Semiconductor devices - Flexible and stretchable semiconductor devices - Part 5: Test method for thermal characteristics of flexible materials

IEC 62951-5:2019 specifies the test method for thermal characteristics of flexible materials. This document includes terms, definitions, symbols, and test methods that can be used to evaluate and determine thermal characteristics of flexible materials for practical use. The measurement method relies on non-contact optical thermometry that is based on temperature dependent optical reflectance. This document is applicable to both substrate and thin-film flexible semiconductor materials that are subjected to bending and stretching.

Dispositifs à semiconducteurs - Dispositifs à semiconducteurs souples et extensibles - Partie 5 : Méthode d’essai pour les caractéristiques thermiques des matériaux souples

L’IEC 62951-5:2019 spécifie la méthode d’essai pour les caractéristiques thermiques des matériaux souples. Le présent document inclut les termes, définitions, symboles et méthodes d’essai pouvant être utilisés pour évaluer et déterminer les caractéristiques thermiques des matériaux souples, dans le contexte d’une utilisation pratique. La méthode de mesure s’appuie sur la thermométrie optique sans contact, qui est elle-même basée sur le facteur de réflexion optique, qui dépend de la température. Le présent document s’applique aux semiconducteurs souples en substrat et en couche mince, qui sont soumis à des contraintes de courbure et d’étirement.

General Information

Status
Published
Publication Date
26-Feb-2019
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
27-Feb-2019
Ref Project

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IEC 62951-5
Edition 1.0 2019-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Semiconductor devices – Flexible and stretchable semiconductor devices –
Part 5: Test method for thermal characteristics of flexible materials
Dispositifs à semiconducteurs – Dispositifs à semiconducteurs souples et
extensibles –
Partie 5: Méthode d’essai pour les caractéristiques thermiques des matériaux
souples
IEC 62951-5:2019-02(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 62951-5
Edition 1.0 2019-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Semiconductor devices – Flexible and stretchable semiconductor devices –
Part 5: Test method for thermal characteristics of flexible materials
Dispositifs à semiconducteurs – Dispositifs à semiconducteurs souples et
extensibles –
Partie 5: Méthode d’essai pour les caractéristiques thermiques des matériaux
souples
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.080.99 ISBN 978-2-8322-6611-3

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 62951-5:2019 © IEC 2019
CONTENTS

FOREWORD ........................................................................................................................... 3

1 Scope .............................................................................................................................. 5

2 Normative references ...................................................................................................... 5

3 Terms and definitions ...................................................................................................... 5

4 Testing method ................................................................................................................ 6

4.1 General ................................................................................................................... 6

4.2 Test apparatus ........................................................................................................ 7

4.3 Test procedures .................................................................................................... 13

4.3.1 General ......................................................................................................... 13

4.3.2 Substrate specimen ....................................................................................... 13

4.3.3 Thin-film specimen ........................................................................................ 14

4.4 Report of results ................................................................................................... 14

Annex A (informative) Example of 3D design of thermoreflectance thermometry .................. 15

Bibliography .......................................................................................................................... 16

Figure 1 – Thermoreflectance signals of substrate and thin-film materials as functions

of temperature ........................................................................................................................ 7

Figure 2 – Reflectance vs. temperature of silicon thin-films (thicknesses of 1,62 µm,

1,64 µm, and 1,67 µm) for the wavelength of 633 nm .............................................................. 7

Figure 3 – Schematic of thermoreflectance thermometry with one laser source that is

used for calibration ................................................................................................................. 8

Figure 4 – Schematic of thermoreflectance thermometry with one laser source that is

used for measurement ............................................................................................................ 9

Figure 5 – Schematic of thermoreflectance thermometry with two lasers of different

wavelengths used for calibration ........................................................................................... 10

Figure 6 – Schematic of thermoreflectance thermometry with two lasers of different

wavelengths used for measurement ...................................................................................... 11

Figure 7 – Optical reflectance of a silicon thin-film (1,526 µm) at 532 nm and 633 nm

as a function of temperature ................................................................................................. 12

Figure 8 – Reflectance ratio of a silicon thin-film as a function of temperature

(λ = 633 nm and λ = 532 nm) ............................................................................................. 12

1 2
Figure 9 – Suspended bending or uniaxial stretching of flexible or stretchable

semiconductor materials ....................................................................................................... 13

Figure A.1 – 3D design of dual wavelength thermoreflectance setup ..................................... 15

---------------------- Page: 4 ----------------------
IEC 62951-5:2019 © IEC 2019 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SEMICONDUCTOR DEVICES –
FLEXIBLE AND STRETCHABLE SEMICONDUCTOR DEVICES –
Part 5: Test method for thermal characteristics of flexible materials
FOREWORD

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International Standard IEC 62951-5 has been prepared by IEC technical committee 47:

Semiconductor devices.
The text of this International Standard is based on the following documents:
FDIS Report on voting
47/2534/FDIS 47/2543/RVD

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 62951 series, published under the general title Semiconductor

devices – Flexible and stretchable semiconductor devices, can be found on the IEC website.

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– 4 – IEC 62951-5:2019 © IEC 2019

The committee has decided that the contents of this document will remain unchanged until the

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the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

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understanding of its contents. Users should therefore print this document using a

colour printer.
---------------------- Page: 6 ----------------------
IEC 62951-5:2019 © IEC 2019 – 5 –
SEMICONDUCTOR DEVICES –
FLEXIBLE AND STRETCHABLE SEMICONDUCTOR DEVICES –
Part 5: Test method for thermal characteristics of flexible materials
1 Scope

This part of IEC 62951 specifies the test method for thermal characteristics of flexible

materials. This document includes terms, definitions, symbols, and test methods that can be

used to evaluate and determine thermal characteristics of flexible materials for practical use.

The measurement method relies on non-contact optical thermometry that is based on

temperature dependent optical reflectance. This document is applicable to both substrate and

thin-film flexible semiconductor materials that are subjected to bending and stretching.

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
3.1
reflectance

ratio of the reflected optical power to the incident optical power at a given wavelength and

temperature for a given surface of materials

Note 1 to entry: Reflectance can be defined as the ratio between reflected and incident radiant or luminous flux.

[SOURCE: IEC 60050-845:1987, 845-04-58, modified – temperature dependence of optical

reflectance is added.]
3.2
thermoreflectance
temperature dependent optical reflectance of a given surface of materials
Note 1 to entry: Thermoreflectance has nothing to do with thermal reflectance.
3.3
local temperature
loc
temperature at a local position in a spatially distributed device or system
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– 6 – IEC 62951-5:2019 © IEC 2019
3.4
average temperature
avg
temperature within a substrate averaged over an area of interest at a given time
(1)
where
n is the total number of measurement point
T (i) is the local temperature at the i measurement point
loc
3.5
initial temperature
local or average temperatures when the sample is about to be powered on (t = 0)
3.6
final temperature

local or average temperatures when the sample is about to be powered off (t = t )

3.7
thermal time constant

time taken to reach 63,2 % of the difference between the initial and the final temperatures

3.8
substrate

materials that are more than 20 times thick of the wavelength of the probing laser

Note 1 to entry: For 633 nm, the thickness criterion to determine the substrate materials is larger than

approximately 12,7 µm.
3.9
thin-film

materials that are less than 20 times thick of the wavelength of the probing laser

Note 1 to entry: For 633 nm, the thickness criterion to determine the thin-film materials is less than approximately

12,7 µm.
4 Testing method
4.1 General

Thermoreflectance is one of non-contact optical thermal characterization techniques that

relies on the change of refractive index of materials as a function of temperature. Depending

on their thickness, flexible semiconductor materials can be categorized as either substrate or

thin-film. For substrate materials, their optical reflectance values change linearly with

temperature. However, optical reflectance values of thin-film materials show highly non-linear

behaviours as shown in Figure 1. For thin-films, non-linear optical reflectance is also strongly

dependent on the sample thickness as shown in Figure 2. Such a non-linearity requires

reflectance measurements at multiple wavelengths. Once optical reflectance values at one or

more wavelengths are calibrated at various temperatures, thermal characterization is enabled.

---------------------- Page: 8 ----------------------
IEC 62951-5:2019 © IEC 2019 – 7 –
Key
1 Substrate
2 Thin-film
Figure 1 – Thermoreflectance signals of substrate and
thin-film materials as functions of temperature
Figure 2 – Reflectance vs. temperature of silicon thin-films (thicknesses of
1,62 µm, 1,64 µm, and 1,67 µm) for the wavelength of 633 nm
4.2 Test apparatus

In case of substrate materials, thermoreflectance signals at a given wavelength tend to

change linearly with increasing temperature. Thin-film materials, however, exhibit highly non-

linear thermoreflectance behaviours as temperature increases. Therefore, single wavelength

optical probing is necessary and sufficient for substrate flexible semiconductor materials and

at least dual wavelength probing is required for thin-film materials. Thermoreflectance ratio at

different wavelengths is still non-linear with temperature but can provide an acceptable match

with the theoretical estimation and more precise temperature measurements. Figure 3 and

Figure 4 show schematics of thermoreflectance thermometry with one laser source used for

calibration and measurement (for example, wavelength, λ = 633 nm herein but other

wavelength can be used), respectively. For calibration, heating or cooling blocks with fixed

temperature are used. The substrate is joule heated with DC or AC (simple periodic sine)

power supplies for actual measurements.
---------------------- Page: 9 ----------------------
– 8 – IEC 62951-5:2019 © IEC 2019
Key
1 Goniometer 2 Motorized xy stages
3 Fixed stage 4 Motorized linear stage
5 Cold temperature block 6 Hot temperature block
7 Objective lens 8 Halogen lamp
9 Multimeter 10 CCD
11 Variable terminal 12 Silicon detector
13 Laser

NOTE The wavelength of the laser, λ, is 633 nm for this example but other wavelength can be used.

Figure 3 – Schematic of thermoreflectance thermometry with
one laser source that is used for calibration
---------------------- Page: 10 ----------------------
IEC 62951-5:2019 © IEC 2019 – 9 –
Key
1 Goniometer 2 Motorized xy stages
3 Fixed stage 4 Motorized linear stage
5 DC or AC power supply 6 Objective lens
7 Halogen lamp 8 Multimeter
9 CCD 10 Variable terminal
11 Silicon detector 12 Laser

NOTE The wavelength of the laser, λ , is 633 nm for this example but other wavelength can be used.

Figure 4 – Schematic of thermoreflectance thermometry with one laser source
that is used for measurement

Figure 5 and Figure 6 show schematics of thermoreflectance thermometry with two lasers of

different wavelengths that are well suited for thin-film materials but can be generally

applicable to substrate materials. Three dimensional design of the dual wavelength

thermoreflectance setup is also shown in Annex A. For calibration, heating or cooling blocks

with fixed temperature are used. The substrate is joule heated with DC or AC (simple periodic

sine) power supplies for actual measurements.

For tight focusing (or smaller focal spots), lasers in setups shown in Figures 3, 4, 5 and 6 are

expanded by a beam expander and focused onto a sample under test using a microscope

objective lens attached to a turret. The focal spot ( d ) is determined by
2 fλ
d =
(2)
---------------------- Page: 11 ----------------------
– 10 – IEC 62951-5:2019 © IEC 2019

where, is the focal length of the lens, is the beam diameter at the lens entrance, and

f D

λ is the wavelength. Typically, 5x expansion is sufficient. The reflected light travels

backwards and is guided towards a silicon photodetector. The photocurrent generated in the

silicon detector is converted into a voltage via a variable terminal or a transimpedance

amplifier and measured with a digital multimeter or a lock-in amplifier.
Key
1 Goniometer 2 Motorized xy stages
3 Fixed stage 4 Motorized linear stage
5 Cold temperature block 6 Hot temperature block
7 Objective lens 8 Halogen lamp
9 Multimeter 10 CCD
11 Variable terminal 12 Silicon detector
13 Low or high pass filter 14 Laser 1
15 Laser 2

NOTE The wavelengths of the laser 1 and laser 2, λ and λ , are 633 nm and 532 nm for this example but other

1 2
wavelengths can be used.
Figure 5 – Schematic of thermoreflectance thermometry with two lasers of
different wavelengths used for calibration
---------------------- Page: 12 ----------------------
IEC 62951-5:2019 © IEC 2019 – 11 –
Key
1 Goniometer 2 Motorized xy stages
3 Fixed stage 4 Motorized linear stage
5 DC or AC power supply 6 Objective lens
7 Halogen lamp 8 Multimeter
9 CCD 10 Variable terminal
11 Silicon detector 12 Low or high pass filter
13 Laser 1 14 Laser 2

NOTE The wavelengths of the laser 1 and laser 2, λ and λ , are 633 nm and 532 nm for this example but other

1 2
wavelengths can be used.
Figure 6 – Schematic of thermoreflectance thermometry with two lasers of
different wavelengths used for measurement

A sample specimen is mounted between two blocks with constant temperature which are

located on a fixed jig and a motorized linear stage, respectively. In general, the temperature

blocks are running during calibration (reflectance vs. temperature at a given wavelength).

Figure 7 shows typical results with a silicon thin-film during calibration where wavelength

dependent non-linear behaviours can be seen. By taking the reflectance ratio as shown in

Figure 8, a calibration curve for a thin-film can be obtained. The thickness of each thin-film

sample is not necessarily measured.
---------------------- Page: 13 ----------------------
– 12 – IEC 62951-5:2019 © IEC 2019

Figure 7 – Optical reflectance of a silicon thin-film (1,526 µm) at 532 nm and 633 nm

as a function of temperature
Figure 8 – Reflectance ratio of a silicon thin-film as a function of temperature
(λ = 633 nm and λ = 532 nm)
1 2

For actual measurements, the sample specimen is joule-heated by using either DC or AC

(simple periodic sine) powers in general. For highly resistive samples, heating methods other

than joule heating shall be used. As shown in Figure 9, the single-axis motorized stage

enables either bending or stretching for flexible or stretchable semiconductor materials, the

dual-axis (xy) motorized stages are used for sample scanning for obtaining an average

temperature, and the goniometer rotates the sample to maintain normal incidence of the

probing laser.
---------------------- Page: 14 ----------------------
IEC 62951-5:2019 © IEC 2019 – 13 –
Figure 9 – Suspended bending or uniaxial stretching of flexible or
stretchable semiconductor materials
4.3 Test procedures
4.3.1 General
The test procedure is as follows:

Determine whether the specimen is substrate or thin-film by measuring reflectance as a

function of temperature varying within a range of user’s interest using the setup shown in

Figure 3. The specimen is mounted on two temperature blocks. To minimize the interface

thermal resistance, a thermal paste is gently and uniformly applied to the contact area. If the

result is linear, the specimen can be regarded as a substrate. If not, it shall be treated as a

thin-film.
4.3.2 Substrate specimen
The test procedure for substrate specimen is as follows.

a) Use the result obtained during the determination of substrate or thin-film specimen as a

calibration plot.

b) Configure the substrate specimen as shown in Figure 4. The thermal paste is gently and

uniformly applied to contact areas.

c) Deform the specimen to result in a finite bending or stretching. Then, power up the sample

specimen with a DC supply and wait a while for the specimen to reach a steady-state

temperature.

d) Obtain local temperatures by measuring optical reflectance at discrete points of interest

and using the calibration plot. Use the goniometer to maintain the normal incidence of the

probing laser.

e) Obtain an average temperature by measuring optical reflectance within an area of interest,

obtaining local temperatures with the aid of calibration plot, and calculating the mean

value. Use the goniometer to maintain the normal incidence of the probing laser.

f) Power up the sample specimen with an AC supply (simple periodic sine). Make sure that

the digital multimeter connected to the silicon detector through the variable terminal is

synchronized with the AC supply.
---------------------- Page: 15 ----------------------
– 14 – IEC 62951-5:2019 © IEC 2019

g) Take reflectance measurements with a time interval (Δt) that is typically equal to or shorter

than 1/500 of the pulse duration. Draw a reflectance vs. time plot and convert it to a

temperature vs. time plot. To obtain the thermal time constant τ, fit the temperature vs.

time plot with
(3)
where T and T are initial and final temperatures, respectively.
i f
h) Unload the sample after any deformation is removed.
4.3.3 Thin-film specimen
The test procedure for thin-film specimen is as follows.

a) Measure reflectance at the midpoint of the suspended sample specimen as a function of

temperature varying within a range of user’s interest at two wavelengths (λ and λ )

1 2

using the setup shown in Figure 5. The local temperature at the midpoint is the average of

the hot and cold temperature blocks. Draw the calibration plot that is the reflectance ratio

( ) vs. temperature graph.

b) Configure the thin-film specimen as shown in Figure 6. The thermal paste is gently and

uniformly applied to contact areas.

c) Deform the specimen to result in a finite bending or stretching. Then, power up the sample

specimen with a DC supply and wait a while for the specimen to reach a steady-state

temperature.

d) Obtain local temperatures by measuring the reflectance ratio at discrete points of interest

and using the calibration plot. Use the goniometer to maintain the normal incidence of the

probing laser.

e) Obtain an average temperature by measuring the reflectance ratio within an area of

interest, obtaining local temperatures with the aid of calibration plot, and calculating the

mean value. Use the goniometer to maintain the normal incidence of the probing laser.

f) Power up the sample specimen with an AC supply (simple periodic sine). Make sure that

the digital multimeter connected to the silicon detector through the variable terminal is

synchronized with the AC supply.

g) Take reflectance measurements at two wavelengths with a time interval (Δt) that is

typically equal to or shorter than 1/500 of the pulse duration. Obtain the reflectance ratio

vs. time plot and convert it to the temperature vs. time plot. To obtain the thermal time

constant τ, fit the temperature vs. time plot with Formula (3).
h) Unload the sample after any deformation is removed.
4.4 Report of results
The report shall include the following items:
a) specimen identification;
b) date of test;
c) atmospheric conditions
...

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