High figure of merit Ce-doped iron-gaetstone magneto-optical thin film and preparation method thereof

Abstract

The application belongs to the field of magneto-optical materials, and particularly relates to a high-optical-value Ce-doped iron garnet magneto-optical film and a preparation method thereof. The application utilizes high laser power to excite a plasma plume with higher kinetic energy and ionization rate; provides additional energy for Ce ions to overcome the barrier to enter the dodecahedron site of the garnet lattice, thereby significantly improving the solid solubility of Ce 3+ valence state, to inhibit the precipitation of Fe elements and non-magnetic CeO2 and improve the proportion of Ce 3+ ions, thereby preparing a high-magneto-optical-optical-value Ce:RIG film on a silicon substrate. Compared with conventional low laser power deposition, the application solves the problems of precipitates and element valence state of the silicon-based polycrystalline magneto-optical film, and provides a new method for preparing a high-optical-value silicon-based Ce:YIG film.

Description

Technical Field

[0001] This invention belongs to the field of magneto-optical materials, specifically relating to a high figure of merit Ce-doped iron garnet magneto-optical thin film and its preparation method. Background Technology

[0002] With the rapid development of optical communication and photonic integration technologies, especially the rise of silicon-based photonics, there is a demand for on-chip monolithic integration of magneto-optical materials with existing CMOS processes on silicon-based platforms. Therefore, the need for miniaturized, high-performance non-reciprocal devices is increasingly urgent. The performance of core components of laser systems, such as optical circulators and optical isolators, directly depends on key magneto-optical materials. Therefore, developing high figure-of-factane Ce-doped iron garnet magneto-optical thin films on silicon substrates is an inevitable technological path to promote the development of next-generation integrated magneto-optical devices (such as optical isolators and circulators) and meet the needs of the radar, sensing, and advanced photonic computing circuit industries.

[0003] Direct bonding and assisted bonding enable silicon-based heterogeneous integration of epitaxial magneto-optical thin films. Direct bonding requires plasma activation of the magneto-optical thin film surface and the silicon substrate surface, followed by contact between the two surfaces and bonding them firmly in a vacuum environment using high temperature and pressure. However, the surface plasma activation process damages the magneto-optical thin film surface, leading to increased surface roughness, increased material transport loss, and weakened magneto-optical effect. Furthermore, current bonding technologies rely on expensive wafer bonding equipment, and the garnet substrate material is difficult to remove, resulting in limited device structure, large size, and high cost.

[0004] For direct deposition, although methods such as magnetron sputtering can achieve wafer-level large-area silicon-based integration of magneto-optical thin films, the magneto-optical material thin films exist in polycrystalline form on the silicon substrate. Polycrystalline materials have numerous defects within their crystal lattices, especially Ce-doped silicon-based iron garnet (Ce:RIG) polycrystalline thin films. Due to the low solid solubility of Ce, a large amount of CeO2 precipitates are present inside the film after room temperature deposition and annealing, making it difficult to prepare Ce:RIG thin films with high figure of merit.

[0005] High-temperature deposition (400℃ to 600℃) offers the advantage of providing sufficient thermal energy to the deposited atoms, promoting their migration and rearrangement on the substrate surface, thereby significantly improving lattice quality and eliminating the thermal stress and microcrack problems associated with prolonged annealing of amorphous films. However, for Ce:YIG films, during high-temperature deposition or post-processing, uneven precipitation of Fe or the formation of non-garnet impurities (such as YFeO3) can easily occur. These precipitates and impurities disrupt lattice integrity, introducing additional light scattering and absorption centers, leading to a significant decrease in the magneto-optical figure of merit (the ratio of Faraday rotation angle to optical loss). Furthermore, Ce in the film... 3+ Low content, most Ce ions are Ce 4+It exists in the form of CeO2 in the film and precipitates as non-magnetic CeO2. In Ce:RIG films, Ce... 3+ It is the main source of Faraday rotation, while Ce 4+ The contribution to Faraday rotation is extremely small, therefore the precipitation of CeO2 leads to a decrease in the Faraday rotation of the thin film. Meanwhile, Ce... 4+ The resulting valence imbalance induces Fe 2+ Ion formation further increases the loss of magneto-optical material thin films.

[0006] Therefore, it is necessary to develop a method that can effectively suppress Fe precipitation and stabilize Ce. 3+ The method for preparing high-quality Ce:RIG thin films on silicon substrates by determining the valence state is crucial for advancing the on-chip integration of magneto-optical devices. Summary of the Invention

[0007] To address the aforementioned problems or shortcomings, and to resolve the issues of easy oxidation and precipitation of CeO2 second phase in existing Ce:RIG magneto-optical thin film materials, 3+ To address the issues of low Ce content and uneven Fe precipitation, this invention provides a high figure of merit Ce-doped iron garnet magneto-optical thin film and its preparation method. By precisely controlling the pulsed laser deposition (PLD) process parameters, especially the laser power, high laser power (high energy density) is used to excite and generate a plasma plume with higher kinetic energy and ionization rate. This provides Ce ions with the additional energy to overcome the potential barrier when entering the dodecahedral lattice sites of the garnet crystal, thereby significantly improving the solid solubility of Ce and stabilizing Ce. 3+ Valence state, to suppress the precipitation of Fe and nonmagnetic CeO2, and to increase Ce 3+ The ion ratio is adjusted to prepare Ce:RIG thin films with high magneto-optical figure of merit on silicon substrates.

[0008] A method for preparing a high figure of merit Ce-doped iron garnet magneto-optical thin film, the specific steps of which are as follows:

[0009] Step 1, Seed layer preparation: A 50-60 nm thick amorphous YIG thin film is deposited on a clean silicon substrate using magnetron sputtering; then rapid thermal annealing is performed to crystallize the amorphous YIG thin film, forming a YIG seed layer with a garnet structure.

[0010] Step 2, Ce:RIG thin film growth: Using pulsed laser deposition, Ce:RIG ceramic is used as the target material to directly grow a 100-110nm Ce:RIG thin film at a high temperature of 700℃-850℃ on the YIG seed layer using high laser power.

[0011] In summary, this invention employs thin-film fabrication processes such as magnetron sputtering or pulsed laser deposition to first deposit a 50-60 nm thick YIG film as a seed layer on a silicon substrate, followed by the deposition of a 100-110 nm thick Ce:RIG film on the YIG. This invention controls the laser power to directly deposit the magneto-optical thin film material at a high temperature of 700℃-850℃, fully combining the dual advantages of high-temperature-promoted crystallization and high-laser-power-enhanced particle kinetic energy. While ensuring the lattice quality of the thin film, it overcomes the thermodynamic tendency of element precipitation, improving the phase purity of the Ce:RIG film and the Ce content in the film. 3+ The content is high, and compared with low laser power deposition, it solves the problems of precipitates and element valence states in silicon-based polycrystalline magneto-optical thin films, which is of great significance for the preparation of high-quality Ce:RIG thin films. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the silicon-based polycrystalline Ce:YIG magneto-optical thin film structure in an embodiment.

[0013] Figure 2 Example: Comparison of EBSD images of silicon-based polycrystalline Ce:YIG magneto-optical thin films and low-laser-power Ce:YIG thin films.

[0014] Figure 3 Example: Comparison of transmission electron microscope images of silicon-based polycrystalline Ce:YIG magneto-optical thin films and low-laser-power Ce:YIG thin films.

[0015] Figure 4 Example: Comparison of atomic force microscopy images of silicon-based polycrystalline Ce:YIG magneto-optical thin films and low-laser-power Ce:YIG thin films.

[0016] Figure 5 Example: X-ray diffraction pattern of silicon-based polycrystalline Ce:YIG magneto-optical thin film.

[0017] Figure 6 Example: Comparison of Faraday rotation at 1550 nm wavelength between silicon-based polycrystalline Ce:YIG magneto-optical thin film and low-laser-power Ce:YIG thin film.

[0018] Figure 7 Example: Comparison of the figures of merit between silicon-based polycrystalline Ce:YIG magneto-optical thin films and low-laser-power Ce:YIG thin film devices. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] A method for preparing a high figure of merit Ce-doped iron garnet magneto-optical thin film, the specific steps of which are as follows:

[0021] Step 1: In this embodiment, magnetron sputtering technology is used to deposit a 55nm amorphous YIG thin film on a silicon substrate as a seed layer, and YIG is crystallized by rapid thermal annealing at a high temperature of 850 °C in an oxygen atmosphere of 2 Torr.

[0022] Step 2: Transfer the substrate with the seed layer from Step 1 into a pulsed laser deposition apparatus. The substrate, with a nominal composition of Ce... 1.4 Y 1.6 Fe5O 12 Using a ceramic target as the source, the background vacuum of the chamber is evacuated to 5 × 10⁻⁶. -7 mbar, pure oxygen is introduced until the pressure reaches 4 × 10 mbar. -3 mbar. The substrate was heated to 750°C and stabilized.

[0023] A KrF excimer laser (wavelength 248 nm) was used to deposit a Ce:YIG film with a pulse energy density of 3.0 J / cm² and a repetition frequency of 10 Hz. By controlling the deposition time, a Ce:YIG film with a thickness of 110 nm was obtained. After deposition, the sample was slowly cooled to room temperature under the same oxygen pressure.

[0024] This embodiment compares EBSD images of silicon-based Ce:YIG thin films with those of Ce:YIG thin films with low laser power, for example... Figure 2 As shown, the Ce:YIG phase purity in this embodiment is as high as 98.29%, which is higher than that of the single-annealed sample (95.88%). The cross-sectional transmission electron microscope image of the silicon-based Ce:YIG thin film tested in this embodiment is shown below. Figure 3 As shown, compared to low-laser-power films, high-laser-power films exhibit significantly reduced intracrystalline precipitation, and the Ce, Fe, and Y elements are uniformly distributed within the film without obvious enrichment. The atomic force microscopy image of the silicon-based Ce:YIG film obtained in the example is shown below. Figure 4 As shown, Ce, Fe, and Y elements are uniformly distributed within the film, with enrichment primarily located at the grain boundaries. Furthermore, as... Figure 6 As shown, the Faraday rotation of the thin film in the example reaches -4500 deg / cm at 1550 nm, which is higher than that of the low-laser-power sample. The deposition test results of the silicon-based Ce:YIG thin film and the low-laser-power Ce:YIG thin film on SiN devices are as follows. Figure 7 As shown, the device figure of merit improved from 18.3 deg / dB to 63.9 deg / dB.

[0025] As can be seen from the above embodiments, the present invention, by preparing magneto-optical thin films with high laser power, can effectively improve the phase purity of Ce:YIG thin films and control intracrystalline precipitation, resulting in an improvement in the Faraday rotation of the thin films. The high-laser-power Ce:YIG thin film preparation process provided by the present invention achieves the preparation of almost pure-phase Ce:YIG thin films, offering a new method for preparing high figure-of-valuation silicon-based Ce:YIG thin films.

Claims

1. A method for preparing a high figure of merit Ce-doped iron garnet magneto-optical thin film, characterized in that, The specific steps are as follows: Step 1: A 50-60 nm thick amorphous YIG film is deposited on a clean silicon substrate using magnetron sputtering; then rapid thermal annealing is performed to crystallize the amorphous YIG film and form a YIG seed layer with a garnet structure. Step 2, Ce:RIG thin film growth: Using pulsed laser deposition, Ce:RIG ceramic is used as the target material to directly grow a 100-110nm Ce:RIG thin film at a high temperature of 700℃-850℃ on the YIG seed layer prepared in step 1 using high laser power.

2. The method for preparing a high figure-of-facts Ce-doped iron garnet magneto-optical thin film as described in claim 1, characterized in that: In step 1, the thickness of the amorphous YIG thin film is 55 nm.

3. The method for preparing a high figure-of-facts Ce-doped iron garnet magneto-optical thin film as described in claim 1, characterized in that: In step 2, Ce:RIG thin films are directly grown at a high temperature of 750℃.

4. The method for preparing a high figure-of-facts Ce-doped iron garnet magneto-optical thin film as described in claim 1, characterized in that: In step 2, the Ce:RIG thin film is grown to a thickness of 110 nm.

5. A high figure of merit Ce-doped iron garnet magneto-optical thin film, characterized in that: The amorphous YIG film with a thickness of 55 nm was prepared using the process described in claim 1. A Ce:RIG film with a thickness of 110 nm was directly grown at a high temperature of 750 °C, and the magneto-optical figure of merit was 63.9 deg / dB.

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