US 11,879,952 B2

9

cell 200. Forming atomic vapor cell 200 in these manners
provides for fabrication of a single vapor cell or an array of
vapor cells as shown in FIG. 4. Here, first optical window
201 and second optical window 202 are anodically bonded.
to this drilled glass plate as intermediate frame 203. For
bonding, second anodic bonding material 213.2, e.g., sili-
con, is formed (e.g., by deposition) on frame bonding
surface 205 or on window bonding surface 204, while
bonding material 213 is formed on the surfaces opposing
those covered by the second bonding material 213.2.

During anodic bonding workpieces (e.g., first optical
window 201, intermediate frame 203, second optical win-
dow 202) are bonded using a combination of elevated
temperature and an applied electric field. The bond is carried
out in a controlled gaseous environment that enables inclu-
sion of alkali atom vapor source 216 to be enclosed inside
cell aperture 206. Anodic bonding can be performed as
described in the Example below or other methods known in
the art, e.g., as described in G. Wallis, Field Assisted Glass
Sealing, Electrocomponent Science and Technology, 1975, 2
(1), 45-53; and K. M. Knowles et al., Anodic Bonding,
International Materials Rev., 2006, 51(5), 273-311, the
disclosures of which are incorporated by reference in their
entirety.

Atomic vapor cell 200 and processes disclosed herein
have numerous beneficial uses including measuring the
electric field of electromagnetic radiation using the spectro-
scopic responses of Rydberg atoms to electromagnetic radia-
tion field, wherein the Rydberg atoms are produced from the
vapor of alkali atom source 216 that is produced when alkali
atom source 216 is heated. An exemplary process is
described in U.S. patent application Ser. No. 15/183,010,
which is incorporated by reference in its entirety.

Advantageously, atomic vapor cell 200 overcomes limi-
tations and technical deficiencies of conventional devices
and conventional processes such as gas cells that include
semiconductor, electrically conductive material, or other
material that perturb RF fields. It should be appreciated that
while conventional gas cells that include silicon for the cell
body are known in the art, e.g., as described in U.S. Pat. No.
10,605,840, the present invention excludes such bulk mate-
rial, and during making atomic vapor cell 200 the second
anodic bonding material 213.2 is converted to an oxide
composition that does not substantially perturb the RF field.
Accordingly, atomic vapor cell 200 can provide higher
precision and accuracy for sensing RF fields than conven-
tional devices.

The articles and processes herein are illustrated further by
the following Example, which is non-limiting.

EXAMPLE

With reference to FIG. 6, a process for making atomic
vapor cell 200 by anodic bonding of non-borosilicate glass

substrates includes providing fused silica or other non- 5

borosilicate glass to be used as glass substrates for first
optical window 201, second optical window 202, and int
mediate frame 203. The glass substrate can have a surface
roughness of 20 Angstroms or less. The glass substrates are
cleaned of particulate matter. First optical window 201,
intermediate frame 203, and second optical window 202 can
be masked such that only surfaces (¢.g., window bonding
surface 204 or frame bonding surface 205) where first
optical window 201 and second optical window 202 contact
intermediate frame 203 are exposed. It should be noted that
intermediate frame 203 can include interframe structure 219
that provide for cell frame wall 208 to cell aperture 206.

10

Masking can be done with a lift-off photoresist or other
sacrificial layer. Thereafter, the process proceeds by coating
first optical window 201 and the second optical window 202
with first thin film 214 and intermediate frame 203 with
second thin film 215; or alternatively coating intermediate
frame 203 with first thin film 214 and second thin film 215
and coating first optical window 201 and second optical
window 202 with thin films 214 and 215 such that opposing
surfaces of the intermediate frame 203 and first and second
optical windows 201, 202 are coated with different thin film.
materials (213.1, 213.2). First thin film 214 can be made
from the anodic bonding material 213, and second thin film
215 can be made from second anodic bonding material 213.2
that can be a material that provides for anodic bonding of
first optical window 201 and second optical window 202 to
intermediate frame 203. The anodic bonding material can be
amorphous silicon or polycrystalline silicon that is formed
only where the glass substrate is exposed to deposition of
first thin film 214 and second thin film 215 such as window
bonding surface 204 or frame bonding surface 205. The
deposition of first thin film 214 made of the anodic bonding
material 213, such as borosilicate glass containing a high
concentration of alkali ions, and second thin film 215 made
of the second anodic bonding material 213.2 such as silicon

5 can be formed ina variety of ways including radio frequency

sputtering, low temperature sputtering, evaporation and
plasma enhanced chemical vapor deposition. First thin film
214 and second thin film 215 can be doped. A film thickness
of first thin film 214 and second thin film 215 independently
can be from 10 nm to 450 nm. If coating intermediate frame
203 with the thin film, frame bonding surface 205.1 and
frame bonding surface 205.2 are coated. Optionally, the
outside, external walls intermediate frame 203 can be coated
too. If coating first optical window 201 or second optical
window 202, coating can occur around the external edges
thereof for easier electrical access to the internal film layer
on window bonding surface 204.

‘Additionally, the process for making atomic vapor cell
200 can include coating intermediate frame 203 or windows
(201, 202) with borosilicate glass thin film containing a high
concentration of alkali ions to form anodic bonding material
213, wherein coating occurs only where the glass substrate
is exposed. The deposition of this borosilicate layer can be
done by a variety of methods including low temperature
sputtering or evaporation. The film thickness can be from 10
nm to 450 nm. If coating intermediate frame 203 in this step,
the faces 205 of intermediate frame 203 can be coated and
optionally the outer walls of intermediate frame 203. If
coating windows (201, 202) in this step, all surfaces of
windows (201, 202) can be coated.

Thereafter, the process includes removing the sacrificial
layer to expose the underlying glass substrate of now-coated
first optical window 201, second optical window 202, or
intermediate frame 203 followed by cleaning all surfaces to
obtain particle-free surfaces. The coated intermediate frame
203 and coated first optical window 201 with deposited thin
films are brought together touching and heated from 300° C
to 450° C. with soaking at the elevated temperature from 30
minutes to 2 hours for uniform temperature distribution.

‘A voltage potential from 800 V to 1100 V is applied from
power source 218 between the silicon thin film and boro-
silicate thin film such that an electric field is generated
between the two layers. The applied electric field are ori-
ented such that its direction points from the silicon thin film
to the borosilicate thin film. Stepping up the voltage from
700 V to maximum voltage avoids electrical arcing. This
step can be completed while applying mechanical pressure



U.S. Patent Jan. 23, 2024 Sheet 3 of 7 US 11,879,952 B2

FIG. 3


US 11,879,952 B2

1
ATOMIC VAPOR CELL AND MAKING AN
ATOMIC VAPOR CELL

CROSS REFERENCE TO RELATED,
APPLICATIONS

‘The application claims priority to U.S. Provisional Patent
Application Ser. No. 63/051,580 filed Jul. 14, 2020, the
disclosure of which is incorporated herein by reference in its
entirety.

ATOMIC VAPOR CELL AND MAKING AN
ATOMIC VAPOR CELL STATEMENT.
REGARDING FEDERALLY SPONSORED
RESEARCH

This invention was made with United States Government
support from the National Institute of Standards and Tech-
nology (NIST), an agency of the United States Department
of Commerce. The Government has certain rights in the
invention. Licensing inquiries may be directed to the Tech-
nology Partnerships Office, NIST, Gaithersburg, MD,
20899; voice 301-975-2573; email tpo@nist.gov; reference
NIST Docket Number 20-057US1.

BRIEF DESCRIPTION,

Disclosed is an atomic vapor cell for performing RF
measurements, the atomic vapor cell comprising: a first
optical window consisting essentially of transparent non-
conducting material and comprising a first window bonding
surface and a first cell window wall, the transparent non-
conducting material of the first optical window being essen-
tially free of electrically conductive materials including
silicon to minimize distortion of radiofrequency fields by the
first optical window; an intermediate frame, disposed on the
first optical window, consisting essentially of transparent
nonconducting material, and comprising: a first frame bond-
ing surface opposing and bonded to the first window bond-
ing surface, a second frame bonding surface, and a cell
frame wall, the transparent nonconducting material of the
intermediate frame being essentially free of electrically
conductive materials including silicon to minimize distor-
tion of radiofrequency fields by the intermediate frame; a
second optical window disposed on the intermediate frame
such that the intermediate frame is interposed between the
first optical window and the second optical window, con-
sisting essentially of transparent nonconducting material,
and comprising: a second window bonding surface opposing

and bonded to the second frame bonding surface, and a 5

second cell window wall, the transparent nonconducting
material of the second optical window being essentially free
of electrically conductive materials including silicon to
minimize distortion of radiofrequency fields by the second

optical window; and a cell aperture bounded by the first cells

window wall of the first optical window, the cell frame wall
of the intermediate frame, and the second cell window wall
of the second optical window, wherein the atomic vapor cell
is hermetically sealed by bonding between the first optical
window and the second optical window to the intermediate
frame.

Disclosed is a process for making an atomic vapor cell
using anodic bonding, the process comprising: providing a
first optical window consisting essentially of transparent
nonconducting material and comprising a first window
bonding surface and a first cell window wall, the transparent
nonconducting material of the first optical window being

20

&

&

2

essentially free of electrically conductive materials includ-
ing silicon to minimize distortion of radiofrequency fields by
the first optical window; forming a first thin film comprising
anodic bonding material on the first window bonding sur-
face; disposing an intermediate frame on the first optical
window, the intermediate frame consisting essentially of
transparent nonconducting material, and comprising: a first
frame bonding surface opposing the first window bonding
surface, a second frame bonding surface, and a cell frame
wall, the transparent nonconducting material of the inter-
mediate frame being essentially free of electrically conduc-
tive materials including silicon to minimize distortion of
radiofrequency fields by the intermediate frame; forming a
second thin film comprising anodic bonding material on the
second window bonding surface; anodically bonding the
first frame bonding surface of the intermediate frame to the
first window bonding surface of the first optical window;
disposing a second optical window on the intermediate
frame such that the intermediate frame is interposed between,
the first optical window and the second optical window, and.
the second optical window consisting essentially of trans-
parent nonconducting material and comprising: a second
window bonding surface opposing the second frame bond-
ing surface, and a second cell window wall, the transparent

| nonconducting material of the second optical window being

essentially free of electrically conductive materials includ-
ing silicon to minimize distortion of radiofrequency fields by
the second optical window; anodically bonding the second
window bonding surface of the second optical window to the
second frame bonding surface of the intermediate frame;
forming, in response to the anodically bonding, a cell
aperture bounded by the first cell window wall of the first
optical window, the cell frame wall of the intermediate
frame, and the second cell window wall of the second optical
window; and hermetically sealing the atomic vapor cell in
response to anodically bonding the first optical window and
the second optical window to the intermediate frame to
make the atomic vapor cell.

Disclosed is a process for making an atomic vapor cell
using anodic bonding, the process comprising: providing a
first optical window consisting ntially of transparent
nonconducting material and comprising a first window
bonding surface and a first cell window wall, the transparent
nonconducting material of the first optical window being
essentially free of electrically conductive materials includ-
ing silicon to minimize distortion of radiofrequency fields by
the first optical window; forming a first thin film comprising
anodic bonding material on the first frame bonding surface;
disposing an intermediate frame on the first optical window,
the intermediate frame consisting essentially of transparent
nonconducting material, and comprising: a first frame bond-
ing surface opposing the first window bonding surface, a
second frame bonding surface, and a cell frame wall, the
‘transparent nonconducting material of the intermediate
frame being essentially free of electrically conductive mate-
rials including silicon to minimize distortion of radiofre-
quency fields by the intermediate frame; forming a second
thin film comprising anodic bonding material on the second
frame bonding surface; anodically bonding the first frame
bonding surface of the intermediate frame to the first win-
dow bonding surface of the first optical window; disposing
a second optical window on the intermediate frame such that
the intermediate frame is interposed between the first optical
window and the second optical window, and the second
optical window consisting essentially of transparent non-
conducting material and comprising: a second window
bonding surface opposing the second frame bonding surface,



U.S. Patent Jan. 23, 2024 Sheet 5 of 7 US 11,879,952 B2

203





U.S. Patent

21

218

Jan. 23, 2024 Sheet 7 of 7 US 11,879,952 B2
216 2i7
7

\ \ 7 Lt

TM_
\ 214
203
208 |
214
202

FIG. 7


a2) United States Patent
Holloway et al.

US011879'

US 11,879,952 B2
Jan. 23, 2024

(10) Patent No.:
(45) Date of Patent:

(54) ATOMIC VAPOR CELL AND MAKING AN
ATOMIC VAPOR CELL

(71) Applicant: Government of the United States of
America, as represented by the
Secretary of Commerce, Gaithersburg,
MD (US)

(72) Inventors: Christopher Lee Holloway, Boulder,
CO (US); John Edward Kitching,
Boulder, CO (US); Alexandra Brae
Artusio-Glimpse, Boulder, CO (US);
Vladimir Anatolyevich Aksyuk,
Gaithersburg, MD (US); Matthew
Thomas Simons, Lafayette, CO (US):
Omar Daniel Lopez, Gaithersburg, MD
(US)

(73) Assignee: GOVERNMENT OF THE UNITED
STATES OF AMERICA, AS
REPRESENTED BY THE
SECRETARY OF COMMERCE,
Gaithersburg, MD (US)

(*) Notice: Subject to any disclaimer, the term of this

patent is extended or adjusted under 35
USC. 154(b) by 174 days.

(21) Appl. No.: 17/374,537
(22) Filed: Jul. 13, 2021

(65) Prior Publication Data
US 2022/0018914 Al Jan. 20, 2022

Related U.S. Application Data

(60) Provisional application No. 63/051,580, filed on Jul.
14, 2020.

(51) Int. Cl.
GOIR 33/26

200

(2006.01)

(52) US. Cl.
cpc GOIR 33/26 (2013.01)
(58) Field of Classification Search
CPC GOIR 33/26; GOIR 29/0885; GOIR 33/0052;

GOIR 3/00
(Continued)
(56) References Cited
U.S. PATENT DOCUMENTS.
6,806,784 B2 10/2004 Hollberg et al.
10,605,840 B1* 3/2020 Amarloo .. GOIR 29/0885

(Continued)

OTHER PUBLICATIONS,

Liew, L-A., et al., “Microfabricated alkali atom vapor cells”,
Applied Physics Letters, 2004, p. 2694-2696, vol. 84 No. 14.

(Continued)

Primary Examiner — Christopher P McAndrew
(74) Attorney, Agent, or Firm — Office of Chief Counsel

for National Institute of Standards and Technology

(57) ABSTRACT

‘An atomic vapor cell for performing RF measurements
includes: a first optical window of transparent nonconduct-
ing material free of electrically conductive materials; an
intermediate frame of transparent nonconducting material
free of electrically conductive materials; a second optical
window disposed on the intermediate frame and including
transparent nonconducting material free of electrically con-
ductive materials to minimize distortion of radiofrequency
fields by the windows and frame; and a cell aperture,
wherein the atomic vapor cell is hermetically sealed by
bonding between the first optical window and the second
optical window to the intermediate frame.

27 Claims, 7 Drawing Sheets



US 11,879,952 B2

5
bonding surface 204.1, second frame bonding surface 205.2,
and cell frame wall 208, the transparent nonconducting
material of intermediate frame 203 being essentially free of
electrically conductive materials including silicon to mini-
mize distortion of radiofrequency fields by intermediate
frame 203; a second optical window 202 disposed on
intermediate frame 203 such that intermediate frame 203 is
interposed between first optical window 201 and second
optical window 202, consisting essentially of transparent
nonconducting material, and comprising: second window
bonding surface 204.2 opposing and bonded to second frame
bonding surface 205.2, anc cond cell window wall 207.2,
the transparent nonconducting material of second optical
window 202 being essentially free of electrically conductive
materials including silicon to minimize distortion of radiof-
requency fields by second optical window 202; and cell
aperture 206 bounded by first cell window wall 207.1 of first
optical window 201, cell frame wall 208 of intermediate
frame 203, and second cell window wall 207.2 of second

optical window 202, wherein atomic vapor cell 200 is 2

hermetically sealed by bonding between first optical window
201 and second optical window 202 to intermediate frame
203.

In an embodiment, atomic vapor cell 200 includes atomic
vapors of alkali metal atoms disposed in cell aperture 206
According to an embodiment, atomic vapor cell 200
includes a source of atomic vapors of alkali metal atoms
disposed in cell aperture 206. The source can be, e.g., a
pellet of a compound or composition that includes alkali
metal. The source can be subjected heating, irradiation, and
the like to produce the atomic vapor of the alkali metal
atoms. Exemplary alkali metals include cesium and
rubidium.

In an embodiment, such as shown in FIG. 4, atomic vapor
cell 200 includes additional cell apertures 206, wherein each
of the cell apertures 206 is sealed from one another such that
each cell aperture 206 is fluidically isolated from all other
cell apertures 206. In this manner the individual cell aper-
tures 206 can independently include atomic vapors, wherein
the atomic vapor in individual cells is the same or different.
Moreover, an array of cell apertures 206 (e.g.. panel C or
panel D of FIG. 4) in atomic vapor cell 200 can be used as
a sensor array, ¢.g., in an imaging device such as an RF
camera. The number of cell aperture 206 can be any number
selected for a particular application such as providing a high
numerical aperture, high spatial resolution, metamaterial
design, optimizing field of view, making atomic vapor cell
200 compact, and the like. A shape of the cell aperture 206
can be selected for similar reasons. In a plurality of cell

apertures 206, they can have same or different cross-sec- 5

tional shapes such as a circular cross-section along lateral
length 212 of cell aperture 206, an ellipsoidal cross-section
along lateral length 212 of cell aperture 206, or a quadri-
lateral cross-section along lateral length 212 of cell aperture

206. Exemplary shapes of cell aperture 206 include a s

parallelepiped shape and a cylindrical shape.

In an embodiment, in forming atomic vapor cell 200, e.g.,
with reference to FIG, 6, anodic bonding material 213.1 and
second anodic bonding material 213.2 are interposed
between first optical window 201 and intermediate frame
203 to bond intermediate frame 203 to first optical window
201, and anodic bonding material 213 interposed between
second optical window 202 and intermediate frame 203 to
bond intermediate frame 203 to second optical window 202.
Here, anodic bonding material 213 can form siloxane bonds.
In this respect, anodic bonding material 213 can be any
material capable of forming bonds between first optical

&

&

6

window 201 and intermediate frame 203 and forming bonds
between intermediate frame 203 and second optical window
202 that preferentially does not produce a conductive layer
therebetween and that preferentially minimizes interactions
between atomic vapor cell 200 and RF fields that perturb the
RF field. Exemplary anodic bonding material 213 is formed
from silicon, borosilicate, polycrystalline silicon, or amor-
phous silicon and the like. It is contemplated that anodic
bonding is formed between two dissimilar materials,
wherein either both of these materials are disposed on
opposite surfaces, or one of the components (c.g., first
optical window 201 or intermediate frame 203) is made
entirely out of one of these materials, e.g., borosilicate glass,
in which case a thin film of the other material, e.g. silicon,
polysilicon, amorphous silicon, is disposed on the opposing
surface.

In an embodiment, the transparent nonconducting mate-
tial of first optical window 201, second optical window 202,
and intermediate frame 203 independently includes, e.g., a
dielectric glass such as fused silica or fused quartz. Accord-
ingly, the transparent nonconducting material is transparent
to radiation and is electrically nonconducting. The transpar-
ent nonconducting material provides insignificant perturba-
tions of the RF field and is advantageous over constructions

5 that include materials that perturb RF fields such as cells

made with semiconductor materials, e.g., silicon.

The sizes of atomic vapor cell 200 and cell aperture 206
are provided by first window thickness 209, second window
thickness 210, frame thickness 211, or lateral length 212.
Planar RF fields are more compatible atomic vapor cell 200
with large size. Moreover, thinner windows 201, 202 are
better for decreasing perturbations with RF fields provided
such the window thickness has structural integrity. Low
power RF measurement and heating are suitable with
smaller atomic vapor cell 200. In this regard, first optical
window thickness 209, second optical window thickness
210, and intermediate frame thickness 211 independently
can be from 1 mm to 50 mm, specifically 50 mm to 2 mm.
Lateral length 212 can be from 1 mm to 50 mm, specifically
2 mm to 20 mm. The volume of cell aperture 206 can be
from 1000 mm* to 50000 mm’, specifically from 1 mm> to
1000 mm*.

Accordingly, atomic vapor cell 200 is configured to detect
radiofrequency radiation. It is contemplated that the radiof-
requency radiation has a wavelength from 0.1 mm to 105
km.

Atomic vapor cell 200 can be made of various elements
and components that are microfabricated, and elements of
atomic vapor cell 200 can be various sizes. Elements of
atomic vapor cell 200 can be made of a material that is
physically or chemically resilient in an environment in
which atomic vapor cell 200 is disposed, including coatings
applied to external surfaces of atomic vapor cell 200 for
environmental protection. The components of atomic vapor
cell 200 can be made of the same or different material.

Atomic vapor cell 200 can be made in various ways. It
should be appreciated that atomic vapor cell 200 includes a
number of optical or mechanical components, wherein such
components can be interconnected and placed in communi-
cation (e.g., optical communication, mechanical communi-
cation, and the like) by physical, chemical, optical, or
free-space interconnects. The components can be disposed
on mounts that can be disposed on a bulkhead for alignment
or physical compartmentalization. As a result, atomic vapor
cell 200 can be disposed in a terrestrial environment or space
environment. The elements of atomic vapor cell 200 can be
made by additive or subtractive manufacturing. In an



US 11,879,952 B2

3

and a second cell window wall, the transparent nonconduct-
ing material of the second optical window being essentially
free of electrically conductive materials including silicon to
minimize distortion of radiofrequency fields by the second
optical window; anodically bonding the second window
bonding surface of the second optical window to the second
frame bonding surface of the intermediate frame; forming, in
response to the anodically bonding, a cell aperture bounded
by the first cell window wall of the first optical window, the
cell frame wall of the intermediate frame, and the second
cell window wall of the second optical window; and her-
metically sealing the atomic vapor cell in response to
anodically bonding the first optical window and the second
optical window to the intermediate frame to make the atomic
vapor cell.

BRIEF DESCRIPTION OF THE DRAWINGS

‘The following description cannot be considered limiting»,

in any way. With reference to the accompanying drawings,
like elements are numbered alike.

FIG. 1 shows: (panel A) a cross-section of an atomic
vapor cell: and (panel B) an exploded cross-sectional view
of the atomic vapor cell;

FIG. 2 shows: (panel A) a cross-section of steps in making
an atomic vapor cell, wherein anodic bonding material is
formed on a frame bonding surface of an intermediate
frame; and (panel B) a cross-section of steps in making an
atomic vapor cell, wherein anodic bonding material is
formed on a window bonding surfaces of a first optical
window and a second optical window;

FIG. 3 shows a perspective view of an atomic vapor cell
made by anodic bonding;

FIG. 4 shows exploded views several atomic vapor cells
with various cell apertures, wherein panel A shows an
atomic vapor cell with a round cross-sectional cylindrical
cell aperture; panel B shows an atomic vapor cell with a
plurality of round cross-sectional cylindrical cell apertures;
panel C shows an atomic vapor cell with a plurality of round
cross-sectional cylindrical cell apertures; and panel D shows
‘an atomic vapor cell with a plurality of rectangular cross
sectional parallelepiped cell apertures;

FIG. 5 shows: (panel A) an intermediate frame with a
‘one-dimensional array of rectangular cell apertures, (panel
B) an intermediate frame with a one-dimensional array of
rectangular cell apertures that are interconnected by trenches
220; and (panel C) an intermediate frame with a two-
dimensional array of circular cell apertures;

FIG. 6 shows components involved in making an atomic
vapor cell according to the Example, wherein the cross-
section shows that the all-dielectric atomic vapor cell
includes upper window with silicon or borosilicate thin film

coating that has been patteed, intermedia frame with upper

and lower borosilicate or silicon thin film coatings that have
been patterned and optionally including interframe struc-
tures 219, lower window with silicon or borosilicate thin
film coating that has been patterned, an alkali atom source,
and a reactive material as a getter for maintaining purity of
vacuum inside the atomic vapor cell;

FIG. 7 shows components involved in making the atomic
vapor cell according to the Example, wherein the interme-
diate frame and the second optical window are brought into
contact for anodic bonding, such that anodic bond occurs
between the lower window and the intermediate frame with
an appropriate thin film while a voltage potential applied to

&

&

5

4

the thin film of the intermediate frame and the thin film of
the lower window that can be performed in vacuum to
evacuate the cell aperture.

DETAILED DESCRIPTION,

A detailed description of one or more embodiments is
presented herein by way of exemplification and not limita-
tion.

Atomic sensors control room temperature atoms in
devices such as Sl-traceable E-field probes an in other
applications ranging from atom-based receivers to imaging
machines. Applications of this sensor technology involve
Rydberg atom-based detectors, sensors, and receivers. Fur-
ther development of atomic sensors needs economic designs
and fabrication processes. The atomic vapor cell and process
for making it herein described provide cost effective pro-
duction using batch microfabrication. Beneficially, atomic
vapor cell and process for making herein include placing
thin-narrow layer of silicon (Si) onto glass windows such
that they can be anodically bonded to form small glass cells,
drilling holes in plates of glass in order to make single vapor
cells or an array of vapor cells for which windows are
anodically bonded, and filling and anodically bonding win-

5 dows to glass cells.

Microfabricated alkali vapor cells, based on anodic bond-
ing of silicon and glass, can be made from large wafers such
that the cost per cell is significantly lower than conventional
glass cells. However, for certain applications, such as sens-
ing of radiofrequency (RF) fields, electrically conductive
materials such as silicon in the vapor cell should be mini-
mized because such materials may distort or entirely block
the RF field.

It has been discovered a method for making an atomic
vapor cell at the wafer-level that minimizes the amount of
silicon used in the process and in the formed atomic vapor
cell. Instead of making a frame onto which glass is bonded
out of silicon, making an atomic vapor cell includes a glass
wafer in which holes that form cell apertures are etched or
abrasively machined. A thin layer, e.g., of polysilicon is
deposited onto the top and bottom surfaces of the glass in
some embodiments. In a certain aspect, top and bottom glass
windows serve as lids that are bonded onto the polysilicon
layer to seal the alkali atoms in the atomic vapor cell.
Because almost all of the resulting atomic vapor cell is glass,
and not silicon, the atomic vapor cell has a much smaller
effect on the RF field than a conventional cell with silicon
walls.

Atomic vapor cell 200 minimizes perturbations to RF
fields caused by interaction of the material of construction of
atomic vapor cell 200 with the RF field due to making
atomic vapor cell 200 with a small, controlled amount of
semiconductive materials such as silicon so that the bulk of
atomic vapor cell 200 is transparent nonconducting material.
In an embodiment, with reference to FIG. 1, FIG. 2, FIG. 3,
and FIG. 4, atomic vapor cell 200 is configured for per-
forming RF measurements and includes: first optical win-
dow 201 consisting essentially of transparent nonconducting
material and comprising first window bonding surface 204.1
and first cell window wall 207.1, the transparent noncon-
ducting material of first optical window 201 being essen-
tially free of electrically conductive materials including
silicon to minimize distortion of radiofrequency fields by
first optical window 201; intermediate frame 203, disposed
on first optical window 201, consisting essentially of trans-
parent nonconducting material, and comprising: first frame
bonding surface 205.1 opposing and bonded to first window



U.S. Patent

Jan. 23, 2024 Sheet 6 of 7

US 11,879,952 B2

L201
213.1

44

= 213.2

~115

29] | 29) | 28

219

+28

213.2

—~15

4
~ 2131

rio
a

L202



U.S. Patent Jan. 23, 2024 Sheet 2 of 7 US 11,879,952 B2

200



US 11,879,952 B2

11

to the stack to force the window 201 and frame 203 together.
The system is maintained at the elevated temperature with
maximum applied voltage for at least 1 hour, particularly for
4 hours or more. While keeping the voltage applied, the
temperature of the window and frame stack is decreased to
room temperature. When the window and the frame are at
room temperature, the voltage is turned off. At this point,
first optical window 201 is bonded to intermediate frame
203,

After first optical window 201 is bonded to intermediate
frame 203, they are disposed in a vacuum chamber. Alkali
atom source 216 and getter 217 are disposed on second
optical window 202, wherein alkali atom source 216 and
getter 217 are activated by controlled local heating, e.g..
from laser light, in a subsequent step. Thereafter, second
optical window 202 is brought together with second thin
film 215 of intermediate frame 203 such that silicon and
borosilicate thin films are touching while leaving a small gap
therebetween so that gas can be removed the interior of
intermediate frame 203 before cell aperture 206 is formed by
anodically bonding second optical window 202 to interm
diate frame 203. To aid in removing residual gas, the
vacuum chamber is evacuated to a pressure that is less than
10°? Torr, e.g., 10-° Torr. The position of second optical
window 202 relative to intermediate frame 203 is manipu-
lated to close the gap between second optical window 202
and intermediate frame 203 as shown in FIG. 7.

The system is then heated from 300° C, to 450° C. and
soaked at the elevated temperate from 30 minutes to 2 hours
for uniform temperature distribution. A voltage potential is
applied between second optical window 202 and interme-
diate frame 203 of the silicon thin film and borosilicate thin
film of second optical window 202 as shown in FIG. 7. The
voltage is increased from 700 V to a maximum of 800 V to
1100 V. The voltage potential is applied so that its polarity
provides an electric field is directed from the silicon thin film.
to the borosilicate thin film. Mechanical pressure can be
applied to force second optical window 202 into contact
with intermediate frame 203. The components are main-
tained at the elevated temperature with maximum applied
voltage for at least 1 hour, and particularly for 4 hours or
more. While keeping voltage supply 218 on and applying
voltage, the temperature is decreased to room temperature.
When first optical window 201, second optical window 202,
and intermediate frame 203 are equilibrated to room tem-
perature, the voltage is turned off. At this point, the pressure
in the vacuum chamber is increased to ambient pressure, and
the anodically bonded atomic vapor cell 200 can be removed
from the vacuum chamber.

Alkali atom source 216 is activated in cell aperture 206 by 5

local heating. Laser heating can be used to activate alkali
atom source 216. Getter 217 is activated in cell aperture 206
by local heating. Laser heating can be used to activate getter
217. Thus formed, atomic vapor cell 200 is substantially an
all-dielectric vapor cell for room temperature Rydberg atom
applications involving radio frequency electric field mea-
surements.

While one or more embodiments have been shown and
described, modifications and substitutions may be made
thereto without departing from the spirit and scope of the
invention. Accordingly, it is to be understood that the present
invention has been described by way of illustrations and not
limitation. Embodiments herein can be used independently
or can be combined.

All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are independently combinable with each
other. The ranges are continuous and thus contain every

20

&

35

0

5

12

value and subset thereof in the range. Unless otherwise
stated or contextually inapplicable, all percentages, when
expressing a quantity, are weight percentages. The suflix (s)
as used herein is intended to include both the singular and
the plural of the term that it modifies, thereby including at
least one of that term (e.g., the colorant(s) includes at least
one colorants). Option, optional, or optionally means that
the subsequently described event or circumstance can or
cannot occur, and that the description includes instances
where the event occurs and instances where it does not. As
used herein, combination is inclusive of blends, mixtures,
alloys, reaction products, collection of elements, and the
like.

As used herein, a combination thereof refers to a combi-
nation comprising at least one of the named constituents,
components, compounds, or elements, optionally together
with one or more of the same class of constituents, compo-
nents, compounds, or elements.

All references are incorporated herein by reference.

The use of the terms “a,” “an,” and “the” and similar
referents in the context of describing the invention (espe-
cially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by con-
text. It can further be noted that the terms first, second,
primary, secondary, and the like herein do not denote any
order, quantity, or importance, but rather are used to distin-
guish one element from another. It will also be understood.
that, although the terms first, second, etc. are, in some
instances, used herein to describe various elements, these
elements should not be limited by these terms. For example,
a first current could be termed a second current, and,
similarly, a second current could be termed a first current,
without departing from the scope of the various described
embodiments. The first current and the second current are
both currents, but they are not the same condition unless
explicitly stated as such.

‘The modifier about used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by
the context (e.g., it includes the degree of error associated
with measurement of the particular quantity). The conjunc-
tion or is used to link objects of a list or alternatives and is

iisjunctive; rather the elements can be used separately or
can be combined together under appropriate circumstances.

What is claimed is:

1. An atomic vapor cell for performing RF measurements,
the atomic vapor cell comprising:

a first optical window consisting essentially of transparent
nonconducting material and comprising a first window
bonding surface and a first cell window wall, the
transparent nonconducting material of the first optical
window being essentially free of electrically conduc-
tive materials including silicon to minimize distortion
of radiofrequency fields by the first optical window;

an intermediate frame, disposed on the first optical win-
dow, consisting essentially of transparent nonconduct-
ing material, and comprising: a first frame bonding
surface opposing and bonded to the first window bond-
ing surface, a second frame bonding surface, and a cell
frame wall. the transparent nonconducting material of
the intermediate frame being essentially free of elec-
trically conductive materials including silicon to mini-
mize distortion of radiofrequency fields by the inter-
mediate frame;

a second optical window disposed on the intermediate
frame such that the intermediate frame is interposed
between the first optical window and the second optical



US 11,879,952 B2

15

first window bonding surface and a first cell window
wall, the transparent nonconducting material of the first
optical window being essentially free of electrically
conductive materials including silicon to minimize
distortion of radiofrequency fields by the first optical
window;

forming a first thin film comprising anodic bonding
material on the first frame bonding surface;

disposing an intermediate frame on the first optical win-
dow, the intermediate frame consisting essentially of
transparent nonconducting material, and comprising: a
first frame bonding surface opposing the first window
bonding surface, a second frame bonding surface, and
acell frame wall, the transparent nonconducting mate-
rial of the intermediate frame being essentially free of
electrically conductive materials including silicon to
minimize distortion of radiofrequency fields by the
intermediate frame;

forming a second thin film comprising anodic bonding

material on the second frame bonding surface;
anodically bonding the first frame bonding surface of the
intermediate frame to the first window bonding surface
of the first optical window;
disposing a second optical window on the intermediate

frame such that the intermediate frame is interposed ~

between the first optical window and the second optical
window, and the second optical window consisting
essentially of transparent nonconducting material and
comprising: a second window bonding surface oppos-
ing the second frame bonding surface, and a second cell

0

16

window wall, the transparent nonconducting material
of the second optical window being essentially free of
electrically conductive materials including silicon to
minimize distortion of radiofrequency fields by the
second optical window:

anodically bonding the second window bonding surface

of the second optical window to the second frame
bonding surface of the intermediate frame;

forming, in response to the anodically bonding, a cell

aperture bounded by the first cell window wall of the
first optical window, the cell frame wall of the inter-
mediate frame, and the second cell window wall of the
second optical window; and

hermetically sealing the atomic vapor cell in response to

anodically bonding the first optical window and the
second optical window to the intermediate frame to
make the atomic vapor cell.

24. The process of claim 23, further comprising forming
atomic vapors of alkali metal atoms in the cell aperture.

25. The process of claim 23, wherein forming the atomic
vapors of alkali metal atoms in the cell aperture occurs prior
to hermetically sealing the atomic vapor cell.

26. The process of claim 24, wherein forming the atomic
vapors of alkali metal atoms in the cell aperture occurs prior
to hermetically sealing the atomic vapor cell.

27. The process of claim 23, further comprising forming
additional cell apertures, wherein each of the cell apertures
are sealed from one another such that each cell aperture is
fluidically isolated from all other cell apertures.

+e Ree


U.S. Patent Jan. 23, 2024 Sheet 1 of 7 US 11,879,952 B2

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US 11,879,952 B2
Page 2

(58) Field of Classification Search
USPC wesscststsentntntntninee 324/305
See application file for complete search history.

(56) References Cited
U.S. PATENT DOCUMENTS

10,859,981 BL * 12/2020 Ramirez-Serrano
2005/0007118 Al 1/2005 Kitching et al
2016/0363617 Al 12/2016 Anderson et al
2020/0002802 A1* 1/2020 Kitching . B23K 1/20
2021/0114926 Al 4/2021 Ramirez-Serrano et al.
2021/0132549 Al 5/2021 Ramirez-Serrano et al.
2021/0156735 AL* 5/2021 Amarloo .... GOLJ 1/0223
2021/0156898 Al 5/2021 Amarloo et al.

C03C 27/06

OTHER PUBLICATIONS,

Knappe, S., et al., “Atomic vapor cells for chip-scale atomic clocks
with improved long-term frequency stability”, Optics Letters, 2005,
p. 2351-2353, vol. 30 No. 18.

Liew, L-A., et al., “Wafer-level filling of microfabricated atomic
vapor cells based on thin-film deposition and photolysis of cesium
azide”, Applied Physics Letters, 2007, p. 114106, vol. 90.

Nieradko, L., et al., “ew approach of fabrication and dispensing of
micromachined cesium vapor cell”, Journal of Micro/
Nanolithography, MEMS, and MOEMS, 2008, p. 033013, vol. 7
No. 3

Woetzel, S., et al., “Microfabricated atomic vapor cell arrays for
magnetic field measurements”, Review of Scientific Instruments,
2011, p. 033111, vol. 82.

Karlen, S., et al., “MEMS atomic vapor cells sealed by Cu—Cu
thermocompression bonding”, IEEE, 2017, p. 625-627.

Maurice, V., et al, “Microfabricated vapor cells filled with a cesium
dispensing paste for miniature atomic clocks”, Applied Physics
Letters, 2017, p. 164103, vol. 110.

Kurashima, Y,, et al., “An all-sapphire Cs gas cell for a chip-seale
atomic clock”, Japanese Journal of Applied Physics, 2019, p.
096506, vol. 58.

Abdullah, S., et al, “Aging studies on micro-fabricated alkali
bufler-gas cells for miniature atomic clocks”, Applied Physics
Letters, 2015, p. 163505, vol. 106.

Straessle, R., etal.,"Microfabricated alkali vapor cell with antirelaxation
wall coating”, Applied Physics Letters, 2014, p. 043502, vol. 105
Wallis, G., “Field Assisted Glass Sealing”, Electrocomponent Sci-
ence and Technology, 1975, p. 45-53, vol. 2 No. 1

Knowles, KM, et al..“Anodic bonding”, International Materials
Review, 2006, p. 273-311, vol. 51 No. 5.

* cited by examiner


US 11,879,952 B2

7

embodiment, elements of atomic vapor cell 200 are selec-
tively etched to remove various different materials using
different etchants and photolithographic masks and proce-
dures. The various layers thus formed can be subjected to
joining by anodic bonding, fusion bonding. or another
bonding technique capable of hermetic sealing to form
atomic vapor cell 200.

In an embodiment, a process for making an atomic vapor
cell using anodic bonding includes: providing first optical
window 201 consisting essentially of transparent noncon-
ducting material and comprising first window bonding sur-
face 204.1 and first cell window wall 207.1, the transparent
nonconducting material of first optical window 201 being
essentially free of electrically conductive materials includ-
ing silicon to minimize distortion of radiofrequency fields by
first optical window 201; forming first thin film 214 com-
prising anodic bonding material 213 on first window bond-
ing surface 204.1; forming second thin film 215 comprising
second anodic bonding material 213.2 on first frame bond-

ing surface 205.1 and the second frame bonding surface 2

205.2; disposing intermediate frame 203 on first optical
window 201, intermediate frame 203 consisting essentially
of transparent nonconducting material, and comprising: first
frame bonding surface 205.1 opposing first window bonding

surface 204.1, second frame bonding surface 205.2, and cell 2

frame wall 208, the transparent nonconducting material of
intermediate frame 203 being essentially free of electrically
conductive materials including silicon to minimize distor-
tion of radiofrequency fields by intermediate frame 203:
forming first thin film 214 comprising anodic bonding
material 213 on second window bonding surface 204.2:
anodically bonding first frame bonding surface 205.1 of
intermediate frame 203 to first window bonding surface
204.1 of first optical window 201; disposing second optical
window 202 on intermediate frame 203 such that interme-
diate frame 203 is interposed between first optical window
201 and second optical window 202, and second optical
window 202 consisting essentially of transparent noncon-
ducting material and comprising: second window bonding
surface 204.2 opposing second frame bonding surface 208.2,
and second cell window wall 207.2, the transparent noncon-
ducting material of second optical window 202 being essen-
tially free of electrically conductive materials including
silicon to minimize distortion of radiofrequency fields by
second optical window 202; anodically bonding second
window bonding surface 204.2 of second optical window
202 to second frame bonding surface 205.2 of intermediate
frame 203; forming, in response to the anodically bonding,
cell aperture 206 bounded by first cell window wall 207.1 of

first optical window 201, cell frame wall 208 of intermediate 5

frame 203, and second cell window wall 207.2 of second
optical window 202; and hermetically sealing atomic vapor
cell 200 in response to anodically bonding first optical
window 201 and second optical window 202 to intermediate
frame 203 to make atomic vapor cell 200.

In an embodiment, a process for making an atomic vapor
cell using anodic bonding includes: providing first optical
window 201 consisting essentially of transparent noncon-
ducting material and comprising first window bonding sur-
face 204.1 and first cell window wall 207.1, the transparent
nonconducting material of first optical window 201 being
essentially free of electrically conductive materials includ-
ing silicon to minimize distortion of radiofrequency fields by
first optical window 201; forming second thin film 215
comprising second anodic bonding material 213.2 on first
frame bonding surface 205.1 and second frame bonding
surface 205.2; disposing intermediate frame 203 on first

&

&

s

8

optical window 201, intermediate frame 203 consisting
essentially of transparent nonconducting material, and com-
prising: first frame bonding surface 205.1 opposing first
window bonding surface 204.1, second frame bonding sur-
face 205.2, and cell frame wall 208, the transparent non-
conducting material of intermediate frame 203 being essen-
tially free of electrically conductive materials including
silicon to minimize distortion of radiofrequency fields by
intermediate frame 203; anodically bonding first frame
bonding surface 205.1 of intermediate frame 203 to first
window bonding surface 204.1 of first optical window 201;
disposing second optical window 202 on intermediate frame
203 such that intermediate frame 203 is interposed between
first optical window 201 and second optical window 202,
and second optical window 202 consisting essentially of
transparent nonconducting material and comprising: second
window bonding surface 204.2 opposing second frame
bonding surface 205.2, and second cell window wall 207.2,
the transparent nonconducting material of second optical
window 202 being essentially free of electrically conductive
materials including silicon to minimize distortion of radiof-
requency fields by second optical window 202; anodically
bonding second window bonding surface 204.2 of second
optical window 202 to second frame bonding surface 205.2
of intermediate frame 203; forming, in response to the
anodically bonding, cell aperture 206 bounded by first cell
window wall 207.1 of first optical window 201, cell frame
wall 208 of intermediate frame 203, and second cell window
wall 207.2 of second optical window 202; and hermetically
sealing atomic vapor cell 200 in response to anodically
bonding first optical window 201 and second optical win-
dow 202 to intermediate frame 203 to make atomic vapor
cell 200. In some embodiments first and second windows are
made of anodic bonding material 213.

In an embodiment, the process for making an atomic
vapor cell using anodic bonding includes forming atomic
vapors of alkali metal atoms in cell aperture 206. In certain
embodiments, forming the atomic vapors of alkali metal
atoms in cell aperture 206 occurs prior to hermetically
sealing atomic vapor cell 200. According to an embodiment,
forming the atomic vapors of alkali metal atoms in cell
aperture 206 occurs after hermetically sealing atomic vapor
cell 200.

In an embodiment, the process for making an atomic
vapor cell using anodic bonding includes forming additional
cell apertures 206, wherein each of the cell apertures 206 are
sealed from one another such that each cell aperture 206 is
fluidically isolated from all other cell apertures 206

Accordingly, with reference FIG. 2A, it should be appre-
ciated that second anodic bonding material 213.2, e.g.,
silicon, can be formed on first frame bonding surface 205.1
and second frame bonding surface 205.2 of intermediate
frame 203, and first optical window 201 and second optical
window 202, e.g., made of anodic bonding material 213, are
then anodically bounded to intermediate frame 203 to form.
atomic vapor cell 200 shown in FIG. 3. Alternatively, with
reference FIG. 2B, second anodic bonding material 213.2 is
formed on first window bonding surface 204.1 of first optical
window 201 and second window bonding surface 204.2 of
second optical window 202 that are then anodically bounded
to intermediate frame 203, e.g., made of anodic bonding
material 213, to form atomic vapor cell 200 shown in FIG.
3. As another option, atomic vapor cell 200 can be made by
drilling holes in intermediate frame 203 to form cell aperture
206. The resulting cell aperture 206 bounded by cell frame
wall 208 cell window wall 207.1, and cell window wall
207.2 are a reservoir for alkali atomic vapor in atomic vapor



US 11,879,952 B2

13

window, consisting essentially of transparent noncon-
ducting material, and comprising: a second window
bonding surface opposing and bonded to the second
frame bonding surface, and a second cell window wall,
the transparent nonconducting material of the second
optical window being essentially free of electrically
conductive materials including silicon to minimize
distortion of radiofrequency fields by the second optical
window;

a cell aperture bounded by the first cell window wall of
the first optical window, the cell frame wall of the
intermediate frame, and the second cell window wall of
the second optical window; and

anodic bonding material interposed between the first
optical window and the intermediate frame that bonds
the intermediate frame to the first optical window and
interposed between the second optical window and the
intermediate frame that bonds the intermediate frame to
the second optical window,

wherein the atomic vapor cell is hermetically sealed by 2

bonding between the first optical window and the
second optical window to the intermediate frame.

2. The atomic vapor cell of claim 1, further comprising
atomic vapors of alkali metal atoms disposed in the cell
aperture.

3. The atomic vapor cell of claim 1, further comprising a
source of atomic vapors of alkali metal atoms disposed in the
cell aperture.

4. The atomic vapor cell of claim 1, further comprising
additional cell apertures, wherein each of the cell apertures
are sealed from one another such that each cell aperture is
fluidically isolated from all other cell apertures.

5. The atomic vapor cell of claim 1, wherein the anodic
bonding material is formed from silicon, borosilicate,
polycrystalline silicon, or amorphous silicon.

6. The atomic vapor cell of claim 1, wherein the cell
aperture comprises a circular cross-section along a lateral
length of the cell aperture.

7. The atomic vapor cell of claim 1, wherein the cell
aperture comprises an ellipsoidal cross-section along a lat-
eral length of the cell aperture.

8. The atomic vapor cell of claim 1, wherein the cell
aperture comprises a quadrilateral cross-section along a
lateral length of the cell aperture.

9. The atomic vapor cell of claim 1, wherein the cell
aperture comprises a parallelepiped shape.

10. The atomic vapor cell of claim 1, wherein the cell
aperture comprises a cylindrical shape.

11. The atomic vapor cell of claim 1, wherein the trans-
parent nonconducting material of the first optical window,
the second optical window, and the intermediate frame
independently comprise fused silica or fused quartz.

12. The atomic vapor cell of claim 1, wherein the first
window thickness of the first optical window is from 1 mm
to 10 mm.

13. The atomic vapor cell of claim 1, wherein the second
window thickness of the second optical window is from 1
mm to 10 mm.

14. The atomic vapor cell of claim 1, wherein the frame
thickness of the intermediate frame is from 1 mm to 10 mm.

15. The atomic vapor cell of claim 1, wherein the volume
of the cell aperture is from 1 mm? to 10 mm*.

16. The atomic vapor cell of claim 1, wherein the atomic
vapor cell is configured to detect radiofrequency radiation.

17. The atomic vapor cell of claim 16, wherein the
radiofrequency radiation has a wavelength from 0.1 mm to
10° km.

0

28

0

38

4

0

45

50

s

14

18. A process for making an atomic vapor cell using
anodic bonding, the process comprisin;
providing a first optical window consisting essentially of
transparent nonconducting material and comprising a
first window bonding surface and a first cell window
wall, the transparent nonconducting material of the first
optical window being essentially free of electrically
conductive materials including silicon to minimize
distortion of radiofrequency fields by the first optical
window;
forming a first thin film comprising anodic bonding
material on the first window bonding surface;

disposing an intermediate frame on the first optical win-
dow, the intermediate frame consisting essentially of
transparent nonconducting material, and comprising: a
first frame bonding surface opposing the first window
bonding surface, a second frame bonding surface, and
a cell frame wall, the transparent nonconducting mate-
rial of the intermediate frame being essentially free of
electrically conductive materials including silicon to
minimize distortion of radiofrequency fields by the
intermediate frame;
forming a second thin film comprising anodic bonding
material on the second window bonding surface;

anodically bonding the first frame bonding surface of the
intermediate frame to the first window bonding surface
of the first optical window;

disposing a second optical window on the intermediate

frame such that the intermediate frame is interposed
between the first optical window and the second optical
window, and the second optical window consisting
essentially of transparent nonconducting material and
comprising: a second window bonding surface oppos-
ing the second frame bonding surface, and a second cell
window wall, the transparent nonconducting material
of the second optical window being essentially free of
electrically conductive materials including silicon to
minimize distortion of radiofrequency fields by the
second optical window;

anodically bonding the second window bonding surface

of the second optical window to the second frame
bonding surface of the intermediate frame;

forming, in response to the anodically bonding, a cell

aperture bounded by the first cell window wall of the
first optical window, the cell frame wall of the inter-
mediate frame, and the second cell window wall of the
second optical window; and

hermetically sealing the atomic vapor cell in response to

anodicaliy bonding the first optical window and the
second optical window to the intermediate frame to
make the atomic vapor cell

19. The process of claim 18, further comprising forming
atomic vapors of alkali metal atoms in the cell aperture.

20. The process of claim 19, wherein forming the atomic
vapors of alkali metal atoms in the cell aperture occurs prior
to hermetically sealing the atomic vapor cell.

21. The process of claim 19, wherein forming the atomic
vapors of alkali metal atoms in the cell aperture occurs prior
to hermetically sealing the atomic vapor cell.

22. The process of claim 18, further comprising forming
additional cell apertures, wherein each of the cell apertures
are sealed from one another such that each cell aperture is
fluidically isolated from all other cell apertures.

23. A process for making an atomic vapor cell using
anodic bonding, the process comprising:

providing a first optical window consisting essentially of

transparent nonconducting material and comprising a