Future Work

7.1 Novel Full Color Transflective Ch-LCD by Inkjet Printing Method

The ink-jet printing (IJP) is a popular technology for desktop publishing and currently became an ideal method for print OTFT/PLED with high resolution since IJP is characteristics of patterning capability, large device area capability, efficiency of using material, and multicolor display fabrication capability. Moreover, it is well known that the cholesteric texture has the advantages of displaying the spectrum ranging from inferred, to visible and even to ultraviolet band, thus Ch-LC material performs outstanding achievement in the aspect of displaying full color capability. To achieve the full color Ch-LCD display, we proposed the first work of using the piezoelectric IJP^[19] to deposit the patterned RGB Ch-LC materials droplets on the corresponding reflective region of sub-pixel on the bottom substrate.

Our objective is to demonstrate that the Ch-LC with extremely high viscosity is compatible with IJP and the Ch-LC droplet with high stability can be deposited on the glass substrate. We first try with green Ch-LC for initial testing. FM-M01 Ch-LC (central wavelength= 550nm, green light band) provided by MERK was utilized for deposition. The printing system was developed by ITRI. The SE-128 piezoelectric printhead provided by Spectra was utilized in this printing system. For obtaining the uniform droplet with the Spectra’s printhead, the viscosity of ink material should be ranging from 1~15 cps to obtain high stable printing. Since the viscosity of Ch-LC was extremely high, thus decreasing the viscosity to 10 cps was the key technique to deposit the cholesteric droplet. As shown in Fig. 12, the viscosity of the cholesteric material was dropped to 10 cps when we increased the temperature to 60˚C. As a

result, the printhead started to squeeze the green cholesteric droplet as shown in Fig.

13. The flying motion image of the droplet was begun at 10µs and was snapped shot at the time interval of 15µs. From this figure, we see that each snap shot at corresponding interval demonstrated a sharp edge around the droplet. Thus, we can conclude each droplet was demonstrated with high stability and the Ch-LC material is highly compatible with the Spectra printing head.

Cholosteric LC (FM-M01-550nm)

0 5 10 15 20 25 30

0 10 20 30 40 50 60 70

Temperature (℃)

Viscosity(CPS)

Fig. 7.1 Relationship between temperature and viscosity of Ch-LC using piezoelectric IJP

As a result, we successfully deposited dot-patterned Ch-LC on the glass substrate, as shown in Fig. 14. The dot diameter was 120µm and lateral and vertical pitches were 300µm and 508µm, respectively. From the figure the satellite dot was very few, and thus the stability to deposit the dot Ch-LC was high. Further, by continuous depositing the dot Ch-LC, we successfully deposit the stripe-patterned Ch-LC on the glass substrate, as shown in Fig. 15. The diameter was still 120µm and the vertical pitch was 508µm. From the figure, only a small number of satellite dots were appeared near the stripe Ch-LC. Thus, the stability to deposit the Ch-LC with the Spectra printhead was high. As the dot- and stripe-patterned Ch-LC with high printing

quality were obtained, various patterning types can be achieved by modifying the computer program to inject the Ch-LC ink in-between the banks or walls with particular patterns, such as mosaic and stripe types.

No

Fig. 7.2 Flying motion of printing Ch-LC droplet by snapping shot at time interval of 15µs.

Fig. 7.3 Cholesteric LC’s dot pattern deposited on the glass substrate by IJP

10us 25us 40us 55us 70us 85us

zzle

10us 25us 40us 55us 70us 85us

Nozzle

508um

300um 120um

120um 508um

Fig. 7.4 Cholesteric LC’s stripe pattern deposited on the glass substrate by IJP 7.2 Future Work

Since the initial injection with green Ch-LC was successfully demonstrated, thus the RGB Ch-LC will be deposited on reflective region patterned with black matrix on the bottom substrate. Then IER film will be position in the transmissive region patterned with high transmittance wall on the bottom substrate. As a result, the full color Ch-display will be obtained, as shown in Fig. 16. Further, IJP technique with Ch-LC can also be used in the color filter application with characteristics of high efficiency. Since Ch-LC is able to display full color capability and was polarizerless (Bragg Reflection), thus, with IJP (no mask is required), 100% reflection can be easily achieved by pattering the left-handed RGB Ch-LC and right-handed RGB Ch-LC^[9]. With the benefits of IJP, the RGB pattern were obtained without using the conventional semiconductor process requiring additional mask charge. Further, according to the simulation results on OC thickness, the optimized transmittance of 14% was obtained at OC thickness ranging from 150~200µm. Thus, to obtain high transmittance with this specific OC thickness, the plastic substrates as an OC layer should be applied. Therefore, the flexible transflective Ch-LCD can be realized with

the plastic IER film on the plastic substrates, and to obtain with full-color capability, the IJP with cholesteric ink will be further applied on the plastic substrates.

Upper substrate

Fig.7.5 Full color transflecitve Ch-LCD with IER film and IJP method