CN110534909B - Terahertz metamaterial converter with switchable ring couples and galvanic couples based on MEMS planar structure reconstruction and preparation method thereof - Google Patents
Terahertz metamaterial converter with switchable ring couples and galvanic couples based on MEMS planar structure reconstruction and preparation method thereof Download PDFInfo
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Abstract
A terahertz metamaterial converter with switchable ring couples and galvanic couples based on MEMS planar structure reconstruction and a preparation method thereof relate to a terahertz metamaterial converter with switchable working modes and a preparation method thereof. The invention aims to solve the problems that the ring pair resonance tuning depth of a planar terahertz metamaterial is small, external equipment required by an excitation mode is complex, the selectable range of an active material is narrow, and the linearity property is small. The electrostatic driving device comprises a base silicon substrate, a comb-tooth type electrostatic driving structure, a fixed metal structure array, a movable metal structure array and a suspension silicon frame. The method comprises the following steps: firstly, depositing a silicon dioxide layer; secondly, patterning the photoresist mask of the anchor structure; thirdly, forming an anchor structure; fourthly, bonding and thinning the structural layer; fifthly, patterning the metal structure unit; sixthly, patterning a photoresist mask; and seventhly, etching the silicon and releasing the MEMS structure. The method is mainly used for preparing the terahertz metamaterial converter with switchable ring couples and galvanic couples.
Description
Technical Field
The invention relates to a terahertz metamaterial converter with switchable working modes and a preparation method thereof.
Background
In classical dynamics, there are usually two large multipole subsystems, an electric multipole and a magnetic multipole, respectively. Of the two large multipole subsystems, electric and magnetic dipoles are most common. The electric dipole can be regarded as a system consisting of a pair of opposite charges, and can be used for an antenna or a local sensor to detect a near field due to the large scattering intensity and the wide electromagnetic resonance line width; the magnetic dipole can be equivalent to a current loop, the electromagnetic resonance line width is relatively narrow, and the low-power nonlinear processor or the optical sensitive device can be used. As a third kind of radiation source, the ring dipole is induced by a ring current to generate a pair of magnetic dipoles with opposite directions, presents an end-to-end state, has a special electromagnetic characteristic of almost no radiation, and has wide application in the fields of nuclear and atomic physics, solid-state physics and classical electrodynamic science. However, the loop dipole mode has a very weak response to incident electromagnetic waves, so that the electromagnetic response is very weak in most cases and is often covered by stronger conventional electric/magnetic poles, thereby seriously hindering the detection and application of the loop dipole.
The metamaterial is an artificially constructed periodically-arranged sub-wavelength structural unit array, and extraordinary electromagnetic properties, such as negative refraction, electromagnetic stealth, optical transformation and the like, which are not possessed by natural materials can be realized by reasonably designing the geometric shape, size and arrangement mode of the structural units. Therefore, through reasonably designing the structural unit of the metamaterial, the traditional electric/magnetic dipole response can be effectively inhibited, so that the response strength of the ring dipole is enhanced to reach an observable level, and the metamaterial has important milestone significance for deeply researching the electromagnetic property of the ring dipole. Through structural design and accurate preparation, a plurality of ring dipoles based on three-dimensional metamaterial structures are reported at present, and good ring magnetic field limitation and high-strength and high-Q-factor ring dipole resonance can be realized. However, due to the limitation of the preparation process, the preparation of the ring dipole of the three-dimensional terahertz metamaterial structure still has great challenges, so that the ring dipole of the existing three-dimensional metamaterial structure mainly works in a microwave frequency band and is difficult to realize in a terahertz high-frequency band.
In recent years, in order to realize the ring pair resonance of terahertz or optical frequency band, the planar metamaterial structure for realizing the ring pair resonance of terahertz attracts people's wide interest and attention, and gradually becomes a new branch and a hot spot of metamaterial research, and the fundamental reason is that the planar terahertz metamaterial is easy to prepare. At present, ring-couple resonance based on a planar terahertz metamaterial structure is designed and prepared, so that the ring-couple resonance has potential application value and application prospect in the fields of communication, safety detection, biochemical sensing and the like. However, the existing loop-pair resonant response based on the planar metamaterial structure mainly depends on structural units, and once the shape and the size of the structural units are determined, the corresponding resonant working wavelength, amplitude and bandwidth are also fixed, so that a single function can be realized only in a limited working bandwidth, and the application range is severely limited and restricted.
In order to overcome the defects, the dynamic control of the ring-couple resonance is realized by integrating the active material in the planar terahertz metamaterial structure unit, so that the terahertz metamaterial structure unit becomes one of the leading-edge scientific and technological fields, and attracts the wide interest and attention of people. For example, in 2017, x.chen et al utilize a planar terahertz metamaterial composed of square split-ring resonators to realize ring-couple resonance, and when a metamaterial structure is integrated with single-layer graphene, the transmission amplitude of the ring-couple resonance can be flexibly regulated and controlled by changing the fermi energy of the graphene. In 2018, M.Gupta et al prepared a planar terahertz metamaterial composed of an open resonant ring array, and integrated a thin silicon structure at the gap of the opening; when the 800nm laser pumping metamaterial structure is adopted, the ring-couple resonance amplitude can be flexibly regulated and controlled by regulating and controlling the power of the pumping light, and when the power of the pumping light is increased to a certain degree, the ring-couple resonance can be converted into the galvanic couple resonance. However, because the active material has frequency-dependent properties, limited selectivity and complexity of external excitation, the modulation depth of the ring pair resonance is inevitably limited, and these defects will bring great difficulty to the practical application of the planar metamaterial ring pair resonance and limit the practical application range thereof.
Disclosure of Invention
The invention aims to solve the problems of small ring pair resonance modulation depth, complex external equipment required by an excitation mode, narrow active material selectable range and small linear property of a planar terahertz metamaterial, and provides a ring pair and couple switchable terahertz metamaterial converter based on MEMS planar structure reconstruction and a preparation method thereof.
A terahertz metamaterial converter capable of switching a ring dipole and a galvanic couple based on MEMS planar structure reconstruction comprises a base silicon substrate, a comb-tooth type electrostatic driving structure, a fixed metal structure array, a movable metal structure array and a suspended silicon frame, wherein the comb-tooth type electrostatic driving structure and the suspended silicon frame are arranged on the base silicon substrate, the suspended silicon frame is connected with the comb-tooth type electrostatic driving structure and is arranged in a suspended manner, the fixed metal structure array is arranged in the suspended silicon frame and on the base silicon substrate, and the movable metal structure array is connected with the suspended silicon frame and is arranged in a suspended manner; the terahertz metamaterial comprises a fixed metal structure array, a movable metal structure array and a terahertz metamaterial, wherein the fixed metal structure array is composed of structural elements which are arranged periodically, the structural elements of the fixed metal structure array are of an E-shaped structure, the movable metal structure array is composed of structural elements which are arranged periodically, the structural elements of the movable metal structure array are of an inverted E-shaped structure, the structural elements of the fixed metal structure array and the structural elements of the movable metal structure array are arranged oppositely in pairs, and the structural elements of the fixed metal structure array and the structural elements of the movable metal structure array which are arranged oppositely in pairs form a functional structural unit of the terahertz metamaterial capable of being switched between coupling and coupling.
A preparation method of a terahertz metamaterial converter with switchable ring couples and galvanic couples based on MEMS planar structure reconstruction is specifically completed according to the following steps:
firstly, depositing a silicon dioxide layer: preparing a silicon dioxide passivation layer on the silicon surface by using a material growth process;
secondly, patterning the photoresist mask of the anchor structure: uniformly coating a layer of photoresist on the surface of the silicon dioxide by using a mechanical spin coating process, and removing the photoresist in a photosensitive area during development after exposure, development and fixation to form a micro-pattern structure to obtain an anchor structure patterned photoresist mask; the photoresist is positive photoresist;
thirdly, forming an anchor structure: etching the silicon dioxide passivation layer by using the anchor structure patterned photoresist as a mask by using an etching process to obtain the etched silicon dioxide passivation layer, and removing the photoresist by using a photoresist removing liquid; etching the silicon surface by taking the etched silicon dioxide passivation layer as a mask, and removing the etched silicon dioxide passivation layer to obtain etched silicon; the etching process is wet etching or dry etching;
fourthly, bonding and thinning the structural layer: bonding the etched silicon with the base silicon substrate 1 by using a silicon-silicon bonding process, coating a protective layer on the edge and the lower surface of the base silicon substrate, thinning the etched silicon by using a KOH solution wet etching process, and removing the protective layer to obtain thinned silicon;
fifthly, patterning the metal structure unit: firstly, spin-coating photoresist on the thinned silicon surface by using a mechanical spin-coating process, and taking an E-shaped pattern array and an inverted E-shaped pattern array area as photosensitive areas through exposure, development and fixation to obtain patterned photoresist; the photoresist is positive photoresist; depositing a metal layer, wherein the thickness of the metal layer is 0.2-0.4 mu m, removing the patterned photoresist by using a photoresist removing liquid, simultaneously stripping the metal layer on the patterned photoresist, and only reserving the metal layer deposited in a photosensitive area, namely depositing an E-shaped patterned metal element array and an inverse E-shaped patterned metal element array on the thinned silicon surface to obtain a patterned metal metamaterial structure;
sixthly, patterning a photoresist mask: utilizing a mechanical spin coating process to spin a photoresist on the surface of the patterned metal metamaterial structure, and forming a micro-pattern structure of a comb-tooth type electrostatic driving structure, a micro-pattern structure of a suspended silicon frame, a micro-pattern structure of a fixed metal structure array and a micro-pattern structure of a movable metal structure array through exposure, development and fixation to obtain a photoresist mask pattern of the micro-pattern structure;
seventhly, etching silicon and releasing the MEMS structure: and taking the photoresist mask graph with the micro-graph structure as a mask, deeply etching silicon by utilizing a deep reactive ion etching technology, releasing the MEMS structure, and removing the photoresist by utilizing a dry method to realize the comb-tooth type electrostatic driving structure, the suspended silicon frame, the fixed metal structure array and the movable metal structure array, so as to obtain the terahertz metamaterial converter with switchable ring couples and galvanic couples based on the reconstruction of the MEMS planar structure.
The principle and the advantages of the invention are as follows:
1. the traditional method for regulating and controlling the ring-couple resonance of the planar terahertz metamaterial is to integrate the terahertz metamaterial and an active material and change the attribute of the active material of a structural unit or the surrounding material through external excitation, so that the ring-couple resonance of the terahertz metamaterial can be flexibly and effectively regulated and controlled. The traditional active materials which are commonly used are semiconductor materials, phase-change materials, superconducting materials, graphene and liquid crystal materials, the tuning capability of the active materials obviously depends on the nonlinear characteristics of the active materials, so that the tuning range is limited, and the selectable range of the active materials is narrow. The electromagnetic property of the terahertz metamaterial depends on the size and the shape of the structural unit, and the comb-tooth-shaped electrostatic driving structure is adopted to drive the suspended silicon frame, so that the movable metal structure array is driven, the regulation and control mode of the MEMS movable structure reconstruction is realized, the geometric shape, the size and the arrangement mode of the structural unit are changed from the ring pair resonance structure essentially, the electromagnetic environment around the structural unit is not changed, the ring pair resonance modulation depth of the planar terahertz metamaterial can be obviously enhanced and improved, the working mode of the terahertz metamaterial is changed, and the problems that the ring pair resonance tuning depth of the traditional planar terahertz metamaterial is small, external equipment required by an excitation mode is complex, the selectable range of an active material is narrow, the linear property is small and the like are solved.
2. The invention adopts the comb-tooth type electrostatic driving structure to drive the movable metal structure array to translate in a plane, regulates and controls the distance and the reconfiguration state between the E-shaped patterned metal element in the structural element of the fixed metal structure array and the reverse E-shaped patterned metal element in the structural element of the movable metal structure array, and can realize double regulation and control of the ring dipole. When the distance between an E-type patterned metal element and an anti-E-type patterned metal element in a functional structural unit of the terahertz metamaterial with switchable ring couples and galvanic couples is gradually changed, the electromagnetic coupling strength between the E-type patterned metal element and the anti-E-type patterned metal element can be changed, and the resonance amplitude modulation of the ring couples is realized; when the E-shaped patterned metal element and the anti-E-shaped patterned metal element are changed from a separated state to a contact state, the conversion of the working mode between the ring couple resonance and the couple resonance can be realized.
3. The line width of the electromagnetic resonance depends on the characteristics and the strength of the scattering phenomenon, and the electromagnetic resonance with different line widths can realize devices with different functions. The electric dipole has high scattering intensity and wide electromagnetic resonance line width, and can be used for an antenna or a local sensor to detect a near field and the like; the ring dipole has relatively narrow electromagnetic resonance line width, and can be used for super-sensitive sensors, modulators, narrow-band filters, nonlinear optical devices and the like. The terahertz metamaterial converter based on MEMS planar structure reconstruction and capable of switching the loop pair and the galvanic couple can realize the coupling mode conversion between the loop pair resonance and the galvanic couple resonance, so that the conversion of various multifunctional devices can be realized.
4. The invention adopts the comb-tooth type electrostatic driving structure to drive the movable metal structure array to translate in a plane, the external excitation adopts electrostatic driving, the excitation mode does not relate to complex equipment, the regulation and control mode is simple, easy to control, flexible and reliable, the preparation process is mature, and the cost is low, thereby enhancing the practicability of the device.
5. According to the terahertz metamaterial converter based on MEMS planar structure reconstruction, when TE waves or TM waves are incident and the distance between two structures changes within the frequency range of 0.05 THz-1.2 THz, electromagnetic response is changed from two resonances to one resonance, and a dual-band and single-band filtering converter can be realized.
Drawings
FIG. 1 is a structural schematic diagram of a terahertz metamaterial converter switchable between a ring pair and a galvanic couple based on MEMS planar structure reconstruction; in the figure, 1 denotes a base silicon substrate, 2 denotes a comb-tooth type electrostatic driving structure, 3 denotes a fixed metal structure array, 4 denotes a movable metal structure array, and 5 denotes a floating silicon frame;
FIG. 2 is a schematic structural diagram of a functional structural unit with switchable ring couples and galvanic couples in a separated state;
FIG. 3 is a schematic structural diagram of a functional structural unit with switchable ring couples and galvanic couples in a contact state;
FIG. 4 is a left side view of FIG. 2; in the drawings, 1 denotes a base silicon substrate, 3-1 denotes an E-type patterned metal element, 3-2 denotes an E-type fixed silicon substrate, 4-1 denotes an inverse E-type patterned metal element, and 4-2 denotes an inverse E-type movable silicon substrate;
FIG. 5 is a schematic diagram illustrating the operation of the growth process in the first five steps according to one embodiment;
FIG. 6 is a schematic diagram of etching a silicon dioxide passivation layer in a third step of the detailed embodiment;
FIG. 7 is a schematic diagram of etching a silicon surface in a fifth step III of the embodiment;
FIG. 8 is a schematic diagram of bonding in step four of the preferred embodiment;
FIG. 9 is a schematic diagram of a metal structure unit in a fifth step of the fifth embodiment;
FIG. 10 is a transmission curve diagram of a TE wave vertically incident on the surface of the metamaterial when d is from 3 μm to 1 μm in a separation state;
FIG. 11 is a transmission curve diagram of a TE wave vertically incident to a metamaterial surface when d is 0 μm;
FIG. 12 is a diagram showing a metamaterial metal surface current distribution and a magnetic dipole pattern in an isolated state, where d is 3 μm, when a TE wave is perpendicularly incident on the metamaterial surface;
fig. 13 is a contact state, d is 0 μm, when TE wave vertically enters the metamaterial surface, the metamaterial metal surface current distribution and the electric dipole directional diagram;
fig. 14 is a graph of calculated dipole moment components of TE wave normal incidence values at d of 3 μm, where a represents the component of ring dipole moment in the y direction, denoted by Ty, a represents the component of electric dipole moment in the y direction, denoted by Py, and ● represents the component of magnetic dipole moment in the x direction, denoted by Mx;
fig. 15 is a transmission curve diagram of TM waves perpendicularly incident to the metamaterial surface when d is 3 μm;
fig. 16 is a transmission curve diagram of TM waves perpendicularly incident to the metamaterial surface when d is 0 μm;
fig. 17 is a separated state, where d is 3 μm, when TM waves are perpendicularly incident to the metamaterial surface, the metamaterial metal surface current distribution and the magnetic dipole pattern;
fig. 18 is a contact state, where d is 0 μm, when TM waves are perpendicularly incident to the metamaterial surface, the metamaterial metal surface current distribution and the electric dipole pattern;
fig. 19 is a graph of dipole moment components calculated from TM wave normal incidence values at d of 3 μm, where a represents the x-direction component of the ring dipole moment, denoted as Tx, a represents the x-direction component of the electric dipole moment, denoted as Px, and ● represents the z-direction component of the magnetic dipole moment, denoted as Mz.
Detailed Description
The first embodiment is as follows: with reference to fig. 1, the present embodiment is a terahertz metamaterial converter switchable between a ring dipole and a galvanic couple based on MEMS planar structure reconstruction, which includes a base silicon substrate 1, a comb-tooth electrostatic driving structure 2, a fixed metal structure array 3, a movable metal structure array 4, and a suspended silicon frame 5, where the comb-tooth electrostatic driving structure 2 and the suspended silicon frame 5 are disposed on the base silicon substrate 1, the suspended silicon frame 5 is connected to the comb-tooth electrostatic driving structure 2, and the suspended silicon frame 5 is disposed in a suspended manner, the fixed metal structure array 3 is disposed in the suspended silicon frame 5 and on the base silicon substrate 1, and the movable metal structure array 4 is connected to the suspended silicon frame 5 and disposed in a suspended manner; the fixed metal structure array 3 is composed of structural elements which are periodically arranged, the structural elements of the fixed metal structure array 3 are in an E-shaped structure, the movable metal structure array 4 is composed of structural elements which are periodically arranged, the structural elements of the movable metal structure array 4 are in an inverted E-shaped structure, the structural elements of the fixed metal structure array 3 and the structural elements of the movable metal structure array 4 are oppositely arranged in pairs, and the structural elements of the fixed metal structure array 3 and the structural elements of the movable metal structure array 4 which are oppositely arranged in pairs form a functional structural unit of the terahertz metamaterial which can be switched between coupling and galvanic couple.
The second embodiment is as follows: with reference to fig. 1 to 4, the present embodiment is different from the first embodiment in that: the structural element of the fixed metal structure array 3 consists of an E-shaped patterned metal element 3-1 and an E-shaped fixed silicon substrate 3-2, the E-shaped fixed silicon substrate 3-2 is arranged on the base silicon substrate 1, and the E-shaped patterned metal element 3-1 is arranged on the E-shaped fixed silicon substrate 3-2; the structural element of the movable metal structure array 4 consists of an inverse E-shaped patterned metal element 4-1 and an inverse E-shaped movable silicon substrate 4-2, the inverse E-shaped movable silicon substrate 4-2 is connected with a suspended silicon frame 5 and is arranged in a suspended mode, and the inverse E-shaped patterned metal element 4-1 is arranged on the inverse E-shaped movable silicon substrate 4-2; the structural parameters of the E-shaped patterned metal element 3-1 and the reverse E-shaped patterned metal element 4-1 are completely the same, and the E-shaped patterned metal element 3-1 and the reverse E-shaped patterned metal element 4-1 are arranged in parallel. The rest is the same as the first embodiment.
In the embodiment, the E-type patterned metal element 3-1 and the anti-E-type patterned metal element 4-1 in the functional structural unit of the terahertz metamaterial with switchable ring couples and galvanic couples form the structural unit of the metamaterial.
The third concrete implementation mode: with reference to fig. 1 to 4, the present embodiment is different from the first or second embodiment in that: the initial distance between the structural element of the fixed metal structure array 3 and the structural element of the movable metal structure array 4 in the functional structural unit of the terahertz metamaterial with the switchable ring pair and the galvanic couple is 3 microns, the movable metal structure array 4 is driven to translate in a plane by loading a driving voltage V on the electrode of the comb-tooth type electrostatic driving structure 2, so that the relative distance between the structural element of the fixed metal structure array 3 and the structural element of the movable metal structure array 4 in the functional structural unit of the terahertz metamaterial with the switchable ring pair and the galvanic couple is d, and d is greater than or equal to 0 micron and less than or equal to 3 microns. The others are the same as in the first or second embodiment.
The fourth concrete implementation mode: with reference to fig. 1 to 4, the present embodiment is different from the first to third embodiments in that: the length of a functional structural unit of the terahertz metamaterial with the switchable ring couples and galvanic couples is Qx, Qx is 210 μm, the width is Qy, Qy is 106 μm, the line widths of the E-type patterned metal element 3-1 and the E-type patterned metal element 4-1 are W, W is 10 μm, the length of a short side is L, L is 50 μm, the length of a long side is 2S, and S is 100 μm. The others are the same as the first to third embodiments.
The fifth concrete implementation mode: the embodiment is a preparation method of a terahertz metamaterial converter with switchable ring couples and galvanic couples based on MEMS planar structure reconstruction, which is specifically completed by the following steps:
firstly, depositing a silicon dioxide layer: preparing a silicon dioxide passivation layer 7 on the surface of the silicon 6 by using a material growth process;
secondly, patterning the photoresist mask of the anchor structure: uniformly coating a layer of photoresist on the surface of the silicon dioxide by using a mechanical spin coating process, and removing the photoresist in a photosensitive area during development after exposure, development and fixation to form a micro-pattern structure to obtain an anchor structure patterned photoresist mask; the photoresist is positive photoresist;
thirdly, forming an anchor structure: etching the silicon dioxide passivation layer 7 by using the anchor structure patterned photoresist as a mask by using an etching process to obtain an etched silicon dioxide passivation layer 7-1, and removing the photoresist by using a photoresist removing solution; secondly, etching the surface of the silicon 6 by taking the etched silicon dioxide passivation layer 7-1 as a mask, and removing the etched silicon dioxide passivation layer 7-1 to obtain etched silicon 6-1; the etching process is wet etching or dry etching;
fourthly, bonding and thinning the structural layer: bonding the etched silicon 6-1 with a base silicon substrate 1 by using a silicon-silicon bonding process, then coating a protective layer on the edge and the lower surface of the base silicon substrate, thinning the etched silicon 6-1 by using KOH solution wet etching, and removing the protective layer to obtain thinned silicon 6-2;
fifthly, patterning the metal structure unit: firstly, spin-coating photoresist on the surface of thinned silicon 6-2 by using a mechanical spin-coating process, and taking an E-shaped pattern array and an anti-E-shaped pattern array area as photosensitive areas through exposure, development and fixation to obtain a patterned photoresist; the photoresist is positive photoresist; depositing a metal layer, wherein the thickness of the metal layer is 0.2-0.4 mu m, removing the patterned photoresist by using a photoresist removing liquid, stripping the metal layer on the patterned photoresist, and only reserving the metal layer deposited in a photosensitive area, so that an E-shaped patterned metal element 3-1 array and an anti-E-shaped patterned metal element 4-1 array are deposited on the surface of the thinned silicon 6-2 to obtain a patterned metal metamaterial structure;
sixthly, patterning a photoresist mask: utilizing a mechanical spin coating process to spin a photoresist on the surface of the patterned metal metamaterial structure, and forming a micro-pattern structure of the comb-tooth type electrostatic driving structure 2, a micro-pattern structure of the suspended silicon frame 5, a micro-pattern structure of the fixed metal structure array 3 and a micro-pattern structure of the movable metal structure array 4 through exposure, development and fixation to obtain a photoresist mask pattern with a micro-pattern structure;
seventhly, etching silicon and releasing the MEMS structure: and taking the photoresist mask graph with the micro-graph structure as a mask, deeply etching silicon by utilizing a deep reactive ion etching technology, releasing the MEMS structure, and removing the photoresist by utilizing a dry method to realize the comb-tooth type electrostatic driving structure 2, the suspended silicon frame 5, the fixed metal structure array 3 and the movable metal structure array 4 so as to obtain the terahertz metamaterial converter based on the ring-couple and couple switchability of the MEMS planar structure reconstruction.
The sixth specific implementation mode: the present embodiment is different from the fifth embodiment in that: in the first step, the material growth process is epitaxy, chemical vapor deposition or thermal oxidation. The rest is the same as the fifth embodiment.
The seventh embodiment: the present embodiment differs from the fifth or sixth embodiment in that: and fifthly, the deposition is sputtering, vacuum evaporation or chemical vapor deposition, and the metal in the metal layer is Au, Cu or Al. The other is the same as the fifth or sixth embodiment.
The specific implementation mode is eight: the fifth to seventh embodiments are different from the fifth to seventh embodiments in that: in the fourth step, the mass fraction of KOH in the KOH solution is 40%. The rest is the same as the fifth to seventh embodiments.
The invention is not limited to the above embodiments, and one or a combination of several embodiments may also achieve the object of the invention.
The following tests were carried out to confirm the effects of the present invention
Example 1: with reference to fig. 1 to 9, a method for preparing a terahertz metamaterial converter switchable between a ring pair and a galvanic couple based on MEMS planar structure reconstruction is specifically completed according to the following steps:
firstly, depositing a silicon dioxide layer: preparing a silicon dioxide passivation layer 7 on the surface of the silicon 6 by using a material growth process;
secondly, patterning an anchor structure by using a photoresist mask: uniformly coating a layer of photoresist on the surface of the silicon dioxide by using a mechanical spin coating process, and removing the photoresist in a photosensitive area during development after exposure, development and fixation to form a micro-pattern structure to obtain an anchor structure patterned photoresist mask; the photoresist is positive photoresist;
thirdly, forming an anchor structure: etching the silicon dioxide passivation layer 7 by using the anchor structure patterned photoresist as a mask by using an etching process to obtain an etched silicon dioxide passivation layer 7-1, and removing the photoresist by using a photoresist removing solution; secondly, etching the surface of the silicon 6 by taking the etched silicon dioxide passivation layer 7-1 as a mask, and removing the etched silicon dioxide passivation layer 7-1 to obtain etched silicon 6-1; the etching process is wet etching or dry etching;
fourthly, bonding and thinning the structural layer: bonding the etched silicon 6-1 with a base silicon substrate 1 by using a silicon-silicon bonding process, then coating a protective layer on the edge and the lower surface of the base silicon substrate, then carrying out wet etching on the etched silicon 6-1 by using a KOH solution with the mass fraction of 40%, and removing the protective layer to obtain thinned silicon 6-2;
fifthly, patterning the metal structure unit: firstly, spin-coating photoresist on the surface of thinned silicon 6-2 by using a mechanical spin-coating process, and taking an E-shaped pattern array and an anti-E-shaped pattern array area as photosensitive areas through exposure, development and fixation to obtain a patterned photoresist; the photoresist is positive photoresist; depositing a metal layer, wherein the thickness of the metal layer is 0.2 mu m, removing the patterned photoresist by using a photoresist removing liquid, simultaneously stripping the metal layer on the patterned photoresist, and only reserving the metal layer deposited in a photosensitive area, namely depositing an E-shaped patterned metal element 3-1 array and an anti-E-shaped patterned metal element 4-1 array on the surface of the thinned silicon 6-2 to obtain a patterned metal metamaterial structure;
sixthly, patterning a photoresist mask: utilizing a mechanical spin coating process to spin a photoresist on the surface of the patterned metal metamaterial structure, and forming a micro-pattern structure of the comb-tooth type electrostatic driving structure 2, a micro-pattern structure of the suspended silicon frame 5, a micro-pattern structure of the fixed metal structure array 3 and a micro-pattern structure of the movable metal structure array 4 through exposure, development and fixation to obtain a photoresist mask pattern with a micro-pattern structure;
seventhly, etching silicon and releasing the MEMS structure: and taking the photoresist mask graph with the micro-graph structure as a mask, deeply etching silicon by utilizing a deep reactive ion etching technology, releasing the MEMS structure, and removing the photoresist by utilizing a dry method to realize the comb-tooth type electrostatic driving structure 2, the suspended silicon frame 5, the fixed metal structure array 3 and the movable metal structure array 4 so as to obtain the terahertz metamaterial converter based on the ring-couple and couple switchability of the MEMS planar structure reconstruction.
The material growth process in the first step is chemical vapor deposition; the Chemical Vapor Deposition (CVD) utilizes the reaction of silane and oxygen to accomplish undoped SiO2And (4) depositing a thin film. The specific reaction process is that the reaction is carried out by a large amount of N2Gas diluted SiH4When the mixed gas with the excessive oxygen is heated to 250-450 ℃, the silane reacts with the oxygen to generate silicon dioxide which is deposited on the surface of the silicon wafer, and the deposition thickness of the obtained silicon dioxide is 300 nm.
And fifthly, the deposition is sputtering, and the metal in the metal layer is Al. The sputtering method is a method for physical vapor deposition of a film, and is characterized in that ions with charges have certain kinetic energy after being accelerated in an electric field, the ions are guided to a target electrode (Al) to be sputtered, under the condition of proper ion energy, target atoms (Al atoms) are sputtered out in the collision process of the incident ions and the target surface atoms, the sputtered Al atoms have certain kinetic energy and are emitted to a substrate along a certain direction, and therefore the film is deposited on the upper surface of the substrate, and the deposition thickness of metal Al is 0.2 mu m.
The terahertz metamaterial converter based on the ring pair and the couple switchable based on the MEMS planar structure reconstruction comprises a base silicon substrate 1, a comb-tooth type electrostatic driving structure 2, a fixed metal structure array 3, a movable metal structure array 4 and a suspended silicon frame 5, wherein the comb-tooth type electrostatic driving structure 2 and the suspended silicon frame 5 are arranged on the base silicon substrate 1, the suspended silicon frame 5 is connected with the comb-tooth type electrostatic driving structure 2, the suspended silicon frame 5 is arranged in a suspended mode, the fixed metal structure array 3 is arranged in the suspended silicon frame 5 and on the base silicon substrate 1, and the movable metal structure array 4 is connected with the suspended silicon frame 5 and arranged in a suspended mode; the fixed metal structure array 3 is composed of structural elements which are periodically arranged, the structural elements of the fixed metal structure array 3 are in an E-shaped structure, the movable metal structure array 4 is composed of structural elements which are periodically arranged, the structural elements of the movable metal structure array 4 are in an inverted E-shaped structure, the structural elements of the fixed metal structure array 3 and the structural elements of the movable metal structure array 4 are oppositely arranged in pairs, and the structural elements of the fixed metal structure array 3 and the structural elements of the movable metal structure array 4 which are oppositely arranged in pairs form a functional structural unit of the terahertz metamaterial which can be switched between coupling and galvanic couple; the structural element of the fixed metal structure array 3 consists of an E-shaped patterned metal element 3-1 and an E-shaped fixed silicon substrate 3-2, the E-shaped fixed silicon substrate 3-2 is arranged on the base silicon substrate 1, and the E-shaped patterned metal element 3-1 is arranged on the E-shaped fixed silicon substrate 3-2; the structural element of the movable metal structure array 4 consists of an inverse E-shaped patterned metal element 4-1 and an inverse E-shaped movable silicon substrate 4-2, the inverse E-shaped movable silicon substrate 4-2 is connected with a suspended silicon frame 5 and is arranged in a suspended mode, and the inverse E-shaped patterned metal element 4-1 is arranged on the inverse E-shaped movable silicon substrate 4-2; the structural parameters of the E-shaped patterned metal element 3-1 and the reverse E-shaped patterned metal element 4-1 are completely the same, and the E-shaped patterned metal element 3-1 and the reverse E-shaped patterned metal element 4-1 are arranged in parallel; the initial distance between the structural element of the fixed metal structure array 3 and the structural element of the movable metal structure array 4 in the functional structural unit of the terahertz metamaterial with the switchable ring pair and the galvanic couple is 3 microns, the movable metal structure array 4 is driven to perform plane translation by loading a driving voltage V on the electrode of the comb-tooth type electrostatic driving structure 2, so that the relative distance between the structural element of the fixed metal structure array 3 and the structural element of the movable metal structure array 4 in the functional structural unit of the terahertz metamaterial with the switchable ring pair and the galvanic couple is d, and d is more than or equal to 0 micron and less than or equal to 3 microns; the length of a functional structural unit of the terahertz metamaterial with the switchable ring couples and galvanic couples is Qx, Qx is 210 μm, the width is Qy, Qy is 106 μm, the line widths of the E-type patterned metal element 3-1 and the E-type patterned metal element 4-1 are W, W is 10 μm, the length of a short side is L, L is 50 μm, the length of a long side is 2S, and S is 100 μm.
Detecting the terahertz metamaterial converter with switchable ring couples and galvanic couples reconstructed based on the MEMS planar structure in embodiment 1 under the normal incidence of TE waves, and combining with FIGS. 10 to 14, wherein FIG. 10 is a separation state, and a transmission curve graph of the surface of the metamaterial with the normal incidence of the TE waves when d is from 3 μm to 1 μm; FIG. 11 is a transmission curve diagram of a TE wave vertically incident to a metamaterial surface when d is 0 μm; FIG. 12 is a diagram showing a metamaterial metal surface current distribution and a magnetic dipole pattern in an isolated state, where d is 3 μm, when a TE wave is perpendicularly incident on the metamaterial surface; fig. 13 is a contact state, d is 0 μm, when TE wave vertically enters the metamaterial surface, the metamaterial metal surface current distribution and the electric dipole directional diagram; fig. 14 is a graph of dipole moment components calculated from TE wave normal incidence values at d of 3 μm, where a represents a component of ring dipole moment in the y direction, denoted by Ty, a represents a component of electric dipole moment in the y direction, denoted by Py, and ● represents a component of magnetic dipole moment in the x direction, denoted by Mx. As can be seen from FIG. 10, under the normal incidence of TE wave, when d is from 3 μm to 1 μm, two resonances occur in the frequency band of 0.05-1.2 THz, and the resonance frequencies are 0.48THz and 0.922THz respectively. The first resonance is a ring dipole resonance and the second resonance is an electric dipole resonance. The amplitude of the first ring dipole resonance becomes progressively shallower as the distance d becomes progressively smaller. As can be seen from fig. 11, when a voltage is applied to the comb-teeth electrostatic driving structure under the vertical incidence of the TE wave, the movable metal structure array 4 moves in a plane to be in contact with the fixed metal structure array 3, that is, d is 0 μm, and at this time, only one resonance occurs in the frequency band of 0.05 to 1.2THz, and the resonance frequency is 0.48THz, which is the same as the first resonance frequency when d is 3 μm. As can be seen from fig. 12, when the movable metal structure array 4 and the fixed metal structure array 3 are in a separated state and d is 3 μm under TE wave incidence, the metal surface current at the first resonance point is distributed in two loops with opposite directions, and the magnetic dipole is formed
The opposite direction shows a ring dipole response mode. From 13, when the movable metal structure array 4 and the fixed metal structure array 3 are in contact with each other under TE wave incidence, the metal surface current at the resonance point 0.48THz points in the same direction, and the electric dipole is formed
The direction is the same, and the electric dipole response mode is shown. As can be seen from fig. 14, at the normal incidence of the TE wave, when d is 3 μm, the ring dipole moment component Ty is significantly enhanced at the resonance frequency of 0.48 THz. Therefore, with reference to fig. 10 to 14, the terahertz metamaterial converter switchable between the ring pair and the galvanic couple based on the MEMS planar structure reconstruction can realize amplitude modulation of the ring dipole, dual-band and single-band filtering conversion, and switching of the ring pair and the galvanic couple at the same frequency.
Detecting the terahertz metamaterial converter based on ring-couple and couple switchable of the reconstruction of the MEMS planar structure in embodiment 1 under the normal incidence of the TM wave, and combining with FIGS. 15 to 19, FIG. 15 is a transmission curve graph of the surface of the TM wave normal incidence metamaterial when d is 3 μm; fig. 16 is a transmission curve diagram of TM waves perpendicularly incident to the metamaterial surface when d is 0 μm; fig. 17 is a separated state, where d is 3 μm, when TM waves are perpendicularly incident to the metamaterial surface, the metamaterial metal surface current distribution and the magnetic dipole pattern; fig. 18 is a contact state, where d is 0 μm, when TM waves are perpendicularly incident to the metamaterial surface, the metamaterial metal surface current distribution and the electric dipole pattern; fig. 19 is a graph of dipole moment components calculated from TM wave normal incidence values at d of 3 μm, where a represents the x-direction component of the ring dipole moment, denoted as Tx, a represents the x-direction component of the electric dipole moment, denoted as Px, and ● represents the z-direction component of the magnetic dipole moment, denoted as Mz. As can be seen from fig. 15, at the normal incidence of the TM wave, when d is 3 μm, two resonances occur in the 0.05 to 1.2THz frequency band, and the resonance frequencies are 0.196THz and 0.398THz, respectively. As can be seen from fig. 16, under the condition of TM wave vertical incidence, a voltage is applied to the comb-tooth electrostatic driving structure, so that the movable metal structure array 4 moves in a plane to be in contact with the fixed metal structure array 3, that is, d is 0 μm, and only one harmonic occurs in the frequency band of 0.05 to 1.2THzThe resonance frequency was 0.405 THz. As can be seen from fig. 17, when the movable metal structure array 4 and the fixed metal structure array 3 are in a separated state and d is 3 μm under the normal incidence of the TM wave, the metal surface current at the first resonance point is distributed in a ring shape with two same directions, and the magnetic dipole is formed
The direction is the same, and the magnetic dipole response mode is shown. As can be seen from fig. 18, when the movable metal structure array 4 and the fixed metal structure array 3 are in a contact state and d is 0 μm under the normal incidence of the TM wave, the metal surface current at the resonance point 0.405THz points in the same direction, and the electric dipole is configured as an electric dipole
The direction is the same, and the electric dipole response mode is shown. As can be seen from fig. 19, at TM wave normal incidence, when d is 3 μm, the magnetic dipole moment component Mz is significantly enhanced at the resonance frequency of 0.196 THz. With reference to fig. 15 to 19, the terahertz metamaterial converter based on MEMS planar structure reconstruction and switchable between a ring pair and a galvanic couple can realize dual-band and single-band filtering conversion.
Claims (6)
1. A terahertz metamaterial converter with switchable ring couples and galvanic couples based on MEMS planar structure reconstruction is characterized by comprising a base silicon substrate (1), a comb-tooth-shaped electrostatic driving structure (2), a fixed metal structure array (3), a movable metal structure array (4) and a suspended silicon frame (5), wherein the comb-tooth-shaped electrostatic driving structure (2) and the suspended silicon frame (5) are arranged on the base silicon substrate (1), the suspended silicon frame (5) is connected with the comb-tooth-shaped electrostatic driving structure (2), the suspended silicon frame (5) is arranged in a suspended mode, the fixed metal structure array (3) is arranged in the suspended silicon frame (5) and on the base silicon substrate (1), and the movable metal structure array (4) is connected with the suspended silicon frame (5) and arranged in the suspended mode; the terahertz metamaterial comprises a fixed metal structure array (3), a movable metal structure array (4) and a movable metal structure array (4), wherein the fixed metal structure array (3) consists of structural elements which are periodically arranged, the structural elements of the fixed metal structure array (3) are in an E-shaped structure, the movable metal structure array (4) consists of structural elements which are periodically arranged, the structural elements of the movable metal structure array (4) are in an inverted E-shaped structure, the structural elements of the fixed metal structure array (3) and the structural elements of the movable metal structure array (4) are oppositely arranged in pairs, and the structural elements of the fixed metal structure array (3) and the structural elements of the movable metal structure array (4) which are oppositely arranged in pairs form a functional structural unit of the terahertz metamaterial with switchable ring pairs and galvanic couples;
the structural element of the fixed metal structure array (3) consists of an E-shaped patterned metal element (3-1) and an E-shaped fixed silicon substrate (3-2), the E-shaped fixed silicon substrate (3-2) is arranged on the base silicon substrate (1), and the E-shaped patterned metal element (3-1) is arranged on the E-shaped fixed silicon substrate (3-2); the structural element of the movable metal structure array (4) consists of an inverse E-shaped patterned metal element (4-1) and an inverse E-shaped movable silicon substrate (4-2), the inverse E-shaped movable silicon substrate (4-2) is connected with a suspended silicon frame (5) and is arranged in a suspended mode, and the inverse E-shaped patterned metal element (4-1) is arranged on the inverse E-shaped movable silicon substrate (4-2); the structural parameters of the E-shaped patterned metal element (3-1) and the reverse E-shaped patterned metal element (4-1) are completely the same, and the E-shaped patterned metal element (3-1) and the reverse E-shaped patterned metal element (4-1) are arranged in parallel.
2. The terahertz metamaterial converter based on MEMS planar structure reconstruction and capable of switching between ring pair and couple is characterized in that the initial distance between the structural elements of the fixed metal structure array (3) and the structural elements of the movable metal structure array (4) in the functional structural unit of the terahertz metamaterial capable of switching between ring pair and couple is 3 μm, the movable metal structure array (4) is driven to perform planar translation by loading a driving voltage V on the electrodes of the comb-tooth-shaped electrostatic driving structure (2), and the relative distance between the structural elements of the fixed metal structure array (3) and the structural elements of the movable metal structure array (4) in the functional structural unit of the terahertz metamaterial capable of switching between ring pair and couple is d, wherein d is more than or equal to 0 μm and less than or equal to 3 μm.
3. The terahertz metamaterial converter based on MEMS planar structure reconstruction and capable of switching between ring pair and couple pair is characterized in that the functional structural unit of the terahertz metamaterial based on MEMS planar structure reconstruction has the length Qx, the length Qx is 210 μm, the width Qy, the length Qy is 106 μm, the line width of the E-type patterned metal element (3-1) and the line width of the reverse E-type patterned metal element (4-1) are W, the W is 10 μm, the short side length is L, the L is 50 μm, the long side length is 2S, and the S is 100 μm.
4. The preparation method of the terahertz metamaterial converter based on the MEMS planar structure reconstruction and capable of switching between the ring pair and the galvanic couple is characterized by comprising the following steps of:
firstly, depositing a silicon dioxide layer: preparing a silicon dioxide passivation layer (7) on the surface of the silicon (6) by using a material growth process;
secondly, patterning the photoresist mask of the anchor structure: uniformly coating a layer of photoresist on the surface of the silicon dioxide by using a mechanical spin coating process, and removing the photoresist in a photosensitive area during development after exposure, development and fixation to form a micro-pattern structure to obtain an anchor structure patterned photoresist mask; the photoresist is positive photoresist;
thirdly, forming an anchor structure: etching the silicon dioxide passivation layer (7) by using the anchor structure patterned photoresist as a mask by using an etching process to obtain an etched silicon dioxide passivation layer (7-1), and removing the photoresist by using a photoresist removing liquid; secondly, etching the surface of the silicon (6) by taking the etched silicon dioxide passivation layer (7-1) as a mask, and removing the etched silicon dioxide passivation layer (7-1) to obtain etched silicon (6-1); the etching process is wet etching or dry etching;
fourthly, bonding and thinning the structural layer: bonding the etched silicon (6-1) with a base silicon substrate (1) by using a silicon-silicon bonding process, then coating a protective layer on the edge and the lower surface of the base silicon substrate (1), thinning the etched silicon (6-1) by using KOH solution wet etching, and removing the protective layer to obtain thinned silicon (6-2);
fifthly, patterning the metal structure unit: firstly, spin-coating photoresist on the surface of thinned silicon (6-2) by using a mechanical spin-coating process, and taking an E-shaped pattern array and an anti-E-shaped pattern array area as photosensitive areas through exposure, development and fixation to obtain patterned photoresist; the photoresist is positive photoresist; depositing a metal layer, wherein the thickness of the metal layer is 0.2-0.4 mu m, removing the patterned photoresist by using a photoresist removing liquid, simultaneously stripping the metal layer on the patterned photoresist, and only reserving the metal layer deposited in a photosensitive area, namely depositing an E-shaped patterned metal element (3-1) array and an anti-E-shaped patterned metal element (4-1) array on the surface of the thinned silicon (6-2) to obtain a patterned metal metamaterial structure; the deposition is sputtering, vacuum evaporation or chemical vapor deposition, and the metal in the metal layer is Au, Cu or Al;
sixthly, patterning a photoresist mask: utilizing a mechanical spin coating process to spin a photoresist on the surface of the patterned metal metamaterial structure, and forming a micro-pattern structure of the comb-tooth type electrostatic driving structure (2), a micro-pattern structure of the suspended silicon frame (5), a micro-pattern structure of the fixed metal structure array (3) and a micro-pattern structure of the movable metal structure array (4) through exposure, development and fixation to obtain a photoresist mask pattern with a micro-pattern structure;
seventhly, etching silicon and releasing the MEMS structure: and taking the photoresist mask graph with the micro-graph structure as a mask, deeply etching silicon by utilizing a deep reactive ion etching technology, releasing the MEMS structure, and removing the photoresist by utilizing a dry method to realize the comb-tooth type electrostatic driving structure (2), the suspended silicon frame (5), the fixed metal structure array (3) and the movable metal structure array (4) so as to obtain the terahertz metamaterial converter capable of switching the ring pair and the galvanic couple based on the reconstruction of the MEMS planar structure.
5. The method for preparing the terahertz metamaterial converter based on the ring-couple and galvanic-couple switchability of the MEMS planar structure reconstruction as claimed in claim 4, wherein the material growth process in the first step is epitaxy, chemical vapor deposition or thermal oxidation.
6. The method for preparing the terahertz metamaterial converter based on the MEMS planar structure reconstruction and capable of being switched between the ring pair and the galvanic couple according to claim 4, wherein the mass fraction of KOH in the KOH solution in the fourth step is 40%.
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