CN114710132B - Elastic wave topological insulator with electrically adjustable frequency and functional assembly - Google Patents

Abstract

The application provides an elastic wave topological insulator with electrically adjustable frequency and a functional component, the elastic wave topological insulator comprises a substrate and a two-dimensional material layer, the two-dimensional material layer is tiled on the substrate, a honeycomb lattice pattern is arranged on the surface of the substrate, the two-dimensional material layer comprises a first area and a second suspended area, the first area is in contact with the substrate, the second area is mismatched with the acoustic impedance between the substrate, and the two-dimensional material layer is constructed into a phonon crystal structure. The application can realize the frequency electric adjustable of the elastic wave topological insulator.

Description

Elastic wave topological insulator with electrically adjustable frequency and functional assembly

Technical Field

The application relates to the field of atomic films, in particular to an elastic topological insulator with electrically adjustable frequency and a functional component.

Background

There is a constant need for precise control of elastic waves in the spatial and frequency domains for practical device applications. Elastic waves have extremely low transmission losses at higher frequencies than acoustic waves in fluids (e.g., aero-acoustic), and are easier to integrate into solid state micro/nano-scale systems. The device area using elastic waves is 5 orders of magnitude smaller than electromagnetic waves at the same operating frequency as compared to electromagnetic waves. These major advantages have led to the widespread use of Surface Acoustic Wave (SAWs) or Bulk Acoustic Wave (BAWs) devices in modern signal processing and sensors. In the last decade, topological Insulators (TI) have rapidly expanded from electronics to classical wave systems, mainly due to the fact that the photons/phonons at their boundaries have "spin-momentum locked" features, bringing about revolutionary transmission channels.

To date, elastomeric topological insulators have been implemented in both macroscopic and microscopic systems, such as those elastomeric systems that exhibit some unprecedented functional components in perforated plates, happy-like high-k planks, and suspended nanofilms. The first order elastic topology insulator provides a highly desirable one-dimensional elastic waveguide technique (1) even if the waveguides are rotated arbitrarily or internally defective, the transmitted energy is not lost. (2) Such a waveguide supports broadband operating frequencies without any dispersion. The second order elastic topology insulator provides a state of zero dimension in space and scattered frequency, so that the elastic wave can be purposefully positioned at a specific frequency and location, for example, at a corner or intersection of a topological boundary. These ideal one-dimensional waveguides and 0-dimensional local area technologies are largely enriched in the means by which one can control elastic waves, and with this, some functional components, such as elastic topology resonators, filters, multiplexers, etc., are also produced. After the implementation of elastic topology insulators, an explicit research direction towards device applications is to miniaturize them and to achieve electrical tuning of frequencies, which is also highly desirable for the advanced signal processor, sensor and SAW and BAW industries. Recently, researchers have demonstrated that some tunable, reconfigurable elastic topology insulators, such as Darabi et al, have experimentally achieved reconfigurable electroacoustic topology insulators by using connecting programmable capacitive switches in a structural array of piezoelectric patches; zhou et al propose an implementation of an adjustable elastic topology interface in a piezoelectric rod system with variable voltage boundaries. These components require complex external circuitry and remain limited to macroscopic dimensions. The solution for chip-level electrically tunable elastic TI is still lacking.

Disclosure of Invention

The application aims to provide an elastic wave topological insulator and a functional component, so as to realize the frequency electric adjustability of the elastic wave topological insulator.

According to a first aspect of the application, an elastic wave topology insulator comprises: the two-dimensional material layer is tiled on the substrate, a honeycomb lattice pattern is arranged on the surface of the substrate, the two-dimensional material layer comprises a first area and a second area, the first area is in contact with the substrate, the second area is in suspension with the substrate, acoustic impedance mismatch is caused between the second area and the substrate, and the two-dimensional material layer is constructed into a phonon crystal structure.

Further, the honeycomb lattice pattern is an array formed by hexagonal single cells, each single cell comprises six round holes which are intersected in sequence, and the distances between the centers of the six round holes in each single cell and the centers of the single cells where the six round holes are located are equal.

Further, the honeycomb lattice pattern is a topologically mediocre lattice or a topologically non-mediocre lattice.

Further, the substrate is made of one of the following materials: SU-8 polymer, silicon dioxide, and piezoelectric GaAs.

Further, the two-dimensional material layer is made of graphene.

According to a second aspect of the application, a functional assembly comprises said elastic wave topology insulator.

Further, the functional component is a beam splitter.

Further, the functional component is a resonator.

Further, the functional component is a filter.

Further, the functional component is a multiplexer.

According to the elastic wave topological insulator and the functional component, the substrate and the two-dimensional material layer are paved on the substrate, the surface of the substrate is provided with the honeycomb lattice pattern, the two-dimensional material layer comprises a first area contacted with the substrate and a second suspended area, acoustic impedance mismatch between the second area and the substrate is achieved, the two-dimensional material layer is constructed into a phonon crystal structure, and the two-dimensional material layer is generally provided with electromechanical sensitivity, so that the mechanical property of the two-dimensional material layer can be easily adjusted by introducing grid voltage to the two-dimensional material layer, and from the aspect of adjustability, external light, magnetism, heat, gas and the like can be used for adjusting the device.

Other characteristic features and advantages of the application will become apparent from the following description of exemplary embodiments, which is to be read with reference to the accompanying drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description, serve to explain the principles of the application. In the drawings, like reference numerals are used to identify like elements. The drawings, which are included in the description, illustrate some, but not all embodiments of the application. Other figures can be derived from these figures by one of ordinary skill in the art without undue effort.

FIGS. 1 a-1 c are a schematic structural view, a top structural view and a side structural view, respectively, of an embodiment of an acoustic wave topology insulator according to the present application;

FIGS. 2 a-2 c are photonic crystal elastic wave dispersion curves of a substrate of an embodiment of an elastic wave topology insulator of the present application;

FIG. 2d is a plot of eigenfrequency as a function of w for an embodiment of an elastic wave topology insulator of the present application above and below the bandgap at Γ;

FIGS. 3a and 3b respectively correspond to the band structures of the elastic wave insulator at distances of 5.5 μm and 6.6 μm from the center of the circular hole;

figures 3c and 3d correspond to the corresponding eigenmodes at the first three energy band high symmetry points of the topologically mediocre and topologically non-mediocre lattices, respectively;

FIG. 4a is a schematic diagram of an elastic TI interface;

FIG. 4b is a band structure calculated from the TI boundary in FIG. 4 a;

FIGS. 4 c-4 e are schematic diagrams of elastic function devices made of TI borders;

FIGS. 5a and 5b are projected energy band diagrams of a zigzag-type and deformed armchair-type interface between an elastic wave topology insulator and a normal insulator, respectively;

FIG. 5c is a top view and a bottom view of a supercell structure used in calculation of the zigzag and deformed armchair interfaces, respectively;

FIG. 6a is a schematic diagram of a quadrilateral phonon crystal formed by the intersection of two types of elastic insulators;

FIG. 6b is a detail view of the center of the crisscross quadrilateral photonic crystal shown in FIG. 6 a;

FIG. 6c is a characteristic frequency spectrum of the quadrilateral phononic crystal of FIG. 6a, wherein points, circles and stars represent body states, boundary states and angle states, respectively;

FIG. 6d is an enlarged view of a portion of the dashed box of FIG. 6 c;

FIG. 6e is a graph of the displacement field distribution of an elastic wave in a two-dimensional state with a frequency of 67.57MHz;

FIG. 6f is a graph of the elastic wave displacement field distribution in one-dimensional boundary state, at 71.167MHz;

FIG. 6g is a graph of the displacement field of an elastic wave in the zero-dimensional angular state, with a frequency of 78.31MHz;

FIG. 7a is a schematic diagram of the introduction of twist and bend structures in a quadrilateral phononic crystal;

FIG. 7b is a characteristic frequency spectrum of a quadrilateral phonon crystal with a defect structure;

FIG. 8a is a schematic diagram of a dual port bandpass filter based on 0D angle state;

FIG. 8b is a transmission spectrum of a dual port bandpass filter based on the 0D angle state;

FIG. 8c is a transmission spectrum of a 0D angular based dual port bandpass filter around 0D angular frequency;

FIG. 8D is an elastic field distribution of 0D angular excitation in a 0D angular based dual port bandpass filter;

FIG. 9a is a schematic diagram of the introduction of a gate voltage on the elastic TI;

FIG. 9b is a plot of Vg versus frequency for an elastic double Dirac point;

fig. 9c is a transmission spectrum at different gate voltages around the operating frequency of the high Q bandpass filter.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application. It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be arbitrarily combined with each other.

The inventors found that: the atomic film (two-dimensional material) not only has excellent mechanical properties, but also has outstanding properties in the aspects of electricity, light, magnetism and the like, so that the properties of the atomic film can be adjusted through electrostatic, optoacoustic or magnetoacoustic coupling, and the atomic film becomes an ideal material of an adjustable device. Phonon crystal (PnC) waveguides made of two-dimensional materials, in particular boron nitride, on patterned substrates were proposed and experimentally verified. Thus, by using a 2D (two-dimensional) material fixed on a patterned substrate, an electrically tunable elastic wave topology insulator is possible in practical applications. In embodiments of the present application, a two-dimensional material is tiled on a honeycomb patterned substrate to form an elastic wave topology insulator. Due to acoustic impedance mismatch between the suspended 2D material and the rigid substrate, elastic topological boundary states and angular states can be realized in the two-dimensional material, and meanwhile, some functional components such as any-direction waveguides, beam splitters, resonators and the like can be realized. Notably, due to the electromechanical sensitivity of these 2D materials, the frequency of all of these elastic wave components is electrically tunable. For example, an operating frequency shift of 7.26% can be achieved in a dual port high Q bandpass filter by simply applying a gate voltage of 5V. Such elastic topology materials and related devices can greatly promote the development of 2D material-based nanoelectromechanical systems and may be directly applied in modern wireless communication technologies at radio or microwave frequencies.

As shown in fig. 1a to 1c, an elastic wave topology insulator of the present application includes: the two-dimensional material layer is tiled on the substrate, a honeycomb lattice pattern is arranged on the surface of the substrate, the two-dimensional material layer comprises a first area and a second area, the first area is in contact with the substrate, the second area is in suspension with the substrate, acoustic impedance mismatch is caused between the second area and the substrate, and the two-dimensional material layer is constructed into a phonon crystal structure.

Specifically, the substrate of the elastic wave topology insulator structure is a substrate with a surface pattern designed as a honeycomb lattice pattern to provide the periodicity and symmetry of the system in order to form dirac points. To form a topological insulator, brillouin zone folding is introduced in the patterned substrate [12,25]This is a widely used method of constructing pseudo-spins and further achieving energy band inversion. The honeycomb lattice pattern is specifically an array of hexagonal cells, each cell comprising six circular holes intersecting in turn. The hexagon in fig. 1a represents a single cell (side a), and the circles in the single cell represent overlapping circular holes (radius r). The distance between the center of each round hole and the center of the unit cell, namely the hole center distance, is marked as w, and the distances between the centers of the six round holes in each unit cell and the centers of the unit cells where the six round holes are located are equal. Such patterned substrates are fully scalable in size. In this embodiment, the geometric parameters of the unit cell may be set to the micrometer scale, where a and r are eachAnd 4.5 μm. Such patterned substrates may be prepared by selective surface etching on a variety of thin film composites or directly etched on single crystals or polycrystals. Such substrate composites are very widely selected, for example SU-8 polymer on Si, silica on sapphire or piezoelectric GaAs on AlGaAs. The present embodiment selects a substrate of heavily doped silicon on which silicon dioxide is deposited as a further numerical modeling material for subsequent application of the gate voltage.

As shown in fig. 1b, a layer of two-dimensional material is laid on such a surface patterned substrate to form the whole structure of the elastic wave topology insulator. There is no particular requirement in the selection of two-dimensional materials, as the mechanical properties are of major concern. In this embodiment, the most common two-dimensional material graphene is selected. According to literature, graphene has a density, thickness, young's modulus, poisson's ratio and internal stress of 2.267g/cm, respectively ³ 0.335nm,1TPa,0.165,0.65N/m. Now, a complete junctionThe build model is created. Obviously, the 2D material may be divided into two areas according to the patterned area, one being the area in contact with the substrate and one being the suspended area, which is completely continuous because of the overlapping circular holes. When the two-dimensional material is in close contact with the substrate, the elastic wave propagates only in the levitation region due to the mismatch in acoustic impedance between the levitated 2D material and the rigid substrate. Thus, such a continuously atomically thin two-dimensional material builds up a phonon crystal structure.

FIGS. 2 a-2 c are photonic crystal elastic wave dispersion curves of a substrate of an embodiment of an elastic wave topology insulator of the present application; wherein the distances w from the circular holes to the center of the honeycomb structure in fig. 2 a-2 c are 5.5 μm, 6 μm, and 6.6 μm, respectively. FIG. 2d is a plot of eigenfrequency as a function of w above and below the bandgap at Γ point for an embodiment of an elastomer wave topology insulator according to the present application; wherein, the lines A and B in the middle chart of FIG. 2d respectively represent the patterns p (p _x And p _y ) And d (d) _xy And d _x ² _-y ² ) The method comprises the steps of carrying out a first treatment on the surface of the The left and right panels in fig. 2d show the planar field distribution of the p and d modes at 5.5 μm and 6.6 μm, respectively.

The band structure of the phonon crystal was obtained by pre-stressing it at the membrane-mechanical module using COMSOL Multiphysics, as shown in fig. 2 b. About 68.5MHz, there is an elastic double dirac at the f point. The phonon crystal is still a standard honeycomb lattice, which is a dirac-like semi-metal that elastic waves can propagate inside when the hole center distance satisfies w=a/Γv3=6 μm. As w increases or decreases, the degeneracy of the dual dirac cone disappears and a resilient band gap is then created, as shown in fig. 2 d. This makes PnC two types of insulators, as the energy band structure formed by the increase and decrease of w is reversed. For example, in the band structure shown in fig. 2a, where w=5.5 μm, the phonon crystal produces an elastic band gap of about 5MHz around the original dirac cone, and there are two different types of bulk modes at the high and low frequencies of the band gap, named d-mode and p-mode, respectively, just like electron spin. Parity symmetry about the x or y axis based on their eigenstatesThe d-mode can be classified as d _xy and d _x ² _-y ² While p-mode can be divided into p _x And p _y This lattice is called the topologically mediocre lattice. Accordingly, fig. 2c is an energy band structure where w is equal to 6.6 μm, and now PnC also has a band gap of 5MHz at the same frequency, but the p and d modes are diametrically opposed, the lattice being topologically non.

The topological phase change can be characterized by a dipole moment P. According to the high symmetry point C ₂ The rotation characteristic value, dipole moment P, can be determined by equation (1).

Wherein eta ⁿ (k) Is the characteristic value (+ -1) of C2 rotation of the nth energy band at K point, C of high symmetry K point ₂ The rotation characteristic value is identified by + -1. As with the labels of fig. 3a and 3b, the topological average lattice (w=5.5 μm) has a dipole moment of 0 for all three energy bands. In contrast, the dipole moments of the three energy bands of the topologically non-mediocre lattice (w=6.6 μm) are 1/2,0, and 1/2, respectively. These non-zero dipole moments ensure the existence of one-dimensional boundary states of the topology. That is, the energy bands of the two insulators are reversed, and when the topological average lattice is in contact with the non-average lattice, a topological phase change occurs to generate a boundary state.

From the above theoretical analysis, to verify the existence of one-dimensional boundary states (the main feature of the topological insulator is the corresponding relationship of the body boundaries), an interface is constructed between the two elastic insulators as shown in fig. 4a, and the super-primitive (super-unit) structure used for calculating the projection energy band is marked by a dashed area box. The band structure is shown in fig. 4 b. In calculation, fourier periodic boundary conditions and fixed boundaries are set up in the horizontal and vertical directions, respectively. It can be seen from the projected energy bands that two boundary-state energy bands occur in the previous energy band, each supporting unidirectional transmission of elastic waves at the interface. These two bands are so-called helical boundary states, and the propagation direction of the waves they support will combine with the pseudo-spins they have, the quantum spin hall effect, which is a boundary feature of the topological insulator.

To demonstrate the characteristics of spin momentum locking and their excellent performance of these boundary states, several elastic wave prototype devices were shown, including (1) elastic waveguides, (2) elastic beam splitters, and (3) coupled waveguide ring resonators, as shown in fig. 4 c-4 e, respectively. Fig. 4 c-4 e show elastic function devices made of TI boundaries, fig. 4c shows arbitrary waveguides, fig. 4d shows beam splitters, and fig. 4e shows critical coupling waveguides with calculated frequencies of 69MHz,69MHz and 69.893MHz, respectively.

In the waveguide, the broadband elastic wave can be bent by an arbitrary angle, for example, 120 ° as shown in the drawing, without back scattering. In the beam splitter, after the elastic wave is incident from the source port, the wave propagates mainly to output ports 1 and 3, but rarely to port 2, because ports 1 and 3 support the same pseudo-rotation +1/2, while port 2 supports the opposite pseudo-rotation-1/2 in the incident direction. In the coupled waveguide ring resonator, at the resonance frequency, the elastic wave entering the ring resonator from the waveguide can be completely confined therein and does not flow out, thereby making the entire system an excellent two-port band-stop filter. Until TI theory was established, none of these functional devices for elastic waves existed, which fully demonstrated the advantages of TI.

A boundary state of the band gap which is hardly visible has been achieved by the above embodiments. However, to form a higher order topology, a boundary state with a large gap needs to be formed. By the design of a specific scheme, a high-order topological state, namely a zero-dimensional angular state, is demonstrated in a 2D system. The specific scheme is realized by increasing the degree of fracture symmetry, and the distance from the round hole to the center of the honeycomb structure can be continuously increased or decreased in the elastic wave structure.

The distances of the lattice and lattice-compressing and lattice-expanding circular holes from the center of the honeycomb structure in the previous build-up boundary state were chosen to be 5.5 μm and 6.6 μm, respectively. Where the two values are reduced or increased to 5 μm and 7.2 μm, respectively. Then, the projected bands of the zigzag-type and deformed armchair-type interfaces are calculated as shown in fig. 5a and 5b, respectively. The supercell structure of the zigzag-type and deformed armchair-type interfaces used in the calculation is shown in FIG. 5 c. The Floquet periodic boundary condition and the fixed boundary condition are used in the calculation.

As shown in fig. 5a and 5b, in the original spiral boundary state with only a small gap, a large band gap occurs around 72MHz, which is caused by a break in the symmetry of the lattice at the interface. Another distinct band gap occurs around 78MHz, between the high frequency boundary and bulk states. Zero-dimensional angle states may occur within these bandgaps. Whether an angular state exists or not can be characterized by further calculating a quadrupole moment, i.e., a topological angular charge (topological corner charge). Due to C _6v Point group symmetry, dipole moment meetingThe quadrupole moment can be defined as the dipole moment

The calculated topological insulator topological angle charges for w=5 μm and 7.2 μm are 0 and 1/2, respectively. These non-zero quadrupole moments demonstrate the existence of a zero-dimensional angle state.

In the following it will be shown how a high order topology is implemented in the proposed two-dimensional system. Fig. 6a shows a tetragonal phonon crystal containing two elastic insulators. The period and geometry parameters of both insulators were identical except for the value of the hole center distance w, which was 7.2 μm for one and 5 μm for the other. According to fig. 2d, the p/d bands of the two insulators are opposite. Inside PnC there are four boundaries, two armchair-type boundaries (boundaries II and IV in the figure) and two deformed zigzag boundaries (boundaries I and III in the figure), along the x and y directions, respectively. An enlarged top view of the intersection of these two types of interfaces is shown in fig. 6 b. The projected energy bands of these two types of boundaries are shown in fig. 5a and 5b, respectively. In the original continuous helical boundary state, a band gap occurs around 72MHz because the symmetry of the lattice breaks at this boundary. Notably, another band gap occurs around 78MHz between the higher frequency edge and the bulk state. The 0D angle state may appear inside these bandgaps, supporting elastic wave localization at the intersection of two types of different topological boundaries (i.e., at the intersection of two dashed lines in fig. 6 a).

To verify this, all eigenstates of the tetragonal PnC were calculated and their spectra were calculated as shown in FIGS. 6c and 6 d. By observing the elastic field distribution of these eigenstates, it was found that 2D states, 1D boundary states and 0D angles exist simultaneously in the 2D system as shown in fig. 6 e-6 g, respectively. For the bulk and boundary states, the elastic wave exists inside and at the boundary of the two elastic insulators and is spectrally continuous. As regards the angular state, it is independent, occurs at the cross-point of the interface of two different types, and its frequencies are separated, in the band gap between the high-frequency boundary state and the bulk state, as shown by the dashed lines in fig. 5a and 5b around 78 MHz.

Topology protection the most notable feature of higher order topologies is the immune nature to defects. To verify this characteristic, defects such as bending and lattice distortion are introduced in the waveguide thereof in the structured quadrangular photonic crystal as shown in fig. 7 a. Then, the characteristic frequency of the structural phonon crystal is calculated. From the characteristic frequency spectrum 7b thereof, it can be seen that even if a defect is introduced, the angular state is stably present and the frequency to which it corresponds is hardly changed.

The zero-dimensional locality of the topological angle states can be used to implement some high Q devices. For example, in optics, high Q cavities based on angular states can be used to design ultra-low threshold lasers. In this embodiment, a dual port filter is implemented for elastic waves using angular states, as shown in fig. 8 a. In practice, the device requires only placement of the sound source at the left hand port of the sample shown in fig. 6a and the receiver at the right hand port of the sample. The two-port transmission spectrum is calculated, as shown in fig. 8b, whose spectral characteristics are highly consistent with the calculated eigenstates (fig. 6 c). In the frequency range of about 69 to 75.5MHz, the two port device has good transmission performance due to the boundary states present in the I and II interfaces. In the frequency range of about 75.5 to 79MHz, transmission will be greatly reduced if the system has neither body nor edge states in these frequencies. However, due to the presence and excitation of the 0D angular state, a significant increase occurs at 78.31MHzThe transmission peak is shown in fig. 8 d. FIG. 8c shows the result of fine calculation of the transmission spectrum at this angle, with theoretical Q and Q.times.f values up to 8.times.10, respectively ⁶ And 6.26X10 ¹⁴ Hz. Although inherent dissipation is not considered in the simulation, in practical cases, high Q values near theoretical are possible.

The main feature of the elastic TI made of 2D material proposed in this embodiment is its electrical tunability, and especially for the micro-acoustic SAW and BAW devices widely used in wireless communication today, it is an important goal to achieve a convenient electrical tunability. For the photoacoustic topological insulator, the topological boundary transmission is required to be at the cost of wasting a large amount of internal structure area, so that the realization of frequency adjustability and internal structure reconfigurability are very important, and the utilization rate of the prepared device can be greatly improved. Since 2D materials are typically electro-mechanically sensitive, their mechanical properties can be easily tuned by introducing a gate voltage to them.

Fig. 9a shows a schematic diagram of the introduction of a gate voltage on an elastic TI device. After applying a voltage across the gate, an electric field will be formed between the 2D material (i.e. graphene in this embodiment) and the substrate (highly doped Si in this embodiment). After the electric field is formed, the 2D material will be subjected to electrostatic pressure and then bend towards the substrate, resulting in additional strain when deformed, ultimately changing the characteristics and operating frequency of the TI device. In numerical analysis, the electrostatic pressure P can be directly introduced into the suspended region of the 2D material _es To simulate the above process. When the direct current voltage V _g P to which the 2D material is subjected when applied to the gate electrode _es Is that

Wherein C is _u ，ε ₀ D and v are the capacitance per unit area between the 2D material and the gate electrode, the vacuum dielectric constant, the distance between the gate and the 2D material, and the real-time displacement of the suspended 2D material during operation, respectively. Equation (3) shows that P _es Is subjected to V _g And d. Thus, d is set to 200nm (this is the previous nanomechanical resonanceTypical values from experimental studies of the instrument), and V was studied _g Impact on device characteristic frequency. FIG. 9b shows V _g And the frequency of the elastic double dirac point as shown in fig. 2 b. Taking the high Q filter shown in fig. 8 as an example, all devices require only 5V gate voltage to achieve frequency modulation of about 6 MHz. Fig. 9c shows the transmission spectrum at different gate voltages. The operating frequency shift of the device can reach 7.26% with a 5V gate voltage applied. Because graphene can withstand ultra-high strain, electrostatic frequency tunability of up to 400% can even be achieved by applying higher gate voltages and more optimized designs.

The embodiment is based on finite element analysis, and provides and demonstrates an elastic wave topological insulator based on two-dimensional materials through numerical simulation, and the elastic wave topological insulator respectively shows a one-dimensional boundary state for an elastic waveguide and a zero-dimensional angle state of a local area in the two-dimensional materials, and various functional element components such as the elastic waveguide, a beam splitter, a high Q value resonator, a band-pass filter and a band-stop filter are derived from the elastic wave topological insulator. Notably, due to the electromechanical sensitivity of the two-dimensional material, effective electrical adjustment of the operating frequency of these components is possible. For example, in a dual-port high-Q band-pass filter based on such elasticity TI, a shift of about 7.26% of the operating frequency can be achieved by applying only a gate voltage of 5V. In summary, the proposed elastic materials and devices can combine integration, high performance, multi-functionality and electrical tunability, which makes them widely applicable in advanced analog signal processors for mobile communications and highly sensitive detectors for the internet of things in the future.

Although the material used in this example was graphene on a SiO2/Si substrate, the selection of either a two-dimensional material or a substrate material was very broad. From the perspective of device size and operating frequency, such devices can be fabricated with a range of hundreds of micrometers to tens of nanometers (with corresponding operating frequencies ranging from several megahertz to several tens of gigahertz) based on today's mature micro-nano processing techniques and 2D material growth and transfer techniques. From an adjustability point of view, external light, magnetism, heat, gas, etc. are possible to adjust such devices in addition to the electrical adjustment demonstrated in this embodiment. These advantages greatly increase the possibilities of application of acoustic topology materials and devices in practice. Along this research path, it is critical to achieve electrical conduction of elastic waves using piezoelectric 2D materials, making this type of device fully compatible with today's micro-acoustic electronic devices (e.g., interdigital transducer based SAW and BAW devices).

The above description may be implemented alone or in various combinations and these modifications are within the scope of the present application.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting. Although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims (10)

1. An elastic wave topology insulator, comprising: the device comprises a substrate and a two-dimensional material layer, wherein the two-dimensional material layer is tiled on the substrate, a honeycomb lattice pattern is arranged on the surface of the substrate, the two-dimensional material layer comprises a first area contacted with the substrate and a second suspended area, acoustic impedance mismatch between the second area and the substrate is achieved, and the two-dimensional material layer is constructed into a phonon crystal structure;

the phonon crystal is a standard honeycomb lattice, and when the center distance of holes is w=a/v3=6μm, the phonon crystal is a dirac-like semi-metal with elastic wave capable of propagating inside; when w increases or decreases, the dual dirac cone simply disappears, and a resilient band gap is created,

the energy band structures formed by the increase and the decrease of w are opposite, so that the phonon crystal becomes two types of insulators;

when w=5.5 μm, the phonon crystal generates an elastic band gap of 5MHz around the original dirac cone, two at the high and low frequencies of the band gapDifferent types of body modes, namely a d mode and a p mode; parity symmetry of eigenstates about the x or y axis, d-mode being divided into d _xy And d _x ² _-y ² The p mode is divided into p _x And p _y The phonon lattice at this time becomes topologically mediocre;

w is equal to 6.6 μm, the phonon lattice has a band gap of 5MHz at the same frequency, but the p and d modes are diametrically opposite, where the phonon lattice is topologically non-trivial.

2. The acoustic wave topology insulator of claim 1, wherein: the honeycomb lattice pattern is an array formed by hexagonal single cells, each single cell comprises six round holes which are crossed in sequence, and the distances between the centers of the six round holes in each single cell and the centers of the single cells where the six round holes are located are equal.

3. The acoustic wave topology insulator of claim 2, wherein: the honeycomb lattice pattern is a topologically mediocre lattice or a topologically mediocre lattice.

4. An acoustic wave topology insulator as recited in claim 3, wherein: the substrate is made of one of the following materials: SU-8 polymer, silicon dioxide, and piezoelectric GaAs.

5. The acoustic wave topology insulator of any of claims 1-4, wherein: the two-dimensional material layer is made of graphene.

6. A functional assembly comprising an elastic wave topology insulator according to any one of claims 1-5.

7. The functional assembly of claim 6, wherein: the functional component is a beam splitter.

8. The functional assembly of claim 6, wherein: the functional component is a resonator.

9. The functional assembly of claim 6, wherein: the functional component is a filter.

10. The functional assembly of claim 6, wherein: the functional component is a multiplexer.