Spin-orbit torque magneto-optical measurement chip, preparation method thereof, magneto-optical measurement device comprising the chip and measurement method of the magneto-optical measurement device

Abstract

The application provides a spin-orbit torque magneto-optical measurement chip on a chip and a preparation method thereof, a magneto-optical measurement device comprising the chip and a measurement method of the magneto-optical measurement device, and belongs to the technical field of ultrafast spin electronics and micro-nano measurement. In order to solve the pain points of the existing measurement scheme, such as picosecond pulse transmission distortion, double photoconductive switch bias crosstalk, low electro-optic synchronization accuracy, and inability to complete magnetic moment reset within a single cycle, the application adopts a structure of on-chip integrated double photoconductive switch and floating electrode with a physical isolation gap, and is matched with a design of three co-source femtosecond laser beam splitting and double delay lines, realizes on-chip generation of excitation and reset double pulses with independent adjustable polarity and timing, completes magnetic moment reset within a single laser repetition cycle, and realizes high time resolution magnetic dynamics measurement in combination with magneto-optical detection. The application can eliminate pulse distortion and bias crosstalk, realize femtosecond electro-optic synchronization, and greatly improve the measurement signal-to-noise ratio and stability.

Description

Technical Field

[0001] This application belongs to the field of ultrafast spintronics and micro / nano measurement technology, specifically relating to an on-chip spin-orbit torque magneto-optical measurement chip and its fabrication method, a magneto-optical measurement device containing the chip, and a measurement method of the magneto-optical measurement device. Background Technology

[0002] Spin-orbit torque (SOT) has become a core technology for next-generation high-speed spin memory and spin logic devices due to its ultrafast magnetization control speed, low power consumption, and high stability. The ultrafast dynamics of magnetization reversal driven by SOT directly determine the limiting switching speed, upper limit of energy consumption, and operational reliability of spin devices. Therefore, achieving high-precision, high-time-resolution in-situ measurement of this dynamics is a core prerequisite for conducting mechanism research and performance optimization of SOT devices.

[0003] Current measurements of SOT ultrafast dynamics rely on picosecond-level electrical pulses to excite magnetization reversal, combined with time-resolved magneto-optical Kerr effect (TR-MOKE) for magnetic state detection. In existing technologies, picosecond electrical pulses are mostly generated using commercially available fast-edge pulse generators and transmitted to the sample stage via coaxial cables. Due to impedance mismatch and signal dispersion effects in the transmission link, the narrow picosecond pulses suffer severe waveform distortion and amplitude attenuation after long-distance transmission, making it impossible to apply pure, parameter-controllable excitation pulses to micro / nano-scale samples. Furthermore, the discrete architecture suffers from low integration and weak anti-interference capabilities.

[0004] At the level of electro-optical synchronization measurement, existing technologies mostly adopt a separate architecture in which electrical pulse generation and optical detection are independent of each other. The timing synchronization of the two relies on electronic delay lines. Due to the limitations of electronic jitter, the synchronization accuracy can only reach the sub-nanosecond level, which cannot meet the capture requirements of ultrafast magnetization dynamics at the femtosecond to picosecond scale. Moreover, the optical delay line structure required by the multi-optical path synchronization scheme is complex, the system is difficult to debug, and the timing stability is poor.

[0005] At the level of weak signal detection, the magneto-optical Kerr signal generated by SOT-driven magnetization reversal is extremely weak, resulting in a very low signal-to-noise ratio for a single measurement. Effective extraction requires a combination of repetitive periodic measurements and lock-in amplification technology. Existing technologies struggle to complete magnetic moment reset within a single pulse cycle, making it impossible to construct a stable and repeatable excitation and detection cycle, thus limiting the application of lock-in amplification. Furthermore, existing dual-pulse excitation schemes struggle to achieve independent bias control of the two pulses, leading to bias crosstalk and compromising the stability and consistency of the pulse waveform, further restricting measurement accuracy and repeatability. Summary of the Invention

[0006] In view of this, this application provides an on-chip spin-orbit torque magneto-optical measurement chip and its fabrication method, a magneto-optical measurement device including the chip, and a measurement method for the magneto-optical measurement device; by integrating dual photoconductive switches and a coplanar waveguide transmission line with isolation gaps on the chip, the problems of bias crosstalk between dual switches and pulse transmission distortion are solved; by using three beams of light split from the same femtosecond laser source in conjunction with dual delay lines, femtosecond-level synchronization of electro-excitation and optical detection is achieved; and by using excitation and reset dual pulses with opposite polarities, magnetic moment reset is achieved within a single cycle, enabling high-sensitivity extraction of weak magneto-optical signals.

[0007] The first aspect of this application provides an on-chip spin-orbit torque magneto-optical measurement chip, comprising a low-temperature grown semi-insulating gallium arsenide substrate. A coplanar waveguide transmission line, a first photoconductive switch, a second photoconductive switch, and two floating electrodes are fabricated on the substrate, along with terminating resistors matched to the characteristic impedance of the coplanar waveguide transmission line. The coplanar waveguide transmission line includes a center signal line and a common ground electrode. The first and second photoconductive switches are electrically connected to the two ends of the center signal line, respectively. The two floating electrodes are electrically connected to the first and second photoconductive switches in a one-to-one correspondence. A physical isolation gap is provided between each floating electrode and the common ground electrode, completely severing the metal DC path between the floating electrode and the common ground electrode, thus achieving independent DC biasing of the first and second photoconductive switches. A sample carrier area for integrating the magnetic sample to be measured is provided at the midpoint of the center signal line, precisely matching the focusing position of the probe light. Terminating resistors are located at both ends of the coplanar waveguide transmission line.

[0008] Furthermore, the substrate of the on-chip spin-orbit torque magneto-optical measurement chip is a low-temperature grown semi-insulating gallium arsenide substrate; the on-chip spin-orbit torque magneto-optical measurement chip includes a coplanar waveguide transmission line, which includes a common ground electrode and a center signal line; one end of the center signal line is electrically connected to a first photoconductive switch, and the other end is electrically connected to a second photoconductive switch; a sample carrying area for placing the sample to be measured is provided at a predetermined position of the center signal line.

[0009] The second aspect of this application provides a method for fabricating an on-chip spin-orbit torque magneto-optical measurement chip, comprising the following steps: Step P1: Selecting a low-temperature grown semi-insulating gallium arsenide substrate and pre-treating the gallium arsenide substrate; Step P2: Defining the photosensitive area windows of the first and second photoconductive switches using photolithography, fabricating an alumina insulating layer in the non-photosensitive area of ​​the substrate, leaving only the photosensitive area as the bare gallium arsenide substrate; Step P3: Simultaneously defining the patterns of the coplanar waveguide transmission line, the first photoconductive switch, the second photoconductive switch, the floating electrode, and the physical isolation gap using an overlay process, depositing a metal electrode layer and completing the process. The process involves a stripping process to form a monolithically integrated pulse generation and transmission structure. The first and second photoconductive switches are positioned at opposite ends of the coplanar waveguide transmission line. A physical isolation gap between the floating electrode and the common ground electrode of the coplanar waveguide transmission line completely severs the direct current path between them. Step P4: Ni-chromium alloy thin-film resistors matching the characteristic impedance of the transmission line are fabricated at both ends of the coplanar waveguide transmission line. Step P5: A patterned sample carrier region is fabricated at the midpoint of the center signal line of the coplanar waveguide transmission line, and a magnetic heterojunction thin film to be measured is deposited, ultimately obtaining an on-chip spin-orbit torque magneto-optical measurement chip.

[0010] A third aspect of this application provides a spin-orbit torque magneto-optical measurement device, including a laser output module, a magneto-optical detection module, and an electrical pulse excitation module; the electrical pulse excitation module includes an on-chip integrated pulse chip and a DC bias power supply; the on-chip spin-orbit torque magneto-optical measurement chip includes a first photoconductive switch and a second photoconductive switch, and correspondingly connected floating electrodes; each floating electrode is provided with a physical isolation gap between itself and the common ground electrode of the on-chip spin-orbit torque magneto-optical measurement chip to cut off the DC and low-frequency paths between the floating electrode and the common ground electrode; wherein, the DC bias power supply is electrically connected to the two floating electrodes one-to-one. The laser output module outputs three co-source periodic femtosecond laser pulses. The first laser triggers the first photoconductive switch to activate, causing the DC bias power supply to generate an excitation pulse that drives the magnetic moment of the sample under test to flip. The second laser triggers the second photoconductive switch to activate, causing the DC bias power supply to generate a reset pulse that drives the magnetic moment of the sample under test to reset. The third laser irradiates the sample under test when its magnetic moment flips to obtain the reflected light during the magnetic moment flip. The magneto-optical detection module obtains the dynamic state of the sample's magnetic moment flip and reset through the reflected light.

[0011] Furthermore, the laser output module includes a femtosecond laser source, a laser beam splitter unit, a first delay line, and a second delay line. The femtosecond laser source is used to output a single-path periodic femtosecond laser pulse, which is split into three co-source femtosecond laser pulses by the laser beam splitter unit. The first laser pulse is a delay-free laser. The second laser pulse undergoes fixed-delay modulation via the first delay line, with the fixed delay being greater than the time required for the magnetic moment of the sample under test to completely reverse. The third laser pulse undergoes periodic-delay modulation via the second delay line.

[0012] Furthermore, the laser output module also includes a chopper, which is located on the main optical path between the femtosecond laser source and the laser beam splitting unit, or in the optical path of the first laser pulse. The chopper is used to synchronously and periodically modulate the laser pulse in the corresponding optical path to provide a synchronous reference signal for phase-locked amplification.

[0013] Furthermore, the two output terminals of the DC bias power supply are used to output DC bias voltages with opposite polarities, so that the first photoconductive switch and the second photoconductive switch generate excitation pulses and reset pulses with matched polarities, respectively, so that the sample under test completes magnetic moment reset within a single laser repetition cycle.

[0014] Furthermore, the substrate of the on-chip spin-orbit torque magneto-optical measurement chip is a low-temperature grown semi-insulating gallium arsenide substrate; the on-chip spin-orbit torque magneto-optical measurement chip includes a coplanar waveguide transmission line, which includes a common ground electrode and a center signal line; one end of the center signal line is electrically connected to a first photoconductive switch, and the other end is electrically connected to a second photoconductive switch; a sample carrying area for placing the sample to be tested is provided at a predetermined position on the center signal line, and the excitation pulse and reset pulse are applied to the sample to be tested through the center signal line.

[0015] Furthermore, the magneto-optical detection module includes a Wollaston prism, a balanced photodetector, and a lock-in amplifier arranged sequentially; the Wollaston prism is used to separate the orthogonal polarization components in the reflected light; the balanced photodetector is used to convert the light intensity difference of the orthogonal polarization components into an electrical signal; and the lock-in amplifier is used to extract the magneto-optical Kerr signal synchronized with the chopper modulation signal.

[0016] Furthermore, the device also includes a control and data acquisition module, which is electrically connected to the first delay line, the second delay line, and the magneto-optical detection module, respectively, for timing synchronization control and data acquisition and analysis.

[0017] The fourth aspect of this application provides a magneto-optical measurement method for spin-orbit torque dynamics, comprising the following steps: Step S1, applying independently adjustable DC bias voltages of opposite polarities to the independent floating electrodes of the first and second photoconductive switches integrated at both ends of an on-chip coplanar waveguide transmission line, ensuring that the DC biases of the first and second photoconductive switches are independent of each other through physical isolation gaps; Step S2, outputting laser pulses with a fixed repetition frequency from a femtosecond laser source, periodically modulating the intensity of the laser using a chopper to provide a reference signal for phase-locked amplification; splitting a single laser pulse into three beams by a laser beam splitting unit, the first laser beam being used to trigger an electro-pulse excitation module to generate an excitation pulse that drives the magnetic moment reversal of the magnetic sample under test. The second laser beam, after being fixed-delayed by the first delay line, generates a reset pulse. The fixed delay is greater than the time required for the magnetic moment of the sample under test to completely reverse, ensuring that the magnetic moment reversal and complete reset are completed within a single laser repetition cycle, thus constructing a stable and repeatable periodic measurement loop. The third laser beam, acting as a probe beam, illuminates the sample under test after passing through the second delay line. By continuously scanning the second delay line with a time delay, reflected light carrying the dynamic information of the magnetic moment of the sample under test during the magnetic moment reversal process is obtained. In step S3, the reflected light is incident on the magneto-optical detection module. Through balanced photoelectric detection and lock-in amplification technology, a high signal-to-noise ratio magneto-optical Kerr signal synchronized with chopper modulation is extracted to obtain the time-series evolution curve of the magnetic moment reversal dynamics of the sample under test.

[0018] By adopting the above scheme, this application proposes an on-chip spin-orbit torque magneto-optical measurement chip and its fabrication method, a magneto-optical measurement device including the chip, and a measurement method of the magneto-optical measurement device, which has the following beneficial effects:

[0019] (1) By integrating on-chip photoconductive switches and coplanar waveguide transmission lines, picosecond pulses are generated directly on the chip, completely avoiding waveform distortion and attenuation caused by long-distance transmission; the innovative floating electrode combined with physical isolation gap design achieves DC isolation of more than 100dB for dual photoconductive switches, and the two biases are completely independent, which can generate dual pulse sequences with fully adjustable polarity, timing, amplitude and width, and complete magnetic moment reset within a single pulse cycle to build a stable repetitive excitation cycle.

[0020] (2) The same femtosecond laser source is used to split the trigger light and probe light, and the whole system shares a unified time reference, which completely eliminates the time jitter of multi-source lasers. The relative timing control of the three lights is achieved by only two optical delay lines, avoiding the inherent jitter of the electronic delay line, and can accurately capture the picosecond-femtosecond scale ultrafast initial process of magnetic moment precession and flipping.

[0021] (3) By completing the magnetic moment reset within a single laser repetition cycle, a stable and repeatable measurement cycle is constructed, providing a core foundation for the application of lock-in amplification technology; in conjunction with balanced photoelectric detection technology, common-mode noise caused by laser power fluctuations and environmental vibrations is effectively suppressed, and measurement efficiency and repeatability are significantly improved.

[0022] (4) The pulse generation, impedance matching transmission, sample carrying and magneto-optical detection are integrated on a single semiconductor chip, which greatly improves the system integration and enhances the anti-electromagnetic interference capability. In-situ integrated measurement can be achieved without repeatedly moving the sample. The pulse parameters are fully programmable and can be adapted to SOT magnetic devices of different structures and sizes. It can also be extended to the measurement of various ultrafast electro-induced phenomena such as ferroelectric reversal and topological spin transport. It has strong versatility and expandability. Attached Figure Description

[0023] The embodiments of this application are described below with reference to the accompanying drawings, in which:

[0024] Figure 1 The schematic diagram shows a top view of an on-chip spin-orbit torque magneto-optical measurement chip according to an embodiment of this application;

[0025] Figure 2 A top view of the spin-orbit torque dynamics magneto-optical measurement device according to an embodiment of this application is shown schematically.

[0026] Figure 3 This schematic diagram illustrates the overall system architecture of a spin-orbit torque magneto-optical measurement device according to an embodiment of this application.

[0027] Figure 4 A flowchart illustrating a spin-orbit torque dynamics magneto-optical measurement method according to an embodiment of this application is shown schematically.

[0028] Figure 5 The schematic diagram illustrates a programmable three-pulse timing diagram of the spin-orbit torque dynamics magneto-optical measurement device according to an embodiment of this application during the measurement process.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1-On-chip spin-orbit torque magneto-optical measurement chip; 2-On-chip coplanar waveguide transmission line; 3-First photoconductive switch; 4-Second photoconductive switch; 5-Dual-channel DC bias power supply; 6-Laser trigger module; 7-Femtosecond laser source; 8-Laser beam splitter unit; 9-First / second delay line; 10-Sample carrier area; 11-Magneto-optical detection module; 12-Wollaston prism; 13-Balanced photodetector; 14-Lock-in amplifier; 15-Control and data acquisition module. Detailed Implementation

[0031] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0033] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0034] Figure 1 The diagram illustrates a top view of an on-chip spin-orbit torque magneto-optical measurement chip according to an embodiment of this application.

[0035] like Figure 1 The chip shown is the core optoelectronic integrated unit of the measurement device of this application. It is a monolithic integrated structure, with all functional structures fabricated on the same semiconductor substrate. There are no separate splicing devices, which eliminates the problems of parasitic parameters, impedance mismatch, signal crosstalk, timing jitter caused by the separate architecture from the root.

[0036] In this embodiment, the substrate of the on-chip spin-orbit torque magneto-optical measurement chip is a low-temperature grown semi-insulating gallium arsenide substrate; the on-chip spin-orbit torque magneto-optical measurement chip includes a coplanar waveguide transmission line, which includes a common ground electrode and a center signal line; one end of the center signal line is electrically connected to a first photoconductive switch, and the other end is electrically connected to the first photoconductive switch; a sample carrying area for placing the sample to be tested is provided at a predetermined position on the center signal line, and the excitation pulse and reset pulse are applied to the sample to be tested through the center signal line.

[0037] The semiconductor substrate serves as the supporting base for all functional structures of the chip and also acts as the light-absorbing active layer for the photoconductive switch. This invention uses a low-temperature grown semi-insulating gallium arsenide (LT-GaAs) substrate, which is the core foundation for simultaneously achieving ultrafast photoconductive response and low-loss RF transmission. AlO... XThe insulating layer is a 50nm thick aluminum oxide film that completely covers the substrate surface outside the photosensitive area of ​​the photoconductive switch, leaving only the photosensitive areas of the first / second photoconductive switches as bare LT-GaAs substrates.

[0038] The first and second photoconductive switches in this application both employ a metal-semiconductor-metal (MSM) planar interdigitated electrode structure. This structure has three major advantages: First, both the electrodes and the photosensitive region are fabricated on the substrate surface, making it fully compatible with CPW transmission line technology and allowing for one-time fabrication. Second, the interdigitated electrodes can significantly increase the collection efficiency of photogenerated carriers and reduce the on-resistance of the switch. Third, the electrode gap can be precisely controlled at the micrometer level, achieving a high electric field intensity at a relatively low bias voltage and improving the switch response speed. When a femtosecond laser is focused onto the photosensitive region, the photon energy is greater than the bandgap of LT-GaAs, generating a large number of electron-hole pairs within 100 fs, causing an instantaneous increase in the conductivity of the photosensitive region. Under the action of a DC bias voltage, a large current is instantly generated, forming a picosecond electrical pulse with a rise time ≤1 ps on the CPW transmission line.

[0039] Each floating electrode is a rectangular metal plane, seamlessly connected at one end to the external electrode of the photoconductive switch, and extending at the other end to a gold wire bonding pad, which is connected one-to-one to the two independent output terminals of the dual-channel DC bias power supply. The gap width between the floating electrode and the ground electrode is the core parameter that determines the DC isolation and RF conduction performance: the smaller the width, the higher the DC isolation, the larger the gap capacitance, and the better the RF conduction performance; for example, a 5μm width can achieve ≥100dB DC isolation while providing a low-impedance RF path for picosecond pulses.

[0040] For DC and low-frequency signals below 100kHz, the capacitor's impedance approaches infinity. The physical isolation gap completely cuts off the metal path between the floating electrode and the common ground electrode, with a DC resistance ≥10¹²Ω and a DC isolation ≥100dB. The two DC bias voltages cannot form a loop through the common ground electrode. Even with ±100V biases of opposite polarities, no crosstalk or short circuit issues will occur, completely solving the core problem of mutual bias interference in existing dual photoconductive switches.

[0041] For picosecond electrical pulses, their spectral components are mainly concentrated in the 1GHz~40GHz radio frequency band. The parallel plate capacitor formed by the physical isolation gap has extremely low impedance for radio frequency signals in this band, and can be regarded as an AC short circuit. The picosecond radio frequency pulse can form a low-impedance radio frequency return path between the floating electrode and the common ground electrode through the gap capacitor, with no obvious transmission loss, waveform distortion and reflection, ensuring that the picosecond pulse generated by the photoconductive switch can be injected completely and cleanly into the CPW transmission line.

[0042] Figure 2 A top view of the spin-orbit torque dynamics magneto-optical measurement device according to an embodiment of this application is shown schematically.

[0043] like Figure 2 As shown, the dual-channel DC bias power supply provides the first / second photoconductive switches with opposite polarities and completely independent DC bias through two independent floating electrodes; the laser output module outputs three femtosecond lasers.

[0044] The first delay-free laser output from the laser beam splitter is transmitted along the optical path to the photosensitive area window of the first photoconductive switch on the left side of the on-chip chip. The optical path axis is completely aligned with the center normal of the photosensitive area, ensuring that the laser focused spot completely covers the photosensitive area.

[0045] The second laser beam first propagates horizontally to the right, and after being fixed-delayed by the first delay line, it is incident on the photosensitive area window of the second photoconductive switch on the right side of the on-chip chip. The optical path axis is completely coincident with the center normal of the photosensitive area. Based on this layout, the optical path length of the first delay line can be precisely and linearly controlled, so that the timing difference between the two trigger beams can be continuously adjusted in the range of 0ns to 10ns, and the control accuracy is ≤10fs.

[0046] The third laser beam is incident on the sample carrier area at the center of the chip; the reflected light from the sample returns along the original incident light path, is redirected by the beam splitter, and is then incident on the magneto-optical detection module 11 on the right, realizing in-situ reflective magneto-optical signal acquisition without any extra optical path loss.

[0047] based on Figure 1 The on-chip spin-orbit torque magneto-optical measurement chip shown in this application also provides the overall architecture of the spin-orbit torque dynamics magneto-optical measurement device.

[0048] Figure 3 A schematic diagram of the overall system architecture of the spin-orbit torque dynamics magneto-optical measurement device according to an embodiment of this application is shown.

[0049] The spin-orbit torque dynamics magneto-optical measurement device shown in the figure includes a laser output module, a magneto-optical detection module 11, and an electrical pulse excitation module. The electrical pulse excitation module includes an on-chip spin-orbit torque magneto-optical measurement chip and a DC bias power supply. The on-chip spin-orbit torque magneto-optical measurement chip includes a first photoconductive switch 3 and a second photoconductive switch 4, as well as corresponding floating electrodes. Each floating electrode is provided with a physical isolation gap between itself and the common ground electrode of the on-chip spin-orbit torque magneto-optical measurement chip to cut off the DC and low-frequency paths between the floating electrode and the common ground electrode. The DC bias power supply is electrically connected to the two floating electrodes one-to-one. The laser output module is used to output three co-source periodic femtosecond laser pulses. The first laser is used to trigger the first photoconductive switch 3 to conduct, so that the DC bias power supply generates an excitation pulse that drives the magnetic moment of the sample under test to flip. The second laser is used to trigger the second photoconductive switch 4 to conduct, so that the DC bias power supply generates a reset pulse that drives the magnetic moment of the sample under test to reset. The third laser is used to irradiate the sample under test when the magnetic moment flips, so as to obtain the reflected light when the magnetic moment of the sample flips. The magneto-optical detection module 11 obtains the dynamic state of the magnetic moment flip and reset of the sample through the reflected light.

[0050] In this embodiment, the excitation pulse and the reset pulse are applied to the sample under test via the central signal line.

[0051] In this embodiment, the first photoconductive switch 3 and the second photoconductive switch 4 are each equipped with an independent floating electrode; the two output terminals of the dual-channel DC bias power supply 5 are respectively electrically connected to the floating electrodes of the first photoconductive switch 3 and the second photoconductive switch 4; a physical isolation gap is provided between each floating electrode and the common ground electrode of the coplanar waveguide transmission line to cut off the DC and low-frequency signal paths between the floating electrode and the common ground electrode of the coplanar waveguide transmission line, so as to realize that the DC bias of the first photoconductive switch 3 and the second photoconductive switch 4 are independent of each other.

[0052] For example, one electrode of each photoconductive switch is connected to the center signal line of the coplanar waveguide, and the other electrode is connected to a separate floating electrode. There is no direct metal connection between the floating electrode and the common ground electrode; they are completely separated by a physical isolation gap. A DC bias voltage is applied between the floating electrode and the center signal line, rather than the common ground electrode, structurally preventing the two bias paths from being shorted through the common ground.

[0053] Specifically, in this application, the physical isolation gap is a T-shaped physical isolation gap. The longitudinal section cuts off the direct metal connection between the floating electrode and the common ground electrode, and the transverse section extends the isolation path to improve DC isolation. DC isolation and RF conduction are achieved through gap capacitance. For DC and low-frequency signals: the gap completely cuts off the metal path, the DC resistance approaches infinity, and the two biases cannot form a loop through the common ground, resulting in no crosstalk. For picosecond-level RF pulses: the plate capacitor formed by the gap has extremely low impedance to RF signals of tens of GHz, which can be regarded as a short circuit. Picosecond pulses can pass through the gap to form an RF loop without loss or distortion. The positive terminal of the first output of the dual-channel DC bias power supply 5 is connected to the floating electrode of the first photoconductive switch 3, and the negative terminal is connected to the center signal line; the negative terminal of the second output is connected to the floating electrode of the second photoconductive switch 4, and the positive terminal is connected to the center signal line; the grounding terminals of the two power supplies are isolated from each other to further avoid crosstalk.

[0054] By employing a floating electrode and a T-shaped physical isolation gap design, a DC isolation of ≥100dB is achieved between the two switches. The two biases are completely independent, and even with ±100V biases of opposite polarity, there is no crosstalk. This is the first time that on-chip generation of two picosecond dual-pulse sequences with opposite polarity and independently adjustable amplitude has been achieved. Simultaneously, the physical isolation gap provides a low-impedance path for the picosecond RF pulses through gap capacitance, ensuring a transmission loss of ≤0.5dB for the picosecond pulses while achieving ultra-high DC isolation, with no waveform distortion, no tailing, and no reflection. This perfectly balances the dual requirements of DC isolation and RF transmission, and its performance far surpasses existing isolation capacitor and isolation resistor solutions.

[0055] In this embodiment, the laser output module includes a femtosecond laser source 7, a laser beam splitter unit 8, a first delay line, and a second delay line. The femtosecond laser source 7 is used to output a single-channel periodic femtosecond laser pulse. The single-channel femtosecond laser pulse is split into three co-source femtosecond laser pulses by the laser beam splitter unit 8. The first laser is a laser without delay. The second laser is subject to fixed time delay control via the first delay line, and the fixed time delay is greater than the time required for the magnetic moment of the magnetic sample under test to completely reverse. The third laser is subject to periodic time delay control via the second delay line.

[0056] Specifically, based on the photoconductive effect, when the first laser beam is incident on the photosensitive region of the first photoconductive switch 3, the photon energy is greater than the bandgap of the substrate semiconductor, instantly generating a large number of photogenerated electron-hole pairs, increasing the switch conductance by several orders of magnitude, and instantly turning on under DC bias, generating an excitation pulse with a picosecond-level rising edge; the second laser beam, after a delay, is incident on the second photoconductive switch 4, similarly generating a reset pulse. Since the trigger source for both switches is the same femtosecond laser source 7, the timing difference between the two pulses is entirely determined by the delay of the first delay line, and the timing control accuracy can reach 10 fs. At the same time, utilizing the carrier recombination characteristics of the low-temperature grown GaAs photoconductive switch, the higher the photoexcitation power, the higher the injected carrier concentration, and the longer the carrier recombination time, thereby stretching the full width at half maximum (FWHM) of the electrical pulse; by adjusting the power of the first and second laser beams, the pulse width can be continuously adjusted within the range of 7 ps to 60 ps, ​​adapting to the measurement needs of different magnetic samples without modifying the chip structure.

[0057] For example, for the first laser, the laser output from the femtosecond laser source 7 is split into the first beam by the laser beam splitting unit 8. This beam is then directly incident on the first photoconductive switch 3 through the laser triggering module 6, serving as the time zero point reference for the entire system. This triggers the generation of an excitation pulse, which drives the sample magnetic moment to flip from its initial state.

[0058] For the second laser, the second beam after being split by the laser beam splitting unit 8 is incident on the first delay line in the first / second delay line 9. After precise time delay control, it is incident on the second photoconductive switch 4 through the laser trigger module 6. The time delay value is set to be greater than the time for the magnetic moment to completely reverse, so as to ensure that after the magnetic moment reverses, a reset pulse is triggered to generate, thereby realizing the complete reset of the magnetic moment within a single laser repetition cycle.

[0059] For the third laser, the third beam after being split by the laser beam splitting unit 8 is incident on the second delay line in the first / second delay line 9. After continuous and scannable time delay adjustment, it is incident on the sample to be tested in the sample carrier area 10 as a time-resolved probe light. During the entire cycle of magnetic moment reversal and reset, the dynamic change information of the magnetic moment is collected point by point.

[0060] In this embodiment, the laser output module provides a unified time reference and optical energy for the entire system, eliminating the jitter error of multi-source synchronization at its source; the electric pulse excitation module realizes the controllable flipping and reset of the magnetic moment, constructing a stable and repeatable measurement cycle; the magneto-optical detection module 11 extracts the dynamic evolution information of the magnetic moment, and the three form a closed-loop measurement system to realize high-precision in-situ measurement of spin orbit torque (SOT) dynamics.

[0061] Meanwhile, the three light sources share the same femtosecond laser source 7 and the same time reference, completely eliminating the inherent time jitter of multiple laser sources and the electronic jitter of the electronic delay line. The long-term timing drift is ≤5fs / hour, and the system stability is greatly improved. Furthermore, by delaying the reset pulse through the second beam, the magnetic moment flip-reset closed loop is completed within a single laser repetition cycle. The initial magnetization state of each measurement cycle is completely consistent, solving the pain point of existing technologies being unable to construct stable repetition cycles and suffering from severe signal drift. This provides a core foundation for the application of lock-in amplification technology.

[0062] In this embodiment, the laser output module further includes a chopper, which is disposed on the main optical path between the femtosecond laser source 7 and the laser beam splitting unit 8, or in the optical path of the first laser pulse; the chopper is used to synchronously periodically modulate the laser pulse in the corresponding optical path to provide a synchronous reference signal for phase-locked amplification.

[0063] Specifically, the chopper can be a mechanical chopper, an electro-optic modulator, or an acousto-optic modulator. Its modulation frequency is completely locked to the reference signal frequency of the lock-in amplifier 14, and the modulation frequency is an integer division of the repetition frequency of the laser pulse output from the femtosecond laser source 7. By periodically switching on and off / modulating the intensity of the laser pulse, the magneto-optical Kerr signal generated by the sample under test carries a periodic characteristic consistent with the modulation frequency. Based on the synchronous reference signal of the chopper, the lock-in amplifier 14 only performs coherent extraction on the magneto-optical signal that is in phase with the modulation frequency. This effectively filters out broadband random noise and common-mode noise caused by laser power drift, environmental vibration, and spatial electromagnetic interference, improving the signal-to-noise ratio of the nV-level weak magneto-optical Kerr signal by 2 to 3 orders of magnitude.

[0064] When the chopper is placed in the main optical path between the femtosecond laser source 7 and the laser beam splitter 8, it can synchronously and in-phase modulate the three co-source laser pulses after beam splitting by the laser beam splitter 8. This ensures that the modulation states of the excitation pulse, reset pulse, and probe light are completely consistent, eliminating the modulation phase difference and timing deviation of each branch optical path after beam splitting, and further improving the phase matching accuracy and long-term stability of the lock-in amplifier. When the chopper is placed in the optical path of the first laser pulse, it only modulates the first laser used to trigger the generation of the excitation pulse, realizing the periodic switching control of the excitation pulse. This makes the magnetic moment reversal behavior completely synchronized with the chopper modulation frequency. The lock-in amplifier 14 only extracts the magneto-optical Kerr signal that is synchronously triggered with the excitation pulse, which can completely shield the background signal interference caused by the reset pulse and ambient stray light. At the same time, there is no need to modulate the reset light and probe light, avoiding the influence of the modulation process on the power, polarization state, and optical path stability of the two lasers. The optical path debugging is more flexible and can be adapted to measurement scenarios with different signal-to-noise ratio requirements.

[0065] In this embodiment, the two output terminals of the DC bias power supply are used to output DC bias voltages with opposite polarities, so that the first photoconductive switch 3 and the second photoconductive switch 4 generate excitation pulses and reset pulses with matched polarities, so that the sample under test completes magnetic moment reset within a single laser repetition cycle.

[0066] The coplanar waveguide transmission line is fabricated on a high-resistivity semiconductor substrate and adopts a planar coplanar waveguide (CPW) structure, which includes a central signal line and two symmetrical common ground electrodes. The two ends of the central signal line are seamlessly connected to the electrodes of the first photoconductive switch 3 and the second photoconductive switch 4, respectively, forming a symmetrical pulse transmission structure at both ends, ensuring that the excitation pulse and the reset pulse can be applied to the sample under test through the same transmission line.

[0067] The sample carrier region 10 is positioned at the midpoint of the central signal line, ensuring that the time it takes for the excitation pulse to travel from the first photoconductive switch 3 at the left end to the sample is exactly the same as the time it takes for the reset pulse to travel from the second photoconductive switch 4 at the right end to the sample, thus avoiding timing errors caused by the transmission path. The magnetic sample to be tested is directly prepared in the sample carrier region 10, forming an ohmic contact with the central signal line. When current flows through the central signal line, a spin current is directly generated in the sample, driving the magnetic moment to flip, eliminating the need for additional lead connections and thus eliminating the influence of parasitic parameters.

[0068] The coplanar waveguide transmission line, the first photoconductive switch 3, the second photoconductive switch 4, and the sample under test are integrated on the same chip. The pulse transmission distance is only a few hundred micrometers to a few millimeters, which is much shorter than the coaxial cable of several meters in the prior art. This completely avoids the dispersion, impedance mismatch, and waveform distortion caused by long-distance transmission. The pulse waveform fidelity is ≥95%, ensuring that the pulse parameters applied to the sample are completely consistent with the design value.

[0069] For example, the first path of the dual-channel DC bias power supply 5 applies a positive DC bias (+5V~+100V, typical value +50V) to the first photoconductive switch 3, and the second path applies a reverse DC bias (-5V~-100V, typical value -50V) to the second photoconductive switch 4. The absolute values ​​of the two voltages can be equal or adjusted independently to adapt to different flipping and reset requirements.

[0070] When the forward-biased first photoconductive switch 3 is triggered, it generates a positive electrical pulse. Current flows through the sample from left to right along the center signal line, generating a positive spin-orbit torque that drives the magnetic moment to flip from its initial state to the opposite state. When the reverse-biased second photoconductive switch 4 is triggered, it generates a reverse electrical pulse. Current flows through the sample from right to left along the center signal line, generating a reverse spin-orbit torque that drives the magnetic moment back to its initial state. The delay of the first delay line is set to 0.5ns~10ns to ensure that the reset pulse is applied after the magnetic moment has completely flipped and before the laser repetition cycle ends, achieving complete reset within a single cycle.

[0071] Taking a femtosecond laser source 7 with a repetition frequency of 80MHz as an example, the single repetition period is 12.5ns, and the maximum delay of the first delay line is set to 10ns to ensure that the reset pulse is triggered at 10ns, and the magnetic moment is completely reset to the initial state before the end of the 12.5ns period. The initial state of the next period is completely consistent with the previous period, thus constructing an infinitely repeating stable measurement period.

[0072] In this embodiment, the device further includes a control and data acquisition module 15, which is electrically connected to the first delay line, the second delay line, and the magneto-optical detection module 11, respectively, for timing synchronization control and data acquisition and analysis.

[0073] In this embodiment, the magneto-optical detection module 11 includes a Wollaston prism 12, a balanced photodetector 13, and a lock-in amplifier 14 arranged sequentially. The Wollaston prism 12 is used to separate the orthogonal polarization components in the reflected light. The balanced photodetector 13 is used to convert the light intensity difference of the orthogonal polarization components into an electrical signal. The lock-in amplifier 14 is used to extract the magneto-optical Kerr signal synchronized with the chopper modulation signal.

[0074] Specifically, the reflected light from the sample under test is incident on the Wollaston prism 12 and separated into two orthogonal linearly polarized components, s-polarization and p-polarization. The two components are respectively incident on two perfectly matched photodiodes of the balanced photodetector 13. The balanced photodetector 13 outputs a differential electrical signal proportional to the difference in light intensity between the two components. The differential electrical signal is input to the lock-in amplifier 14. The reference signal of the lock-in amplifier 14 is synchronized with the modulation frequency of the chopper, and only the magneto-optical Kerr signal synchronized with the excitation is extracted.

[0075] Among them, balanced detection can eliminate common-mode noise caused by laser power fluctuations, environmental vibrations, and temperature drift, while lock-in amplification can filter out all random noise that is out of sync with the excitation. The combination of the two reduces the system baseline noise and enables unattended stable measurement.

[0076] Furthermore, the device also includes a substrate on which the coplanar waveguide transmission line is located; the substrate has a resistivity greater than or equal to 10. 7 Gallium arsenide substrate grown at low temperature with an Ωcm depth; the center signal line width of the coplanar waveguide transmission line is 10μm~100μm, and the gap between the center signal line and the common ground electrode is 10μm~100μm.

[0077] For example, typical parameters are a center signal line width of 50μm and a gap of 50μm between the signal line and the common ground electrode. Under these parameters, the characteristic impedance of the coplanar waveguide based on the GaAs substrate is exactly 50Ω, which is a perfect match for standard RF systems. The size can be adjusted in the range of 10μm to 100μm to meet the needs of different operating frequencies and different current carrying capacities: small size (10μm width and 10μm gap) is suitable for ultra-high operating frequencies above 100GHz, and large size (100μm width and 100μm gap) is suitable for high current carrying requirements.

[0078] Furthermore, the femtosecond laser source 7 is a Ti:sapphire femtosecond laser amplifier with a center wavelength of 800nm, an output laser pulse width of less than or equal to 150fs, and a repetition frequency of 80MHz or 1kHz; the resolution of the first delay line and the second delay line is less than or equal to 10fs, and the delay range is 0ns to 10ns.

[0079] Figure 4 A flowchart illustrating a spin-orbit torque dynamics magneto-optical measurement method according to an embodiment of this application is shown.

[0080] like Figure 4 The present invention provides a magneto-optical measurement method for spin-orbit torque dynamics, which includes the following steps:

[0081] Step S1: Apply independent adjustable DC bias voltages with opposite polarities to the independent floating electrodes of the first and second photoconductive switches integrated at both ends of the on-chip coplanar waveguide transmission line, and ensure that the DC biases of the first and second photoconductive switches are independent of each other through physical isolation gaps.

[0082] For example, an on-chip spin-orbit torque magneto-optical measurement chip is fixed to an oxygen-free copper sample holder. The independent floating electrodes of two photoconductive switches are connected to the two outputs of a dual-channel isolated DC bias power supply via gold wire bonding, with the common ground electrode reliably grounded. An independently adjustable ±0V~±100V DC bias with opposite polarities is applied to the two floating electrodes, with 10μA overcurrent protection and a step-up voltage increase method. The DC path between the floating electrodes and the common ground is physically isolated, verifying that the DC isolation of the two switches is ≥100dB, the leakage current is ≤1nA, and the pulse waveform has no crosstalk distortion. This ensures that the dual switch biases are completely independent, providing the hardware foundation for dual-pulse sequence generation.

[0083] In step S2, the laser output from the femtosecond laser source is split into three beams by the laser beam splitting unit. The first laser beam is used to trigger the electrical pulse excitation module to generate an excitation pulse that drives the magnetic moment reversal of the magnetic sample under test. The second laser beam is delayed by the first delay line. After the magnetic moment of the magnetic sample under test is completely reversed, the electrical pulse excitation module is triggered to generate a reset pulse that drives the magnetic moment of the magnetic sample under test to reset to the initial state. The third laser beam is used as a probe beam and is then used to irradiate the magnetic sample under test after passing through the second delay line. By continuously scanning the second delay line with time delay, the reflected light carrying the dynamic information of the magnetic moment of the magnetic sample under test during the magnetic moment reversal process is obtained.

[0084] For example, a Ti:sapphire femtosecond laser source (center wavelength 800nm, pulse width ≤150fs, repetition frequency 80MHz / 1kHz) is preheated until its power stabilizes. The laser is then split into three beams with a power ratio of 4:3:3 using a two-stage unpolarized beam splitter prism. The first beam is a delay-free reference beam, focused onto the photosensitive region of the first photoconductive switch, and its trigger moment is defined as the system time zero point, generating an excitation pulse. The second beam is delayed by a fixed time of 1ns to 10ns via a first delay line, ensuring that the magnetic moment is completely reversed before triggering the second photoconductive switch to generate a reset pulse, completing the system reset within a single laser cycle. The third beam is continuously scanned and controlled by a second delay line from 0ns to 10ns with a step size of 10fs, focused onto the sample-bearing region to form a periodic probe beam, which generates reflected light carrying magnetic moment information after irradiating the sample.

[0085] Step S3: The reflected light is incident on the magneto-optical detection module to obtain the ultrafast dynamic state of the magnetic moment reversal of the magnetic sample under test.

[0086] For example, the orthogonal polarization components of the reflected light are separated by a Wollaston prism, and the intensity difference is converted into a differential electrical signal by a balanced photodetector to suppress common-mode noise such as laser power fluctuations. The lock-in amplifier reference signal is synchronized with the chopper modulation frequency to extract a high signal-to-noise ratio magneto-optical Kerr signal. A control module achieves complete synchronization between delayed line scanning and data acquisition, recording the magneto-optical signals corresponding to different time delays in real time and plotting magnetization dynamics curves. After smoothing and baseline correction preprocessing of the raw data, core dynamic parameters such as the Gilbert damping coefficient, SOT effective field, and magnetic moment reversal time are extracted to complete the quantitative acquisition and analysis of the ultrafast magnetization dynamics.

[0087] Based on the above-mentioned on-chip spin-orbit torque magneto-optical measurement chip, this application also discloses a method for fabricating an on-chip spin-orbit torque magneto-optical measurement chip, comprising the following steps:

[0088] Step P1: Select a low-temperature grown semi-insulating gallium arsenide substrate and pretreat the gallium arsenide substrate.

[0089] For example, a low-temperature grown semi-insulating gallium arsenide substrate is selected, and the gallium arsenide substrate is pretreated to remove organic contaminants, particulate impurities, and intrinsic oxide layers from the substrate surface, thereby improving the adhesion between the subsequent thin film and the substrate. In a preferred embodiment of this step, after the substrate pretreatment is completed, rapid thermal annealing can be used to optimize the carrier recombination characteristics and resistivity uniformity of the substrate.

[0090] Step P2: Define the photosensitive region windows of the first and second photoconductive switches using photolithography, prepare an aluminum oxide insulating layer in the non-photosensitive region of the substrate, and retain only the photosensitive region as an exposed gallium arsenide substrate.

[0091] For example, photoresist is spin-coated onto the pre-treated substrate surface, followed by pre-baking, deep ultraviolet exposure, and development to form a window pattern matching the size of the photosensitive area. An atomic layer deposition process is used to deposit a 50nm thick aluminum oxide insulating layer on the substrate surface at a deposition temperature of 150℃ to ensure conformal coverage of the insulating layer in the non-photosensitive area. After deposition, acetone ultrasonic stripping is used to remove the photoresist and the aluminum oxide insulating layer on the photoresist surface, leaving only the aluminum oxide insulating layer in the non-photosensitive area of ​​the substrate, while the photosensitive area is an exposed gallium arsenide substrate.

[0092] Step P3 involves simultaneously defining the patterns of the coplanar waveguide transmission line, the first photoconductive switch, the second photoconductive switch, the floating electrode, and the physical isolation gap through an overlay process. A metal electrode layer is deposited and a stripping process is completed to form a monolithically integrated pulse generation and transmission structure. The first and second photoconductive switches are placed at both ends of the coplanar waveguide transmission line, and the physical isolation gap between the floating electrode and the common ground electrode of the coplanar waveguide transmission line completely cuts off the metal DC path between them.

[0093] For example, a deep violet overlay etching process is used to complete the pattern definition, with an overlay alignment accuracy of ≤0.1μm, ensuring that the electrodes of the photoconductive switch are completely aligned with the photosensitive area window prepared in step P2; after the pattern definition is completed, a magnetron sputtering process is used to sequentially deposit a chromium adhesion layer with a thickness of 5nm and a gold electrode layer with a thickness of 100nm to form a metal electrode stack; after sputtering, an acetone ultrasonic lift-off process is used to remove the photoresist and the metal layer on the surface of the photoresist to form the target monolithic integrated structure.

[0094] Step P4: Prepare nickel-chromium alloy thin-film resistors at both ends of the coplanar waveguide transmission line that match the characteristic impedance of the transmission line.

[0095] For example, impedance matching resistor patterns are defined at both ends of a coplanar waveguide transmission line using an overlay process. A nickel-chromium alloy thin film is deposited using a magnetron sputtering process. A thin film resistor with a resistance of 50Ω is prepared by pattern design, which is completely matched with the characteristic impedance of the coplanar waveguide transmission line. After sputtering, a stripping process is used to complete the patterning, and finally, terminating matching resistors are formed at both ends of the coplanar waveguide transmission line to eliminate signal reflection of picosecond pulses at the end of the transmission line and ensure the integrity of the pulse waveform.

[0096] Step P5: A patterned sample carrier region is prepared at the midpoint of the center signal line of the coplanar waveguide transmission line, and a thin film of the magnetic heterojunction to be tested is deposited to finally obtain the on-chip spin-orbit torque magneto-optical measurement chip.

[0097] For example, the sample carrier region pattern is defined at the midpoint of the center signal line of the coplanar waveguide transmission line using an overlay process. Then, a magnetic heterojunction thin film to be tested is deposited in the sample carrier region using magnetron sputtering or molecular beam epitaxy. The magnetic heterojunction to be tested is a heavy metal / ferromagnetic metal perpendicular magnetic anisotropy heterojunction or a two-dimensional van der Waals magnetic heterojunction. After deposition, the patterning is completed by photolithography combined with argon ion etching to obtain the target measurement chip.

[0098] Figure 5 The schematic diagram illustrates a programmable three-pulse timing diagram of the spin-orbit torque dynamics magneto-optical measurement device according to an embodiment of this application during the measurement process.

[0099] like Figure 5 As shown, pulse 1 is the excitation pulse. In this application, the moment when the first laser triggers the first photoconductive switch to generate pulse 1 is taken as the system time zero point t0. This moment is the unique time reference for the entire system, and all timing sequences are precisely controlled with reference to t0. Pulse 1 is a picosecond-level positive electrical pulse. The pulse width can be continuously and programmably adjusted within the range of 7ps to 60ps by the trigger optical power, and the amplitude can be continuously adjusted within the range of 0 to 100V by the bias voltage. Its core function is to drive the magnetic moment of the sample under test to flip from the initial magnetization state through the spin-orbit torque effect.

[0100] Pulse 2 is a picosecond electrical pulse with the opposite polarity to pulse 1. Its delay time relative to the zero point t0 is t1, which is precisely controlled by the first delay line, with an adjustable range of 0ns to 10ns and an adjustment accuracy ≤10fs. T1 must be greater than the complete flip time of the magnetic moment of the sample under test. This ensures that pulse 2 is applied to the sample only after the magnetic moment has completely flipped, driving the magnetic moment back to its initial magnetization state through the reverse spin orbital torque. The system reset is completed within a single laser repetition cycle 4, ensuring that the initial magnetization state is completely consistent in each laser repetition cycle, thus establishing a stable and repeatable measurement cycle. The pulse width and amplitude of pulse 2 are independently adjustable from pulse 1 and can be flexibly optimized according to the sample reset requirements.

[0101] Pulse 3 corresponds to the continuous scanning range t2 of the second delay line, where t2 is adjustable from 0 to t1, completely covering the entire dynamic process of the magnetic moment from flipping, precession, relaxation to reset, with no time measurement blind zone. Through continuous scanning of the second delay line, the probe light can illuminate the sample at any time within the t2 range, acquiring the magnetic moment state information at the corresponding moment. Finally, the complete magnetization dynamics curve of the magnetic moment changing with time is obtained through point-by-point scanning. The scanning step size of the probe light can be flexibly set within the range of 10 fs to 1 ps. The smaller the step size, the higher the time resolution, enabling precise capture of the ultrafast magnetic moment response at the picosecond to femtosecond scale.

[0102] Those skilled in the art will understand that the features described in the various embodiments of this disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments of this disclosure can be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0103] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. An on-chip spin-orbit torque magneto-optical measurement chip, characterized in that, The invention includes a low-temperature grown semi-insulating gallium arsenide substrate, on which a coplanar waveguide transmission line, a first photoconductive switch, a second photoconductive switch, two floating electrodes, and a terminating resistor matched with the characteristic impedance of the coplanar waveguide transmission line are fabricated. The coplanar waveguide transmission line includes a center signal line and a common ground electrode. The first photoconductive switch and the second photoconductive switch are electrically connected to the two ends of the center signal line, and the two floating electrodes are electrically connected to the first photoconductive switch and the second photoconductive switch respectively. Each of the floating electrodes is provided with a physical isolation gap between itself and the common ground electrode. The physical isolation gap completely cuts off the metal DC path between the floating electrode and the common ground electrode, so that the DC bias of the first photoconductive switch and the second photoconductive switch are independent of each other. The center signal line has a sample carrying area at its midpoint for integrating the magnetic sample to be tested. The sample carrying area is precisely matched with the focusing position of the probe light. The terminating resistors are set at both ends of the coplanar waveguide transmission line.

2. The chip according to claim 1, characterized in that, The substrate of the chip is a low-temperature grown semi-insulating gallium arsenide substrate; The chip includes a coplanar waveguide transmission line, which includes a common ground electrode and a center signal line. One end of the center signal line is electrically connected to the first photoconductive switch, and the other end is electrically connected to the second photoconductive switch; The center signal line is provided with a sample carrying area at a predetermined position for placing the sample to be tested.

3. A method for fabricating an on-chip spin-orbit torque magneto-optical measurement chip, characterized in that, The method includes the following steps: Step P1: Select a low-temperature grown semi-insulating gallium arsenide substrate and pre-treat the gallium arsenide substrate; Step P2: Define the photosensitive area windows of the first and second photoconductive switches using photolithography, prepare an aluminum oxide insulating layer in the non-photosensitive area of ​​the substrate, and leave only the photosensitive area as the exposed gallium arsenide substrate; Step P3: Simultaneously define the patterns of the coplanar waveguide transmission line, the first photoconductive switch, the second photoconductive switch, the floating electrode, and the physical isolation gap through an overlay process; deposit a metal electrode layer and complete the stripping process to form a monolithically integrated pulse generation and transmission structure; wherein, the first photoconductive switch and the second photoconductive switch are respectively placed at both ends of the coplanar waveguide transmission line, and the physical isolation gap between the floating electrode and the common ground electrode of the coplanar waveguide transmission line completely cuts off the metal DC path between them; Step P4: Prepare nickel-chromium alloy thin-film resistors at both ends of the coplanar waveguide transmission line that match the characteristic impedance of the transmission line; Step P5: A patterned sample carrier region is prepared at the midpoint of the center signal line of the coplanar waveguide transmission line, and a thin film of the magnetic heterojunction to be tested is deposited to finally obtain the on-chip spin-orbit torque magneto-optical measurement chip.

4. A magneto-optical measurement device for spin-orbit torque dynamics, characterized in that, Includes a laser output module, a magneto-optical detection module, and an electrical pulse excitation module; The electropulse excitation module includes an on-chip spin-orbit torque magneto-optical measurement chip and a DC bias power supply. The on-chip spin-orbit torque magneto-optical measurement chip includes a first photoconductive switch and a second photoconductive switch, as well as corresponding floating electrodes. Each floating electrode is provided with a physical isolation gap between itself and the common ground electrode of the on-chip spin-orbit torque magneto-optical measurement chip to cut off the DC and low-frequency paths between the floating electrode and the common ground electrode. The DC bias power supply is electrically connected to the two floating electrodes in a one-to-one correspondence. The laser output module is used to output three co-originating periodic femtosecond laser pulses. The first laser is used to trigger the first photoconductive switch to turn on, so that the DC bias power supply generates an excitation pulse that drives the magnetic moment of the sample under test to flip. The second laser is used to trigger the second photoconductive switch to turn on, so that the DC bias power supply generates a reset pulse that drives the magnetic moment of the sample under test to reset. The third laser is used to irradiate the sample under test when the magnetic moment flips, so as to obtain the reflected light when the magnetic moment of the sample under test flips. The magneto-optical detection module acquires the dynamic state of sample magnetic moment reversal and reset through reflected light.

5. The apparatus according to claim 4, characterized in that, The laser output module includes a femtosecond laser source, a laser beam splitter unit, a first delay line, and a second delay line; The femtosecond laser source is used to output a single-channel periodic femtosecond laser pulse, which is then divided into three co-source femtosecond laser pulses by the laser beam splitting unit. The first laser path is a delay-free laser; the second laser path is subject to fixed time delay control via the first delay line, the fixed time delay being greater than the time required for the magnetic moment of the sample under test to completely reverse; and the third laser path is subject to periodic time delay control via the second delay line.

6. The apparatus according to claim 5, characterized in that, The laser output module also includes a chopper, which is disposed on the main optical path between the femtosecond laser source and the laser beam splitting unit, or disposed in the optical path of the first laser pulse. The chopper is used to synchronously and periodically modulate the laser pulses in the corresponding optical path, providing a synchronous reference signal for lock-in amplification.

7. The apparatus according to claim 4, characterized in that, The two output terminals of the DC bias power supply are used to output DC bias voltages with opposite polarities, so that the first photoconductive switch and the second photoconductive switch generate excitation pulses and reset pulses with matched polarities, respectively, so that the sample under test completes magnetic moment reset within a single laser repetition cycle.

8. The apparatus according to claim 4, characterized in that, The magneto-optical detection module includes a Wollaston prism, a balanced photodetector, and a lock-in amplifier arranged in sequence. The Wollaston prism is used to separate the orthogonally polarized components in the reflected light; The balanced photodetector is used to convert the light intensity difference of the orthogonal polarization components into an electrical signal. The lock-in amplifier is used to extract the magneto-optical Kerr signal that is synchronized with the chopper modulation signal.

9. The apparatus according to claim 5, characterized in that, The device also includes a control and data acquisition module, which is electrically connected to the first delay line, the second delay line, and the magneto-optical detection module, respectively, for timing synchronization control and data acquisition and analysis.

10. A method for measuring the dynamics of spin-orbit torque using magneto-optical methods, characterized in that, The method includes the following steps: Step S1: Apply independent adjustable DC bias voltages with opposite polarities to the independent floating electrodes of the first photoconductive switch and the second photoconductive switch integrated at both ends of the on-chip coplanar waveguide transmission line, and ensure that the DC biases of the first photoconductive switch and the second photoconductive switch are independent of each other through physical isolation gaps. Step S2: A femtosecond laser source outputs laser pulses with a fixed repetition frequency. The laser intensity is periodically modulated by a chopper to provide a reference signal for lock-in amplification. A single laser pulse is split into three beams by a laser beam splitter. The first laser beam is used to trigger the electrical pulse excitation module to generate an excitation pulse that drives the magnetic moment reversal of the magnetic sample under test. The second laser beam is generated as a reset pulse after being fixedly delayed by a first delay line. The fixed delay is greater than the time required for the magnetic moment of the magnetic sample under test to completely reverse, ensuring that the magnetic moment reversal and complete reset are completed within a single laser repetition cycle, thus constructing a stable and repeatable periodic measurement cycle. The third laser beam is used as a probe beam and illuminates the magnetic sample under test after passing through a second delay line. By continuously scanning the second delay line with a time delay, reflected light carrying the dynamic information of the magnetic moment of the magnetic sample under test during the magnetic moment reversal process is obtained. Step S3: The reflected light is incident on the magneto-optical detection module. By using balanced photoelectric detection and lock-in amplification technology, a high signal-to-noise ratio magneto-optical Kerr signal synchronized with chopper modulation is extracted to obtain the time-series evolution curve of the magnetic moment reversal dynamics of the magnetic sample under test.

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