CN103941577A - Atom gas cavity device with double reflectors and groove-shaped structure and manufacturing method thereof - Google Patents

Abstract

The invention relates to an atomic gas cavity device with a double mirror and a groove-shaped structure and a manufacturing method thereof. The atomic gas cavity device is composed of a cavity structure surrounded by a layer of silicon wafer with grooves provided at the bottom with a reflector and a layer of glass sheet with a reflector inside through bonding. The cross-section of the groove is an inverted trapezoidal structure, which is formed by (100) type single crystal silicon wafer through silicon anisotropic wet etching, and the side wall of the groove is the {111} crystal plane of the silicon wafer. There is a reflector inside the glass sheet and at the bottom of the groove of the silicon sheet, which are used for multiple reflections of the laser light. The atomic gas cavity device described in the present invention can be used in systems such as atomic clocks and magnetometers. Laser light is reflected multiple times between double mirrors, thereby increasing the interaction space length between laser light and atomic gas, and making the coherent layout trap effect signals The signal-to-noise ratio is enhanced, which is conducive to improving the stability of the system.

Description

Atomic gas cavity device with double-mirror and groove-shaped structure and fabrication method thereof

technical field

The invention belongs to the technical field of micro-electro-mechanical system (MEMS) device manufacturing and packaging, and the technical field of atomic physics devices, and specifically relates to a micro-atomic cavity structure based on MEMS technology and a manufacturing method thereof.

Background technique

Atomic clocks can measure time with an accuracy of one billionth of a second or even higher. Atomic clocks are currently the most accurate artificial clocks, and their related research is of great significance. CPT (Coherent Population Trapping, coherent layout trapping effect) atomic clock is an atomic clock frequency source realized by using two-color coherent light to interact with atoms to prepare atoms into a coherent state, and using the CPT signal as a microwave frequency discrimination signal. Due to the characteristics of easy miniaturization, low power consumption and high frequency stability, the CPT atomic clock has been valued by research institutions in various countries since it was proposed, and in-depth research has been carried out.

The CPT atomic clock is a complex system, and its core component is the atomic gas cavity. Using the now mature MEMS technology to make a miniature atomic gas cavity can reduce the size of the passive CPT atomic clock to the chip level. Chip-level CPT atomic clocks can greatly reduce the size and power consumption of atomic clocks, realize battery power supply, and can be produced in batches and at low cost. They have huge markets in various fields of military and civilian use, so they have become an important development direction for atomic clocks.

At present, the atomic gas cavity structure of the chip-level CPT atomic clock is usually a sandwich structure with a silicon wafer in the middle and glass on both sides. First make a through hole on the single crystal silicon wafer, and then bond it with a Pyrex glass sheet to form a half-cavity structure. After the alkali metal and buffer gas are filled, it is bonded with another piece of Pyrex glass sheet to form a sealed structure. The optical path length of the interaction between light and atoms in the alkali metal atom gas cavity structure of this structure is limited by the thickness of the silicon wafer and the silicon processing technology, usually 1 mm to 2 mm, and it is difficult and expensive to further increase the thickness, thus limiting the interaction between light and atoms. Due to the action optical path, the signal-to-noise ratio of the CPT signal is low, which affects the frequency stability of the CPT atomic clock.

Contents of the invention

On the basis of existing research, in order to further improve the optical path of the interaction between light and atoms, increase the signal-to-noise ratio of the CPT signal, and increase the frequency stability, the present invention provides an atomic gas cavity with double mirrors and a groove-shaped structure Devices and methods of making them.

The atomic gas chamber device with double reflection mirrors and groove-shaped structure comprises a silicon wafer and a glass wafer, one side of the silicon wafer is provided with a groove, and the inner bottom of the groove is provided with a lower reflector; one side of the glass wafer is An upper reflection mirror is provided; the silicon wafer and the glass wafer are bonded to form an atomic gas cavity device, and the upper reflection mirror on the glass wafer is correspondingly located in the groove of the silicon wafer and corresponds to the lower reflection mirror.

The cross section of the groove is an inverted trapezoid, the groove is formed by wet etching, the type of silicon wafer is (100) type silicon wafer, and the angle between the side wall of the groove formed by etching and the glass sheet is 54.7 degrees.

The width W of the groove is the width of the bottom surface of the inverted trapezoidal cross section, and is more than twice the thickness H of the silicon wafer.

The specific preparation steps of the atomic gas cavity device with double mirrors and groove-shaped structure are as follows:

1). Make grooves on the silicon wafer

Select a (100) type silicon wafer, use silicon dioxide as a mask layer to perform anisotropic wet etching, and form more than one hundred grooves with an inverted trapezoidal cross section on one side of the silicon wafer;

2). Make a reflector on the glass

Using evaporation process or sputtering process, using hard mask or lift-off technology, make more than one hundred metal film mirrors on one side of the glass sheet, that is, the upper mirror; at the bottom of each groove on the silicon wafer Make more than one hundred metal film mirrors, that is, lower mirrors;

3). Silicon-glass bonding

Silicon-glass bonding is carried out, and alkali metal vapor and buffer gas are introduced at the same time, so that the silicon wafer and the glass wafer are sealed to form an atomic gas cavity device;

4). Scribing

Divide the entire silicon wafer with the groove on the silicon wafer as a unit to form more than one hundred single atomic gas cavity devices.

The alkali metal vapor is rubidium vapor or cesium vapor, and the buffer gas is a mixed gas of 85% nitrogen, 10% hydrogen and 5% carbon dioxide.

Beneficial technical effect of the present invention is embodied in the following aspects:

1. The atomic gas cavity device of the present invention makes the optical path between the laser and the alkali metal atoms mainly determined by the width of the bottom of the groove, so it is not limited to the thickness of the silicon wafer, and it is easy to increase the laser and the atomic cavity by changing the size of the atomic cavity. The length of the interaction space between gases enhances the signal-to-noise ratio of the coherent layout trapping effect signal, which is conducive to improving the stability of the system;

2. The manufacturing technology of the atomic gas chamber device of the present invention is mainly based on mature MEMS processes such as silicon anisotropic wet etching process and silicon-glass anode bonding, so the cost is low and easy to implement;

3. Based on the characteristics of batch processing of MEMS, in the same batch of tape-out, the manufacture of atomic gas cavities of different sizes can be completed.

Description of drawings

Fig. 1 is a cross-sectional view of the structure of the present invention.

Fig. 2 is a key dimension identification diagram of the atomic gas cavity device of the present invention.

Fig. 3 is a schematic diagram of the optical path of the laser in the atomic gas cavity device of the present invention.

Fig. 4 is a schematic diagram of the optical path of a laser in a conventional atomic gas cavity.

In the figure above: silicon wafer 1, glass wafer 2, atomic gas cavity 3, upper mirror 4, lower mirror 5, H is the thickness of the silicon wafer, W is the width of the bottom of the groove, α is the side wall of the groove and the glass angle between slices.

Detailed ways

The present invention will be further described through the embodiments below in conjunction with the accompanying drawings.

Example 1

Referring to FIG. 1 and FIG. 2 , an atomic gas cavity device with double mirrors and a groove-shaped structure includes a silicon wafer 1 and a glass wafer 2 . One side of the silicon chip 1 is provided with a groove, the cross section of the groove is an inverted trapezoid, and the inner bottom of the groove is provided with a lower reflector 5; one side of the glass sheet 2 is provided with an upper reflector 4; the silicon chip 1 and the glass sheet 2 The atomic gas cavity is formed by bonding 3 The device, the upper mirror 4 on the glass sheet 2 is correspondingly located in the groove of the silicon wafer 1, and corresponds to the lower mirror 5.

As shown in Figure 3, the optical path of the laser in the atomic gas cavity 3 device is mainly determined by the width W of the bottom of the groove, and the optical path can be changed by adjusting the size of W. Referring to Figure 4, in a traditional atomic gas cavity device, the laser is directly injected from the top and emitted from the bottom, and the optical path is determined by the thickness H of the silicon wafer.

The specific preparation steps of the atomic gas cavity device with double mirrors and groove-shaped structure are as follows:

1. Select an N(100) type silicon wafer 1 with a thickness of 0.5-1 mm, use silicon dioxide as a mask, and use potassium hydroxide solution to perform anisotropic wet etching process to form two hundred silicon wafers on the silicon wafer 1. The cross section is an inverted trapezoidal groove, the side wall of the groove is the {111} crystal plane, and the width of the bottom of the groove is 3mm. The corrosion temperature of potassium hydroxide is 60°C;

2. Using the evaporation process and the stripping technique, make two hundred metal film mirrors on one side of the glass sheet 2, that is, the upper mirror 4; make two hundred metal film mirrors at the bottom of each groove of the silicon chip 1 Reflector, i.e. lower reflector 5;

3. Carry out silicon-glass bonding, and pass rubidium vapor and buffer gas at the same time, so that silicon wafer 1 and glass wafer 2 are sealed to form an atomic gas cavity device; the buffer gas is 85% nitrogen, 10% hydrogen and 5% carbon dioxide Composed of gas mixtures. The process conditions of anodic bonding are: temperature 400°C, voltage 600V;

4. Dicing

Taking the grooves on the silicon wafer 1 as a unit, the entire silicon wafer 1 is divided to form two hundred individual atomic gas cavity 3 devices.

Example 2

The structure of the atomic gas chamber of the present embodiment is as shown in Figure 1, and the specific implementation is as follows:

1. Select a P(100) silicon wafer 1 with a thickness of 0.5-1 mm, use silicon nitride as a mask, and perform anisotropic wet etching through TMAH solution to form an inverted trapezoidal cross section on the silicon wafer 1. One hundred and fifty grooves, the side walls of the grooves are {111} crystal planes, and the lateral width of the through holes is 5mm. The corrosion temperature of TMAH solution is 80°C;

2. Using the sputtering process and hard mask technology, one hundred and fifty metal film mirrors, namely the upper mirror 4, are fabricated on one side of the glass sheet 2; at the bottom of each groove of the silicon wafer 1 Make one hundred and fifty metal film reflectors, that is, the lower reflector 5;

3. Carry out silicon-glass bonding, and feed cesium vapor and buffer gas at the same time, so that silicon wafer 1 and glass wafer 2 form a sealed atomic gas chamber device; the buffer gas is 85% nitrogen, 10% hydrogen and 5% hydrogen Mixed gas composed of carbon dioxide, the process conditions of anodic bonding are: temperature 400°C, voltage 600V;

4. Scribing, using the grooves on the silicon wafer 1 as a unit, divide the entire silicon wafer 1 to form one hundred and fifty individual atomic gas cavity 3 devices.

Claims (5)

1. the atomic gas chamber device with double mirror and groove type structure, is characterized in that: comprise silicon chip and glass sheet, a side of described silicon chip is provided with groove, and groove inner bottom part is provided with lower catoptron; One side of described glass sheet is provided with upper reflector; Silicon chip and glass sheet form atomic gas chamber device by bonding, and the upper reflector correspondence on glass sheet is positioned at the groove of silicon chip, and corresponding with lower catoptron.

2. the atomic gas chamber device with double mirror and groove type structure as claimed in claim 1, it is characterized in that: the xsect of described groove is inverted trapezoidal, groove is that wet etching forms, the type of silicon chip is (100) type silicon chip, and the sidewall of groove and the angle of glass sheet that corrosion forms are 54.7 degree.

3. the atomic gas chamber device with double mirror and groove type structure as claimed in claim 2, is characterized in that: the bottom width of the xsect that the width W of described groove is inverted trapezoidal, and be more than the twice of silicon wafer thickness H.

4. the manufacture method of the preparation atomic gas chamber device with double mirror and groove type structure as claimed in claim 1, is characterized in that concrete preparation manipulation step is as follows:

1). on silicon chip, make groove

The silicon chip of (100) type of selection, utilizes silicon dioxide to carry out anisotropic wet corrosion as mask layer, on a side of silicon chip, forms the groove that more than 100 xsect is inverted trapezoidal;

2). at making catoptron on glass

Adopt evaporation technology or sputtering technology, utilize hard mask or lift-off technology, on a side of glass sheet, make more than 100 metal film catoptrons, i.e. upper reflector; The bottom of the each groove on silicon chip makes more than 100 metal film catoptrons, descends catoptron;

3). silicon on glass bonding

Carry out silicon on glass bonding, pass into vapour of an alkali metal and buffer gas simultaneously, make silicon chip and glass sheet sealing form atomic gas chamber device;

4). scribing

Taking the groove on silicon chip as unit, whole silicon chip is divided, form 100 above single atomic gas chamber devices.

5. manufacture method as claimed in claim 4, is characterized in that: described in step 3), vapour of an alkali metal is rubidium steam or caesium steam, the mixed gas of the nitrogen that described buffer gas is 85%, 10% hydrogen and 5% carbon dioxide.