Baek-woon Lee

51.2: Reducing Gray-Level Response to One Frame: Dynamic Capacitance Compensation

A novel driving scheme, named Dynamic Capacitance Compensation (DCC), for active-matrix (AM) LCDs was developed. It takes the charge-&-hold nature of AM-LCDs into consideration to enhance the switching speed. By incorporating DCC and faster liquid crystal, a TFT-LCD whose response time was less than 10 ms for all gray levels with the on + off time of 8.4 ms was developed. DCC can be applied to any kind of LCD modes to reduce the gray response time to less than 1 frame.

51.1: Novel Simultaneous Emission Driving Scheme for Crosstalk‐free 3D AMOLED TV

A novel driving scheme based on simultaneous emission is reported for 2D/3D AMOLED TVs. The new method reduces left-right crosstalk without sacrificing luminance. The new scheme greatly simplifies the pixel circuit as the number of transistors for Vth compensation is reduced from 6 to 3. The capacitive load of scan lines is reduced by 48%, enabling very high refresh rate (240 Hz).

9.2: Implementation of RGBW Color System in TFT‐LCDs

Last year, we introduced a TFT-LCD with RGBW color system. The primary advantage of the RGBW system is that its optical efficiency is at least 50% higher than the RGB system. However, it is not a simple task to incorporate the new color system into the existing infrastructure of the RGB system: the driving circuitry, fabrication of color filter, and color conversion. In this report, the practical hurdles are discussed and the solutions are presented.

Numerical Analysis of High-Index Nano-Composite Encapsulant for Light-Emitting Diodes

We used two-dimensional finte-difference-time-domain (FDTD) software to study the transition behavior of nano-particles from scatterers to an optically uniform medium. We measured the transmission efficiency of the dipole source, which is located in the high refractive index medium (index=2.00) and encapsulated by low index resin (index=1.41). In an effort to compose index-matched resin and to reduce internal reflection, high-index nano-particles are added to low-index resin in simulations of various sizes and densities. As the size of the nano-particles and the average spacing between particles are reduced to 0.02 λ and 0.07 λ respectively, the transmission efficiency improves two-fold compared to that without nano-particles. The numerical results can be used to understand the optical behavior of nano-particles and to improve the extraction efficiency of high brightness light-emitting diodes (LEDs), through the use of nano-composite encapsulant.

41.5L: Late-News Paper: LCDs: How Fast is Enough?

The switching speed has become critical once again for LCDs to enter the TV market. In this report, three motion artifacts resulting from the slow response are identified: decrease of dynamic contrast ratio, stroboscopic motion, and blurred edge. It is shown that the first two artifacts disappear completely when the response time is less than 1 frame. However, moving edges cannot maintain the sharpness even if the switching speed is infinite, due to the nature of the hold-type displays. We show that when LCDs response within half a frame, the quality of moving images is almost as good as that of zero-response time LCDs. Employing response-overshoot can enhance the image quality even further.

Micro‐cavity design of bottom‐emitting AMOLED with white OLED and RGBW color filters for 100% color gamut

— Two optical structures used for a bottom-emitting white organic light-emitting diode (OLED) is reported. An RGBW color system was employed because of its high efficiency. For red, green, and blue (RGB) subpixels, the cavity resonance was enhanced by the use of a dielectric mirror, and for the white (W) subpixel, the mirror was removed. The optical length of the cavities was controlled by two different ways: by the thickness of the dielectric filter on top of the mirror or by the angle of oblique emission. With both methods, active-matrix OLEDs (AMOLEDs) that reproduced a color gamut exceeding 100% of the NTSC (National Television System Committee) standard were fabricated. More importantly, the transmission of a white OLED through R/G/B color filters was significantly higher (up to 50%) than that of a conventional structure not employing a mirror, while at the same time as the color gamut increased from ∼75 to ∼100% NTSC.

L-2: Late-News Paper: The RGBW Advantage for AMOLED

The combination of white OLED and color filter (CF) is the most mature solution for making large-area AMOLEDs. The system can benefit from introducing a white subpixel. We compared the power efficiencies of RGB and RGBW system. As a basis for the comparison, we also propose a reference video called FC in which every color point in the cubic RGB space has the equal probability of appearance. We found that the RGBW system has 16.7% lower power consumption and 23% lower current stress (thus longer lifetime) for the reference video. We also analyzed various kinds of videos from DVD movies, HDTVs and IT graphics to find that in these actual video materials, there is much more utilization of white so that the power consumption is roughly a half of that for the FC video. The reduction is so significant that the W OLED + RGBW CF system has 60% lower power consumption than the RGB CF system and only 50% higher power consumption than the RGB OLED (no CF).

X-ray Scattering Studies of Phase-Separated Composite Organic Film Cells

The authors report X-ray scattering experiments on phase-separated composite organic film (PSCOF) structures mixed with ferroelectric liquid crystals (FLCs). We discuss the effect of the local layer structure in a PSCOF cell on the ratio of the concentration between prepolymer and liquid crystals. The ratio of optimized concentration in terms of optical characteristics for a PSCOF liquid crystal display are 30 wt % for prepolymer (NOA65) and 70 wt % for FLCs (Felix). We found that the layer structure in a ferroelectric liquid crystal cell made of 30 wt % NOA65 and 70 wt % Felix is a tilted-bookshelf layer structure. The angles 15 and 17° are the tilted-bookshelf angles at 65 and 58 °C, respectively. These layer tilt angles are almost same as the molecular tilt angles of ferroelectric liquid crystals in the Sm C* phase. We understand that this result comes from compensating for layer buckling. We consider that the PSCOF-mode local layer structure is an excellent solution to the problem of zig-zag defects and mechanical shock for application in future televisions and plastic ferroelectric liquid crystal displays (FLCDs).

62.2: Adaptive White Extension for Peak Luminance Increase in RGBWAMOLED

RGBW AMOLED panel, compare to the RGB panel, has lower power consumption and current stress and as result — bigger life time. Using special algorithms and RGB subpixels (as additional white) permits to increase brightness of this panel up to 2 times. At the same time its very important to keep panel current at permissible range. We propose an algorithm, what permits to increase brightness of the RGBW AMOLED panel and limit its summary current at the same time.

21.1: Distinguished Paper: 120 Hz 3D Driving for AMOLED with Interleaved Scan and Emission Operation

3D displays have required 1/240 s of scan time to properly display a stereoscopic image. In this report, a new driving method is proposed that provides 1/120 s of scan time, thus enabling higher resolution. The pixels are arranged as two groups: Even and Odd. One group performs scanning while the other group is emitting and in the next field, these roles are swapped. Therefore, the entire frame time can be used for data input, rather than 1/2 of the frame time as in the previous method.