IEC TR 62715-5-61:2024

IEC TR 62715-5-61 ®
Edition 1.0 2024-08
TECHNICAL
REPORT
colour
inside
Flexible displays –
Part 5-61: Overview of measurement and application scenarios of stretchable
displays
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IEC TR 62715-5-61 ®
Edition 1.0 2024-08
TECHNICAL
REPORT
colour
inside
Flexible displays –
Part 5-61: Overview of measurement and application scenarios of stretchable

displays
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120  ISBN 978-2-8322-9517-5

– 2 – IEC TR 62715-5-61:2024 © IEC 2024
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Stretchable devices technology . 6
4.1 General . 6
4.2 Stretchable device structure . 7
4.3 Classification of stretching types . 7
4.3.1 General . 7
4.3.2 One-axis stretching . 7
4.3.3 Bi-axis stretching . 8
4.3.4 Multi-curvature stretching . 8
4.3.5 Others . 8
4.4 Application scenarios of stretchable displays . 9
4.4.1 General . 9
4.4.2 Dynamic applications . 9
4.4.3 Static applications . 9
5 Considerations for development of measurement methods . 10
5.1 General . 10
5.2 Two-dimensional stretchability . 10
5.3 Controlled generation of three-dimensional stretching . 11
5.4 Examples of three-dimensional stretchability . 12
5.4.1 General . 12
5.4.2 Three-dimensional stretchability measures based on length ratio. 12
5.4.3 Three-dimensional stretchability measures based on area ratio . 14
5.4.4 Performance evaluation of three-dimensional stretchability measures . 15
5.5 Luminance and colour measurement from three-dimensional surface . 18
Bibliography . 22

Figure 1 – Pixel structure of a stretchable display . 7
Figure 2 – One-axis stretching display device . 7
Figure 3 – Bi-axis stretching display device . 8
Figure 4 – Multi-curvature stretching display device . 8
Figure 5 – Twisting display device . 8
Figure 6 – Example of dynamic display applications . 9
Figure 7 – Example of stretchable display for wearable application [3] . 9
Figure 8 – Example of stretchable display for centre fascia application . 10
Figure 9 – An example to generate 3D dimensional stretching (sphere with fixture
guide) . 11
Figure 10 – Schematic cross-sectional view to explain 3D stretchability measures . 13
Figure 11 – Performance comparison of length ratio–based measures . 17
Figure 12 – Performance comparison of area ratio–based measures . 18
Figure 13 – Example luminance sensitivity to LMD focus offset . 19

Figure 14 – Example of 2D luminance intensity map with moiré pattern at best focus . 20
Figure 15 – Example of imaging LMD luminance sensitivity to LMD focus offset . 20
Figure 16 – Example of 2D luminance intensity map with LMD offset by 1 cm from best
focus. 21

Table 1 – Different configurations of controlled stretching (all numbers in mm) . 17

– 4 – IEC TR 62715-5-61:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FLEXIBLE DISPLAYS –
Part 5-61: Overview of measurement and
application scenarios of stretchable displays

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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shall not be held responsible for identifying any or all such patent rights.
IEC TR 62715-5-61 has been prepared by IEC technical committee 110 Electronic displays. It
is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
110/1647/DTR 110/1668/RVDTR
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 Report is English.

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 in the IEC 62715 series, published under the general title Flexible displays,
can be found on the IEC website.
Future documents in this series will carry the new general title as cited above. Titles of existing
documents in this series will be updated at the time of the next edition.
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, or
• revised.
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– 6 – IEC TR 62715-5-61:2024 © IEC 2024
FLEXIBLE DISPLAYS –
Part 5-61: Overview of measurement and
application scenarios of stretchable displays

1 Scope
This part of IEC 62715, which is a Technical Report, provides an overview of stretchable display
technologies and application scenarios for stretchable displays. This document introduces
special considerations for development of measurement methods for stretchable displays.
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 terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
stretchable display device
flexible display panel and module whose surface area and shape can change when stretched
3.2
stretchable display
device to which a stretchable display panel or module is applied
3.3
stretchability
extent to which stretchable display device can be stretched
4 Stretchable devices technology
4.1 General
Various types of flexible displays have been introduced to the market [1] to [8] . They include
foldable, rollable and slidable types. Recently, development of a new type of flexible display
has been reported by academic societies as well as display industries. It is a stretchable display
device. Unlike previous flexible display technologies, the size of the surface area can be
changed. Furthermore, stretchable displays can have shapes with multi-curvatures in any
direction. Thus, stretchable displays are often called freeform displays.
___________
Numbers in square brackets refer to the Bibliography.

4.2 Stretchable device structure
Figure 1 a) illustrates an example of the pixel structure of a stretchable display with island-
bridge structure. The black square in the upper left corner of Figure 1 a) represents a single
pixel. Figure 1 b) illustrates an enlarged image of the black square in Figure 1 a). A pixel
consists of rigid and stretchable areas. In Figure 1 b) a pixel area is represented by four sub-
areas. The upper left area represents the rigid area. It can be called a light emitting region
because light emitting devices, for example light emitting diodes (LEDs) (including mini LED
and micro LED) and organic light emitting diodes (OLEDs), are placed at the rigid area. This
area usually remains unchanged during stretching. The remaining three sub-areas in Figure 1
b) can be stretched when external force is applied.

a) Pixel structure b) Enlarged image of white box in a)

Figure 1 – Pixel structure of a stretchable display
4.3 Classification of stretching types
4.3.1 General
There are numerous ways to change the area and shape of a stretchable display. However,
types of stretching can be grouped according to the stretching direction and shape.
4.3.2 One-axis stretching
A stretchable display device stretched in single axis is called a "one-axis stretching" display
device. Figure 2 illustrates typical stretchable display devices in "one-axis stretching".

a) Flat type b) Fixed curvature type

Figure 2 – One-axis stretching display device

– 8 – IEC TR 62715-5-61:2024 © IEC 2024
4.3.3 Bi-axis stretching
A stretchable display device stretched by two axis is called a "bi-axis stretching" display device.
Figure 3 illustrates the common style of a "bi-axis stretching" display device.

Figure 3 – Bi-axis stretching display device
4.3.4 Multi-curvature stretching
A stretchable display device stretched with more than one curvature is called a "multi-curvature
stretching" display device. Figure 4 shows the common style of this kind of stretchable display
device, which has two different curvatures.

Figure 4 – Multi-curvature stretching display device
4.3.5 Others
A stretchable display device could be twisted in any direction. Figure 5 shows an example of a
twisting display device.
Figure 5 – Twisting display device

4.4 Application scenarios of stretchable displays
4.4.1 General
Due to their free-form characteristics, stretchable display devices are expected to be used in a
wide variety of applications. Therefore, it will be a difficult task to predict or enumerate all user
application scenarios of stretchable display devices. However, depending on whether the
stretchable display is used only in a stretched state or not, it can be divided into a static and
dynamic applications.
4.4.2 Dynamic applications
A study reported in 2017 that the 9,1-inch stretchable display was stretched to convex/concave
shapes [6]. Figure 6 schematically illustrates the stretchable display with three different levels
of convex shape change.
Figure 6 – Example of dynamic display applications
Stretchable display devices are suitable for wearable applications as illustrated in Figure 7 [3].
The surface of stretchable display devices can be uneven or can be twisted.

Figure 7 – Example of stretchable display for wearable application [3]
4.4.3 Static applications
Mobility applications are a key area where stretchable display devices can be used. Figure 8
conceptually illustrates how stretchable display devices can be utilized in the centre fascia of
an automobile.
– 10 – IEC TR 62715-5-61:2024 © IEC 2024

Figure 8 – Example of stretchable display for centre fascia application
5 Considerations for development of measurement methods
5.1 General
The aim of this document is to identify critical measurement issues that are of importance for
the development of the measurement standards of stretchable displays. This document focuses
on the special considerations for the measurement unique to the stretchable displays.
Stretchability is a major performance factor of stretchable display devices. Especially, the
measurement of stretchability in three-dimensional stretching has not yet been formally defined.
In addition, measurements of luminance and colour from three-dimensional surface have not
been defined.
In addition, it is worthwhile to mention the following requirements of optical measurement
standards for displays.
• measurements can be made by the panel makers, set makers, testing agencies or consumer
organizations by utilizing publicly available information;
• methods should be repeatable, and results can be identically reproducible;
• use of special (and very expensive) measuring devices can be undesirable.
5.2 Two-dimensional stretchability
Two-dimensional stretchability can be measured using an area ratio or length ratio. However,
measurement of the elongation ratio has been widely utilized for two-dimensional stretching of
stretchable display devices both in industry and academic communities. It is defined using a
ratio in length as follows:
 L 
as
ε % −×1 100 %
( ) ( ) (1)
 
2DLeng
L
 bs 
where
ε is the stretched ratio,
L is the length after stretching,
as
L is the length before stretching.
bs
=
Before and after the maximum stretching, the length of the stretchable display device is
measured in the direction of the stretching. Manufacturers can declare the maximum stretching
capability that satisfies the pre-determined durability conditions. It is desirable to standardize
the durability conditions in future as an IEC standard, for example, IEC 62715-6-6x. The
advantage of the elongation ratio is that the calculation is simple and measurement method is
well established.
5.3 Controlled generation of three-dimensional stretching
3D stretchability is determined based on the measurements before and after 3D stretching.
Thus, 3D stretchability depends on the types of 3D stretching applied to the stretchable displays.
However, there are numerous ways to change the shape of a stretchable display by 3D
stretching. This is why a unified and controlled way to create 3D stretching will first be agreed
to. Furthermore, the first and second requirements specified in 5.1 will be reflected in designing
a controlled generation of 3D stretching. In addition, the durability conditions will be specified
(in the future by an IEC standard, for example, IEC 62715-6-6x) based on the same controlled
generation of 3D stretching.
Figure 9 illustrates an example to generate a controlled 3D stretching. Figure 9 represents a
cross-sectional view. An external object to generate a three-dimensional stretching is a sphere
attached a to cylinder in Figure 9. It is assumed that the sphere is moved upward by an electric
motor as shown in the right side of Figure 9. A fixture guide sits on the top of the stretchable
display and remains unchanged during the generation of three-dimensional stretching. it is a
thin but rigid plate with a circular opening. However, it is represented as two separated
rectangles in the cross-sectional view of Figure 9. The fixture guide serves to limit the range of
three-dimensional stretching. The diameter of the circular hole of fixture guide is bigger than
the diameter of the sphere object to generate three-dimensional stretching. The half of
difference in diameters of the circular hole of fixture guide and that of the sphere object can be
called as a gap between the fixture guide and sphere. The use of a fixture guide is optional.
When fixture guides are not utilized, the shape of three-dimensional stretching appears less
steep. In addition, the durability of the deformed panel can be affected by the shape of the
fixture guide and the size of the gap between the fixture gu
...