US 11,069,507 B2

9

thickness of the substrate 155. Alternatively or additionally,
the ground planes 164 and 156a-156b can be connected via
portions that extend over one or more side edges of the
substrate 155. In another example, the sample carrier 114d
can employ a microstrip configuration, where the monolithic
ground plane 164 is disposed on the backside of substrate
155 without any ground planes on the topside of substrate
155, as shown in FIGS. 4H-41.

Although the source leads 158 in each of FIGS. 4A-4I is
primarily designed to transmit RF signals, the source leads
158 can also be used to transmit lower frequency or no
frequency signals. Thus, the sample carrier 114d can be used
to deliver signals from DC up to 100 GHz to the specimen
112. However, in some embodiments, it may be beneficial to
simultaneously apply DC voltages to the specimen 112
while separately applying RF signals to the specimen 112.
For example, the sample carrier 114d can employ a first
transmission line configuration 166 designed to transmit RF
signals to the specimen, and a separate second transmission
line configuration 168 designed to bias the specimen 112
with a DC voltage, as illustrated in FIG. 4J. The first
transmission line configuration 166 illustrated in FIG. 4] has
the coplanar waveguide configuration of FIGS. 4A-4B, with
source lead 158, between ground planes 156a, 1566, elec-
trically connected to the specimen 112 at one end and
electrically connected to a conductor of the TEM sample
holder at the other. However, any of the other RF transmis-
sion line configurations illustrated in FIGS. 4C-4I are also
possible. The second transmission line configuration 168

can have a conventional configuration without any ground 3

planes for transmission of DC signals. For example, FIG. 4]
illustrates a pair of leads 170, 172 for the second transmis-
sion line configuration 168. Each lead 170, 172 can be
electrically connected to the specimen 112 at one end and

electrically connected to a respective conductor of the TEM 3

sample holder at the other. The DC biasing leads 170, 172,
the RF transmission lead 158, and the ground planes 156a,
156d may also be formed from the same layer of conductive
material, for example, via patterning and etching to define
the desired geometries. Although a particular number of
leads for RF and DC signal transmission are shown in FIG.
4J, any number of leads are possible according to one or
more contemplated embodiments.

In some embodiments, it may be desirable to include
circuitry on the sample carrier 114d to interact with the
transmitted RF signal and/or the specimen 112. Such cir-
cuitry may be integrally formed on the sample carrier 114d
(for example, over a topside or backside surface of the
dielectric substrate and connected with the RF transmission
lead, such as by a multilayer interconnect system, a via
interconnect, or via wirebonding) or formed as a separate
chip coupled to the sample carrier 114d (for example,
disposed on a topside surface or within a recess on the
topside surface of the dielectric substrate). For example, the
sample carrier 114d can have a recess 176 into which a
semiconductor chip 174 is disposed, as illustrated in FIG.
4K. The semiconductor chip 174 can have one or more
circuits 184, for an example, an amplifying circuit, config-
ured to interact with an RF signal. The semiconductor chip
174 can have an input terminal 182 (e.g., bond pad) elec-
trically connected to a respective conductor of the TEM
sample holder, for example, via wire 178. The semiconduc-
tor chip 174 can have an output terminal 186 (e.g., bond pad)
electrically connected to an input end of the source lead 158
of the coplanar waveguide, for example via wire 180. An RF
signal delivered via the conductor of the TEM sample holder
can thus be processed by semiconductor chip 184 (e.g.,

S

3

40

&

10
amplified) before being transmitted to the specimen 112 by
the signal lead 158 of the coplanar waveguide. Other chip
functionalities and arrangements are also possible according
to one or more contemplated embodiments.

Although the features of FIGS. 4A-4K have been illus-
trated separately, the inclusion of one feature does not
preclude the use of the other. Indeed, features from any of
FIGS. 4A-4K can be combined together in certain embodi-
ments. For example, the tapered features of FIGS. 4E could
be applied to the RF transmission line configurations of
FIGS. 4C-4D and 4F-4K. In another example, the multiple
source lead configuration of FIG. 4C-4D could be applied to
the RF transmission line configurations of FIGS. 4F-4K. In
still another example, the RF transmission line configura-

$s tions of FIGS. 4F-41 could be used in the sample carriers of

FIGS. 4J-4K. In some embodiments, different RF transmis-
sion line configurations can be combined on the sample
carrier, for example, by combining FIGS. 4A, 4F, and/or 4H.
Thus, embodiments of the disclosed subject matter are not
limited to the configurations separately illustrated in the
figures; rather, embodiments include all practical combina-
tions of the features illustrated in the figures or otherwise
described herein. Indeed, the various combinations of RF
transmission line configurations, DC biasing leads, and/or

S supplemental circuitry can allow a user to customize the

sample carrier to a particular experiment and/or specimen.

FIGS. 5A-SD illustrate a particular exemplary configura-
tion of a sample carrier 114d with eight coplanar waveguides
formed by source leads 158 between pairs of ground planes
156. Each source lead 158 has a first section at end 162 distal
from recess 144 where the specimen will be disposed, and
a second section at end 164 proximal to recess 144. The first
section has a substantially constant first width while the
second section has a substantially constant second width that
is less than the first width. Between the first and second
sections, each source lead 158 has a variable width that
gradually tapers from the first width to the second width. To
accommodate different geometries for specimen 112, the
outermost leads adjacent to edges of the sample carrier 114d
can be bent at 168 so as to be substantially perpendicular to
the other leads as they approach the specimen 112. The leads
158 can be arranged such that specimen 112 has a four-fold
rotational symmetry with respect to the sample carrier 114d,
thereby allowing for additional experimentation sites on
each specimen. The eight leads 158 can thus enable experi-
mentation on different regions of the same specimen 112 and
can allow for more complex electrical stimuli and measure-
ments,

Dimensions of the sample carrier 114d, as well as dimen-
sions and location of through-hole 140 and/or through-hole
146, may tailored to match the configuration of the TEM
system into which the specimen assembly 114 is installed
and/or dimensions of the specimen 112. For example, FIG.
5D illustrates dimension of an exemplary sample carrier that

5 can be used in a JEOL TEM system with a 2 mm objective

pole-piece gap. For example, contact pads for the source
leads are 1.375 mm in length with conductor widths (S) and
gaps (W) of 400 um and 50 pum, respectively, to provide a
large area for making perpendicular contact with each CPW.
The dimensions, S and W, are then reduced to 200 jum and
25 um at a taper of about 22 pm/mm and 2.8 um/mm,
respectively, over 8.925 mm. The six inner leads then
continue 2 mm to the 3.4 mmx3.4 mm specimen through-
hole. The two outermost leads instead continue 2.9125 mm

5 before curving 90° into the specimen hole along a 3xS radius

of curvature. The substrate may have a thickness (H) that is
less than or equal to 500 um. Other TEM systems may


U.S. Patent Jul. 20, 2021 Sheet 4 of 8 US 11,069,507 B2

162
| 14h 114d
f 156 146 /

488 IN (we 4
y ey) LW
820 mm 7

14a FIG.5A 4
414d 158 158 188 158 158
—_—— W/ / /
Ze ; i
“Led “de
156
2 166
fe es
Z LA 158
ELA TTITTT TTT f

| im ih 7 Fy
I’ af
A / f/ / | i
/ 156 / 168 188 FIG, 5B 166186

14a 162

164

156

FIG. 5C


US 11,069,507 B2

17

10. The specimen assembly of claim 1, wherein:

the dielectric substrate is formed by one or more of
polytetrafluoroethylene (PTFE), quartz, glass-rein-
forced epoxy, beryllia, alumina, or gallium arsenide;

the dielectric substrate has a thickness of 500 jim or less;
and

the conductive layer comprises a metal coating over a
surface of the dielectric substrate.

11. The specimen assembly of claim 1, wherein:

the dielectric substrate with the conductive layer forms
multiple coplanar waveguides, each having first and
second leads, and

adjacent ones of the multiple coplanar waveguides share
‘a common second lead between the corresponding first
leads.

12. A method for in situ transmission electron microscopy

(TEM), comprising:

mounting a specimen to a sample carrier, which com-
prises a dielectric substrate with a conductive layer that
forms a coplanar waveguide configured to transmit an
electrical signal to a specimen held by the sample
carrier, the coplanar waveguide having a first lead
formed by the conductive layer and a pair of second
leads formed by the conductive layer, the first lead
being between the second leads and spaced from the
second leads by respective gaps;

mounting the sample carrier to a TEM sample holder,
which comprises a head portion, a back end portion,
and a shaft portion between the head and back end

portions, the sample carrier being disposed within a 3

recess of the head portion;
installing the TEM sample holder to a transmission elec-
tron microscope such that the sample carrier with
specimen is disposed within a vacuum environment of
the microscope;
connecting a radio-frequency (RF) source to a connector
of the TEM sample holder; and
applying one or more electrical signals from the RF
source to the specimen within the transmission electron
microscope via the TEM sample holder and the sample
carrier, each electrical signal having a frequency
between 3 kHz and 300 GHz, inclusive.
13. The method of claim 12, further comprising:
at a same time as or in response to the applying one or
more electrical signals, irradiating the specimen with
an electron beam and detecting the electron beam after
passing through the specimen to form a TEM image.
14. The method of claim 12, wherein the mounting the
specimen comprises wirebonding a wire between a first lead
of the sample carrier and a terminal of the specimen.
15. The method of claim 12, wherein the mounting the
sample carrier to the TEM sample holder comprises cou-
pling coaxial cabling, which extends from the connector

8

25

2

40

50

18
through the shaft portion to the head portion of the TEM
sample holder, to at least the first lead.
16. The method of claim 12, wherein the dielectric
substrate with the conductive layer forms multiple coplanar
waveguides, each having first and second leads, and adjacent
ones of the multiple coplanar waveguides share a common
second lead between the corresponding first leads.
17. The method of claim 16, wherein the mounting the
specimen comprises wirebonding a wire between each first
lead of the sample carrier and a corresponding terminal of
the specimen.
18. The method of claim 16, wherein:
the connecting comprises connecting the RF source to a
plurality of connectors of the TEM sample holder; and

the mounting the sample carrier to the TEM sample holder
comprises coupling multiple coaxial cables to the first
leads, respectively,

wherein each coaxial cable extends from a respective one

of the connectors through the shaft portion to the head
portion of the TEM sample holder.

19. A method for in situ transmission electron microscopy
(TEM), comprising:

via a sample carrier, applying one or more electrical

signals from a radio-frequency (RF) source to a speci-
men within a vacuum chamber of a transmission elec-
tron microscope: and

at a same time or in response to the applying the one or

more electrical signals, irradiating the specimen with
an electron beam and detecting the electron beam after
passing through the specimen,

wherein each electrical signal has a frequency between 3

kHz and 300 GHz, inclusive,

the sample carrier comprises a dielectric substrate with a

conductive layer that forms multiple coplanar wave-
guides for transmitting the one or more electrical
signals to the specimen, and

the coplanar waveguides comprise multiple first leads and

second leads formed from the conductive layer, each
first lead being between and spaced from a pair of
adjacent second leads by respective gaps.
20. The method of claim 19, wherein:
the one or more electrical signals are conveyed from the
RF source by coaxial cables that extend from outside
the vacuum chamber to respective input ends of the first
leads within the vacuum chamber, each coaxial cable
being disposed within a TEM sample holder,
the sample carrier is mounted to a head portion of the
TEM sample holder, and

a back end portion of the TEM sample holder includes RF
connectors that connect the RF source to the coaxial
cables,


US 11,069,507 B2

1
RADIO-FREQUENCY (RF) TRANSMISSION
SYSTEMS, DEVICES, AND METHODS FOR

IN SITU TRANSMISSION ELECTRON
MICROSCOPY

CROSS REFERENCE TO RELATED
APPLICATION,

The present application claims the benefit of U.S. Provi-
sional Application No. 62/814,152, filed Mar. 5, 2019, which
is hereby incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH

This invention was made with government support under
7ONANB16H003 awarded by the National Institute of Stan-
dards and Technology (NIST). The government has certain
rights in the invention.

FIELD

The present disclosure relates generally to transmission
electron microscopes, and more particularly, to radio-fre-
quency (RF) or microwave excitation of a specimen for in
situ transmission electron microscopy.

BACKGROUND

The field of electron microscopy has primarily developed 3

around four separate tracks: instrumentation, detector tech-
nology, analysis techniques, and in situ capabilities. Past
developments along the in situ track have yielded improved
capabilities in heating, cooling, straining, high-pressure gas,

liquid, electrical biasing, and optical excitation. Yet conven- 3

tional in situ transmission electron microscopy (TEM) is not
able to adequately investigate electrical stimuli in the radio-
frequency (RF) or microwave regime. While many modern
electronic devices employ RF signals, the lack of existing in
situ capabilities in the RF regime prevent TEM character-
ization of such devices, for example, to microscopically
investigate interactions between RF stimuli and materials.
Embodiments of the disclosed subject matter may address
‘one or more of the above-noted problems and disadvantages,
among other things.

SUMMARY

Embodiments of the disclosed subject matter provide a
specimen assembly for in situ transmission electron micros-
copy (TEM) and methods for use thereof in delivering to a
specimen within a TEM system broadband alternating (AC)
electrical signals in the radio-frequency (RF) or microwave
regimes. The specimen assembly mitigates losses that would
otherwise occur with high frequency signal transmission in
conventional TEM setups. An RF signal can be transmitted
from an RF or microwave source through cables within the
microscope to a sample holder of the assembly, where a
sample carrier mounted on the sample holder conveys the
RE signal to a specimen using one or more coplanar wave-
guides, Thus, the specimen can be interrogated or actuated
by the RF signal while in the vacuum chamber of the
microscope, thereby allowing subsequent or simultaneous
investigation by the electron beam of the microscope for in
situ characterization of the specimen.

In one or more embodiments, a specimen assembly for in
situ transmission electron microscopy (TEM) comprises a

20

3

40

45

6:

2

sample carrier, The sample carrier can have a dielectric
substrate with a conductive layer that forms a coplanar
waveguide. The coplanar waveguide can be configured to
transmit an electrical signal to a specimen held by the
sample carrier. The coplanar waveguide can have a first lead
formed by the conductive layer and a pair of second leads
formed by the conductive layer. The first lead can be
between the second leads and spaced from the second leads
by respective gaps. The electrical signal can have a fre-
quency in the RF regime (3 kHz and 300 GHz), for example,
up to 100 GHz.

In one or more embodiments, a method for in situ TEM
can comprise mounting a specimen to a sample carrier. The
sample carrier can comprise a dielectric substrate with a
conductive layer that forms a coplanar waveguide. The
coplanar waveguide can be configured to transmit an elec-
trical signal to a specimen held by the sample carrier. The
coplanar waveguide can have a first lead formed by the
conductive layer and a pair of second leads formed by the
conductive layer. The first lead can be between the second
leads and spaced from the second leads by respective gaps.
The method can further comprise mounting the sample
carrier to a TEM sample holder. The TEM sample holder can
have a head portion, a back end portion, and a shaft portion
between the head and back end portions. The sample carrier
can be disposed within a recess of the head portion. The
method can further comprise installing the TEM sample
holder to a transmission electron microscope such that the
sample carrier with specimen is disposed within a vacuum
environment of the microscope. The method can also com-
prise connecting a RF source to a connector of the TEM
sample holder. The method can further comprise applying
one or more electrical signals from the RF source to the
specimen within the transmission electron microscope via
the TEM sample holder and the sample carrier. Each elec-
trical signal can have a frequency in the RF regime (3 kHz
and 300 GHz), for example, up to 100 GHz.

In one or more embodiments, a method for in situ TEM
can comprise, via a sample carrier, applying one or more
electrical signals from an RF source to a specimen within a
vacuum chamber of a transmission electron microscope.
Each electrical signal can have a frequency in the RF regime
(3 kHz and 300 GHz), for example, up to 100 GHz. The
sample carrier can comprise a dielectric substrate with a
conductive layer that forms multiple coplanar waveguides
for transmitting the one or more electrical signals to the
specimen. The coplanar waveguides can comprise multiple
first leads and second leads formed from the conductive
layer. Each first lead can be between and spaced from a pair
of adjacent second leads by respective gaps. The method can
further comprise, at a same time or in response to the
applying the one or more electrical signals, irradiating the
specimen with an electron beam and detecting the electron
beam after passing through the specimen.

Objects and advantages of embodiments of the disclosed
subject matter will become apparent from the following
description when considered in conjunction with the accom-
panying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS.

Embodiments will hereinafter be described with reference
to the accompanying drawings, which have not necessarily
been drawn to scale. Where applicable, some elements may
be simplified or otherwise not illustrated in order to assist in


U.S. Patent Jul. 20, 2021 Sheet 6 of 8 US 11,069,507 B2

0.024 r , t r r t t :
1mm

0.00 4
0.02
S. -0.044
0.064
# 0.084
6.404

dB)

Frequency (GHz)
FIG. 6

5mm

° aes
SS

50pm 400um  TM

D4 496 um =~
2 4 6 8 0 1 14 18

Frequency (GHz)
FIG. 7



US 11,069,507 B2

Sheet 5 of 8

Jul. 20, 2021

U.S. Patent

foe eee

qs ‘Old

ae:

o Ae

208:



U.S. Patent Jul. 20, 2021 Sheet 8 of 8 US 11,069,507 B2

wi DC carrier

oS ee ee
ro) ea aon
= ~20 a As Measured
fa As measured wio cartier / ~ With DC Carrier
wn om
rn Without Carrier
3 With RF Carrier
wl with DC Carrier
£ = RF
5 34 w/DC carrier a!
eed
a ° ~
as pore BC RF CRE
9 1 72 3 4 5 6 7 $ 3
oe Frequency (GHz)
FIG. 9A
w/ DC cartier wi RF carier
~~ 10 30
a ~— With DC Carrier
Se — With RF Carrier |,
a
-10 om
“ 10
ij-20 3
9 G@ be
: ~30 if
& -a0}, ~10 8
F 20
h 759 -
&
605 t 2 5 339

3 4 5 é
Frequency (GHz)
FIG. 9B


a2 United States Patent

Katz et al.

US011069507B2

US 11,069,507 B2
Jul. 20, 2021

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

(54)

(71)

(72)

(73)

(*)

(21)
(22)
(65)

(60)

(51)

RADIO-FREQUENCY (RF) TRANSMISSION
SYSTEMS, DEVICES, AND METHODS FOR
IN SITU TRANSMISSION ELECTRON
MICROSCOPY

Applicants: University of Maryland, College Park,
College Park, MD (US); National
Institute of Standards and
‘Technology, Gaithersburg, MD (US)

Inventors: Michael Katz, Washington, DC (US);
Karl Schliep, North Bethesda, MD

(US); June Lau, Rockville, MD (US);
Jason J. Gorman, Silver Spring, MD

ws)

Assignees: University of Maryland, College Park,
College Park, MD (US); Government
of the United States of America, as
represented by the Secretary of
Commerce, National Institute of
Standards and Technology,
Gaithersburg, MD (US)

Notice: Subject to any disclaimer, the term of this

patent is extended or adjusted under 35
U.S.C. 154(b) by 0 days.

Appl. No.: 16/809,736
Filed: Mar. 5, 2020

Prior Publication Data
US 2020/0286706 Al Sep. 10, 2020

Related U.S. Application Data

Provisional application No. 62/814,152, filed on Mar.
5, 2019.

Int. Cl.
HOLS 37/20 (2006.01)
HOLS 37/26 (2006.01)

(52) US. CL
CPC vaccsneee HOLT 37/20 (2013.01); HOLS 37/26
(2013.01); HOLJ 2237/2008 (2013.01)
(58) Field of Classification Search
CPC ..... HO1J 37/20; HO1J 37/26; HOLJ 2237/2008
See application file for complete search history.

(56) References Cited
U.S. PATENT DOCUMENTS

6,317,083 B1* 11/2001 Johnson HO1LQ 1/243,

343/700 MS

OTHER PUBLICATIONS

Goncalves et al., ‘Probing microwave fields and enabling in-situ
experiments in a transmission electron microscope’ Sep. 1, 2017,
Sci Rep. 7: 11064.*

* cited by examiner

Primary Examiner — Eliza W Osenbaugh-Stewart
(74) Attorney, Agent, or Firm —RowanTree Law Group,
PLLC; Frederick F. Rosenberger

(7) ABSTRACT

A sample carrier for in situ transmission electron micros-
copy (TEM) has a dielectric substrate with a conductive
layer that forms a coplanar waveguide. The coplanar wave-
guide has a first and second leads formed by the conductive
layer. The first lead is between an adjacent pair of second
leads and is spaced from the second leads by a respective
gap. The coplanar waveguide is configured to transmit an
electrical signal to a specimen held by the sample carrier, in
particular, an electrical signal having a frequency in the
radio-frequency (RF) regime (3 kHz-300 GHz), for
example, up to 100 GHz. The sample carrier may be
mounted to a TEM sample holder, which supports the
sample carrier within a vacuum chamber of the microscope
and provides electrical connection between the leads of the
sample carrier and an RF source external to the vacuum
chamber.

20 Claims, 8 Drawing Sheets



US 11,069,507 B2

5

detector (HPD) or a monolithic active pixel sensor (MAPS),
in which case the fluorescent screen 122 may be omitted.
The specimen assembly 114 can be connected to an RF
source 126, for example, by one or more coaxial cables. The
specimen assembly 114 is configured to transmit an RE
electrical signal from the RF source 126 to the specimen 112
while minimizing, or at least reducing, transmission losses.
The controller 128 can be operatively coupled to the RF
source 126 and/or the electron source 104 for control
thereof. For example, the controller 128 can control the RF
source 126 to send an RF signal to the specimen 112 via the
specimen assembly 114. In some embodiments, source 126
can be configured to generate electrical signals of a variety
of different frequencies, for example, from DC (0 Hz) up to
100 GHz. Alternatively or additionally, source 126 can
comprise multiple electrical sources, each of which is con-
figured to generate electrical signals in a specific frequency
regime (e.g., one source for DC voltage and another source
for RF). The specimen assembly 114 is configured to trans-
mit to the specimen the electrical signals from the source
126 over the entire frequency range (e.g., 0 Hz to 100 GHz).
The controller 128 may also control the electron source
104 to simultaneously emit the electron beam 106, such that
a TEM analysis can be performed by the microscope system
100 while the specimen 112 is excited or driven by the RF
signal. Alternatively or additionally, the controller 128 may
control the electron source 104 to emit the electron beam
106 shortly after application of the RF signal to the specimen
112 (e.g., on the order of milliseconds), for example, to
perform the TEM analysis subsequent to the RF excitation.
In some embodiments, the excitation with the RF signal
and/or the emission of electron beam 106 may be substan-
tially continuous when the specimen 112 is within the
vacuum environment of the electron optical column 102.

In some embodiments, the controller 128 can control 3

other components of the microscope system 100 and coor-
dinate application of the RF signal therewith. For example,
the controller 128 can be operatively coupled to an RF
beamline component inserted into the electron optical col-
umn 102. The RF beamline component may be connected to
RF source 126 to receive an RF signal therefrom, which
signal may be the same or different from that transmitted to
the specimen 112. For example, the RF beamline component
can be configured to “chop” the electron beam 106 into
beamlets in order to perform time-resolved TEM imaging.
Alternatively or additionally, the RF source 126 can be
coupled to one or more defiectors within the TEM system
100, for example, as part of a beat frequency analysis. Other
variations for connections to RF source 126 and/or control
by controller 128 are also possible according to one or more
contemplated embodiments.

FIGS. 2-3 illustrate a simplified configuration of an exem-
plary specimen assembly 114 that can be used to perform in
situ TEM. The specimen assembly 114 includes a TEM
holder having a head portion 114a, a back end portion 114c,
and an intermediate shaft portion 1144 between the head and
back end portions. At least the back end portion 114c can be
constructed to interface with support structures of the micro-
scope such that the head portion 114a extends into the
electron beam path within the electron optical column of the
microscope in a substantially cantilever fashion. The back
end portion 114c can also include one or more connectors
136 (e.g., RF connectors) to electrical conductors 134 (e.g.,
RF coaxial cables) that extend within the TEM holder from
the back end portion 114c through the shaft portion 1146 to
the head portion 114a to convey electrical signals to a
specimen 112

2

40

6

The specimen assembly 114 further includes a sample
carrier 114d that is mounted at the head portion 114a of the
TEM holder. For example, the head portion 114a can include
a recess 138 into which the sample carrier 114d fits. A ledge
142 can support the sample carrier 114d within the recess
138. In some embodiments, the specimen assembly 114 can
include features that allow securing of the head portion 114a
of the TEM holder and sample carrier 114d to each other. For
example, the sample carrier 114d can include one or more
mounting holes 152, through which a screw or similar
fastener can pass to interface with a mounting hole (not
shown) of the TEM holder in order to secure the sample
carrier 114d to the head portion 114a, Alternatively or
additionally, other mechanisms for releasably attaching the

5 sample carrier 114d to the head portion 14a can be used,

such as, but not limited to, soldering or an interference fit.

Similarly, the sample carrier 114d can include a recess
144 into which the specimen 112 fits. A ledge 146 can
support the specimen 112 within the recess 144. The speci-
men 112 can be releasably retained within the recess 144
(e.g., when sample carrier 114d is intended to be reused for
other specimens) or permanently retained within the recess
144 (e.g., when sample carrier 114d is a one-off test piece)
For example, the specimen 112 can be releasably attached

Ss within recess 144 of the sample carrier 114d via a solder, an

interference fit, or any other reversible attachment means.
Alternatively, the specimen 112 can be permanently attached
within recess 144 of the sample carrier 114d via, for
example, chemical bonding, welding, adhesive, or any other
irreversible attachment means.

The head portion 114a can also include a through-hole
140 that overlaps with the recess 138 in plan view, and the
sample carrier 114d can also include a through-hole 148 that
overlaps with both recesses 138, 144 in plan view. Each
through-hole 140, 148 can be designed to allow electrons
passing through specimen 112 to proceed uninhibited for
detection. In some embodiments, the through-hole 140 may
be centered with and fully contained within borders of recess
138 in plan view. In other embodiments, the through-hole
140 may be off center from recess 138, for example, when
having a size corresponding to and/or aligned with through-
hole 148 of the sample carrier 114d. For example, through-
hole 148 can be fully contained within borders of through-
hole 140 in plan view.

In some embodiments, the specimen 112 can be mounted
to a surface of the sample carrier 114d overlying the
through-hole 148 instead of within recess 144. For example,
the sample carrier 114d can include a mounting structure,
such as one or more pins, ridges, or other protrusions, that
functions similarly to the recess 144 to retain the specimen
112 in position on the carrier 114d surface. In some embodi-
ments, through-hole 140 and/or through-hole 148 may be
omitted in favor of a thinned layer of material, a TEM grid,
or any other electron beam transmissive material. In other

5 embodiments, for example, when applied to an electron

microscope that doesn’t require electron beam transmission
through the specimen (e.g., scanning electron microscope),
the through-hole 140 and/or through-hole 148 can be omit-
ted altogether.

The sample carrier 114d can include one or more leads
150 (e.g., conductive traces formed from a metal coating or
other conductive layer) on its surface that are coupled to the
electrical conductors 134 via one or more respective con-
nections 132. For example, the electrical conductors 134 can

5 be exposed as bare wire at the head portion 114a, which

wires are coupled to an input end (e.g., distal from specimen
112) of the one or more leads 150. For example, the


US 11,069,507 B2

3

the illustration and description of underlying features.
Throughout the figures, like reference numerals denote like
elements.

FIG. 1 is a simplified schematic diagram of an in situ
transmission electron microscopy (TEM) system, according
to one or more embodiments of the disclosed subject matter.

FIG. 2 is a simplified schematic diagram of a TEM holder
and sample carrier for use in performing in situ TEM,
according to one or more embodiments of the disclosed
subject matter.

FIG. 3 is an exploded view of a TEM holder, sample
carrier, and specimen, according to one or more embodi-
ments of the disclosed subject matter.

FIGS. 4A-4B are plan and cross-sectional views, respec-
tively, of an exemplary sample carrier having a single
coplanar waveguide, according to one or more embodiments
of the disclosed subject matter.

FIGS. 4C-4D are plan and cross-sectional views, respec-
tively, of an exemplary sample carrier having multiple
coplanar waveguides, according to one or more embodi-
ments of the disclosed subject matter.

FIG. 46 is a plan view of an exemplary sample carrier
having a tapered lead, according to one or more embodi-
ments of the disclosed subject matter.

FIGS. 4F-4G are plan and cross-sectional views, respec-
tively, of an exemplary sample carrier having a single
grounded coplanar waveguide, according to one or more
embodiments of the disclosed subject matter.

FIGS. 4H-4I are plan and cross-sectional views, respec-

tively, of an exemplary sample carrier having a single 3

microstrip transmission line, according to one or more
embodiments of the disclosed subject matter.

FIG. 4J is a plan view of an exemplary sample carrier
having separate lead configurations for RF and DC signal

transmission, according to one or more embodiments of the 3

disclosed subject matter.

FIG. 4K is a plan view of an exemplary sample carrier
having additional circuit elements for interacting with a
transmitted RF signal, according to on or more embodiments
of the disclosed subject matter.

FIG. SA is a plan view of an exemplary sample carrier
with multiple coplanar waveguides installed in a TEM
sample holder, according to one or more embodiments of the
disclosed subject matter,

FIGS. 5B-SC are close-up plan views of an input end
portion and a specimen support portion, respectively, of the
sample carrier of FIG. 5A.

FIG. 5D is a plan view with exemplary dimensions for the
sample carrier of FIG. 5A.

FIG. 6 are graphs of simulated S-parameters for trans-
mission (S3,) and reflection (S,,) of electrical power as a
function of electrical signal frequency for various lengths of
a coplanar waveguide having a lead width of 400 um and
gap of 50 jum.

FIG. 7 shows graphs of simulated S-parameters for trans-
mission ($,,) of electrical power as a function of electrical
signal frequency for various lengths of a coplanar wave-
guide that has a lead width that tapers from 400 jum to 200
jum at a constant impedance of 50 ohms (panel a) and at a
constant gap width of 50 um (panel b), and for various taper
widths of the coplanar waveguide that has a constant length
of 10 mm and at a constant impedance of 50 ohms (panel c)
and at a constant gap width of 50 jum (panel d).

FIG. 8A is a contour plot of the coplanar waveguide
dimensional parameter space defined by lead width (S), gap
width (W), dielectric constant (e,), and the total width of the
coplanar waveguide (e.g., L=S+3W).

2

&

4

FIG. 8B is a contour plot of simulated insertion loss (S3,)
of coplanar waveguide structures for six different substrate
materials (¢,=2, 3.8, 3.3, 6.7, 10, 13.1) and for various lead
widths.

FIG. 8C is a graph of total width of a coplanar waveguide
versus frequency averaged insertion loss (S3,) for the six
different substrate materials.

FIG. 9A is a graph of reflected power (S,,) for various
testing setups comparing performance for a standard sample
carrier and for the sample carrier of FIG. 5D.

FIG. 9B is a graph of transmitted power (S,,) across only
the standard sample carrier and the sample carrier of FIG.
5D.

DETAILED DESCRIPTION

Embodiments of the disclosed subject matter relate to a
specimen assembly for radio-frequency (RF) excitation of a
specimen for in situ transmission electron microscopy
(TEM). The assembly includes a sample carrier that supports
the specimen thereon within the vacuum chamber of a
transmission electron microscope. A TEM holder supports
the sample carrier thereon and conveys an electrical signal

s from an RF source external to the microscope to an input end

of the sample carrier. The sample carrier includes one or
more leads (e.g, electrical traces) that transmits the electri-
cal signal to the specimen. In particular, the sample carrier
employs one or more coplanar waveguides to transmit the
electrical signal, which has a frequency in the RF regime
(e.g., 3 kHz-300 GHz) or the microwave regime (e.g., 300
MHz-300 GHz), to terminals on the specimen in a low-loss
manner.

During electrical signal transmission to the specimen or
shortly thereafter, the specimen can be irradiated with an
electron beam from the microscope to perform an in situ (or
in operando) analysis of the specimen, for example, as a
function of excitation frequency of the transmitted electrical
signal. Embodiments of the disclosed subject matter can be
used in various applications, such as, but not limited to, the
characterization of semiconductor devices (¢.g., next gen-
eration wireless communication devices that employ gra-
phene or other materials) and magnetic device (e.g.. spin
valves) at their operating frequencies, high-throughput in
situ fatigue testing, and observation of RF phenomena using
ultrafast TEM techniques.

FIG. 1 illustrates a generalized setup of an in situ TEM
system 100 employing an exemplary specimen assembly
114. The TEM system 100 includes an electron optical
column 102, which houses various components of the sys-
tem and is maintained under vacuum during interrogation of
specimen 112. An electron beam source 104 (e.g., electron
gun) can emit an electron beam 106 toward specimen 112
supported within the beam path by assembly 114 between
objective lens pole pieces 110, 116. One or more condenser
lenses 108 (e.g., magnetic lens) can be used to focus the
electron beam 106 onto the specimen 112. The electron
beam transmitted through the specimen 112 is collected by
one or more intermediate lenses 118 (e.g., magnetic lens)
and focused by one or more projector lenses 120 (e.g,
magnetic lens) onto a fluorescent screen 122 to convert the
electrons into light in the visible regime, which light can be
captured by detector 124 (e.g., charge-coupled device
(CCD), complementary metal-oxide-semiconductor
(CMOS) imager, etc.) and processed into an image by
controller 128. Alternatively, detector 124 can be a direct
electron detector, such as, but not limited to, a hybrid pixel


U.S. Patent Jul. 20, 2021 Sheet 7 of 8 US 11,069,507 B2

225

250
275,
150
225
30

75

Gap Width (um)

50

25

8

Oo 209 300 300 590
Conductor Width (um)
FIG. 8A

3

8
a te
zs 3
Ed “3,
a * EY
5 > a4"
2 2
oan oS

°

FIG. 8B

Ave. So; (dB)

seme PTFE Beryllia

woe Quartz see: Alumina Ne
~o7 coi FRG mmm Gals ‘*
100 200 300 409 30D 600

Waveguide Width (um)
FIG. 8C

Gahs


U.S. Patent Jul. 20, 2021 Sheet 3 of 8 US 11,069,507 B2

144
11a 1
SK rE Pa
189 jgsanogy 154
160 Ie pL —
—— iS Baonnel 4866 156a 188 456 114d
14a
Ng
/ v
fi / \
1628 /* 1620 2
164 140
160 FIG. 4F FIG. 4G
144
14
° n 12
‘0 meg ea
— Co encl 138 458 444d
SS ig eo \
ta al
158
>
4
V
A 132
14d ——«— [ \ 442
ea 164 140
160 FIG. 4H FIG. 41
114a 2
SS
189 PAY 184
SU ‘ime AE
15a] |S fsogact 156b
—~d ‘al oe
168
I 1438
<a
186
184
182

FIG. 4) 8 FIG. AK


US 11,069,507 B2

11

require different dimensions or configurations for the sample
carrier 114d and/or other components of the specimen
assembly 114.

As noted above, the characteristic impedance of the CPW.
structure is related to the conductor width (S), the gap width
(W), the substrate thickness (H), and the dielectric constant
(e,) of the substrate material. For example, in the configu-
ration of FIGS. SA-SD, eight source leads are spread out
across a 5 mm width of the sample carrier 114d. The width
(L) of each CPW, which is defined as the width (S) of the
source lead plus the width (W) of each gap plus half of the
width (G) of each ground plane (e.g., L=S+2W+G), is thus
limited to 625 um (ie. 5 mm/8). Using equation (1) above
and setting Z,=0, the dimensional parameter space of the
CPW structure can be determined.

The variation of ¢, with different spatial dimensions of the
CPW are shown within the dielectric constant range
(1<e,<15) in FIG. 8A, delimited by thick black contours.
The contour lines outline regions of constant e, for CPW
with a 50 characteristic impedance. The contours are
bound by two solid black curves (for ¢,=1 and ¢,=15),
outlining a feasible ¢,. range. The contours correspond to the
dielectric constants for exemplary materials for the sample
carrier substrate, in particular, polytetrafluoroethylene
(PTFE) (¢,=2. shown in maroon), quartz (¢,=3.8, shown in
red), FR-4 glass epoxy (¢,=4.4, shown in orange), beryllia
(¢,=6.7, shown in green), alumina (¢,=10, shown in biue),
and gallium arsenide (GaAs, shown in purple) (e,=13.1).

In some embodiments, the width of the ground plane can

be equal to the width of the gap (e.g., G=W), such that the 3

CPW width is given by L=S+3W. In FIG. 8A, the triangle
formed by the grey line intercepting all contours defines the
region where the CPW width L=S+3W. Using this parameter
space and the six substrate materials, the transmission prop-

erties of multiple CPW can be explored to determine an 3

optimal design for sample carrier 114d that minimizes, or at
least reduces, loss in transmission of RF signals to the
specimen.

FIG. 6 shows graphs of simulated S-parameters for trans-
mission (S,,) and reflection (S,,) of electrical power as a
function of electrical signal frequency for various lengths of
a CPW having a source lead width (S) of 400 um and gap
width (W) of 50 um. As shown in FIG. 6, there is a
systematic increase in losses in the $,, parameter as the
length of the CPW increases. Additionally, the frequency
responses become sinusoidal as the length increases. How-
ever, these additional losses due to longer CPW are rela-
tively small. Indeed, since they result in no more than 3%
loss for certain frequencies, they may in general be ignored.

FIG. 7 shows graphs of simulated S-parameters for trans-
mission (S,,) of electrical power as a function of electrical
signal frequency for various lengths of a CPW that has a
source lead width that tapers from 400 jum to 200 jum at a
constant impedance of 50Q (panel a) and at a constant gap
width of 50 jum (panel b), and for various taper widths of the
source lead of the CPW, which has a constant length of 10
mm, at a constant impedance of 50 ohms (panel c) and at a
constant gap width of 50 um (panel d). As suggested by FIG.
7, varying the length of the taper (e.g., effectively varying
the angle of taper) may have a minimal effect on the
scattering pattern for the CPW (having a total length of 10
mm) when impedance is kept constant at 502. However, if
the taper gap is fixed at 50 1m while the conductor tapers,
a more pronounced effect may be observed, as suggested by
panels a and b. However, this effect may have relatively little
impact on the total transmission. For a fixed taper length of
10 mm, the effect of the amount of taper can be seen in

0

0

40

&

0

12

panels c and d for a constant impedance of 502 and a
constant gap width of 50 um, respectively. Varying the end
conductor width produced a much stronger effect that could
lead to upwards of 20% loss.

FIG. 8B is a contour plot of simulated insertion loss (S3,)
of coplanar waveguide structures for six different substrate
materials (¢,=2, 3.8, 3.3, 6.7, 10, 13.1) and for various lead
widths, in particular, conductor widths (S) ranging from
50-600 um in 50 micron increments (12 total S values) for
each of substrate material. The gap widths (W) for each
simulation were chosen such that the resulting CPW had
Z5=50Q, by solving equation (1) for W for each conductor
width (e.g., twelve different S values) and for each substrate
material (e.g., six different e, values). The carrier length was
set at 10 mm long. The substrate thickness (H) was set as
500 jm. The gap width (W) was varied so that there was a
ground trace having a width of G=W between the CPW gap
and the edge of the substrate. As suggested by FIG. 8B,
insertion loss generally increases with increasing ¢,, loss
increases with increasing conductor widths, and loss
increases for CPW structures with low ¢, and small S (and
commensurately small W),

To better understand average performance over the entire
simulated frequency range, an average transmission coefli-
cient S51. ay. Was calculated based on the S,, averaged across
the entire frequency range for each material and for each of
the CPW widths investigated. The relationship between
source lead width S of the CPW, and the frequency-averaged
transmission for the six dielectric materials is shown in FIG.
8C. As suggested by FIG. 8C, large losses may result for
configurations where ¢,=2 and $=50 ym and W=1.6 pm.
FIG. 8C also suggests that increasing the dielectric constant
of the substrate (e.g., going from PTFE to GaAs), generally
increases the average insertion losses for all CPWs with
source lead width (S) greater than 300 jum. For the same
insertion loss, the overall CPW width may be reduced by
using a material with a higher dielectric constant. FIGS.
8A-8C further suggests that an optimal configuration for the
sample carrier 114d may be a dielectric substrate of quartz
substrate, with a source lead of the CPW having a width (S)
of 200 um and a gap width (W) of 19 um.

To experimentally test these results, sample carriers 114d
(ie., RF carrier) according to the configuration of FIG. 5D
were fabricated by laser cutting and mounted to the head
portion 114a of a TEM holder. Using a vector network
analyzer (VNA), the performance of the fabricated RF
carriers 114d were compared against conventional DC bias-
ing sample carriers. The RF carrier 114d and the conven-
tional DC biasing carrier were both formed with gold-coated
copper layer covering a dielectric substrate of FR-4 glass
epoxy. The VNA measured the return loss ($,,) of both
carrier types over a frequency range of 0.1-9 GHz. A
mini-coaxial cable was used to measure the reflected power
(S,,) of the TEM holder without an inserted carrier for each

5 input in order to yield a baseline value for the measurement

setup. Each scan used a 1 kHz intermediate frequency, a
power of 0.1 mW, and was signal averaged over four
measurements. The RF cables connecting the RF power
source with the connectors of the TEM holder inserted in the
TEM system were 2.5 m long,

FIG. 9A shows the results of the experimental comparison
of the RF carrier 114d and the conventional DC biasing
carrier. In the top panel of FIG. 9A, three reflected power
(S,,) loss spectra are shown, corresponding to the 2.5 m RF

cable alone (“Cable”), the TEM holder plus the conventional

DC biasing carrier (“With DC Carrier”), and the complete
assembly of RF cable, TEM holder, and conventional DC


US 11,069,507 B2

15

a computer-readable medium. The steps of a method or
algorithm disclosed herein may be embodied in a processor
executable software module, which may reside on a com-
puter-readable medium. Instructions can be compiled from
source code instructions provided in accordance with a
programming language. The sequence of programmed
instructions and data associated therewith can be stored in a
computer-readable medium (e.g., a non-transitory computer
readable medium), such as a computer memory or storage
device, which can be any suitable memory apparatus, such
as, but not limited to read-only memory (ROM), program-
mable read-only memory (PROM), electrically erasable
programmable read-only memory (EEPROM), random-ac-
cess memory (RAM), flash memory, disk drive, etc.

As used herein, computer-readable media includes both
computer storage media and communication media, includ-
ing any medium that facilitates the transfer of a computer
program from one place to another. Thus, a storage media
may be any available media that may be accessed by a
computer. By way of example, and not limitation, such
computer-readable media may comprise RAM, ROM,
EEPROM, CD-ROM or other optical disk storage, magnetic
disk storage or other magnetic storage devices, or any other
medium that may be used to carry or store desired program
code in the form of instructions or data structures and that
may be accessed by a computer.

Also, any connection is properly termed a computer-
readable medium. For example, if the software is transmitted
from a website, server, or other remote source using a

transmission medium (¢.g., coaxial cable, fiber optic cable, 3

twisted pair, digital subscriber line (DSL), or wireless tech-
nologies such as infrared, radio, and microwave), then the
transmission medium is included in the definition of com-
puter-readable medium. Moreover, the operations of a

method or algorithm may reside as one of (or any combi- 3

nation of) ora set of codes and/or instructions on a machine-
readable medium and/or computer-readable medium, which
may be incorporated into a computer program product.

One of ordinary skill in the art will readily appreciate that
the above description is not exhaustive, and that aspects of
the disclosed subject matter may be implemented other than
as specifically disclosed above. Indeed, embodiments of the
disclosed subject matter can be implemented in hardware
and/or software using any known or later developed sys-
tems, structures, devices, and/or software by those of ordi-
nary skill in the applicable art from the functional descrip-
tion provided herein.

In this application, unless specifically stated otherwise,
the use of the singular includes the plural, and the separate
use of “or” and “and” includes the other, i.e., “and/or.”
Furthermore, use of the terms “including” or “having,” as
well as other forms such as “includes,” “included,” “has,” or
“had,” are intended to have the same effect as “comprising”
and thus should not be understood as limiting.

Any range described herein will be understood to include
the endpoints and all values between the endpoints. When-
ever “substantially,” “approximately,” “essentially,” “near,”
or similar language is used in combination with a specific
value, variations up to and including 10% of that value are
intended, unless explicitly stated otherwise.

It is thus apparent that there is provided, in accordance
with the present disclosure, RF transmission systems,
devices, and methods for in situ transmission electron
microscopy. Many alternatives, modifications, and varia-
tions are enabled by the present disclosure. While specific
examples have been shown and described in detail to
illustrate the application of the principles of the present

S

2

40

&

60

16

invention, it will be understood that the invention may be
embodied otherwise without departing from such principles.
For example, disclosed features may be combined, rear-
ranged, omitted, etc. to produce additional embodiments,
while certain disclosed features may sometimes be used to
advantage without a corresponding use of other features
Accordingly, Applicants intend to embrace all such alterna-
tive, modifications, equivalents, and variations that are
within the spirit and scope of the present invention.

The invention claimed is:

1. A specimen assembly for in situ transmission electron
microscopy (TEM), the specimen assembly comprising:

a sample carrier comprising a dielectric substrate with a
conductive layer that forms a coplanar waveguide
configured to transmit an electrical signal to a specimen
held by the sample carrier, the coplanar waveguide
having a first lead formed by the conductive layer and
a pair of second leads formed by the conductive layer,
the first lead being between the second leads and
spaced from the second leads by respective gaps,

wherein the electrical signal has a frequency between 3
kHz and 300 GHy, inclusive.

2. The specimen assembly of claim 1, wherein the sample
carrier has a recessed portion configured to hold the speci-
men therein, and the first and second leads extend from a
first region distal from the recessed portion to a second
region adjacent to the recessed portion.

3. The specimen assembly of claim 2, wherein a through-
hole is formed within the recessed portion, the through-hole
allowing an electron beam of a transmission electron micro-
scope to pass through the sample carrier.

4. The specimen assembly of claim 2, wherein the first
lead is tapered along at least a portion of its length, such that
a width of the first lead at the first region is greater than a
width of the first lead at the second region.

5. The specimen assembly of claim 4, wherein the tapered
portion is greater than half of an overall length of the first
lead.

6. The specimen assembly of claim 4, wherein each
second lead is tapered along at least a portion of its length,
such that a width of the second lead at the first region is less
than a width of the second lead at the second region.

7. The specimen assembly of claim 2, further comprising
a specimen disposed in the recessed portion, wherein at least
the first lead is electrically coupled to an electrical terminal
of the specimen such that the electrical signal is conveyed
from the sample carrier to the electrical terminal of the
specimen.

8. The specimen assembly of claim 7, wherein the first
lead is electrically coupled to the electrical terminal of the
specimen via a wirebond.

9. The specimen assembly of claim 1, further comprising:

a TEM sample holder comprising:

a head portion with a recess configured to hold the
sample carrier therein;

a back end portion with a radio-frequency (RF) con-
nector, which is configured to connect to an RF
source that generates the electrical signal:

a shaft portion between the head and back end portions;
and

co-axial cabling coupling the RF connector to at least
the first lead,

wherein the back end portion is configured to be disposed
outside a vacuum environment of a transmission elec-
tron microscope, and the head portion is configured to
be disposed inside the vacuum environment of the
transmission electron microscope.


US 11,069,507 B2

U.S. Patent Jul. 20, 2021 Sheet 2 of 8
114d 4144 138
414a
Ne
169 6
Suice
~ s _—
sS 156a 158 tsep 40
BA
_ 1 t
_ 4 {I |
186a qT | \
= qh |
AZ tie ‘\ 442
0 FIG. 4A FIG. 4B 40
414d 144 438
/
114a AL
412 186b
| 488
G 45] G
a TRAY,
TM 156¢ 114d
ia Ez _f,
Da VA
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ee pet t
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156b ji [hy wy lw
a [ tida jf — — 142
150 156 140
1600 FIG. AC sg 158 aay FIG. 4D
~ y il 4112
F i
=| ae
po 4560

Ly

he

160

FIG. 4E


U.S. Patent Jul. 20, 2021 Sheet 1 of 8 US 11,069,507 B2

400 104



US 11,069,507 B2

7

conductors 134 can be electrically coupled to the leads 150
of the sample carrier 114d via soldering, conductive adhe-
sive, wirebonding, mechanical contact, or any other electri-
cal coupling means. At an opposite output end (e.g., proxi-
mal to specimen 112), the one or more leads 150 are coupled
to corresponding terminals on the specimen 112 (e.g., bond
pads or the like) via respective wires, for example, via
soldering, conductive adhesive, wirebonding, or the like.
The leads 150 can be formed from a substantially planar
layer of metal, such as, but not limited, to gold, copper, or
aluminum. Alternatively or additionally, the leads 150 can
be formed from a layer of any conductive material, such as,
but not limited to, a doped semiconductor material or a
superconducting material.

‘The sample carrier 114d and its leads 150 are designed to
transmit electrical signals received from the electrical con-
ductors 134 via connections 132 to the specimen 112, in
particular, signals having a frequency in the RF regime.
However, due to transmission line losses and wavelengths
nearing the feature sizes of the carrier 114d, the signal
transmission properties of the carrier are highly dependent
on its geometry and the layout of the leads. To limit power
losses resulting from the material of the sample carrier 114d,
radiation, and reflections, the sample carrier 114d employs a
coplanar waveguide (CPW) structure.

For example, FIGS. 4A-4B show an exemplary configu-
ration of TEM holder head portion 114a and sample carrier
114d employing a single CPW structure. The sample carrier

114d has a dielectric substrate 155 with a thickness, H. On 3

a surface of the substrate 155 is formed a plurality of
conductive traces (e.g., metal trace), for example, a single
source lead 158 between a pair of ground planes 156a, 1560.
The source lead 158 has a width, S, and is separated from

each ground plane 156a, 1566 by a respective gap having a 3

width, W. An end of the source lead 158 distal from
specimen 112 can be coupled to a conductor 134 extending
through the specimen assembly 114, for example, via wire
160. The other end of the source lead 158 can be coupled to
a terminal 154 of the specimen 112, for example, by wire
bonding of a wire 159 thereto.

For the CPW structure illustrated in FIGS. 4A-4B, the
conductor width (S), the gap width (W), the substrate
thickness (H), and the dielectric constant of the carrier
material (¢,) are related to the characteristic impedance (Z,)
through the following equations:

__30nK(ks)
eat Kiko)

ay

(ep = 1) Ktki) K(k)
2 Ki) Kiko)

Q)

eq = 1+

In equation (1) and (2), e,is the effective dielectric constant
and is dependent on the geometric parameters Ko, k,, and k’,
which are given as:

Ss 3)
saw

sini. =)

ho =

S

40

&

50

3!

60

8
-continued

VI-k.

Finally, K(k) is the complete elliptical integral of the first
kind. Using these equations and the physical constraints of
the sample carrier 114d and specimen assembly 114 gener-
ally, a feasible parameter space can be explored, as discussed
in further detail below.

Although FIGS. 4A-4B illustrate a single CPW structure,
practical embodiments of the disclosed subject matter may
include more than one source lead and pairs of ground
planes. For example, FIGS. 4C-4D illustrate an exemplary
configuration employing a dual CPW structure, where each
source lead 1582, 158d is coupled to a respective terminal
154 of the specimen 112 at one end and coupled to a
respective conductor 134 at the opposite end, for example,
via wires 160a, 1605. In such a configuration, the ground
planes between the adjacent source leads 158a, 1585 may be
shared. For example, the source lead 158a is disposed
between and spaced from ground planes 1562, 1565 by
respective gaps, and the source lead is disposed between and
spaced from ground planes 156b, 156c by respective gaps.
As with the configuration of FIGS. 4A-4B, each source lead

Ss 158a, 158b can have a width S and can be spaced from the

adjacent ground planes 156a-156c by gaps of width W.
Although FIGS. 4A-4D illustrate leads 158 and ground
planes 156 that have a substantially constant width along its
length, it may be advantageous in some embodiments to
have a variable width. For example, a larger width for the
source lead 158 may be desirable at the end distal from the
specimen 112 to assist in coupling to an end of conductor
134 from the shaft portion 1146, whereas a smaller width
may be desirable at the end proximal to the specimen 112 for
optimal transmission of an RF signal. In some embodiments,
the source lead 158 may thus be gradually tapered (e.g.,
linearly tapered) along at least a portion of its length, for
example, as shown in FIG. 4. The gradual tapering may be
effective to minimize or at least reduce any back reflection
of the RF signal transmitted by the source lead 158 while
accommodating the desired different widths of the source
lead 158. The ground planes 156a, 156b may adopt a
complementary shape to the source lead 158 to maintain the
desired width of the gap with the source lead 158. In some

5 embodiments, the length, L,, over which the source lead 158

is tapered is greater than a length, L,, over which the source
lead 158 has a constant width. For example, the tapered
portion can be greater than half of an overall length of the
source lead 158. In some embodiments, the source lead 158
can include a substantially constant first width section at the
end distal from the specimen 112 and a substantially con-
stant second width section at the end proximal to the
specimen 112. A tapered section can extend between and
connect the first width section to the second width section.

Although FIGS. 4A-4E illustrate leads 150 configured as
a coplanar waveguide for RF signal transmission, embodi-
ments of the disclosed subject matter are not limited thereto.
Indeed, other RF/microwave transmission line configura-
tions can also be used according to one or more contem-
plated embodiments. For example, the sample carrier 114d
can employ a grounded coplanar waveguide configuration,
where a monolithic ground plane 164 is disposed on a
backside of substrate 155 and is electrically coupled to
ground planes 156a, 156 on the topside of substrate 155, as

5 shown in FIGS. 4F-4G. The backside ground plane 164 can

be physically connected to the topside ground planes 156a,
156d by one or more vias 162a, 1626 that extend through a


US 11,069,507 B2

13

biasing carrier (“As Measured”). Note that the “With DC
Carrier” results were obtained by subtracting the “Cable”
results from the “As Measured” results. Note that signals
above 0 dB are results of signal averaging artefacts rather
than signal gain. For the middle and bottom panels of FIG.
9A, a high-pass filter was used to remove oscillations and
highlight differences in performance. The measurement pro-
cedure was repeated for the RF carriers 114d and the TEM
holder alone, as shown in the middle panel of FIG. 9A.
Finally, the bottom panel of FIG. 9A was achieved by
subtracting the TEM holder plus RF cable measurements to
yield a more direct comparison of the conventional DC
biasing carrier versus the RF carrier 114d with respect to RF
frequencies.

‘As suggested by the top panel of FIG. 9A, most of the
return losses observed (up to -40 dB at 4 GHz) were due to
the 2.5 m mini-coaxial cable. The middle panel of FIG. 94
shows the return loss with and without carriers inserted into
the TEM holder. As expected, losses increased when any
carrier was inserted into the holder, particularly within the
500 MHz to 3.5 GHz range. However, comparison of the
performance of the DC biasing carrier with the RF carrier
114d in the bottom panel of FIG. 9A indicates that the return
loss is reduced for frequencies above 1 GHz for the RF
carrier 114d. The bottom panel of FIG. 9A also illustrates
how the carriers oscillate between reflecting and absorbing
signals across the 0.5-3.5 GHz band. A positive S, , indicates
that the carrier reflected more signal back to the launch port
than the TEM holder without a carrier installed. A negative

S,, indicates that the carrier absorbed power that would have 3

been reflected by the TEM holder without a carrier installed.

Although the above S,, results provide information about
the losses of each carrier, power transmission (S,,) mea-
surements may provide a more useful characterization of the

carriers. Thus, FIG. 9B provides a graph of transmitted 3

power (S5,) for a conventional DC biasing carrier and for the
RF carrier 114d according to FIG. 5D. To measure the
transmission properties of the carriers, two adjacent leads
were shorted at the through-hole end (e.g., proximal to the
specimen location) for both the conventional DC biasing
carrier and the RF carrier 114d. The TEM holder and carrier
responses were isolated by subtracting the S,, losses for
each cable from the recorded S,, transmission across the
carriers. FIG. 9B shows the transmission loss of the con-
ventional DC biasing carrier (blue series), the transmission
loss of the RF carriers 114d (green series), and the difference
(red series) obtained by subtracting the RF carrier response
from the conventional DC biasing carrier response. Note
that the negative S,, values in the different values corre-
spond to frequencies where the RF carrier 114d transmitted
with less loss than the conventional DC biasing carrier.
As suggested by FIG. 9B, both carrier configurations
show 30 dB loss above 6 GHz, which loss accelerates
rapidly beyond 6 GHz. However, the RF carrier 114d
generally outperformed the conventional DC biasing carrier
over the frequency bands of approximately 0-0.8 GHz,
1.75-3.4 GHz, and 4.8-5.35 GHz, in particular yielding -20
dB, 3 dB, -7 dB, 4 dB, and -2 dB, respectively, for the RF
carrier 114d relative to the conventional DC biasing carrier
when averaged over each of the frequency ranges. Indeed,
the TEM holder with the RF carrier 114d has an average
transmission loss of -13 dB under 6 GHz, while the TEM
holder with conventional DC biasing carrier had a transmis-
sion loss of -16 dB, a percent difference of 33%.
Although the discussion above has focused on excitation
and analysis in the RF regime, embodiments of the disclosed
subject matter may instead be applied to electrical signals

S

2

40

&

14
having a frequency in the microwave regime, for example,
between 300 MHz and 300 GHz, inclusive, or 500 MHz up
to 100 GHz, inclusive. In such embodiments, the RF source
may instead be considered a microwave source, and the RF
signals may instead be considered a microwave signal.

While the discussion above has focused on the use of the
specimen assembly with a transmission electron micro-
scope, embodiments of the disclosed subject matter are not
necessarily limited thereto. Indeed, the disclosed specimen
assembly can be used in other applications where low-loss
transmission of an RF or microwave signal from a source
external to a vacuum environment to a specimen within the
vacuum environment is desired. Such applications can
include, but are not limited to, other electron microscopes
(e.g., scanning electron microscope) or other charged-par-
ticle beam apparatuses in general (e.g., ion beam). In such
alternative applications for the specimen assembly, the
imaging might use transmitted electrons, scattered electrons,
secondary electrons, or any other radiation in response to the
charged-particle interrogation beam and/or RF drive signal

Although particular components and configuration have
been illustrated in the figures and discussed in detail herein,
embodiments of the disclosed subject matter are not limited
thereto. Indeed, one of ordinary skill in the art will readily
appreciate that different components or configurations can
be selected and/or components added to provide the same
effect. In practical implementations, embodiments may
include additional components or other variations beyond
those illustrated, for example, additional focusing elements
along the beam path according to a particular microscope
configuration. Accordingly, embodiments of the disclosed
subject matter are not limited to the particular configurations
specifically illustrated and described herein.

It will be appreciated that the aspects of the disclosed
subject matter, for example, the control system 128, can be
implemented, fully or partially, in hardware, hardware pro-
grammed by software, software instruction stored on a
computer readable medium (e.g., a non-transitory computer
readable medium), or any combination of the above. For
example, components of the disclosed subject matter,
including components such as a control unit, controller,
processor, user interface, or any other feature, can include,
but are not limited to, a personal computer or workstation or
other such computing system that includes a processor,
microprocessor, microcontroller device, or is comprised of
control logic including integrated circuits such as, for
example, an application specific integrated circuit (ASIC).

Features discussed herein can be performed ona single or
distributed processor (single and/or multi-core), by compo-
nents distributed across multiple computers or systems, or
by components co-located in a single processor or system.
For example, aspects of the disclosed subject matter can be
implemented via a programmed general purpose computer,
an integrated circuit device, (e.g., ASIC), a digital signal
processor (DSP), an electronic device programmed with
microcode (e.g., a microprocessor or microcontroller), a
hard-wired electronic or logic circuit, a programmable logic
circuit (¢.g., programmable logic device (PLD), program-
mable logic array (PLA), field-programmable gate array
(EPGA), programmable array logic (PAL)), software stored
on a computer-readable medium or signal, an optical com-
puting device, a networked system of electronic and/or
optical devices, a special purpose computing device, a
semiconductor chip, a software module or object stored on
a computer-readable medium or signal.

When implemented in software, functions may be stored
on or transmitted over as one or more instructions or code on