03-12-2012, 02:34 PM
Full-Color Polymer-LED Display with a-Si TFT Backplane by Ink-Jet Printing
[attachment=42258]
Abstract
We have developed a 14.1 inch full color polymer LED display,
based on an a-Si TFT backplane, using ink jet printing, which
does not show visible swathe marks during display operation. To
remove the swathe marks, we have developed the single path
printing technology for the hole-conduction layer deposition to
significantly reduce the complexity of interlacing printing across
the panel, which is known as an alternative to remove the swathe
marks. In addition, we have adopted the interlayer process to
increase the lifetime of ink jet printed displays. These technologies
will enable the scale-up of the ink jet printed AMOLED
applications to larger size displays, such as desktop monitors and
TVs.
Introduction
In the past few years, Organic Light-emitting Diode (OLED)
displays have been considered as an alternative for the next
generation of displays due to its advantages such as wide viewing
angle, fast response time and less costly manufacturing processes.
Up until now, four major techniques have been developed for the
OLED manufacturing: evaporation method using fine metal
shadow mask, white OLED with color filter, laser induced
thermal imaging (LITI), and ink jet printing. Among them, the ink
jet printing method has very good potential because of its
scalability, fast throughput, minimal waste of the material and
simple overall processing, and several papers have been reported
in this field. [1-4]. However, emission differences between, or
even within, the printing swathes cause bad non-uniformities
across the panel and these are easily detectable by eye. To remove
these swathe marks, various kinds of interlacing methods are
widely used across the panel by column, row, or both. However,
the interlacing technique requires specific optimization depending
on the display size, and also prolongs the processing time since
multiple passes of the head are required.
Experimental
For the process development, we have used the 14.1 inch WXGA
amorphous Si TFT backplane, having a bottom emission structure
after panel fabrication. ITO was used as the transparent anode, but
an adapted amorphous ITO process was developed to prevent
underneath signal line corrosion by the ITO etchant. Onto this
ITO anode, we formed the polymer bank structure to contain the
ink; the material used for the polymer bank was a type of
polyacrylate, which gave a positive angle bank slope. Before ink
jet printing, it was imperative to treat substrate with a plasma
surface conditioning process, which leaves the ITO surface in a
hydrophilic state and the bank surface hydrophobic enough to
contain the PEDT ink.
Polymers were printed with a Spectra SX print head having 128
nozzles. To print full color displays requires the printing of four
separate layers: hole-injection material (polyethylene
dioxythiophene / polystyrene sulphonate (PEDT/PSS)) goes onto
the whole display area, followed by printing of RGB layers.
Results and Discussion
For each of the four inks we measured and optimized drop
volumes, directionality and velocity before printing. To ensure
acceptable well filling it was necessary to achieve good drop
placement. Although there are many factors that affect drop
placement, the significant factors are the drop directionality and
mechanical placement of the nozzle over the well caused by stage
non-linearity, bow, thermal effects and alignment tolerance. By
adopting different printing offset values for each of eight subsections
across the display active area, mechanical placement
error can be reduced to ≤± 3 μ m (Fig. 1).
Conclusions
We have developed a 14.1 inch full color polymer LED display
based on an a-Si TFT backplane, which is effective in showing the
possibility of making large OLED display panels by ink jet
printing. Interlayer technology was also adopted into the real
active matrix panel, which significantly enhanced the lifetime of
every color.
[attachment=42258]
Abstract
We have developed a 14.1 inch full color polymer LED display,
based on an a-Si TFT backplane, using ink jet printing, which
does not show visible swathe marks during display operation. To
remove the swathe marks, we have developed the single path
printing technology for the hole-conduction layer deposition to
significantly reduce the complexity of interlacing printing across
the panel, which is known as an alternative to remove the swathe
marks. In addition, we have adopted the interlayer process to
increase the lifetime of ink jet printed displays. These technologies
will enable the scale-up of the ink jet printed AMOLED
applications to larger size displays, such as desktop monitors and
TVs.
Introduction
In the past few years, Organic Light-emitting Diode (OLED)
displays have been considered as an alternative for the next
generation of displays due to its advantages such as wide viewing
angle, fast response time and less costly manufacturing processes.
Up until now, four major techniques have been developed for the
OLED manufacturing: evaporation method using fine metal
shadow mask, white OLED with color filter, laser induced
thermal imaging (LITI), and ink jet printing. Among them, the ink
jet printing method has very good potential because of its
scalability, fast throughput, minimal waste of the material and
simple overall processing, and several papers have been reported
in this field. [1-4]. However, emission differences between, or
even within, the printing swathes cause bad non-uniformities
across the panel and these are easily detectable by eye. To remove
these swathe marks, various kinds of interlacing methods are
widely used across the panel by column, row, or both. However,
the interlacing technique requires specific optimization depending
on the display size, and also prolongs the processing time since
multiple passes of the head are required.
Experimental
For the process development, we have used the 14.1 inch WXGA
amorphous Si TFT backplane, having a bottom emission structure
after panel fabrication. ITO was used as the transparent anode, but
an adapted amorphous ITO process was developed to prevent
underneath signal line corrosion by the ITO etchant. Onto this
ITO anode, we formed the polymer bank structure to contain the
ink; the material used for the polymer bank was a type of
polyacrylate, which gave a positive angle bank slope. Before ink
jet printing, it was imperative to treat substrate with a plasma
surface conditioning process, which leaves the ITO surface in a
hydrophilic state and the bank surface hydrophobic enough to
contain the PEDT ink.
Polymers were printed with a Spectra SX print head having 128
nozzles. To print full color displays requires the printing of four
separate layers: hole-injection material (polyethylene
dioxythiophene / polystyrene sulphonate (PEDT/PSS)) goes onto
the whole display area, followed by printing of RGB layers.
Results and Discussion
For each of the four inks we measured and optimized drop
volumes, directionality and velocity before printing. To ensure
acceptable well filling it was necessary to achieve good drop
placement. Although there are many factors that affect drop
placement, the significant factors are the drop directionality and
mechanical placement of the nozzle over the well caused by stage
non-linearity, bow, thermal effects and alignment tolerance. By
adopting different printing offset values for each of eight subsections
across the display active area, mechanical placement
error can be reduced to ≤± 3 μ m (Fig. 1).
Conclusions
We have developed a 14.1 inch full color polymer LED display
based on an a-Si TFT backplane, which is effective in showing the
possibility of making large OLED display panels by ink jet
printing. Interlayer technology was also adopted into the real
active matrix panel, which significantly enhanced the lifetime of
every color.