Preparation method of vacuum-bonded tail-pipe-free multi-reflection-cavity-containing air chamber

Abstract

The invention discloses a preparation method of a vacuum-bonded tail-pipe-free multi-reflection-cavity-containing gas chamber, belongs to the technical field of atomic devices, and compared with a traditional multi-reflection-cavity-containing atomic gas chamber, the method has the advantages that the phenomenon that a glass blowing technology inevitably causes tail pipe fusion, and the gas chamber cannot be subjected to multi-reflection-cavity-containing gas chamber fusion is avoided; the positioning of each part and the anodic bonding in vacuum are ensured through a machined mold, and the preparation of the standard atomic gas chamber with the completely controllable size is realized. In the field of helium atom magnetometers, the method is operated under full vacuum, is cleaner, and can effectively avoid the gas chamber quality problem caused by other stray gases. The gas filling pressure range of the atomic gas chamber prepared by the method can be changed from below 1 torr to close to 1 atmospheric pressure. The standardized atomic air chamber prepared by the invention can be used in precision measuring instruments such as atomic magnetometers, nuclear magnetic resonance gyroscopes, atomic clocks and the like, and has great significance in wide application of the precision measuring instruments.

Description

Technical Field

[0001] The invention belongs to the technical field of atomic devices, and in particular relates to a method for preparing a vacuum-bonded tail-free gas chamber containing multiple reflection cavities. Background Art

[0002] Atomic devices based on atomic spectroscopy include atomic clocks, atomic magnetometers, nuclear magnetic resonance gyroscopes, etc. These atomic devices play an important role in frequency calibration, magnetic field sensing, navigation, and cutting-edge physics research. As the core component, the atomic gas cell, and the improvements made in the preparation direction of the atomic gas cell, are of great significance to improving the performance of these atomic gas cells and broadening their application range.

[0003] Due to the special chemical properties of the atoms inside the atomic gas chamber, in many cases, the preparation plan of the gas chamber needs to be completed in a vacuum pipe system to isolate the air outside the gas chamber. The early atomic gas chamber preparation plan was mainly glass blowing technology. The sealed atomic gas chamber was prepared by melting the glass gas chamber connected to the vacuum pipe at high temperature. Since the gas chamber needs to be connected to the pipe to facilitate the operation of the atomic components in the gas chamber, there must be a glass tube connecting the gas chamber and the pipe system. Since the glass tube needs to be melted to prepare an independent atomic gas chamber, the atomic gas chamber prepared by this process generally leaves an unfixed and unavoidable tail pipe. Alkali metal-based atomic gas chambers often work in a heating environment to maintain a certain gaseous atomic density. On the one hand, the tail pipe will affect the temperature gradient of the entire gas chamber and thus affect the performance of the atomic device. On the other hand, it will also enrich the solid atoms and seriously hinder the stability of the atomic device.

[0004] Anodic bonding is one of the most important packaging technologies in the MEMS field and has been widely used in the standardized preparation of atomic gas chambers. This technology can achieve a tight bond between two different materials to achieve the purpose of sealing by adding appropriate high temperature and electric field between glass and metal, alloy or semiconductor materials. Common bonding materials are generally glass and silicon wafers. During the bonding process, the glass is connected to the high-voltage negative electrode and the silicon wafer is connected to the high-voltage positive electrode. Under the action of high temperature and electric field, the Na in the glass + The ions and electrons in the silicon wafer will migrate in a directional manner, forming Na+ near the bonding area between the glass and silicon wafer. + Ion depletion layer, at this time, O 2- The ions and silicon react chemically to form a tight silicon-oxide bond, thus combining the two materials. By etching a certain number of small holes on the silicon wafer in advance, the silicon wafer and two pieces of glass are bonded and sealed to obtain a series of millimeter-scale tail-free atomic gas chambers.

[0005] The signal-to-noise ratio of atomic devices is closely related to the geometric properties of the atomic gas chamber. The distance of interaction between light and atoms is limited by the size of the atomic gas chamber, while the signal strength of the system is positively correlated with the distance of interaction between light and atoms. A common solution is to add a multi-reflection cavity to double the distance of interaction between light and atoms without changing the size of the gas chamber. The multi-reflection cavity involved in the present invention is the Herriott cavity, which is a geometric optical cavity composed of a pair of cylindrical reflectors with fixed curvature. In order to achieve multiple reflections, the relative main axis angle and relative distance of the cylindrical reflectors need to be more precisely controlled. The earliest work on applying the Herriott cavity to the field of atomic magnetometers was carried out by Princeton University in the United States. The early Herriott cavity was fixed in the atomic gas chamber by glue. This fixing method severely limited its wide application in the field of atomic devices. This laboratory has developed a technology for applying anodic bonding to the preparation of atomic gas chambers containing Herriott cavities and multi-reflection cavities. A cylindrical reflector of fixed size is fixed by a machined mold, the reflector is fixed on a silicon wafer by using an anodic bonding technique, and finally the gas chamber is sealed by using an anodic bonding technique, thereby preparing a batch of atomic gas chambers containing Herriott cavities and multiple reflection cavities.

[0006] The existing preparation scheme of atomic gas chamber containing Herriott cavity and multiple reflection cavity generally requires the use of glass blowing technology to fill specific atoms into the gas chamber, which will inevitably lead to the appearance of tail pipe, a structure that cannot be accurately controlled. On the one hand, this structure will affect the uniformity of atomic gas chamber heating, thereby generating temperature gradient and affecting the performance of atomic devices. On the other hand, during long-term use, this structure will cause atoms to be easily enriched in the tail pipe, affecting the normal operation of atomic devices. Inspired by the MEMS process, we combined the preparation scheme of atomic gas chamber containing Herriott cavity and multiple reflection cavity with the vacuum anode bonding part of MEMS process, and proposed a standardized atomic gas chamber preparation scheme without tail pipe. On the one hand, this scheme helps to solve several defects of traditional gas chamber containing tail pipe, and can also prepare a standard atomic gas chamber with simple appearance, which provides convenience for the establishment of theoretical model and the comparison between theory and experiment, and is conducive to verifying the correctness of theoretical model. Summary of the invention

[0007] The present invention proposes a method for preparing a vacuum-bonded tail-free gas chamber containing multiple reflection cavities. Different from the prior art, the present technical solution combines the MEMS process preparation scheme of atomic gas chambers with the traditional preparation scheme of atomic gas chambers containing Herriott cavities to prepare tail-free atomic gas chambers containing multiple reflection cavities that retain the characteristics of the MEMS process. The present invention prepares a silicon wafer with multiple reflection cavities fixed by the prior art, completes the steps of filling atoms and sealing in the traditional gas chamber preparation scheme in a vacuum anode bonding system, realizes the characteristics of no tail tubes in the MEMS process on the newly prepared gas chamber, and successfully integrates the multiple reflection cavities into the atomic gas chamber to improve the signal-to-noise ratio. On the one hand, this solution helps to solve a series of problems introduced by the tail tube structure in the traditional atomic gas chamber during the experiment. On the other hand, compared with the traditional gas chamber containing tail tubes, the tail-free gas chamber structure is simpler and more convenient for theoretical modeling, which helps to establish and correct the theoretical model.

[0008] The objective of the present invention is achieved through the following technical solutions:

[0009] A method for preparing a vacuum-bonded tailless tube-containing multi-reflection cavity air chamber comprises the following steps:

[0010] Step 1: Use a wafer dicing machine to cut out silicon wafers;

[0011] Step 2: Cleaning and ultrasonicating the silicon wafer cut in step 1 and the glass cover with a single-side opening and no tail pipe;

[0012] Step 3: Bonding the silicon wafer in step 2 to the multi-reflection cavity mirror to obtain a silicon wafer bonded with the multi-reflection cavity mirror;

[0013] Step 4: Place the silicon wafer bonded with multiple reflective cavity mirrors in step 3 and the single-sided open glass cover without tail tube in step 2 in a vacuum sealing device, fill the single-sided open glass cover without tail tube with atoms and gas, and then provide high temperature and electric field for bonding.

[0014] In the above technical solution, in step 1, the silicon wafer is single-sided polished, has a size of 21 mm×33 mm, and is 0.5 mm thick.

[0015] In the above technical solution, in step 2, the cut silicon wafer and the glass cover with a single-side opening are placed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide (concentrated sulfuric acid: hydrogen peroxide = 3:1) for cleaning, and then ultrasonically treated with acetone, isopropanol and water respectively.

[0016] In the above technical scheme, in step three, the silicon wafer and the multi-reflection cavity mirror are fixed by using an anodic bonding device, and a DC voltage of about 1000 V is applied at a high temperature of about 300 ° C, wherein the high-voltage positive electrode is connected to the silicon wafer, and the high-voltage negative electrode is connected to the multi-reflection cavity mirror. After a bonding process of about two hours, a silicon wafer bonded with a multi-reflection cavity mirror is obtained.

[0017] In the above technical solution, in step 4, a vacuum under certain conditions is pre-evacuated, and after the operation of filling atoms and gases is completed, a high temperature of about 300°C and a certain degree of electric field are provided in the vacuum system for bonding.

[0018] In the above technical solution, in step 4, when the pre-filled gas pressure is less than 100 torr, the common pre-filled background gas is easily broken down by the high voltage, resulting in bonding failure. It is necessary to pre-bond for 30 minutes at a voltage not exceeding 300 V under a given pre-filled gas pressure to initially seal the gas chamber, and then fill it with background gas of about several hundred torr, and increase the bonding voltage to 1000 V to improve the bonding strength.

[0019] In the above technical solution, in step 4, when the pre-filled gas pressure is higher than 200 torr, the pre-bonding step is skipped and a higher voltage is directly added for final bonding.

[0020] An atomic gas chamber is an atomic gas chamber made by adopting the method for preparing a vacuum-bonded tail-free gas chamber containing multiple reflection cavities.

[0021] An atomic magnetometer comprises an atomic gas chamber, wherein the atomic gas chamber is manufactured by adopting the above-mentioned method for preparing a vacuum-bonded tail-tube-free gas chamber containing multiple reflection cavities.

[0022] Beneficial effects:

[0023] 1. Compared with the traditional preparation scheme of atomic gas chamber containing multiple reflection cavities, by referring to the preparation scheme of MEMS process gas chamber, an atomic gas chamber containing multiple reflection cavities without tail pipe is obtained, which can solve the temperature gradient and long-term stability problems easily caused by the gas chamber containing tail pipe.

[0024] 2. Compared with the existing common MEMS process gas chamber preparation scheme, the gas chamber prepared by this scheme has four light-transmitting surfaces, while the MEMS process gas chamber has only two light-transmitting surfaces, which limits the scope of application of this scheme. In addition, this scheme integrates multiple reflection cavities, which is very helpful for improving the signal-to-noise ratio of the system.

[0025] 3. The existing air chamber has no tail pipe and has a simple structure. Compared with the traditional air chamber with a tail pipe, the deviation between the theoretical results and the experimental results caused by the tail pipe can be directly eliminated during theoretical modeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the traditional gas chamber preparation process;

[0027] Figure 2 It is a silicon wafer with a multi-reflection cavity;

[0028] Figure 3 This is a simplified diagram of the vacuum anodic bonding device seen from the observation window;

[0029] Figure 4 It is a silicon wafer with a multi-reflection cavity and a glass cover with a single opening without a tail pipe, which is sealed by vacuum anodic bonding.

[0030] Among them, 1 is a silicon wafer, 2 is an atomic adding module, 3 is a silicon wafer bonded with a multi-reflection cavity mirror, and 4 is a single-sided open glass cover without a tail pipe. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example

[0033] A method for preparing a vacuum-bonded tailless tube-containing multi-reflection cavity air chamber comprises the following steps:

[0034] Step 1: Use a wafer dicing machine to cut out a 21 mm × 33 mm single-side polished 0.5 mm thick silicon wafer 1.

[0035] Step 2: The cut silicon wafer and the single-sided open tail pipe-free glass cover 4 are placed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide (concentrated sulfuric acid: hydrogen peroxide = 3:1) for cleaning, and then ultrasonically treated with acetone, isopropanol and water respectively to meet the anodic bonding requirements.

[0036] Step 3: Use the laboratory-made anodic bonding device to fix the silicon wafer and the multi-reflection cavity mirror. At a high temperature of about 300 °C, apply a DC voltage of about 1000 V, where the high-voltage positive electrode is connected to the silicon wafer and the high-voltage negative electrode is connected to the multi-reflection cavity mirror. After about two hours of bonding, a silicon wafer 3 bonded with a multi-reflection cavity mirror is obtained.

[0037] Step 4: Place the prepared silicon wafer 3 with multi-reflection cavity mirrors and the single-sided open tailless glass cover 4 in the built vacuum anodic bonding device, first pre-evacuate the vacuum under certain conditions, use the atom addition module 2 to complete the operation of filling atoms and gases, and then provide a high temperature of about 300 ° C and a certain degree of electric field in the vacuum system for bonding. Different atomic gas chambers have different gas components, and their bonding processes are slightly different due to the vacuum breakdown voltage. When the pre-filled gas pressure is less than 100 torr, first pre-bond the gas chamber for 30 minutes at a voltage of no more than 300 V under the given pre-filled gas pressure to initially seal the gas chamber, and then fill it with about hundreds of torr of background gas, and increase the bonding voltage to 1000 V to improve the bonding strength; when the pre-filled gas pressure is higher than 200 torr, the pre-bonding step can be skipped and a higher voltage can be directly added for the final bonding.

[0038] Figure 1 This is a schematic diagram of the traditional square gas chamber preparation process. Taking the filling of alkali metal rubidium as an example, the left pipe is connected to the vacuum pump and the gas cylinder, and the valve controls the gas extraction and injection. The right pipe is connected to the chemical reactant for preparing rubidium. The high temperature generated by the flame is used to drive the rubidium into the square gas chamber, and finally the high temperature generated by the flame is used to melt the square gas chamber connecting pipe to complete the sealing of the gas chamber.

[0039] Figure 2 The figure shows a silicon wafer sample with a fixed multi-reflection cavity obtained by anodic bonding of the silicon wafer and the reflector sample after the standard cleaning process mentioned above. Since this process does not involve the manipulation of atoms that may react with the atmosphere, the anodic bonding step does not need to be performed in a vacuum environment. Through the machined mold, we can easily improve the positioning accuracy between the reflectors to less than 0.1 mm.

[0040] Figure 3 The figure shows a schematic diagram of the vacuum anodic bonding device observed from the observation window. 2 is a module for filling atoms in a vacuum environment. Taking the alkali metal atom rubidium as an example, due to its active chemical properties and easy reaction with oxygen and water, we need a sealed alkali metal source to be placed in the structure. After the vacuum is evacuated, the displacement stage located outside the vacuum cavity is used to control the collision between the atom adding module 2 and the mechanical structure where the silicon wafer 3 bonded with a multi-reflection cavity mirror is located, so that the conical tube at the bottom of the atom adding module 2 is broken, and then the alkali metal rubidium is diffused by heating under the action of temperature, so that it evaporates into the interior of the glass cover 4 with a single-sided opening and no tail tube.

[0041] If the atomic component being operated, such as helium, can be directly charged through an external gas cylinder, this mechanism can be ignored. By operating the displacement mechanism outside the vacuum chamber, the single-sided open tail tube-free glass cover 4 and the silicon wafer 3 bonded with a multi-reflection cavity mirror are bonded together, and then the sample is heated to 300°C and voltage is applied to achieve anodic bonding in the vacuum chamber to seal the atomic gas chamber. Figure 3 The standard vacuum flange port on display is connected to gas cylinders of different components. The valve is used to control the amount and type of gas charged, so that atomic gas chambers pre-filled with gases of different components can be prepared. The gas chamber prepared in the whole process avoids melting the glass with the operating flame, so the size and shape of the entire gas chamber can be precisely controlled through mechanical processing to achieve standardized preparation.

[0042] Figure 4 The figure shows the atomic gas chamber sample prepared after vacuum anodic bonding. The final atomic gas chamber can be obtained by anodic bonding the silicon wafer containing the cavity mirror and the glass cover without the tail tube in the vacuum chamber. Figure 4 Atomic gas cell sample shown.

[0043] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a vacuum bonded tailless tube-free multi-reflection cavity air chamber, characterized in that: The steps include: Step 1: Use a wafer dicing machine to cut out silicon wafers; Step 2: Clean and ultrasonically treat the silicon wafer cut in step 1 and the glass cover with a single-side opening and no tail pipe; Step 3: Bonding the silicon wafer in step 2 to the multi-reflection cavity mirror to obtain a silicon wafer bonded with the multi-reflection cavity mirror; Step 4: Place the silicon wafer bonded with multiple reflective cavity mirrors in step 3 and the single-sided open glass cover without tail tube in step 2 in a vacuum sealing device, fill the single-sided open glass cover without tail tube with atoms and gas, and then provide high temperature and electric field for bonding.

2. The method for preparing a vacuum bonded tailless tube-containing multi-reflection cavity air chamber according to claim 1, characterized in that: In step 1, the silicon wafer is single-sided polished, has a size of 21 mm×33 mm, and is 0.5 mm thick.

3. The method for preparing a vacuum bonded tailless tube-containing multi-reflection cavity air chamber according to claim 1, characterized in that: In step 2, the cut silicon wafer and the glass cover with a single-side opening are cleaned and then ultrasonically treated.

4. The method for preparing a vacuum-bonded tailless multi-reflection cavity air chamber according to claim 3, characterized in that: The samples were cleaned with a mixed solution of concentrated sulfuric acid and hydrogen peroxide and ultrasonically treated with acetone, isopropanol and water.

5. The method for preparing a vacuum bonded tailless multi-reflection cavity air chamber according to claim 1, characterized in that: In step three, the silicon wafer and the multi-reflection cavity mirror are fixed using an anodic bonding device. A DC voltage of 1000 V is applied at 300°C. The positive electrode is connected to the silicon wafer and the negative electrode is connected to the multi-reflection cavity mirror. After two hours of bonding, a silicon wafer bonded with a multi-reflection cavity mirror is obtained.

6. The method for preparing a vacuum-bonded tailless air chamber containing multiple reflection cavities according to claim 1, characterized in that: In step 4, pre-vacuuming is performed, and after the operation of filling atoms and gases is completed, 300°C and an electric field are provided in the vacuum system for bonding.

7. The method for preparing a vacuum-bonded tailless multi-reflection cavity air chamber according to claim 1, characterized in that: In step 4, when the pre-filled gas pressure is less than 100 torr, pre-bond for 30 minutes at a voltage no greater than 300 V under the given pre-filled gas pressure to initially seal the gas chamber, then fill with background gas of several hundred torr, and increase the bonding voltage to 1000 V to enhance the bonding strength.

8. The method for preparing a vacuum bonded tailless tube-containing multi-reflection cavity air chamber according to claim 1, characterized in that: In step 4, when the pre-fill gas pressure is higher than 200 torr, the pre-bonding step is skipped and a higher voltage is directly applied for bonding.

9. An atomic gas chamber, characterized in that: The atomic gas chamber is an atomic gas chamber made by the method for preparing a vacuum-bonded tail-free gas chamber containing multiple reflection cavities as described in any one of claims 1 to 7 above.

10. An atomic magnetometer, comprising an atomic gas chamber, characterized in that: The atomic gas chamber is an atomic gas chamber made by the method for preparing a vacuum-bonded tail-free gas chamber containing multiple reflection cavities as described in any one of claims 1 to 7 above.

Images