mass transfer with elastomer stamps for microled … x-celeprint.pdfyield map, 150 mm wafer array...

© X-Celeprint 2018 15/30/2018ECTC 2018, San Diego

Frontiers in Assembly

Mass transfer with elastomer stamps for microLED displays.

Matt Meitl

X-Celeprint, Inc.

[email protected]


The best materials for the best displays

The materials identify the display. The best displays will use the best materials.

Brightest, fastest, most efficient, extra-functional, multi-sensory, computational “systems on a panel”.

Bridging the gap between wafer and panel is the way to get the best displays.

Wafer Fabricated Devices

Single-crystal Fine lithography

(ICs, LEDs, Lasers, etc…)

Advanced displays

of all sizes:


The Elastomer Stamp

Low-pressure injection molded silicone rubber on glass backing,

with lithographically-defined “posts” for selective transfer.

The stamp is…

i. …compliant in z…

→ high transfer yield.

ii. …transparent…

→ high-accuracy placement.

iii. …simple, inexpensive, high-fidelity

construction….

→ scalable, high-throughput


Elastomer stamp capability demonstrations

Yield map, 150 mm wafer array transfer:

displacement at 3σ: +/- 1.5 µm

i. …compliant (forgiving) in z…

→ high transfer yield.

ii. …transparent

→ high-accuracy placement.

iii. …simple, inexpensive, high-fidelity

construction….

→ scalable, high-throughput


Transferring micron-scale objects with stamp

3 µm and 5 µm GaN transferred with stamp:

3 x 10 µm2 8 x 15 µm2

microLEDs suitable for micro assembly with elastomer stamp:


Passive matrix microLED by printing

Transfer to display substrate with pre-patterned column metal:

PMiLED array interconnection:

Stamp:

LED source wafer

→ Different “source” for each color

LED sites on “target” panel

1 cm

…on glass & plastic:

Cu

Au

microLED


Active matrix microLED

traces + insulator on panel substrate

print iLEDs print µ-ICsinterconnect,

operate

1 cm

microIC

CuAu


Viewing angle and color

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-90 -60 -30 0 30 60 90

Rel

ativ

e Lu

min

ance

Polar Angle (degrees)

0 degrees

45 degrees

90 degrees

135 degrees

u’ v’ x y

Area 107.1% 90.6%

Overlap 93.3% 84.1%

Relative to Rec. 2020:

0.0E+0

2.0E-6

4.0E-6

6.0E-6

8.0E-6

0.0E+0

5.0E-7

1.0E-6

1.5E-6

2.0E-6

400 500 600 700 Rad

ian

t Fl

ux

(W/n

m)

Rad

ian

t Fl

ux

(W/n

m)

Wavelength (nm)

Spectral Radiant Flux

1 cm


Larger active matrix displays:

Print row drivers and column drivers to reduce external I/O count:

• Column drivers demultiplex data

• Row drivers run progressive scan of data load and PWM

5.1” Diagonal AMILED display 320 x 160, 70 ppi:


320 x 160 AMILED, 70 ppi

R

G

BVdd

Col

Row

Gnd

Row, column, power, and

ground into each pixel:

Cu redistribution layer

interconnects microLEDs, ICs, and

row/col drivers (not shown).

Vdd

Col

Ro

w

Gnd


Functional Yield of Sub-Pixels in 5.1” display

Implementation of redundancy in

microICs, microLEDs, row & column

lines.

Remaining yield impactors:

• Forward voltage of LEDs

• Metallization defects (laser cut)

• Transfer (typ. < 3 sub-pixels)

Red: 99.98% (9 dark)

Green: 99.95% (28 dark)

Blue: 99.95% (24 dark)


Display test and additive repair

printable components with interconnection structures target substrate populate target

Operate display; identify defects repair by print repaired system

+

Simple passive matrix

display prototype:


Display prototypes by interconnect-at-print with spikes

Looking through substrate, see “divots”

produced by spikes contacting metal at four

corners of interposer.

Note repaired pixel on 2nd row from bottom, 3rd column

from left: engine printed in redundant site by single-post

stamp.

Simple passive matrix display

prototype.


Active matrix “pixel engines” with interconnection structures

Interconnect-at-print pixel engine

The SEM images of this slide show a fully formed

pixel engine that uses thin film metal to

interconnect micro LEDs, a micro IC, and

conductive spikes at the bottom of the device.

The images below show the devices

interconnected in arrays on a display substrate.


An assembly-centric display fab

Pixel engines (supplied on wafer)

Metallized panels

Mass-transfer Micro-assembly,

Test & repair.

Advanced flat panel displays…

…of all sizes.

Additive assembly with electrical interconnection can finish displays at the “print, test & repair” process modules.


Thanks from the X-Celeprint team

mass transfer with elastomer stamps for microled … x-celeprint.pdfyield map, 150 mm wafer array...

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