Micromechanical optical switch based on plasma absorber

Abstract

The invention belongs to the field of radio frequency MEMS devices, and relates to a micromechanical optical switch based on a plasma absorber. Comprising a top driving structure which comprises a cantilever structure and a surface plasma infrared absorption structure; a bottom electrode structure; a support structure; and the top driving structure is arranged on the upper surface of the bottom electrode structure, so that a cavity is formed between the top driving structure and the bottom electrode structure. According to the micro-mechanical optical switch, the plasma infrared absorption structure is adopted to realize nearly perfect absorption of infrared signals with specific wavelengths, and meanwhile, the zigzag cantilever structure is adopted to provide a larger elastic coefficient and lower equivalent stiffness, so that the micro-mechanical optical switch with high detection rate and high response rate is realized; an independent sensor which does not need to be maintained frequently becomes possible, and the method has an important application prospect for a wireless sensor network.

Description

Technical Field

[0001] The present application belongs to the field of radio frequency MEMS devices and relates to a micromechanical optical switch based on a plasma absorber. Background Art

[0002] With the development and application of radio frequency (RF) communication systems and the Internet of Things (IOT), RF devices based on microelectromechanical systems (MEMS) technology have become the development trend of future RF front-ends. The progress of nanotechnology and microelectromechanical systems (MEMS) has greatly improved these properties of sensors and has become the key to the surge in micro devices used in the Internet of Things (IoT). For unattended sensor networks (such as forest fires, earthquakes, territorial invasions, chemical warfare threats, etc.), they will continue to consume power to monitor the environment even when there is no relevant data to detect. Micromechanical optical switches will allow these devices to consume power only when triggered by specific signals, thereby greatly reducing the power consumption of remotely deployed sensor networks. By effectively absorbing and utilizing infrared signals, detecting low levels of incident infrared radiation and waking up responding devices (such as radio transmitters), the system can remain in a dormant state at near zero power consumption in the absence of specific infrared signals.

[0003] The micromechanical optical switch is triggered when it receives specific infrared radiation. The sandwich structure of metal-dielectric layer-metal can confine the incident infrared light signal in the dielectric layer through plasma resonance and convert it into heat energy. The heat energy is transferred to the dual-material cantilever, causing the cantilever structure to deform due to thermal impedance mismatch, and then mechanical displacement is generated to close the switch. However, the traditional absorption layer material has a low absorption rate for light energy, and the received light signal is easily interfered by other wavelength signals other than the specific wavelength signal. It takes a certain response time from the received signal to the switch closing. If the switch closing gap is too small, it will cause the switch to be accidentally touched and the circuit to be turned on. If the closing gap is too large, the displacement generated by the received light signal will not be enough to close the switch. Therefore, it is an urgent problem to improve the utilization rate of light energy, better confine the heat to the cantilever structure, optimize the infrared absorption structure to achieve high absorption rate of light signals, and design the cantilever structure to reduce the threshold power of the optical switch. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a micromechanical optical switch, which can be closed when receiving a specific signal to make the circuit conductive, and automatically disconnected after the specific signal disappears.

[0005] This application provides the following technical solutions:

[0006] A micromechanical optical switch based on a plasma absorber comprises a top driving structure, a bottom electrode structure and a supporting structure. The supporting structure is arranged on the upper surface of the bottom electrode structure and is used to support the top driving structure so that a cavity is formed between the top driving structure and the bottom electrode structure. The top driving structure comprises a cantilever structure and a surface plasma infrared absorption structure. The surface plasma infrared absorption structure comprises a top metal array, a dielectric layer and a bottom metal layer arranged in sequence. The top metal array is arranged on the upper surface of the dielectric layer and is a periodic array composed of plasma metal blocks with a side length of 2.6 μm, and the period is 3.2 μm. The dielectric layer is a material with a low thermal expansion coefficient, and a part of the dielectric layer extends to form a first layer of the cantilever structure. The bottom metal layer is a material with a high thermal expansion coefficient, and the bottom metal layer is arranged on the lower surface of the dielectric layer, and a part of the bottom metal layer extends to form a second layer of the cantilever structure.

[0007] Furthermore, the cantilever structure includes four folded cantilevers bent at right angles in the middle, which are rotationally symmetrically arranged around the surface plasma infrared absorption structure. The supporting structure includes four supporting blocks. One end of each cantilever structure is connected to the endpoint of one side of the surface plasma infrared absorption structure, and the other end is connected to the supporting block.

[0008] Furthermore, the dielectric layer is silicon dioxide with a thickness of 200 nm.

[0009] Furthermore, the bottom metal layer is aluminum with a thickness of 400 nm.

[0010] Furthermore, the material of the top metal array is gold, and the thickness is 50 nm.

[0011] Furthermore, the material of the support structure is silicon dioxide with a thickness of 1.9 μm.

[0012] Furthermore, the bottom electrode structure is an aluminum metal flat plate.

[0013] Compared with the prior art, the micromechanical optical switch provided by the present invention is a micromechanical optical switch triggered by an optical signal. By designing a metal array configured on the top of a surface plasma infrared absorption structure, and analyzing multiple groups of surface metal arrays with different side lengths and periods, it is found that when the period of the surface metal array is 3.2μm and the side length of the metal block is 2.6μm, a specific optical signal can be accepted to excite plasma resonance, achieving near-perfect absorption of the optical signal, improving the conversion rate of light energy to thermal energy, and thus improving the response capability of the optical switch. Compared with the vertical cantilever configured in the middle of the four sides of the infrared absorption structure, the bi-material folded cantilever configured at the four ends of the surface plasma infrared absorption structure reduces the equivalent stiffness of the cantilever as a whole and improves the elastic coefficient, thereby better confining the heat to the cantilever structure and reducing the heat energy lost to the substrate through the support shaft, thereby improving the energy utilization rate, achieving a lower infrared threshold power, and improving the optical switch detection rate. The surface plasma infrared absorption structure dielectric layer is also used as the low thermal expansion coefficient material layer of the dual-material cantilever. The surface plasma infrared absorption bottom metal is also used as the high thermal expansion coefficient material layer of the dual-material cantilever, which improves the integration of the optical switch, reduces the overall thickness of the optical switch, and limits the heat to the cantilever structure as much as possible, achieving a lower infrared threshold power and improving the optical switch detection rate. The micromechanical optical switch provided by the present invention relies on plasma-enhanced thermomechanical coupling to selectively obtain light energy in a specific spectral band, converts light energy into heat energy and conducts it to the cantilever through the dual-material thermal impedance mismatch to cause the cantilever to bend, and mechanically establishes a conduction channel between the device terminals without any additional power supply, which directly translates into near-zero standby power consumption, and has important application prospects in the development of wireless sensor networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A three-dimensional structural diagram of a micromechanical optical switch provided in Example 1 of the present invention;

[0015] Figure 2 A three-dimensional structural diagram of a micromechanical optical switch provided in Comparative Example 1 of the present invention;

[0016] Figure 3 A transverse cross-sectional view of a micromechanical optical switch provided in Embodiment 1 of the present invention;

[0017] Figure 4 A transverse cross-sectional view of a surface plasma infrared absorption structure of a micromechanical optical switch provided in Example 1 of the present invention;

[0018] Figure 5 A spectrum response diagram of a surface plasma infrared absorption structure of a micromechanical optical switch provided in Examples 1-3 of the present invention;

[0019] Figure 6A three-dimensional thermal stress distribution diagram of a micromechanical optical switch provided in Examples 1-3 of the present invention and Comparative Example 1;

[0020] Figure 7 A voltage displacement diagram of a micromechanical optical switch provided in Example 1 of the present invention and Comparative Example 1;

[0021] In the figure: 1-cantilever structure; 2-surface plasma infrared absorption structure; 3-support structure; 4-bottom electrode structure; 5-top metal array; 6-dielectric layer; 7-bottom metal layer. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below.

[0023] It should be noted that the terms used in this application are generally terms commonly used by those skilled in the art. If there is any inconsistency with the commonly used terms, the terms in this application shall prevail.

[0024] As used herein, the term "top metal array" refers to a periodic array of metal squares.

[0025] Herein, the term “period” refers to the period of the top metal array, which is the sum of the side length of a single gold square and the distance between adjacent gold squares.

[0026] As used herein, the term “dual-material cantilever” refers to a cantilever composed of two layers of materials having different thermal expansion coefficients.

[0027] As used herein, the term "absorption peak bandwidth" refers to the wavelength width at half the peak value of the absorption peak of the spectral response curve.

[0028] As used herein, the term "edge width" refers to the distance from the edge of the plasma array overlying the dielectric layer to the edge of the dielectric layer.

[0029] Herein, the term "closed gap distance" refers to the distance from the surface plasmon infrared absorption structure to the bottom electrode structure.

[0030] In this document, the terms "upper" and "lower" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the equipment or components referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0031] As used herein, the terms "comprises," "comprising," or any other variation thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific circumstances.

[0032] Example 1

[0033] A micromechanical optical switch based on a plasmonic absorber is provided, such as Figure 1 , 3 4, including: a top driving structure, a bottom electrode structure 4 and a support structure 3, the top driving structure includes a cantilever structure 1 and a surface plasma infrared absorption structure 2, the support structure 3 is arranged on the upper surface of the bottom electrode structure 4, and is used to support the top driving structure, so that the top driving structure is suspended above the bottom electrode structure 4, and a cavity is formed between the surface plasma infrared absorption structure 2 and the bottom electrode structure 4. The bottom electrode structure 4 is a 100nm thick aluminum metal flat plate. The cantilever structure 1 includes four folded cantilevers bent at right angles in the middle, and the folded cantilevers are double-material cantilevers, which are rotationally symmetrically arranged around the surface plasma infrared absorption structure 2, and the support structure 3 includes four support blocks, which are 1.9μm thick square silicon dioxide, located at the end of each folded cantilever, connecting the folded cantilever and the bottom electrode.

[0034] One end of each folded cantilever is connected to an end point of one side of the surface plasma infrared absorption structure 2, and the other end is connected to a support block. The length of the cantilever connected to the support block is 140 μm, the length of the cantilever connected to the surface plasma infrared absorption structure 2 is 60 μm, and the width of the cantilever is 16 μm. The surface plasma infrared absorption structure 2 includes a top metal array 5, a dielectric layer 6 and a bottom metal layer 7 arranged in sequence, the top metal array 5 is arranged on the upper surface of the dielectric layer 6, the dielectric layer 6 uses 200 nm thick silicon dioxide as a low thermal expansion coefficient material, and its thermal expansion coefficient is 0.5e-61 / K, and a part of the dielectric layer 6 extends to form the first layer of the folded cantilever, the bottom metal layer 7 is a 400 nm thick aluminum layer, as a high thermal expansion coefficient material, and its thermal expansion coefficient is 23.1e-61 / K, the bottom metal layer 7 is arranged on the lower surface of the dielectric layer 6, and a part of the bottom metal layer 7 extends to form the second layer of the folded cantilever.

[0035] The surface plasmon infrared absorption structure 2 is a square structure with a side length of 120 μm and a cross section as shown in FIG. Figure 4As shown, it includes three layers, the top metal array 5 is a 50nm thick gold array, the 200nm thick silicon dioxide dielectric layer 6 is arranged on the lower surface of the gold array, and the bottom metal layer 7 is a 400nm thick aluminum plate, which is located on the lower surface of the silicon dioxide dielectric layer 6. Figure 4 As shown, the side length a of a single gold square is 2.6 μm, the period p is 3.2 μm, and the edge width is 12 μm.

[0036] Example 2

[0037] This embodiment provides a micromechanical optical switch based on a plasma absorber. The side length of a single gold square is 2 μm, the period is 2.4 μm, and the other parameters are the same as those in Embodiment 1.

[0038] Example 3

[0039] This embodiment provides a micromechanical optical switch based on a plasma absorber. The side length of a single gold square is 3.6 μm, the period is 4 μm, and the other parameters are the same as those in Embodiment 1.

[0040] Comparative Example 1

[0041] This embodiment provides a micromechanical optical switch based on a plasmon absorber. The cantilever structure 1 uses four straight cantilevers. The width of the straight cantilever is 16 μm, the length of the straight cantilever is 100 μm, and the other parameters are the same as those in Embodiment 1. Figure 2 shown.

[0042] Through Lumerical v202 FDTD simulation analysis software, we get the following Figure 5 The spectral response diagram is shown. Figure 5 It can be seen that when a plasma array is used on the top of the infrared absorption structure, when infrared radiation of a specific wavelength is irradiated to the metasurface, the photons and the surface electrons of the top gold layer produce surface plasma resonance, which in turn forms a magnetic dipole resonance in the middle silicon dioxide layer, forming a resonant absorption peak. The absorption rate reaches 98% at a wavelength of 9.5μm, achieving near-perfect absorption of infrared signals of a specific wavelength.

[0043] Through COMSOL Multiphysics simulation analysis software, we get the following Figure 6 The three-dimensional thermal stress distribution diagram is shown.

[0044] Figure 6 The thermal stress distribution diagram of the micromechanical optical switch provided for Examples 1-3 and Comparative Example 1 is shown in FIG. Figure 6It can be seen that the displacement at g is the smallest and it hardly moves; g is a fixed point (because of the support structure, it will not move downward); the displacement at b is the largest. The heat energy lost through air and thermal radiation in Examples 1-3 and Comparative Example 1 is basically the same. In Examples 1-3, due to the increase in the length of the folded cantilever, less heat energy is lost to the substrate through the support block. Compared with the straight cantilever structure of Comparative Example 1, the distribution of the folded cantilever structure has a higher ratio of heat energy at the cantilever to the overall heat energy, indicating that the folded cantilever structure of Examples 1-3 can better confine the heat energy to the cantilever and improve the energy utilization of the micromechanical optical switch.

[0045] Figure 7 The voltage displacement diagram of a micromechanical optical switch provided in Example 1 of the present invention and Comparative Example 1 shows that, when 1 μW thermal power and 1 V electrostatic bias voltage are provided, the maximum displacement of the straight cantilever structure reaches 0.35 μm, and the maximum displacement of the folded cantilever structure reaches 1.6 μm at point b. The folded cantilever structure has a higher elastic coefficient and a lower equivalent stiffness, which increases the optical switch response rate by four times, thereby realizing a micromechanical optical switch with a high detection rate.

[0046] The above description is only a preferred example of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the subject matter and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A micromechanical optical switch based on a plasmon absorber, characterized in that: The invention comprises a top driving structure, a bottom electrode structure (4) and a support structure (3), wherein the support structure (3) is arranged on the upper surface of the bottom electrode structure (4) and is used to support the top driving structure so that a cavity is formed between the top driving structure and the bottom electrode structure (4), wherein the top driving structure comprises a cantilever structure (1) and a surface plasma infrared absorption structure (2), wherein the surface plasma infrared absorption structure (2) comprises a top metal array (5), a dielectric layer (6) and a bottom metal layer (7) which are arranged in sequence, and wherein the top metal array (5) ) is arranged on the upper surface of the dielectric layer (6), the top metal array (5) is a periodic array composed of surface plasma metal blocks with a side length of 2.6 μm, and the period is 3.2 μm, the dielectric layer (6) is a low thermal expansion coefficient material, a portion of the dielectric layer (6) extends to form the first layer of the cantilever structure (1), the bottom metal layer (7) is a high thermal expansion coefficient material, the bottom metal layer (7) is arranged on the lower surface of the dielectric layer (6), and a portion of the bottom metal layer (7) extends to form the second layer of the cantilever structure (1).

2. The micromechanical optical switch according to claim 1, characterized in that: The cantilever structure (1) comprises four folded cantilevers bent at right angles in the middle, which are arranged rotationally symmetrically around the surface plasma infrared absorption structure (2); the support structure (3) comprises four support blocks, one end of each cantilever structure (1) is connected to an end point on one side of the surface plasma infrared absorption structure (2), and the other end is connected to the support block.

3. The micromechanical optical switch according to claim 1, characterized in that: The dielectric layer (6) is silicon dioxide and has a thickness of 200 nm.

4. The micromechanical optical switch according to claim 1, characterized in that: The bottom metal layer (7) is aluminum and has a thickness of 400 nm.

5. The micromechanical optical switch according to claim 1, characterized in that: The material of the top metal array (5) is gold, and the thickness is 50nm.

6. The micromechanical optical switch according to claim 1, characterized in that: The support structure (3) is made of silicon dioxide and has a thickness of 1.9 μm.

7. The micromechanical optical switch according to claim 1, characterized in that: The bottom electrode structure (4) is an aluminum metal flat plate.

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