JP2014103350A - Alkali metal cell, atomic oscillator, and method of manufacturing alkali metal cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkali metal cell which has high reliability and stability.SOLUTION: The alkali metal cell comprises: a substrate in which an opening penetrating from one surface to the other surface is formed; a first transparent substrate bonded to the other surface of the substrate; and a second transparent substrate bonded to the one surface of the substrate. In the opening of the substrate, an alkali metal is sealed in a space surrounded by the first transparent substrate and the second transparent substrate. The substrate and the second transparent substrate are bonded together by a first bonding metal layer formed of a first bonding metal and a second bonding metal layer formed of a second bonding metal to seal the space. The second bonding metal has a higher melting temperature than the first bonding metal. With this configuration, the above problem is solved.

Description

  The present invention relates to an alkali metal cell, an atomic oscillator, and a method for manufacturing an alkali metal cell.

  There is an atomic clock (atomic oscillator) as a clock for measuring extremely accurate time, and a technique for downsizing the atomic clock has been studied. An atomic clock is an oscillator based on the amount of transition energy of electrons constituting atoms such as alkali metals, and in particular, the transition energy of electrons in alkali metal atoms is very precise in the absence of disturbance. Since the value is obtained, frequency stability that is several orders of magnitude higher than that of the crystal oscillator can be obtained.

  There are several types of such atomic clocks. Among them, the CPT (Coherent Population Trapping) type atomic clock has a frequency stability that is about three orders of magnitude higher than that of a conventional crystal oscillator, and is ultra-compact. Therefore, ultra-low power consumption can be desired (Non-Patent Documents 1 and 2).

  In the CPT type atomic clock, as shown in FIG. 1, a light source 910 such as a laser element, an alkali metal cell 940 encapsulating an alkali metal, and a photodetector 950 that receives laser light transmitted through the alkali metal cell 940; The laser beam is modulated, and two transitions of electrons in the alkali metal atom are simultaneously performed and excited by sideband wavelengths appearing on both sides of the carrier wave having a specific wavelength. The transition energy in this transition is invariant, and when the sideband wavelength of the laser light coincides with the wavelength corresponding to the transition energy, a transparency phenomenon occurs in which the light absorption rate in the alkali metal is lowered. In this manner, the wavelength of the carrier wave is adjusted so that the light absorption rate by the alkali metal is lowered, and the signal detected by the photodetector 950 is fed back to the modulator 960, and the modulator 960 This is an atomic clock characterized by adjusting the modulation frequency of the laser light from the light source 910. The laser light is emitted from the light source 910 and applied to the alkali metal cell 940 via the collimating lens 920 and the λ / 4 plate 930.

  As an alkali metal cell in such an ultra-small atomic clock, a method of producing using an MEMS (Micro Electro Mechanical Systems) technique is disclosed (Patent Documents 1 to 4). In the methods disclosed in these documents, an opening is first formed in a Si substrate by a photolithography technique and an etching technique, and then the glass and the Si substrate are joined by anodic bonding. The anodic bonding is performed by applying a voltage of about 250 V to 1000 V to the interface between the glass and the Si substrate at a temperature of 200 ° C. to 450 ° C. Thereafter, an alkali metal and a buffer gas are put in, and sealing is performed by bonding glass to the opening portion on the upper surface by anodic bonding. An alkali metal cell is formed by cutting out the cell formed in this way for each cell.

As a method of encapsulating the alkali metal in the cell, a method of directly dropping and encapsulating Cs (cesium) metal in a vacuum (Non-patent Document 3), a solution in which CsCl is mixed with an aqueous BaN ₆ solution is introduced into the cell, After sealing the cell, react at 200 ° C. to generate Cs metal (Non-patent Document 3), react with BaN ₆ + CsCl in an ampoule with heater to generate Cs metal and evaporate it in the cell A method of transferring (Non-Patent Document 4), a method of forming CsN ₃ in a cell by a normal vapor deposition method and sealing the cell, and then irradiating UV light to generate Cs and N ₂ (Non-Patent Document 5), There is a method in which a Cs dispenser that is stable in the atmosphere is put into the cell and the cell is sealed, and then only the Cs dispenser is irradiated with a laser beam and heated to generate Cs (Non-patent Document 6).

By the way, when sealing a cell by anodic bonding, oxygen, OH, H ₂ O, etc. generated in the anodic bonding react with an alkali metal in the cell. For example, in the case of Cs, Cs _x O _y is generated. Therefore, there is a problem that the transmissivity of the laser light fluctuates, a frequency shift occurs, and the short-term stability of the frequency is deteriorated.

  Further, in the method described in Non-Patent Document 6, since the Cs dispenser after generating Cs remaining in the cell adsorbs the gas in the cell, the pressure in the cell fluctuates, which causes the frequency. There is a problem that a shift occurs and the long-term reliability as a frequency oscillator is impaired.

  The present invention has been made in view of the above, and in an alkali metal cell, there are few impurities such as oxygen, and it is highly reliable by not including a material that is a supply source of Cs. An object of the present invention is to provide a highly stable alkali metal cell and an atomic oscillator.

  According to one aspect of the present embodiment, a substrate in which an opening penetrating from one surface to the other surface is formed, a first transparent substrate bonded to the other surface of the substrate, and the substrate A second transparent substrate bonded to one surface, and an alkali metal is enclosed in a space surrounded by the first transparent substrate and the second transparent substrate in the opening of the substrate The substrate and the second transparent substrate are formed by a first bonding metal layer formed of a first bonding metal and a second bonding metal layer formed of a second bonding metal. The space is sealed by bonding, and the second bonding metal has a melting temperature higher than that of the first bonding metal.

  According to another aspect of the present embodiment, two or more openings that penetrate the substrate are formed in the substrate, and a groove that spatially connects the two openings is formed on one surface of the substrate. A step of bonding a first transparent substrate to the other surface of the substrate, a step of installing a compound containing an alkali metal in one of the openings, and one surface of the substrate The first bonding metal formed of the first bonding metal around the two or more openings or at a portion corresponding to the periphery of the two or more openings on one surface of the second transparent substrate Forming a layer, and forming a second bonding metal layer formed of a second bonding metal on a groove portion of the substrate or a portion corresponding to the groove portion on one surface of the second transparent substrate One of the surfaces of the substrate and one of the second transparent substrates. A first bonding metal layer, and an alkali metal is generated from the compound containing the alkali metal, and the alkali metal is introduced into the other opening through the groove from the one opening. And a step of bonding the substrate and the second transparent substrate with the second bonding metal layer in the groove after supplying the alkali metal to the other opening. It is characterized by that.

  According to another aspect of the present embodiment, one opening that does not penetrate the substrate on one surface of the substrate, another opening that penetrates the substrate, and one surface of the substrate A step of forming a groove for spatially connecting the one opening and the other opening, a step of bonding a first transparent substrate to the other surface of the substrate, and an alkali in the one opening. A step of installing a compound containing a metal; and the one opening and the other opening on one surface of the substrate, or the one opening on the one surface of the second transparent substrate. Forming a first bonding metal layer formed of the first bonding metal on a portion corresponding to the periphery of the other opening, and a groove portion of the substrate or one surface of the second transparent substrate; In the portion corresponding to the groove portion in FIG. A step of forming a composite metal layer, a step of bonding one surface of the substrate and one surface of the second transparent substrate with a first bonding metal layer, and an alkali metal from the compound containing the alkali metal. And supplying the alkali metal to the other opening through the groove from the one opening, and supplying the alkali metal to the other opening, and then the second in the groove. A step of bonding the substrate and the second transparent substrate with a bonding metal layer.

  According to the present invention, an alkali metal cell and an atomic oscillator having high reliability and high stability can be provided.

Illustration of atomic oscillator Process drawing (1) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (2) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (3) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (4) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (5) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (6) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (7) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (8) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (9) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (10) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (11) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (12) of the manufacturing method of the alkali metal cell in 1st Embodiment Process drawing (13) of the manufacturing method of the alkali metal cell in 1st Embodiment Structure diagram of alkali metal cell in the first embodiment Explanatory drawing of the manufacturing method of the alkali metal cell in 1st Embodiment Explanatory drawing (1) of the manufacturing method of the alkali metal cell in 2nd Embodiment Explanatory drawing (2) of the manufacturing method of the alkali metal cell in 2nd Embodiment Explanatory drawing (3) of the manufacturing method of the alkali metal cell in 2nd Embodiment Explanatory drawing (4) of the manufacturing method of the alkali metal cell in 2nd Embodiment. Explanatory drawing (5) of the manufacturing method of the alkali metal cell in 2nd Embodiment Explanatory drawing (6) of the manufacturing method of the alkali metal cell in 2nd Embodiment. Explanatory drawing of the manufacturing method of the alkali metal cell in 3rd Embodiment Explanatory drawing (1) of the manufacturing method of the alkali metal cell in 4th Embodiment Explanatory drawing (2) of the manufacturing method of the alkali metal cell in 4th Embodiment Explanatory drawing (3) of the manufacturing method of the alkali metal cell in 4th Embodiment Explanatory drawing (4) of the manufacturing method of the alkali metal cell in 4th Embodiment Explanatory drawing (5) of the manufacturing method of the alkali metal cell in 4th Embodiment Explanatory drawing (1) of the manufacturing method of the alkali metal cell in 5th Embodiment Explanatory drawing (2) of the manufacturing method of the alkali metal cell in 5th Embodiment Explanatory drawing of the atomic oscillator in the sixth embodiment Structural diagram of atomic oscillator in sixth embodiment Explanatory diagram of atomic energy level explaining CPT method Illustration of output wavelength during surface emitting laser modulation Correlation diagram between modulation frequency and amount of transmitted light

  The form for implementing this invention is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
The alkali metal cell and the method for producing the alkali metal cell in the first embodiment will be described with reference to FIGS.

  First, as shown in FIG. 2, a Si (silicon) substrate 110 is prepared. The Si substrate 110 has a thickness of 1.5 mm, and both surfaces are mirror-finished. 2A is a top view in this step, and FIG. 2B is a cross-sectional view taken along the alternate long and short dash line 2A-2B in FIG. 2A.

  Next, as shown in FIG. 3, the Si substrate 110 has two openings, that is, a first opening 111, a second opening 112, and a first opening 111 and a second opening. A groove 113 is formed between the groove 112 and the substrate 112. The first opening 111 and the second opening 112 formed in the Si substrate 110 penetrate the Si substrate 110, and the groove 113 is formed only on one surface of the Si substrate 110 and penetrates the Si substrate 110. Not done. In the present embodiment, the first opening 111 may be referred to as one opening and the second opening 112 may be referred to as another opening. 3A is a top view in this step, and FIG. 3B is a cross-sectional view taken along the alternate long and short dash line 3A-3B in FIG. 3A.

  Specifically, a region where the first opening 111, the second opening 112, and the groove 113 are formed by applying a photoresist to one surface of the Si substrate 110 and performing exposure and development by an exposure apparatus. A resist pattern (not shown) having an opening is formed. Thereafter, Si in a region where the resist pattern is not formed is removed to a depth half the thickness of the Si substrate 110 by dry etching such as ICP (Inductively Coupled Plasma) etching to form a recess. As a result, a part of the first opening 111 and the second opening 112 and a groove 113 are formed on one surface of the Si substrate 110.

Thereafter, a photoresist is applied to the other surface of the Si substrate 110, and exposure and development are performed by an exposure apparatus, so that the first opening 111 and the second opening 112 are not formed in the region where the opening is formed. The illustrated resist pattern is formed. Thereafter, Si in a region where the resist pattern is not formed is removed by dry etching such as ICP etching, and the Si substrate 110 is penetrated to form the first opening 111 and the second opening 112. . Since the groove 113 is formed only on one surface of the Si substrate 110, it does not penetrate the Si substrate 110. Dry etching on the Si substrate 110 is performed by a Bosch process in which etching is performed by alternately supplying SF ₆ and C ₄ F ₈ . In the Bosch process, highly anisotropic etching can be performed on the Si substrate 110 at high speed. The power applied in this ICP etching is 2 kW.

  The first opening 111, the second opening 112, and the groove 113 can be formed by wet etching in addition to the dry etching described above. Specifically, a SiN film (not shown) is formed on both surfaces of the Si substrate 110 by low pressure CVD (Chemical Vapor Deposition). Thereafter, a photoresist is applied on the formed SiN film, and exposure and development are performed by an exposure apparatus. As a result, a resist pattern (not shown) having openings in regions where the first openings 111, the second openings 112, and the grooves 113 are formed is formed on one surface of the Si substrate 110. On the other surface, a resist pattern (not shown) having openings in regions where the first openings 111 and the second openings 112 are formed is formed.

Thereafter, by performing dry etching using CF ₄ as an etching gas, the SiN film in a region where the resist pattern is not formed is removed, and a resist pattern (not shown) is further removed. Thereafter, wet etching is performed using a KOH (30 wt%) solution at a temperature of 85 ° C. to remove Si in the region where the SiN film is not formed in the Si substrate 110, and the first opening 111. And the 2nd opening part 112 and the groove part 113 are formed. At this time, since the first opening 111 and the second opening 112 are removed from both the one surface and the other surface of the Si substrate 110, the Si substrate 110 can be penetrated. The groove 113 is not penetrated through the Si substrate 110 because it is removed from one surface of the Si substrate 110. Thereafter, the SiN film is removed by wet etching using a solution for removing SiN or dry etching. The wet etching of the Si substrate 110 performed at this time is anisotropic etching, and the side surfaces of the formed first opening 111, second opening 112, and groove 113 have an inclination angle of 54.7 °. A reverse slope may be formed.

  Next, as shown in FIG. 4, a first glass substrate 121, which is a first transparent substrate, is bonded to the other surface of the Si substrate 110 by anodic bonding. Specifically, in the vacuum chamber, the first glass substrate 121 is brought into contact with the other surface of the Si substrate 110, and −800 V is applied to the first glass substrate 121 at a temperature of 380 ° C. Join. Thereby, the first glass substrate 121 covers the other opening side of the first opening 111 and the second opening 112 formed in the Si substrate 110. In this step, since an alkali metal material or the like is not yet installed, the alkali metal is not oxidized by oxygen or the like generated by anodic bonding. In the above description, the case of anodic bonding has been described. However, instead of anodic bonding, the other surface of the Si substrate 110 and the first glass substrate 121 may be bonded by direct bonding. 4A is a top view in this step, and FIG. 4B is a cross-sectional view taken along the alternate long and short dash line 4A-4B in FIG. 4A.

  Next, as shown in FIG. 5, a resist pattern 161 having an opening 161 a is formed on one surface of the Si substrate 110 in a region where a junction metal film to be described later is formed. Specifically, a photoresist is applied to one surface of the Si substrate 110, and exposure and development are performed by an exposure apparatus to form a resist pattern 161 having an opening 161a. When forming the resist pattern, the photoresist and the gas are used to apply the photoresist without leakage along the inner wall surfaces of the first opening 111 and the second opening 112 formed in the Si substrate 110. You may use the spray coat which sprays the liquid which mixed. 5A is a top view in this step, and FIG. 5B is a cross-sectional view taken along the alternate long and short dash line 5A-5B in FIG. 5A.

  Next, as illustrated in FIG. 6, a bonding metal film 131 is formed on one surface of the Si substrate 110. Specifically, a metal laminated film made of Au: 700 nm / Cr: 10 nm is formed on the surface on which the resist pattern 161 is formed by sputtering or vacuum evaporation. Thereafter, by immersing in an organic solvent or the like, the metal laminated film formed on the resist pattern 161 is removed together with the resist pattern 161 by lift-off, and the junction metal film 131 is formed from the remaining metal laminated film. 6A is a top view in this step, FIG. 6B is a cross-sectional view taken along the alternate long and short dash line 6A-6B in FIG. 6A, and FIG. It is sectional drawing cut | disconnected by the dashed-dotted line 6C-6D in Fig.6 (a).

  Next, as shown in FIG. 7, a Cs dispenser that is a compound 140 containing an alkali metal such as Cs or Rb on the first glass substrate 121 in the first opening 111 formed in the Si substrate 110. Is installed. In the present embodiment, the region formed by the first opening 111 in which the compound material 140 containing an alkali metal is thus installed may be referred to as a raw material chamber. 7A is a top view in this step, and FIG. 7B is a cross-sectional view taken along the alternate long and short dash line 7A-7B in FIG. 7A.

  Next, as shown in FIG. 8, a second glass substrate 122 that is a second transparent substrate is prepared, and a bonding portion metal film 132 is formed on one surface of the second glass substrate 122. Specifically, a photoresist is applied to one surface of the second glass substrate 122, and exposure and development are performed by an exposure apparatus, whereby an opening is formed in a region where the bonding portion metal film 132 is formed (not shown). A resist pattern is formed. Thereafter, a metal laminated film made of Au: 700 nm / Cr: 10 nm is formed on the surface on which the resist pattern is formed by sputtering or vacuum deposition. Thereafter, the metal laminated film formed on the resist pattern is removed together with the resist pattern by being lifted off by being immersed in an organic solvent or the like, and bonded by the metal laminated film remaining on one surface of the second glass substrate 122. A partial metal film 132 is formed. The junction metal film 132 formed in this way is formed so as to correspond to the junction metal film 131 formed on one surface of the Si substrate 110. 8A is a top view in this step, FIG. 8B is a cross-sectional view taken along the alternate long and short dash line 8A-8B in FIG. 8A, and FIG. It is sectional drawing cut | disconnected in the dashed-dotted line 8C-8D in Fig.8 (a).

  Next, as shown in FIG. 9, a first bonding metal layer 151 made of the first bonding metal is formed on the bonding portion metal film 132 of the second glass substrate 122. In the present embodiment, the first bonding metal layer 151 is made of an AuSn (weight ratio: Au: Sn = 10: 90) alloy having a melting temperature of 217 ° C.

  Specifically, the first bonding metal layer 151 is formed by applying a photoresist to one surface of the second glass substrate 122 on which the bonding portion metal film 132 is formed, and performing exposure and development with an exposure apparatus. A resist pattern (not shown) having an opening in a region where the film is formed is formed. Thereafter, a metal film made of AuSn (weight ratio: Au: Sn = 10: 90) is formed by vacuum deposition or sputtering, and then immersed in an organic solvent or the like to form a metal formed on the resist pattern. The film is removed together with the resist pattern by lift-off. As a result, the first bonding metal layer 151 is formed on the bonding portion metal film 132 on one surface of the second glass substrate 122. The first bonding metal layer 151 thus formed has a width of about 20 μm and a thickness of about 20 μm. 9A is a top view in this step, FIG. 9B is a cross-sectional view taken along the dashed line 9A-9B in FIG. 9A, and FIG. It is sectional drawing cut | disconnected in the dashed-dotted line 9C-9D in Fig.9 (a).

  Next, as shown in FIG. 10, in the second glass substrate 122, a second bonding metal layer 152 formed of the second bonding metal is formed in a portion corresponding to the groove 113 in the Si substrate 110. . In the present embodiment, the second bonding metal layer 152 is formed of an AuSn (weight ratio: Au: Sn = 80: 20) alloy having a melting temperature of about 280 ° C.

  Specifically, a photoresist is applied to one surface of the second glass substrate 122 on which the bonding portion metal film 132 is formed, and exposure and development are performed by an exposure apparatus, whereby the second bonding metal layer 152 is formed. A resist pattern (not shown) having an opening in a region where the film is formed is formed. Thereafter, a metal film made of AuSn (weight ratio: Au: Sn = 80: 20) is formed by vacuum deposition or sputtering, and then immersed in an organic solvent or the like to form a metal formed on the resist pattern. The film is removed together with the resist pattern by lift-off. As a result, the second bonding metal layer 152 is formed in a portion corresponding to the groove 113 of the Si substrate 110 on one surface of the second glass substrate 122. The second bonding metal layer 152 thus formed has a width of about 20 μm and a thickness of about 20 μm. 10A is a top view in this step, FIG. 10B is a cross-sectional view taken along the dashed line 10A-10B in FIG. 10A, and FIG. It is sectional drawing cut | disconnected in the dashed-dotted line 10C-10D in Fig.10 (a).

  Next, as shown in FIG. 11, one surface of the Si substrate 110 and one surface of the second glass substrate 122 are bonded by the first bonding metal layer 151. 11A is a top view in this step, FIG. 11B is a cross-sectional view taken along the alternate long and short dash line 11A-11B in FIG. 11A, and FIG. It is sectional drawing cut | disconnected in the dashed-dotted line 11C-11D in Fig.11 (a).

  Specifically, the junction metal film 131 formed on one surface of the Si substrate 110 and the second glass substrate 122 in a vacuum chamber in which nitrogen gas serving as a buffer gas is introduced to form a nitrogen atmosphere. The second bonding metal film 152 formed on one surface of the first metal film is brought into contact. Thereafter, pressurization is performed at a temperature of 217 ° C. or higher, for example, 230 ° C. for 30 minutes. Thereby, one surface of the Si substrate 110 and one surface of the second glass substrate 122 are bonded by the first bonding metal layer 151. In this way, the second glass substrate 122 is bonded to the first opening 111 and the second opening 112 in the Si substrate 110 by the first bonding metal layer 151, and the second glass substrate 122 is bonded to the second opening 112. The glass substrate 122 is closed. Thereby, a sealed space including the first opening 111, the second opening 112, and the groove 113 is formed.

  In such joining using AuSn (weight ratio: Au: Sn = 10: 90), a gas such as oxygen is not generated during the joining, and therefore a compound 140 containing an alkali metal is added. Impurities such as oxygen do not enter the first opening 111.

  At the bonding temperature (about 230 ° C.) in the first bonding metal layer 151, the melting temperature of the second bonding metal forming the second bonding metal layer 152 is 280 ° C. The metal layer 152 does not melt. Therefore, although the second bonding metal layer 152 is formed on the second glass substrate 122, the space formed by the first opening 111 and the space formed by the second opening 112 are spatially interposed via the groove 113. Stay connected.

  Next, as shown in FIG. 12, an alkali metal gas is generated from the compound 140 containing an alkali metal installed in the first opening 111. 12A is a top view in this step, and FIG. 12B is a cross-sectional view taken along the alternate long and short dash line 12A-12B in FIG. 12A.

  Specifically, when a Cs dispenser that is stable in the atmosphere is used as the compound 140 containing an alkali metal, it is heated by irradiating the Cs dispenser installed in the first opening 111 with a laser beam, Cs gas, which is an alkali metal gas, is generated. Since the irradiated laser light is condensed and heated on the compound 140 containing an alkali metal, the second bonding metal having a melting temperature of 280 ° C. does not melt. Cs contained in the compound 140 containing an alkali metal has a melting point of about 28 ° C., and the laser 140 is irradiated to heat the compound 140 containing an alkali metal to a melting point or higher, whereby Cs becomes a liquid and a gas. Cs that has become gas or the like passes through the groove 113 and enters the second opening 112. In the above description, the case where the alkali metal is generated by irradiating the compound 140 containing an alkali metal with laser light has been described. However, the compound 140 containing an alkali metal is heated or irradiated with ultraviolet light (UV light). By doing so, an alkali metal may be generated.

  Next, as shown in FIG. 13, the second bonding metal layer 152 formed on the second glass substrate 122 is heated to a bonding temperature of 280 ° C. or higher and melted, and then cooled to be second. The groove 113 is closed by the bonding metal layer 152. As a result, the space in the first opening 111 and the space in the second opening 112 are closed and spatially separated. An AuSn (weight ratio: Au: Sn = 80: 20) alloy, which is the second bonding metal forming the second bonding metal layer 152, is a kind of brazing material and has good wettability. Accordingly, when the AuSn (weight ratio: Au: Sn = 80: 20) alloy, which is the second bonding metal, is heated to become a liquid, it tends to wet and spread on the bonding metal films 131 and 132 formed of the metal material. . Therefore, the groove 113 can be easily closed by heating the second bonding metal layer 152 to 280 ° C. or higher and then cooling it. At this time, in order to prevent the first bonding metal layer 151 from being melted, the portion where the second bonding metal layer 152 is formed can be irradiated with laser light, or only this portion can be partially heated. It is preferable to heat by a method. 13A is a top view in this step, FIG. 13B is a cross-sectional view taken along the alternate long and short dash line 13A-13B in FIG. 13A, and FIG. It is sectional drawing cut | disconnected in the dashed-dotted line 13C-13D in Fig.13 (a).

  Next, as shown in FIG. 14, the region in which the first opening 111 is formed and the region in which the second opening 112 are formed are cut and separated by dicing or the like. 14A is a top view in this step, and FIG. 14B is a cross-sectional view taken along the alternate long and short dash line 14A-14B in FIG. 14A.

  The alkali metal cell in the present embodiment is formed by the region where the second opening 112 thus separated is formed. Since the alkali metal cell manufactured by such a process has a small amount of impurities such as oxygen contained in the cell which is the second opening 112, it is highly reliable and stable when used in an atomic oscillator. A high-grade atomic oscillator.

  Further, for example, if the compound 140 containing an alkali metal after releasing the alkali metal remains inside the alkali metal cell, the gas inside the alkali metal cell is adsorbed to change the pressure inside the alkali metal cell. In this case, the reliability is lowered. However, since the alkali metal cell 140 in this embodiment does not contain the compound 140 containing the alkali metal after releasing the alkali metal, the pressure inside the cell formed by the second opening 112 is not contained. Can be kept constant over the long term.

  FIG. 15 shows an alkali metal cell in the present embodiment. In the alkali metal cell in the present embodiment, the inside of the cell is formed by the second opening 112, and the first glass substrate 121 is bonded to the other surface of the Si substrate 110 by anodic bonding. . Further, on one surface of the Si substrate 110, the second glass substrate 122 is formed of the first bonding metal and the second bonding metal is formed of the first bonding metal layer 151 and the second bonding metal. Joined by layer 152. Here, the melting temperature of the first bonding metal forming the first bonding metal layer 151 is 217 ° C., and the melting temperature of the second bonding metal forming the second bonding metal layer 152 is 280 ° C. Therefore, the bonding temperature of the second bonding metal forming the second bonding metal layer 152 is higher than the bonding temperature of the first bonding metal forming the first bonding metal layer 151.

  As the first bonding metal, AuSn (weight ratio Au: Sn = 10: 90), AuSn (weight ratio Au: Sn = 80: 20), or the like can be used. The second bonding metal includes AuSn (weight ratio Au: Sn = 80: 20), AuGe (weight ratio Au: Ge = 87.5: 12.5), AuSi (weight ratio Au: Ge). = 96.8: 3.2) etc. can be used. The melting temperature of AuGe (weight ratio: Au: Ge = 87.5: 12.5) is 361 ° C., and the melting temperature of AuSi (weight ratio: Au: Ge = 96.8: 3.2) is 363 ° C. is there. In the present embodiment, the bonding temperature of the second bonding metal forming the second bonding metal layer 152 is higher than the bonding temperature of the first bonding metal forming the first bonding metal layer 151. Any combination of materials may be used.

  For example, when AuSn (weight ratio is Au: Sn = 10: 90) is used as the first bonding metal, AuSn (weight ratio is Au: Sn = 80: 20) is used as the second bonding metal. AuGe (weight ratio is Au: Ge = 87.5: 12.5), AuSi (weight ratio is Au: Ge = 96.8: 3.2), etc. can be used. When AuSn (weight ratio is Au: Sn = 80: 20) is used for the first bonding metal, AuGe (weight ratio is Au: Ge = 87.5: 12.5), AuSi (weight ratio: Au: Ge = 96.8: 3.2) or the like can be used. Further, when AuSn is used for both the first bonding metal and the second bonding metal, AuSn (weight ratio: Au: Sn = 10: 90) is used as the first bonding metal, and the second bonding metal is used. AuSn (weight ratio Au: Sn = 80: 20) is used for the metal. In this case, the first bonding metal contains more Sn than the second bonding metal.

  Further, as described above, when the compound 140 containing an alkali metal cell is sealed inside the cell formed by the first opening 111, it is sealed together with a buffer gas such as nitrogen instead of sealing in a vacuum. It is preferable to do. When alkali metal atoms inside the cell collide with the cell walls, the internal state of the alkali metal atom changes, and the frequency stability decreases when used in an atomic oscillator. For this reason, by enclosing a buffer gas such as nitrogen inside the cell, it is possible to reduce the probability that alkali metal atoms collide with the inner wall of the cell, and therefore it is possible to suppress a decrease in frequency stability. . As the buffer gas, an inert gas is preferable, and examples thereof include nitrogen, neon, argon, and a mixed gas of neon and argon.

  Further, in the method of manufacturing an alkali metal cell in the present embodiment, a resist pattern 162 having an opening 162a shown in FIG. 16 may be used instead of the resist pattern 161 having the opening 161a shown in FIG. . Such a resist pattern 162 can be formed by using a dry film resist. Specifically, a dry film resist is attached to one surface of the Si substrate 110, and exposure and development are performed by an exposure apparatus, whereby a resist pattern 162 having an opening 162a in a region where the joint metal film 131 is formed. Can be formed. In the subsequent steps, as shown in FIG. 6, a metal laminated film made of Au: 700 nm / Cr: 10 nm is formed on the surface on which the resist pattern 162 is formed by sputtering or vacuum evaporation. Thereafter, the metal laminated film formed on the resist pattern 162 is removed by lift-off together with the resist pattern 162 by dipping in an organic solvent or the like, and the junction metal film 131 is formed from the remaining metal laminated film. it can.

  Further, the first bonding metal layer 151 may be formed on one surface of the Si substrate 110, and is formed on one surface of the second glass substrate 122 as described above. There may be. The second bonding metal layer 152 may be formed in the groove 113 of the Si substrate 110, and corresponds to the groove 113 on one surface of the second glass substrate 122 as described above. It may be formed in a part.

[Second Embodiment]
Next, a second embodiment will be described. In consideration of the case where the alkali metal cell manufacturing method and the alkali metal cell according to the present embodiment are cut by dicing, the second bonding metal layer 152 is formed at two locations corresponding to the groove 113 of the Si substrate 110. To form.

  First, as shown in FIG. 17, a substrate in which a first glass substrate 121 is bonded to the other surface of the Si substrate 110 is produced. Two junction metal films 131 are formed between the first opening 111 and the second opening 112 on one surface of the Si substrate 110. The first opening 111 is provided with a compound 140 containing an alkali metal. This step corresponds to the step shown in FIG. 7 in the method for manufacturing an alkali metal cell in the first embodiment, and can be manufactured by the same manufacturing method as in the first embodiment. FIG. 17A is a top view in this step, and FIG. 17B is a cross-sectional view taken along the alternate long and short dash line 17A-17B in FIG.

  Next, as illustrated in FIG. 18, the bonding metal film 132 is formed on one surface of the second glass substrate 122, and the first bonding metal layer 151 is formed on the bonding metal film 132. . The bonding metal film 132 and the first bonding metal layer 151 correspond to the bonding metal film 131 formed on the Si substrate 110 shown in FIG. 17 and the first opening 111 and the second opening 112. Between the two, two are formed. This step corresponds to the step shown in FIG. 10 in the method for manufacturing an alkali metal cell in the first embodiment, and can be manufactured by the same manufacturing method as in the first embodiment. 18A is a top view in this step, and FIG. 18B is a cross-sectional view taken along the alternate long and short dash line 18A-18B in FIG. 18A.

  Next, as shown in FIG. 19, one surface of the Si substrate 110 and one surface of the second glass substrate 122 are bonded by the first bonding metal layer 151. This step corresponds to the step shown in FIG. 11 in the method for manufacturing an alkali metal cell in the first embodiment, and can be manufactured by the same manufacturing method as in the first embodiment. FIG. 19A is a top view in this step, and FIG. 19B is a cross-sectional view taken along the alternate long and short dash line 19A-19B in FIG. 19A.

  Next, as shown in FIG. 20, after generating an alkali metal gas or the like from the compound 140 containing an alkali metal, the groove 113 is formed by the second bonding metal layer 152 formed on the second glass substrate 122. Block. Specifically, the second bonding metal layer 152 formed on the second glass substrate 122 is heated to 280 ° C. or higher and melted, and then cooled, whereby the groove 113 is formed by the second bonding metal layer 152. Block it. As a result, the space in the first opening 111 and the space in the second opening 112 are closed and spatially separated. At this time, the groove 113 between the first opening 111 and the second opening 112 is blocked by the second bonding metal layer 152 formed at two locations. This step corresponds to the step shown in FIG. 13 in the method for manufacturing an alkali metal cell in the first embodiment, and can be manufactured by the same manufacturing method as in the first embodiment. 20A is a top view in this step, and FIG. 20B is a cross-sectional view taken along the alternate long and short dash line 20A-20B in FIG. 20A.

  Next, as shown in FIG. 21, the region in which the first opening 111 is formed and the region in which the second opening 112 are formed are cut and separated by dicing or the like. At this time, since the dicing blade is not in contact with the second bonding metal layer 152 by cutting between the two second bonding metal layers 152 by dicing, the second bonding metal layer is not contacted with the second bonding metal layer 152. In 152, it can isolate | separate, without a hole etc. opening. This step corresponds to the step shown in FIG. 14 in the method for manufacturing an alkali metal cell in the first embodiment, and can be manufactured by the same manufacturing method as in the first embodiment. FIG. 21A is a top view in this step, and FIG. 21B is a cross-sectional view taken along the alternate long and short dash line 21A-21B in FIG.

  FIG. 22 shows an alkali metal cell according to this embodiment manufactured in this manner. In the alkali metal cell in the present embodiment, since the dicing blade does not come into contact with the second bonding metal layer 152 at the time of cutting by dicing, the yield in manufacturing the alkali metal cell can be improved. Further, since leakage can be suppressed, a highly reliable alkali metal cell can be manufactured.

  The contents other than the above are the same as those in the first embodiment.

[Third Embodiment]
Next, a third embodiment will be described. In the method of manufacturing an alkali metal cell in the present embodiment, a compound 140 containing an alkali metal is installed in an opening that does not penetrate through the Si substrate 110.

  Specifically, as shown in FIG. 23, a second opening 112 that penetrates the Si substrate 110, and a first opening 111a and a groove 113 that do not penetrate the Si substrate 110 are formed. . The first opening 111a can be formed by a process similar to the process of forming the groove 113 in the manufacturing method according to the first embodiment. The process shown in FIG. 23 corresponds to the process shown in FIG. 13 in the method for manufacturing an alkali metal cell in the first embodiment, and is manufactured by the same manufacturing method as in the first embodiment. Can do. Note that FIG. 23A is a top view in this step, and FIG. 23B is a cross-sectional view taken along the alternate long and short dash line 23A-23B in FIG.

  In this way, the first opening 111a that does not penetrate the Si substrate 110 is formed, and the compound 140 containing an alkali metal is placed in the first opening 111a, whereby the compound 140 containing the alkali metal is heated to a higher temperature. It becomes possible to heat to. Thereby, alkali metal gas, such as Cs, can be generated efficiently.

  The contents other than the above are the same as those in the first embodiment.

[Fourth Embodiment]
Next, a fourth embodiment will be described. In the manufacturing method of the alkali metal cell in the present embodiment, the shape of the groove is different from the shape of the groove 113 in the first embodiment.

  First, as shown in FIG. 24, a Si substrate 110 is prepared. The Si substrate 110 has a thickness of 1.5 mm, and both surfaces are mirror-finished. This step corresponds to the step shown in FIG. 2 in the method for manufacturing an alkali metal cell in the first embodiment. Note that FIG. 24A is a top view in this step, and FIG. 24B is a cross-sectional view taken along the alternate long and short dash line 24A-24B in FIG.

Next, as shown in FIG. 25, a SiN film (not shown) is formed on both surfaces of the Si substrate 110 by low pressure CVD. Thereafter, a photoresist is applied on the SiN film formed on one surface of the Si substrate 110, and exposure and development are performed by an exposure apparatus. Thus, a resist pattern (not shown) having an opening in a region where the groove 213 is formed is formed on the SiN film on one surface of the Si substrate 110. Thereafter, by performing dry etching using CF ₄ as an etching gas, the SiN film in a region where the resist pattern is not formed is removed, and a resist pattern (not shown) is further removed.

  Thereafter, wet etching is performed using a KOH (30 wt%) solution at a temperature of 85 ° C., thereby removing Si in a region where no SiN film is formed in the Si substrate 110 and forming a groove 213. The formed groove 213 does not penetrate the Si substrate 110. Thereafter, the SiN film is removed by wet etching using a solution for removing SiN or dry etching. The wet etching of the Si substrate 110 is anisotropic etching, and a reverse inclination with an inclination angle θ of 54.7 °, that is, a tapered reverse inclination is formed on the side surface of the formed groove 213. . Specifically, a reverse inclination is formed in which the inclination angle θ on the side surface of the groove 213 is 54.7 °, the width on the surface side of one surface of the Si substrate 110 is a, and the width on the bottom surface side is b. In this case, a groove 213 having a relationship of a> b is formed. 25A is a top view in this step, FIG. 25B is a cross-sectional view taken along the alternate long and short dash line 25A-25B in FIG. 25A, and FIG. It is sectional drawing cut | disconnected in the dashed-dotted line 25C-25D in Fig.25 (a).

  Next, as illustrated in FIG. 26, two openings, that is, a first opening 111 and a second opening 112 are formed in the Si substrate 110. The first opening 111 and the second opening 112 formed in the Si substrate 110 pass through the Si substrate 110, and the first opening 111 and the second opening 112 have a groove 213. To be more connected.

  Specifically, a photoresist is applied to one surface of the Si substrate 110, and exposure and development are performed by an exposure apparatus, whereby openings are formed in regions where the first opening 111 and the second opening 112 are formed. A resist pattern (not shown) is formed. Thereafter, Si in a region where the resist pattern is not formed is removed to a depth half the thickness of the Si substrate 110 by dry etching such as ICP etching to form a recess. Thereby, a part of the first opening 111 and the second opening 112 is formed on one surface of the Si substrate 110.

Thereafter, a photoresist is applied to the other surface of the Si substrate 110, and exposure and development are performed by an exposure apparatus, so that the first opening 111 and the second opening 112 are not formed in the region where the opening is formed. The illustrated resist pattern is formed. Thereafter, Si in a region where the resist pattern is not formed is removed by dry etching such as ICP etching, and the Si substrate 110 is penetrated to form the first opening 111 and the second opening 112. . Dry etching on the Si substrate 110 is performed by a Bosch process in which etching is performed by alternately supplying SF ₆ and C ₄ F ₈ . In the Bosch process, highly anisotropic etching can be performed on the Si substrate 110 at high speed. The power applied in this ICP etching is 2 kW. This step corresponds to the step shown in FIG. 3 in the method for manufacturing an alkali metal cell in the first embodiment. FIG. 26A is a top view in this step, and FIG. 26B is a cross-sectional view taken along the alternate long and short dash line 26A-26B in FIG.

  Next, as shown in FIG. 27, the first glass substrate 121 is bonded to the other surface of the Si substrate 110, and the first bonding metal layer 151 is formed on one surface of the second glass substrate 122. Furthermore, a second bonding metal layer 152 is formed at a position corresponding to the groove 213 of the Si substrate 110. Thereafter, the Si substrate 110 and the second glass substrate 122 are bonded by the first bonding metal layer 151 by heating to about 230 ° C. Thereafter, the compound 140 containing the alkali metal is heated to generate an alkali metal, and then further heated to 280 ° C. and cooled to close the groove 213 with the second bonding metal layer 152. This step corresponds to the step shown in FIG. 13 in the method for manufacturing an alkali metal cell in the first embodiment, and can be manufactured by the same manufacturing method as in the first embodiment. 27A is a top view in this step, FIG. 27B is a cross-sectional view taken along the alternate long and short dash line 27A-27B in FIG. 27A, and FIG. It is sectional drawing cut | disconnected in the dashed-dotted line 27C-27D in Fig.27 (a).

  Next, as shown in FIG. 28, the region in which the first opening 111 is formed and the region in which the second opening 112 are formed are cut and separated by dicing or the like. This step corresponds to the step shown in FIG. 14 in the method for manufacturing an alkali metal cell in the first embodiment, and can be manufactured by the same manufacturing method as in the first embodiment. Note that FIG. 28A is a top view in this step, and FIG. 28B is a cross-sectional view taken along the alternate long and short dash line 28A-28B in FIG.

  Through the above steps, the alkali metal cell in this embodiment can be manufactured. The alkali metal cell produced in this way in this embodiment is the same as the alkali metal cell in the first embodiment.

  In the manufacturing method of the alkali metal cell in the present embodiment, since the side surface of the groove portion 213 is formed in a tapered shape, the bonding portion metal film 131 can be formed without a gap, so that the second bonding metal layer 152 is formed. It is possible to make the joining by the more reliable. For example, when the side surface of the groove portion is not tapered but formed substantially vertically, even if the bonding portion metal film 131 is formed by sputtering or vacuum deposition, the bonding portion metal film 131 is not formed on the side surface of the groove portion. There is. In this case, the melted second bonding metal does not sufficiently wet and spread on the side surface of the groove portion, cannot completely close the groove portion, and a gap is formed. However, in the present embodiment, since the side surface of the groove 213 is formed in a taper shape, even if the bonding metal film 131 is formed by sputtering or vacuum evaporation, the bonding metal is formed on the side of the groove 213. A film 131 can be formed. As a result, the second bonding metal in which the groove 213 is melted can be wetted and spread without gaps, and can be more completely closed by the second bonding metal layer 152.

  The contents other than the above are the same as in the first embodiment.

[Fifth Embodiment]
Next, a fifth embodiment will be described. The manufacturing method of the alkali metal cell in this Embodiment can manufacture two or more cells simultaneously with respect to one raw material chamber.

  Specifically, as shown in FIG. 29, the Si substrate 300 is formed with an opening 310 serving as a raw material chamber penetrating the Si substrate 300 and openings 321 322 323 324 serving as cells. . Further, a groove 331 is formed between the opening 310 and the opening 321, a groove 332 is formed between the opening 310 and the opening 322, and a groove 333 is formed between the opening 310 and the opening 323. A groove 334 is provided between the opening 310 and the opening 324. The openings are spatially connected to each other by these grooves.

  A first glass substrate (not shown) is bonded to the other surface of the Si substrate 300 by anodic bonding. Further, one surface of the Si substrate 300 is not surrounded by the first bonding metal layer 151 that is heated to about 230 ° C. and cooled around the opening 310 and the openings 321, 322, 323, and 324. The illustrated second glass substrate is bonded.

  A second bonding metal layer 152 is formed on one surface of the second glass substrate at portions corresponding to the grooves 331, 332, 333, and 334 formed on the Si substrate 300. Therefore, after generating an alkali metal such as Cs from the compound material 140 containing the alkali metal, the second bonding metal layer 152 formed on the second glass substrate is melted by heating to 280 ° C. or higher, and then cooled. By doing so, the groove portion can be closed by the second bonding metal layer 152.

  After that, the alkali metal cell in this embodiment can be manufactured by cutting the periphery of the region where the openings 321, 322, 323, and 324 are formed by dicing or the like. Thus, for example, in the case shown in FIG. 29, four alkali metal cells can be simultaneously produced by the openings 321, 322, 323, and 324 with respect to the opening 310 serving as one raw material chamber. Therefore, an alkali metal cell can be manufactured at low cost. The opening 310 in the present embodiment corresponds to the first opening 111 in the first embodiment, and the openings 321, 322, 323, and 324 are the same as those in the first embodiment. This corresponds to the second opening 112. Further, the groove portions 331, 332, 333, and 334 correspond to the groove portion 113 in the first embodiment.

  Further, in this embodiment, as shown in FIG. 30, one opening 310 serving as a raw material chamber and eight openings 341, 342, 343, 344, 345, 346, 347, and 348 serving as cells are formed. It may be what has been done. Between adjacent openings 310, 341, 342, 343, 344, 345, 346, 347, 348, grooves 351, 352, 353, 354, 355, 356, 357, 358, 359, 359, 360, 361 and 362 are provided. The openings are spatially connected to each other by these grooves. Specifically, a groove 351 is provided between the opening 310 and the opening 348, a groove 352 is provided between the opening 310 and the opening 342, and a groove is provided between the opening 310 and the opening 344. A groove 354 is provided between the opening 310 and the opening 346. Further, a groove 355 is formed between the opening 348 and the opening 341, a groove 356 is formed between the opening 341 and the opening 342, and a groove 357 is formed between the opening 342 and the opening 343. A groove 358 is provided between the opening 343 and the opening 344. Further, a groove 359 is provided between the opening 344 and the opening 345, a groove 360 is provided between the opening 345 and the opening 346, and a groove 361 is provided between the opening 346 and the opening 347. A groove 362 is provided between the opening 357 and the opening 348.

  A first glass substrate (not shown) is bonded to the other surface of the Si substrate 300 by anodic bonding. On one surface of the Si substrate 300, a first bonding that has been heated to about 230 ° C. and then cooled around the opening 310 and the openings 341, 342, 343, 344, 345, 346, 347, and 348. A second glass substrate (not shown) is bonded by the metal layer 151.

  Further, one surface of the second glass substrate corresponds to the grooves 351, 352, 353, 354, 355, 356, 357, 358, 359, 359, 360, 361, 362 formed in the Si substrate 300. A second bonding metal layer 152 is formed in the portion. Therefore, after generating an alkali metal such as Cs from the compound material 140 containing the alkali metal, the second bonding metal layer 152 formed on the second glass substrate is melted by heating to 280 ° C. or higher, and then cooled. By doing so, the groove portion can be closed by the second bonding metal layer 152.

  After that, the alkali metal cell in this embodiment can be manufactured by cutting the periphery of the region where the openings 341, 342, 343, 344, 345, 346, 347, and 348 are formed by dicing or the like. it can. Thus, for example, in the case shown in FIG. 30, eight alkali metal cells are simultaneously formed by the openings 341, 342, 343, 344, 345, 346, 347, and 348 with respect to the opening 310 serving as one raw material chamber. Can be produced. Therefore, an alkali metal cell can be manufactured at low cost.

  The contents other than the above are the same as in the first embodiment. Further, this embodiment can be applied to the second to fourth embodiments.

[Sixth Embodiment]
Next, a sixth embodiment will be described. The present embodiment is an atomic oscillator using an alkali metal cell in the first to fifth embodiments. The atomic oscillator in the present embodiment will be described based on FIG. The atomic oscillator in this embodiment is a CPT-type small atomic oscillator and includes a light source 410, a collimating lens 420, a λ / 4 plate 430, an alkali metal cell 440, a photodetector 450, and a modulator 460. This atomic oscillator makes light of two different wavelengths out of the light including the sideband emitted from the light source 410 incident on the alkali metal cell 440, and thereby has a light absorption characteristic due to the quantum interference effect by two types of resonance light. It controls the oscillation frequency.

  As the light source 410, a surface emitting laser element is used. The alkali metal cell 440 is filled with Cs (cesium) atomic gas as an alkali metal, and uses the transition of the D1 line. The photodetector 450 uses a photodiode.

  In the atomic oscillator in this embodiment, the light emitted from the light source 410 is irradiated to the alkali metal cell 440 in which the cesium atom gas is enclosed, and the electrons in the cesium atom are excited. The light transmitted through the alkali metal cell 440 is detected by the photodetector 450, and the signal detected by the photodetector 450 is fed back to the modulator 460, and the surface emitting laser element in the light source 410 is modulated by the modulator 460.

  Based on FIG. 32, the atomic oscillator in the present embodiment will be described. The atomic oscillator in the present embodiment is formed on the circuit board 471 in the vertical direction. An alumina substrate 472 is provided on the circuit board 471, and a surface emitting laser element that serves as the light source 410 is provided on the alumina substrate 472. The alumina substrate 472 is provided with a surface emitting laser heater 473 for controlling the temperature of the light source 410 and the like. An ND (Neutral Density) filter 474 is provided above the light source 410. The ND filter 474 is installed at a predetermined position by a heat insulating spacer 475 made of glass or the like. A collimator lens 420 is provided above the ND filter 474, and a λ / 4 plate 430 is provided above the collimator lens. The λ / 4 plate 430 is installed at a predetermined position by a spacer 476 formed of silicon or the like. An alkali metal cell 440 is provided on the λ / 4 plate 430. The alkali metal cell 440 includes two glass substrates 441. The two glass substrates 441 are opposed to each other, the edge portions are connected by the silicon substrate 442, and the glass substrate 441 and the silicon substrate 441 are connected to each other. A portion surrounded by the substrate 442 is filled with alkali metal. Note that in the alkali metal cell 440, a surface through which laser light is transmitted is formed by the glass substrate 441. Cell heaters 477 are provided on both sides of the alkali metal cell 440, and the alkali metal cell 440 can be set to a predetermined temperature. A photo detector 450 is provided above the alkali metal cell 440, and the photo detector 450 is installed at a predetermined position by a spacer 478 made of silicon.

  Next, FIG. 33 shows a structure of atomic energy levels related to CPT. Utilizing the fact that the light absorptance decreases when electrons are excited simultaneously from two ground levels to the excited level. The surface emitting laser uses an element having a carrier wavelength close to 894.6 nm. The wavelength of the carrier wave can be tuned by changing the temperature or output of the surface emitting laser. As shown in FIG. 34, sidebands are generated on both sides of the carrier by modulation, and the frequency difference is modulated at 4.6 GHz so that the frequency difference matches the 9.2 GHz that is the natural frequency of the Cs atom. . As shown in FIG. 35, the laser beam passing through the excited Cs gas is maximized when the sideband frequency difference matches the natural frequency difference of Cs atoms. Therefore, the modulation frequency of the surface emitting laser element in the light source 410 is adjusted by feedback in the modulator 460 so that the output of the photodetector 450 maintains the maximum value. Since the natural frequency of the atom is extremely stable, the modulation frequency becomes a stable value, and this information is extracted as an output. When the wavelength is 894.6 nm, a wavelength in the range of ± 1 nm is required.

  In the atomic oscillator in the present embodiment, any one of the alkali metal cells in the first to fifth embodiments is used as the alkali metal cell 440. Further, in the alkali metal cell 440 of the atomic oscillator in the present embodiment, the silicon substrate 442 corresponds to the Si substrate 110 in the first embodiment or the like. The glass substrate 441 corresponds to the first glass substrate 121 and the second glass substrate 122 in the first embodiment and the like.

In this embodiment, Cs is used as the alkali metal, and a surface emitting laser having a wavelength of 894.6 nm is used in order to use the transition of the D1 line, but 852.3 nm when the C2 D2 line is used. Can also be used. Rb (rubidium) can also be used as the alkali metal, and 795.0 nm can be used when the D1 line is used, and 780.2 nm can be used when the D2 line is used. The modulation frequency when using Rb is modulated at 3.4 GHz for ⁸⁷ Rb and 1.5 GHz for ⁸⁵ Rb. Even in these wavelengths, a wavelength in the range of ± 1 nm is required.

  As mentioned above, although the form which concerns on implementation of this invention was demonstrated, the said content does not limit the content of invention.

110 Si substrate 111 First opening (one opening)
112 Second opening (other opening)
113 Groove 121 First Glass Substrate 122 Second Glass Substrate 131 Bonding Metal Film 132 Bonding Metal Film 140 Compound 151 Containing Alkali Metal First Bonding Metal Layer 152 Second Bonding Metal Layer 410 Light Source 420 Collimating Lens 430 λ / 4 plate 440 Alkali metal cell 450 Photodetector 460 Modulator

US Pat. No. 6,806,784 US Patent Application Publication No. 2005/0007118 JP 2009-212416 A JP 2009-283526 A

Applied Physics Letters, Vol. 85, pp. 1460-1462 (2004) Comprehensive Microsystems, vol. 3, pp. 571-612 Applied Physics Letters, Vol. 84, pp. 2694-2696 (2004) OPTICS LETTERS, Vol. 30, pp. 2351-2353 (2005) Applied Physics Letters, Vol. 90, 114106 (2007) J. et al. Micro / Nanolith. MEMS MOEMS 7 (3), 033013 (2008)

Claims (18)

A substrate on which an opening penetrating from one surface to the other surface is formed;
A first transparent substrate bonded to the other surface of the substrate;
A second transparent substrate bonded to one surface of the substrate;
Have
In the opening of the substrate, an alkali metal is sealed in a space surrounded by the first transparent substrate and the second transparent substrate,
The substrate and the second transparent substrate are bonded by a first bonding metal layer formed of a first bonding metal and a second bonding metal layer formed of a second bonding metal. The space is sealed,
The alkali metal cell, wherein the second bonding metal has a melting temperature higher than that of the first bonding metal.   The alkali metal cell according to claim 1, wherein the first bonding metal is formed of a material containing AuSn.   3. The alkali metal cell according to claim 1, wherein the second bonding metal is formed of a material containing any one of AuSn, AuGe, and AuSi.   The first bonding metal and the second bonding metal are both formed of a material containing AuSn, and the first bonding metal contains more Sn than the second bonding metal. The alkali metal cell according to claim 1. A groove portion connected to the opening is formed on one surface of the substrate,
5. The alkali metal cell according to claim 1, wherein the substrate is bonded to the second transparent substrate by the second bonding metal layer in the groove portion.   The alkali metal cell according to claim 5, wherein the groove portion is formed so that a surface side of one surface of the substrate is wide and a bottom surface side is narrow.   The alkali metal cell according to claim 1, wherein the substrate is a silicon substrate.   The alkali metal cell according to claim 1, wherein one or both of the first transparent substrate and the second transparent substrate are glass substrates.   The alkali metal cell according to claim 1, wherein the other surface of the substrate and the first transparent substrate are bonded by anodic bonding or direct bonding.   The alkali metal cell according to claim 1, wherein the alkali metal is cesium or rubidium. The alkali metal cell according to any one of claims 1 to 10,
A light source for irradiating the alkali metal cell with laser light;
A photodetector that detects light transmitted through the alkali metal cell out of the laser light applied to the alkali metal cell from the light source;
An atomic oscillator characterized by comprising:   Of the light including the sideband emitted from the light source, the light having two different wavelengths is incident on the alkali metal cell, thereby controlling the oscillation frequency by the light absorption characteristic due to the quantum interference effect by the two types of resonance light. The atomic oscillator according to claim 11. Forming two or more openings penetrating the substrate in the substrate, and forming a groove portion spatially connecting the two openings on one surface of the substrate;
Bonding a first transparent substrate to the other surface of the substrate;
Installing a compound containing an alkali metal in one of the openings;
The first bonding metal is formed around the two or more openings on one surface of the substrate or at a portion corresponding to the periphery of the two or more openings on one surface of the second transparent substrate. Forming a first bonding metal layer;
Forming a second bonding metal layer formed of a second bonding metal on a groove portion of the substrate or a portion corresponding to the groove portion on one surface of the second transparent substrate;
Bonding one surface of the substrate and one surface of the second transparent substrate with a first bonding metal layer;
A step of generating an alkali metal from the compound containing the alkali metal and supplying the alkali metal to the other opening through the groove from the one opening;
After supplying the alkali metal to the other opening, and bonding the substrate and the second transparent substrate by the second bonding metal layer in the groove;
A method for producing an alkali metal cell, comprising: One opening that does not penetrate the substrate on one surface of the substrate, another opening that penetrates the substrate, and the one opening and the other opening on one surface of the substrate are spatially arranged. Forming a groove to be connected to,
Bonding a first transparent substrate to the other surface of the substrate;
Installing a compound containing an alkali metal in the one opening;
A portion corresponding to the periphery of the one opening and the other opening on one surface of the substrate or the periphery of the one opening and the other opening on one surface of the second transparent substrate Forming a first bonding metal layer formed of the first bonding metal;
Forming a second bonding metal layer formed of a second bonding metal on a groove portion of the substrate or a portion corresponding to the groove portion on one surface of the second transparent substrate;
Bonding one surface of the substrate and one surface of the second transparent substrate with a first bonding metal layer;
A step of generating an alkali metal from the compound containing the alkali metal and supplying the alkali metal to the other opening through the groove from the one opening;
After supplying the alkali metal to the other opening, and bonding the substrate and the second transparent substrate by the second bonding metal layer in the groove;
A method for producing an alkali metal cell, comprising:   The other opening is separated by cutting between the one opening and the other opening, and the inside of the alkali metal cell is formed by the separated other opening. The method for producing an alkali metal cell according to claim 13 or 14.   The method for producing an alkali metal cell according to any one of claims 13 to 15, wherein the second bonding metal has a melting temperature higher than that of the first bonding metal.   The alkali metal cell according to any one of claims 13 to 16, wherein the first bonding metal and the second bonding metal are materials including any of AuSn, AuGe, and AuSi. Production method.   The alkali metal according to any one of claims 13 to 17, wherein the alkali metal is generated by irradiating the compound containing the alkali metal with any one of laser light, ultraviolet light, and heating. A manufacturing method of a metal cell.

Images