Room temperature optical and microwave conversion device based on bulk acoustic resonator and thin film resonator and preparation method thereof

Abstract

The application provides a room-temperature light and microwave conversion device based on a bulk acoustic resonator and a thin film vibrator and a preparation method thereof, and relates to the technical field of light to microwave conversion. The room-temperature light and microwave conversion device comprises: an optical input assembly; an acoustic force coupling assembly comprising: a bonding layer; a thin film vibrator chip comprising: a silicon nitride thin film vibrator substrate, a silicon nitride thin film, having a suspended vibrator region, and a metasurface structure for forming a high-Q optical Fabry-Perot cavity to confine laser in the cavity, so that the pressure generated by the photon cycle drives the thin film to vibrate; the thin film vibrator chip and the bulk acoustic resonator chip form a sealed capacitor cavity through the bonding layer, which is used for converting the vibration of the thin film vibrator chip into an electrical signal; and a microwave reading and output assembly for receiving the microwave signal output by the acoustic force coupling assembly. Through the innovative cooperative structure design and on-chip integration process, the application constructs a direct and low-consumption path from light to microwave, and realizes efficient conversion at room temperature.

Description

Technical Field

[0001] This application relates to the field of optical-to-microwave technology, and more specifically, to a room-temperature optical-to-microwave conversion device based on a bulk acoustic resonator and a thin-film oscillator, and its fabrication method. Background Technology

[0002] Optical-to-microwave technology is the core means to achieve extremely high stability and accuracy of optical frequency references in the microwave frequency band, and it plays an irreplaceable role in many cutting-edge technology fields.

[0003] Currently, the mainstream solution for high-performance optical-to-microwave conversion relies on an optical frequency comb system. Its typical architecture involves locking an ultra-stable laser to a Fabry-Perot optical reference cavity with an ultra-high Q value to generate a continuous laser with an extremely narrow linewidth. This laser then drives a mode-locked femtosecond laser to form an optical frequency comb. Finally, a photodetector converts the beat frequency signal between the optical frequency comb lines into a microwave signal.

[0004] In the pursuit of system miniaturization, researchers have also attempted to combine high-performance optical resonators and microwave resonators discretely. Among these, silicon nitride thin-film oscillators, as high-performance optical microcavities, possess extremely low intrinsic optical loss, supporting very high optical quality factors. Furthermore, their excellent mechanical properties enable them to support high-Q mechanical vibration modes, providing an ideal platform for photomechanical interactions. Through metasurface technology, subwavelength structures can be designed on their surfaces to achieve precise manipulation of light waves, enhancing the intensity of light-matter interactions. Bulk acoustic wave resonators exhibit unique advantages in the microwave band. Utilizing the piezoelectric effect and standing wave resonance of acoustic waves in solids, they can achieve extremely high quality factors in the GHz band, while also being small in size, low in power consumption, and highly compatible with semiconductor processes, facilitating chip-level integration.

[0005] However, existing technologies have significant drawbacks: on the one hand, traditional optical frequency comb systems are extremely complex and costly, with core components relying on extreme operating environments such as vacuum and low temperatures, resulting in poor environmental robustness and hindering practical engineering applications; on the other hand, in discrete combination schemes, the silicon nitride thin-film oscillator and bulk acoustic resonator lack a direct and efficient coordination mechanism, and multiple cross-domain interface conversions lead to a significant reduction in overall conversion efficiency. Furthermore, existing solutions cannot simultaneously and efficiently utilize the high optical Q-value and strong photomechanical interaction advantages of the silicon nitride thin-film oscillator with the high microwave Q-value and low phase noise advantages of the bulk acoustic resonator, presenting a technical bottleneck in cross-frequency domain coordination. Summary of the Invention

[0006] To address at least one of the aforementioned problems, this application proposes a room-temperature light-to-microwave conversion device and its fabrication method based on a bulk acoustic resonator and a thin-film oscillator. Through innovative synergistic structural design and on-chip integration process, a direct, low-power path from light to microwave is constructed, eliminating dependence on complex peripheral support systems and achieving efficient conversion at room temperature. This device is suitable for next-generation communications (such as 6G), high-precision radar, atomic clocks, and quantum information processing systems.

[0007] According to a first aspect of this application, at least one embodiment of this application provides a room-temperature optical-to-microwave conversion device based on a bulk acoustic resonator and a thin-film oscillator, comprising: an optical input component for generating a pump laser; an acoustic-mechanical coupling component optically coupled to the optical input component, wherein the acoustic-mechanical coupling component includes a three-dimensional stacked structure formed by flip-chip bonding, comprising: a bonding layer; a thin-film oscillator chip, comprising: a silicon nitride thin-film oscillator substrate; a silicon nitride thin film formed on the surface of the silicon nitride thin-film oscillator substrate, the silicon nitride thin film having a suspended oscillator region, the suspended oscillator region having a metasurface. The structure includes a metasurface structure for forming a high-Q optical Fabry-Perot cavity to confine the pump laser within the cavity, allowing the pressure generated by photon circulation to drive the vibration of the silicon nitride thin film; a first microwave electrode formed on the surface of the silicon nitride thin film for extracting microwave signals; a bulk acoustic wave resonator chip, with the thin-film resonator chip and the bulk acoustic wave resonator chip forming a sealed cavity through the bonding layer, for converting the vibration of the thin-film resonator chip into an electrical signal; and a microwave readout and output component electrically connected to the acoustic coupling component for receiving the microwave signal output by the acoustic coupling component.

[0008] For example, in some embodiments of this application, the optical input component includes: a pump laser for generating the pump laser, wherein the output frequency of the pump laser matches the optical resonant mode of the silicon nitride thin film; and an optical path coupling component for injecting the pump laser into the suspended oscillator region.

[0009] For example, in some embodiments of this application, the metasurface structure is a two-dimensional photonic crystal structure, including periodically arranged holes or pillars.

[0010] For example, in some embodiments of this application, the bulk acoustic wave resonator chip includes: a bulk acoustic wave resonator substrate; a lower electrode formed on the surface of the bulk acoustic wave resonator substrate; and a piezoelectric layer formed on the surface of the lower electrode for sensing vibration and converting the vibration into an electrical signal through the piezoelectric effect.

[0011] For example, in some embodiments of this application, the bonding layer includes: metal pads formed on the thin-film oscillator chip and the bulk acoustic wave resonator chip, respectively, and the metal pads include gold bumps, solder balls and / or indium pillars.

[0012] For example, in some embodiments of this application, the microwave readout and output component includes: a second microwave electrode electrically connected to the acoustic coupling component for extracting the microwave signal output by the acoustic coupling component; a low-noise amplifier for amplifying the microwave signal; and a bandpass filter for filtering the microwave signal.

[0013] According to a second aspect of this application, at least one embodiment of this application provides a method for fabricating a room-temperature light-to-microwave conversion device, comprising:

[0014] Fabricating a silicon nitride thin-film oscillator chip includes: depositing a silicon nitride thin film on a first substrate surface by low-pressure chemical vapor deposition; spin-coating photoresist on the upper and lower surfaces of the silicon nitride thin film; exposing and developing the photoresist on the lower surface; removing the silicon nitride in a target area on the lower surface by reactive ion etching; after removing the silicon nitride in the target area on the lower surface, wet etching the exposed first substrate with potassium hydroxide to form a suspended oscillator region; depositing a metal layer on the upper surface of the silicon nitride thin film; patterning the metal layer by electron beam exposure and wet etching to form metal pads and microwave electrodes; and fabricating a metasurface structure in the suspended oscillator region by electron beam lithography to obtain the silicon nitride thin-film oscillator chip.

[0015] Fabricating a bulk acoustic wave resonator chip includes: fabricating a lower electrode on the surface of a second substrate by electron beam evaporation or sputtering; epitaxially growing a piezoelectric layer on the surface of the lower electrode by metal-organic chemical vapor deposition; patterning the piezoelectric layer by electron beam exposure and wet etching; and fabricating metal pads on the lower electrode to obtain the bulk acoustic wave resonator chip.

[0016] Fabricating an acoustic-mechanical coupling component includes: aligning the bulk acoustic resonator chip and the silicon nitride thin-film oscillator chip, and bonding them by flip-chip bonding to form the acoustic-mechanical coupling component with a sealed cavity.

[0017] For example, in some embodiments of this application, it further includes: optically coupling the optical input component to the acoustic coupling component; and electrically connecting the microwave readout and output component to the acoustic coupling component.

[0018] For example, in some embodiments of this application, the first substrate is a double-polished single-crystal silicon substrate; the second substrate is a sapphire substrate, a silicon substrate, and / or a silicon carbide substrate.

[0019] For example, in some embodiments of this application, the lower electrode comprises molybdenum, gold and / or aluminum; the piezoelectric layer comprises aluminum nitride, lithium niobate and / or zinc oxide.

[0020] Through the above exemplary embodiments, the room-temperature light-to-microwave conversion device and its fabrication method based on a bulk acoustic resonator and a thin-film oscillator provided in this application have at least one of the following beneficial effects:

[0021] Cross-frequency domain synergistic efficiency: Through an innovative optical-acoustic-mechanical coupling structure, the high optical Q value and strong photomechanical interaction advantages of silicon nitride thin film oscillators are deeply integrated with the high microwave Q value and low phase noise advantages of bulk acoustic resonators, avoiding the efficiency loss and noise accumulation caused by multiple conversions in discrete schemes, and achieving efficient conversion between light and microwave.

[0022] Compact on-chip integration: The flip-chip bonding technology is used to achieve three-dimensional heterogeneous integration of optical oscillators and microwave oscillators, which solves the technical problem of efficient coupling of devices of different materials and different frequency bands. The device has a compact structure and is easy to mass-produce at the chip level.

[0023] Room temperature practical application: High-performance conversion can be achieved at room temperature and atmospheric pressure without the need for complex vacuum and cooling systems, with strong environmental robustness and reduced engineering application costs;

[0024] Flexible bidirectional conversion: It supports bidirectional coherent conversion between light and microwave and between microwave and light, adapts to a variety of cutting-edge application scenarios, and has broad versatility and promotional value.

[0025] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0026] The above and other objects, features, and advantages of this application will become more apparent from the detailed description of exemplary embodiments with reference to the accompanying drawings. The drawings described below are merely some embodiments of this application and are not intended to limit the scope of this application.

[0027] Figure 1 This is a schematic diagram of the overall structure of the room temperature light-to-microwave conversion device according to an embodiment of this application;

[0028] Figure 2 This is a schematic diagram of the three-dimensional stacked structure of the acoustic coupling component according to an embodiment of this application;

[0029] Figure 3 This is a top view of the thin-film oscillator chip structure according to an embodiment of this application;

[0030] Figure 4 This is a schematic diagram of the vibration of a thin-film oscillator chip according to an embodiment of this application;

[0031] Figure 5This is a schematic diagram of the microwave-to-optical conversion process according to an embodiment of this application;

[0032] Figure 6 This is a process flow diagram of the silicon nitride thin-film oscillator chip fabrication process according to an embodiment of this application;

[0033] Figure 7 This is a flowchart illustrating the fabrication process of the bulk acoustic wave resonator chip according to an embodiment of this application.

[0034] Figure 8 This is an enlarged schematic diagram of the metasurface structure according to an embodiment of this application.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1-Optical input components,

[0037] 11-Pump laser; 12-Optical path coupling component;

[0038] 2-Acoustic-mechanical coupling assembly,

[0039] 21-Thin-film oscillator chip,

[0040] 211-Silicon nitride thin film oscillator substrate, 212-Silicon nitride thin film, 213-Suspended oscillator region, 214-Metasurface structure, 215-First microwave electrode;

[0041] 22-bulk acoustic resonator chip,

[0042] 221 - Bulk acoustic wave resonator substrate, 222 - Lower electrode, 223 - Piezoelectric layer;

[0043] 23-bonding layer;

[0044] 3-Microwave Readout and Output Components

[0045] 31-Second microwave electrode, 32-Low noise amplifier, 33-Bandpass filter. Detailed Implementation

[0046] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0047] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0048] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0049] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0050] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of exemplary embodiments, and the modules or processes in the drawings are not necessarily essential for implementing this application, and therefore cannot be used to limit the scope of protection of this application.

[0051] Figure 1 This is a schematic diagram of the overall structure of the room temperature light-to-microwave conversion device according to an embodiment of this application.

[0052] like Figure 1 As shown, the overall structure of the room temperature light-to-microwave conversion device includes: an optical input component 1, an acoustic-mechanical coupling component 2, and a microwave readout and output component 3.

[0053] Among them, the optical input component 1 is used to generate pump laser and efficiently inject it into the acoustic coupling component 2.

[0054] According to an example embodiment, the optical input component 1 includes a pump laser 11 and an optical path coupling component 12.

[0055] The pump laser 11 is used to generate continuous laser light of a specific wavelength. Its output frequency matches the optical resonant mode of the subsequent silicon nitride thin film, ensuring that the laser can be efficiently coupled into the optical microcavity. The optical path coupling component 12, which employs a lens group or fiber taper, is used to inject the pump laser into the suspended oscillator region of the silicon nitride thin film with low loss, ensuring efficient transmission of the optical field.

[0056] The acoustic coupling component 2 is the core of the device, and it is optically coupled to the optical input component 1. For example... Figure 2 As shown, the acoustic coupling component 2 is a three-dimensional stacked structure formed by flip-chip bonding, which is used to realize optical force driving and acoustic-electric conversion.

[0057] According to an example embodiment, the acoustic coupling component 2 includes a thin-film oscillator chip 21, a bulk acoustic resonator chip 22, and a bonding layer 23, which together form a sealed cavity.

[0058] The thin-film oscillator chip 21 includes a silicon nitride thin-film oscillator substrate 211, a silicon nitride thin film 212, and a first microwave electrode 215.

[0059] A silicon nitride thin film 212 is formed on the surface of a silicon nitride thin film oscillator substrate 211. The silicon nitride thin film 212 has a suspended oscillator region 213. For example... Figure 3 As shown, the suspended oscillator region 213 has a metasurface structure 214. The metasurface structure 214 is used to form a high-Q optical Fabry-Perot cavity to confine the pump laser within the optical Fabry-Perot cavity, so that the radiation pressure generated by photon circulation drives the silicon nitride thin film 212 to vibrate. A first microwave electrode 215 is formed on the surface of the silicon nitride thin film 212 to extract microwave signals.

[0060] like Figure 8 As shown, the metasurface structure 214 is a two-dimensional photonic crystal structure, including periodically arranged holes or pillars.

[0061] The bulk acoustic wave resonator chip 22 includes a bulk acoustic wave resonator substrate 221, a lower electrode 222, and a piezoelectric layer 223.

[0062] The bulk acoustic wave resonator substrate 221 possesses high phase velocity, good temperature stability, and low propagation loss, providing a stable carrier for bulk acoustic wave resonance. A lower electrode 222 is formed on the surface of the bulk acoustic wave resonator substrate 221. A piezoelectric layer 223 is formed on the surface of the lower electrode 222 to sense vibrations and convert them into electrical signals via the piezoelectric effect. When the silicon nitride thin film vibrates under the influence of light, its vibration modulates the resonant characteristics of the bulk acoustic wave resonator chip 22 through the bonding interface and microcavity via the piezoelectric effect. The bulk acoustic wave resonator chip 22 utilizes its piezoelectric effect to directly convert this mechanical vibration into a weak electrical signal, which is extracted through the electrode antenna of the first microwave electrode 215 on the thin-film resonator chip 21, i.e., a microwave signal.

[0063] According to some embodiments, in a high-overtone bulk acoustic resonator, the piezoelectric layer 223 serves as a phonon source for the acoustic cavity, providing multiple acoustic modes in the GHz range, which allow for good coupling with the acoustic modes of the mechanical oscillator. The piezoelectric layer 223 emits phonon energy into the bulk acoustic resonator substrate 221, which acts as a phonon Fabry-Perot cavity that confines all phonon modes. The free spectral range between successive high-overtone bulk acoustic modes is an inverse function of the thickness of the bulk acoustic resonator substrate 221. The interface between the lower electrode 222 and the bulk acoustic resonator substrate 221 is crucial for efficient power transfer from the phonon source (piezoelectric layer 223) to the phonon cavity (bulk acoustic resonator substrate 221).

[0064] The bonding layer 23 includes metal pads formed at corresponding positions on the thin-film resonator chip 21 and the bulk acoustic wave resonator chip 22, respectively. The metal pads can be gold bumps, solder balls, or indium pillars. Precise alignment and bonding of the thin-film resonator chip 21 and the bulk acoustic wave resonator chip 22 are achieved using a flip-chip bonding machine. After bonding, a nanoscale sealed cavity is formed between the two chips, with an internal vacuum or inert gas environment. This cavity serves multiple functions: protection (preventing contamination and physical damage to the device), acoustic isolation (reducing damping of mechanical vibrations by ambient air and ensuring a high Q value), and coupling bridge (forming an acoustic coupling channel).

[0065] The microwave readout and output component 3 is electrically connected to the acoustic coupling component 2 and is used to receive microwave signals.

[0066] According to an example embodiment, the microwave readout and output component 3 includes a second microwave electrode 31, a low-noise amplifier 32, and a bandpass filter 33.

[0067] The second microwave electrode 31, in the form of an electrode antenna, is electrically connected to the acoustic coupling assembly 2 and is used to extract microwave signals. The low-noise amplifier 32 amplifies the microwave signal, increasing its strength. The bandpass filter 33 filters out out-of-band noise from the microwave signal, ensuring the purity of the output microwave signal.

[0068] The room-temperature light-to-microwave conversion device provided in this application achieves bidirectional conversion between optical and microwave signals through the synergistic effect of photomechanical, acoustic coupling, and piezoelectric effects. The specific workflow is as follows:

[0069] (a) Light to microwave conversion

[0070] (1) Optical injection: The continuous laser generated by the pump laser is injected into the suspended oscillator region of the thin film oscillator chip through the optical path coupling component. The laser frequency is matched with the optical resonance mode of the silicon nitride thin film and is completely reflected and coupled by the high Q value optical Fabry-Perot cavity formed by the metasurface structure. The optical field is greatly confined within a small volume.

[0071] (2) Photodynamic drive: Photons circulate in the cavity to generate radiation pressure, which drives the silicon nitride thin film to vibrate at its mechanical resonant frequency.

[0072] (3) Acoustic-mechanical coupling: The mechanical vibration of the thin film is transmitted to the bulk acoustic wave resonator chip through the solid coupling cavity (microcavity and bonding interface) formed by flip-chip bonding, causing periodic changes in the electrostatic field strength between piezoelectric layers. The piezoelectric layer converts electrical energy into mechanical energy, which excites the bulk acoustic wave resonator substrate to generate bulk vibration. This vibration mode is reflected back and forth in the substrate to form equally spaced bulk acoustic wave modes. The reflected bulk acoustic wave modes further affect the piezoelectric effect of the piezoelectric layer, strengthening the coupling transmission of mechanical vibration.

[0073] (4) Microwave generation: The bulk acoustic resonator chip uses the piezoelectric effect to directly convert mechanical vibration into a weak electrical signal.

[0074] (5) Signal output: The electrical signal is led out through the first microwave electrode of the thin film oscillator chip, amplified by a low noise amplifier and filtered by a bandpass filter, and outputs a high-purity, low-phase-noise microwave signal.

[0075] like Figure 4 As shown, when the silicon nitride thin-film oscillator chip is excited by optical radiation, the silicon nitride thin-film oscillator will undergo mechanical vibration. When at vibration displacements B, A, and C, the electric field strength between the piezoelectric layers of the bulk acoustic wave resonator chip is modulated from weak to strong, thereby causing the piezoelectric layers of the bulk acoustic wave resonator chip to generate bulk mechanical vibration. This converts electrical energy into mechanical energy, excites the acoustic mode of the bulk acoustic wave resonator substrate, and reflects it back to the surface, further converting the mechanical energy into electrical energy, thus modulating the electric field strength between the piezoelectric layers. Finally, the reflected microwave signal is read out by pumping and detecting the first microwave electrode of the silicon nitride thin-film oscillator chip, thereby realizing the conversion from light to microwave. This conversion process can be achieved in a vacuum at room temperature.

[0076] (II) Microwave to Light Conversion

[0077] The conversion of microwaves to light is the reverse process described above, such as... Figure 5 As shown:

[0078] (1) Microwave injection: The microwave pump signal is applied to the first microwave electrode of the thin film oscillator chip, and the bulk acoustic wave mode in the substrate is excited through the piezoelectric layer of the bulk acoustic wave resonator chip.

[0079] (2) Acoustoelectric coupling: The bulk acoustic wave resonates in the acoustic cavity (substrate of the bulk acoustic resonator) and continuously acts on the lower electrode, modulating the electric field strength between the electrodes.

[0080] (3) Electric field drive: The alternating electric field drives the silicon nitride thin film oscillator chip to undergo forced vibration through electrostatic force.

[0081] (4) Optical field modulation: The probe light is injected through the optical input port. The probe light and the displacement of the thin film oscillator are coupled by radiation pressure. The optical field is modulated by phase or amplitude and output.

[0082] (5) Signal output: The optical information converted from the original microwave signal is demodulated from the output light field to realize the conversion from microwave to light.

[0083] This application also provides a method for fabricating a room-temperature light-to-microwave conversion device, which includes four core steps: fabrication of a silicon nitride thin-film oscillator chip, fabrication of a bulk acoustic resonator chip, fabrication of an acoustic-mechanical coupling component, and device assembly, as detailed below:

[0084] (I) Fabrication of silicon nitride thin film oscillator chips

[0085] like Figure 6 As shown, the fabrication of the thin-film oscillator chip includes:

[0086] (1) Substrate selection and silicon nitride deposition: A double-polished single-crystal silicon wafer with a thickness of 400-600μm is selected. A silicon nitride film with a thickness of 80-120nm is deposited on the double-polished surface of the silicon wafer using a low-pressure chemical vapor deposition (LPCVD) device. The deposition process ensures that the silicon nitride film has low stress and high optical quality.

[0087] Photoresist spin coating and exposure development: Photoresist S1813 was spin-coated on both the upper and lower surfaces of the deposited silicon nitride film. The spin coating parameters were 3000 rpm and 1 minute. After the upper surface was coated, it was baked at 115°C for 2 minutes. The lower surface was also baked at 115°C for 2 minutes after the upper surface was coated. The area to be etched on the lower surface was exposed using a laser direct writing device. The area was developed with MIF319 developer for 1 minute. After development, it was baked at 115°C for 2 minutes.

[0088] (2) Reactive ion etching: The silicon nitride in the development area of ​​the lower surface is etched by reactive ion etching (RIE) equipment, and the photoresist on the upper and lower surfaces is removed after etching is completed.

[0089] (3) Formation of suspended oscillator region: The silicon substrate is etched by potassium hydroxide wet etching, and the etching byproducts are removed by piranha solution, and finally a silicon nitride suspended thin film oscillator with a size of 400μm×400μm-600μm×600μm is formed.

[0090] (4) Metal layer preparation: An aluminum layer with a thickness of 40-60 nm was deposited on the surface of the silicon nitride thin film by electron beam evaporation. After evaporation, the electron beam etchant PMMAA9 was spin-coated. The spin-coating parameters were 4000 rpm, 1 minute, and 180°C baking for 2 minutes.

[0091] (5) Patterning: The metal image area is exposed by electron beam exposure. After exposure, the metal is developed for 45 seconds with a developer solution with a volume ratio of MIBK:IPA=1:3 and then baked at 180°C for 8 minutes. The metal layer is patterned by wet etching of the developed area with alkaline developer solution to form metal pads (not shown in the figure) and microwave electrodes.

[0092] According to some embodiments, the microwave electrode is a metal layer, and the material can be aluminum.

[0093] (6) Metasurface structure preparation: Two-dimensional photonic crystal metasurface structure is prepared in the suspended oscillator region by electron beam lithography to form periodically arranged holes or pillars, ensuring that the lattice edge length, hole diameter and other parameters of the metasurface structure meet the design requirements.

[0094] (II) Fabrication of Bulk Acoustic Resonator Chip

[0095] like Figure 7 As shown, the fabrication of the bulk acoustic wave resonator chip includes:

[0096] (1) Substrate selection and lower electrode preparation: A sapphire substrate with a thickness of 200-300 μm is selected, and a metal layer with a thickness of 40-60 nm is prepared on the surface of the sapphire substrate by electron beam evaporation or sputtering technology as the lower electrode.

[0097] According to some embodiments, the bulk acoustic wave resonator substrate can be a sapphire substrate, a silicon substrate, and / or a silicon carbide substrate. Sapphire has a high velocity of sound, meaning that sound waves propagate faster within it, which is beneficial for improving the performance of acoustic devices. Sapphire exhibits excellent temperature stability, maintaining stable performance over a wide temperature range, which is particularly important for acoustic devices that need to operate in varying temperature environments. The low loss during sound wave propagation in sapphire helps maintain the clarity and intensity of the acoustic signal, improving the sensitivity and accuracy of the acoustic device.

[0098] The lower electrode can be a ductile metal material, such as molybdenum, gold, and aluminum.

[0099] (2) Piezoelectric layer growth: A piezoelectric material with a thickness of 500 nm-1.5 μm is epitaxially grown on the surface of the lower electrode using a metal-organic chemical vapor deposition (MOCVD) device to form a piezoelectric layer.

[0100] According to some embodiments, piezoelectric layers have a significant piezoelectric effect, which can convert mechanical stress into electrical energy or electrical energy into mechanical vibration. They are widely used in sensors, transducers and microelectromechanical systems, such as aluminum nitride, lithium niobate or zinc oxide.

[0101] (3) Patterning of piezoelectric layer: Spin-coat the surface of piezoelectric material with electron beam lithography PMMAA9. The spin-coating parameters are 4000 rpm and 1 minute, and bake at 180°C for 2 minutes. Expose the piezoelectric material to the preset shape (e.g., circle, diameter 200 μm) by electron beam exposure. After exposure, develop with a developer solution with a volume ratio of MIBK:IPA=1:3 for 45 seconds, and bake at 180°C for 8 minutes. The developed area is etched by alkaline developer to achieve patterning of piezoelectric layer.

[0102] (III) Preparation of acoustic-mechanical coupling components

[0103] (1) Bonding pillar preparation: Indium pillars are deposited in the bonding area of ​​the bulk acoustic resonator chip using an electron beam evaporation device, and the indium pillars at the bonding position are retained by the lift-off process to form the bonding pillars.

[0104] (2) Alignment and bonding: Align and level the bulk acoustic wave resonator chip and the silicon nitride thin film oscillator chip using flip-chip bonding equipment to ensure that the resonant structure of the bulk acoustic wave resonator is aligned with the center of the suspended oscillator area; set the bonding process parameters: bonding temperature 200-350℃, bonding pressure 50-150N, bonding time 30-60 minutes, and perform bonding treatment to form a stable electrical and mechanical connection between the metal pads, while forming a nanoscale sealed cavity between the two chips.

[0105] (iv) Assembly of the device

[0106] Optical path coupling: Align the optical path coupling component of the optical input component with the optical path of the suspended oscillator region of the acoustic coupling component to ensure that the pump laser can be efficiently injected into the optical Fabry-Perot cavity.

[0107] Circuit connection: Complete the circuit assembly of the low-noise amplifier, bandpass filter and second microwave electrode of the microwave readout and output component, and electrically connect the second microwave electrode of the microwave readout and output component to the acoustic coupling component.

[0108] Performance tuning: Adjust the output frequency of the pump laser to match the optical resonant mode of the silicon nitride thin film, test the purity and conversion efficiency of the microwave signal output, and complete the device fabrication.

[0109] Example 1

[0110] Fabrication of silicon nitride thin-film oscillator chip: A 500μm thick double-polished single-crystal silicon wafer was selected, and a 100nm thick silicon nitride thin film was deposited by LPCVD; S1813 photoresist was spin-coated on the upper and lower surfaces, and the etched area on the lower surface was exposed by laser direct writing. The photoresist was removed after RIE etching; the silicon substrate was wet-etched with potassium hydroxide to form a 500μm×500μm suspended oscillator region; a 50nm thick aluminum layer was evaporated by electron beam, and the pattern was patterned by electron beam exposure to form metal pads and microwave electrodes; a metasurface structure was fabricated in the suspended oscillator region with a lattice edge length of 733nm, a hole diameter of 525nm, and a pattern diameter of 200μm.

[0111] Fabrication of bulk acoustic wave resonator chip: A 250μm thick sapphire substrate was selected, and a 50nm thick molybdenum layer was deposited by electron beam evaporation as the lower electrode; a 1μm thick aluminum nitride piezoelectric layer was grown by MOCVD; the piezoelectric layer was patterned into a circle with a diameter of 200μm by electron beam exposure; and a matching gold bump metal pad was prepared.

[0112] Acoustic coupling component fabrication: Indium pillars are deposited at the bonding points of the upper chip; the two chips are aligned with a flip-chip bonding device, and the bonding temperature is set to 300℃, the pressure to 100N, and the time to 40 minutes to form a vacuum-sealed cavity.

[0113] Device assembly: A fiber optic taper is used as the optical path coupling component and aligned with the optical path of the suspended oscillator region; the second microwave electrode is an electrode antenna, electrically connected to the acoustic coupling component, and connected to a low-noise amplifier and a bandpass filter to complete the device assembly.

[0114] Through the above exemplary embodiments, the room-temperature optical-to-microwave conversion device based on a bulk acoustic resonator and a thin-film resonator provided in this application has the following beneficial effects: This application can achieve efficient cross-frequency domain synergistic conversion. By utilizing an innovative optical-acoustic-mechanical coupling structure, it deeply integrates the high optical Q value and strong photomechanical interaction advantages of silicon nitride thin-film resonators with the high microwave Q value and low phase noise advantages of bulk acoustic resonators, avoiding the efficiency loss and noise accumulation caused by multiple conversions in discrete solutions, and significantly improving the conversion efficiency of light and microwave. Secondly, this application can achieve the advantages of on-chip integration and compactness. It uses flip-chip bonding technology to realize the three-dimensional heterogeneous integration of optical and microwave resonators, solving the problems of different materials and different This application addresses the technical challenge of efficient coupling of frequency band devices. The device boasts a robust and compact structure, enabling mass production using standard semiconductor processes, and possesses significant commercial potential. Furthermore, it achieves a breakthrough in room-temperature practical application, eliminating the need for complex vacuum and cooling systems. It maintains high performance and stable operation under ambient temperature and pressure, exhibiting strong environmental robustness and completely eliminating dependence on extreme operating environments, thus reducing engineering application costs. Finally, this application supports bidirectional conversion for flexible adaptation, enabling efficient and low-noise conversion from light to microwave, as well as microwave-to-light modulation output through the reverse process. This allows it to adapt to various cutting-edge application scenarios such as next-generation communications, high-precision radar, atomic clocks, and quantum information processing, demonstrating broad versatility and widespread application value.

[0115] It should be clearly understood that this application describes how specific examples are formed and used, but this application is not limited to any details of these examples. Rather, based on the teachings of the disclosure of this application, these principles can be applied to many other embodiments.

[0116] Furthermore, it should be noted that the above figures are merely illustrative representations of the processes included in the method according to exemplary embodiments of this application, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0117] Exemplary embodiments of this application have been specifically shown and described above. It should be understood that this application is not limited to the detailed structures, arrangements, or implementation methods described herein; rather, this application is intended to cover various modifications and equivalent arrangements that fall within the objectives and scope of the appended claims.

Claims

1. A room-temperature optical-to-microwave conversion device based on a bulk acoustic resonator and a thin-film oscillator, characterized in that, include: Optical input components for generating pump laser; An acoustic-mechanical coupling component is optically coupled to the optical input component, wherein the acoustic-mechanical coupling component includes a three-dimensional stacked structure formed by flip-chip bonding, comprising: Bonding layer; Thin-film oscillator chips, including: Silicon nitride thin-film oscillator substrate; A silicon nitride thin film is formed on the surface of the silicon nitride thin film oscillator substrate. The silicon nitride thin film has a suspended oscillator region. The suspended oscillator region has a metasurface structure. The metasurface structure is used to form a high-Q optical Fabry-Perot cavity to confine the pump laser within the optical Fabry-Perot cavity, so that the pressure generated by photon circulation drives the silicon nitride thin film to vibrate. A first microwave electrode is formed on the surface of the silicon nitride thin film and is used to extract microwave signals. A bulk acoustic wave resonator chip, wherein the thin-film oscillator chip and the bulk acoustic wave resonator chip form a sealed cavity through the bonding layer, for converting the vibration of the thin-film oscillator chip into an electrical signal, wherein the bulk acoustic wave resonator chip comprises: Substrate for bulk acoustic resonator; The lower electrode is formed on the surface of the bulk acoustic resonator substrate; A piezoelectric layer is formed on the surface of the lower electrode to sense vibration and convert the vibration into an electrical signal through the piezoelectric effect. A microwave readout and output component, electrically connected to the acoustic coupling component, is used to receive the microwave signal output by the acoustic coupling component. The first microwave electrode receives a microwave pump signal, which is converted into an optical signal by the bulk acoustic resonator chip and the thin-film oscillator chip, and the optical signal is output via the metasurface structure.

2. The room temperature light-to-microwave conversion device as described in claim 1, characterized in that, The optical input component includes: A pump laser for generating the pump laser, wherein the output frequency of the pump laser is matched with the optical resonant mode of the silicon nitride thin film; An optical path coupling component is used to inject the pump laser into the suspended oscillator region.

3. The room temperature light-to-microwave conversion device as described in claim 1, characterized in that, The metasurface structure is a two-dimensional photonic crystal structure, comprising periodically arranged holes or pillars.

4. The room temperature light-to-microwave conversion device as described in claim 1, characterized in that, The bonding layer includes: Metal pads are formed on the thin-film oscillator chip and the bulk acoustic wave resonator chip, respectively, and the metal pads include gold bumps, solder balls and / or indium pillars.

5. The room-temperature light-to-microwave conversion device as described in claim 1, characterized in that, The microwave readout and output component includes: The second microwave electrode is electrically connected to the acoustic coupling component and is used to extract the microwave signal output by the acoustic coupling component. A low-noise amplifier is used to amplify the microwave signal; A bandpass filter is used to filter the microwave signal.

6. A method for preparing a room-temperature light-to-microwave conversion device according to any one of claims 1-5, characterized in that, include: Fabrication of silicon nitride thin-film oscillator chips includes: A silicon nitride thin film was deposited on the surface of a first substrate by low-pressure chemical vapor deposition. Photoresist is spin-coated on the upper and lower surfaces of the silicon nitride film. The photoresist on the lower surface is exposed and developed. The silicon nitride in the target area on the lower surface is removed by reactive ion etching. After removing the silicon nitride from the target area on the lower surface, the exposed first substrate is etched by a potassium hydroxide wet etching process to form the suspended oscillator region. A metal layer is deposited on the upper surface of the silicon nitride thin film by vapor deposition, and the metal layer is patterned by electron beam exposure and wet etching to form metal pads and microwave electrodes. A metasurface structure was fabricated in the suspended oscillator region using electron beam lithography to obtain the silicon nitride thin film oscillator chip. Fabricating a bulk acoustic wave resonator chip, including: The lower electrode is fabricated on the surface of the second substrate by electron beam evaporation or sputtering; A piezoelectric layer is epitaxially grown on the surface of the lower electrode by organometallic chemical vapor deposition. The piezoelectric layer was patterned using electron beam lithography and wet etching. A metal pad is fabricated on the lower electrode to obtain the bulk acoustic wave resonator chip. Fabrication of an acoustic-mechanical coupling assembly includes: The bulk acoustic resonator chip and the silicon nitride thin film oscillator chip are aligned and bonded by flip-chip bonding to form the acoustic-mechanical coupling component with a sealed cavity.

7. The preparation method according to claim 6, characterized in that, Also includes: Optical path coupling is performed between the optical input component and the acoustic coupling component; The microwave readout and output component is electrically connected to the acoustic coupling component.

8. The preparation method according to claim 6, characterized in that, The first substrate is a double-polished single-crystal silicon substrate; The second substrate is a sapphire substrate, a silicon substrate, and / or a silicon carbide substrate.

9. The preparation method according to claim 6, characterized in that, The lower electrode comprises molybdenum, gold, and / or aluminum; The piezoelectric layer comprises aluminum nitride, lithium niobate, and / or zinc oxide.

Images