Advanced Technologies in Fabrication and Interconnection of Flexible Displays and Substrates Tom Bert TFCG-Microsystems – Elintec Ghent University

Advanced Technologies in Fabrication and Interconnection of Flexible Displays and Substrates

Tom Bert

TFCG-Microsystems – ElintecGhent University

Overview

1. Flexible Display Interconnectiona. Low temperature flip-chipb. Interconnection of TCPackaged driverchips to displays

2. Flexible Display TechnologyElectrophoretic Image Displays

3. Flexible Displays Driver Designa. Field emission large areab. High voltage drivers

Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates

Demands for use inside a smart-card:

flexibility, bendability thin transparency low-temperature assembly cheap and fast technology

Substrate: polyethersulphone (PES) + conductive ITO layer

Assembly: use of adhesives (ICA and ACA)


1a. Low temperature flip chip

1. ICA on substrate

2. Pre-curing of ICA

3. Dispensing of NCA

4. Placing of the die

5. Thermocompression

Isotropic Conductive Adhesives (ICA) +

Non Conductive Adhesives (NCA) = NICA


US Patent No. 6,555,414

Screenprinting of ICA: electroformed nickel stencil with tapered walls smaller stencil holes than pads to avoid bridging


1a. NICA-technology

Dispensing of NCA:exact amount of NCA has to be dispensed in spiderweb pattern

Pre-curing of ICA:to avoid the washing out of the ICA

Chip placement and thermocompression:

no self-alignment with adhesives

first only pressure, then pressure + heat

→ no voids inside


1a. NICA-technology


1b. ACA-technology

• limited amount of process steps and process time • soft conductive particles needed with high pressure bonding

Bonding temperature: 130CBonding time: 15 secBonding force: 1.5 kgf

Low curing temperature needed to avoid damaging the plastic


1b. ACA-technology

NICA-technologyNICA-technology

Average StDev

Overall 3.12 Ω 1.92 ΩBump finish

Au-bumps 3.05 Ω 2.00 ΩNi/Au-bumps 3.19 Ω 1.86 Ω

Chip thickness150 um 3.21 Ω 1.95 Ω250 um 3.05 Ω 1.91 Ω

Pad distributionArea 3.17 Ω 2.09 Ω

Peripheral 3.07 Ω 1.76 Ω


Measurements

150 m thick chips : 80% yield250 m thick chips : 100% yield

ACA-technologyACA-technology Contact resistance from 0.6 to 7 Ωdependant on the number of particles

Contact Resistance Distribution

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7 8 9

Resistance (Ohm)

# o

f m

easu

rem

ents

TCPackaged chip

Flexible substrate (PI)

Chi

p

Chi

p

Two technologies, both using anisotropic conductive adhesives:


1b. Interconnection of TCPackaged driverchips to displays

Direct Flip-Chip assembly of driverchips onto the display

Interconnection of TCPackaged (Tape Carrier) driverchips to the display

Measurements of contact resistance:4-point measurements and daisy chains

Difficulties: Small pitches Low temperature/pressure bonding (plastics) Flexibility



TCPackaged chip

Flexible substrate (PI)

Chi

pDisplay substrate

Flexible substrate (PET/stainless steel)

Pitches: 250, 200, 150, 120, 100, 80 and 60 micron



4-point measurementdaisy chains

Test structure on display

u uPI foil

i i


1b. Teststructure

2. Electrophoretic Image Display

V >0 V <0


Movement of colored pigmentsin a colored solvent

Pigments: optical response

Micelles: electrical responseand …


2a. EPID Technology


3.0E-08

1.8E-07

3.3E-07

4.8E-07

0 1 2 3 4 5 6 7 8 9 10

t (s)

Cu

rren

t (A

)

0,5V from -10V

2V from -10V

10V from -10V

3.0E-08

9.0E-08

1.5E-07

2.1E-07

0 1 2 3 4 5 6 7 8 9 10

t(s)

Cu

rre

nt

(A)

2V from -2V

2V from -5V

2V from -8V

2b. EPID Modelling: electrical


2b. EPID Modelling: optical

Complete model: both electrical and optical (even thermal)

Helps understanding contributions of the different parameters

Optimization of the display characteristics


EPID Modelling:

3a. Flexible Large Area FED display

Each pixel comprises of one MicroCRTcathode

anode

gate


Field Emission by means of Carbon nanotubes

MicroCRT’s plugged into flexible foam to form flexible display

microCRTAddressing Flex microchip

Electronics help to:• Improve uniformity• Expand lifetime


MicroCRT’s individually adressed (microchip)• no peripheral drivers• optical sensor on chip

• pixel luminance control• pixel aging compensation

40 tiles, 800 pixels, 4 m for SVGA or any size

30 tiles600 pixels3 mor smaller

Large Area Display• consisting of tiles of 20 x 20 pixels• resolution: 800 x 600• dimensions: 4m on 3m


Design of the microchip

• Each microchip (each pixel) is digitally adressable

• High Voltage analogous cathode driver (up to 100 V)

• On-chip optical feedback-circuit

1 chip = Same CMOS technology!



3b. High Voltage Driver chips

Reflective bistable displays:• Very high voltage levels (typ. 20V to 50V rms)

• Very complex waveforms on rows and columns

Presented driver chip provides:- a very compact alternative - high degree of flexibility:

• 120 rows and 160 columns (1/16 VGA resolution) • 100V driving capability on all outputs• Very complex multi-level HV output waveforms• Numerous addressing schemes • Ultra-low power consumption ( 2W per output)• 3 - 5V battery power supply


3b. High Voltage Driver chips

Courtesy of Eastman Kodak Display and Components Division


3b. High Voltage Driver chips: GUI

GUI: Description of display configuration and definition of driving scheme

Conclusion


Visit our website: come.to/tfcg

1. Flexible Display Interconnectiona. Low temperature flip-chip: below 130°Cb. TCPackaged driverchips: below 150°C

2. Flexible Display TechnologyEPID: electrical and optical simulation

3. Flexible Displays Driver Designa. Field emission large area: complete chip designb. High voltage driver: multifunctional tool

Thank you

Questions?


Tom Bert was born in 1979 and became a Master in Engineering, Electronics in 2002. Since then he works for the Thin Film Components Group (TFCG) at the department of Electronics and Information Systems (Elis) of the Ghent University. He works on the physical modeling of electronic paper.

The TFCG Microsystems group is involved in the research on design and technology of microsystems. The research focuses on the embedding of microelectronics in new applications in the field of biomedics, textile, automotive, telecom and displays. The underlying generic technology platform comprises thin film, thick film, laminate, flex technology and laser structuring. The technology platform enables high density interconnection and packaging on rigid and flexible substrates, optical interconnect and the fabrication of different microsystems on rigid and flexible substrates.

On the design site the research efforts are focussed on mixed-mode CMOS technologies looking at smart interface technologies for automotive and display applications. By means of Technology CAD (TCAD) DMOS and IGBT's were succesfully integrated in 0.35 and 0.7 CMOS technologies. Using these CMOS technologies, dedicated high voltage, low power display drivers were developed for addressing bistable displays. Other highlights are a fine line technology and packaging technology for cellular phone, a low temperature flip chip technology for smart cards, a multilayer flex technology for smart band-aid, and a liquid crystal on silicon technology for high performance high resolution displays.

The group has recently moved to new facilities at the Technology Park of Gent University. The new 2000 m2 cleanroom building is equiped with a 600 m2 cleanroom facilities. More info can be found at the website of TFCG Microsystems: http://www.elis.ugent.be/ELISgroups/tfcg/index.html

In August 2004 a spin -off company GEMIDIS was created for the development of LCOS imagers for HDTV, control rooms and D-cinema.


Documents

Advanced Technologies in Fabrication and Interconnection of Flexible Displays and Substrates Tom Bert TFCG-Microsystems – Elintec Ghent University