Building Ac i e Ma ix By Addi i e Manu ac u ing (BAMBAM)
H.Leb un, C.Lincheneau, E.Fuchs (Aledia);A. Wia owska, D. Swide ek (XTPL); A. Ve suypens, S. Rammeloo, P. Willem (Ba co) ; N.
F uehau ; H. Bau (USTUTT) ; W. Wal a ens, I.Nakonechnyi, K. De Nol (Qus omDo ) ; J.B own, M. Mei l (XDisplay); A. Fecio u,
D.Gomez (X-Celep in )
Abs ac
The o e all objec i e o he BAMBAM p ojec is o
demons a e he easibili y o an ac i e-ma ix µLED display
wi hou TFT on glass consis ing. I will ep esen an ad anced
in lexible display solu ion, ha ing p omise o imp o ed
b igh ness, powe consump ion, and obus ness ela i e o
o he lexible displays. The p ojec will esul in key
echnologies o he g owing lexible µLED indus y, which
will open doo s o a display indus y in Eu ope and o i
wi hin ci cula economy p inciples.
Au ho Keywo ds
Mic oled, Ac i e Ma ix, Display, Flexible, Mass T ans e ,
P in ing, Addi i e Manu ac u ing, Pixel, D i e , µIC.
1. Display manu ac u ing s anda ds
In s anda d displays ( o sma phone, IT, TV) based on
O ganic Ligh Emi ing Diodes (OLEDs) (Figu e 1), all he
ac i e elemen s, p o iding he cu en o he emissi e elemen s
in pixels, a e manu ac u ed oge he by successi e coa ings
and s uc u ing by pho oli hog aphy o hin ilm laye s o build
an ac i e ma ix o hin ilm ansis o s (TFT) on huge glass
subs a es.
Figu e 1: P inciple o an OLED display
The TFT echnology induces high ma ke ba ie o any en an
and has a emendous ene gy consump ion. In he case o
TFT/LCD, OLED o TFT/µLED, he TFT ac i e ma ix is
made on e y la ge glass subs a es, up o 10m², wi h a 2 o
4µm esolu ion limi and a he cos o expensi e
semiconduc o ac o ies wi h he size o se e al socce ields
and mainly loca ed in Asia.
These ac o ies ha e a e y high elec ical ene gy consump ion
(≈500MWh/y ./ ac o y) (1). They a e no a sus ainable
solu ion o an o e all educ ion o humani y's ecological
ene gy- ela ed oo p in . And ollowing China’s 20B$/yea
in es men in se e al new ac o ies since 2017, each
p oduc ion line, equi ing an in es men o a ew billion eu os,
his manu ac u ing and en i onmen al oo p in will con inue.
Besides, his huge igu e p e en s any newcome om
en e ing he ma ke unless i is ully inancially suppo ed by
local go e nmen s. I is hus e y di icul o Eu ope o e-
en e his ma ke wi hou a echnical dis up ion.
O he d awbacks o he hin ilm laye -based echnologies on
glass a e he a he high inpu impedance o he me al coa ings
ha a e used o he cu en supplies o he pixels and he e y
limi ed a ailabili y o h ough glass ias (TGV). Though
h ough-glass ias a e being de eloped (2), hey a e e y
expensi e o display echnologies (3) hence p e en ing any
di ec con ac om he ea side o he glass o he cen e o he
display a ea and any oppo uni y o op imize he ol age d op
on he powe supplies.
When ope a ing he display, each emissi e pixel is d i en by a
small elec ical cu en . On glass, conside ing he lack o TGV,
his cu en can only be supplied om he edges o he display
a ea. Then, conside ing he impedance o he me al laye s,
om he edges o he display a ea o he cen al pixel elemen ,
he e can be a signi ican d op in he powe supply ol ages o
he LED due he joule e ec . To compensa e o he ol age-
d op on he powe bus lines, he designe mus inc ease he
powe supply ol age, leading o e y signi ican inc ease in
powe consump ion.
Fo OLED and LCD, he e is a need o a seal ing o p o ec
he liquid c ys al o he OLED om mois u e o oxygen. I
adds ano he cons ain on he pe iphe y o he display as
shown on Figu e 2. I is impossible o design a seamless
display on glass. La ge ideo walls made o assembled LCD
o OLED panels a e always showing a iny bu isible da k
a ea be ween each single display elemen . Thus, la ge OLED
o LCD displays ha e o be manu ac u ed on single pieces o
glass which bo h limi s he display a ea o ex ends he mo he
glass size hus he ac o y cos .
Figu e 2: Edge o a LCD o an OLED panel
2. Display oppo uni y wi h µLEDs
A new display echnology is eme ging. The p inciple o his
echnology is o ha e a µLED a each pixel o he pic u e. On
he o he end, µLEDs (Figu e 3) a e manu ac u ed on a
sepa a e subs a e and cu in o single elemen s which a e hen
ans e ed on he display subs a e.
Figu e 3: P inciple o a µLED display
Such high- esolu ion displays equi e ans e ing e y small
LEDs down o a size o 15µm o less, o educe µLED display
cos s which mos ly dependen on µLED sizes and quan i y.
µLED a e no g own on he same subs a e as hei con ol
elec onics. P in ed ci cui boa ds (PCB), igid o lexible, a e
made o successi e lamina ion o insula ing laye and a he
hick me al laye s. They o e in e es ing solu ions as a
backplane on which o assemble he µLED. Compa ed o
glass, many me al laye s wi h e y low esis i i y and h ough
PCB ias a e a ailable. They enable low impedance and easy
ans e o any equipo en ial o he ea ace o he panel. Thus,
hey o e solu ions o se e al issues he displays on glass a e
acing. They also o e , wi h same o e en be e design ules,
he oppo uni y o ha e lexible panels. Flexible TFT displays
a e on polyimide o on ul a- hin glass a e complex o
manu ac u e, wi h lowe yield and he e o e signi ican ly mo e
expensi e.
Wi h LEDs on PCB, as shown on Figu e 4 , since h ough PCB
ias a e a ailable i is possible o pu each display elemen nex
o each o he wi hin a pixel pi ch. LEDs on PCB he e o e
d ama ically imp o e he isual expe ience (uni o m pixels, no
edge be ween panels) while emendously educing ene gy
consump ion a he same ime.
Figu e 4: PCB iling o la ge displays
Being able o assemble LED displays on PCB o lex oils o
build bigge displays wi h he e y agg essi e pixel pi ch
enabled by he mic o p in ing solu ion pa es he way o a new
e a in he consume elec onics wo ld.
3. The BAMBAM p ojec : making ac i e
µLED p in ing on lexible oil possible.
All displays on glass, LCDs, and OLEDs, use hin ilm
ansis o s (TFT) o con ol he amoun o ligh emi ed by each
pixel. When mo ing om glass o PCB subs a es, he TFTs
a e no a ailable anymo e. To cope wi h his issue and o o e
e en mo e unc ionali ies in each pixel, ALEDIA has been
de eloping he concep o he ac i e µLED pixel, o Sma
PIXEL. Each LED is physically a ached o a d i ing ci cui
on CMOS in a wa e - o-wa e p ocess p io o he ans e on
he display su ace. This is possible due o ALEDIA’s pa en ed
p ocess o g ow LED nanowi e GaN di ec ly on silicon,
making he wa e - o-wa e p ocess indus ially easible. I is
indeed much mo e di icul o assemble wo di e en ma e ials
in a wa e - o-wa e p ocess while i is e y common o ha e
2D LED on sapphi e and a CMOS ci cui on silicon. ALEDIA
can he e o e p opose ac i e µLED pixel elemen s ha do no
equi e he use o TFTs on glass.
Fo s anda d OLED displays, he cos o he display is di ec ly
ela ed o he su ace o he displaying a ea: he cos o he
ac i e ma ix on glass and OLED is almos he same o 65”
ull HD and a 65” 4K. Fo a µLED displays he cos o he
display is de ined by he quan i y o µLEDS and he size o
each µLED ( he smalle he μLEDs, he mo e can be
manu ac u ed om a single wa e , he cheape hey a e). Thus,
a i s glance, he cos o he LEDs o a 65" 4K TV display
will be 4 imes he cos o he LEDs o a 65” ull HD,
conside ing ha i is possible o use he same LEDs pe pixel
in bo h cases and ha luminance is su icien . I is a majo
challenge o he display LED manu ac u e s o educe he size
o he LED o make he cos o displays compa ible wi h he
ma ke ends and expec a ions.
Howe e , PCBs, which can o e e y low impedance bus lines
o powe planes, canno achie e e y igh design ole ances.
The ypical ace wid h and spacing ha can be manu ac u ed
on la ge size PCBs on high olumes and low cos , is bigge
han 50µm. I is one o de o magni ude la ge han he
ole ances ou inely achie able on glass. Conside ing a 4
con ac s RBG chip (1R, 1G, 1B and 1 common) o an ac i e
pixel wi h 4 con ac s (Row, Column, VDD and GND), i would
be possible o conside a 15x15µm chip o ans e on an
ac i e ma ix on glass while using a PCB equi es a chip o a
leas 150x150µm². Al hough an RGB chip o 150x150µm² is
almos good enough o se e all display sizes abo e 12" in ull
HD s anda d, when changing he size o he LED om
15x15µm² o 150x150µm², he cos pe LEDs is mul iplied by
100 (no conside ing he dicing s ee impac and he yield
impac ).
The BAMBAM p ojec will b ing o TRL4 he addi i e
p ocesses o p in ac i e µLEDs (ALEDIA’s Sma Pixels)
displays on lexible oils. This will be achie ed h ough each
pa ne s’ ields o expe ise o de elop a new dis up i e
display echnology consis ing o he ollowing key-elemen s:
✓ Epi axially g own blue GaN μ-LED on Si-wa e ,
allowing unp eceden ed wa e - o-wa e bonded o
CMOS d i ing ci cui y (ac i e μ-LED) hough known
and mas e ed p ocesses in ound ies. [Aledia, XDisplay]
✓ Mass- ans e able by elas ome s amps compa ible wi h
di e en subs a es ( lexible/ igid) a e wa e -dicing
[Aledia, XCelep in ]
✓ Con ac ed by μ-p in ing wi h Ag-in used ink (bo h o
powe and signal dis ibu ion) by de eloping (i)
dedica ed ink o mula ions compa ible wi h µLED
applica ion and lexible oils and (ii) expanding p in ing
p ocess o µLED displays [XTPL, Uni e si y o
S u ga ]
✓ Colo -con e sion by μ-p in ing wi h QD in used ink
(bo h o ed and g een) h ough he de elopmen o a
p ocess-s able and RoHS-complian QD-ink ha
enables ou s anding wide-colo gamu mic o displays
wi h an e icien colo con e sion o he blue µLEDs o
ed and g een. [XTPL, Uni e si y o S u ga ,
Qus omDOT]
✓ Ha ing a s ong oo hold in, and unde s anding o , he
p o essional b2b isualiza ion ma ke allowing o
implemen as soon as TRL3 and 4 he eco-design o he
display o ensu e he minimal en i onmen al impac
[Ba co]
The mic o p in ing solu ion p oposed by XTPL(4) and he
Uni e si y o S u ga o e s he oppo uni y o ha e e y
na ow me al lines, down o 1µm in wid h, bu also o ha e a
e y accu a e posi ioning o he lines wi h espec o he
s uc u es hey a e in e connec ing. They should p o ide
simila design ole ances as pho oli hog aphy on glass bu hey
can be used on PCB. Mic o p in ing o na ow me al lines
could also be compa ed o wi e bonding (Figu e 5) o
componen s placed on a PCB (COB echnology o Chip On
Boa d). Howe e , he minimum size o he wi es is 15µm and
he size o he bonding pads canno be lowe han 40µm which
does b ing a signi ican imp o emen compa ed o s anda d
PCB design ole ances. and gi es ano he bene i o he
na ow sil e wi es.
Wi h µp in ing o na ow me al lines on PCBs, i is possible
o:
✓ Ha e e y small µLED dimensions, down o he ange o
30µm o 60µm size o RGB componen s (ie 10 o 20µm)
size is no limi ed anymo e by he design ules o he
PCB
✓ Take ad an age o he low impedance o me al laye s on
PCBs
✓ Ha e access o iling wi h seamless iles (which is no
possible on glass) hus enable he manu ac u ing o
la ge displays bu based on smalle elemen s, eques ing
smalle machines oo p in o manu ac u ing
✓ Ha e access o subs a es and en i e displays wi hou he
huge CAPEX o a TFT display ab.
Figu e 5: con ac be ween µLED and subs a e
I he pu pose o he BAMBAM p ojec o conside all addi i e
solu ions: elec ical, op ical o assembly o manu ac u e la ge
lexible ac i e µLEDs displays on s anda d PCBs o lex oils.
4. Ac i e MLEDs o sa e ene gy.
Sa ing ene gy du ing manu ac u ing. TFT ac o ies a e no
a sus ainable solu ion o an o e all educ ion o humani y's
ecological ene gy- ela ed oo p in . Each plan has a e y high
ene gy consump ion: a Gen 6 TFT-LCD panel plan uses
506GWh. This co esponds o he elec ici y consump ion o a
100 000 inhabi an s ci y. The new display design de eloped in
BAMBAM emo es he need o TFT panels and consequen ly
he need o ully TFT-dedica ed plan s, o egula ound ies
used h oughou he mic o-elec onics sec o s, he e o e
inducing scale economies by allowing a single plan o
manu ac u e se e al ypes o de ices. A ypical IC ound y
consumes hal he ene gy o an a e age TFT plan . The
inc ease in ene gy consump ion by a ound y manu ac u ing
µLED displays will be ma ginal compa ed o he ixed ene gy
consump ion ha will happen anyway (wi h o wi hou he
added display manu ac u ing ac i i y).
Sa ing ene gy du ing he use phase. Wi h ac i e ma ix
LTPS TFTs, i is es ima ed ha he powe loss in he TFTs
eaches almos 70%. In such displays, only 30% o he powe
goes o he emi e ma e ial o de ice. E en i μ-LEDs a e
wice as e icien as OLEDs, hen he whole display will only
ge o be a ound 15% mo e e icien ” The dis up i e
echnology p oposed in BAMBAM will no su e om hese
TFT losses as (a) he CMOS d i ing elec onics is in eg a ed
in he μ-LED, and (b) he conside ed subs a es (RF4, lex oil)
allow powe supplies planes and h ough subs a e ias wi h a
esis i i y much lowe han ITO by a ac o o 100 o 1000.As
such, he echnology de eloped in BAMBAM is expec ed o
ha e a powe consump ion o 0.2W/dm2 (@ 300ni ) o lowe
by 2030, oughly hal ing he Speci ic ene gy use in W/dm2 o
new TVs by 2030(5).
An eco-designed app oach o he Eu opean display
indus y. Besides ene gy sa ings, BAMBAM will posi i ely
impac he en i onmen h ough wo majo le e s: a be e
eusabili y and he educ ion o F-gas consump ion, all o hem
esul ing om he emo al o he TFT laye . 98% o a cu en
TV can be ecycled. Howe e , his is a om easy ega ding
he LCD and OLED panels, which a e complex sandwiches
(Figu e 6) (6) which a e he mally ea ed in incine a ion plan s
o eco e he small amoun o con ained me al.
The glass ac ion, accoun ing o 85% o he panel, ends up in
he slag oge he wi h oxidized me als, and no ecycling
p ocess is ye a ailable a indus ial scale. The in insic design
p oposed by he BAMBAM p ojec , allow µLEDS emo al
om he subs a e o example h ough ab asion, o be
ecycled o eco e ma e ials o in e es (Si, Ga no ably i he
Ga concen a ion is >100ppm). Consequen ly, he subs a e
(glass, PCB, lexible oil…) does no su e om a he mal
ea men and can be eused and esubmi ed o mic o-
p in ing o µLEDS, sil e wi es and colo con e sion.
In BAMBAM, LED con ac s o he backplane a e made
h ough sil e wi es di ec ly p in ed on he me als (Cu) on he
subs a es ( lex oil o PCB), hus emo ing he need o
conduc i e laye s o indium- in oxide ( igu e 6). Indium (6) is
s ill used in he LED manu ac u ing p ocess bu o a 10% o
he p e ious coa ed su ace. I is conside ed as a s a egic
ma e ial mos ly used o displays since p oduc ion boomed
om 149 ons in 1994 o 819 ons in 2014. While QDs used
o colo con e sion a e based on InP co e ma e ial, hey a e
co e ed wi h II-VI shells, as ZnSe o ZnS. Indium con en in
QD ma e ial is hus e y low.
Figu e 6: ITO laye s in LCD
Finally, F-gas a e conside ed supe g eenhouse gas. SF6 o
example is conside ed 23500 imes mo e ha m ul o he
clima e in e ms o i s global wa ning po en ial han CO2 and
has an es ima ed li e ime in he a mosphe e o 3200 yea s. The
echnology de eloped in he BAMBAM p ojec will
con ibu e o he u he educ ion in he use and emission o
hese supe g eenhouse gasses as dic a ed by EU-legisla ion as
he o al su ace a ea ha will need o be e ched o he same
display a ea (i.e., Si-wa e o densely packed μ-LED and
d i ing elec onics) will be signi ican ly less han o he
cu en TFT/LCD, and eme ging TFT/μ-LED echnology (i.e.,
LTPS wa e mus be e ched a he same size as he inal
display). This implies a lowe need o he use and
consump ion o hese chemicals.
A he co e o he BAMBAM concep is he econcilia ion o
he de eloped echnologies wi h he end-use s needs and
equi emen s as well as wi h exis ing and upcoming
en i onmen al egula ions. To ensu e ha his is achie ed,
speci ica ions ha a e an op imal comp omise be ween end-
use needs and equi emen s, en i onmen al pe o mances and
echnical cons ain s will be de ined ea ly in he p ojec . As a
i s s ep, he ma e ial and p ocesses will be de eloped, and
hei pe o mance and compa ibili y will be assessed h ough
es ehicles. In a second s ep, he p ocesses will be u he
de eloped and in eg a ed in o display demons a o s. The
a ge ed es ehicle will be su icien ly ep esen a i e o he
inal demons a o o decouple he p ocess de elopmen
aspec s om mo e sys em ela ed aspec s ha will be equi ed
o he ull demons a o . The echnical and en i onmen al
pe o mance o he de eloped p ocesses and ma e ials will be
con inuously assessed du ing he p ojec and he combina ion
o bo h will be conside ed o design he inal display design
and ope a ional a chi ec u e. The main componen o he
a ge ed display, he a ge ed p ocesses and he associa ed
challenges a e desc ibed below.
5. Acknowledgmen
BAM-BAM pa ne s hanks Eu opean commission o
g an ing his p ojec (P ojec Re : 101070085; HORIZON-
CL4-2021-DIGITAL-EMERGING-01-31).
Aledia hanks Benkei o hei s ong suppo
6. Conclusion
BAMBAM will combine he de elopmen o cu ing-edge
ma e ials wi h he de elopmen o p ocesses o he addi i e
manu ac u ing o µLED displays. This includes:
• The de elopmen o a high- esolu ion p in ing p ocess o
enable con ac ing o smalle µLEDs on o new subs a es
• The de elopmen o µLED o educed size and hei
compa ibili y wi h sil e mic o-wi ing.
• The de elopmen o a new p in ing echnology o he
pa e ning o a QD-based colo con e sion module
(CCM) a a lowe pi ch bo h a wa e and chip le el
• The in eg a ion o hese echnologies in o ully
unc ional display demons a o s
7. Re e ences
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E alua ion_o _Ene gy_Conse a ion_Pe o mance_on_Elec
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/link/570a424408aed09e91711162/ download
2-h ps://www.agc.com/en/p oduc s/elec o ic/de ail/ g .h ml;
Laakso e al., IEEE Access, 2018 (6) pp. 44306
3-h ps://con i .a las.jp/guide/e en -img/idw2020/AMD4-
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4-A. Wia owska, P. Kowalczewski, M. Dusza, M. Zięba, K.
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Science and Technology · Feb ua y 2020 DOI:
10.1080/10643389.2020.1729073
