A high-q gigahertz topological acoustic surface wave resonator

Abstract

The application discloses a high-Q gigahertz topological acoustic surface wave resonant cavity, comprising two kinds of phononic crystals which are spliced with each other, and the phononic crystals are lithium niobate with nanoscale etching grooves on the surface. The application constructs a topological interface state by splicing the phononic crystals with different topological properties, and excites the acoustic surface wave based on the piezoelectric effect through an interdigital transducer, so that the acoustic surface wave resonant cavity is excited, and finally the acoustic surface wave resonant cavity with high Q value and extremely small mode size is realized. The highest Q value measured in the experiment is 6400. The acoustic surface wave resonant cavity realized by the application has the advantages of topological protection property, high Q value, extremely small volume mode, gigahertz working frequency and low transmission loss, and can fully enhance the coupling effect with a superconducting quantum bit, a solid-state quantum defect, a microwave field and an optical photon, and will play an important role in the corresponding research.

Description

Technical Field

[0001] This invention relates to a surface acoustic wave resonator, and more particularly to a high-Q gigahertz topological surface acoustic wave resonator. Background Technology

[0002] Surface acoustic waves (SAWs) are sound waves that propagate on the surface of an elastic solid and whose amplitude decays within the solid. Based on piezoelectric materials such as lithium niobate, aluminum nitride, gallium nitride, and gallium arsenide, SAWs can be effectively coupled to electromagnetic fields through the piezoelectric effect. Therefore, they have been widely used in 5G communication filters, light modulation via acousto-optic effects, and driving solid-state electron spins through spin-orbit coupling.

[0003] Surface acoustic wave (SAW) resonators, with their strong electromechanical coupling efficiency, near-solid surface transmission, and gigahertz resonant frequency, can replace other micromechanical resonators, such as suspended optomechanical nanocavities, bulk acoustic cavities, and two-dimensional material micromechanical cavities, playing a crucial role in coupling studies with superconducting qubits, solid-state quantum defects, microwave fields, and optical photons. In studies of coupling with other fields, resonant cavities with high Q-value, small-volume modes are in demand to significantly enhance their interactions.

[0004] One-dimensional topological phononic crystals possess simple geometries and mature manufacturing techniques, and can realize resonant cavities with smaller mode sizes and robustness, resulting in higher quality factors (Q). However, no topological surface acoustic wave resonant cavity has yet been experimentally verified. Summary of the Invention

[0005] Purpose of the invention: The present invention aims to provide a high-Q gigahertz topological surface acoustic wave resonator with a high Q value and a smaller mode size.

[0006] Technical solution: The high Q-value gigahertz topological surface acoustic wave resonator of the present invention includes two kinds of phononic crystals spliced ​​together, wherein the phononic crystal is lithium niobate with nanoscale etched grooves on its surface.

[0007] Preferably, the two phononic crystals have the same phononic bandgap, but the vibration modes corresponding to each band are reversed, that is, they have different topological properties. By splicing phononic crystals with different properties, a topological interface state is constructed, and a high-Q surface acoustic wave resonator is finally realized.

[0008] Preferably, the surface acoustic wave phonon crystal is prepared by argon ion beam etching.

[0009] Preferably, the lattice period of the phononic crystal is 0.8 to 2 μm, so that its operating frequency reaches 1.0 GHz to 2.5 GHz; the width of the etching groove is selected between 100 nm and 1000 nm, and the etching depth is 20 nm to 300 nm.

[0010] As a preferred embodiment, to improve the coupling efficiency of the device, the surface acoustic wave is excited and received by a unidirectional interdigital transducer. The interdigital transducer excites the surface acoustic wave based on the piezoelectric effect, thereby exciting the resonant cavity.

[0011] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the realized topological surface acoustic wave resonator has a high Q value (the highest experimentally measured Q value can reach 6400), an operating frequency higher than gigahertz, and a smaller mode size (3.973 μm) compared with resonators realized by other means. 2 It exhibits greater robustness due to the protective effect of topological effects. Higher Q and smaller mode size enhance the coupling between high-frequency phonons and other particles, such as qubits, solid-state quantum defects, and photons. Attached Figure Description

[0012] Figure 1 This invention provides a cross-sectional schematic diagram of a high-Q gigahertz topological surface acoustic wave resonator and dispersion curves corresponding to different types of phononic crystals; wherein, (a) is a schematic diagram of the specific structure, (b) is the dispersion curve of surface acoustic waves propagating on the surface of single-crystal lithium niobate, (c) is the dispersion curve corresponding to phononic crystal 1, and (d) is the dispersion curve corresponding to phononic crystal 2.

[0013] Figure 2 The scanning electron microscope and atomic force microscope (AFM) structures of the gigahertz topological surface acoustic wave resonator prepared for the final experiment of this invention are characterized. Among them, (a) is a scanning electron microscope image of the structure, which consists of an interdigital transducer and a phononic crystal. The lower half is an enlarged view of the corresponding transducer and phononic crystal. (b) is an atomic force microscope image of the phononic crystal.

[0014] Figure 3 The following are the structural transmission characteristic curves tested in the experiment of this invention: (a) is the broadband transmission characteristic curve of the structure; (b) is an enlarged view of the transmission characteristic curve in the operating frequency domain of the resonant cavity; (c) shows the effect of the number of phonon crystals on the quality factor and coupling efficiency of the resonant cavity.

[0015] Figure 4 The energy field distribution and out-of-plane displacement field distribution corresponding to the topological resonant state calculated by the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0017] like Figure 1(a) shows a cross-sectional schematic diagram of the high-Q gigahertz topological surface acoustic wave resonator of the present invention. In the figure, E-IDT is the interdigital transducer for exciting the sound source, PnC1 is phonon crystal 1, PnCs2 is phonon crystal 2, Interface is the splicing interface between the two phonon crystals, R-IDT is the interdigital transducer for receiving the sound source, a is the structural period of the phonon crystals (phonon crystals 1 and 2 have the same period), d1 is the length of the etched groove of phonon crystal 1, d2 is the length of the unetched portion of phonon crystal 2, and SAW indicates the transmitted surface acoustic wave. The phonon crystals are formed by etching grooves on the surface of lithium niobate at a 128-degree Y-cut, and the corresponding etched grooves of phonon crystals 1 and 2 are located at different positions. The etched groove of phonon crystal 1 is located at its center and is symmetrical about the central axis, while the etched grooves of phonon crystal 2 are located on both sides and are also symmetrical about the central axis. Furthermore, the sum of the lengths of the two etched grooves of phonon crystal 2 is equal to the length of the etched groove of phonon crystal 1.

[0018] The principle behind this invention for realizing a resonant cavity is that two phononic crystals have the same phononic bandgap, with a frequency of approximately 1.05 GHz, such as... Figure 1 (c) and (d). However, the vibrational modes corresponding to each band are different, as shown in the inset of the figure, confirming that the vibrational modes of the two phononic crystals are reversed. The vibrational modes are related to the topological properties of the phononic crystal, thus confirming that these two types of phononic crystals have different topological properties. Due to the body-edge correspondence of topological insulators, there must exist an interface state in the band gap.

[0019] like Figure 1 As shown in (a), the constructed interface states are excited by an interdigital transducer. The excited surface acoustic waves propagate through the free surface and then couple to the interface, forming a resonant cavity. Finally, the acoustic signal is received by a receiving interdigital transducer. The dispersion curve corresponding to the free surface of lithium niobate is shown in Figure [Figure number missing]. Figure 1 As shown in (b).

[0020] like Figure 2 (a) shows the final device fabricated using an argon ion beam etching process. The interdigital transducer operates at a frequency of 1.01–1.11 GHz, with a bandwidth of approximately 100 MHz and out-of-band rejection of 20 dB. Figure 3 As shown in (a).

[0021] The central region of the device is the phonon crystal region. Figure 2 (a) The magnified view shows the interface region, and the realized phononic crystal surface is smooth. Furthermore, its structural parameters are characterized using atomic force microscopy, such as... Figure 2 As shown in (b), the phononic crystal lattice period is 1.9 μm, the groove etching width is 880 nm, and the groove etching depth is 120 nm.

[0022] After the device was fabricated, its transmission characteristic curve was tested using a network analyzer. Figure 3 As shown in (a), the transmission curve reveals that the phononic crystal has a bandgap of approximately 30 MHz, achieving an acoustic suppression of 20 dB, and exhibits a resonant mode within the bandgap. The resonant cavity operates at a frequency of 1.0574 GHz, and its 3 dB quality factor (Q) reaches 6400. Figure 3 (b) As shown in the enlarged view.

[0023] like Figure 4 The energy field distribution of the resonant cavity obtained through numerical simulation shows that its surface displacement field decays exponentially with increasing distance from the interface. Furthermore, A is calculated using the following formula. eff =∫(E em +E k +E els )dr / max(E em +E k +E els The mode size of the resonant cavity was found to be 3.973 μm. 2 , equal to 0.26λ 2 Among them, A eff For the pattern size, E em E k E els These represent the electromagnetic, kinetic, and elastic energy densities, respectively. λ is the surface acoustic wave wavelength of 3.9 μm.

[0024] The period number of the phonon crystals on both sides of the interface has a significant impact on the quality factor and coupling effect of the resonant cavity. Therefore, we prepared a series of experimental samples, tested their performance, and obtained... Figure 3 (c). It can be seen that as the number of phononic crystal cycles increases, its corresponding Q value increases, but its coupling efficiency decreases. Coupling efficiency refers to the difference between the transmission rate of the phononic crystal device and the free surface transmission rate.

Claims

1. A high-Q gigahertz topological surface acoustic wave resonator, characterized in that, The device comprises two phononic crystals spliced ​​together, wherein the phononic crystals are lithium niobate with nanoscale etched grooves on their surfaces; the two phononic crystals have the same phononic bandgap, but the vibration modes corresponding to each band are reversed, i.e., they have different topological properties; by splicing the two phononic crystals together, a topological interface state is constructed; to improve the coupling efficiency of the device, surface acoustic waves are excited and received through a unidirectional interdigital transducer; the Q value of this resonant cavity can reach 6400; The phononic crystal is prepared by argon ion beam etching; the lattice period of the phononic crystal is 0.8 to 2 μm; the operating frequency of the phononic crystal reaches 1.0 GHz to 2.5 GHz; the width of the etching grooves on the surface of the phononic crystal is 100 nm to 1000 nm; and the etching depth of the etching grooves on the surface of the phononic crystal is 20 nm to 300 nm.

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