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8/12/2019 Biobarrier Harlin Al2o3johansson
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Atomic Layer Deposition Process for Barrier Applications of Flexible Packaging
Petri Johansson, Kimmo Lahtinen and Jurkka Kuusipalo
Tampere University of Technology, Paper Converting and Packaging Technology (TUT/PCT)
Tommi Kriinen, Philipp Maydannik and David Cameron
Lappeenranta University of Technology, Advanced Surface Technology Research Laboratory (LUT/ASTRaL)
ABSTRACT
Atomic layer deposition (ALD) is a process where thin films of material are deposited in a controlled manner one
atomic layer at a time. The main advantages of ALD are the extreme degree of conformality and uniformity which
can be obtained regardless of the orientation or shape of the substrate; there are no pinholes in the film. The abilityto do roll-to-roll coating would open huge possibilities for the technique, because barrier layers are required to avoid
the diffusion of water or oxygen through polymer or paper webs for example in the food packaging industry.
According to barrier test results, the aluminum oxide coating provided by the ALD batch process improved the
oxygen and water vapor barrier as a function of coating thickness by a large amount. As an oxygen barrier, a thin 10
nm coating is already able to obtain ten times lower transmission levels than the uncoated structure. As a watervapor barrier, the thickness of the polymer layer becomes practically meaningless once the thickness of the ALD
layer increases above 40 nm. With over 100 nm thickness, the water vapor transmission rates of the structures were
reduced below the level of 1 g/m2/24h (23C, 50% RH). These results encourage the continuation of investigations
towards roll-to-roll solutions of ALD processing.
INTRODUCTION
The purpose of atomic layer deposition (ALD) process is to produce a thin, gas-tight and stable coating from
gaseous precursors. ALD is based on chemical reactions on the surface of a substrate. Precursors are fed to thereaction chamber, including the substrate, one at the time such that the substrate is exposed to only one precursor ata time. The molecules are attached to the substrate as a monolayer via covalent bonding. After the reaction is
finished and the surface is saturated with attached precursor molecules, the excess gas and reaction products are
removed from the chamber by flushing the space with an inert gas such as nitrogen. A typical ALD cycle consists of
four stages. The cycle starts by introducing the first precursor into the chamber which is flushed in the second stage.
Then, another precursor is fed in and flushed, completing the four stages. After the complete reaction cycle, one
atomic layer of desired coating is chemically bonded to the substrate surface. Figure 1 shows the principles of theALD reaction cycle. /1,4/
The actual ALD coating consists of several reaction cycles. One reaction cycle is able to achieve about 0.1 nm layer
thickness depending on the coating material and process parameters. The thickness of a typical ALD coating is
determined by the number of cycles and varies roughly from 1 to 100 nm. Temperature in the chamber can varyfrom room temperature to several hundreds of degrees Celsius. The role of temperature is to provide activation
energy for the ALD process (thermal ALD). The reaction can also be activated using plasma (plasma assisted ALD).
Plasma-assisted ALD provides lower cycle periods and process temperatures for the system than thermal ALD. /1-
3/
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Fig. 1. Principles of ALD reaction cycle /4/.
It is possible to use ALD to deposit a range of different materials. These include e.g. oxides, nitrides and carbides
/1/. In addition, it is possible to produce nanolaminates using different materials in atom-thick layers one after
another. ALD is particularly applicable to substrates with different shapes, even 3D, because thickness variations ofALD coatings are very low since the coating thickness is controlled by a self-limiting reaction at the surface.
Because of the chemical bonding the adhesion with the substrate is commonly excellent. The oxide precursors havebeen reported to adhere to most kinds of polymers even if they lack typical chemical functional groups such as
hydroxyl (-OH) species. /3,5/
Batch atomic layer deposition process
ALD processing techniques can be divided in two categories regarding substrate handling: batch and continuous
processes. The batch process is a traditional technique in which the substrate to be coated remains stationary and the
precursors are pulsed in turn onto the surface of the substrate. The actual coating process occurs in a modularchamber which is filled with substrates In a chamber the substrates can be located close to each other because the
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In the literature, significant barrier properties have been reported for Al2O3layers deposited on polymer surfaces by
the ALD method /6-8/. According to Groner et al. /6/, WVTR values as low as 1*10-3g/m2/24h have been achieved
for very thin (10-25 nm) Al2O3films. The purpose of this study was to investigate the applicability of such ALD
layers for flexible packaging. Batch ALD equipment was used to provide Al2O3coatings on LDPE, PP, PET and
PLA extrusion-coated papers. The WVTRs and O2TRs of the produced materials were tested in order tocharacterize the barrier properties obtained. The results of this study are employed as trend-setters for the futurestudies concerning continuous ALD process.
MATERIALS AND METHODS
The materials to be tested in the study were paper/polymer/Al2O3structures in which the polymer layer wasdeposited by extrusion coating and the aluminum oxide in a batch ALD process. The extrusion coating trials were
performed at the pilot line of TUT/PCT. Four extrusion coating polymers were chosen for the study: LDPE
(CA7230, Borealis), PP (WF420HMS, Borealis), PET (Lighter C98, Equipolymers) and PLA (test grade). The aimwas to select polymers with significant scatter in heat resistance, transport and surface properties. The PLA coating
brought also the aspect of biodegradable polymer into the study. Table 1 shows selected thermal and physicalproperties of the used polymers.
Table 1. Selected thermal and physical properties of the polymers used in the study /9-11/.TmC
TgC
WVTR (38C, 90% RH)
g/m2/24h
O2TR (23C, 0% RH)
cm3/m
2/24h
LDPE 109 -110 17 9400
PP 163 -18 10 4000
PET 247 78 69 150
PLA 150 - 165 55-65 290 660
*Barrier values measured for 25 g/m2extrusion-coated paper
The LDPE-coated paper samples were produced with three different coating weights: 18, 27 and 36 g/m2. With the
other polymers, only one coating weight was performed:25 g/m2. A one-side mineral-coated paper, Lumiflex 90
from Stora Enso, was used as a substrate. The non-pigmented side of the paper was extrusion-coated. Beforehand,
the substrate was pre-treated with corona discharge equipment (2 kW) in order to obtain good adhesion with the
polymer.
The batch ALD equipment shown in Figure 2 (Beneq TFS 500 operated by LUT/ASTRaL) was used to producealuminum oxide (Al2O3) coatings on polymer surfaces. The thicknesses of the layers were 10-200 nm measured by
spectroscopic ellipsometry from Silicon (100) reference samples placed in the same deposition batch.
Trimethylaluminum (TMA) and ozone (O3) were used as precursors for the coatings. All the coatings were produced
in thermal ALD processes having different reactor temperatures (65, 100 or 150C). One deposition cycle consistedof a 250 ms TMA pulse, 6 s purge, 3 s ozone pulse and 6 s purge. The deposition started with 40 s ozone pulse and
90 s purge.
The water vapor transmission rate (WVTR) measurements of the study were made according to SCAN P22:68 (cup
method) In the method a sample is placed against an aluminum dish containing calcium chloride The sample is
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The oxygen transmission rate (O2TR) measurements of the study were performed with Mocon Ox-Tran Model 2/21
according to a standard ASTM D 3985. In the performed test series, the coated side of the sample was sealed against
a test cell using vacuum grease, thus the paper side was facing oxygen during measurements. The active test area
was 50 cm2. 10% oxygen was used as a test gas. The O2TR measurements were made at 23C, 0% RH conditions.
Both WVTR and O2TR results tabulated in the diagrams of this paper are mean values of two parallelmeasurements.
RESULTS AND DISCUSSION
Al2O3layers deposited on LDPE- and PP-coated paper
In a preliminary test, thin Al2O3layers were deposited on the surface of LDPE-coated papers. A low reactor
temperature (65C) was used for the depositions because of the low melting point of LDPE. 120, 350 and 600 cycles
provided approximately 10, 25 and 40 nm Al2O3coatings, respectively. With three LDPE coating weights (18, 27and 36 g/m2) and three ALD layer thicknesses, nine different structures were obtained from the depositions. Figures
4 and 5 show the WVTR (38C, 90% RH) and O2TR (23C, 0% RH) results measured for the structures. The resultsare compared to the reference values measured for the corresponding structures without an Al2O3layer.
0
4
8
12
16
20
24
28
LDPE 18 g/m2 LDPE 27 g/m2 LDPE 36 g/m2
WVTR(g/m2/24h)
Paper / LDPE / Al2O3 (T = 65 C)
Refer.
10 nm
25 nm
40 nm
Fig. 4. WVTR (38C, 90% RH) results for paper/LDPE/Al2O3structures having 10-40 nm Al2O3layer.
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0
2000
4000
6000
8000
10000
12000
14000
LDPE 18 g/m2 LDPE 27 g/m2 LDPE 36 g/m2
O2TR
(cm3/m2/24h)
Paper / LDPE / Al2O3 (T = 65 C)
Refer.
10 nm
25 nm
40 nm
Fig. 5. O2TR (23C, 0% RH) results for paper/LDPE/Al2O3structures having 10-40 nm Al2O3layer.
According to the results, a thin 10 nm ALD coating is already able to obtain considerably improved oxygen barrier
properties for the structure. Concerning water vapor barrier, the decrease of the transmission level is not as dramatic.
Polyethylene, being a good moisture barrier itself, provides already an efficient moisture block which is only
moderately improved by the ALD coating. Nonetheless, the WVTR levels are still considerably decreased and thebarrier effect of the polymer becomes almost meaningless with 40 nm Al2O3layer.
In order to obtain further barrier improvements, thicker A12O3coatings were produced in the study. By performing
more ALD cycles, coatings with thicknesses between 100 and 200 nm were deposited on LDPE- and PP-coatedpapers. This time, the WVTRs were measured in two atmospheric conditions (23C, 50% RH and 38C, 90% RH) in
order to characterize the influence of climatic conditions on the results. The O2TRs were again measured at 23C,
0% RH. The results of the WVTR and O2TR tests are shown in Figures 6 and 7. The thicknesses of the LDPE and
PP layers in the structures were approximately 25 g/m2.
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LDPE LDPE + 100 nm PP PP + 130 nm
23C, 50% R H 4,55 0,39 4,24 0,29
38C, 90% R H 16,74 2,56 10,48 1,94
0
1
2
3
4
56
7
8
9
10
11
12
13
14
15
16
17
WVTR(g/m2/24h)
Paper / Polymer / Al2O3 (T = 65 C)
Fig. 6. WVTR (23C, 50% RH and 38C, 90% RH) results for paper/polymer/Al2O3structures having 100 nmAl2O3layer.
LDPE LDPE + 100 nm PP PP + 130 nm
23 C, 0 % RH 9400 590 4000 230
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
O
2TR(cm3/m2/24h)
Paper / Polymer / Al2O3 (T = 65 C)
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Influence of reactor temperature on the barrier performance
In general, the thermal ALD process produces more controlled ALD layers when using higher reactor temperature
/1/. The influence of reactor temperature on the moisture barrier properties was tested by using two temperatures, 65and 100C, for the Al2O3deposition. PP-coated paper was used as a substrate in the test due to the PPs suitablemelting temperature. The results obtained from the WVTR test are shown in Figure 8.
reference130 nm / 1200
cycles, 65 C,
130 nm / 1660
cycles, 65 C,
80 nm / 1200
cycles, 100 C,
90 nm / 1660
cycles, 100 C,
23 C, 50 % RH 4,24 0,29 0,22 0,59 0,48
38 C, 90 % RH 10,48 1,94 2,69 3,54 4,02
0
1
2
3
4
5
6
7
8
9
10
11
WVTR(g/m2/24h)
Paper / PP / Al2O3
Fig. 8. Influence of reactor temperature and ALD layer thickness on WVTR of PP-coated paper.
According to the results, the use of higher reactor temperature leads to a thinner Al2O3coating and, thus, higherWVTR value. In other words, the higher deposition speed achieved with low reactor temperature (65C) produces
better barrier properties for the structure with an equal number of ALD cycles. This was also observed from the
O2TR results. The higher film growth rate at lower deposition temperature is a well known behavior for this type of
ALD processes /4,12,13/. The phenomenon can be explained through incomplete chemical reactions during the ALD
cycles leading to a higher concentration of compounds formed by hydrocarbons in the film. In result, the lower
reactor temperature used seems to have an advantage over the higher ones regarding the barrier properties of the
obtained structure, even if a perfectly controlled ALD process is not achieved in the reactor.
Al2O3layers deposited on PET- and PLA-coated paper
In addition to LDPE and PP, the ALD coatings were deposited on PET- and PLA-coated paper substrates. The ALDcoatings were again made at 65C temperature except for the two test points with paper/PET/Al2O3structure that
were made at 150C. Figure 9 shows the WVTR results obtained for the paper/PET/Al2O3structures made at 65 and
150C temperatures. According to the results, the increased reactor temperature increased also the WVTR of the
t i l th ith PP Th f th 65C t t t b id d ti l t
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reference
120 nm /
1200 cycles
65 C
190 nm /
1660 cycles
65 C
80 nm / 1200
cycles 150 C
90 nm / 1660
cycles 150 C
23 C, 50 % RH 19 0,1 0,6 6 5,1
38 C, 90 % RH 69 0,8 5,6 21 17
0
10
20
30
40
50
60
70
WV
TR(g/m2/24h)
Paper / PET (27 g/m2) / Al2O3
Fig. 9. WVTR (23C, 50% RH and 38C, 90% RH) results for paper/PET/Al 2O3structures.
reference65 C, 1200
cycles
65 C, 1660
cycles
150 C, 1200
cycles
150 C, 1660
cycles
23 C, 0 % RH 150 2 0,9 2000 2000
0
20
40
60
80
100
120
140
160
180
200
O2TR(cm3/m2/
24h)
Paper / PET (27 g/m2) / Al2O3
Fig. 10. O2TR (23C, 0% RH) results for paper/PET/Al2O3structures.
Figure 10 shows the O2TR results for the paper/PET/Al2O3structures. Remarkable oxygen barrier improvements
were found for the structures when using 65C reactor temperature. The O 2TR values found were significantly lowerthan the ones achieved with the other polymers. However, with the 150C ALD process the oxygen barrier of the
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reference 65 nm / 600 cycles110 nm / 1200
cycles
23 C, 50 % RH 72 3,9 4,1
38 C, 90 % RH 290 55 53
0
50
100
150
200
250
300
WVTR(g/m2/24h)
Paper / PLA (25 g/m2) / Al2
O3
(T = 65 C)
Fig. 11. WVTR (23C, 50% RH and 38C, 90% RH) results for paper/PLA/Al 2O3structures.
reference65 nm / 600
cycles
110 nm / 1200
cycles
200 nm / 1660
cycles23 C, 0 % RH 660 94 53 12
0
100
200
300
400
500
600
700
O2TR(cm3/m2/2
4h)
Paper / PLA (25 g/m2) / Al2O3 (T = 65 C)
Fig. 12. O2TR (23C, 0% RH) results for paper/PLA/Al2O3structures.
CONCLUSIONS
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LDPE ref PP ref PET ref PLA ref LDPE + ALD PP + ALD PET + ALD PLA + ALD
23 C, 50 % RH 4,6 4,2 19 72 0,4 0,3 0,1 4,1
38 C, 90 % RH 17 10 69 290 2,6 1,9 0,8 53
0
10
20
30
40
50
60
70
80
WVTR(g/m
2/24h)
Paper / Polymer / Al2O3 (T = 65 C) [Ref. and 1200 cycles]
Fig. 13. Comparison between the WVTR results.
1000
1500
2000
2500
3000
3500
4000
4500
5000
O2TR(cm3/
m2/24h)
Paper / Polymer / Al2O3 (T=65 C) [Ref. and 1200 cycles]
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ACKNOWLEDGEMENTS
The financial supports of the Finnish Funding Agency of Technology and Innovation (TEKES), Stora Enso Oyj,UPM-Kymmene Oyj and Savcor Face Group Oy are gratefully acknowledged.
REFERENCE
1. Ritala M and Leskel M. Atomic Layer Deposition. In: Nalwa (ed) Handbook of thin film material, Vol. 1.
Deposition and processing of thin films. Stanford Scientific Corporation. USA, 2002.
2. Sneck S. High Capacity Atomic Layer Deposition for Industrial Coating Applications. SVC 50th
AnnualTechnical Conference Proceedings. April 28- May 3, 2007. Louisville, KY.
3. Groner M, Fabreguette F, Elam J and George S. Low-Temperature Al2O3Atomic Layer Deposition. Chemistryof Materials 16, 4 (2004).
4. Puurunen R. Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water
process. Journal of Applied Physics 97, 12 (2005).
5. Ferguson J, Weimer A and George S. Atomic Layer Deposition of Al2O3on Polyethylene Particles. Chemistry
of Materials 16, 26 (2004).
6. Groner M, George S, McLean R and Carcia P. Gas diffusion barriers on polymers using Al2O3atomic layer
deposition. Applied Physics Letters 88, 051907 (2006).
7. Carcia P, McLean R, Reilly M, Groner M and George S. Ca test of Al2O3gas diffusion barriers grown by atomic
layer deposition on polymers. Applied Physics Letters 89, 031915 (2006).
8. Langereis E, Creatore M, Heil S, van de Sanden M and Kessels W. Plasma-assisted atomic layer deposition of
Al2O3moisture permeation barriers on polymers. Applied Physics Letters 89, 081915 (2006).
9. Borealis. Polyolefins for Extrusion Coating, 2ndEd. Austria, 2008.
10. Equipolymers. Lighter C98. Product Data Sheet. July 2004.
11. Callister Jr, W. Chapter 16 in: Materials Science and Engineering, An Introduction, 5thEd. John Wiley & Sons,
Inc. New York, NY, 2000.
12. Matero R, Rahtu A, Ritala M, Leskel M and Sajavaara T. Effect of water dose on the atomic layer depositionrate of oxide thin films. Thin Solid Films 368, 1 (2000).
13. Elliot S, Scarel C, Wiemer C, Fanciulli M and Pavia G. Ozone-Based Atomic Layer Deposition of Alumina
from TMA: Growth, Morphology, and Reaction Mechanisms. Chemistry of Materials 18, 16 (2006).
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Atomic Layer Deposition Processfor Barrier Applications of
Flexible Packaging
Presented by:Petri JohanssonTampere University of Technology
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IntroductionIntroduction
The purpose of atomic layer deposition (ALD)process is to produce a thin, tight and stablecoating from gaseous precursors.
The main advantage of ALD is the conformalityand uniformity which can be obtained
regardless of the orientation or shape of thesubstrate. I.e., there are no pinholes in thefilm.
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IntroductionIntroduction
In ALD process, thin films of material aredeposited one atomic layer at a time.
.
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IntroductionIntroduction
exhaust
pump
precursor A precursor B
movement gas leakageweb
purge purge
L
One possible solution of continuous ALD
Roll-to-roll ALD would open huge possibilities. Itwould allow all the flexibility and surface control
capabilities of ALD to a large scale production.
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IntroductionIntroduction
The ALD coating consists of several reactioncycles. One reaction cycle is able to achieveabout 0.1 nm layer depending on the coatingmaterial and process parameters. Thickness of
a typical ALD layer can vary from 1 to over 100nm.
The role of temperature in the ALD process isto provide activation energy. The reactortemperature can vary from room temperature
to several hundreds of degrees Celsius.
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MaterialsMaterials and methodsand methods
The materials tested in the study werepaper/polymer/Al
2
O3
structures.
Polymer layer via extrusion coating
Al2O3 layer in a batch ALD process
4 extrusion coating polymers were used in the
study: LDPE, PP PET and PLA.
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MaterialsMaterials and methodsand methods
Trimethylaluminum (TMA) and ozone (O3) wereused as precursors for the Al
2
O3
-coatings.
All the coatings were produced in thermal ALDprocesses having different reactor
temperatures of 65, 100 or 150 C. One deposition cycle consisted of a 250 ms
TMA pulse, 6 s purge, 3 s ozone pulse and 6 spurge. The deposition started with 40 s ozonepulse and 90 s purge.
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MaterialsMaterials and methodsand methods
The barrier properties against water vapor andoxygen were measured for the obtainedmaterials.
The water vapor transmission rate (WVTR)
measurements were made according to SCANP22:68 (cup method).
2 atmospheric conditions (normal and tropical)were used in the WVTR -measurements:
23 C, 50 % RH and 38 C, 90 % RH.
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MaterialsMaterials and methodsand methods
The oxygen transmission rate (O2TR)measurements were made according to astandard ASTM D 3985.
The active test area was 50 cm2 ,10 % oxygen
was used as a test gas and the measurementswere made at 23 C, 0 % RH conditions.
Each WVTR and O2TR result shown in thediagrams is a mean value of two replicates.
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ResultsResults and discussionand discussion
Al2O3 layers deposited on LDPE-coated paper
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ResultsResults and discussionand discussion
Al2O3 layers deposited on LDPE-coated paper
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ResultsResults and discussionand discussion
Al2O3 layers deposited on LDPE- and PP-coated paper
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ResultsResults and discussionand discussion
The influence of reactor temperature
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ResultsResults and discussionand discussion
Al2O3 layers deposited on PET-coated paper
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ResultsResults and discussionand discussion
Al2O3 layers deposited on PET-coated paper
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ResultsResults and discussionand discussion
Al2O3 layers deposited on PLA-coated paper
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ResultsResults and discussionand discussion
Al2O3 layers deposited on PLA-coated paper
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ConclusionsConclusions
Comparison between the WVTR results
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ConclusionsConclusions
Comparison between the O2TR results
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AcknowledgementsAcknowledgements
We wish to thank:
TEKES, Stora Enso, UPM-Kymmene and Savcorfor financial support.
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Thank you
Presented by:
Petri JohanssonResearcher
Tampere University of