Modulator and preparation method

Abstract

The invention relates to the technical field of optical devices, in particular to a modulator and a preparation method thereof.The modulator comprises a substrate layer, n SiO2 layers and n GST layers, the n SiO2 layers and the n GST layers are arranged on the substrate layer in a crossed mode, and the first layer, from top to bottom, of the substrate layer is the GST layer; the modulator further comprises a electrodes which are correspondingly arranged on the n GST layers; a = n = 3. The n SiO2 layers and the n GST layers which are arranged in a crossed mode are respectively 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 from top to bottom. According to the invention, the GST layer is subjected to phase change crystallization layer by layer, so that the transmissivity of the modulator in an infrared band is gradually reduced, the modulation depth is also changed in a stepped manner, and the modulation depth corresponding to a full-crystalline state and full-amorphous state GST structure is higher than 80%.

Description

Technical Field

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

[0002] Germanium antimony telluride, full name Ge2Sb2Te5, hereinafter referred to as GST, is a phase change material whose optical properties change with temperature, can be switched between amorphous state and crystalline state, has non-volatility, and can maintain the phase change state without additional energy. GST can be combined with a metasurface to realize the function of a tunable optical device.

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

[0004] And currently most research focuses on the mixed state of GST in amorphous state and crystalline state, using different annealing temperatures to adjust the ratio of its crystalline state and amorphous state, and then controlling light. Although the control conditions involved are very strict, the actual effect is unstable. For example, in the Journal of Changchun University of Science and Technology (Natural Science Edition), the article titled "Optical Modulator Based on Multilayer Ge2Sb2Te5" obtained a well-performing amorphous a-GST film by radio frequency sputtering method. After annealing treatments at 160°C and 220°C, its metastable c-GST and final stable h-GST were obtained, that is, by precisely controlling the phase change of GST, the transformation from amorphous a-GST to cubic c-GST and then to hexagonal h-GST was realized, and the optical properties of these different phases were used to control light. However, in the actual application of the above technical solution, considering that c-GST is between a-GST and h-GST, the change fluctuates with the crystallization temperature. When the temperature control accuracy is insufficient, the temperature control characteristics formed by the c-GST metasurface are unstable.

[0005] Based on this, those skilled in the art need to provide a brand-new modulator and its preparation method to overcome the technical problem of low accuracy in controlling the crystallization state of the GST layer 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, so as to provide a modulator and a preparation method thereof.

[0007] A modulator includes a substrate layer and n SiO2 layers and n GST layers arranged crosswise on the substrate layer, wherein the first layer from bottom to top on the substrate layer is a GST layer; the modulator also includes a electrodes arranged correspondingly on the n GST layers. Specifically: n = a = 3. The n layers of SiO2 layers and n layers of GST layers arranged crosswise from top to bottom are: 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 their heights from bottom to top are 50 nm, 150 nm, 50 nm, 50 nm, 150 nm, and 50 nm respectively.

[0008] Preferably, both the n layers of SiO2 layers and the n layers of GST layers are thin films obtained by a magnetron sputtering process.

[0009] Preferably, the a electrodes are obtained by controlling with an interdigital electrode mask.

[0010] Preferably, the a electrodes are all made of magnetron sputtered gold.

[0011] Preferably, the substrate layer uses a dielectric material with low absorption loss in the infrared band.

[0012] A modulator preparation method for realizing the preparation of the described modulator includes the following steps: S1. First, soak and clean the substrate layer with acetone and absolute ethanol, then soak and rinse the substrate layer with deionized water, and finally dry it with a nitrogen gun; S2. Use the magnetron sputtering process to sputter a first GST layer with a thickness of 50 nm on the top surface of the substrate layer; S3. Place the interdigital electrode mask on the first GST layer, and put the overall device prepared at this time into a vacuum chamber to make the first electrode made of magnetron sputtered gold; S4. Use the magnetron sputtering process to sequentially sputter a first SiO2 layer with a thickness of 150 nm and a second GST layer with a thickness of 50 nm on the first electrode; S5. Place the interdigital electrode mask on the second GST layer, and put the overall device prepared at this time into a vacuum chamber to make the second electrode made of magnetron sputtered gold; S6. Use the magnetron sputtering process to sequentially sputter a second SiO2 layer with a thickness of 50 nm and a third GST layer with a thickness of 150 nm on the second electrode; S7. Place the interdigital electrode mask on the third GST layer, and put the overall device prepared at this time into a vacuum chamber to make the third electrode made of magnetron sputtered gold; S8. Use the magnetron sputtering process to sputter a third SiO2 layer with a thickness of 50 nm on the third electrode; It also includes using a spectrophotometer to test the transmittance of each structure, specifically: Since when electromagnetic waves are incident on the multi-layer amorphous GST structure of the modulator prepared in step S8, a high-transmission phenomenon will occur; therefore, the following steps are sequentially executed: S9. Control the first GST layer to directly transform into a crystalline state through the first electrode. The dielectric constant of GST increases, becoming a metallic state, enhancing the reflection and absorption of light, and initially reducing the light transmittance. S10. Then control the second GST layer to directly transform into a crystalline state through the second electrode. The dielectric constant of GST increases, becoming a metallic state, enhancing the reflection and absorption of light. Measure the transmittance of the overall structure at this time using a spectrophotometer to obtain the measurement result of the secondary reduction of the light transmittance. S11. Control the third GST layer to directly transform into a crystalline state through the third electrode. The dielectric constant of GST increases, becoming a metallic state, enhancing the reflection and absorption of light. Measure the transmittance of the overall structure at this time using a spectrophotometer to obtain the measurement result of the tertiary reduction of the light transmittance. At this time, all three GST layers are in a metallic state, thereby achieving the modulation of the infrared transmittance.

[0013] The technical solution of the present invention has the following advantages: The present invention provides a modulator based on multi-layer GST. The GST layer and the SiO2 layer are cross-combined together, and then by reasonably designing the thickness of each thin film layer, using the phase transformation characteristics of GST and the metal composite structure, the modulation effect on the mid-infrared band is achieved, avoiding the unstable effect of needing to control the crystallization degree of the GST layer, and realizing the modulation of electromagnetic waves. The structure design of the present invention is simple, adopting a simple lithography-free multi-layer film structure, which is conducive to the simplification and miniaturization of the overall device structure. Further, the GST and SiO2 used in the present invention have mature processing technologies and controllable costs. Compared with the previous infrared modulators, the present invention gradually reduces the transmittance of the modulator in the infrared band by electrically exciting the phase change crystallization of the GST layer layer by layer, and the modulation depth also changes in a stepwise manner, presenting a dynamic adjustment of the modulation range of the modulator. The modulation depth corresponding to the fully crystalline and fully amorphous GST structures is higher than 80%. Description of the Drawings

[0014] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0015] Figure 1 It is a schematic structural diagram of a modulator of the present invention; Figure 2 It is a top view of an electrode structure in a modulator of the present invention; Figure 3 It is a top view of a two-layer electrode structure in a modulator of the present invention; Figure 4Top view of a three-layer electrode structure in a modulator of the present invention; Figure 5 Curve of the infrared transmittance of the modulator of the present invention varying with the crystallization of each GST layer layer by layer; Figure 6 Curve of the modulation depth of the modulator of the present invention varying with the crystallization of the GST layer layer by layer. Specific implementation manner

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0017] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0018] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0019] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] Embodiment 1 This embodiment discloses a modulator, including 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 up on the substrate layer is a GST layer; The modulator also includes a electrodes arranged correspondingly on the n GST layers; As Figure 1Specifically: n = a = 3. Based on the considerations of the design of the multilayer film system, the thickness of each layer was optimized. The n SiO2 layers and n GST layers arranged in a cross pattern 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 their heights from bottom to top are h6 = 50 nm, h5 = 150 nm, h4 = 50 nm, h3 = 50 nm, h2 = 150 nm, and h1 = 50 nm respectively. The height h of the substrate layer sub is set according to actual requirements.

[0021] Specifically: The a electrodes are obtained by controlling with an interdigital electrode mask template, and the number of fingers is 2. And since all the a electrodes are made of magnetron-sputtered gold with a thickness of 10 nm, therefore Figure 1 the electrodes are not drawn temporarily in

[0022] Moreover, in order to make the heating efficiency of the interdigital electrodes more uniform and reduce the influence of the thickness and occupancy rate of the metal on the transmittance, the design interval of the electrodes is increased and the number is decreased. The metal gold Au is used as an example for the electrodes.

[0023] In this embodiment, the n SiO2 layers and the n GST layers are both thin films obtained by magnetron sputtering process.

[0024] In this embodiment, the magnetron-sputtered metal materials include but are not limited to gold, silver, platinum, nickel, etc.

[0025] The substrate layer uses a dielectric material with low absorption loss in the infrared band, including but not limited to glass, alumina, zinc sulfide, etc.

[0026] Each GST layer uses GST, and the ratio of the three elements in GST is 22.2 wt%: 22.2 wt%: 55.6 wt%.

[0027] Embodiment 2 This embodiment discloses a modulator preparation method, which is applied to a modulator in Embodiment 1. This embodiment mainly utilizes the characteristic that the electromagnetic parameters of the phase change material are adjustable. Selecting the GST material with non-volatility can be used to combine with the metasurface to obtain a tunable metasurface. In this embodiment, the phase change temperature of the GST material is about 160 °C. The initial state of the GST material is amorphous. After high-temperature annealing above 160 °C, the GST material can be transformed from the amorphous state to the crystalline state. On the contrary, if the amorphous GST material is to be obtained again, a rapid high-temperature annealing process at 640 °C is required to achieve it. That is to say, this phase change process is reversible.

[0028] Since the SiO2 layer, as a common passivation layer, can effectively inhibit the component diffusion and external pollution of the GST material and improve the optical stability and durability of the thin film, two thin film materials, GST and SiO2, are selected.

[0029] Specifically, it includes the following steps: S1. In this embodiment, the substrate layer is made of glass; the glass substrate layer is soaked and cleaned successively with acetone and absolute ethanol, and then the soaked and cleaned glass substrate layer is soaked and rinsed with deionized water, and the glass substrate layer is dried after soaking and rinsing.

[0030] S2. A first GST layer with a thickness of 50 nm is sputtered on the top surface of the glass substrate layer by using the magnetron sputtering process; S3. The interdigital electrode mask plate is placed on the first GST layer, and the whole device prepared at this time is placed in a vacuum chamber to make the first electrode by magnetron sputtering gold; specifically, in this embodiment, all the interdigital electrode mask plates are patterned interdigital electrode mask plates; as Figure 2 is a top view of a layer of electrode structure; S4. A first SiO2 layer with a thickness of 150 nm and a second GST layer with a thickness of 50 nm are successively sputtered on the first electrode by using the magnetron sputtering process; S5. The interdigital electrode mask plate is placed on the second GST layer, and the whole device prepared at this time is placed in a vacuum chamber to make the second electrode by magnetron sputtering gold; as Figure 3 is a top view of a two-layer electrode structure; S6. A second SiO2 layer with a thickness of 50 nm and a third GST layer with a thickness of 150 nm are successively sputtered on the second electrode by using the magnetron sputtering process; S7. The interdigital electrode mask plate is placed on the third GST layer, and the whole device prepared at this time is placed in a vacuum chamber to make the third electrode by magnetron sputtering gold; S8. A third SiO2 layer with a thickness of 50 nm is sputtered on the third electrode by using the magnetron sputtering process; as Figure 3 is a top view of a three-layer electrode structure; It also includes using a spectrophotometer to measure the transmittance of each structure during the phase change layer by layer. Specifically: Since when electromagnetic waves are incident on the multi-layer amorphous GST structure of the modulator prepared in step S8, a high-transmittance phenomenon will occur; therefore, the following steps are sequentially executed: S9. Control the first GST layer to directly transform into a crystalline state through the first electrode. The dielectric constant of GST increases, becoming a metallic state, enhancing the reflection and absorption of light, and initially reducing the light transmittance. The actual specific operation is to apply a preset current to the first GST layer through the first electrode, and use the resistance of the first GST layer within a preset time to achieve local heating, raising the temperature to the crystallization temperature and maintaining it for a sufficient time. The range of the preset current is: a current of 25–35 mA, a pulse width of 300–500 ns, and a pulse number of 10–50 times.

[0031] S10. Similarly, then control the second GST layer to directly transform into a crystalline state through the second electrode. The dielectric constant of GST increases, becoming a metallic state, enhancing the reflection and absorption of light. Measure the transmittance of the overall structure at this time through a spectrophotometer to obtain the measurement result of the secondary reduction of the light transmittance. S11. Similarly, the third electrode controls the third GST layer to directly transform into a crystalline state. The dielectric constant of GST increases, becoming a metallic state, enhancing the reflection and absorption of light. Measure the transmittance of the overall structure at this time through a spectrophotometer to obtain the measurement result of the tertiary reduction of the light transmittance. At this time, all three GST layers are in a metallic state, thereby achieving the modulation of the infrared transmittance.

[0032] Such as Figure 5 is the curve of the infrared transmittance of the modulator prepared in this embodiment changing with the crystallization of each GST layer layer by layer. When all three GST layers are in an amorphous state and there is no 0-layer crystalline state, it is recorded as the 0-layer situation. From top to bottom, when a total of 1 GST layer is in a crystalline state, it is recorded as the 1-layer situation; when a total of 2 GST layers are in a crystalline state, it is recorded as the 2-layer situation; when a total of 3 GST layers are in a crystalline state, it is recorded as the 3-layer situation. Through Figure 5 It can be seen that when all three GST layers are in an amorphous state, there are two resonance peaks. The first resonance peak = 2128 nm, the first transmittance = 92.01%, the second resonance peak = 2392 nm, the second = 91.1%. The transmittance gradually decreases as the number of crystalline layers of the GST layer increases.

[0033] In addition, based on the proposed transmission spectrum, the modulation depth is also used in this embodiment to evaluate the regulation performance of the prepared modulator. The specific expression is: ; In the formula: is the transmittance when all GST layers in the modulator structure are a-GST, is the transmittance when h-GST exists in the structure.

[0034] Such as Figure 6The modulation depth variation curve of the modulator prepared in this embodiment with the layer-by-layer crystallization of the GST layer. The 1-0 case corresponds to the transmittance comparison between 1 layer of h-GST and 0 layer of h-GST in the GST layer; the 2-0 case corresponds to the transmittance comparison between 2 layers of h-GST and 0 layer of h-GST in the GST layer; the 3-0 case corresponds to the transmittance comparison between 3 layers of h-GST and 0 layer of h-GST in the GST layer.

[0035] Through Figure 6 It can be seen that when 1 layer of the GST layer crystallizes, the modulation depth varies in the range of 17.80% - 33.22%; when 2 layers of the GST layer crystallize, the modulation depth varies in the range of 56.25% - 82.52%; when 3 layers of the GST layer crystallize, the modulation depth varies in the range of 88.32% - 96.89%. The metasurface structure of the multi-layer GST layer has achieved the effect of stepwise light regulation.

[0036] Obviously, the above embodiments are examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

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

2. The modulator according to claim 1, wherein The n SiO₂ layers and n GST layers are both thin films obtained by magnetron sputtering process.

3. A modulator according to claim 1, characterized in that, The a electrodes are obtained by controlling with an interdigital electrode mask plate.

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

5. A modulator according to claim 1, wherein The substrate layer uses a dielectric material with low absorption loss in the infrared band.

6. A method for preparing a modulator, characterized in that, To realize the preparation of a modulator as described in any one of claims 1-5, it includes the following steps: S1. First, soak and clean the substrate layer with acetone and absolute ethanol, then soak and rinse the substrate layer with deionized water, and finally dry it with a nitrogen gun. S2. Use the magnetron sputtering process to sputter a first GST layer with a thickness of 50 nm on the top surface of the substrate layer. S3. Place the interdigital electrode mask plate on the first GST layer, and put the whole device prepared at this time into the vacuum chamber to make the first electrode made of magnetron sputtered gold. S4. Use the magnetron sputtering process to sequentially sputter a first SiO₂ layer with a thickness of 150 nm and a second GST layer with a thickness of 50 nm on the first electrode. S5. Place the interdigital electrode mask plate on the second GST layer, and put the whole device prepared at this time into the vacuum chamber to make the second electrode made of magnetron sputtered gold. S6. Use the magnetron sputtering process to sequentially sputter a second SiO₂ layer with a thickness of 50 nm and a third GST layer with a thickness of 150 nm on the second electrode. S7. Place the interdigital electrode mask plate on the third GST layer, and put the whole device prepared at this time into the vacuum chamber to make the third electrode made of magnetron sputtered gold. S8. Use the magnetron sputtering process to sputter a third SiO₂ layer with a thickness of 50 nm on the third electrode. It also includes using a spectrophotometer to test the transmittance of each structure. Specifically: When electromagnetic waves are incident on the multi-layer amorphous GST structure of the modulator prepared in step S8, a high-transmittance phenomenon will occur; therefore, the following steps are sequentially executed: S9. Control the first GST layer to directly transform into a crystalline state through the first electrode. The dielectric constant of GST increases and becomes a metallic state, enhancing the reflection and absorption of light, and realizing a preliminary reduction in the transmittance of light. S10. Then control the second GST layer to directly transform into a crystalline state through the second electrode. The dielectric constant of GST increases and becomes a metallic state, enhancing the reflection and absorption of light. Measure the transmittance of the whole structure at this time with a spectrophotometer to obtain the measurement result of a secondary reduction in the transmittance of light. S11. The third electrode controls the third GST layer to directly transform into a crystalline state, the dielectric constant of GST increases, it becomes a metallic state, the reflection and absorption of light are enhanced. The transmittance of the overall structure is measured by a spectrophotometer at this time, and the measurement result of the light transmittance decreasing three times is obtained. At this time, all three GST layers are in a metallic state, thereby realizing the modulation of the infrared transmittance.

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