Liquid Crystal Display (LCD)

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

Light passes through liquid crystals, following the direction in which the molecules are arranged.

1 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 in a fixed direction, liquid crystal molecules line up parallelly along the grooves. Light passes through liquid crystals, following the direction in which the molecules are arranged. When the molecule arrangement is twisted 90 degrees as shown in the figure, the light also twists 90 degrees as it passes through the liquid crystals. LCD When two polarizing filters are arranged along perpendicular polarizing axes, light entering from above is re-directed 90 degrees along the helix arrangement of the liquid crystal molecules so that it passes through the lower filter. bright dark When voltage is applied, the liquid crystal molecules straighten out of their helix pattern and stop redirecting the angle of the light, thereby preventing light from passing through the lower filter.

Simple matrix and active matrix LCD Passive matrix LCD Active matrix LCD Low quality Simple production High quality High cost The X electrodes are laid on the lower substrate of the liquid crystal

In active matrix LCDs, switching transistors (TFTs) or diodes are attached to each pixel to switch each one on or off. X and Y electrodes are formed on the same substrate as TFT (or diode) arrays.

com/ LCD: Nomenclature Two different modes for light source -Transmissive (Backlight) -Reflective mode http://ganter.free.fr/siteanglais/pages/tft1.

2 Simple matrix and active matrix LCD Passive matrix LCD Active matrix LCD Low quality Simple production High quality High cost The X electrodes are laid on the lower substrate of the liquid crystal cell, and the Y electrodes are laid on the upper substrate. Electrical signals are applied to the X and Y conductors with the proper timing to select the target pixels. In active matrix LCDs, switching transistors (TFTs) or diodes are attached to each pixel to switch each one on or off. X and Y electrodes are formed on the same substrate as TFT (or diode) arrays. The switching signals are applied to the X electrodes. Video signals are then applied to the Y electrodes. LCD: Nomenclature Two different modes for light source -Transmissive (Backlight) -Reflective mode The type of liquid crystal -TN (Twisted Nematic) -STN (Super Twisted Nematic) The method of applying voltage - Simple matrix - Active matrix The materials for TFT - Amorphous Si (Easy to fabricate in a large dimension) - Low Temperature Polycrystalline Si (fast response due to the high mobility of electron, requires costive laser crystallization process)

LCD: Nematic state, TN, STN A form of liquid crystal with an appearance of moving, threadlike structures, particularly visible when observed in thick specimens with polarized light.

This form has one optical axis that occupies the direction of an applied magnetic field. http://www.photonics.com/dictionary/lookup/xq/asp/url.lookup/entrynum.3472/letter.n/pu./qx/lookup.

This extra rotation gives the crystal a much steeper voltage-brightness response curve and also widens the angle at which the display can be viewed before losing much contrast.

3 LCD: Nematic state, TN, STN A form of liquid crystal with an appearance of moving, threadlike structures, particularly visible when observed in thick specimens with polarized light. During this phase, the molecules of the crystal are parallel and able to travel past each other following the direction of their longitudinal axes. This form has one optical axis that occupies the direction of an applied magnetic field. Super-twisted nematic LCDs Twisted nematic displays rotate the director of the liquid crystal by 90 o, but super-twisted nematic displays employ up to a 270 o rotation. This extra rotation gives the crystal a much steeper voltage-brightness response curve and also widens the angle at which the display can be viewed before losing much contrast. With the sharper response, it is possible to achieve higher contrast with the same voltage selection ratio. LCD: Transmissive or Reflective In transmissive mode, the LCD pixels are illuminated from behind (i.e. opposite the viewer) using a cold cathode fluorescent lamp (CCFL) or LED. Transmissive LCDs offer wide color gamut, high contrast and are typically used in laptop personal computers. Transmissive LCDs offer the best performance under lighting conditions varying from complete darkness to an office environment. In very bright outdoor environments they tend to wash out unless they have high brightness backlights. Reflective LCD pixels reflect incident light originating from the ambient environment or from a frontlight. Reflective LCDs can offer very low power (especially without a front light) and are often used in small portable devices such as handheld games, PDA s or other portable instrumentation. Reflective LCDs offer the best performance under lighting conditions typical of office environments and brighter. Under dim lighting conditions, reflective LCDs will require a frontlight. Transflective LCDs combine transmissive and reflective characteristics. The pixels in a transflective display are partially transmitting and are illuminated by a backlight. The pixels are also partially reflective, so under ambient illumination they also reflect light from the environment. Transflective LCDs are often used in devices that will be used under a wide variety of lighting conditions (from complete darkness to full sunlight). Under dim lighting conditions transflective LCDs offer visual performance similar to transmissive LCDs, while under bright lighting conditions they offer visual performance similar to reflective LCDs.

LCD: Reflective http://www.fujitsu.com/kr/services/pc/pda/index.html Preparation of ploy-si for TFT by Laser Crystallization http://www.lambdaphysik.com/images/sitepages/sitepag es_paragraph_id_719.

Laser crystallization is a process that melts the amorphous silicon thin film by using a KrF excimer laser (wavelenth=248 nm), and let the melt resolidify to form polysilicon.

Most importantly, the energy deposited onto the sample is essentially confined in a shallow region on the silicon surface and the entire process takes only about the order of 100 ns.

4 LCD: Reflective Preparation of ploy-si for TFT by Laser Crystallization es_paragraph_id_719.jpg Laser crystallization is an efficient technology for obtaining highperformance polycrystalline Si thin film transistors (poly-si TFTs) for advanced flat panel display applications. Laser crystallization is a process that melts the amorphous silicon thin film by using a KrF excimer laser (wavelenth=248 nm), and let the melt resolidify to form polysilicon. Laser crystallization has been shown to be a promising technique for crystallization of amorphous silion due to its low cost and high efficiency. Most importantly, the energy deposited onto the sample is essentially confined in a shallow region on the silicon surface and the entire process takes only about the order of 100 ns. This is the reason why excimer laser crystallization is a low temperature processing technique or a low thermal butget processing technique. Therefore by using laser crystallization, inexpansive glass or even flexible plastic can be used as substrate. Polysilicon is a better material for fabricating thin film transistors (TFTs) becasue it has better electrical properties than amorphous silicon. Less grain boundaries (bigger grains) is prefered in order to increase field mobility. With high quality poly-silicon produced, integration of driver circuitary and improvement on display performance can be achieved. Therefore, the task for laser crystallization is to increase grain size and improve uniformity by controlling the resolidification direction (grain growth direction) by effectively controlling the temperature field inside the silicon layer. In addition, the recrystallization process is still not very well understood. Therefore, the goal of this research project is to understand the recrystallization process by different optical and electrical probing techniques and also to practically study different temperature controlling techniques to control grain growth. Text from

5 Shortcoming of LCD: Poor viewing angle LCD: it is like blind in the window!

Touch Screen in LCD display 1. Polyester Film 2. Upper Resistive Circuit Layer 3.

Lower Resistive Circuit Layer 5. Insulating Dots 6. Glass/Acrylic Substrate 7.

Lower Resistive Circuit Layer, producing a circuit switch from the activated area. 8.

converts them into the digital X and Y coordinates of the activated area. http://www.

6 Touch Screen in LCD display 1. Polyester Film 2. Upper Resistive Circuit Layer 3. Conductive ITO (Transparent Metal Coating) 4. Lower Resistive Circuit Layer 5. Insulating Dots 6. Glass/Acrylic Substrate 7. Touching the overlay surface causes the (2) Upper Resistive Circuit Layer to contact the (4) Lower Resistive Circuit Layer, producing a circuit switch from the activated area. 8. The touchscreen controller gets the alternating voltages between the (7) two circuit layers and converts them into the digital X and Y coordinates of the activated area. LCD with other displays Med. size Large size Small size Large size

The display in the future 41-80 inch: large living-room HDTV (Projection TV>PDP PDP PDP>TFT-LCD) 21-40 inch: living-room HDTV, (CRT PDP-CRT PDP=CRT=TFT-LCD) 10-20 inch: PC

phone, DSC, DVC, watch PDA (STN-LCD OLED>TFT-LCD OLED) 1 inch: Head-mount display for wearable computer ( LcoS LCoS LCoS) 1 inch: Head Mount Display for Wearable Computer

7 The display in the future inch: large living-room HDTV (Projection TV>PDP PDP PDP>TFT-LCD) inch: living-room HDTV, (CRT PDP-CRT PDP=CRT=TFT-LCD) inch: PC monitor, personal TV, Notebook (CRT CRT=TFT-LCD TFT-LCD=OLED=CRT) 5-9 inch: PDA, mobile computer, telematics (GPS & ITS), (STN-LCD TFT-LCD TFT-LCD=OLED) 2-4 inch: mobile phone, DSC, DVC, watch PDA (STN-LCD OLED>TFT-LCD OLED) 1 inch: Head-mount display for wearable computer ( LcoS LCoS LCoS) 1 inch: Head Mount Display for Wearable Computer Requires quality screen because it should be projected to a large area. Liquid crystal on silicon. Ubiquitous computing

1 inch: LCOS (Liquid crystal on Silicon): Principle

Si single crystal Highly integrated structure

reflective LCD using Si single crystal - High

Compact size Limitation - Contrast 1 inch: LCOS

8 1 inch: LCOS (Liquid crystal on Silicon): Principle Reflective LCD Light source are given from the front Si single crystal Highly integrated structure Projection Optics are required Highly integrated reflective LCD using Si single crystal - High resolution and high speed (Si single crystal) - Compact size Limitation - Contrast 1 inch: LCOS (Liquid crystal on Silicon)

DLP A DLP chip's micromirrors are mounted on tiny hinges that enable them to tilt either toward the light source in a DLP projection system (ON) or away from it (OFF)-creating a light or dark pixel

9 DLP A DLP chip's micromirrors are mounted on tiny hinges that enable them to tilt either toward the light source in a DLP projection system (ON) or away from it (OFF)-creating a light or dark pixel on the projection surface. The bit-streamed image code entering the semiconductor directs each mirror to switch on and off up to several thousand times per second. When a mirror is switched on more frequently than off, it reflects a light gray pixel; a mirror that's switched off more frequently reflects a darker gray pixel. In this way, the mirrors in a DLP projection system can reflect pixels in up to 1,024 shades of gray to convert the video or graphic signal entering the DLP chip into a highly detailed grayscale image. DLP Add color

10 DLP

Solid State Devices 4B6

Solid State Devices 4B6 Lecture 13 Projection and 3D displays: LCD, DLP and LCOS Daping Chu Lent 2016 Development of flat panel displays (FPDs) (LCD) in early days 1 A 105 inch TFT-LCD 4k2k curved panel