Temperature control adjustable terahertz absorption switch based on vanadium dioxide

Abstract

The invention discloses a conductivity-adjustable terahertz wave switching device based on a temperature control phase change material vanadium dioxide film. The structure is characterized by comprising a gold reflecting layer, a silicon dioxide depletion layer and a vanadium dioxide pattern layer which are sequentially overlapped from bottom to top. A depletion layer can cause loss of incident electromagnetic waves. The reflecting layer reflects incident electromagnetic waves to the depletion layer. Metal excited SPP causes local enhancement of the surrounding electromagnetic field. The introduction of the vanadium dioxide pattern design enhances the effect of a local electric field, thereby enhancing the absorptivity of the absorber. The switching device has the characteristics of small size, quick response, simple preparation process and large-scale production, and the switching function is quickly realized by adjusting the temperature.

Description

Technical Field

[0001] The invention relates to the technical field of optical communication, in particular to a tunable switch device for controlling local SPP absorption of terahertz spectrum by vanadium dioxide. Background Art

[0002] Surface plasmon polaritons (SPP) are electromagnetic modes between light waves and mobile surface charges that are realized by changing the subwavelength structure of the metal surface. They can support surface plasmon waves transmitted at the interface between metal and dielectric, thereby transmitting light energy, and are not limited by the diffraction limit. Because of the unique properties of SPP, it plays an important role in manipulating light energy at the nanoscale. Electromagnetic waves in the terahertz band (0.1-10THz) have unique properties and have broad application prospects in safety detection, non-destructive testing, communications, bioimaging and other fields. However, the materials and device technologies in the terahertz band are still under development, especially the control and modulation technology of terahertz waves. At present, using phase change materials to realize the modulation and switching functions of terahertz waves is an effective method. Vanadium dioxide (VO2) is a typical phase change material that can undergo a metal-insulator phase transition at a specific temperature (about 68°C), thereby significantly changing its optical and electrical properties. This characteristic has made vanadium dioxide widely used in optoelectronic modulators, smart windows and other fields. Combining VO2 with localized surface plasmons (SPPs) can achieve efficient regulation of terahertz waves, thereby developing terahertz absorbers with excellent performance.

[0003] "T-shaped tunable infrared optical switch based on vanadium dioxide with dual-wavelength channels" was published in Optics & Laser Technology in Volume 168 in January 2024. This article proposes a T-shaped tunable infrared optical switch based on a plasma structure composed of metal nanorods and vanadium dioxide thin films. The dynamic adjustment strategy based on the insulator-metal transition of vanadium dioxide and the polarization sensitivity of the switch was studied in depth to achieve the modulation of wavelength and spectral reflection intensity. F Guinneton's team used the characteristics of vanadium dioxide to optimize the performance of infrared switches, further proving that vanadium dioxide has a wide range of applications in switching, sensing, and infrared wave modulation. However, there are still many problems that need to be overcome, including its complex structure and low modulation depth. Summary of the invention

[0004] The purpose of the present invention is to address the shortcomings of the prior art, solve the limitation that the absorber cannot be actively adjusted according to the external environment, and propose a terahertz wave switching device with adjustable conductivity based on a temperature-controlled phase change material vanadium dioxide film. The device has a simple structure and low manufacturing cost, and can effectively regulate the absorption of terahertz waves to realize the switching function of terahertz waves. This device can achieve perfect absorption of incident terahertz waves. When vanadium dioxide is in a low temperature state, the absorption rate is extremely low. As the temperature rises, the absorption rate increases. When vanadium dioxide changes from an insulating phase to a metallic phase, the absorption spectrum gradually stabilizes. The absorption efficiency modulation depth before and after the phase change can reach 98.49%, making the absorber adjustable. The absorber can achieve polarization angle-independent absorption of electromagnetic waves. Due to the phase change characteristics of vanadium dioxide, the absorber can switch between the ON and OFF states according to temperature changes.

[0005] The technical solution for achieving the purpose of the present invention is:

[0006] A terahertz wave switch device with adjustable conductivity based on temperature-controlled phase-change material vanadium dioxide film. It includes a top vanadium dioxide pattern layer, a second silicon dioxide layer, and a third gold reflective layer. The free electrons on the metal surface interact rapidly with the incident light, causing the micro-light field to change rapidly and increasing the average distance between the micro-light field and the underlying microstructure. The conductivity of metal objects is relatively high because they have a large number of free electrons, which leads to a large loss of refracted waves and a large loss of reflected waves. It is difficult for electromagnetic waves to penetrate metal objects, resulting in a shielding effect. Based on the surface plasmon resonance technology, a vanadium dioxide surface plasmon micro-nano sensing structure is proposed by utilizing its strong local characteristics. In addition, since the thickness of the vanadium dioxide film is comparable to the wavelength of mid-infrared or visible light, the change in Fresnel reflection loss has a great impact, which also has an important impact on the measurement accuracy of Drude attenuation. This error can be avoided by measuring in the THz band. The frequency of THz waves is much lower than the plasma oscillation frequency of general materials, and its photon energy is between 0.1 and 40 meV. Therefore, the attenuation of transmitted THz waves comes from only two aspects: Fresnel reflection attenuation and Drude attenuation, and will not be affected by processes such as interband absorption.

[0007] The vanadium dioxide pattern layer is used to adjust the absorption characteristics of localized surface plasmons (SPP) through phase change characteristics. It is prepared by electron beam lithography technology to form a periodic pattern. The conductivity of vanadium dioxide is changed by adjusting the temperature, thereby achieving the regulation of the absorption rate.

[0008] The silicon dioxide depletion layer will cause the loss of incident electromagnetic waves and is used to isolate the pattern layer and the metal reflective layer to prevent mutual interference. The silicon dioxide dielectric layer is deposited by chemical vapor deposition (CVD) method and has a thickness of 21 μm.

[0009] The metal reflective layer reflects the incident electromagnetic wave to the depletion layer, reflects the unabsorbed terahertz wave, and enhances the absorption efficiency. The SPP excited by the metal will cause local enhancement of the surrounding electromagnetic field. The free electrons on the metal surface interact rapidly with the incident light, causing the micro-light field to change rapidly and increasing the average distance between the micro-light field and the underlying microstructure. It is difficult for electromagnetic waves to penetrate metal objects, resulting in a shielding effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A three-dimensional schematic diagram of a metamaterial sensor composed of multiple layers of materials;

[0011] Figure 2 This is a top view of the main structure of the unit. DETAILED DESCRIPTION

[0012] The following is combined with Figure 1 , 2 The content of the present invention is further explained, but the present invention is not limited thereto.

[0013] Please refer to the attached figure Figure 1 : 3D schematic diagram of a metamaterial sensor composed of multiple layers of materials. The top layer is a vanadium dioxide pattern layer 1, the second layer is a silicon dioxide depletion layer 2, and the third layer is a metal reflective layer of gold 3.

[0014] The vanadium dioxide pattern layer 1 first prepares a substrate. A high-quality silicon wafer is selected as the substrate, and the organic matter and oxide layer on the surface are removed using conventional cleaning steps (such as RCA cleaning method). After that, the silicon wafer is dried for use. A VO2 film is deposited on the surface of the silicon wafer using pulsed laser deposition (PLD) or DC magnetron sputtering method. A layer of electron beam photoresist (such as PMMA) is coated on the surface of the VO2 film, and an electron beam lithography (EBL) device is used to expose the photoresist according to the designed pattern. After exposure, development is performed, and the developer is usually a MIBK (1:3) solution, the development time is 1 minute, and then it is rinsed with IPA and dried. The developed VO2 film is etched using a reactive ion etching (RIE) device. The residual photoresist is removed to obtain a patterned VO2 layer. The geometric parameters of 13.5μm, 22μm, and 1μm represent the width of the square, the outer ring length of the square ring, and the width of the gap of the outer ring, respectively. The width of the inner ring air cavity is 18μm.

[0015] The silicon dioxide depletion layer 2 (thickness 21 μm) is deposited on the patterned VO2 layer by plasma enhanced chemical vapor deposition. If the surface of the SiO2 layer is uneven, a chemical mechanical polishing (CMP) method can be used to flatten it to ensure good contact between the layers.

[0016] The metal reflective layer 3 (thickness of 2 μm) reflects the incident electromagnetic wave to the depletion layer, reflects the unabsorbed terahertz wave, and enhances the absorption efficiency. The SPP excited by the metal will cause local enhancement of the surrounding electromagnetic field. The free electrons on the metal surface interact rapidly with the incident light, causing the micro-light field to change rapidly and increasing the average distance between the micro-light field and the underlying microstructure. It is difficult for electromagnetic waves to penetrate metal objects, resulting in a shielding effect.

Claims

1. A terahertz wave switching device with adjustable conductivity based on temperature-controlled phase-change material vanadium dioxide film. The modulator can realize the switching function of the metamaterial absorber. The sensor consists of a periodic unit cell array, and its main structure is a square ring composed of two vanadium dioxide. The absorber unit cell consists of a gold reflection layer, a silicon dioxide depletion layer and a vanadium dioxide pattern layer. The depletion layer causes the loss of the incident electromagnetic wave. The reflection layer reflects the incident electromagnetic wave to the depletion layer. The SPP excited by the metal causes local enhancement of the surrounding electromagnetic field. The introduction of the vanadium dioxide pattern design enhances the local electric field effect, thereby enhancing the absorptivity of the absorber.

2. According to claim 1, the vanadium dioxide pattern layer 1 (thickness is 1 μm), the silicon dioxide depletion layer 2 (thickness is 21 μm). The metal reflective layer 3 (thickness is 2 μm). The geometric parameters of the width of the square, the outer ring length of the square ring and the width of the gap of the outer ring are 13.5 μm, 22 μm and 1 μm respectively. The width of the inner ring air cavity is 18 μm.

3. A terahertz wave switch device with adjustable conductivity. Its characteristics are: The structure can be switched from reflection to absorption by temperature regulation, and a switch function is proposed. While having a high absorption rate, a high modulation depth can be achieved by simply changing the temperature.

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