DE102021212479A1 - Vapor cell, sensor with vapor cell and method of manufacturing a vapor cell - Google Patents

Abstract

The invention relates to a vapor cell having a substrate with a substrate plane, a substrate base and a substrate wall extending from the substrate base and forming a vapor cell cavity being formed in the substrate, the substrate wall having at least two openings for light to shine through, and a glass cover for enclosing the vapor cell cavity. The invention further relates to a method for producing such a vapor cell and a sensor with such a vapor cell, a light source arrangement for radiating light into one of the at least two openings in the substrate wall and a photodetector arrangement for receiving light from another of the at least two openings in the substrate wall.

Description

The present invention relates to a vapor cell, a sensor with such a vapor cell and a method for producing such a vapor cell.

Background of the Invention

Quantum sensors can be used for atomic clocks, magnetometers, gyroscopes, quantum memories, light sources, precision measuring devices and imaging, among other things. These quantum sensors are based on the precise control of a prepared atomic gas in a closed sample volume. This sample volume can be realized by steam cells. In these, alkali atoms such as potassium (K), cesium (Cs) or rubidium (Rb) can be present in gaseous form and under a defined pressure.

CN 108 844 532 A discloses a micro-miniature NMR gyroscope. It features a 2-window nuclear gas chamber manufactured using MEMS technology. The two glass windows are arranged in such a way that a window plane is arranged in the two longer directions of extension. A normal vector of the two window planes extends in the shortest extension direction. A wafer plane is located between the two glass window planes, which forms an etched central area which is bounded by chamber walls in the direction of the wafer plane. If light is to pass through the central area of the wafer plane, this is only possible in the direction of the normal vector from one glass window plane to the other glass window plane. As a result, an extension of a light beam in the center area between the chamber walls is very short. The distance that a light beam is exposed to a volume of gas is correspondingly short.

US 2005/0 046 851 A1 discloses a vapor cell that allows prolonged passage of a light beam. However, this vapor cell is not a MEMS vapor cell and is accordingly complicated and expensive to manufacture.

The DE 10 2019 219 061 A1 discloses a way of measuring three directions of rotation using an NMR gyroscope.

Disclosure of Invention

According to the invention, a steam cell, a sensor with such a steam cell and a method for producing such a steam cell with the features of the independent patent claims are proposed. Advantageous configurations are the subject of the dependent claims and the following description.

In detail, the vapor cell according to the invention has a substrate, in particular a silicon substrate, with a substrate plane, with a substrate base and a substrate wall extending from the substrate base and forming a vapor cell cavity being formed in the substrate, the substrate wall having at least two openings for light to pass through . In addition, the vapor cell includes a glass cover for enclosing the vapor cell cavity, which is preferably formed by a glass reflow process, i.e., thermally softening and "flowing" the glass. Borosilicate glass, phosphorus silicate glass or borophosphorus silicate glass is preferably suitable as the glass.

As a result, the advantageous and tried-and-tested production options for wafer or semiconductor structures can be combined with the optical advantages of a glass layer for light transmission.

Due to the reflow process, the glass cover surrounds (or encloses) the substrate wall and connects to the substrate base. A gas-tight volume is thus formed. In particular, inclined glass walls (and not just parallel ones) can also be produced in relation to the substrate plane, so that radiation through the vapor cell is possible parallel to the substrate plane. For this purpose, the substrate wall has the at least two openings, which, however, also lie within the volume enclosed by the glass cover. In particular, the glass cover can enclose an angle of less than 90° and/or greater than 45° with the substrate plane. Sloping glass walls also prevent excitation light, usually laser light, from reflecting back into the light source and resulting damage to the light source.

In conventional vapor cells with glass bottoms and glass lids, only radiation perpendicular to the substrate plane is possible, so that the interaction length is very small. In the case of the invention, the interaction length is limited only by the “horizontal” expansion of the vapor cell, which can be chosen more or less as large as desired. In order to prevent the softened glass from penetrating into the vapor cell during the reflow process, particularly in the case of large expansions, supporting structures such as columns, horizontal bars or the like can be formed in the vapor cell.

Preferably the glass cover is bonded (prior to heating) to the substrate wall. An even better seal can thus be achieved.

In order to achieve the greatest possible interaction length, the substrate wall preferably has have two pair of openings for light transmission, which are placed in the substrate wall so that they are as far away from each other as possible. If the substrate wall is cylindrical, the two openings of a pair are located opposite one another at a diameter, ie the straight line connecting the pair is a diameter. It goes without saying that the substrate wall can also run polygonally, for example rectangularly, or elliptically or in any other shape.

In order to make it possible to measure in several directions, the substrate wall preferably has two such pairs of openings for the passage of light. In a preferred embodiment, the straight lines connecting the two pairs are then expediently perpendicular to one another.

The vapor cell preferably contains an inert gas and alkali metal to form a sensor. In particular, the noble gas can be xenon, helium, krypton or neon or a special isotope mixture of the gases, for example Xe-129 and Xe-131. A noble gas mixture with a specially adjusted isotope mixture of, for example, xenon with at least one other gas such as helium, neon or krypton is also conceivable. Filling with other gases is also conceivable. Nitrogen in particular is advantageous as a further filling gas for NMR gyroscope vapor cells. This serves as a buffer gas and ensures that the alkali metal atoms and the noble gas atoms do not lose their spin polarization due to wall collisions. The alkali metal is preferably rubidium. This is particularly advantageous as it is gaseous at around 110 to 120°C and rubidium electron spins couple well with xenon nuclear spins.

A sensor according to the invention has a vapor cell according to the invention, a light source arrangement for radiating light, in particular pump or excitation light and/or sample or evaluation light, into one of the at least two openings in the substrate wall, and a photodetector arrangement for receiving light from another of the at least two openings in the substrate wall. A compact and robust sensor that is particularly easy to produce is thus presented. Such a sensor can in particular be an NMR gyroscope or a time sensor.

The light source arrangement and the photodetector arrangement are preferably arranged on a common sensor substrate and can thus form an electronic part of the sensor. All other necessary electrical components for contacting (in particular also through the sensor substrate by means of electrical feedthroughs), power supply, etc. can also be arranged on the common sensor substrate. Optical components, e.g. for beam shaping or beam deflection, such as polarization filters, mirrors, prisms, lenses, screens, etc. can also be easily placed there. On the one hand, a large number of vapor cells and, on the other hand, a large number of electronic parts can be manufactured separately and then simply assembled to form a sensor.

A polarization-separating element such as a Wollaston prism with two detectors is preferably located in the detection path. Intensities for mutually orthogonal polarization directions can be determined in this way.

The electronics part is preferably enclosed in an encapsulation, which is preferably gas-tight, so that in particular a desired atmosphere, e.g. protective gas atmosphere (with inert gas and/or nitrogen, etc.), can prevail there. The encapsulation can be at least partially formed by substrate walls and/or the glass cover and/or other sealing elements such as plastic or synthetic resin.

Further advantages and refinements of the invention result from the description and the attached drawing.

The invention is shown schematically in the drawings using an exemplary embodiment and is described below with reference to the drawings.

character list

• 1a shows a preferred embodiment of a vapor cell according to the invention in a schematic sectional view,
• 1b in a top view.
• 2a shows an electronic part of a preferred embodiment of a sensor according to the invention in a schematic sectional view,
• 2 B in a top view.
• 3 shows a preferred embodiment of a sensor according to the invention with a vapor cell according to 1 and electronics according to 2 .
• 4 shows a further preferred embodiment of a sensor according to the invention with a vapor cell according to FIG 1 and electronics according to 2 .
• 5 shows the preferred embodiment of the sensor according to the invention 3 in a top view.
• 6 shows a further preferred embodiment of a sensor according to the invention in a plan view.
• 7a shows steps of a preferred embodiment of a method according to the invention for producing a vapor cell in a schematic sectional view,
• 7b in a top view.
• 8a shows steps of an alternative preferred embodiment of a method according to the invention for producing a vapor cell in a schematic sectional view,
• 8b in a top view.

Embodiments of the invention

1 shows in views a and b a preferred embodiment of a vapor cell 110 according to the invention in a schematic sectional view ( 1a ) and a plan view ( 1b ).

The vapor cell 110 has a substrate 11 with a substrate plane or main extension plane 10 running horizontally in the figure. A substrate base 11a is formed in the substrate 11 and extends along the substrate plane 10 in the present case. A substrate wall 11b, which, as shown in the top view in FIG 1b becomes clear, is circular or cylindrical and forms or surrounds a vapor cell cavity 9 . In the vapor cell cavity 9 there is an inert gas, in particular xenon, with alkali atoms, in particular rubidium.

In the side wall 11b, two openings 13 are formed opposite one another on a diameter, which are presently in the form of slots or gaps in the side wall 11b.

A glass cover 12 for enclosing the vapor cell cavity 9 is arranged above the substrate 11 and is formed by a glass reflow process such that a region 12a of the cover 12 outside the vapor cell cavity is connected to the substrate bottom 11a, a region 12b of the cover 12 den Vapor cell cavity 9 terminates at the top and a region 12c of the cover 12 forms sloping walls which enclose an angle of approximately 75-80° here with the substrate base 11a and the substrate plane 10. As later in 3 to see, this avoids a vertical incidence of light and the resulting potentially disruptive reflections into the light source.

2 shows in views a and b an electronics part 200 of a preferred embodiment of a sensor according to the invention (see 3 ) in a schematic sectional view ( 2a ) and a plan view ( 2 B ).

The electronics part 200 has a light source arrangement 201 for generating a polarized pump laser beam and/or polarized evaluation laser beam 8b. The light source arrangement 201 can thus have one or two laser light sources. For example, a pump laser should emit circularly polarized light at a frequency that is suitable for polarizing the electron spins of the rubidium atoms. An evaluation laser beam should interact with the electron spins of the rubidium due to the Faraday effect.

Furthermore, the electronics part 200 has a photodetector arrangement 205, which in the present case, in addition to one or two photodetectors, e.g. in the form of photodiodes, has a beam deflector 203, here in the form of a beam splitter prism, e.g. in the form of a Wollaston prism, as a result a sensor plane is not vertical to the direction of the incident light, but is substantially parallel thereto and parallel to the sensor substrate in the figure. This allows the sensor plane to be enlarged. The beam splitter prism also acts here as a polarizing beam splitter, so that a differential signal can be formed between the two directions of polarization in order to increase the signal-to-noise ratio.

The light source arrangement 201 and the photodetector arrangement 205 are arranged on a common sensor substrate 202 . Both the light source arrangement 201 and the photodetector arrangement 205 can be contacted by means of feedthroughs 204 (vias) in the sensor substrate 202, so that electrical contact can be made from the top in 2a or from the side of sensor substrate 202 facing away from the arrangements.

In 3 1 shows a preferred embodiment of a sensor according to the invention, comprising a vapor cell 110 according to FIG 1 and an electronic part 200 according to FIG 2 having. The electronics part 200 is arranged above the vapor cell cavity 9 of the vapor cell 110 or, in a preferred embodiment, on the glass cover 12 . Vapor cell 110 and electronics part 200 are oriented to one another in such a way that the light or laser beam 8b runs through the areas 12c of the glass cover 12 and the openings 13 in the substrate wall 11b.

4 shows a further preferred embodiment of a sensor according to the invention with a vapor cell 110 according to FIG 1 and an electronic part 200 according to FIG 2 , Which is essentially according to the embodiment 3 corresponds, in which, however, the electronics part also through the Glasab cover 12 from the environment (hermetically or gas-tight) is completed. For this purpose, for example, further side walls 11c protruding from the substrate base 11a are structured in the substrate 11 and support the glass cover 12 at their upper end in the figure. In particular, they can also be connected to the glass cover 12 there. In order to form an encapsulation for the electronics, the glass cover is finally firmly connected at its top to the sensor substrate 202, eg glued.

The side walls 11c can, for example, be cylindrical, polygonal (in particular rectangular), etc. around the in 3 shown arrangement completely or partially run around. The further cavity formed in this way, surrounding the vapor cell cavity 9, serves to accommodate the assemblies of the electronic part 200, which is arranged upside down above the vapor cell 110 or placed on it. As an alternative to the side walls 11c or in addition (for example on sides without walls 11c), another seal can also be provided between the substrate 12 and the sensor substrate 202, for example using plastic or synthetic resin. A desired atmosphere can prevail within the encapsulation, for example a protective gas atmosphere.

In 5 is the preferred embodiment of the sensor according to the invention 3 shown in a plan view. 6 shows an alternative embodiment of a sensor according to the invention in a plan view, in which two laser beams 8a, 8b, which are perpendicular to one another in the example shown, each pass through two associated openings 13 in the substrate wall 11b. A light source arrangement 201a, 201b and a photodetector 202a, 202b are provided for each of the laser beams 8a, 8b.

On the in the 5 and 6 The rectangular borders shown can have full or partial side walls 11c, as in 4 as shown, or other seals may be provided to form encapsulated or hermetically sealed sensors.

From the 3 until 6 it becomes clear that the interaction length of light and gas in the invention is advantageously determined by the horizontal extent of the vapor cell in the figures, which is in particular significantly longer than a vertical extent (determined by wafer thicknesses). This significantly improves the sensitivity and the signal-to-noise ratio.

In 7 is in views a and b schematically a first preferred embodiment of a method according to the invention for producing a vapor cell according to the invention in a schematic sectional view ( 7a ) and a plan view ( 7b ) shown. The steps run from top to bottom in the figures.

In a first step, a substrate 11 is provided and substrate material is removed in such a way that a substrate bottom 11a and a substrate wall 11b extending from the substrate bottom, here essentially vertically, forming a vapor cell cavity 9, have two openings 13, and in the case of the embodiment according to 4 additional side walls 11c) are formed. In particular, a silicon substrate is provided for this purpose and processed by subsequent material removal steps in such a way that the shape shown and described is obtained. In particular, known etching methods, in particular wet etching methods, can be used for this purpose.

In a later step, to provide a desired atmosphere containing the gas mixture to be provided in the vapor cell cavity 9, a layer of glass 12, such as borosilicate glass, is applied in the form of a disc to the substrate wall 11b. In particular, the glass layer 12 can then be bonded to the substrate wall 11b and optionally to the side walls 11c, in order to create a permanent connection at this point.

Finally, the glass layer 12 is heated in a glass reflow process in such a way that it softens and flows down at unsupported points, ie towards the bottom of the substrate, thereby forming the glass cover 12 for enclosing the vapor cell cavity 9 . Supports can be brought about in particular by substrate columns or substrate beams, which are left standing within the vapor cell cavity during manufacture.

The glass cover 12 is connected in a gas-tight manner to the substrate base 11a in regions 12a, so that the vapor cell cavity 9 is enclosed in a gas-tight manner.

In 8th is in views a and b another preferred embodiment of a method according to the invention for producing a vapor cell 110 in a schematic sectional view ( 8a ) and a plan view ( 8b ) shown. The embodiment according to 8th differs from the embodiment according to 7 essentially in that the contents of the vapor cell are subsequently introduced after the cover has been formed. In this case, as related to 7 described, obtained a steam cell, but in which the steam cell cavity 9 is not yet filled.

In a later step, an opening 14 is made in the lid area 12b of the glass cover 12, through which the desired gas mixture is introduced into the vapor cell cavity 9. For example, the opening may be drilled or formed by a laser configured to create an opening by melting the glass.

The opening 14 is then closed again, for example by fusing. For example, a glass ball can be placed on the opening 14 and the opening can be closed by melting it using a laser.

In order to form a sensor, the electronics part 200 (not shown in the figures) is then applied to the vapor cell and expediently firmly connected to the vapor cell or its glass cover, for example glued. This is expediently done in a desired gas atmosphere, which is thus preserved for the electronic part in its encapsulation.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• CN108844532A [0003]
• US20050046851A1 [0004]
• DE 102019219061 A1 [0005]

Claims (18)

Having a vapor cell (110). a substrate (11) with a substrate plane (10), a substrate base (11a) and a substrate wall (11b) extending from the substrate base and forming a vapor cell cavity (9) being formed in the substrate (11), the substrate wall (11b ) has at least two openings (13) for light (8, 8a, 8b) to pass through, and a glass cover (12) for enclosing the vapor cell cavity (9). Vapor cell (110) after claim 1 , wherein the glass cover (12) is formed by a glass reflow process. Vapor cell (110) after claim 1 or 2 , wherein the glass cover (12) surrounds the substrate wall (11b) and is connected to the substrate bottom (11a) outside of the vapor cell cavity (9). Vapor cell (110) after claim 3 , wherein the glass cover (12) encloses an angle of less than 90° and/or greater than 45° with the plane of the substrate. A vapor cell (110) as claimed in any preceding claim, wherein the glass cover (12) is bonded to the substrate wall (11b). Vapor cell (110) according to any one of the preceding claims, wherein the substrate wall (11b) has two pair of openings (13) for transmission of light (8, 8a, 8b) which are placed in the substrate wall (11b) so that they have the greatest possible distance from each other. Vapor cell (110) after claim 6 , wherein the substrate wall (11b) has two such pairs of openings (13) for the passage of light (8, 8a, 8b). Vapor cell (110) according to one of the preceding claims, wherein the substrate wall (11b) forms a cylindrical, rectangular or elliptical vapor cell cavity (9) and/or wherein support structures for supporting the glass cover (12) are formed in the vapor cell cavity (9). A vapor cell (110) according to any one of the preceding claims, wherein the substrate (11) is a silicon substrate and/or wherein the glass cover (12) contains borosilicate glass, phosphosilicate glass or borophosphosilicate glass, and/or wherein the vapor cell cavity (9) contains an inert gas and alkali metal contains. sensor with a vapor cell (110) according to any one of the preceding claims, a light source arrangement (201) for radiating light (8) into one of the at least two openings (13) in the substrate wall (11b), a photodetector arrangement (203) for receiving light (8) from another of the at least two openings (13) in the substrate wall (11b). sensor after claim 10 , wherein the light source arrangement (201) and the photodetector arrangement (203) are arranged on a common sensor substrate (202). sensor after claim 11 wherein an encapsulation for the light source assembly (201) and/or the photodetector assembly (203) is formed between the sensor substrate (202) and the glass cover (12). sensor after claim 12 , wherein the encapsulation is formed at least partially by substrate walls (11c) and/or the glass cover (12) and/or other sealing elements. Sensor after one of Claims 11 until 13 , wherein the light source arrangement (201) and the photodetector arrangement (203) are contacted by means of electrical feedthroughs through the common sensor substrate (202). Sensor after one of Claims 10 until 14 , wherein the photodetector arrangement (203) has a beam deflector (204) and a sensor plane (205) which is not perpendicular to the direction of the light emerging from the other of the at least two openings (13) in the substrate wall (11b). A method of manufacturing a vapor cell (110) according to any one of Claims 1 until 9 , comprising the steps: - providing a substrate (11, 11a, 11b), - removing substrate material such that the substrate bottom (11a) and the substrate wall (11b) extending from the substrate bottom and forming a vapor cell cavity (9) have at least two openings (13) for transmission of light (8, 8a, 8b), - applying a glass layer (12) to the substrate wall (11b), - heating the glass layer so that it softens and the glass cover (12) to enclose the vapor cell cavity (9) forms. procedure after Claim 16 , with the additional step: - bonding the glass layer to the substrate wall (11b) before heating and/or - providing a gaseous atmosphere in the vapor cell cavity (9) prior to heating or introducing a gaseous atmosphere into the vapor cell cavity (9) after heating. procedure after Claim 16 or 17 , with the additional step: - applying an electronic part (200) to the vapor cell (110) to form a sensor.

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