06/10/2017. Displays: basic LCD technology. Basic LCD technology. Basic LCD technology. Basic LCD technology

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Displays: basic LCD technology Basic LCD technology Liquid crystals are mesophases between crystalline solids and isotropic liquids.

themselves into cholesteric structures 4-n-pentyl-4-cyano-biphenyl The aromatic biphenyl (C₆H₅)₂ component is the rigid core, the

With balanced rigid and flexible parts, the molecule exhibits liquid crystal phase To permit light propagation, a suitable

Wu, Fundamentals of Liquid Crystal Devices, 2006 John Wiley & Sons Basic LCD technology In a twisted nematic display the LC is

When a sufficiently high electric field is applied across the cell, the liquid crystal is tilted toward the field direction

Temperatures above +100º C damage the display's internal coatings.

1 Displays: basic LCD technology Basic LCD technology Liquid crystals are mesophases between crystalline solids and isotropic liquids. Calamitic (=elongated) molecules are used in LCDs Longitudinally asymmetric (chyral) molecules can be used, which organize themselves into cholesteric structures 4-n-pentyl-4-cyano-biphenyl The aromatic biphenyl (C₆H₅)₂ component is the rigid core, the hydrocarbon chain is the flexible tail. The core favors both orientational and positional order while the tail does not. With balanced rigid and flexible parts, the molecule exhibits liquid crystal phase To permit light propagation, a suitable relationship must exist between the direction of the electric field of the light (polarization) and the orientation of the molecules D.-K. Yang and S.-T. Wu, Fundamentals of Liquid Crystal Devices, 2006 John Wiley & Sons D.-K. Yang and S.-T. Wu, Fundamentals of Liquid Crystal Devices, 2006 John Wiley & Sons Basic LCD technology In a twisted nematic display the LC is anchored parallel to the cell surface by the alignment layers. The total twist angle is 90 deg here. When a sufficiently high electric field is applied across the cell, the liquid crystal is tilted toward the field direction Normalized transmittance Basic LCD technology Temperature effects LCD's will recover from brief exposure to isotropic temperatures. Temperatures above +100º C damage the display's internal coatings. At low temperatures the display's response time increases due to the fluid's increased viscosity. Change to crystalline state does not imply permanent damage. Typ. threshold voltage vs. temperature of a TN fluid Threshold increase becomes significant below ~0 (compare to voltage values in the transmittance curves in previous slide) D.-K. Yang and S.-T. Wu, Fundamentals of Liquid Crystal Devices, 2006 John Wiley & Sons

Basic LCD technology Basic LCD technology Twisted nematic (TN), thin-film-transistor (TFT) technology

contrast of a TN cell rapidly decreases in the upper direction and in the lower diagonal directions.

figure). A pair of wide-view films can reduce the effect Iso-contrastratio plots D.-K. Yang and S.-T.

technology Equipotential lines In-Plane-Switching (normally black) analysis polarizer:.

problem with IPS: above the electrodes the electric field is unable to twist the LC the light

2 Basic LCD technology Basic LCD technology Twisted nematic (TN), thin-film-transistor (TFT) technology Due to optical anisotropy of liquid crystals and off-axis light leakage from crossed polarizers, the contrast of a TN cell rapidly decreases in the upper direction and in the lower diagonal directions. In the lower direction the contrast remains high, but gray-scale inversion is observed (not shown in figure). A pair of wide-view films can reduce the effect Iso-contrastratio plots D.-K. Yang and S.-T. Wu, Fundamentals of Liquid Crystal Devices, 2006 John Wiley & Sons IPS - LCD technology IPS - LCD technology Equipotential lines In-Plane-Switching (normally black) analysis polarizer:. thinner display reduced parallax error input polarizer: Note light is transmitted when V = on A problem with IPS: above the electrodes the electric field is unable to twist the LC the light transmittance is lower

Fringe-Field-Switching FFS - LCD technology here, the strip electrodes have the same electrical potential, so that they can be placed close together.

5 in 1920 x 1080 (16:9) 401 ppi 1300:1 contrast ratio 500 cd/m2 max brightness [-- OLED display --] iphone X (Sep2017) 5.8 in 2436 x 1125 (19.

merck-performance-materials.com/en/display/function_of_lcd_technologies/function_of_lcd_technologies.

3 Fringe-Field-Switching FFS - LCD technology here, the strip electrodes have the same electrical potential, so that they can be placed close together. This in turn allows higher transmission, since the area above the electrodes can also contribute to the switching process. analysis polarizer:. iphone in 1920 x 1080 (16:9) 401 ppi 1300:1 contrast ratio 500 cd/m2 max brightness [-- OLED display --] iphone X (Sep2017) 5.8 in 2436 x 1125 (19.5:9) 458 ppi 1M:1 contrast LCD technology Form factor is 3:2 input polarizer: - 4k (4096x2150, digital cinema) or UHD (3840x2160) displays to come (to be used e.g. in VR headsets) (Lu 2007) Transflective IPS Dual-layer LCD The front- and rearpolarizers of the two panels must be properly oriented! A l/4 filter [oriented at 45 it converts linear pol. to circular; then viceversa, at further 45 ] is traversed twice by both the back (1x 2 filters = 90 ) and reflected light (2x 1 filter = 90 ) BUT two added filters absorb light without sunlight, the display looks washed-out needs stronger backlight power consumption, heat Google: 3M lcd optics 101 for more info on lcd filters - 8+8=16 bit images - T max = 2 % (14%*14%) - L max/l min = 90,000 (300:1)*(300:1) - Basic image processing: Y Y Y Source: Philips Research - FIMI

4 later: Barco Dual-layer LCD Dual-layer LCD Source: Philips Research - FIMI see industrial LCD datasheet (Kyocera) Colour LCDs Colour LCDs Google: 3M lcd optics 101 Generate colour pictures using a Bayer filter Chromaticity diagram (CIE 1931) Source: Hitachi and find detailed animated info on lcd structure [See also color.m]

LED-illuminated LCD LED-illuminated LCD LEDs differ

control Isamu Akasaki, Hiroshi Amano Nagoya University,

of California, Santa Barbara, CA, USA for the invention

has enabled bright and energy-saving white light

colors, - small, - environmentally friendly (?

displays LED spectra compared to Cold Cathode

5 LED-illuminated LCD LED-illuminated LCD LEDs differ from old gas discharge lamps: Necessity of white point control Isamu Akasaki, Hiroshi Amano Nagoya University, Japan Shuji Nakamura Univ. of California, Santa Barbara, CA, USA for the invention [1990] of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources" - can be switched fast, - are available in all colors, - small, - environmentally friendly (??), - low voltage LED-illuminated LCD Quantum dot displays LED spectra compared to Cold Cathode Fluorescent Lamp + colour filters NOTE: thin and strong peaks at RGB freqs. can be obtained using QUANTUM DOT devices

6 QD Vision provided Nexxus Lighting (NC) Quantum dot displays Quantum dot displays Note: «Triluminos» was already used by Sony in 2007 for a different, short-lived technology Modulated LED + LC displays Modulated LED + LC displays (Seetzen 03) Seetzen 07 Trentacoste 06

7 Modulated LED + LC displays Modulated LED + LC displays Seetzen 07 Trentacoste 06 Seetzen 07 Trentacoste 06 Modulated LED + LC displays Modulated LED + LC displays Seetzen 07 Trentacoste 06 Seetzen 07 Trentacoste 06

Modulated LED + LC displays Various prototypes /

contrast Dolby Vision approach https://www.dolby.

V370H1-L01, 250:1 simultaneous contrast ratio and 1920

- For a full white box occupying the center third of

(Trentacoste 2007) Dolby SIM2 (HDR47ES6MB) 2202 LEDs,

8 Modulated LED + LC displays Various prototypes / professional market products: More colour, more contrast Dolby Vision approach Watt LEDs on a 18.8mm hexagonal closepacking matrix, each LED individually controlled with 256 steps. - The LCD panel is a 37 in Chi Mei Optoelectronics V370H1-L01, 250:1 simultaneous contrast ratio and resolution. - For a full white box occupying the center third of the screen, the maximum luminance is measured as 4760 cd/m2. - For a black image, the min. luminance is zero, all LEDs are off. (Trentacoste 2007) Dolby SIM2 (HDR47ES6MB) 2202 LEDs, 6000 (2300?) cd/m2, ANSI contrast 20,000, air-cooled Dolby prototype 2014: 18,000 LEDs? Dolby16_UnifiedApproachHDR.pdf Plasma technology Production discontinued in 2014

9 06/10/2017 IGZO (InGaZnO) TFT More (IEEE Spectrum 2010) e-ink.pdf electrowetting.pdf IEEE ELECTRON DEVICE LETTERS, VOL. 33, NO. 4, APRIL 2012, P IGZO (InGaZnO) TFT IGZO (InGaZnO) TFT

Oxide semiconductor thin-film transistors (TFTs) have attracted attention as leading devices for nextgeneration displays because of their transparency, flexibility,

The current drivability of amorphous silicon TFTs is insufficient for use in organic LED (OLED) displays, and the poor uniformity of polycrystalline silicon TFTs is a

So far, amorphous IGZO has been mainly investigated as a TFT channel material.

5-inch flexible OLED using CAAC IGZO TFT drivers A c-axis aligned crystal (CAAC) film is closer to a single crystal than an amorphous material.

The CAAC differs from a polycrystal, which generally has a, b, and c axes oriented at random and with clear grain boundaries.

10 Oxide semiconductor thin-film transistors (TFTs) have attracted attention as leading devices for nextgeneration displays because of their transparency, flexibility, high-speed operations, and larger sizes. These features are not available simultaneously in existing silicon-based TFTs. The current drivability of amorphous silicon TFTs is insufficient for use in organic LED (OLED) displays, and the poor uniformity of polycrystalline silicon TFTs is a critical issue for large-size displays. Oxide semiconductor TFTs are expected to overcome such shortcomings. The crystalline structure of InGaZnO4 was found in So far, amorphous IGZO has been mainly investigated as a TFT channel material. However, reliability issues such as degradation under temperature stress have not been solved sufficiently inch flexible OLED using CAAC IGZO TFT drivers A c-axis aligned crystal (CAAC) film is closer to a single crystal than an amorphous material. It has c- axis alignment like a single crystal, but its a-b plane has a mosaic pattern and no grain boundaries. The CAAC differs from a polycrystal, which generally has a, b, and c axes oriented at random and with clear grain boundaries. Figure shows plane and crosssectional transmission electron microscopy (TEM) images of our thin film, respectively. The crystal structure in the film is hexagonal when seen from the c-axis. It has a layered structure when seen from the direction perpendicular to the c-axis. CAAC IGZO TFT Projectors: LCD Projectors: LCoS Liquid Crystal on Silicon (Sony: SXRD, Silicon X-tal Reflective Display) Polarization is managed by splitters no films on the LC Is traversed twice by light can be thin fast High aperture ratio efficient

Projectors: LCoS Projectors: Digital Light Processing Projectors: light sources By combining a laser, a fluorescent element and an LED Casio has created an original

Casio has achieved high brightness output of green light, (difficult with conventional semiconductor light sources), by efficiently converting blue laser light into

11 Projectors: LCoS Projectors: Digital Light Processing Projectors: light sources By combining a laser, a fluorescent element and an LED Casio has created an original mercuryfree hybrid light source capable of generating high brightness. Casio has achieved high brightness output of green light, (difficult with conventional semiconductor light sources), by efficiently converting blue laser light into green light using a fluorescent element. Projectors: light sources Laser Display Conference, Yokohama, 2013 * lm ( ANSI lumen) laser projector * Free-space coupled laser source (i.e. no fiber coupling) * Semiconductor lasers: * blue and red are direct diodes * green is frequency converted IR laser diode * Wavelengths: 460 nm for blue, 532 nm for green and 637 nm for red. Resulting colour gamut completely encompasses DCI colour gamut. * Total optical laser power: about 600W. * The power of the lasers is white balanced to standard DCI (D63) white point, without the need for electronic color correction. * Optical architecture: K DMDs, color splitting prism. * Low Speckle [Interference always exists between light and object features (optical fibers, screen) having size close to wavelength Light is sourced by a laser is coherent highly correlated spatially and temporally stable interference SPECKLE NOISE]

Performances Performances luminance contrast nit (cd/m^2) n:1 Display LCD 300-500 500-1000... PLASMA 1000-1500 1000-10,000.

manufacturers often employ various methods of distorting the calculation of dynamic range, such as altering room illumination

objects, outdoor, sunny: few tens cd/m^2 Dark objects, indoor, natural light: few cd/m^2 LCD Display, indoor, white: 269 cd/m^2

9 cd/m^2 DLP projector, dark indoor, black: 0.05 cd/m^2 Projection screen, indoor, natural light 39.

.. or mixing up static (spatial) and dynamic (temporal) contrast values 3-D State of the Art in Stereoscopic and Autostereoscopic

12 Performances Performances luminance contrast nit (cd/m^2) n:1 Display LCD PLASMA , OLED <LCD >>LCD luminous flux lumen (cd*steradians) Projector LCD DLP Comment: Display manufacturers often employ various methods of distorting the calculation of dynamic range, such as altering room illumination between measurements (Trentacoste 2007) White paper, direct sunlight: cd/m^2 White paper, outdoor, sunny: 1630 cd/m^2 Dark objects, outdoor, sunny: few tens cd/m^2 Dark objects, indoor, natural light: few cd/m^2 LCD Display, indoor, white: 269 cd/m^2 LCD Display, indoor, black: 1.92 cd/m^2 LCD Display, indoor, off: 1.15 cd/m^2 DLP projector, dark indoor, white (100 ): 57.9 cd/m^2 DLP projector, dark indoor, black: 0.05 cd/m^2 Projection screen, indoor, natural light 39.7 cd/m^2 -- Bad case dynamic range: ( ) / ( ) = 2.5 DLP projector, dark indoor, white (69 ) 183 cd/m^2... or mixing up static (spatial) and dynamic (temporal) contrast values 3-D State of the Art in Stereoscopic and Autostereoscopic Displays Hakan Urey, Senior Member IEEE, Kishore V. Chellappan, Erdem Erden, Student Member IEEE, and Phil Surman Proceedings of the IEEE Vol. 99, No. 4, April 2011 Displays_3D_Urey11.pdf

13 The type of 2-D signal f(x,y) we deal with is represented by a real function of two integer variables f ( x, y) f ( xt, yt ) f ( x, y ) x xt, y yt x y a a a x a y A 2-D function is causal if f(x,y)=0 for x,y<0 It is semicausal if f(x,y)=0 for x<0, (x=0 and y<0) A 2-D system is causal or semicausal Data domain Frequency domain if the "previous" input data are located left/above the dashed lines

The Moiré pattern is an aliasing effect, often

In this case it takes the form of a low-frequency

before quantization can improve the appearance of

The existence of pixels having amplitude close to the

Note: the binarization threshold is the same See

More visually effective algorithms exist

15 The Moiré pattern is an aliasing effect, often visible on finely textured regions. In this case it takes the form of a low-frequency vertically running sinusoid : dithering Adding noise before quantization can improve the appearance of coarsely quantized images. The existence of pixels having amplitude close to the threshold(s) is made apparent. Note: the binarization threshold is the same See Matlab A randomized version of halftone printing. More visually effective algorithms exist (Floyd-Steinberg: error diffusion) see ErrorDiffusion.pdf Sub-pixel dithering can be used to increase the graylevel resolution in (medical) colour displays

Liquid Crystal Display (LCD)

Liquid Crystal Display (LCD) When coming into contact with grooved surface in a fixed direction, liquid crystal molecules line up parallelly along the grooves. When coming into contact with grooved surface