A three-dimensional wide-field linear magnetic sensor and its fabrication method

Abstract

This invention discloses a three-dimensional wide-field linear magnetic sensor and its fabrication method, belonging to the field of magnetic sensor technology. The sensor employs a Cr / Pt / Co / Ta multilayer film structure, which is stacked sequentially from bottom to top on a thermally oxidized Si substrate. The Cr layer serves as the orbital current source layer, the Pt layer as the orbital current-spin current conversion layer and spin current source layer, the Co layer as the magnetic layer, and the Ta layer as the protective layer and spin current source layer. During fabrication, each layer is first deposited using an ultra-high vacuum magnetron sputtering system according to a specific process, followed by microfabrication using laser direct writing and Ar ion etching to fabricate a four-terminal Hall bar device. The sensor's sensitivity in both the x and y directions is ≥200 V·A. ‑1 ·T ‑1 Furthermore, the linear response range is ≥ ±60 Oe, and the z-direction sensitivity is ≥ 1900 V·A. ‑1 ·T ‑1 Furthermore, with a linear response range of ≥±10Oe, it can achieve three-dimensional magnetic field detection through a single device, significantly reducing size and improving integration, making it suitable for miniaturized equipment scenarios such as robot micro-sensing and chip-level magnetic positioning.

Description

Technical Field

[0001] This invention belongs to the field of magnetic sensor technology, specifically a three-dimensional wide-field linear magnetic sensor and its fabrication method. Background Technology

[0002] Magnetic sensors accurately determine physical parameters such as position, orientation, and angle by sensing magnetic field strength and distribution. They are widely used in robotics, aerospace, medical diagnostics, and automotive sensing. Currently, magnetic sensors mainly include Hall effect sensors, magnetoresistive (AMR, GMR, or TMR) sensors, and superconducting quantum interference devices (SQUIDs). Traditional methods for achieving three-dimensional spatial detection involve integrating multiple sensors, which suffers from problems such as large size, poor integration, and difficulty in orthogonal calibration.

[0003] In recent years, spin-orbit moment (SOT) based magnetic sensors have attracted significant attention from both the scientific and industrial communities. Because they can achieve three-dimensional magnetic field detection within a single device, they effectively overcome the integration problem of traditional magnetic sensors in three orthogonal planes, greatly improving the overall system performance and spatial integration. However, SOT magnetic sensors still have some limitations in terms of device sensitivity and linear response range, particularly the incompatibility between high sensitivity and a wide linear range. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a three-dimensional wide-field linear magnetic sensor, comprising a Cr layer, a Pt layer, a Co layer, and a Ta layer sequentially stacked on a thermally oxidized Si substrate from bottom to top, forming a Cr / Pt / Co / Ta multilayer film structure; wherein the Cr layer is an orbital current source layer, the Pt layer is an orbital current-spin current conversion layer and a spin current source layer, the Co layer is a magnetic layer, and the Ta layer is a protective layer and a spin current source layer;

[0005] The sensor has a sensitivity of ≥200 V·A in both the x and y directions. -1 ·T -1 The linear response range is ≥ ±60 Oe, and the out-of-plane sensitivity in the z-direction is ≥ 1900 V·A. -1 ·T -1 The linear response range is ≥ ±10 Oe.

[0006] Preferably, the thickness of the oxide layer on the thermally oxidized Si substrate is 180-220 nm.

[0007] Preferably, the thickness of the Cr layer is 0.8-3 nm and the purity is ≥99.99%; the thickness of the Pt layer is 0.8-1.2 nm and the purity is ≥99.99%.

[0008] Preferably, the Co layer has a thickness of 0.8-1.2 nm and a purity of ≥99.99%; the Ta layer has a thickness of 0.8-2 nm and a purity of ≥99.99%.

[0009] Preferably, the sensor is a four-terminal Hall effect device, and the Hall effect device has a length of 75-85 μm and a width of 8-12 μm.

[0010] This invention also provides a method for fabricating a three-dimensional wide-field linear magnetic sensor, comprising the following steps:

[0011] Step 1: Provide a thermally oxidized Si substrate as a substrate, and pretreat the substrate;

[0012] Step 2: Using an ultra-high vacuum magnetron sputtering system, Cr, Pt, Co and Ta layers are sequentially deposited on the pretreated substrate to prepare a Cr / Pt / Co / Ta multilayer film.

[0013] Step 3: The Cr / Pt / Co / Ta multilayer film is microfabricated to form a four-terminal Hall effect device, thus obtaining a three-dimensional wide-field linear magnetic sensor.

[0014] Preferably, the pretreatment in step 1 is as follows: the thermally oxidized Si substrate is ultrasonically cleaned in acetone, alcohol and ultrapure water in sequence, and then dried with high-purity N2.

[0015] Preferably, the background vacuum of the ultra-high vacuum magnetron sputtering system described in step 2 is ≤3.75×10⁻⁶. -10 Torr was deposited using DC sputtering; the purity of the Cr, Pt, Co, and Ta targets used in the deposition process was ≥99.99%.

[0016] Preferably, the deposition process parameters for each layer in step 2 are as follows:

[0017] Cr layer deposition: argon flow rate 28-32 sccm, sputtering power 28-32 W, growth rate 0.020-0.023 nm / s, deposition thickness 0.8-3 nm;

[0018] Pt layer deposition: argon flow rate 18-22 sccm, sputtering power 13-17 W, growth rate 0.015-0.018 nm / s, deposition thickness 0.8-1.2 nm;

[0019] Co layer deposition: argon flow rate 58-62 sccm, sputtering power 28-32 W, growth rate 0.010-0.012 nm / s, deposition thickness 0.8-1.2 nm;

[0020] Ta layer deposition: argon flow rate 18-22 sccm, sputtering power 28-32 W, growth rate 0.016-0.018 nm / s, deposition thickness 0.8-2 nm.

[0021] Preferably, the microfabrication process in step 3 includes the following sub-steps:

[0022] Sub-step 3.1: The Cr / Pt / Co / Ta multilayer film sample was sequentially ultrasonically cleaned with acetone, alcohol, and ultrapure water, and then dried with high-purity N2;

[0023] Sub-step 3.2: Coat the sample surface with S1805 photoresist and perform spin coating using a spin coater. First, spin the photoresist at a speed of 2000 r / min for 10 s, then spin it at a speed of 8500 r / min for 60 s. After that, place the sample on a heating stage at 100-110℃ for baking.

[0024] Sub-step 3.3: Use a laser direct writing device with a wavelength of 405nm to perform ultraviolet exposure, with an exposure dose of 75-85mJ / cm² and an exposure time of 155-170s;

[0025] Sub-step 3.4: Place the exposed sample in ZX-238 developer for 40-50 seconds, then fix it by immersing it in deionized water for 25-35 seconds;

[0026] Sub-step 3.5: The fixed sample is etched using an Ar ion etching system with an etching energy of 280-320 eV, a beam current of 23-27 mA, and an etching rate of 0.016-0.017 nm / s.

[0027] Sub-step 3.6: Remove the adhesive and clean the etched sample to obtain a four-terminal Holbar device.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention is based on a Cr / Pt / Co / Ta multilayer film structure, which enables high-sensitivity and wide-linearity magnetic field detection of three-dimensional magnetic field components (x, y, z) through a single device. It significantly reduces device size, improves spatial integration, and meets the needs of miniaturized devices such as robot micro-sensing and chip-level magnetic positioning. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the Cr / Pt / Co / Ta multilayer film structure and the Holbar test.

[0031] Figure 2 The anomalous Hall curves of Cr(1nm) / Pt(1nm) / Co(1nm) / Ta(1nm) Hall devices under different currents are shown.

[0032] Figure 3 The graph shows the linear response of the Cr(1nm) / Pt(1nm) / Co(1nm) / Ta(1nm) Hallbar device in three directions. Detailed Implementation

[0033] This invention provides a three-dimensional wide-field linear magnetic sensor and its fabrication method, which utilizes an ultra-high vacuum magnetron sputtering system to prepare Cr / Pt / Co / Ta magnetic multilayer films. All thin film samples involved in this study were prepared using a magnetron sputtering system with a base vacuum of 3.75 × 10⁻⁶ in the sample growth chamber. -10 Torr experiment used DC sputtering for sample preparation. The target materials used were all 2 inches in diameter, including: a 2 mm thick high-purity Cr target with a purity of 99.99%; a 4 mm thick high-purity Ta target with a purity of 99.99%; a 4 mm thick high-purity Pt target with a purity of 99.99%; and a 1 mm thick high-purity Co target with a purity of 99.99%.

[0034] In the fabrication experiment of Cr / Pt / Co / Ta multilayer films, a thermally oxidized Si substrate (with an oxide layer of approximately 200 nm) was used as the substrate. By adjusting parameters such as argon flow rate and sputtering power, the deposition conditions were gradually optimized, and a scheme for fabricating multilayer films with excellent vertical magnetic anisotropy was finally determined. The specific steps are as follows:

[0035] First layer (Cr layer): Argon gas with a flow rate of 30 sccm is introduced, sputtering power is set to 30W, growth rate is 0.0217nm / s, and a Cr layer (orbital flow source layer) with a thickness of 1nm is deposited on the substrate surface.

[0036] Second layer (Pt layer): Adjust the argon flow rate to 20 sccm, reduce the sputtering power to 15 W, and the growth rate to 0.0167 nm / s to deposit a 1 nm thick Pt layer (orbital-spin conversion layer and spin source layer); Third layer (Co layer): Increase the argon flow rate to 60 sccm, maintain a sputtering power of 30 W, and the growth rate to 0.0107 nm / s to deposit a 1 nm thick Co layer (magnetic layer).

[0037] The fourth layer (Ta layer): The argon flow rate was adjusted to 20 sccm, the sputtering power was increased to 30W, and the growth rate was 0.0168 nm / s to deposit a 1 nm thick Ta layer (protective layer and spin flow source layer), which both prevents the oxidation of the Co layer and provides spin flow.

[0038] Subsequently, the multilayer film sample was microfabricated using laser direct writing and argon ion etching techniques to fabricate a four-terminal Hall bar device. The Hall bar device prepared in this experiment has a length of 80 μm and a width of 10 μm. Before exposure, the sample needs to undergo ultrasonic cleaning, N2 drying, spin coating, and baking. The entire process is carried out in an ultra-clean photolithography laboratory: the sample is ultrasonically cleaned in beakers of acetone, alcohol, and ultrapure water in sequence, and then dried with high-purity N2 to ensure the cleanliness of the sample surface. The clean sample is placed in the center of the spin coater turntable and held firmly. A small amount of S1805 photoresist (positive resist) is drawn up using a dropper and 3 drops are dropped onto the sample surface. The KW-4B spin coater is set to low speed of 2000 r / min and spin coating time of 10 s, followed by high speed of 8500 r / min and spin coating time of 60 s to ensure that the photoresist is evenly distributed on the sample surface.

[0039] The sample was then baked on a 105°C heating stage to ensure complete adhesion of the photoresist to the thin film sample surface. Subsequently, the sample was subjected to UV exposure (λ=405nm) using a laser direct writing system (DMO Micro Writer Baby Plus laser direct writing system, UK) at an exposure dose of 80mJ / cm². 2 The exposure time was 162s. The film sample was developed in developer (ZX-238) for 45s and fixed by immersion in deionized water for 30s.

[0040] During the development process, the photoresist in the exposed areas is dissolved through a chemical reaction with the developer, exposing the thin film. The unexposed areas form the Holbar pattern, with the surface of the pattern consisting of unreacted photoresist. Then, the sample with the device pattern (covered by photoresist) undergoes Ar ion etching using the K24004 Ar ion etching system developed by Beijing Yongchang Pat Plasma Technology Co., Ltd. The sample is placed in the sample chamber, and the areas not covered by photoresist are bombarded at high speed by argon ions and detached from the sample surface. The unexposed areas, i.e., the photoresist-covered device pattern, are preserved.

[0041] The etching process parameters were: Ar ion etching energy of 300 eV, beam current of 25 mA, and etching rate stabilized at 0.01667 nm / s. After etching, the sample underwent resist removal and cleaning steps to finally obtain the Hall bar device. Figure 1 As shown.

[0042] The Cr layer serves as both a buffer layer and an orbital current source layer. As a buffer layer, Cr facilitates the layered growth of Pt, reduces surface roughness, yields a high-quality Pt layer, and improves the orbital current-spin current conversion efficiency. Simultaneously, Cr possesses significant orbital Hall conductivity (σ>0), enabling the generation of orbital current. This means it can convert in-plane (x-axis) current into orbital current carrying orbital angular momentum perpendicular to the film surface (z-axis), which is then converted into spin current through the Pt layer with strong spin-orbit coupling. Due to the Pt spin Hall angle θ... SH Since the spin flow from the orbital flow conversion is greater than 0, the spin angular momentum carried by the spin flow generated by the spin Hall effect of Pt itself has the same direction. Therefore, their superposition has a reinforcing effect. This spin flow is then injected upward along the z-axis into the ferromagnetic metal Co layer, producing SOT.

[0043] For the top-layer Ta, there is also a strong spin-orbit coupling effect. When the charge flow in the x-direction passes through the Ta layer, it generates a spin flow in the -z-direction that is injected downward into the Co layer, producing SOT. Due to the spin Hall angle θ of Ta... SH Since the spin angular momentum is less than 0, the direction of the spin angular momentum carried by the downward-injected spin flow is consistent with that of the upward-injected spin angular momentum from the lower layer, thus enhancing the SOT (Sequential Oscillation of the Co) effect in the Co layer. It can be seen that there are three types of spin flows injected into the Co layer: spin flows converted from Cr layer orbital flows through Pt, spin flows generated by the spin Hall effect in the Pt layer, and spin flows generated by the spin Hall effect in the Ta layer. These three types of spin flows injected into the Co layer carry spin angular momentum in the same direction, superimpose each other, and significantly improve the SOT efficiency.

[0044] In summary, this structural design effectively enhances the sensor's ability to detect weak magnetic fields, while simultaneously solving the problem of the incompatibility between sensitivity and a wide linear response range.

[0045] A Cr(1nm) / Pt(1nm) / Co(1nm) / Ta(1nm) multilayer film was grown at room temperature on a thermally oxidized Si substrate using magnetron sputtering to fabricate a SOT linear magnetic sensor. By gradually increasing the test current, the coercivity in the anomalous Hall curve of the sample gradually decreased, as shown... Figure 2 As shown in (a), when the write current reaches 15mA, the anomalous Hall loops are nearly coincident, indicating that the Oersted field, SOT effective field, ferromagnetic coupling field, demagnetizing field and thermal effect in the device are almost in equilibrium at this time.

[0046] like Figure 2 As shown in (b), a write current of ±16mA was applied to the device while the magnetic field was varied in the z-direction. It can be seen that the device exhibits good linear response characteristics within the range of ±10Oe. Figure 3As shown, the linear relationship between the anomalous Hall resistance and the magnetic field in the z, x, and y directions is illustrated. It can be seen that the z-direction exhibits ultra-high sensitivity (exceeding 1900 V·A). -1 ·T -1 Under these conditions, the linear response range reaches ±10 Oe, while the sensitivity in the x and y directions exceeds 200 V·A. -1 ·T -1 Under these conditions, the linear response range reaches ±60 Oe, approximately three times that of similar linear magnetic sensors. These results demonstrate that the Cr / Pt / Co / Ta magnetic sensor possesses high sensitivity and wide-field response characteristics for detecting spatial magnetic field components, making it a promising candidate for application in three-dimensional magnetic sensor devices.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A three-dimensional wide-field linear magnetic sensor, characterized in that, It includes a Cr layer, a Pt layer, a Co layer and a Ta layer stacked sequentially on a thermally oxidized Si substrate from bottom to top, forming a Cr / Pt / Co / Ta multilayer film structure; the Cr layer is an orbital current source layer, the Pt layer is an orbital current-spin current conversion layer and a spin current source layer, the Co layer is a magnetic layer, and the Ta layer is a protective layer and a spin current source layer. The sensor has a sensitivity of ≥200 V·A in both the x and y directions. -1 ·T -1 Furthermore, the linear response range is ≥ ±60 Oe, and the out-of-plane sensitivity in the z-direction is ≥ 1900 V·A. -1 ·T -1 And the linear response range is ≥ ±10 Oe; The Cr layer has a thickness of 0.8-3 nm and a purity of ≥99.99%; the Pt layer has a thickness of 0.8-1.2 nm and a purity of ≥99.99%. The Co layer has a thickness of 0.8-1.2 nm and a purity of ≥99.99%; the Ta layer has a thickness of 0.8-2 nm and a purity of ≥99.99%.

2. The three-dimensional wide-field linear magnetic sensor according to claim 1, characterized in that, The thickness of the oxide layer on the thermally oxidized Si substrate is 180-220 nm.

3. The three-dimensional wide-field linear magnetic sensor according to claim 1, characterized in that, The sensor is a four-terminal Hall bar device, with a length of 75-85 μm and a width of 8-12 μm.

4. A method for fabricating a three-dimensional wide-field linear magnetic sensor, characterized in that, Includes the following steps: Step 1: Provide a thermally oxidized Si substrate as a substrate, and pretreat the substrate; Step 2: Using an ultra-high vacuum magnetron sputtering system, Cr, Pt, Co and Ta layers are sequentially deposited on the pretreated substrate to prepare a Cr / Pt / Co / Ta multilayer film. Step 3: The Cr / Pt / Co / Ta multilayer film is microfabricated to form a four-terminal Hall effect device, thus obtaining a three-dimensional wide-field linear magnetic sensor. The deposition process parameters for each layer in step 2 are as follows: Cr layer deposition: argon flow rate 28-32 sccm, sputtering power 28-32 W, growth rate 0.020-0.023 nm / s, deposition thickness 0.8-3 nm; Pt layer deposition: argon flow rate 18-22 sccm, sputtering power 13-17 W, growth rate 0.015-0.018 nm / s, deposition thickness 0.8-1.2 nm; Co layer deposition: argon flow rate 58-62 sccm, sputtering power 28-32 W, growth rate 0.010-0.012 nm / s, deposition thickness 0.8-1.2 nm; Ta layer deposition: argon flow rate 18-22 sccm, sputtering power 28-32 W, growth rate 0.016-0.018 nm / s, deposition thickness 0.8-2 nm.

5. The preparation method according to claim 4, characterized in that, The pretreatment described in step 1 is as follows: the thermally oxidized Si substrate is placed in acetone, alcohol and ultrapure water for ultrasonic cleaning in sequence, and then dried with high-purity N2.

6. The preparation method according to claim 4, characterized in that, The background vacuum of the ultra-high vacuum magnetron sputtering system described in step 2 is ≤3.75×10⁻⁶. -10 Torr was deposited using DC sputtering; the purity of the Cr, Pt, Co, and Ta targets used in the deposition process was ≥99.99%.

7. The preparation method according to claim 4, characterized in that, The microfabrication process described in step 3 includes the following sub-steps: Sub-step 3.1: The Cr / Pt / Co / Ta multilayer film sample was sequentially ultrasonically cleaned with acetone, alcohol, and ultrapure water, and then dried with high-purity N2; Sub-step 3.2: Coat the sample surface with S1805 photoresist and perform spin coating using a spin coater. First, spin the photoresist at a speed of 2000 r / min for 10 s, then spin it at a speed of 8500 r / min for 60 s. After that, place the sample on a heating stage at 100-110℃ for baking. Sub-step 3.3: Use a laser direct writing device with a wavelength of 405nm to perform ultraviolet exposure, with an exposure dose of 75-85mJ / cm² and an exposure time of 155-170s; Sub-step 3.4: Place the exposed sample in ZX-238 developer for 40-50 seconds, then fix it by immersing it in deionized water for 25-35 seconds; Sub-step 3.5: The fixed sample is etched using an Ar ion etching system with an etching energy of 280-320 eV, a beam current of 23-27 mA, and an etching rate of 0.016-0.017 nm / s. Sub-step 3.6: Remove the adhesive and clean the etched sample to obtain a four-terminal Holbar device.

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