cobalt, nickel and the like have wide sources, low cost and simple preparation, and are one of the abnormal Hall device active layers with the most practical values. However, the current abnormal hall resistance signals in iron, cobalt and nickel materials are small, and the thickness of the active layer must be reduced in order to increase the abnormal hall resistance of the active layer, improve the sensitivity and reduce the volume of the element. When the thin film is very thin, the polycrystalline or granular film material is likely to enter into a super paramagnetic state in a high temperature region, the magnetization intensity is greatly reduced, the Hall resistivity is directly dependent on the magnetization intensity, and therefore the Hall resistivity is greatly reduced, so that the abnormal Hall element is likely to fail, and therefore, an appropriate active layer thickness is selected and the super paramagnetic state caused by too small crystal grains is avoided. In addition, in the polycrystalline and granular film active layer materials, as the longitudinal resistivity is large, more joule heat is generated when the polycrystalline and granular film active layer materials are applied to a device, the power consumption is large, and the normal operation of the device is not facilitated. Therefore, how to enhance the abnormal hall effect of the transition metal material, improve the stability and reduce the power consumption becomes a problem which needs to be solved urgently.

Disclosure of Invention

Based on the problems in the prior art pointed out in the background art, the invention provides an abnormal hall element with an active layer made of Fe and Cr bimetallic co-doped single crystal Ni film and a preparation method thereof, aiming at solving the problems of small abnormal hall resistivity and poor temperature stability of the abnormal hall element with the active layer made of a transition metal material. Compared with a monocrystalline Ni film (Phys. Rev. Lett., 2009, 103, 087206), the saturated abnormal Hall resistivity is improved by nearly 5 times, and the sensitivity of the abnormal Hall element and the detection capability of the magnetic variable are improved; the longitudinal resistivity of the element is small and is between 20 and 60 mu omega cm, and the Joule heat can be reduced and the power consumption can be reduced when the element works; in addition, the element has wide working temperature range, does not generate superparamagnetic attenuation at high temperature, and has wide application in the fields of magnetoelectric signal conversion and the like.

In order to solve the problems, the technical scheme provided by the invention is as follows:

an abnormal Hall element comprises a substrate, an active layer, a metal electrode layer and a protective layer, wherein the active layer is coated on the substrate by ion beam sputtering, the metal electrode layer is contacted with the active layer, and the protective layer directly covers the active layer; the substrate is a single crystal substrate material; the active layer is a Fe and Cr co-doped monocrystal Ni film, the atomic ratio of Ni, Fe and Cr in the film is 83-92: 5-14: 3, and the thickness of the active layer is 2 nm-30 nm.

The abnormal Hall element is characterized in that the substrate is selected from single crystal MgO and single crystal LaAlO₃Single crystal MgAl₂O₄Single crystal Al₂O₃Single crystal GaAs, single crystal SrTiO₃Or a zirconia single crystal (YSZ) to which an yttrium stabilizer is added, preferably MgO (hereinafter referred to as MgO (100)) having a (100) crystal plane orientation.

The abnormal Hall element is characterized in that the active layer is a Fe and Cr co-doped monocrystal Ni film, and the atomic ratio of Ni, Fe and Cr in the film is 83-92: 5-14: 3.

In the abnormal hall element, the thickness of the active layer is preferably 4 nm.

Further, the atomic ratio of the three elements of Ni, Fe and Cr in the film is 87:10: 3.

In the abnormal hall element, the part of the metal electrode layer connected with the active layer is positioned between the active layer and the substrate or above the active layer, and the metal electrode layer is made of conductive metal; the shape of the active layer and the electrodes can be made according to the requirements of the anomalous hall element, preferably "cross", square or rectangular; the protective layer directly covers the active layer.

The invention also provides a preparation method of any abnormal Hall element, which comprises the following specific preparation steps:

1) forming a pattern of an active layer to be deposited on a substrate by using a photoetching and masking method;

2) fixing a substrate on a rotating table of an ion beam deposition system, fixing a Ni target material in a chamber, and placing Fe and Cr particles on the Ni target material;

3) evacuating the vacuum chamber of the ion beam deposition system to a pressure of less than 5 x 10^-5Pa；

4) Turning on an ion beam power supply and a heating power supply, and preheating the substrate, wherein the heating temperature is 250-350 ℃;

5) filling high-purity Ar gas with the purity of more than 99.999 percent into the vacuum chamber, wherein the flow of the filled Ar gas is 2-5 sccm, and the air pressure of the chamber is kept to be 0.8 multiplied by 10^-2~2.0 × 10^-2Pa, sputtering beam current of 15-30 mA, and pre-sputtering for 15-45 min;

6) keeping the heating temperature of the substrate unchanged, opening a baffle of the substrate, and sputtering to obtain an Fe and Cr co-doped single crystal Ni film active layer with the required thickness;

7) sending the sample to a secondary vacuum chamber through a magnetic rotating shaft, taking out the sample, and removing the photoresist; forming an electrode pattern by using a photoetching and masking method, conveying a sample into a magnetron sputtering vacuum chamber, and continuously preparing a conductive metal layer to form an electrode;

8) sending the sample to a secondary vacuum chamber through a magnetic rotating shaft, taking out the sample, and removing the photoresist; forming a pattern for depositing a protective layer above the active layer film on the substrate by using a photoetching and masking method, wherein the pattern for depositing the protective layer completely covers the active layer film, and feeding a sample into a vacuum chamber to prepare the protective layer.

The preparation method is further characterized in that the substrate is single crystal MgO (100).

The preparation method is further characterized in that in the step 4), the heating temperature is 300 ℃, and the preheating time is 30 min.

The preparation method is further characterized in that in the step 5), the Ar gas is filled with the flow rate of 3sccm, and the pressure of the chamber is kept to be 1.5 multiplied by 10^-2Pa, sputtering beam current of 20 mA, and pre-sputtering for 30 min; the deposition rate of sputtering in step 6) was 0.4 nm/min.

The invention provides a miniature Hall element which takes a Fe and Cr co-doped monocrystal Ni film as an active layer and works by utilizing the principle of abnormal Hall effect of a magnetic material. The active layer is prepared by taking a ferromagnetic transition metal material Ni with wide sources as a main body and adopting an ion beam sputtering method, the Fe and Cr bimetallic co-doping is successfully realized in the single crystal Ni film, the preparation method of the active layer is simple, the expansibility is strong, and the thickness and the crystallinity of the film can be more accurately controlled. The active layer of the Hall element provided by the invention utilizes different electronic structures, spin characteristics, scattering strength and the like of Ni, Fe and Cr elements to realize the regulation and control of an intrinsic source, a lateral jump source and an oblique scattering source of an abnormal Hall effect, the abnormal Hall resistivity is improved under a proper doping proportion, and the saturated abnormal Hall resistivity is increased by about 5 times compared with a pure Ni film. Experiments show that when the thickness of the active layer is 4nm, the sensitivity of the abnormal Hall element and the detection capability of the magnetic variable can be obviously improved, compared with the traditional material, the element has the advantages of small resistivity, less generated Joule heat, small volume, wide working temperature range, no occurrence of a super-paramagnetic state, good stability and wide application in the fields of magnetoelectric signal conversion and the like.

Drawings

Fig. 1 is a pattern of an active layer prepared in example 1;

FIG. 2 is a pattern of an electrode prepared in example 1;

FIG. 3 is an XRD pattern of the active layer in example 1-1;

FIG. 4 is a graph of an ω scan of the active layer in example 1-1;

FIG. 5 is a view of a phi scan of the active layer in example 1-1;

fig. 6 is a graph of abnormal hall resistivity versus magnetic field for the abnormal hall element of example 1 having active layers of different thicknesses;

fig. 7 is a graph of abnormal hall resistivity versus temperature for the abnormal hall element of example 1 having active layers of different thicknesses.

Detailed Description

The invention will now be further illustrated by means of specific examples.

Example 1

Providing an abnormal Hall element, which consists of a substrate, an active layer, a metal electrode layer and a protective layer, wherein the active layer covers the substrate, the metal electrode layer is in contact with the active layer, and the protective layer directly covers the active layer; the substrate is single crystal MgO (100); the active layer is a Fe and Cr co-doped monocrystal Ni film, and the preparation method of the abnormal Hall element comprises the following steps:

1) the substrate is patterned into a cross pattern with an active layer to be deposited by photolithography and masking, as shown in fig. 1. The shaded part in the figure has no photoresist, the side length of the central square of the pattern is 1.0 μm, and the length of the protruding part on the four sides of the central square is 0.2 μm;

2) the method comprises the following steps of (1) enabling a substrate to be a magnesium oxide (100) single crystal substrate of a composite fertilizer crystal, measuring the size of the substrate to be 5mm multiplied by 10 mm multiplied by 0.5 mm, respectively measuring 20 mL of acetone, 20 mL of absolute ethyl alcohol and 20 mL of deionized water, placing the substrate in a polytetrafluoroethylene groove, carrying out ultrasonic cleaning for 10min by using the acetone, the absolute ethyl alcohol and the deionized water in sequence, drying the cleaned substrate by using high-purity nitrogen, fixing the substrate in a substrate tray by using a kapton tape, covering a mask plate, and quickly transferring and fixing the substrate to a rotating table of an ion beam deposition system; fixing a Ni target with the purity of 99.99 percent in a chamber of an ion beam deposition system, and placing 3 mm multiplied by 3 mm and one piece of Fe and Cr particles on the target respectively;

3) opening the mechanical pump and the molecular pump to vacuumize so that the pressure of the vacuum chamber is less than 5 × 10^-5Pa；

4) Turning on an ion beam power supply and a heating power supply, preheating for 30min, adjusting a heating knob to heat the substrate to 300 ℃, wherein the heating rate is 10 ℃/min, and maintaining for 30min at 300 ℃;

5) charging high-purity Ar gas with purity of more than 99.999 percent into the vacuum chamber, controlling the flow rate to be 3sccm through a flowmeter, and keeping the pressure of the gas in the chamber to be 1.5 multiplied by 10^-2Pa, adjusting a power supply knob to enable discharge voltage to be 70V, increasing filament current until discharge current just occurs, then adjusting acceleration voltage to be 250V, beam current voltage to be 750V, sputtering beam current to be 20 mA, and pre-sputtering for 30 min;

6) keeping the temperature of the substrate at 300 ℃, opening a baffle of the substrate, and controlling the sputtering time at the deposition rate of 0.4nm/min to obtain Fe and Cr co-doped single crystal Ni film series samples with different thicknesses;

7) sending the sample to a secondary vacuum chamber through a magnetic rotating shaft, taking out the sample, and removing the photoresist; a rectangular pattern of four electrodes to be deposited is formed on the substrate outside the four sides of the active layer by means of photolithography and masking, as shown in fig. 2. The shaded portions in the pattern are the pattern of electrodes to be deposited. Each of the electrode patterns has an overlapping portion of 0.15 μm with the active layer, respectively. Sending the sample into a magnetron sputtering vacuum chamber, and continuously preparing a titanium layer with the thickness of 40 nm and a gold layer with the thickness of 200 nm to form electrodes;

8) sending the sample to a secondary vacuum chamber through a magnetic rotating shaft, taking out the sample, and removing the photoresist; and forming a square pattern of the protective layer to be deposited above the active layer on the substrate by using a photoetching and masking method, wherein the side length of the square is 0.5-1.2 mu m, completely covering the active layer film, and conveying the sample into a magnetron sputtering vacuum chamber to prepare the silicon dioxide protective layer. And (3) sputtering the silicon dioxide target by radio frequency, setting the sputtering power to be 200W and the sputtering time to be 10min, and obtaining the abnormal Hall element.

The thicknesses of the active layers of the anomalous hall elements obtained in examples 1-1 to 1-5 are shown in the following table

Phase analysis was performed on the Fe and Cr-co-doped single crystal Ni thin film (i.e., active layer) sample obtained in example 1-1 using a D8 Discover Plus type high-resolution X-ray diffractometer (HRXRD) of BRUKER, germany, and the measurement results are shown in fig. 3 to 5.

Wherein: fig. 3 is an XRD chart, which shows that there are two diffraction peaks at 2 θ =43 ° and 51.8 °, respectively corresponding to the (200) plane of MgO and the (200) plane of Ni, and there are no other diffraction peaks, and it can be preliminarily determined as an epitaxial single crystal Ni film, and since the doping ratio is low, it is impossible to see whether there is doping by XRD;

FIG. 4 is an ω -scan for characterizing the crystal quality of the thin film, wherein the smaller the full width at half maximum, the better the single crystal quality (generally, the full width at half maximum is 1 ° is regarded as excellent), and it can be seen that the full width at half maximum of the sample is 2 ° and the crystal quality is general, mainly caused by doping;

FIG. 5 is a drawing showing

And scanning a graph to represent the epitaxial quality of the single crystal sample on the single crystal substrate, wherein the diffraction peak intensities of the film are approximately equal and relatively sharp, and 4 diffraction peaks exist, which indicates that the sample has 4-fold symmetry and shows better epitaxial quality as a whole.

The test data show that the preparation method provided by the invention can successfully extend the Fe and Cr co-doped single crystal Ni film, and the crystal quality and the extension quality are good.

The proportion of Ni, Fe and Cr elements in the series of active layer samples is tested by utilizing inductively coupled plasma emission spectroscopy (ICP), and the result shows that the prepared film is Ni₈₇Fe₁₀Cr₃。

The resistivity of the abnormal Hall element with the active layer of different thickness is tested in the range of 5K to 300K by using PPMS-9 produced by Quantum Design company in America, and the result shows that the resistivity range is 20-60 mu omega cm and is far smaller than that of the common semiconductor and particle film materials.

FIG. 6 is an abnormal Hall resistivity (. rho.) of 5 typical elements of examples 1-1 to 1-5, in which the thickness of the active layer is 4nm, 6 nm, 10 nm, 13 nm and 22 nm_xy) A graph of the abnormal hall resistivity versus magnetic field for the abnormal hall element of the active layer of different thickness provided in example 1 at 300K as a function of the magnetic field strength H, and table 1 shows the corresponding data.

TABLE 1

Will rho_xyExtending the saturation field part of the H curve to a position with H =0 to obtain the saturated abnormal Hall resistivity rho of the sample_AH. The value of the saturation abnormal hall resistivity reflects the quality of the hall performance of the thin film material, and the high saturation abnormal hall resistivity is an essential parameter of the high-performance abnormal hall element. As can be seen from fig. 5, the saturated abnormal hall resistivities of the abnormal hall elements having the active layers of no thickness were all greater than 0.13 μ Ω cm, which is higher than that of the undoped single crystal Ni thin film, indicating that co-doping increased the saturated abnormal hall resistivity of the elements and increased the abnormal hall performance of the elements. In addition, the value of the abnormal hall resistivity is gradually increased along with the reduction of the film thickness of the active layer, wherein the maximum saturated abnormal hall resistivity of the abnormal hall element is generated when the active layer is 4nm, the value of the abnormal hall resistivity reaches 0.64 mu omega cm, and the abnormal hall element is increased by about 5 times compared with a pure single crystal Ni film, so that the sensitivity of the abnormal hall element and the detection capability of magnetic variables are improved.

The saturated abnormal hall resistivity of the abnormal hall elements of the active layers of different thicknesses was measured in the range of 5K to 300K using PPMS-9 manufactured by Quantum Design, usa, and the results are shown in fig. 7:

table 2 shows the corresponding data, where the abnormal hall resistivity is in μ Ω cm.

The change of the saturated abnormal Hall resistivity along with the temperature directly reflects the working stability of the element, and the result shows that the abnormal Hall resistivity of the abnormal Hall element with the 4nm active layer is changed by 18 percent and is far lower than that of Ni-SiO under the same condition₂The change in the material of the particulate membrane was 70%.

The above description has fully demonstrated the Fe and Cr co-doped single crystal Ni thin film active layer according to the present invention, and the micro abnormal hall element using the Fe and Cr co-doped single crystal Ni thin film as the active layer and operating on the principle of abnormal hall effect of magnetic material. The invention successfully prepares the Fe and Cr co-doped monocrystal Ni film active layer material by adopting an ion beam sputtering method, further improves the abnormal Hall resistivity and the detection capability of magnetic variables of elements, has good temperature stability and low temperature resistance, and has wide application in the fields of magnetic field sensors, magnetoelectric signal conversion, automobile industry and the like. It should be emphasized that the method is equally applicable to other similar doping systems. It will be apparent to those skilled in the art that modifications and enhancements can be made without departing from the scope of the claims and are within the scope of the invention.

Claims

1. An abnormal Hall element comprises a substrate, an active layer, a metal electrode layer and a protective layer, wherein the active layer is coated on the substrate by ion beam sputtering, the metal electrode layer is contacted with the active layer, and the protective layer directly covers the active layer; the substrate is a single crystal substrate material; the active layer is a Fe and Cr co-doped monocrystal Ni film, the atomic ratio of Ni, Fe and Cr in the film is 83-92: 5-14: 3, and the thickness of the active layer is 2 nm-30 nm.

2. An abnormal hall element as claimed in claim 1 wherein the portion of the metal electrode layer connected to the active layer is located between the active layer and the substrate or above the active layer, the electrode layer being formed of a conductive metal.

3. Abnormal hall element as claimed in claim 1, characterized in that the substrate is selected from the group comprising monocrystalline MgO, monocrystalline LaAlO₃Single crystal MgAl₂O₄Single crystal Al₂O₃Single crystal GaAs, single crystal SrTiO₃Or a single crystal of zirconia with yttrium stabilizer added.

4. An anomalous hall element as claimed in claim 1, wherein said substrate is a single crystal MgO having a (100) crystal plane orientation.

5. An abnormal hall element according to any one of claims 1 to 4 wherein the active layer is a single crystal Ni film co-doped with Fe and Cr, and the atomic ratio of the three elements Ni, Fe and Cr in the film is 83 to 92:5 to 14: 3.

6. An abnormal hall element as claimed in claim 5, wherein the atomic ratio of the three elements Ni, Fe and Cr in said thin film is 87:10: 3.

7. Abnormal hall element according to claim 6, characterized in that the active layer has a thickness of 4 nm.

8. A method of manufacturing an abnormal Hall element according to any of claims 1 to 7, comprising the specific steps of:

9. The method of claim 8, wherein in step 4), the heating temperature is 300 ℃ and the preheating time is 30 min.

10. The method of claim 9, wherein in step 5), the Ar gas is introduced at a flow rate of 3sccm, and the chamber pressure is maintained at 1.5 x 10^-2Pa, sputtering beam current of 20 mA, and pre-sputtering for 30 min; the deposition rate of sputtering in step 6) was 0.4 nm/min.