Modulator and preparation method

Abstract

The present invention relates to the field of optical device technology, and more specifically to a modulator and a method for fabricating the modulator. The modulator comprises a substrate layer and n SiO2 layers and n GST layers interlaced on the substrate layer, wherein the first layer from the bottom to the top of the substrate layer is a GST layer. The modulator also comprises a number of electrodes disposed corresponding to the n GST layers, where a = n = 3. The interlaced n SiO2 layers and n GST layers are, from top to bottom, a third SiO2 layer, a third GST layer, a second SiO2 layer, a second GST layer, a first SiO2 layer, and a first GST layer. The present invention gradually reduces the transmittance of the modulator in the infrared band by crystallizing the GST layers layer by layer through phase change, resulting in a step-wise change in modulation depth. The modulation depths corresponding to both fully crystalline and fully amorphous GST structures are greater than 80%.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and in particular to a modulator and a preparation method thereof. Background Art

[0002] Germanium antimony telluride (Ge2Sb2Te5), or GST for short, is a phase-change material whose optical properties change with temperature. It can switch between amorphous and crystalline states, is nonvolatile, and requires no additional energy to maintain the phase transition. GST can be combined with metasurfaces to enable tunable optical devices.

[0003] First, the preparation of existing GST-based metasurfaces mostly relies on complex lithography technology to add microstructures to the structure, but this will increase manufacturing costs and limit large-scale applications.

[0004] Currently, most research focuses on the mixed state of GST, which consists of amorphous and crystalline phases. These phases are adjusted by varying annealing temperatures to control the ratio of the crystalline and amorphous phases, and then manipulate light. While these control conditions are rigorous, the actual results are often unstable. For example, a paper titled "Optical Modulator Based on Multilayer Ge2Sb2Te5," published in the Journal of Changchun University of Science and Technology (Natural Science Edition), demonstrates the use of radio frequency sputtering to produce high-performance amorphous a-GST films. Annealing at 160°C and 220°C yields the metastable c-GST and final stable h-GST phases. By precisely controlling the phase transition of GST, the researchers achieved a transition from amorphous a-GST to cubic c-GST and then to hexagonal h-GST. The optical properties of these different phases are then exploited to manipulate light. However, in practical applications, these technical solutions consider that c-GST lies between a-GST and h-GST, and its changes fluctuate with crystallization temperature. Without sufficient temperature control precision, the temperature control characteristics of the c-GST metasurface are unstable.

[0005] Based on this, those skilled in the art need to provide a new modulator and a preparation method thereof to overcome the technical problem of low precision in controlling the crystalline state of the GST layer by using different annealing temperatures. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defects existing in the above-mentioned prior art, thereby providing a modulator and a preparation method.

[0007] A modulator comprises a substrate layer and n SiO2 layers and n GST layers arranged crosswise on the substrate layer, wherein the first layer from the bottom to the top of the substrate layer is a GST layer; the modulator further comprises a number of electrodes arranged correspondingly on the n GST layers;

[0008] Specifically: n=a=3, the cross-arranged n SiO2 layers and n GST layers are, from top to bottom, the third SiO2 layer, the third GST layer, the second SiO2 layer, the second GST layer, the first SiO2 layer and the first GST layer, and the heights from bottom to top are 50nm, 150nm, 50nm, 50nm, 150nm, and 50nm respectively.

[0009] Preferably, the n-layer SiO2 layer and the n-layer GST layer are thin films obtained by magnetron sputtering process.

[0010] Preferably, a electrodes are obtained by controlling an interdigitated electrode mask.

[0011] Preferably, each of the a electrodes is made of magnetron sputtered gold.

[0012] Preferably, the substrate layer is made of a dielectric material with low absorption loss in the infrared band.

[0013] A method for preparing a modulator, comprising the following steps:

[0014] S1. First, soak and clean the substrate layer with acetone and anhydrous ethanol, then soak and rinse the substrate layer with deionized water, and finally blow dry with a nitrogen gun;

[0015] S2. A first GST layer having a thickness of 50 nm is sputtered on the top surface of the substrate layer using a magnetron sputtering process;

[0016] S3. The interdigitated electrode mask is placed on the first GST layer, and the overall device now prepared is placed in a vacuum chamber to magnetron sputter gold to form a first electrode;

[0017] S4 using a magnetron sputtering process sequentially sputtering a first SiO2 layer having a thickness of 150nm and a second GST layer of 50nm on the first electrode;

[0018] S5. The interdigitated electrode mask is placed on the second GST layer, and the overall device now prepared is placed in a vacuum chamber to magnetron sputter gold to form a second electrode;

[0019] S6. A second SiO2 layer having a thickness of 50 nm and a third GST layer of 150 nm were sequentially sputtered on the second electrode using a magnetron sputtering process;

[0020] S7. The interdigitated electrode mask is placed on the third GST layer, and the overall device prepared at this time is placed in a vacuum chamber to magnetron sputter gold to form a third electrode;

[0021] S8. A third SiO2 layer having a thickness of 50 nm is formed on the third electrode by sputtering using a magnetron sputtering process;

[0022] It also includes the use of a spectrophotometer to test the transmittance of each structure, specifically:

[0023] Since high transmittance occurs when electromagnetic waves are incident on the multilayer amorphous GST structure of the modulator prepared in step S8, the following steps are performed in sequence:

[0024] S9. The first electrode controls the first GST layer to directly change into a crystalline state, the dielectric constant of the GST increases, and the GST becomes metallic, thereby enhancing the reflection and absorption of light and achieving a preliminary reduction in light transmittance;

[0025] S10. The second GST layer is then directly phase-changed into a crystalline state by a second electrode. The dielectric constant of the GST increases, and the layer becomes metallic, thereby enhancing the reflection and absorption of light. The transmittance of the overall structure is then measured by a spectrophotometer, and the measurement result of the secondary decrease in light transmittance is obtained.

[0026] S11. The third electrode controls the third GST layer to directly change into a crystalline state. The dielectric constant of GST increases, and it becomes metallic. The reflection and absorption of light are enhanced. The transmittance of the overall structure at this time is measured by a spectrophotometer, and the measurement result of the light transmittance being reduced three times is obtained. At this time, the three GST layers are all in a metallic state, thereby realizing the modulation of the infrared transmittance.

[0027] The technical solution of the present invention has the following advantages:

[0028] The present invention provides a modulator based on multi-layer GST, which cross-combines GST layers with SiO2 layers, and then through the reasonable design of the thickness of each film layer, the phase transformation characteristics of GST and the metal composite structure are utilized to achieve modulation of the mid-infrared band, avoiding the unstable effect of controlling the degree of crystallization of the GST layer, and achieving modulation of electromagnetic waves. The structural design of the present invention is simple, and a simple non-photolithography multi-layer film structure is adopted, which facilitates the simplification and miniaturization of the overall structure of the device. Furthermore, the GST and SiO2 used in the present invention have mature processing technology and controllable costs. Compared with previous infrared modulators, the present invention uses electrical excitation to phase-change crystallize the GST layer layer by layer, so that the transmittance of the modulator in the infrared band is gradually reduced, and the modulation depth also changes in a step-by-step manner, showing a dynamically adjustable control range of the modulator. The modulation depth corresponding to the fully crystalline and fully amorphous GST structures is higher than 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 Schematic diagram of the structure of a modulator of the present invention;

[0031] Figure 2 A top view of an electrode structure in a modulator of the present invention;

[0032] Figure 3 A top view of a two-layer electrode structure in a modulator of the present invention;

[0033] Figure 4 A top view of a three-layer electrode structure in a modulator of the present invention;

[0034] Figure 5 The infrared transmittance of the modulator of the present invention changes with the crystallization of each GST layer layer by layer;

[0035] Figure 6 This is a curve showing the change in modulation depth of the modulator of the present invention as the GST layer crystallizes layer by layer. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0037] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0039] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] Example 1

[0041] This embodiment discloses a modulator, comprising a substrate layer and n silicon dioxide layers and n GST layers arranged crosswise on the substrate layer, wherein the first layer from the bottom to the top of the substrate layer is a GST layer;

[0042] The modulator also includes a number of electrodes arranged correspondingly on n GST layers;

[0043] like Figure 1 Specifically: n=a=3, based on the consideration of multilayer film design, the thickness of each layer is optimized: the cross-arranged n-layer SiO2 layer and n-layer GST layer are respectively: the third SiO2 layer, the third GST layer, the second SiO2 layer, the second GST layer, the first SiO2 layer and the first GST layer from top to bottom, and the heights from bottom to top are h6=50nm, h5=150nm, h4=50nm, h3=50nm, h2=150nm, h1=50nm. The substrate layer height h sub Set according to actual needs.

[0044] Specifically:

[0045] The a electrodes are controlled by the interdigitated electrode mask, and the interdigitation index is 2; and since the a electrodes are made of magnetron sputtered gold with a thickness of 10nm, Figure 1 The electrodes are not drawn yet.

[0046] In order to make the heating efficiency of the interdigital electrodes more uniform and reduce the impact of metal thickness and occupancy on transmittance, the electrode design spacing is increased and the number is reduced. The electrodes are made of metal Au as an example.

[0047] In this embodiment, both the n-layer SiO 2 layer and the n-layer GST layer are thin films obtained by magnetron sputtering process.

[0048] In this embodiment, the magnetron sputtering metal materials include but are not limited to gold, silver, platinum, and nickel.

[0049] The substrate layer is made of dielectric materials with low absorption loss in the infrared band, including but not limited to glass, aluminum oxide, zinc sulfide, etc.

[0050] Each GST layer uses GST, and the ratio of the three elements in GST is 22.2wt%:22.2wt%:55.6wt%.

[0051] Example 2

[0052] This embodiment discloses a method for preparing a modulator, which is applied to a modulator in Example 1. This embodiment mainly utilizes the characteristic that the electromagnetic parameters of the phase change material are adjustable, and selects a non-volatile GST material that can be used to combine with the metasurface to obtain an adjustable metasurface. In this embodiment, the temperature of the GST material phase change is approximately 160°C. The GST material is initially amorphous, and after high-temperature annealing >160°C, the GST material can be transformed from an amorphous state to a crystalline state. On the contrary, if the amorphous GST material is to be obtained again, a rapid high-temperature annealing process of 640°C is required, which means that this phase change process is reversible.

[0053] And because the SiO2 layer, as a common passivation layer, can effectively inhibit the diffusion of components of the GST material and external contamination, and improve the optical stability and durability of the film, both GST and SiO2 film materials are selected.

[0054] The specific steps include:

[0055] S1. In this embodiment, the substrate layer is made of glass. The glass substrate layer is sequentially soaked and cleaned with acetone and anhydrous ethanol, and then the soaked and cleaned glass substrate layer is soaked and rinsed with deionized water. After soaking and rinsing, the glass substrate layer is blown dry.

[0056] S2. A first GST layer having a thickness of 50 nm is sputtered on the top surface of the glass substrate layer using a magnetron sputtering process;

[0057] S3. The interdigitated electrode mask is placed on the first GST layer, and the overall device prepared at this time is placed in a vacuum chamber to magnetron sputter gold to form a first electrode; specifically, in this embodiment, all interdigitated electrode masks are patterned interdigitated electrode masks; as Figure 2 A top view of a layer of electrode structure;

[0058] S4 using a magnetron sputtering process sequentially sputtering a first SiO2 layer having a thickness of 150nm and a second GST layer of 50nm on the first electrode;

[0059] S5. The interdigitated electrode mask is placed on the second GST layer, and the overall device now prepared is placed in a vacuum chamber to magnetron sputter gold to form a second electrode; Figure 3 It is a top view of the two-layer electrode structure;

[0060] S6. A second SiO2 layer having a thickness of 50 nm and a third GST layer of 150 nm were sequentially sputtered on the second electrode using a magnetron sputtering process;

[0061] S7. The interdigitated electrode mask is placed on the third GST layer, and the overall device prepared at this time is placed in a vacuum chamber to magnetron sputter gold to form a third electrode;

[0062] S8. A third SiO2 layer having a thickness of 50 nm is formed on the third electrode by a magnetron sputtering process; Figure 3 It is a top view of the three-layer electrode structure;

[0063] It also includes the use of a spectrophotometer to test the transmittance of each structure in real time during the layer-by-layer phase change, specifically:

[0064] Since high transmittance occurs when electromagnetic waves are incident on the multilayer amorphous GST structure of the modulator prepared in step S8, the following steps are performed in sequence:

[0065] S9. The first electrode is used to control the first GST layer to directly phase-transform into a crystalline state. This increases the dielectric constant of the GST layer, transforming it into a metallic state. This enhances its reflection and absorption of light, thereby achieving a preliminary reduction in light transmittance. The specific operation is to apply a preset current to the first GST layer through the first electrode. Within a preset time, the resistance of the first GST layer is used to locally increase the temperature, raising it to the crystallization temperature and maintaining it for a sufficient period of time. The preset current range is 25–35 mA, with a pulse width of 300–500 ns and a pulse frequency of 10–50.

[0066] S10. Similarly, the second electrode controls the second GST layer to directly change into a crystalline state. The dielectric constant of the GST increases, and the GST becomes metallic, which enhances its reflection and absorption of light. The transmittance of the overall structure is measured using a spectrophotometer, and the measurement result of a secondary decrease in light transmittance is obtained.

[0067] S11. Similarly, the third electrode controls the third GST layer to directly change into a crystalline state. The dielectric constant of GST increases, and it becomes metallic, thereby enhancing the reflection and absorption of light. The transmittance of the overall structure is measured by a spectrophotometer at this time, and the measurement result of the light transmittance being reduced three times is obtained. At this time, all three GST layers are in a metallic state, thereby achieving modulation of the infrared transmittance.

[0068] like Figure 5This is the infrared transmittance curve of the modulator prepared in this embodiment as each GST layer is crystallized layer by layer. When all three GST layers are amorphous, there is no 0-layer crystallization, which is recorded as the 0-layer situation. From top to bottom, when there is a total of 1 GST layer in the crystallization state, it is recorded as the 1-layer situation; when there are a total of 2 GST layers in the crystallization state, it is recorded as the 2-layer situation; when there are a total of 3 GST layers in the crystallization state, it is recorded as the 3-layer situation. Figure 5 It can be seen that when all three GST layers are in amorphous state, there are two resonance peaks. The first resonance peak is =2128nm, first transmittance =92.01%, the second resonance peak =2392nm, second =91.1%. The transmittance gradually decreases as the number of GST crystal layers increases.

[0069] In addition, based on the proposed transmission spectrum, the modulation depth is also used in this embodiment to evaluate the control performance of the prepared modulator. The specific expression is: ;

[0070] Where: is the transmittance when all GST layers in the modulator structure are a-GST, is the transmittance when h-GST exists in the structure.

[0071] like Figure 6 This graph shows the modulation depth variation of the modulator fabricated in this example as the GST layers crystallize layer by layer. Case 1-0 compares the transmittance of a single h-GST layer with zero h-GST layers; case 2-0 compares the transmittance of two h-GST layers with zero h-GST layers; and case 3-0 compares the transmittance of three h-GST layers with zero h-GST layers.

[0072] pass Figure 6 It can be seen that when one GST layer is crystallized, the modulation depth varies from 17.80% to 33.22%, when two GST layers are crystallized, the modulation depth varies from 56.25% to 82.52%, and when three GST layers are crystallized, the modulation depth varies from 88.32% to 96.89%. The metasurface structure with multiple GST layers has achieved the effect of step-by-step light modulation.

[0073] Obviously, the above embodiments are provided for illustrative purposes only and are not intended to limit the embodiments. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to enumerate all embodiments here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A modulator, characterized in that: The modulator comprises a substrate layer and n SiO2 layers and n GST layers arranged crosswise on the substrate layer, wherein the first layer from the bottom to the top of the substrate layer is a GST layer; the modulator also comprises a layer of electrodes arranged correspondingly on the n GST layers; Specifically: n=a=3, the cross-arranged n SiO2 layers and n GST layers are, from top to bottom, the third SiO2 layer, the third GST layer, the second SiO2 layer, the second GST layer, the first SiO2 layer and the first GST layer, and the heights from bottom to top are 50nm, 150nm, 50nm, 50nm, 150nm, and 50nm respectively.

2. A modulator according to claim 1, characterized in that The n-layer SiO2 layer and the n-layer GST layer are both thin films obtained by magnetron sputtering process.

3. A modulator according to claim 1, characterized in that: The a-layer electrodes are controlled by the interdigitated electrode mask.

4. A modulator according to claim 1, characterized in that: The a-layer electrodes are all made of magnetron sputtered gold.

5. A modulator according to claim 1, characterized in that: The substrate layer is made of a dielectric material with low absorption loss in the infrared band.

6. A method for preparing a modulator, characterized in that: The preparation of a modulator according to any one of claims 1 to 5 comprises the following steps: S1. First, soak and clean the substrate layer with acetone and anhydrous ethanol, then soak and rinse the substrate layer with deionized water, and finally blow dry with a nitrogen gun; S2. A first GST layer having a thickness of 50 nm is sputtered on the top surface of the substrate layer using a magnetron sputtering process; S3. The interdigitated electrode mask is placed on the first GST layer, and the overall device now prepared is placed in a vacuum chamber to magnetron sputter gold to form a first electrode; S4 using a magnetron sputtering process sequentially sputtering a first SiO2 layer having a thickness of 150nm and a second GST layer of 50nm on the first electrode; S5. The interdigitated electrode mask is placed on the second GST layer, and the overall device now prepared is placed in a vacuum chamber to magnetron sputter gold to form a second electrode; S6. A second SiO2 layer having a thickness of 50 nm and a third GST layer of 150 nm were sequentially sputtered on the second electrode using a magnetron sputtering process; S7. The interdigitated electrode mask is placed on the third GST layer, and the overall device prepared at this time is placed in a vacuum chamber to magnetron sputter gold to form a third electrode; S8. A third SiO2 layer having a thickness of 50 nm is formed on the third electrode by sputtering using a magnetron sputtering process; It also includes the use of a spectrophotometer to test the transmittance of each structure, specifically: Since high transmittance occurs when electromagnetic waves are incident on the multilayer amorphous GST structure of the modulator prepared in step S8, the following steps are performed in sequence: S9. The first electrode controls the first GST layer to directly change into a crystalline state, the dielectric constant of the GST increases, and the GST layer becomes metallic, thereby enhancing the reflection and absorption of light and achieving a preliminary reduction in light transmittance. S10. The second GST layer is then directly phase-changed into a crystalline state by a second electrode. The dielectric constant of the GST increases, and the layer becomes metallic, thereby enhancing the reflection and absorption of light. The transmittance of the overall structure is then measured by a spectrophotometer, and the measurement result of the secondary decrease in light transmittance is obtained. S11. The third electrode controls the third GST layer to directly change into a crystalline state. The dielectric constant of GST increases, and it becomes metallic. The reflection and absorption of light are enhanced. The transmittance of the overall structure at this time is measured by a spectrophotometer, and the measurement result of the light transmittance being reduced three times is obtained. At this time, the three GST layers are all in a metallic state, thereby realizing the modulation of the infrared transmittance.

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