IEC TS 62607-6-8:2023

Nanomanufacturing - Key control characteristics - Part 6-8: Graphene - Sheet resistance: In-line four-point probe

IEC TS 62607-6-8:2023 establishes a method to determine the key control characteristic sheet resistance RS [measured in ohm per square (Ω/sq)], by the in-line four-point probe method, 4PP.
The sheet resistance RS is derived by measurements of four-terminal electrical resistance performed on four electrodes placed on the surface of the planar sample.
The measurement range for RS of the graphene samples with the method described in this document goes from 10−2 Ω/sq to 104 Ω/sq.
The method is applicable for CVD graphene provided it is transferred to quartz substrates or other insulating materials (quartz, SiO2 on Si, as well as graphene grown from silicon carbide.
The method is complementary to the van der Pauw method (IEC 62607-6-7) for what concerns the measurement of the sheet resistance and can be useful when it is not possible to reliably place contacts on the sample boundary.

General Information

• Status: Published
• Publication Date: 06-Jun-2023
• ICS: 07.120 - Nanotechnologies
• Technical Committee: TC 113 - Nanotechnology for electrotechnical products and systems
• Drafting Committee: WG 8 - TC 113/WG 8
• Current Stage: PPUB - Publication issued
• Start Date: 12-Jul-2023
• Completion Date: 07-Jun-2023

Standards Content (Sample)

IEC TS 62607-6-8
®

Edition 1.0 2023-06
TECHNICAL
SPECIFICATION

colour
inside


Nanomanufacturing – Key control characteristics –
Part 6-8: Graphene – Sheet resistance: In-line four-point probe

IEC TS 62607-6-8:2023-06(en)

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IEC TS 62607-6-8

®


Edition 1.0 2023-06




TECHNICAL



SPECIFICATION








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inside










Nanomanufacturing – Key control characteristics –

Part 6-8: Graphene – Sheet resistance: In-line four-point probe


























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ICS  07.120 ISBN 978-2-8322-7113-1




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® Registered trademark of the International Electrotechnical Commission

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– 2 – IEC TS 62607-6-8:2023  IEC 2023
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
3.1 General terms . 8
3.5 Key control characteristics measured in accordance with this standard . 9
3.6 Terms related to the measurement method . 9
4 General . 10
4.1 Measurement principle . 10
4.2 Sample preparation method . 11
4.3 Description of measurement apparatus . 11
4.4 Ambient conditions during measurement . 11
4.5 Related standards . 12
5 Measurement procedure . 12
5.1 Calibration of measurement equipment . 12
5.2 Detailed protocol of the measurement procedure . 12
5.3 Measurement accuracy . 13
6 Data analysis and interpretation of results . 13
7 Results to be reported . 14
7.1 Cover sheet . 14
7.2 Product and sample identification . 14
7.3 Measurement conditions . 14
7.4 Measurement results . 14
Annex A (informative) Effects of ambient conditions on graphene resistance
measurements . 17
A.1 General . 17
A.2 Temperature (T) . 17
A.3 Relative humidity (RH) . 17
Annex B (normative) More specific cases . 18
B.1 Non-equidistant probes . 18
B.2 Proximity to the edge . 18
B.3 Non-equidistant probes and proximity to the edge . 18
Annex C (informative) Experimental example . 19
C.1 Sample . 19
C.2 Ambient conditions. 19
C.3 Instrumentation . 19
C.4 Sampling plan . 19
C.5 Measurement procedure . 20
C.6 Results . 20
Annex D (informative) Other standards related to the measurement of sheet
resistance . 21
Bibliography . 22

Figure 1 – Schematic representation of the four-point probe method (left) and detail of
the structure of a spring-mounted probe (right) . 11

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IEC TS 62607-6-8:2023  IEC 2023 – 3 –
Figure 2 – Schematic representation of a possible measurement location . 12
Figure 3 – Schematic view of possible sample plans for a) circular and b) square
substrates . 15
Figure C.1 – Sampling plan used for the present example. 20

Table 1 – Example of measurable values for R , and the corresponding measurement
S
settings and type-B uncertainty, when using a current source Keithley 2602B System
SourceMeter® and a Nano Volt / Micro Ohm Meter (1y calibration specifications) . 13
Table 2 – Sampling plan for circular substrates . 15
Table 3 – Results of R measured in accordance with this document . 16
S
Table C.1 – Measured values for V and R (p) using the described procedure and
S
equipment . 20

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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

NANOMANUFACTURING –
KEY CONTROL CHARACTERISTICS –

Part 6-8: Graphene – Sheet resistance: In-line four-point probe

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
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the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC TS 62607-6-8 has been prepared by IEC technical committee 113: Nanotechnology for
electrotechnical products and systems. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
113/678/DTS 113/745/RVDTS

Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.

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IEC TS 62607-6-8:2023  IEC 2023 – 5 –
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts of the IEC TS 62607 series, published under the general title
Nanomanufacturing – Key control characteristics, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

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– 6 – IEC TS 62607-6-8:2023  IEC 2023
INTRODUCTION
Graphene is a single layer of carbon atoms arranged in a honeycomb lattice. Graphene has
shown many outstanding properties, among which is a high electrical conductivity. Nowadays
2 2
graphene can be easily grown and transferred on large area (cm to even m ) and even
roll-to-roll supports using chemical vapour deposition (CVD) techniques. This is already
enabling its commercial applications in electrotechnical products.
Electrical conductivity of graphene samples can depend on many factors: structural quality,
contamination, coupling with the physical support used for a given application to name a few.
On practical grounds, the sheet resistance, R , is a quantity which can be used as global
S
measure of the local conductivity of a sample with finite geometrical dimensions. In order to
check the reproducibility of the electrical properties of graphene, the sheet resistance is clearly
a key control characteristic for this material.
The in-line four-point probe method (4PP) allows the measurement of the sheet resistance of
samples of arbitrary shape, with isotropic conductivity and uniform carrier density by performing
four-terminal resistance measurements with electrical contact provided by a commercially
available dedicated tool. The method is fast (it takes a few minutes) and easy to implement,
since many commercial fixtures are available.
The four-terminal resistance measurements approach allows to minimize the effect of the
contact resistance that appears between graphene and the measurement probes.
The 4PP method provides a certain degree of spatial resolution in principle, depending on the
sampling plan adopted to map the sample area.
In this document it is explained how to specifically apply the 4PP method on chemical vapour
deposited graphene on rigid insulating support and perform a reliable estimation of the sample
KCC sheet resistance, R , also considering the non-ideal nature of commercial graphene.
S

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IEC TS 62607-6-8:2023  IEC 2023 – 7 –
NANOMANUFACTURING –
KEY CONTROL CHARACTERISTICS –

Part 6-8: Graphene – Sheet resistance: In-line four-point probe



1 Scope
This part of IEC TS 62607 establishes a method to determine the key control characteristic
• sheet resistance R [measured in ohm per square (Ω/sq)],
S
by the
• in-line four-point probe method, 4PP.
The sheet resistance R is derived by measurements of four-terminal electrical resistance
S
performed on four electrodes placed on the surface of the planar sample.
• The measurement range for R of the graphene samples with the method described in this
S
−2 4
document goes from 10 Ω/sq to 10 Ω/sq.
• The method is applicable for CVD graphene provided it is transferred to quartz substrates
or other insulating materials (quartz, SiO on Si, as well as graphene grown from silicon
2
carbide.
• The method is complementary to the van der Pauw method (IEC 62607-6-7) for what
concerns the measurement of the sheet resistance and can be useful when it is not possible
to reliably place contacts on the sample boundary.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

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– 8 – IEC TS 62607-6-8:2023  IEC 2023
3.1 General terms
3.1.1
graphene
graphene layer
single-layer graphene
monolayer graphene
single layer of carbon atoms with each atom bound to three neighbours in a honeycomb
structure
Note 1 to entry: It is an important building block of many carbon nano-objects.
Note 2 to entry: As graphene is a single layer, it is also sometimes called monolayer graphene or single-layer
graphene and abbreviated as 1LG to distinguish it from bilayer graphene (2LG) and few-layer graphene (FLG).
Note 3 to entry: Graphene has edges and can have defects and grain boundaries where the bonding is disrupted.
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.1]
3.1.2
bilayer graphene
2LG
two-dimensional material consisting of two well-defined stacked graphene layers
Note 1 to entry: If the stacking registry is known, it can be specified separately, for example, as "Bernal stacked
bilayer graphene".
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.6]
3.1.3
few-layer graphene
FLG
two-dimensional material consisting of three to ten well-defined stacked graphene layers
[SOURCE: ISO/TS 80004-13:2017, 3.1.2.10]
3.2
key control characteristic
KCC
product characteristic which can affect safety or compliance with regulations, fit, function,
performance, quality, reliability or subsequent processing of the final product
Note 1 to entry: The measurement of a key control characteristic is described in a standardized measurement
procedure with known accuracy and precision.
Note 2 to entry: It is possible to define more than one measurement method for a key control characteristic if the
correlation of the results is well-defined and known.
[SOURCE IEC TS 62565-1:2023, 3.1]

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IEC TS 62607-6-8:2023  IEC 2023 – 9 –
3.3
blank detail specification
BDS
structured generic specification providing a comprehensive set of key control characteristics
which are needed to describe a specific product without assigning specific values or attributes
Note 1 to entry: Examples of nano-enabled products are: nanocomposites and nano-subassemblies.
Note 2 to entry: Blank detail specifications are intended to be used by industrial users to prepare their detail
specifications used in bilateral procurement contracts. A blank detail specification facilitates the comparison and
benchmarking of different materials. Furthermore, a standardized format makes procurement more efficient and more
error robust.
[SOURCE IEC TS 62565-1:2023, 3.2]
3.4
detail specification
DS
specification based on a blank detail specification with assigned values and attributes
Note 1 to entry: The characteristics listed in the detail specification are usually a subset of the key control
characteristics listed in the relevant blank detail specification. The industrial partners define only those
characteristics which are required for the intended application.
Note 2 to entry: Detail specifications are defined by the industrial partners. Standards development organizations
will be involved only if there is a general need for a detail specification in an industrial sector.
Note 3 to entry: The industrial partners may define additional key control characteristics if they are not listed in the
blank detail specification.
[SOURCE IEC TS 62565-1:2023, 3.3]
3.5 Key control characteristics measured in accordance with this standard
3.5.1
sheet resistance
R
S
electrical resistance of a conductor with a square shape (width equal to length) and thickness
significantly smaller than the lateral dimensions (thickness much less than width and length)
Note 1 to entry: There is no definition of the unit ohm per square (Ω/sq) in the International System of units (SI).
Nevertheless, R is a normalized quantity, in which the symbol represents the SI ohm. So there is no ambiguity
S
to the SI, provided the measurements are performed with
concerning the traceability of measurements of R
S
calibrated instrumentation.
[SOURCE: IEC TS 61836:2007, 3.4.79, modified – The entry has been adapted to this
document.]
3.6 Terms related to the measurement method
3.6.1
four-point probe method
4PP
method to measure electrical sheet resistance of thin films that uses separate pairs of current-
carrying and voltage-sensing electrodes
Note 1 to entry: The method is local with a characteristic length scale defined by the probe distance, and generally
requires the resistivity variations to be on a much larger scale than the probe spacing. Depending on the positions
of the sample-probe contact of the four probe contacts with the surface, different geometrical factors must be used
to extract the sheet resistance.
[SOURCE: ISO/TS 80004-13:2017, 3.3.3.1, modified – The entry has been adapted to this
document.]

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– 10 – IEC TS 62607-6-8:2023  IEC 2023
3.6.2
in-line four-point probe method
type of four-point probe measurement where four-point electrodes are aligned in a row
Note 1 to entry: In this method, four probes contact the test sample in a linear arrangement. A voltage drop is
measured between the two inner probes while a current source supplies current through the outer probes.
Note 2 to entry: The distance between the probes needs to be small compared to the lateral dimensions of the
sample so that edge effects on the electric field in the sample can be neglected.
Note 3 to entry: The resistance of the sample can be calculated by Ohm's law. Geometrical factors can be used for
corrections if the sample is too small or if the measurement is performed close to the edges of the sample.
[SOURCE: IEC TS 62607-6-9:2022, 3.2.3, modified – Note 2 to entry has been deleted.]
3.6.3
van der Pauw method
vdP
type of four probe measurement for samples of arbitrary shape
Note 1 to entry: The van der Pauw method requires four probes placed arbitrarily around the perimeter of the
sample, in contrast to the linear four-point probe which is placed on the top of the sample.
Note 2 to entry: The van der Pauw method provides an average sheet resistivity of the sample.
[SOURCE: IEC TS 62607-6-9:2022, 3.2.4, modified – Notes 1 and 4 to entry have been
deleted.]
4 General
4.1 Measurement principle
The 4PP method consists in placing four probes evenly spaced in a straight line on the sample
1
to be measured. For ideal conditions no geometrical information is needed to measure R [1] .
S
To achieve this the sample should be a 2D infinite layer, i.e. i) the distance between probes, s,
should be ideally negligible compared to the dimensions of the sample and ii) the distance x
between the probes and the sample edge should be large compared to s. To retrieve R , a
S
current I is applied through the two external probes and the voltage V is measured between the
internal probe pair. The measured I and V quantities are then used to calculate the sheet
resistance using a formula. In practice, this formula can contain corrections, depending on, for
example, sample dimensions, inter-probe distance, distance between the probes and the
sample edge. Additional considerations for non-equidistant probes are given in Annex B.
___________
1
 Numbers in square brackets refer to the bibliography.

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IEC TS 62607-6-8:2023  IEC 2023 – 11 –

Figure 1 – Schematic representation of the four-point probe method (left) and
detail of the structure of a spring-mounted probe (right)
4.2 Sample preparation method
The sample is measured as it is delivered by the supplier. No special sample preparation is
required. The substrate supporting the graphene layer should be planar and insulating to
prevent any contribution of the volume resistivity of the substrate. The sample shall be stored
at the ambient conditions of 4.4 prior to the measurements.
4.3 Description of measurement apparatus
Figure 1 shows a schematic representation of the 4PP measurement setup, consisting of the
4PP tool (in contact with the sample), a current source and a voltmeter.
The measurement instrumentation necessary to carry out measurements with the in-line four-
point probe method consists of a current source and a voltmeter. The source and measurement
range of the instrumentation, for measuring monolayer CVD graphene, should be of 1 µA to
1 mA for the current source and 1 mV to 1 V for the voltmeter, considering typical five- or
six-digit commercial instruments.
A sample holder fitted with four needle spring-mounted probes is necessary to accommodate
and contact the sample. The probes shall have a very limited lateral swing in order not to scratch
the graphene sample when placed in contact. The outer contacts are used to inject the current
while the inner contacts are used to probe the resulting voltage (commercial 4PP are already
configured this way). If a custom fixture is used, the insulation resistance between the contacts
10
shall be the highest possible, and at least of the order of 10 Ω.
Point probes shall have internal springs to keep appropriate contact. An example of the internal
structure around the probe pin is shown in Figure 1. Resistance is measured by pushing the
probe in the direction of the arrow. A spring is installed in the root of the probe pin, and the
force applied to the pin shall be controlled by an appropriate choice of the components or the
commercial fixture.
4.4 Ambient conditions during measurement
Being a carbon monolayer, graphene electrical properties can be strongly affected by ambient
conditions with strong variations induced by specific sample characteristics due to the growth
process (see Annex A for details).
In order to obtain results which can be reasonably compared with other measurements
performed in accordance with this document, the required ambient conditions are
T = (23 ± 1) °C, RH = (50 ± 4) %.

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– 12 – IEC TS 62607-6-8:2023  IEC 2023
4.5 Related standards
Annex D includes a list of related standards published by other standards development
organizations.
5 Measurement procedure
5.1 Calibration of measurement equipment
The current source and the voltmeter shall be calibrated and within the specified calibration
period.
5.2 Detailed protocol of the measurement procedure
A detailed example of the application of this procedure is given in Annex C.
Turn on the equipment for the time indicated in manuals before using it. Instrumenta
...