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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)
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
US Patent No. 6,555,414
Screenprinting of ICA: electroformed nickel stencil with tapered walls smaller stencil holes than pads to avoid bridging
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
1a. NICA-technology
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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:
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
1b. Interconnection of TCPackaged driverchips to displays
TCPackaged chip
Flexible substrate (PI)
Chi
pDisplay substrate
Flexible substrate (PET/stainless steel)
Pitches: 250, 200, 150, 120, 100, 80 and 60 micron
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
1b. Interconnection of TCPackaged driverchips to displays
4-point measurementdaisy chains
Test structure on display
u uPI foil
i i
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
1b. Teststructure
2. Electrophoretic Image Display
V >0 V <0
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
Movement of colored pigmentsin a colored solvent
Pigments: optical response
Micelles: electrical responseand …
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
2a. EPID Technology
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
2b. EPID Modelling: optical
Complete model: both electrical and optical (even thermal)
Helps understanding contributions of the different parameters
Optimization of the display characteristics
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
EPID Modelling:
3a. Flexible Large Area FED display
Each pixel comprises of one MicroCRTcathode
anode
gate
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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!
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
3b. High Voltage Driver chips
Courtesy of Eastman Kodak Display and Components Division
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
3b. High Voltage Driver chips: GUI
GUI: Description of display configuration and definition of driving scheme
Conclusion
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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?
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates
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.
Advanced Technologies in Fabrication and interconnection of Flexible Displays and Substrates