Integrated atomic gas chamber for electromagnetic wave detection and preparation method thereof

Abstract

The invention relates to an integrated atomic gas chamber for wide-spectrum and high-sensitivity electromagnetic wave detection and a preparation method thereof, and belongs to the field of electromagnetic wave measurement. Aiming at the problem that the volume of the gas chamber needs to be improved, according to the preparation method, a metal antenna and an electrode are prepared on a glass substrate, the metal antenna and the electrode are bonded with a silicon substrate corroded with a Rydberg gas chamber to form an integrated atomic gas chamber, each gas chamber is divided into a working cavity, a release cavity and a buffer cavity, the working cavity is communicated with the release cavity, the buffer cavity is arranged outside the working cavity, and the working cavity is communicated with the release cavity. An alkali metal releasing agent is placed in the releasing cavity, after activation, alkali metal steam atoms are diffused to the working cavity, the atom probe for microwave / radio frequency sensing is integrated and compressed to a plane, and the system size is remarkably reduced. In order to solve the problem that the system detection sensitivity needs to be enhanced, a group of metal antennas and electrodes are arranged in the working cavity, the antennas increase the action area of atoms and a space electromagnetic field, the electrodes increase the electromagnetic field intensity acting with the atoms, and the detection sensitivity is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic wave measurement, and particularly relates to an integrated atomic gas cell for electromagnetic wave detection and a preparation method thereof. Background Art

[0002] The detection and reception of electromagnetic wave signals are usually realized by electronic methods, that is, through a link composed of a series of electronic components such as antennas and low-noise amplifiers. Therefore, limited by electronic thermal noise, the detection sensitivity of existing radio frequency systems has encountered a bottleneck and approaches the electronic noise limit. Microwave detection based on Rydberg atoms is a new system technology approach. The coupling light, probe light and atoms interact to excite the atoms to the Rydberg highly excited state. The energy level frequency difference resonates with the microwave to be detected and interacts, causing a change in the absorption of the atomic gas mass. The intensity change of the microwave / radio frequency electromagnetic field is mapped to the intensity change of the probe light transmitted through the gas mass. This process maps microwave measurement to light intensity measurement, avoiding the interference of electronic circuit thermal noise and having an extremely excellent sensitivity limit limited by quantum projection noise. At the same time, the energy levels of highly excited state atoms are rich, and a single medium can cover the detection of a large frequency spectrum range from 100 kHz long wave to 1 THz terahertz wave.

[0003] Existing atomic gas cells have problems such as large volume and low detection efficiency, which limit the detection sensitivity that can actually be obtained by this technology. The atomic gas cell is fabricated by a glass sintering process, and its shape is usually spherical, cylindrical, or cubic with a size of about 10 cm. The medium interacts with the probe light and coupling light through free space light. The device has a large volume, is sensitive to environmental disturbances, and requires a low-vibration platform for support in the working environment, making it difficult to use flexibly. The diameters of the coupling light and probe light interacting with the atoms are on the order of about 1 mm. To ensure the light intensity of the laser, the light field diameter cannot be further increased. Therefore, the atoms excited to the Rydberg state are mainly in the light field, and the effective volume interacting with the electromagnetic wave to be detected is limited, resulting in limited microwave energy interacting with the atoms and restricting the detection ability of the microwave field based on highly excited state atoms.

[0004] As disclosed in Reference Document 1 (Chinese Invention Patent "Fiber-Coupled Atomic Gas Cell Rydberg Atom Quantum Microwave Measurement Device and Method", publication number CN117929421A, publication date July 2024), a fiber-coupled integrated Rydberg atomic gas cell is disclosed, as Figure 1As shown in the figure, the optical fiber is bonded to the end face of the atomic gas cell, and the collimation coupling of the optical path is ensured, forming a Rydberg atomic gas cell integrated with an optical fiber interface, replacing the traditional free-space optical path, and improving the problems such as sensitivity to environmental disturbances caused by spatial optical coupling and difficulty in flexible deployment of the sensing probe. A typical preparation process of the Rydberg atomic gas cell includes: 1) filling the atomic gas cell 33 of the optical fiber-coupled atomic gas cell probe with alkali metal atoms; 2) debugging the optical fiber-coupled atomic gas cell probe so that the beam collimation ports 31 with pigtails on the left side and the beam collimation ports 32 with pigtails on the right side of the optical fiber-coupled atomic gas cell have the same position of the beam collimation output end face. The input polarized light enters the atomic gas cell 33 through the beam collimation port 31 with a pigtail on the left side. Adjust the three-dimensional adjustment frame 201 provided on the beam collimation port 31 with a pigtail on the left side and the second three-dimensional adjustment frame 202 provided on the beam collimation port 32 with a pigtail on the right side to adjust the positions of the beam collimation output end faces of the beam collimation port 31 with a pigtail on the left side and the beam collimation port 32 with a pigtail on the right side. Use a power meter 204 to monitor the output power of the beam collimation port 32 with a pigtail on the right side until the output power value displayed on the power meter is the largest. At this time, the first beam collimation port 31 with a pigtail and the second beam collimation port 32 with a pigtail are on the same straight line. 3) Debug the optical fiber-coupled atomic gas cell probe so that the polarization plane directions of the beam collimation ports with pigtails on both sides of the optical fiber-coupled atomic gas cell are the same. Replace the power meter with a polarizer and rotate the beam collimation output end faces of the beam collimation port 31 with a pigtail on the left side and the beam collimation port 32 with a pigtail on the right side until the detected polarization plane is the same as the original polarization direction of the laser. 4) Use ultraviolet-curing optical glue to bond and fix the beam collimation port 31 with a pigtail on the left side and the beam collimation port 32 with a pigtail on the right side on the connection surfaces on both sides of the atomic gas cell 33.

[0005] Through the above process, the fiber coupling integration of the Rydberg atomic gas cell can be realized. The coupling light and the detection light are transmitted in the optical fiber, and the atomic gas cell is excited by the glued and fixed fiber collimator. The light weight, flexibility, and anti-environmental disturbance of the optical fiber enable the atomic gas cell to get rid of the bondage of free-space optical coupling. Through the light weight, flexibility, and anti-environmental disturbance characteristics of the optical fiber, the stability and deployment flexibility of the atomic microwave probe are improved. However, there are still the following problems:

[0006] (1) The volume of the atomic gas cell is large, which is not conducive to use. The atomic gas cell integrated with an optical fiber coupler is a glass gas cell made by sintering and blowing glass. The gas cell is a three-dimensional structure such as a cylinder or a cube, and the geometric size is on the order of ~10 cm. As a probe for microwave sensing measurement, the large volume of the gas cell is not conducive to array networking and limits the spatial resolution ability of the probe. The glass material and the three-dimensional structure make the mechanical strength of the Rydberg atomic probe poor and easy to break.

[0007] (2) The preparation efficiency of the atomic gas cell is low. Existing technologies use discrete glass gas cells, which need to be processed one by one and cannot be prepared in batches, resulting in low efficiency of gas cell preparation.

[0008] (3) The interaction between Rydberg atoms and microwaves is weak. The geometric size of the atomic gas cell used in existing technologies is on the order of ~10 cm. Coupling light, probe light and atoms interact to excite Rydberg atoms. This process requires a strong laser intensity, so the light field in the beam cross-section is concentrated and the size is on the order of ~1 mm. Only the Rydberg atoms in the beam can interact with the microwave field signal to be measured in space. For the microwave field distributed in space, the limited aperture volume results in only a small amount of field energy interacting with atoms for detection, which limits the sensitivity of Rydberg atom microwave measurement. Summary of the Invention

[0009] Aiming at the problems that the above existing technical solutions do not improve the gas cell volume and do not enhance the detection sensitivity of the system, the present invention proposes an integrated atomic gas cell for electromagnetic wave detection and its preparation method, which not only integrates and compresses the atomic probe for microwave / radio frequency sensing onto a plane, significantly reducing the system volume. In addition, by integrating the antenna and the electrode in the gas cell, the antenna increases the interaction area between atoms and the spatial electromagnetic field, and the tapered electrode increases the electromagnetic field intensity, jointly enhancing the interaction between electromagnetic waves and atoms and improving the detection sensitivity of the sensing system.

[0010] The integrated atomic gas cell provided by the present invention includes: preparing a metal antenna and a metal electrode on a glass substrate, the width of the metal antenna changes from wide to narrow and the narrowest part is connected to the metal electrode, and a thin film matching resistor is prepared at the end of the metal electrode; and etching a Rydberg gas cell on a silicon substrate. The Rydberg gas cell is divided into a working chamber, an atomic release chamber and a buffer chamber. The working chamber and the atomic release chamber are connected to form a chamber area, and a buffer chamber is arranged in a circle outside the chamber area; the side wall of the chamber formed by etching forms a flat inclined surface with the silicon substrate plane. Bonding the glass substrate with the metal antenna and the metal electrode and the silicon substrate with the etched Rydberg gas cell to form a closed gas cell; after bonding, the metal antenna and the metal electrode are located in the working chamber of the Rydberg gas cell; an alkali metal releasing agent is filled in the atomic release chamber. Activating the alkali metal releasing agent generates alkali metal vapor atoms, which diffuse into the working chamber and serve as the working medium for microwave detection. The coupling light and the probe light are reflected by the inclined surface of the gas cell to interact with the atoms in the gas cell, exciting the Rydberg state.

[0011] The preparation method of the integrated atomic gas cell provided by the present invention includes the following steps:

[0012] Step 1: Prepare the antenna and the electrode, including:

[0013] Step 1.1: Use thick film lithography on a glass substrate to pattern the antenna and microwave electrode; the width of each antenna gradually narrows and the narrowest part is connected to the electrode. The antenna is used to collect electromagnetic waves in space and concentrate the electromagnetic field at the connected electrode.

[0014] Step 1.2: Deposit a metal seed layer on the substrate with the photoresist pattern.

[0015] Step 1.3: Electroplate a metal layer on the substrate with the deposited seed layer according to the designed dimensions and thickness of the antenna and electrode.

[0016] Step 1.4: Lift off the photoresist on the substrate and the metal above the photoresist to form the antenna and electrode made of metal.

[0017] Step 1.5: Fabricate a thin film matching resistor at the end of the metal electrode, and the pattern of the matching resistor is aligned with the end of the electrode.

[0018] Step 2: Prepare the gas chamber, including:

[0019] Step 2.1: Deposit a silicon nitride thin film on a silicon substrate, and then use photoresist to define the pattern of the Rydberg gas chamber; the Rydberg gas chamber is divided into a working chamber, an atomic release chamber, and a buffer chamber. The working chamber is connected to the atomic release chamber to form a chamber area, and a buffer chamber is set around the chamber area.

[0020] Step 2.2: Using the photoresist as a mask, dry-etch the silicon nitride thin film on the substrate where there is no photoresist to form a window for etching to prepare the Rydberg gas chamber cavity, and then remove the photoresist mask.

[0021] Step 2.3: Using silicon nitride as a mask, wet-etch the silicon substrate to form the Rydberg gas chamber cavity, and then remove the silicon nitride thin film.

[0022] Step 2.4: Bond the glass substrate with the fabricated antenna and electrode and the silicon substrate with the etched Rydberg gas chamber cavity to form a closed gas chamber; an alkali metal releasing agent is filled in the atomic release chamber, and the antenna and electrode on the glass substrate are located in the working chamber of the silicon substrate.

[0023] Step 2.5: Activate the alkali metal releasing agent to generate alkali metal vapor atoms that diffuse into the working chamber.

[0024] Step 2.6: Package the closed gas chamber, construct an optical path with an optical fiber and optical micro-devices, and make the coupling light and detection light reflect through the inclined surface of the gas chamber to interact with the atoms in the gas chamber and excite the Rydberg state.

[0025] Furthermore, the present invention provides a method for detecting microwave signals, using the integrated atomic cell proposed by the present invention as a detection antenna for microwave signals in space. This method first excites the alkali metal atomic vapor in the atomic cell to the Rydberg state through coupling light and detection light, then transmits the signal to be detected through the glass of the atomic cell into the working chamber, where it interacts with the Rydberg state atoms, and finally converts the intensity change of the detection light into an electrical signal output through a photoelectric converter.

[0026] Furthermore, the present invention provides a method for signal down-conversion processing, using the integrated atomic cell proposed by the present invention as a superheterodyne receiver. This method first collects microwave signals in space through an external antenna, then transmits them through a cable to a MEMS (Micro-Electro-Mechanical System technology) antenna, and the MEMS antenna transmits the signal to the internal antenna of the atomic cell, while another group of MEMS antennas transmits the local oscillator signal to the same internal antenna of the atomic cell; the detection optical signal output by the atomic cell is converted by photoelectric conversion into an electrical signal that is superheterodyne mixed with the local oscillator signal.

[0027] The advantages and positive effects of the present invention are as follows:

[0028] (1) Compared with the existing electrical technologies, the integrated atomic cell implemented by the present invention has a better detection sensitivity limit and a larger frequency detection range.

[0029] (2) The integrated atomic cell of the present invention fabricates the antenna and electrodes inside the closed cell, enhancing the effective interaction area and intensity of the Rydberg atoms, and further improving the detection sensitivity of the system.

[0030] (3) The integrated atomic cell of the present invention and its fabrication method avoid the processing difficulties caused by the antenna and electrodes passing through the cell wall in terms of technology.

[0031] (4) The integrated atomic cell structure and its fabrication method provided by the present invention can realize a microwave measurement probe with low leakage rate, planarization, and wafer-level batch fabrication. The fabricated cell is not limited to the silicon-glass type cell, and similar structures such as glass-silicon-glass can also be used.

[0032] (5) The present invention also provides two usage modes of the implemented integrated atomic cell. The first is used as an antenna of a microwave system to directly receive and measure microwaves; the second is used as a radio frequency front end to process the microwave signals received by an external antenna; both usage models implemented by the atomic cell of the present invention improve the detection sensitivity of the system. Description of the Drawings

[0033] Figure 1 is a schematic diagram of a fiber-coupled integrated Rydberg atomic cell disclosed in Reference Document 1;

[0034] Figure 2 It is a process step diagram for preparing an integrated Rydberg atomic cell of the present invention;

[0035] Figure 3 It is a process flow diagram for preparing an integrated Rydberg atomic cell of the present invention;

[0036] Figure 4 It is an example diagram of the connection between the antenna and the electrode of a single atomic cell in an embodiment of the present invention;

[0037] Figure 5 It is a schematic diagram of a Rydberg atomic cell made of a glass - silicon - glass three - layer material prepared in an embodiment of the present invention;

[0038] Figure 6 It is a schematic diagram of the integrated atomic cell of the present invention directly detecting microwave signals as an antenna;

[0039] Figure 7 It is a schematic diagram of the integrated atomic cell of the present invention realizing down - conversion processing of signals as a superheterodyne receiver. Detailed implementation manners

[0040] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0041] The integrated atomic cell disclosed in the embodiment of the present invention, that is, the integrated Rydberg atomic cell, its preparation process steps are as Figure 2 shown, and the corresponding process flow is as Figure 3 shown. As Figure 2 and Figure 3 shown, the preparation of the integrated Rydberg atomic cell in the embodiment of the present invention mainly includes two parts. The first part is to prepare the antenna and the electrode, and the second part is to prepare the cell.

[0042] The steps for preparing the antenna and the electrode are as follows 1.1~1.5:

[0043] Step 1.1: Lithographically define the antenna and electrode patterns. Use thick - film lithography for the antenna and microwave electrode patterns. The antenna is used to collect electromagnetic waves in space. The electrode is connected to the antenna and the width of the antenna changes from wide to narrow. As Figure 4 shown, the two triangular regions represent an antenna, and the middle rectangular region represents the electrode. The two triangles correspond to the positive and negative poles of the antenna. The antenna gradually narrows from wide and connects to the two electrodes. The antenna concentrates the collected electromagnetic field at the connected metal electrodes. The electromagnetic field is mainly distributed in a very small gap between the metal electrodes, so that the electric field at the electrode gap is enhanced. Under the condition of constant power, the electric field strength is increased until the characteristic size of the electromagnetic field mode transmitted by the electrode is 1 mm, that is, Figure 4The spatial distribution of the electromagnetic field between the metal electrodes shown is at the 1 mm scale. The antenna pattern is selected according to the operating frequency band. For example, if the short-wave application frequency band is of concern, a fractal microstrip antenna pattern can be adopted. In the integrated atomic cell of the present invention, since the diameters of the probe light and the coupling light are relatively small, at the 1 mm scale, the direct coupling efficiency with the electromagnetic wave in space is low. Therefore, an antenna is added in the cell to increase the interaction area between the atoms and the spatial electromagnetic field and improve the detection sensitivity of the system.

[0044] As Figure 2 shown, in the embodiment of the present invention, a borosilicate glass wafer is used as the substrate, such as selecting a Corning BF33 wafer as the substrate. Typically, AZ4260 photoresist is used for photolithography. It is pre-spin-coated at a speed of 600 rpm for 10 s and then spin-coated officially at a speed of 3000 rpm for 40 s. The thickness of the photoresist is about 4 μm. The substrate photoresist is baked on a hot plate at 110 °C for 70 s. Contact ultraviolet lithography is adopted, and vacuum contact mode is used for exposure. The typical exposure dose is 250 mJ / cm 2 ; An alkaline developer is used for development. Observe the change of the pattern until the pattern is developed completely and add 10 s, and then immerse it in deionized water for fixing. The typical developer is AZ 400K, and the development time is 100 s. The developed substrate is baked on a hot plate at 120 °C for 90 s.

[0045] Step 1.2: Sputtering deposition of the metal seed layer. Deposit the metal seed layer on the substrate with the photoresist pattern. Generally, it includes two layers of metals. The first layer is a thin metal layer for enhancing the adhesion of the metal film, and the second layer is a high-conductivity layer for ensuring the low-loss transmission of electromagnetic signals.

[0046] Typically, in the embodiment of the present invention, magnetron sputtering is used for the deposition of the metal film, and its step coverage effect is better than that of electron beam evaporation, which is convenient for the subsequent electroplating process. DC target sputtering is used to deposit the first layer of Ti (titanium) film for enhancing adhesion. The process gas is Ar (argon) gas, the gas pressure is 1.5 mTorr, the DC power is 250 W, the deposition rate is 0.1 nm / s, the deposition time is 100 s, and the thickness is 10 nm. DC target sputtering is used to deposit the second layer of Au (gold) film for transmitting the electromagnetic field. The process gas is Ar gas, the gas pressure is 10 mTorr, the DC power is 200 W, the deposition rate is 1 nm / s, the deposition time is 200 s, and the thickness is 200 nm.

[0047] Step 1.3: Electroplating a thick metal layer on the seed layer. Deposit a thick metal layer on the seed layer on the wafer surface through the electroplating process to reach the designed size thickness of the antenna and the electrode.

[0048] Typically, in the embodiments of the present invention, an organic Au electroplating solution is used, which is less dangerous than a cyanide electroplating solution. The electroplating solution is heated to 60 °C and excited by a pulsed power supply. The current density is set to 2 A / dm 2 , the current excitation period is 20 ms, the duty cycle is 25%, the deposition rate is 10 μm / h, and a 2-μm-thick film is formed after depositing for 12 minutes.

[0049] Step 1.4: Lift-off to form metal antennas and electrodes. The photoresist and the metal above it are removed by lift-off to form antenna and electrode patterns made of metal.

[0050] Typically, in the embodiments of the present invention, the substrate is fixed to a fixture and immersed in a solution that can dissolve the photoresist. Typical solutions are acetone or methyl ethyl ketone. The solution is heated to 50 °C, and a low-power ultrasound with a power of 10 W is applied to dissolve the photoresist on the substrate and peel off the metal layer deposited on the top of the photoresist.

[0051] Step 1.5: Prepare a matching resistor. A thin-film matching resistor is prepared at the end of the metal electrode, and its preparation method is carried out according to the previous steps 1.1, 1.2, and 1.4.

[0052] Additionally, when performing step 1.1, the definition of the matching resistor pattern needs to be aligned with the end of the electrode for photolithographic alignment. Differently, when performing step 1.2, it is changed to depositing a thin-film resistor. Typically, a NiCr alloy is used to form a thin-film resistor with a microwave impedance of 50 ohms.

[0053] The steps for preparing the gas chamber are as follows 2.1 to 2.6:

[0054] Step 2.1: Deposit a silicon nitride film and define the chamber pattern. An intrinsic silicon wafer is used as the substrate to prepare an atomic gas chamber. A silicon nitride film is deposited as a mask for subsequent chamber etching, and the area of the chamber on the wafer substrate is defined by photolithography. The gas chamber structure is divided into three parts: a working chamber, an atomic release chamber, and a buffer chamber. The chamber area includes the working chamber and the atomic release chamber. Working chamber: Align and cover the antenna and electrode areas on the borosilicate glass in subsequent processes. Atomic release chamber: Used to place an alkali metal release agent to generate alkali metal atoms as a microwave detection medium. Buffer chamber: As a buffer layer to reduce the equivalent leakage rate of the working chamber and extend the life of the gas chamber. The working chamber and the atomic release chamber are connected to form the chamber area, and a buffer chamber is set in a circle outside it.

[0055] In the embodiments of the present invention, a dense silicon nitride thin film is deposited by the LPCVD (low-pressure chemical vapor deposition) process, rather than the PECVD (plasma-enhanced chemical vapor deposition) or ICP-CVD (inductively coupled plasma chemical vapor deposition) process. Typically, the deposition is carried out at a temperature of 800 °C, using the process gases of dichlorosilane SiH2Cl2 and ammonia NH3. The process gas pressure is set to 300 mTorr, the deposition rate is 4 nm / min, and the deposition time is 62 minutes, forming a silicon nitride Si3N4 thin film with a thickness of 250 nm on both the front and back sides of the substrate. The silicon nitride thin film on the back is used to prevent the back side of the silicon substrate from being corroded in the subsequent steps.

[0056] Typically, on the silicon nitride thin film formed on the substrate, in the embodiments of the present invention, Microposit S1813 positive photoresist is used for lithographically defining the Rydberg cell pattern. It is pre-spun at a speed of 500 rpm for 10 s and then spun at a speed of 5000 rpm for 40 s. The corresponding thickness of the photoresist is about 1.3 μm. The substrate photoresist is baked on a hot plate at 115 °C for 60 s. Contact ultraviolet lithography is adopted, and exposure is carried out using the vacuum contact mode. The typical exposure dose is 150 mJ / cm 2 ; It is developed using an alkaline developer, and the change of the pattern is observed until the pattern is completely developed and an additional 5 s is added, and then it is immersed in deionized water for fixing. The typical developer is AZ 400K, the development time is 25 s, and the fixing time is 25 s. The developed substrate is baked on a hot plate at 120 °C for 90 s.

[0057] Step 2.2: Dry etching to define the chamber area. Using the photoresist as a mask, the silicon nitride thin film in the non-photoresist part of the etched-defined pattern is etched to form a window for etching to prepare the gas chamber cavity, and then the photoresist mask is removed.

[0058] Typically, in the embodiments of the present invention, the reactive ion etching (RIE) process is used to remove the silicon nitride thin film. The process gas combination of SF6 + Ar is used, the process gas pressure is 100 mTorr, the radio frequency power is 200 W, the etching rate is ~50 nm / min, and the over-etching time is 10% for a total etching time of 5'30'' to ensure complete etching of Si3N4.

[0059] Typically, a microwave plasma asher with a frequency of 2.45 GHz is used to remove the photoresist. O2 and Ar are used as process gases, and the gas flow rates are 200 sccm and 50 sccm respectively. The process gas pressure is 10 Pa, and the typical ashing rate is 300 nm / min. The ashing time T0 is determined according to the specific thickness of the photoresist, and 10 s is added to T0 to ensure complete removal of the photoresist. In addition, a wet method can also be used, such as removing the photoresist with solutions such as acetone and methyl ethyl ketone under the condition of water bath heating.

[0060] Step 2.3: Form a chamber by wet etching. Using silicon nitride as a mask, silicon is wet-etched to form an atomic chamber, and then the Si3N4 film is removed.

[0061] Typically, hot KOH (potassium hydroxide) solution is used for etching. 35% concentration of KOH is used as the etching solution, which is heated to 80 °C. The etching rate is 100 μm / h. After etching for 10 hours, a chamber with a depth of 1 mm is formed, and the chamber does not completely penetrate the silicon wafer substrate. For <100>-oriented silicon substrates, due to the anisotropy of this wet etching, the sidewalls of the etched chamber naturally form a fixed angle of 54.7° with the substrate plane and have atomic-level roughness.

[0062] Typically, BOE (buffered oxide etch) solution is used to remove the silicon nitride film. A 49% concentration of hydrofluoric acid (HF) solution and a 40% concentration of ammonium fluoride solution are mixed in a ratio of 1:6 to form BOE solution. The substrate wafer is immersed in the BOE solution. The etching rate of the BOE solution for silicon nitride is 10 nm / s. Observe that the film etching is complete, and an additional 30 s of over-etching time is added to ensure complete film etching. In addition, RIE dry etching can also be used to remove the silicon nitride film.

[0063] Step 2.4: Form a closed gas chamber by anodic bonding. Bond the glass substrate with the antenna and electrode structure prepared and the silicon-based substrate with the etched chamber to form a closed airtight chamber.

[0064] Typically, anodic bonding process is used to complete the bonding of the glass substrate and the silicon substrate. Alkali metal release agent particles are filled in the atomic release chamber on the silicon-based substrate; alignment is performed using a contact exposure machine to align the antenna and electrode patterns on the glass substrate with the working chamber on the silicon substrate, and they are fixed by a fixture; the fixture and the wafer are transferred to a wafer bonding equipment. Under a vacuum environment and at a temperature of 380 °C, a voltage of 900 V and a pressure of 1.5 kN are applied and maintained for 15 mins to complete the airtight packaging of the Rydberg gas chamber.

[0065] Step 2.5: Release the alkali metal working medium. Activate the alkali metal release agent to generate rubidium or cesium vapor atoms, which diffuse into the working chamber as the working medium for microwave detection.

[0066] Typically, the gas chamber is placed on a hot plate and heated to 150 °C, and irradiated with an ultraviolet lamp for 24 hours to make the alkali metal release agent react to generate alkali metal vapor atoms such as rubidium (Rb) or cesium (Cs), and their concentration reaches the saturated vapor pressure. If a single-atom gas chamber is needed, the gas chambers prepared in batches on the wafer can be decomposed into multiple independent gas chambers by scribing with a grinding wheel.

[0067] Step 2.6: Encapsulation of optical components. For the convenience of using the gas chamber, the gas chamber can be selected for encapsulation. An optical path is constructed through optical fibers and optical micro-devices, so that the coupled light and the detection light interact with the atoms in the gas chamber through the inclined plane inclination reflection of the gas chamber, and the Rydberg state is excited.

[0068] The integrated atomic gas chamber prepared in the embodiment of the present invention includes: a metal antenna and a metal electrode prepared on a glass substrate, and a Rydberg gas chamber etched on a silicon substrate; the glass substrate prepared with the metal antenna and the metal electrode and the silicon substrate etched with the Rydberg gas chamber are bonded to form a closed gas chamber. After bonding, the metal antenna and the metal electrode are located in the working cavity of the Rydberg gas chamber. The width of the metal antenna changes from wide to narrow, and the narrowest part is connected to the metal electrode. A thin-film matching resistor is prepared at the end of the metal electrode. The metal electrode can be a traveling-wave electrode or a lumped electrode. The Rydberg gas chamber is divided into a working cavity, an atomic release cavity, and a buffer cavity. The working cavity and the atomic release cavity are connected to form a cavity area, and a buffer cavity is arranged in a circle outside the cavity area. An alkali metal releasing agent is filled in the atomic release cavity. When the alkali metal releasing agent is activated to generate alkali metal vapor atoms, they diffuse into the working chamber and serve as the working medium for microwave detection.

[0069] In the embodiment of the present invention, the typical size of the prepared integrated atomic gas chamber is: the working cavity is 5×10 mm. The transverse width of the working cavity depends on the antenna size and can be on the order of mm. The longitudinal size (the direction of laser transmission) is slightly longer and can be on the order of 10 mm to increase the laser-atom-microwave field interaction length; the buffer cavity is a square ring with a width of 5 mm; the atomic release cavity is 2×2 mm and can accommodate a spherical alkali metal releasing agent.

[0070] As Figure 4 shown, there is a combination of an antenna and an electrode in each atomic gas chamber prepared in the embodiment of the present invention. In this example, the sizes of the antenna and the electrode are about 2-3 mm. The transverse width of the specific atomic gas chamber will be determined according to the antenna size.

[0071] As Figure 5 shown, according to the above preparation method, the embodiment of the present invention can also prepare an integrated atomic gas chamber made of three-layer materials of glass-silicon-glass. When preparing, in step 2.3, the silicon is etched until it is completely penetrated during the wet etching to form the chamber. An anodic bonding process is performed on the upper surface of the silicon substrate with the glass substrate prepared with the antenna and the electrode as in step 2.4, and an anodic bonding process is performed on the lower surface of the silicon substrate with a glass substrate to form a glass-silicon-glass atomic gas chamber. Compared with the glass-silicon gas chamber, this can transmit light in the vertical direction in the figure for use in some special applications.

[0072] As Figure 6As shown in the figure, in the embodiment of the present invention, the prepared integrated Rydberg atomic cell is used as an antenna to detect microwave signals in space, which can be direct detection or superheterodyne detection. Glass is a microwave transparent material. Atoms in the cell detect electromagnetic waves, and the antenna plays a role in enhancing the detection sensitivity. The antenna collects electromagnetic waves in space and concentrates them at the electrodes. Traditional technologies are restricted by the beam cross-sectional size and have a relatively small interaction volume with electromagnetic waves in space. The antenna in the integrated Rydberg atomic cell of the present invention greatly increases the coupling ability to microwave signals in space and improves the detection sensitivity of the system. At the same time, the characteristic spacing of the electrodes connected by the antenna is on the order of 10 - 100 μm. The reduction of the microwave electrode spacing enhances the binding ability to the collected microwave signals and greatly increases the field strength of the collected microwave field. Since the output signal of Rydberg atomic microwave detection is proportional to the field strength, the detection sensitivity of the system is improved. As Figure 6 shown, the coupling light and the detection light excite the alkali metal atomic vapor in the cell to the Rydberg state. The signal to be detected passes through the glass of the cell and enters the working chamber of the cell, interacts with the Rydberg state atoms, changes the absorption rate of the detection light by the atomic vapor, and the intensity of the detection light reflects the intensity of the electromagnetic wave to be measured. The intensity change of the detection light is converted into an electrical signal output through a photoelectric converter.

[0073] As Figure 7 shown, in the embodiment of the present invention, the prepared integrated Rydberg atomic cell is used as a superheterodyne receiver. The external antenna collects microwave signals in space and transmits them to the MEMS antenna through a cable. The MEMS antenna emits the signal to the antenna in the cell with high directivity. At the same time, another group of MEMS antennas emits a local oscillator signal with a certain power to the same antenna in the cell. The output detection light signal in the cell is converted by photoelectric conversion into an output signal that is superheterodyne mixed with the local oscillator signal. The smaller microwave electrode spacing in the cell improves the binding ability to the microwave field, and under the condition of power conservation, it improves the field strength of the electromagnetic field interacting with the atoms and enhances the detection sensitivity of the system.

[0074] Using the integrated Rydberg atomic cell provided by the present invention for electromagnetic wave detection has a better detection sensitivity limit and a larger frequency detection range than the current electrical technology for electromagnetic wave detection.

[0075] The electromagnetic wave detection technology based on classical electronics is limited by electronic thermal noise, and its ultimate noise is limited by electronic thermal noise. The noise limit is , where k is the Boltzmann constant and T is the temperature.

[0076] For the electromagnetic wave detection technology based on Rydberg atoms of the present invention, its noise limit is quantum projection noise, and the theoretical noise limit is , where c is the speed of light, is the vacuum permittivity, is the Planck constant, is the effective receiving aperture, i.e., the effective area of the chamber for receiving the electromagnetic field, is the atomic electric dipole moment, is the number of Rydberg atoms interacting with the electromagnetic field, is the decoherence time.

[0077] The electromagnetic field measurement based on Rydberg atoms in the present invention can use a single working medium, such as Cs atomic vapor or Rb atomic vapor, and can support electromagnetic field measurements in a large frequency range of 100 kHz to 1 THz, including long wave, medium wave, short wave, radio frequency, millimeter wave, and terahertz frequency bands. By changing the coupling light frequency and selecting different Rydberg energy levels, the adjustment of the working frequency range can be achieved. For example, using the Rydberg state of cesium atoms can perform electromagnetic field detection in the frequency range of 100 kHz to 2 GHz; using the Rydberg state of cesium atoms can perform electromagnetic field detection in the frequency range of 20 to 40 GHz; using the or Rydberg state of cesium atoms can perform electromagnetic field detection near 320 GHz.

[0078] Except for the technical features described in the specification, they are all well-known technologies to those skilled in the art. The present invention omits the description of well-known components and well-known technologies to avoid redundancy and unnecessarily limit the present invention. The embodiments described in the above examples do not represent all embodiments consistent with the present application. Based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. An integrated atomic gas cell, characterized in that, Comprising at least one independent atomic gas chamber, each atomic gas chamber including: a metal antenna and a metal electrode prepared on a glass substrate, the width of the metal antenna becoming narrower from wide and the narrowest part being connected to the metal electrode, and a thin-film matching resistor being prepared at the end of the metal electrode; and a Rydberg gas chamber being etched on a silicon substrate, the Rydberg gas chamber being divided into a working chamber, an atomic release chamber, and a buffer chamber, the working chamber communicating with the atomic release chamber to form a chamber area, and a circle of buffer chamber being arranged outside the chamber area; the side wall of the chamber formed by etching forms an inclined surface with the plane of the silicon substrate; bonding the glass substrate with the metal antenna and the metal electrode and the silicon substrate with the etched Rydberg gas chamber to form a closed gas chamber; after bonding, the metal antenna and the metal electrode are located in the working chamber; An alkali metal releasing agent is filled in the atomic release chamber, the alkali metal releasing agent is activated to generate alkali metal vapor atoms, which diffuse into the working chamber and serve as the working medium for microwave detection; the coupling light and the coupling light are reflected by the inclined surface of the gas chamber to interact with the atoms in the gas chamber, exciting the Rydberg state.

2. The integrated atomic gas cell according to claim 1, characterized in that, Each of the atomic gas chambers described contains an antenna and two electrodes, the positive and negative poles of the antenna are respectively connected to one electrode, and the antenna concentrates the collected electromagnetic field to the connected electrode; under the condition of constant power, the electric field strength is increased so that the characteristic size of the electromagnetic field mode transmitted at the gap between the two electrodes is 1 mm.

3. The integrated atomic gas cell according to claim 1 or 2, characterized in that, The sizes of the antenna and the electrodes in each of the atomic gas chambers are set at 2 - 3 mm, and the distance between the two electrodes is 10 - 100 μm.

4. A preparation method of an integrated atomic gas cell, characterized in that, Including the following steps: Step 1: Prepare the antenna and the electrode, including: Step 1.1: Use thick photoresist to lithograph the antenna and microwave electrode patterns on the glass substrate; the width of each antenna becomes narrower from wide and the narrowest part is connected to the electrode, and the antenna is used to collect electromagnetic waves in space and concentrate the electromagnetic field to the connected electrode; Step 1.2: Deposit a metal seed layer on the substrate with the photoresist pattern; Step 1.3: Electroplate a metal layer on the substrate with the deposited seed layer according to the designed size and thickness of the antenna and the electrode; Step 1.4: Lift off the photoresist on the substrate and the metal above the photoresist to form the antenna and the electrode made of metal; Step 1.5: Prepare a thin-film matching resistor at the end of the metal electrode, and the pattern of the matching resistor is aligned with the end of the electrode; Step 2: Prepare the gas chamber, including: Step 2.1: Deposit a silicon nitride thin film on the silicon substrate, and then use photoresist to define the Rydberg gas chamber pattern; the Rydberg gas chamber is divided into a working chamber, an atomic release chamber, and a buffer chamber, the working chamber communicates with the atomic release chamber to form a chamber area, and a circle of buffer chamber is arranged outside the chamber area; Step 2.2: Using the photoresist as a mask, dry-etch the silicon nitride thin film in the non-photoresist part on the substrate to form a window for etching and preparing the Rydberg gas chamber cavity, and then remove the photoresist mask; Step 2.3: Using silicon nitride as a mask, wet-etch the silicon substrate to form the Rydberg gas chamber cavity, and then remove the silicon nitride thin film; Step 2.4: Bond the glass substrate with the antenna and electrode prepared thereon and the silicon substrate etched with the Rydberg cell cavity to form a closed chamber; fill the atomic release chamber with an alkali metal release agent, and the antenna and electrode on the glass substrate are located in the working chamber of the silicon substrate; Step 2.5: Activate the alkali metal release agent to generate alkali metal vapor atoms that diffuse into the working chamber; Step 2.6: Package the closed chamber, construct an optical path with an optical fiber and optical micro-devices, and enable the coupling light and the probe light to interact with the atoms in the chamber through the inclined plane reflection of the chamber, thereby exciting the Rydberg state.

5. The preparation method according to claim 4, characterized in that, In the step 1.2, the deposition of the metal thin film by magnetron sputtering includes: depositing the first layer of titanium thin film by direct current target sputtering for enhancing the adhesion, and the process gas is argon; depositing the second layer of gold thin film by direct current target sputtering for transmitting the electromagnetic field, and the process gas is argon.

6. The preparation method according to claim 4, characterized in that, In the step 2.1, a silicon nitride thin film is deposited by using a low-pressure chemical vapor deposition (LPCVD) process to form silicon nitride thin films on both the front and back sides of the silicon substrate.

7. The preparation method according to claim 4, characterized in that, The integrated atomic chamber is prepared with a three-layer material of glass-silicon-glass. In the step 2.3, the silicon substrate is wet-etched until it is completely penetrated, and the upper surface of the silicon substrate is bonded with the glass substrate prepared with the antenna and electrode, and the lower surface of the silicon substrate is bonded with a glass substrate.

8. The preparation method according to claim 4, wherein In the step 2.1, an intrinsic silicon wafer is used as the substrate, and the substrate is a silicon substrate with a <100> crystal orientation. After wet etching in the step 2.3, the sidewall of the etched chamber naturally forms a fixed angle of 54.7° with the substrate plane and has atomic-level roughness.

9. A microwave signal detection method, which uses the integrated atomic chamber according to any one of claims 1 to 3 as a detection antenna for microwave signals in a detection space; the method first excites the alkali metal atom vapor in the atomic chamber to the Rydberg state through the coupling light and the probe light, then transmits the signal to be detected through the glass of the atomic chamber into the working chamber to interact with the Rydberg state atoms, and finally converts the intensity change of the probe light into an electrical signal output through a photoelectric converter.

10. A method for signal down-conversion processing, using the integrated atomic cell according to any one of claims 1 to 3 as a superheterodyne receiver; the method first collects microwave signals in space through an external antenna, and then transmits them to the MEMS antenna through a cable. The MEMS antenna transmits the signals to the internal antenna of the atomic cell, and at the same time, another group of MEMS antennas transmits the local oscillator signals to the same internal antenna of the atomic cell; The detection optical signal output by the atomic chamber is converted into an electrical signal that is superheterodyne mixed with the local oscillator signal through photoelectric conversion; Among them, MEMS represents microelectromechanical system technology.

Images