Cavity optical power device and method of manufacturing the same

Abstract

This application discloses a cavity optical quantum device and its fabrication method. The device consists of a microwave circuit chip and a mechanical oscillator chip flip-bonded together. The microwave circuit chip includes: a substrate having a deposition region and a plurality of first leveling alignment marks around the deposition region on a first surface of the substrate; a first metal layer formed on the first surface, including a microwave circuit located in the deposition region and a first bonding region; the mechanical oscillator chip includes: a substrate having a cavity; a silicon nitride thin film formed on a second surface of the mechanical oscillator chip substrate, with a central region located on the cavity to form a suspended thin film region; a second metal layer formed on the surface of the silicon nitride thin film, including a thin film electrode region, a second bonding region, and a plurality of second leveling alignment marks, with the thin film electrode region located at the center; the size of the thin film electrode region is smaller than that of the suspended thin film region and aligned with its center; the second bonding region corresponds to the first bonding region; the microwave circuit is aligned with the center of the thin film electrode region; and the second leveling alignment marks correspond to the first leveling alignment marks respectively.

Description

Technical Field

[0001] This application relates to the field of micro-nano device technology, specifically to a cavity optoelectronic quantum device and its fabrication method. Background Technology

[0002] In research fields such as precision measurement and sensing, testing of fundamental problems in quantum mechanics, and hybrid quantum information processing, micro / nano devices based on the radiation-pressure interaction of mechanical oscillators made of semiconductor thin film materials show promising application prospects. In recent years, based on micro / nano fabrication technology, the fabrication and research of quantum devices using various types of oscillators have achieved unprecedented progress. As an important class of solid-state quantum information processing devices, they also have significant applications in the fields of quantum information and quantum computing, including the preparation, transmission, and storage of quantum states, as well as serving as interfaces between various types of quantum systems.

[0003] Two-dimensional thin-film mechanical oscillator quantum devices, as a type of solid-state quantum information processing device, rely entirely on micro- and nanofabrication techniques for their fabrication. The typical process flow includes: fabricating a planar microwave optical cavity, which is usually an LC resonant circuit comprising a capacitor and an inductor. The general fabrication method involves depositing a layer of superconducting material (such as niobium, tantalum, or niobium-titanium nitride) on a high-resistivity silicon substrate, then spin-coating photoresist to transfer the circuit pattern onto the photoresist, followed by etching to complete the circuit fabrication on the silicon substrate; obtaining a two-dimensional thin-film mechanical oscillator, which is typically a low-dissipation material with a high quality factor (such as silicon nitride, silicon carbide, or diamond). A superconducting metal film is usually fabricated on the mechanical oscillator, and coupling the superconducting metal film with the capacitor structure on the planar microwave optical cavity forms a combined capacitor, achieving coupling between the microwave and the mechanical oscillator; and assembling the planar microwave optical cavity and the two-dimensional thin-film mechanical oscillator, ensuring proper alignment and maintaining a good distance between them.

[0004] Currently, two-dimensional thin-film mechanical oscillator quantum devices fabricate the two types of chips separately and couple them by alignment and fixing them with epoxy resin adhesive. However, this method has many limitations and shortcomings, including: the direct contact between the thin-film oscillator and the microwave circuit leads to uncontrollable spacing, resulting in uncontrollable coupling strength between the thin-film oscillator and the microwave circuit; and the use of epoxy resin adhesive to fix the two chips will generate strain at low temperatures. The large stress will affect the relative position of the two chips, thus affecting the vibration performance of the thin film, the performance of the mechanical oscillator chip, and the stability of the device. Summary of the Invention

[0005] In order to address the above-mentioned deficiencies in the field, this application aims to provide a cavity optoelectronic quantum device and a method for fabricating the same.

[0006] According to one aspect of this application, a quantum device is provided, comprising a microwave circuit chip and a mechanical oscillator chip, wherein the microwave circuit chip and the mechanical oscillator chip are flip-bonded to each other, wherein... Microwave circuit chips include: A microwave circuit chip substrate, having a deposition region on a first surface and a plurality of first leveling alignment marks surrounding the deposition region; and A first metal layer is formed on a first surface of a microwave circuit chip substrate and includes a microwave circuit located in the settling region and a first bonding region located between the settling region and a plurality of first leveling alignment marks. Mechanical oscillator chips include: Mechanical oscillator chip substrate with a cavity; A silicon nitride thin film is formed on the second surface of the mechanical oscillator chip substrate. The central region of the silicon nitride thin film constitutes a suspended thin film region, which is located on the cavity. The second metal layer is formed on the surface of the silicon nitride thin film and includes a thin film electrode region, a second bonding region and a plurality of second leveling alignment marks, wherein the thin film electrode region is located at the center of the second metal layer; The thin film electrode region is smaller than the suspended thin film region. The center of the thin film electrode region is aligned with the center of the suspended thin film region. The second bonding region is opposite to and corresponds to the first bonding region. The microwave circuit is aligned with the center of the thin film electrode region. Multiple second leveling alignment marks are opposite to and correspond to multiple first leveling alignment marks. The second bonding region is located between the suspended thin film region and the second leveling alignment marks.

[0007] According to some embodiments of this application, the depth of the settling zone is 50-500 nm.

[0008] According to some embodiments of this application, the microwave circuit chip substrate is a silicon substrate with a thickness of 200-500 μm; The substrate for the mechanical oscillator chip is a silicon substrate with a thickness of 200-500μm.

[0009] According to some embodiments of this application, the material of the first metal layer includes: Nb, Ta, and / or NbTiN; The thickness of the first metal layer is 20-500 nm; The thickness of the silicon nitride film is 50-500 nm; The material of the second metal layer is aluminum; The thickness of the second metal layer is 10-50 nm.

[0010] According to some embodiments of this application, the distance a between the first bonding region and the settling region is 10-500 μm, and the distance c between the first bonding region and the first leveling alignment mark is 1-1000 μm.

[0011] According to some embodiments of this application, the mechanical oscillator chip is a first polygon or a first circle, the side length of the first polygon is 0.1-3mm, and the diameter of the first circle is 0.2-3mm; The thin-film electrode region is a second polygon or a second circle, wherein the side length of the second polygon is 0.05-1.5 mm and the diameter of the second circle is 0.1-1.5 mm.

[0012] According to some embodiments of this application, the distance b between the second leveling alignment mark and the second bonding region is 5-100 μm.

[0013] According to another aspect of this application, a method for fabricating a cavity optical quantum device is also provided. The quantum device includes a microwave circuit chip and a mechanical oscillator chip. The fabrication method includes: A first photoresist pattern is formed on the first surface of a microwave circuit chip substrate, and then the first photoresist pattern is etched to form a deposition area and multiple first leveling alignment marks. A first metal layer is grown on a first surface of a microwave circuit chip substrate to cover the microwave circuit chip substrate and a plurality of first leveling alignment marks; A second photoresist pattern is formed on the surface of the first metal layer, and the second photoresist pattern is etched to obtain a microwave circuit located in the deposition area and a first bonding area located between the deposition area and multiple first leveling alignment marks, thereby obtaining a microwave circuit chip. Fabrication of a mechanical oscillator chip substrate with a cavity; A silicon nitride thin film is formed on the second surface of the mechanical oscillator chip substrate; A second metal layer is formed on the surface of a silicon nitride thin film; A third photoresist pattern is formed on the surface of the second metal layer, and then the third photoresist pattern is etched to obtain a metallized surface consisting of a thin film electrode region, a second bonding region, and multiple second leveling alignment marks; wherein, the silicon nitride thin film has a suspended thin film region; Using multiple first leveling alignment marks and multiple second leveling alignment marks, the first bonding region of the microwave circuit chip and the second bonding region of the mechanical oscillator chip are flip-bonded, wherein the microwave circuit and the thin film electrode region are aligned at the center.

[0014] According to some embodiments of this application, the depth of the settling zone is 50-500 nm; The microwave circuit chip substrate is a silicon substrate with a thickness of 200-500μm; The first metal layer material includes: Nb, Ta, NbTiN, with a thickness of 20-500 nm; The second metal layer is made of aluminum and has a thickness of 10-50 nm. The substrate for the mechanical oscillator chip is a silicon substrate with a thickness of 200-500μm; The thickness of silicon nitride films is 50-500 nm.

[0015] According to some embodiments of this application, the distance a between the first bonding region and the settling region is 10-500 μm, and the distance c between the first bonding region and the first leveling alignment mark is 1-1000 μm; The mechanical oscillator chip is a first polygon or a first circle; the side length of the first polygon is 0.1-3mm, and the diameter of the first circle is 0.2-3mm; The thin-film electrode region is a second polygon or a second circle; the side length of the second polygon is 0.05-1.5 mm, and the diameter of the second circle is 0.1-1.5 mm. The second leveling alignment mark is located on the periphery of the second bonding region, and the distance b between it and the second bonding region is 5-100 μm.

[0016] This application achieves controllable coupling strength between the microwave circuit and the thin-film mechanical oscillator by depositing a substrate on the microwave circuit chip, effectively controlling the distance between them. This significantly enhances the coupling between the mechanical oscillator and the microwave cavity, thereby further improving the performance of the quantum device. Furthermore, this application uses metal-to-metal bonding instead of epoxy resin adhesive, increasing the fixation strength and avoiding the unpredictable effects of epoxy resin deformation at low temperatures on the thin-film oscillator, thus greatly improving the device's reliability. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation process of the settling zone and the first leveling alignment mark in an example embodiment of this application. Figure 2 This is a schematic diagram of the settlement zone and the first leveling alignment mark plane in an example embodiment of this application. Figure 3 This is a flowchart illustrating the fabrication process of the microwave circuit and the first bonding region in an example embodiment of this application. Figure 4 This is a planar schematic diagram of a microwave circuit chip in an example embodiment of this application. Figure 5 This is a cross-sectional view of the mechanical oscillator chip structure in an example embodiment of this application. Figure 6 This is a flowchart illustrating the metallization process of a mechanical oscillator chip in an example embodiment of this application. Figure 7 This is a cross-sectional view of the metallized mechanical oscillator chip structure of an example embodiment of this application. Figure 8 This is a plan view of the metallized mechanical oscillator chip structure of an example embodiment of this application. Figure 9This is a cross-sectional schematic diagram of a device in a flip-chip bonding process according to an example embodiment of this application. Figure 10 The images show a cross-sectional view and a partial enlarged view of the flip-chip bonding of the microwave circuit chip and the mechanical oscillator chip in an example embodiment of this application. Figure 11 This is a graph showing the change of pressure over time in the flip-chip bonding process of an example embodiment of this application. Figure 12 This is a graph showing the temperature change over time in the flip-chip bonding process of an example embodiment of this application. Figure 13 This is a schematic diagram of the equivalent circuit of a quantum device in an example embodiment of this application. Figure 14 This is a schematic diagram of a quantum device placed in a sample box for reading, representing an example embodiment of this application. Figure 15 The images shown are physical diagrams of quantum devices used in exemplary embodiments and comparative examples of this application. Figure 16A -D is a thin-film region diagram of the quantum device in the example embodiments and comparative examples of this application. Detailed Implementation The technical solution of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] It should be particularly noted that similar substitutions and modifications made to this application are obvious to those skilled in the art, and they are all considered to be included in this application. Those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0019] Unless otherwise specified, this application is conducted under standard conditions or conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, whose manufacturers are not specified, are all conventional products that can be obtained commercially.

[0020] The following is a detailed description of this application.

[0021] Currently, two-dimensional thin-film mechanical oscillator quantum devices fabricate the two types of chips separately and couple them through alignment and fixation using epoxy resin adhesive. This method has the following limitations and shortcomings: The coupling strength between the thin-film oscillator and the microwave circuit is uncontrollable: When microwave circuits and mechanical oscillators are fabricated directly on silicon substrates, there is not enough space, making it difficult to adjust the distance between the two chips to maintain the appropriate coupling strength.

[0022] Using epoxy resin to fix the two types of chips will cause strain at low temperatures: Since quantum devices need to operate in an extremely low temperature range (≈10 mK), the epoxy resin will generate large stress at low temperatures, which will cause the fixing position of the mechanical oscillator chip and the microwave circuit chip to change, making it impossible to couple well; or it will cause the stress distribution of the mechanical oscillator chip to change, affecting the performance of the mechanical oscillator chip and resulting in poor device stability.

[0023] Based on the above-mentioned technical problems, this application provides a cavity optical quantum device and its fabrication method, including a method for fabricating a microwave circuit chip and a flip-chip bonding process, so that the fabricated and assembled split quantum device has controllable coupling strength and good stability at low temperature.

[0024] In the fabrication of microwave circuit chips, this application utilizes a process of depositing a silicon substrate to leave a distance between the mechanical oscillator thin film and the microwave circuit, thus avoiding the problem of uncontrollable spacing caused by direct contact between the thin film oscillator and the microwave circuit. Furthermore, by controlling the depth of silicon substrate deposition, the spacing can be controlled, thereby achieving precise control of the coupling strength.

[0025] Furthermore, this application precisely controls the capacitance value of the metal formed by the corresponding upper and lower microwave circuit chip and the mechanical oscillator chip, ensuring stable and controllable coupling performance of the quantum device. Specifically, the deposition process directly sets the electrode spacing between the microwave circuit and the thin-film electrode region by precisely controlling the depth of the substrate deposition area, achieving quantitative adjustment of the capacitance value based on the physical characteristics of capacitance. The flip-chip bonding process ensures precise alignment of the upper and lower chips through leveling alignment marks, maintaining a stable electrode facing area. Simultaneously, metal bonding avoids deformation and displacement at low temperatures, eliminating capacitance fluctuations. The two processes work synergistically to lock down the core influencing factors of capacitance from both spacing and alignment perspectives, achieving precise control over this crucial physical quantity of capacitance.

[0026] This application utilizes flip-chip bonding technology to achieve tight bonding between metals. At low temperatures, the large stress generated by the epoxy resin will not affect the relative position of the two chips and thus the vibration performance of the thin film. It can maintain a stable relative position and achieve stable and reliable coupling.

[0027] Furthermore, this application provides the following technical solutions to address the aforementioned technical problems.

[0028] In some examples, this application provides a method for fabricating a cavity optical quantum device, comprising: Fabrication of microwave circuit chips, such as Figure 1 , Figure 3 As shown: Steps I-III: Spin-coat photoresist 2 on the first surface of the microwave circuit chip substrate 1 to form a first photoresist pattern 3.

[0029] Step IV: Etch the first photoresist pattern 3 to form a settling area A and multiple first leveling alignment marks B.

[0030] Step V: Remove residual photoresist.

[0031] Steps VI-VII: A first metal layer 4 is grown on the first surface of the microwave circuit chip substrate 1 to cover the microwave circuit chip substrate 1 (including the settling area A) and a plurality of first leveling alignment marks B.

[0032] Step VIII: Spin-coat photoresist 5 onto the surface of the first metal layer 4 to form a second photoresist pattern.

[0033] Step IX-X: Etch the second photoresist pattern to obtain the microwave circuit C located in the settling region A, and the first bonding region D located between the settling region A and a plurality of first leveling alignment marks B.

[0034] Metallization of mechanical oscillator chips, such as Figure 6 As shown: Steps XI-XII: Prepare or fabricate a mechanical oscillator chip substrate 11 with cavity 12; form a silicon nitride thin film 5 on the second surface of the mechanical oscillator chip substrate 11; form a second metal layer 6 on the surface of the silicon nitride thin film 5 of the mechanical oscillator chip.

[0035] Steps XIII-XV: Spin-coat photoresist 7 onto the surface of the second metal layer 6 to form a third photoresist pattern, and etch the third photoresist pattern to obtain a metallized surface composed of a thin film electrode region F, a second bonding region G, and multiple second leveling alignment marks H.

[0036] The silicon nitride thin film 5 has a suspended thin film region E located on the cavity 12.

[0037] The size of the thin film electrode region F is smaller than that of the suspended thin film region E and is aligned with the center of the suspended thin film region E; the second bonding region G is located between the suspended thin film region E and the second leveling alignment mark H, and corresponds to the first bonding region D; the multiple second leveling alignment marks H are opposite to and correspond to the multiple first leveling alignment marks B.

[0038] Inverted bonding, such as Figure 9 As shown: O is the pressure cantilever, with a motor connected to its upper part; R is the direction of pressure application; P is the vacuum nozzle; Q is the bottom tray.

[0039] The surface of the first bonding region D of the microwave circuit chip is flip-bonded to the second bonding region G of the mechanical oscillator chip using multiple first leveling alignment marks B and multiple second leveling alignment marks H; wherein the microwave circuit C is aligned with the center of the thin film electrode region F.

[0040] Optionally, the microwave circuit chip substrate 1 is a silicon substrate; the thickness of the microwave circuit chip substrate 1 is 200-500 μm. The material of the first metal layer 4 includes: Nb, Ta, NbTiN; the thickness of the first metal layer 4 is 20-500 nm; the material of the second metal layer 6 is aluminum; the thickness of the second metal layer 6 is 10-50 nm.

[0041] Optionally, the depth of the settling zone A is 50-500 nm. This depth is designed to be the coupling spacing d.

[0042] Optionally, the distance a between the first bonding region D and the settling region A is 10-500 μm, and the distance c between the first bonding region D and the first leveling alignment mark B is 1-1000 μm.

[0043] The mechanical oscillator chip substrate 11 is a silicon substrate with a thickness of 200-500μm; the silicon nitride thin film 5 has a thickness of 50-500nm.

[0044] The mechanical oscillator chip is polygonal or circular; the side length of the polygon is 0.1-3mm, and the diameter of the circle is 0.2-3mm; the thin film electrode area is polygonal or circular; the side length of the polygon is 0.05-1.5mm, and the diameter of the circle is 0.1-1.5mm.

[0045] The second leveling alignment mark H region is located on the periphery of the second bonding region G, and the distance b between it and the second bonding region G is 5-100μm.

[0046] like Figure 10 As shown, a quantum device according to an example embodiment of this application includes a microwave circuit chip and a mechanical oscillator chip, wherein the microwave circuit chip and the mechanical oscillator chip are flip-bonded to each other, wherein... The microwave circuit chip includes a microwave circuit chip substrate 1 and a first metal layer 4.

[0047] The first surface of the microwave circuit chip substrate 1 has a deposition region A and a plurality of first leveling alignment marks B around the deposition region; a first metal layer 4 is formed on the first surface of the microwave circuit chip substrate 1 and includes a microwave circuit C located in the deposition region A and a first bonding region D located outside the deposition region, the first bonding region D being located between the deposition region A and the plurality of first leveling alignment marks B.

[0048] The mechanical oscillator chip includes: a mechanical oscillator chip substrate 11 with a cavity 12, a silicon nitride thin film 5, and a second metal layer 6.

[0049] A silicon nitride thin film 5 is formed on the second surface of the mechanical oscillator chip substrate 11. The central region of the silicon nitride thin film constitutes the suspended thin film region E, which is located on the cavity 12. The second metal layer 6 is formed on the surface of the silicon nitride thin film 5, including a thin film electrode region F, a second bonding region G, and a plurality of second leveling alignment marks H, wherein the thin film electrode region F is located at the center of the second metal layer 6.

[0050] In this configuration, the size of the thin film electrode region F is smaller than that of the suspended thin film region E. The centers of the thin film electrode region F and the suspended thin film region E are aligned. The second bonding region G and the first bonding region D are opposite to each other and correspond to each other. The microwave circuit C is aligned with the center of the thin film electrode region F. Multiple second leveling alignment marks H and multiple first leveling alignment marks B are opposite to each other and correspond to each other. The second bonding region G is located between the suspended thin film region E and the second leveling alignment marks B.

[0051] Optionally, the depth of sedimentation region A is 50-500 nm; the microwave circuit chip substrate 1 is a silicon substrate with a thickness of 200-500 μm; the first metal layer material includes Nb, Ta, and NbTiN, with a thickness of 20-500 nm; the second metal layer material is aluminum with a thickness of 10-50 nm. The mechanical oscillator chip substrate is a silicon substrate with a thickness of 200-500 μm. The thickness of the silicon nitride thin film is 50-500 nm.

[0052] Optionally, the distance a between the first bonding region D and the settling region A is 10-500 μm, and the distance c between the first bonding region D and the first leveling alignment mark B is 1-1000 μm.

[0053] The mechanical oscillator chip is polygonal or circular, with the side length of the polygon being 0.1-3mm and the diameter of the circle being 0.2-3mm.

[0054] The thin-film electrode region F is either polygonal or circular, with the side length of the polygon being 0.05-1.5 mm and the diameter of the circle being 0.1-1.5 mm.

[0055] The second leveling alignment mark H region is located on the periphery of the second bonding region G, and the distance b between it and the second bonding region G is 5-100μm.

[0056] The technical solution of this application will be further described below with reference to specific embodiments.

[0057] Example 1 Fabrication of microwave circuit chips: A high-resistivity silicon substrate, polished on both sides, was cleaned with acetone and IPA. S1813 photoresist was spin-coated onto the first surface of the microwave circuit chip substrate at 3000 rpm for 60 seconds, followed by baking at 115°C for 2 minutes. After exposure using a laser direct-write system, the substrate was developed with MIF319 developer to form the deposition area and the first leveling alignment mark photoresist pattern. After completion, a post-baking process was performed at 115°C for 2 minutes. Oxygen plasma is used to treat the areas not covered by photoresist after exposure and development to remove any possible residual photoresist.

[0058] A reactive ion etching (RIE) system was used to etch the unprotected silicon substrate area. The etching parameters were SF6:CHF3 = 10 sccm: 40 sccm, RF power of 100 W, gas pressure of 2 Pa, etching time of 90 s, and etching depth of 150 nm (i.e., coupling spacing d). After etching, the silicon substrate was cleaned with acetone and IPA to remove the photoresist, obtaining the deposition area and multiple first leveling alignment marks.

[0059] Niobium film was deposited on the surface of a microwave circuit chip substrate using magnetron sputtering, covering the deposition area and the first leveling alignment mark. The process parameters were: RF power 50W, growth time 980 s, gas pressure 3.3mTorr, and thickness 100nm.

[0060] Photoresist S1813 was spin-coated onto the niobium film surface at 3000 rpm for 60 s, followed by baking at 115℃ for 2 min. After exposure using a laser direct-write system, the film was developed with MIF319 developer to form the photoresist pattern for the microwave circuit. Post-baking was then performed at 115℃ for 60 s.

[0061] Oxygen plasma is used to treat the areas not covered by photoresist after exposure and development to remove any possible residual photoresist.

[0062] The unprotected niobium film area was etched using a reactive ion etching (RIE) system with the following etching parameters: CF4:SF6:CHF3 = 50 sccm: 5 sccm: 5 sccm, RF power 100 W, gas pressure 2 Pa, and etching time 160 s. The etched chip was then stripped of the photoresist using acetone and isopropanol. Oxygen plasma is then used to remove any remaining photoresist to obtain the microwave circuit and the first bonding region.

[0063] Fabrication of mechanical array chips: An aluminum film was deposited onto the prepared mechanical oscillator chip using electron beam evaporation. A ma-N2410 electron beam resist was then spin-coated onto the aluminum film surface at 4000 rpm for 60 s, followed by baking at 90°C for 3 min. Exposure was performed using an electron beam exposure system, and development was carried out with D525 developer. The developer simultaneously etched the aluminum not protected by the electron beam resist to form a pattern. After development, the resist was removed and cleaned using acetone and IPA to obtain the thin film electrode area, the second bonding area, and multiple second leveling alignment marks.

[0064] Inverted bonding: The prepared microwave circuit chip was subjected to Ar ion bombardment treatment with the following parameters: power 50 W, time 90 s. This removed the oxide layer on the metal surface, activated the metal surface, and facilitated intermetallic bonding.

[0065] The metallized mechanical oscillator chip is used as the lower wafer, and the prepared microwave circuit chip is used as the upper wafer. A nozzle is used to attach the microwave circuit chip to the pressure cantilever, and the lower wafer is attached to the bottom tray. Before bonding, a leveling operation is performed using multiple first and second leveling alignment marks to ensure that the upper and lower wafers have the same level (the leveling alignment marks are as follows). Figure 2 and Figure 8 As shown), take any three marks and measure the distance between the corresponding marks on the upper and lower plates respectively. Use the principle of three points determining the plane to adjust the distance between the three points to be equal (error less than 0.1μm). Then measure the distance at the fourth mark for verification (error less than 0.1μm). After ensuring leveling, perform alignment to determine the relative position of the upper and lower plates, so that the center of the aluminum metallized area in the lower plate is aligned with the center of the capacitor part in the upper plate. After leveling, the bonding process begins. The pressure cantilever is slowly lowered to bring the upper and lower wafers into contact. The bonding pressure and temperature are then gradually increased over time, reaching the bonding pressure and temperature linearly after 10 minutes. After maintaining the bonding pressure and temperature for 40 minutes, heating is stopped, allowing the temperature to decrease naturally and the pressure to decrease linearly and slowly to 0 within 10 minutes. Once the pressure reaches 0, the bonded device can be removed. The changes in bonding pressure and temperature over time are shown below. Figure 11 , Figure 12 As shown. Bonding parameters: bonding pressure is 100 N, bonding temperature is 300℃, and the total process time is 1 hour.

[0066] Comparative Example The device as described in the examples was prepared using existing methods in the art, specifically by manually positioning it under a microscope and then attaching it with adhesive.

[0067] This technology has three main drawbacks: manual positioning lacks accuracy; the adhesive has significant stress at low temperatures, causing the mechanical oscillator chip to twist and deform, reducing the reliability of the device; and the bonding distance is uncontrollable, making it difficult to precisely control the spacing between chips by manually applying pressure.

[0068] like Figure 15 As shown, the left image shows a physical object bonded with glue, while the right image shows a physical object bonded with metal in an embodiment of this application.

[0069] Comparison table of thin film regions with different bonding methods

[0070] Application examples like Figure 13 The diagram shown is an equivalent circuit diagram of the quantum device in Example Embodiment 1 of this application.

[0071] Where Cr represents the parasitic capacitance of the circuit, and Lr represents the effective capacitance of the circuit. Arrows in the diagram indicate the effective capacitance formed by the metallization layer on the mechanical oscillator thin film and the microwave circuit chip. A superconducting metal film (such as aluminum) is fabricated on the surface of the mechanical oscillator, which, together with the capacitor structure in the microwave circuit (such as a parallel-plate capacitor), forms a variable combined capacitance C. m The vibration of the mechanical oscillator changes the spacing between the capacitor's plates, thus modulating the capacitance value.

[0072] Microwave circuits are typically LC resonant cavities, with a resonant frequency of . C t The total capacitance includes the inherent circuit capacitance Cr and the combined capacitance C. m The vibration of the mechanical oscillator causes C m The change in the frequency of the mechanical oscillator modulates the resonant frequency ω0, thus achieving frequency modulation of the microwave signal by the mechanical motion. This frequency modulation effect manifests as a dispersive coupling, where energy exchange occurs between the displacement of the mechanical oscillator and the number of microwave photons. Its Hamiltonian can be expressed as: H_int = g0a†a (b† + b) Where a† and a are the microwave photon generation and annihilation operators, b† and b are the mechanical phonon generation and annihilation operators, and g0 is the single-photon coupling strength and capacitance gradient. C m / x is proportional to the distance between the mechanical oscillator and the microwave circuit. By controlling the deposition depth of the silicon substrate, the distance between the mechanical oscillator and the microwave circuit can be precisely adjusted, thereby controlling the distance between them. C m / x, and thus g0, can be adjusted to achieve flexible design of the coupling strength. Generally, to achieve a larger coupling strength, the two should be kept as close as possible. However, if the distance is too close, the thin film will often generate an attractive force with the microwave circuit chip, causing the thin film to adhere to the microwave circuit chip. This distance is usually 100nm-200nm. Typically, the distance can be set at 200nm to avoid possible adsorption of the thin film. This dispersive coupling mechanism enables the mechanical oscillator to exchange energy efficiently with microwave photons.

[0073] The quantum signal processing chip described in this application is primarily tested using a network analyzer, a spectrum analyzer, and a microwave source. The device is first placed in a sample box made of oxygen-free copper, and microwave signals are read via inductive coupling using an external wireless readout coil. Its configuration is as follows: Figure 14 As shown (where X is the mechanical oscillator chip, Y is the reading coil, and Z is the tail circuit chip).

[0074] The sample box was placed in a dilution refrigerator and cooled to 10 mK. A fully attenuated input signal was then fed into the microwave circuit at the input signal port. The resonant frequency of the microwave circuit was obtained at the output signal port. Then, a strong drive microwave signal is input to the input signal port. - ,in The resonant frequency is the frequency of the mechanical oscillator. A photo-induced transparency phenomenon will occur nearby; this method can be used to determine the frequency of the mechanical oscillator. Next, a red-edged pump signal is input to the input signal port. - Through the aforementioned dispersive coupling mechanism, the system can generate a photon and annihilate a phonon. The microwave photon is dissipated into the environment through the microwave circuit. This process continues in the device until the number of thermal phonons is less than 1. Ultimately, the mechanical oscillator can be cooled to the quantum ground state, providing a foundation for realizing quantum information processing functions such as quantum state transmission and quantum entanglement.

[0075] In the fabrication of microwave circuit chips, this application utilizes a process of depositing a silicon substrate to leave a distance between the mechanical oscillator thin film and the microwave circuit, thus avoiding the problem of uncontrollable spacing caused by direct contact between the thin film oscillator and the microwave circuit. Furthermore, by controlling the depth of silicon substrate deposition, the spacing can be controlled, thereby achieving flexible control of the coupling strength.

[0076] This application also addresses the problem of deformation under high stress at low temperatures when using epoxy resin to fix two types of chips. It utilizes flip-chip bonding technology to achieve tight bonding between the metals, preventing deformation and delamination at low temperatures and maintaining a stable relative position for stable and reliable coupling.

[0077] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A cavity optical quantum device, characterized in that, It includes a microwave circuit chip and a mechanical resonator chip, wherein the microwave circuit chip and the mechanical resonator chip are flip-bonded to each other, wherein, The microwave circuit chip includes: A microwave circuit chip substrate, having a settling region on a first surface and a plurality of first leveling alignment marks surrounding the settling region; and A first metal layer is formed on the first surface of the microwave circuit chip substrate and includes a microwave circuit located in the settling region and a first bonding region located between the settling region and the plurality of first leveling alignment marks. The mechanical oscillator chip includes: Mechanical oscillator chip substrate with a cavity; A silicon nitride thin film is formed on the second surface of the mechanical oscillator chip substrate, and the central region of the silicon nitride thin film constitutes a suspended thin film region located on the cavity; and A second metal layer is formed on the surface of the silicon nitride thin film, including a thin film electrode region, a second bonding region, and a plurality of second leveling alignment marks, wherein the thin film electrode region is located at the center of the second metal layer; Wherein, the size of the thin film electrode region is smaller than that of the suspended thin film region, the center of the thin film electrode region and the suspended thin film region are aligned, the second bonding region and the first bonding region are opposite to each other and correspond to each other, the microwave circuit is aligned with the center of the thin film electrode region, the plurality of second leveling alignment marks are opposite to and correspond to the plurality of first leveling alignment marks, wherein the second bonding region is located between the suspended thin film region and the second leveling alignment marks.

2. The cavity optical quantum device according to claim 1, characterized in that, The depth of the sedimentation zone is 50-500 nm.

3. The cavity optoelectronic quantum device according to claim 1 or 2, characterized in that, The microwave circuit chip substrate is a silicon substrate with a thickness of 200-500μm; The substrate of the mechanical oscillator chip is a silicon substrate with a thickness of 200-500μm.

4. The cavity optical quantum device according to claim 1, characterized in that, The material of the first metal layer includes: Nb, Ta and / or NbTiN; The thickness of the first metal layer is 20-500 nm; The silicon nitride film has a thickness of 50-500 nm; The material of the second metal layer is aluminum; The thickness of the second metal layer is 10-50 nm.

5. The cavity optical quantum device according to claim 1, characterized in that, The distance (a) between the first bonding region and the settling region is 10-500 μm, and the distance (c) between the first bonding region and the first leveling alignment mark is 1-1000 μm.

6. The cavity optical quantum device according to claim 5, characterized in that, The mechanical oscillator chip is a first polygon or a first circle, wherein the side length of the first polygon is 0.1-3mm and the diameter of the first circle is 0.2-3mm; The thin-film electrode region is a second polygon or a second circle, wherein the side length of the second polygon is 0.05-1.5 mm and the diameter of the second circle is 0.1-1.5 mm.

7. The cavity optical quantum device according to claim 6, characterized in that, The distance (b) between the second leveling alignment mark and the second bonding area is 5-100 μm.

8. A method for fabricating a cavity optoelectronic quantum device, characterized in that, The quantum device includes a microwave circuit chip and a mechanical oscillator chip, and the method includes: A first photoresist pattern is formed on the first surface of a microwave circuit chip substrate, and then the first photoresist pattern is etched to form a deposition area and a plurality of first leveling alignment marks. A first metal layer is grown on the first surface of the microwave circuit chip substrate to cover the microwave circuit chip substrate and the plurality of first leveling alignment marks; A second photoresist pattern is formed on the surface of the first metal layer, and the second photoresist pattern is etched to obtain a microwave circuit located in the settling area and a first bonding area located between the settling area and the plurality of first leveling alignment marks, thereby obtaining a microwave circuit chip. Fabrication of a mechanical oscillator chip substrate with a cavity; A silicon nitride thin film is formed on the second surface of the mechanical oscillator chip substrate; A second metal layer is formed on the surface of the silicon nitride film; A third photoresist pattern is formed on the surface of the second metal layer, and then the third photoresist pattern is etched to obtain a metallized surface consisting of a thin film electrode region, a second bonding region, and a plurality of second leveling alignment marks; wherein the silicon nitride thin film has a suspended thin film region; Using the plurality of first leveling alignment marks and the plurality of second leveling alignment marks, the first bonding region of the microwave circuit chip and the second bonding region of the mechanical oscillator chip are flip-chip bonded, wherein the microwave circuit is aligned with the center of the thin film electrode region.

9. The preparation method according to claim 8, characterized in that, The depth of the settling zone is 50-500 nm; The microwave circuit chip substrate is a silicon substrate with a thickness of 200-500μm; The first metal layer material includes: Nb, Ta, NbTiN, with a thickness of 20-500 nm; The substrate of the mechanical oscillator chip is a silicon substrate with a thickness of 200-500μm; The thickness of the silicon nitride film is 50-500 nm; The second metal layer is made of aluminum and has a thickness of 10-50 nm.

10. The preparation method according to claim 8, characterized in that, The distance (a) between the first bonding region and the settling region is 10-500 μm, and the distance (c) between the first bonding region and the first leveling alignment mark is 1-1000 μm; The mechanical oscillator chip is a first polygon or a first circle; the side length of the first polygon is 0.1-3mm, and the diameter of the first circle is 0.2-3mm; The thin-film electrode region is a second polygon or a second circle; the side length of the second polygon is 0.05-1.5mm, and the diameter of the second circle is 0.1-1.5mm. The second leveling alignment mark is located on the periphery of the second bonding area and is 5-100 μm away from the second bonding area.

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