Substrate, method for manufacturing substrate, and method for manufacturing unit cell

Abstract

The present invention addresses the problem of providing a highly versatile substrate, a production method for the substrate, and a production method for a unit cell using the substrate. This problem is solved by providing a substrate characterized in that a plurality of alkali metal azide spots are formed on a substantially flat surface.

Description

[Technical Field]

[0001] The present invention relates to a substrate, a method for manufacturing a substrate, and a method for manufacturing a unit cell using the substrate. [Background technology]

[0002] Cells containing sealed atomic gases (hereinafter also referred to as gas cells) are used in atomic devices such as high-precision atomic clocks based on the frequency of the electromagnetic waves absorbed by the atoms, and atomic magnetic sensors that utilize optical pumping of the atoms. A known method for producing such gas cells involves preparing a cell container by glass fusion or blowing, blowing an alkali metal gas and a buffer gas into the container, and sealing the gases by pinch-off (Non-Patent Documents 1 and 2).

[0003] However, the manufacturing methods disclosed in Non-Patent Documents 1 and 2 are complicated, make it difficult to miniaturize the cells, and are unsuitable for mass production. Therefore, from the perspective of miniaturizing the cells and reducing costs through mass production, methods of manufacturing cells using a wafer process are being considered (Non-Patent Documents 3 and 4). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] J. Gouloumet, B. Leuenberger, C. Schori, S. Grop, and R. Rochat, “Progress towards a compact and low-power miniaturized Rubidium Oscillator (mROTM)” IEEE / MTT-S International Microwave Symposium, 2020, p.876-879 [Non-patent document 2] H. Zhang, H. Herdian, AT Narayanan, A. Shirane, M. Suzuki, K. Harasaka, K. Adachi, S. Goka, S. Yanagimachi, and K. Okada, “ULPAC: A Miniatured Ultralow-power Atomic Clock” IEEE Journal Of Solid-State Circuits, 2019, 54(11), p.3135-3148 [Non-patent document 3] S. Karlen, J. Gobet, T. Overstolz, J. Haesler, and S. Lecomte, “Lifetime assessment of RbN3-filled MEMS atomic vapor cells with Al2O3 coating” Optics express, 2017, 25(3), p.2187-2194 [Non-patent document 4] L. Liew, J. Moreland, and V. Gerginov, “Wafer-level filling of microfabricated atomic vapor cells based on thin-film deposition and photolysis of cesium azide” Applied Physics Letters, 2007, 90(11), 114106 Summary of the Invention [Problem to be solved by the invention]

[0005] The gas cell manufacturing method described in Non-Patent Document 3 describes adding an RbN3 solution with a pipette to a cavity in a substrate on which partitions that separate multiple cells are formed, drying the solution, and sealing the opening by anodically bonding glass. However, while gas cells are required to be designed in size and shape to match the atomic device to be used, the gas cell manufacturing method described in Non-Patent Document 3 does not allow for changing the cell shape after distributing RbN3 into the cell, making it less versatile.

[0006] The gas cell manufacturing method described in Non-Patent Document 4 describes forming a CsN3 film by vapor deposition in a cavity of a substrate on which partition walls that separate multiple cells are formed, and then sealing the opening by anodic bonding with glass. However, even with the manufacturing method described in Non-Patent Document 4, it is not possible to change the cell shape after distributing CsN3 to the cells, and it has low versatility. Furthermore, the vapor deposition method is prone to CsN3 explosion and bumping during heating, and the formed CsN3 film is non-uniform, and the amount of Cs enclosed is not quantitative, making it impossible to obtain uniform unit cells.

[0007] The present invention has been made in light of the above-mentioned circumstances, and an object of the present invention is to provide a highly versatile substrate, a method for manufacturing the substrate, and a method for manufacturing a unit cell using the substrate. [Means for solving the problem]

[0008] The gist of the present invention is as follows. [1] A substrate having a plurality of spots of alkali metal azide formed on a substantially flat surface. [2] The substrate according to [1], having a plurality of spot-shaped depressions on the substantially flat surface, in which spots of the alkali metal azide are formed. [3] The method for manufacturing a substrate according to [1] or [2], wherein a coating film formed from a liquid containing an alkali metal azide is formed in spots on the substrate member. [4] A method for manufacturing a substrate according to [3], in which a mask surface having spot-shaped holes is formed on a substrate member, a liquid containing the alkali metal azide is applied to the mask surface to form a coating film, and then the mask is removed. [5] The method for manufacturing a substrate according to [3], wherein a liquid containing the alkali metal azide is applied onto a substrate member to form a coating film, and then the coating film is partially removed to leave the alkali metal azide in spots on a substantially flat surface. [6] A method for manufacturing a substrate according to [2], wherein a liquid containing an alkali metal azide is applied to a substrate member so that the liquid remains only in the recessed portion, and a coating film formed from the liquid containing alkali metal azide is formed in the recessed portion in a spot-like manner. [7] A cell assembly assembly step of stacking a partition wall separating the alkali metal azide spots and a second substrate facing the substrate via the partition wall on the substrate according to [1] or [2]. The cell assembly is irradiated with ultraviolet light. death , alkali metal azides By decomposing vaporization to make process, and then cutting out a unit cell from the cell assembly. [8] The method for manufacturing a unit cell according to [7], wherein the cell assembly assembly is assembled under vacuum conditions in which a buffer gas may be introduced. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a highly versatile substrate, a method for manufacturing a substrate, and a method for manufacturing a unit cell using the substrate. Furthermore, the substrate can be easily manufactured. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a substrate according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of a member used in the manufacturing process of the substrate shown in FIG. [Figure 3]FIG. 3 is a schematic cross-sectional view showing another example of the substrate according to the embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an example of a cell assembly assembly step in the method for manufacturing a unit cell according to an embodiment of the present invention. [Figure 5] FIG. 5 is a schematic cross-sectional view showing an example of a unit cell obtained by the method for producing a unit cell according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a substrate, a method for manufacturing a substrate, and a method for manufacturing a unit cell using the substrate according to the present invention will be described in detail with reference to the illustrated examples as needed. However, the present invention is not limited to the illustrated examples below, and appropriate modifications can be made within the scope of the present invention, and all such modifications are within the technical scope of the present invention.

[0012] (Substrate 1) As shown in FIGS. 1 and 3 , the substrate 1 of the present invention has a substantially flat surface 11 on which multiple alkali metal azide spots 2 are formed. Hereinafter, this substrate will also be referred to as an “alkali metal azide spot-formed substrate.” Furthermore, the substrate before the formation of alkali metal azide spots will also be referred to as a “substrate member.” In the present invention, the “substantially flat surface” of the substrate refers to a surface that does not have large irregularities that would serve as partition walls separating multiple cells when the substrate is used to form a cell assembly. The surface may have slight irregularities that would not serve as partition walls. Specifically, the surface may have spot-like depressions 12 with a depth of 20% or less of the substrate thickness. The alkali metal azide spot-formed substrate 1 does not have any portions that would serve as partition walls separating multiple cells when the substrate is used to form a cell assembly, allowing for greater flexibility in the design of the size and shape of the unit cells to be fabricated, making the substrate highly versatile. Furthermore, since the alkali metal azide spot formation substrate 1 does not have the partition wall, it can be manufactured without going through the complicated process of individually introducing raw materials serving as alkali metal sources into each of the multiple partitioned cells, and can be manufactured easily if necessary.

[0013] As the material for the substrate member 13 is intended for use in a gas cell using the alkali metal azide spot forming substrate 1 as an atomic clock, atomic magnetic sensor, quantum gyroscope, etc. that utilizes laser spectroscopy, a transparent material that is optically transparent is preferred, and heat-resistant glass is more preferred.

[0014] The thickness of the substrate member 13 can be set as appropriate, but from the viewpoint of strength, it is preferably 100 μm or more, more preferably 500 μm or more, and from the viewpoint of light transmittance, it is preferably 1.0 mm or less, more preferably 0.8 mm or less. Note that when the substrate member 13 has a depression 12, the thickness of the substrate member 13 refers to the thickness of a portion that does not have the depression 12.

[0015] The alkali metal azide spot 2 is a spot containing an alkali metal azide, and preferably a spot consisting only of an alkali metal azide. If the alkali metal azide spot 2 is a spot consisting only of an alkali metal azide, this is preferable because impurities that can adsorb the buffer gas are not generated in the cell when a gas cell is fabricated using the alkali metal azide spot formation substrate 1. If the buffer gas in the cell is adsorbed by impurities, the internal pressure in the cell may change, which may shift the frequency of the electromagnetic waves absorbed by the alkali metal or change the temperature characteristics of the alkali metal.

[0016] Examples of alkali metal azides include lithium azide, sodium azide, potassium azide, rubidium azide, and cesium azide, with rubidium azide and cesium azide being preferred, and rubidium azide being more preferred. Since the transition frequency of rubidium atoms is lower than that of cesium atoms and the like, when a gas cell using the alkali metal azide spot formation substrate 1 is used in an atomic clock or the like, if the alkali metal azide is rubidium azide, it is possible to reduce the power consumption of the electronic circuit.

[0017] Since alkali metal azides are stable substances at room temperature and normal pressure, alkali metal azide spot formed substrate 1 can be stored and transported at room temperature and normal pressure.

[0018] The shape of the alkali metal azide spot 2 is not particularly limited and may be, for example, circular, elliptical, or polygonal. The size of the alkali metal azide spot 2 can be set appropriately, but the circle-equivalent diameter of the alkali metal azide spot 2 is, for example, preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more, and is preferably 2.0 mm or less, and more preferably 1.5 mm or less.

[0019] The shape and size of the multiple alkali metal azide spots 2 may be the same or different, but are preferably the same. If the multiple alkali metal azide spots 2 have the same shape and size, a unit cell with a uniform amount of alkali metal encapsulation can be easily manufactured using the alkali metal azide spot formation substrate 1. It is more preferable that the multiple alkali metal azide spots 2 are formed in a uniform pattern.

[0020] When the substrate member 13 has a plurality of spot-shaped depressions 12 on the substantially flat surface 11, the alkali metal azide spots 2 may be formed in the depressions 12.

[0021] The shape of the depressions 12 is not particularly limited and may be, for example, a bowl shape, a bottomed cylindrical shape, a bottomed polygonal pillar shape, an inverted cone shape, or an inverted polygonal pyramid shape (a bottomed pillar shape is shown in the illustrated example). The size of the depressions 12 can be set as appropriate, but the outer diameter of the depressions 12 is, for example, preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more, in terms of circle equivalent diameter. The depth of the depressions 12 is preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more, from the viewpoint of reliably retaining the alkali metal azide-containing liquid in the depressions 12 during the formation of the alkali metal azide spots 2 described below. Furthermore, from the viewpoint of ensuring a substantially flat surface 11, the depth is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. The ratio of the depth of the recess 12 to the thickness of the substrate member 13 is preferably 0.1% or more, more preferably 1% or more, even more preferably 10% or more, and is preferably 20% or less, more preferably 18% or less, and even more preferably 15% or less.

[0022] The shapes and sizes of the plurality of recesses 12 may be the same or different, but are preferably the same. If the shapes and sizes of the plurality of recesses 12 are the same, it is easy to make the shapes and sizes of the plurality of alkali metal azide spots 2 the same, and unit cells with a uniform amount of alkali metal enclosed can be easily produced using the alkali metal azide spot-formed substrate 1.

[0023] (Method of manufacturing alkali metal azide spot-formed substrate 1) A substrate 1 having a plurality of alkali metal azide spots 2 formed on a substantially flat surface 11 (alkali metal azide spot-formed substrate) can be produced by forming a coating film formed from a liquid containing an alkali metal azide in the form of spots on a substrate member 13 having a substantially flat surface 11.

[0024] Examples of the liquid containing an alkali metal azide include a solution in which an alkali metal azide is dissolved and a dispersion in which an alkali metal azide is dispersed. A solution in which an alkali metal azide is dissolved is preferred because it is easier to make the content of alkali metal azide in the multiple alkali metal azide spots 2 more uniform.

[0025] Examples of the solvent for the alkali metal azide-containing liquid include water, methanol, ethanol, isopropyl alcohol, acetonitrile, acetone, N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide, with water or methanol being preferred and methanol being more preferred.

[0026] The concentration of the alkali metal azide in the alkali metal azide-containing solution is not particularly limited, and is, for example, preferably 0.5 wt % or more, more preferably 1.0 wt % or more, and preferably 15 wt % or less, more preferably 10 wt % or less. If the alkali metal azide concentration is within the above range, a cell containing an amount of alkali metal suitable for use in an atomic device can be easily obtained.

[0027] Methods for forming spots of a coating film formed from an alkali metal azide-containing liquid on the substrate member 13 include, for example, using an inkjet machine or a dispenser to drop appropriate amounts of the alkali metal azide-containing liquid into spots, but preferred are the following formation methods A, B, and C. Formation methods A, B, and C are possible because the substrate member 13 does not have large irregularities that would serve as partition walls separating multiple cells when a cell assembly is formed, and they do not require the complicated process of individually introducing raw materials into each of the multiple separated cells, allowing the alkali metal azide spot-formed substrate 1 to be easily produced.

[0028] ((Formation method A)) Formation method A is a method in which a mask surface (mask layer) having spot-shaped holes is formed on a substantially flat surface 11 of a substrate member 13, a liquid containing an alkali metal azide is applied to this mask surface to form a coating film, and then the mask is removed.

[0029] The mask having spot-shaped holes in forming method A is not particularly limited as long as it can be removed in a subsequent process, and may be an adhesive tape with spot-shaped holes formed therein, or a mask formed from a photoresist and a photomask, which is generally referred to as a lift-off method.

[0030] In the formation method A, the alkali metal azide-containing liquid may be applied using a coating machine such as a spin coater so as to obtain a coating film (i.e., alkali metal azide spots 2) of uniform thickness after drying as described below. If the coating film has a uniform thickness after drying, unit cells with a uniform amount of alkali metal encapsulation can be easily produced using the alkali metal azide spot-formed substrate 1.

[0031] In the formation method A, the coating film is formed by removing the liquid component from the alkali metal azide-containing solution, i.e., drying. The drying method is not particularly limited, but examples include heating and drying using high-temperature air or a hot plate.

[0032] In the formation method A, a method for removing the mask can be selected appropriately depending on the mask formed. For example, when a mask surface is formed using an adhesive tape with spot-shaped holes formed therein, the adhesive tape can be peeled off so that no adhesive remains.

[0033] ((Formation method B)) Formation method B is a method in which a liquid containing an alkali metal azide is applied to a substantially flat surface 11 of a substrate member 13 to form a coating film, and then the coating film is partially removed to leave the alkali metal azide in spots on the substantially flat surface 11.

[0034] The application of the alkali metal azide-containing liquid and the formation of the coating film in the forming method B are similar to the application of the alkali metal azide-containing liquid and the formation of the coating film in the forming method A.

[0035] In the formation method B, examples of a method for partially removing the coating film to leave the alkali metal azide in spots on the substantially flat surface 11 include a method using a photoresist and a photomask, which is generally called an etching method.

[0036] ((Formation method C)) Formation method C is a method in which a liquid containing an alkali metal azide is applied to a substantially flat surface 11 of a substrate member 13 having a plurality of depressions 12 as shown in FIG. 2 so that the liquid remains only in the depressions 12, thereby forming a coating film in the depressions 12.

[0037] The substrate member 13 used in formation method C has a plurality of recesses 12 formed in advance on at least one surface. The method for forming the recesses 12 is not particularly limited as long as it can form a plurality of uniform recesses 12, and examples thereof include processing with an ultrashort pulse laser and chemical etching. Examples and preferred embodiments of the shape and size of the recesses 12 to be formed are the same as those described for the recesses 12 in the description of the substrate 1 above.

[0038] In forming method C, the alkali metal azide-containing liquid may be applied using a coating machine such as a spin coater, and is applied so that the alkali metal azide-containing liquid remains only in the recesses 12 of the substrate member 13. As a method for leaving the alkali metal azide-containing liquid only in the recesses 12 of the substrate member 13, for example, when a spin coater is used for coating, the excess liquid outside the recesses 12 may be removed by simply using the rotational centrifugal force of the spin coater, or the liquid outside the recesses 12 may be removed by tilting or standing vertically the substrate member 13 after coating with the alkali metal azide-containing liquid. If the substrate member 13 has a plurality of recesses 12, it is not necessary to form a mask surface before forming a coating film or to perform a step of partially removing the formed coating film.

[0039] The formation of the coating film in the forming method C is similar to the formation of the coating film in the forming method A.

[0040] (Manufacturing Method of Unit Cell 7) The method for manufacturing the unit cell 7 shown in FIG. 5 includes the steps of assembling a cell assembly 5 by laminating a partition wall 3 separating the alkali metal azide spots 2 shown in FIG. 4 and a second substrate 4 facing the alkali metal azide spot forming substrate 1 via the partition wall 3; death Alkali Metal Azides By decomposing vaporization to make and then cutting out unit cells from the cell assembly 5. Conventional substrates in which an alkali metal source is arranged on a substrate having partition walls that separate the cells have limited flexibility in designing unit cells, but by using the alkali metal azide spot-formed substrate 1, the shape of the partition walls 3 can be designed appropriately to suit the application of the cell, making it possible to manufacture unit cells 7 having the desired size and shape.

[0041] ((Assembly process of cell assembly 5)) Cell assembly 5 is a laminated structure in which alkali metal azide spot formation substrate 1 and second substrate 4 are joined via partition wall 3. By sealing through-holes 31 in partition wall 3 with alkali metal azide spot formation substrate 1 and second substrate 4, internal space 6 of the cell is formed as an airtight space.

[0042] The partition wall 3 serves to separate the alkali metal azide spots 2, and is a plate-like member having a plurality of through-holes 31 in the thickness direction.

[0043] The material of the partition wall 3 is not particularly limited, and examples thereof include glass, metal, resin, and silicon. Glass and silicon are preferred, and silicon is more preferred, as they are suitable for microfabrication by etching or the like.

[0044] The thickness a (see FIG. 4) of the partition walls 3 can be set appropriately, but is preferably 0.1 mm or more, more preferably 0.3 mm or more, and is preferably 5.0 mm or less, more preferably 3.0 mm or less, for example.

[0045] The through holes 31 in the partition walls 3 can be formed by microfabrication such as etching or blasting. The size and shape of the through holes 31 can be set appropriately as long as the partition walls 3 do not overlap the alkali metal azide spots 2 on the alkali metal azide spot formation substrate 1 when the cell assembly 5 is assembled. Therefore, the size and shape of the resulting unit cells 7 can be adjusted to a desired size and shape depending on the intended use of the cell.

[0046] As the material for the second substrate 4, a transparent material having optical transparency is preferred, and heat-resistant glass is more preferred, since the cell using this substrate is intended for use as an atomic clock, atomic magnetic sensor, etc.

[0047] The thickness of the second substrate 4 can be set appropriately, but is preferably 80 μm or more, more preferably 100 μm or more, and is preferably 1.0 mm or less, more preferably 0.8 mm or less, for example.

[0048] The method for bonding the partition wall 3 to the alkali metal azide spot-formed substrate 1 and the second substrate 4 can be selected appropriately depending on the materials used, and is not particularly limited. Examples of the bonding method include anodic bonding, direct bonding, and surface activated bonding. Anodic bonding is preferred because it easily achieves airtight bonding.

[0049] Because elemental alkali metals are oxidized in the presence of oxygen and moisture in a short time, the bonding between the partition wall 3 and the alkali metal azide spot formation substrate 1 and the second substrate 4 (particularly, the bonding that forms the internal space 6 of the cell as an airtight space) is preferably performed under vacuum conditions, such as in a vacuum chamber. Furthermore, because the internal state of the alkali metal atoms changes when the elemental alkali metals in the cell collide with the cell's inner wall, it is preferable to seal a buffer gas inside the cell. The bonding between the partition wall 3 and the alkali metal azide spot formation substrate 1 and the second substrate 4 (particularly, the bonding that forms the internal space 6 of the cell as an airtight space) is preferably performed in a buffer gas atmosphere by introducing the buffer gas under vacuum conditions. Examples of the buffer gas include inert gases such as nitrogen gas, neon gas, argon gas, and a mixture of nitrogen gas and argon gas.

[0050] The order in which the partition wall 3 is bonded to the alkali metal azide spot forming substrate 1 and the second substrate 4 is not particularly limited. For example, the partition wall 3 may be bonded to the second substrate 4 before the alkali metal azide spot forming substrate 1 is bonded, or the partition wall 3 may be bonded to the alkali metal azide spot forming substrate 1 before the second substrate 4 is bonded, or the partition wall 3 may be bonded to the alkali metal azide spot forming substrate 1 and the second substrate 4 simultaneously. However, when bonding the partition wall 3 to the alkali metal azide spot forming substrate 1, the alkali metal azide spots 2 on the alkali metal azide spot forming substrate 1 are aligned with the through holes 31 in the partition wall 3 so that no alkali metal azide is present on the bonding surface. Furthermore, by ensuring that the number of alkali metal azide spots 2 accommodated in the through holes 31 in the partition wall 3 is the same among the multiple through holes 31, unit cells 7 with a uniform amount of alkali metal filled can be manufactured.

[0051] ((Alkali metal azide vaporization process)) The cell assembly 5 is irradiated with energy rays such as ultraviolet light, which decomposes (reduces) the alkali metal azide and vaporizes it, generating alkali metal gas in the internal space 6 of the cell partitioned by the alkali metal azide spot forming substrate 1, the partition wall 3, and the second substrate 4. The decomposition also produces nitrogen gas, which is an inert gas and can be used as a buffer gas. Thus, if the alkali metal source is an alkali metal azide, no impurities other than the alkali metal gas and nitrogen gas that serves as the buffer gas are generated, reducing the possibility of changes in the properties of the alkali metal in the cell.

[0052] ((Unit cell 7 cutting process)) The cell assembly 5 can be separated along the dashed line X shown in FIG. 4 by blade dicing, laser dicing, water dicing, or the like to cut out the unit cells 7.

[0053] The unit cell 7 obtained in this manner can be used in atomic devices such as atomic clocks and atomic magnetic sensors.

[0054] This application claims the benefit of priority to Japanese Patent Application No. 2021-039388, filed on March 11, 2021. The entire contents of the specification of Japanese Patent Application No. 2021-039388, filed on March 11, 2021, are incorporated herein by reference. [Explanation of symbols]

[0055] 1. Substrate (alkali metal azide spot formation substrate) 11 Substantially flat surface 12 depression 13 Substrate material 2. Spot of alkali metal azide 3 Bulkhead 31 Through hole 4 Second board 5. Cell Assembly 6 Cell interior space 7 Unit Cell a Thickness of the partition wall

Claims

1. A substrate having a plurality of spots of alkali metal azide formed on a substantially flat surface, wherein the substantially flat surface does not have any partition walls and may include depressions of 20% or less of the substrate thickness.

2. 2. The substrate according to claim 1, wherein the substantially flat surface has a plurality of spot-shaped depressions, and the alkali metal azide spots are formed in the depressions.

3. 3. The method for manufacturing a substrate according to claim 1, wherein the coating film formed from the solution containing the alkali metal azide is formed in spots on the substrate member.

4. 4. The method for manufacturing a substrate according to claim 3, wherein a mask surface having spot-shaped holes is formed on a substrate member, the alkali metal azide-containing liquid is applied to the mask surface to form a coating film, and the mask is then removed.

5. 4. The method for manufacturing a substrate according to claim 3, wherein the alkali metal azide-containing liquid is applied to a substrate member to form a coating film, and then the coating film is partially removed to leave the alkali metal azide in spots on a substantially flat surface.

6. 3. The method for manufacturing a substrate according to claim 2, wherein the alkali metal azide-containing liquid is applied to the substrate member so that it remains only in the recessed portions, and a coating film formed from the alkali metal azide-containing liquid is formed in the recessed portions in the form of spots.

7. a cell assembly assembly step of stacking a partition wall separating the alkali metal azide spots on the substrate according to claim 1 or 2 and a second substrate facing the substrate via the partition wall; a step of irradiating the cell assembly with ultraviolet light to decompose the alkali metal azide and thereby vaporize the alkali metal; and then cutting out a unit cell from the cell assembly.

8. The method for manufacturing a unit cell according to claim 7 , wherein the step of assembling the cell assembly is carried out under vacuum conditions in which a buffer gas may be introduced.

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