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intro_lcd [2026/05/28 11:38] – [Liquid crystal display (LCD)] yusufabdillahintro_lcd [2026/06/05 10:46] (current) – [Working principle] yusufabdillah
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-# Liquid crystal display (LCD)+====== Liquid crystal display (LCD)======
  
 Liquid crystal display, or in short LCD, is a type of display that **does not produce its own light**. Instead, it uses light from an external source and controls it through optical shutter technology. Liquid crystal display, or in short LCD, is a type of display that **does not produce its own light**. Instead, it uses light from an external source and controls it through optical shutter technology.
 The main component of an LCD is the liquid crystal (LC), a material that has properties between a liquid and a solid. When electricity is applied, the liquid crystals twist or tilt, controlling how much light passes through polarized filters to create images on the screen. The main component of an LCD is the liquid crystal (LC), a material that has properties between a liquid and a solid. When electricity is applied, the liquid crystals twist or tilt, controlling how much light passes through polarized filters to create images on the screen.
  
---- +===== TFT LCD =====
-- +
-## TFT LCD+
  
-TFT LCD, or Thin film transistor liquid crystal display, is an active matrix display in which individual transistors control the sub-pixels. The transistors work as rapid electronic switches, which makes it possible to achieve a higher degree of voltage regulation, speed, and contrast compared to passive matrix displays.+ 
 +TFT LCD, or **Thin-Film-Transistor** liquid crystal display, is an **active matrix display** in which individual transistors control the sub-pixels. The transistors work as rapid electronic switches, which makes it possible to achieve a higher degree of voltage regulation, speed, and contrast compared to passive matrix displays.
  
 The TFT circuitry is constructed on a glass substrate through semiconductor fabrication technology. This construction enables individual pixels to retain their charge during the intervals between refreshments with the aid of storage capacitors. The TFT circuitry is constructed on a glass substrate through semiconductor fabrication technology. This construction enables individual pixels to retain their charge during the intervals between refreshments with the aid of storage capacitors.
  
----- +===== Working principle=====
-- +
-## Working principle+
  
-The working principle of TFT LCD starts with the generation of light. Since LCD does not emit any light of its own, a BLU composed of LEDs or CCFL generates uniform light ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). The generated light then passes through a polarizer that permits only those waves of light having particular polarization ((Yang, Deng-Ke, and Shin-Tson Wu. Fundamentals of liquid crystal devices. John Wiley & Sons, 2014.)).+The working principle of TFT LCD starts with the generation of light. Since LCD does not emit any light of its own, a backlight unit (BLU) composed of LEDs or CCFL generates uniform light ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). The generated light then passes through a polarizer that permits only those waves of light having particular polarization ((Yang, Deng-Ke, and Shin-Tson Wu. Fundamentals of liquid crystal devices. John Wiley & Sons, 2014.)).
  
 This display controls light at the sub-pixel level by employing an active matrix technology. In this technology, each pixel is attached to a thin film transistor that functions as an electronic switch. These switches apply voltage across a layer of liquid crystals sandwiched between two glass substrates. As a result, the liquid crystal molecules get twisted and change polarization of the incoming light waves. This display controls light at the sub-pixel level by employing an active matrix technology. In this technology, each pixel is attached to a thin film transistor that functions as an electronic switch. These switches apply voltage across a layer of liquid crystals sandwiched between two glass substrates. As a result, the liquid crystal molecules get twisted and change polarization of the incoming light waves.
  
-After the light is modulated, it passes through color filters made up of red, green, and blue (RGB) sub-pixels ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). By adjusting the intensity of these colors, the display can produce millions of different colors. Finally, the light passes through a second polarizer, called the analyzer, which is placed perpendicular to the first polarizer. Depending on how much the liquid crystals rotate the light, the analyzer either blocks or allows the light to pass, creating dark and bright areas that form the final image on the screen.+After the light is modulated, it passes through colour filters made up of red, green, and blue (RGB) sub-pixels ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). By adjusting the intensity of these colours, the display can produce millions of different colours. Finally, the light passes through a second polarizer, called the analyzer, which is placed perpendicular to the first polarizer. Depending on how much the liquid crystals rotate the light, the analyzer either blocks or allows the light to pass, creating dark and bright areas that form the final image on the screen.
  
-{{ :tft_lcd_display-0808_2048x2048.gif?600 |}}+<figure center |working principle LCD> 
 +{{ :tft_lcd_display-0808_2048x2048.gif | https://www.flyrobo.in/blog/tft-lcd-display?srsltid=AfmBOopt4kZhBhd7kuTj5JpsQgBkrGzl59Ex_V_-J-OvUnRaKuTo68F5}} 
 +<caption> [[https://www.flyrobo.in/blog/tft-lcd-display?srsltid=AfmBOopt4kZhBhd7kuTj5JpsQgBkrGzl59Ex_V_-J-OvUnRaKuTo68F5 | Working principle of LCD ]] </caption> 
 +</figure>
  
-----+=====  Core component =====
  
-- 
-## Core component 
  
 <figure center |structure-of-lcd> <figure center |structure-of-lcd>
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 </figure> </figure>
  
-#### Backlight unit+====  Backlight unit ==== 
  
 Backlight unit (BLU) serves as the **primary light source in LCD displays** because LCD panels are incapable of producing their own light. It produces a uniform beam of white light, which illuminates the entire screen. Although cold cathode fluorescent lamps (CCFL) was the go-to option for a long time, LEDs are being widely used nowadays owing to their superior energy-efficiency and lack of any hazardous substance like mercury ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). BLUs are categorized primarily into two categories; edge lit type, in which the LEDs are placed around the edges of the screen, and direct lit BLUs in which LEDs are placed directly behind the screen. The light guide plate (LGP), as well as various optical films like diffusers and prism films, play a vital role inside the BLU. Reflectors are also incorporated into the BLU to reflect back the light that escapes and enhance energy-efficiency. More advanced BLUs now use mini-LED technology for local dimming, allowing much higher contrast ratios and better image quality ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)). Backlight unit (BLU) serves as the **primary light source in LCD displays** because LCD panels are incapable of producing their own light. It produces a uniform beam of white light, which illuminates the entire screen. Although cold cathode fluorescent lamps (CCFL) was the go-to option for a long time, LEDs are being widely used nowadays owing to their superior energy-efficiency and lack of any hazardous substance like mercury ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). BLUs are categorized primarily into two categories; edge lit type, in which the LEDs are placed around the edges of the screen, and direct lit BLUs in which LEDs are placed directly behind the screen. The light guide plate (LGP), as well as various optical films like diffusers and prism films, play a vital role inside the BLU. Reflectors are also incorporated into the BLU to reflect back the light that escapes and enhance energy-efficiency. More advanced BLUs now use mini-LED technology for local dimming, allowing much higher contrast ratios and better image quality ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)).
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-#### Polarizers+====  Polarisers ====
  
-The polarizer films are present on either side of the liquid crystal layer and **regulate the polarization of light** that goes through the screen. These films are usually made up of stretched polyvinyl alcohol (PVA) along with dichroic substances like iodine, and they are surrounded by triacetyl cellulose (TAC) films ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). Both these polarizers are positioned at right angles to each other, which means that light is allowed to pass only if the liquid crystal layer changes the orientation of the light polarization. Superior polarizer films ensure deeper black levels and more accurate color representation due to strong polarization over a broad wavelength range. 
  
 +The polariser films are present on either side of the liquid crystal layer and **regulate the polarisation of light** that goes through the screen. These films are usually made up of stretched polyvinyl alcohol (PVA) along with dichroic substances like iodine, and they are surrounded by triacetyl cellulose (TAC) films ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). Both these polarisers are positioned at right angles to each other, which means that light is allowed to pass only if the liquid crystal layer changes the orientation of the light polarisation. Superior polariser films ensure deeper black levels and more accurate colour representation due to strong polarisation over a broad wavelength range.
 +
 +
 +====  TFT array on glass ====
  
-#### TFT array on glass 
  
 TFT array forms the **electronic backplane** of the LCD panel. It is made of transistors and bus lines formed on a glass substrate, which is mostly an alkali-free alumina borosilicate glass ((Lehmann, M., & Hischier, R., Part III Electronic Devices. Swiss Centre for Life Cycle Inventories. ecoinvent report No.18, 2007. 13-15.)). Subpixels contain a TFT and a storage capacitor for holding the pixel voltage constant. The TFT array fabrication process involves multiple photolithography processes ranging from four to eight ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). An example of a TFT array is the inverted staggered (bottom-gate) type, where the gate electrode is fabricated first to provide protection to the semiconductor layer from light emission. TFT array forms the **electronic backplane** of the LCD panel. It is made of transistors and bus lines formed on a glass substrate, which is mostly an alkali-free alumina borosilicate glass ((Lehmann, M., & Hischier, R., Part III Electronic Devices. Swiss Centre for Life Cycle Inventories. ecoinvent report No.18, 2007. 13-15.)). Subpixels contain a TFT and a storage capacitor for holding the pixel voltage constant. The TFT array fabrication process involves multiple photolithography processes ranging from four to eight ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). An example of a TFT array is the inverted staggered (bottom-gate) type, where the gate electrode is fabricated first to provide protection to the semiconductor layer from light emission.
  
  
-#### Liquid crystal layer+====  Liquid crystal layer ====
  
-The LC layer acts as the **optical modulator** in the display. This layer fills the extremely thin space, normally about 4 microns, between the TFT and color filter substrates ((Yang, Deng-Ke, and Shin-Tson Wu. Fundamentals of liquid crystal devices. John Wiley & Sons, 2014.)). The liquid crystal substance consists of organic substances having optical anisotropy, which means that such materials have the ability to manage light polarization as it passes through the cell. The initial orientation of the molecules is determined by alignment layers, which are thin films of polyimide that have been rubbed or UV-treated ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). The application of voltage causes the liquid crystal molecules to tilt or rotate in order to manage the amount of light passing through the display. It is crucial to keep a uniform distance between the layers since any inconsistencies will result in defects in brightness and image quality. The latest technology involves using the one drop filling (ODF) process to dispense the LC material before vacuum-bonding the substrates. 
  
 +The LC layer acts as the **optical modulator** in the display. This layer fills the extremely thin space, normally about 4 microns, between the TFT and colour filter substrates ((Yang, Deng-Ke, and Shin-Tson Wu. Fundamentals of liquid crystal devices. John Wiley & Sons, 2014.)). The liquid crystal substance consists of organic substances having optical anisotropy, which means that such materials have the ability to manage light polarisation as it passes through the cell. The initial orientation of the molecules is determined by alignment layers, which are thin films of polyimide that have been rubbed or UV-treated ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). The application of voltage causes the liquid crystal molecules to tilt or rotate in order to manage the amount of light passing through the display. It is crucial to keep a uniform distance between the layers since any inconsistencies will result in defects in brightness and image quality. The latest technology involves using the one drop filling (ODF) process to dispense the LC material before vacuum-bonding the substrates.
  
-#### Color filter layer 
  
-The color filter (CF) substrate is the uppermost layer in an LCD, responsible for **producing the red, green, and blue (RGB) colors** seen on the display. It features a black matrix that prevents light leakages between sub-pixels, as well as RGB patterns made using photo-resist materials based on pigments. A transparent conductor film, such as Indium Tin Oxide (ITO), is also deposited on it to make an electrical connection with the TFT layer. An overcoat layer is also coated on the color filter substrate to provide protection to the liquid crystals and smoothen out the surface. The column spacers are directly created on the color filter substrate to keep a proper distance between the two substrates ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). Some advanced LCDs have the color filter directly coated on the TFT array, called Color Filter on Array (COA).+==== Colour filter layer ====
  
  
-#### Driver circuits+The colour filter (CF) substrate is the uppermost layer in an LCD, responsible for **producing the red, green, and blue (RGB) colours** seen on the display. It features a black matrix that prevents light leakages between sub-pixels, as well as RGB patterns made using photo-resist materials based on pigments. A transparent conductor film, such as Indium Tin Oxide (ITO), is also deposited on it to make an electrical connection with the TFT layer. An overcoat layer is also coated on the colour filter substrate to provide protection to the liquid crystals and smoothen out the surface. The column spacers are directly created on the colour filter substrate to keep a proper distance between the two substrates ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). Some advanced LCDs have the colour filter directly coated on the TFT array, called Colour Filter on Array (COA). 
 + 
 + 
 +==== Driver circuits ==== 
  
 Driver ICs are high-speed integrated circuits that will help to convert the video signal into the required electrical voltage **to operate the display pixels**. The gate drivers turn on the transistors in rows while the source drivers pass the image data along the data lines. The driver ICs could be connected via tape automated bonding (TAB) on flexible film substrates or could even be directly mounted on the glass via chip on glass (COG) ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). In advanced LTPS/Oxide displays, some of the driver circuits could be directly embedded within the glass substrate itself for thinner bezels and reduced cost. The timing controller (T-con) controls the synchronization of image data with the refresh rate of the display. Driver ICs are high-speed integrated circuits that will help to convert the video signal into the required electrical voltage **to operate the display pixels**. The gate drivers turn on the transistors in rows while the source drivers pass the image data along the data lines. The driver ICs could be connected via tape automated bonding (TAB) on flexible film substrates or could even be directly mounted on the glass via chip on glass (COG) ((Souk, Jun, et al., eds. Flat panel display manufacturing. John Wiley & Sons, 2018.)). In advanced LTPS/Oxide displays, some of the driver circuits could be directly embedded within the glass substrate itself for thinner bezels and reduced cost. The timing controller (T-con) controls the synchronization of image data with the refresh rate of the display.
  
----- + 
-- +===== Panel types ===== 
-## Panel types+
  
 The panel type determines the orientation of the liquid crystals (LCs) as well as their movement to control light. The panel type determines the orientation of the liquid crystals (LCs) as well as their movement to control light.
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 </figure> </figure>
  
-#### Twisted nematic (TN)+====  Twisted nematic (TN) ==== 
  
 Twisted nematic (TN) was the first widely used TFT-LCD technology. In TN panels, the liquid crystal molecules twist 90 degrees between the two substrates. When no voltage is applied, light passes through the crossed polarizers, making the display appear bright, it is normally white. When voltage is applied, the molecules align with the electric field and block the light. TN panels are known for their fast response times and low production costs, but they have limited viewing angles and noticeable color changes when viewed from the side ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)). To improve viewing performance, manufacturers often add compensation films. Although newer technologies are now more common, TN panels are still used in affordable monitors and some high-speed gaming displays ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)). Twisted nematic (TN) was the first widely used TFT-LCD technology. In TN panels, the liquid crystal molecules twist 90 degrees between the two substrates. When no voltage is applied, light passes through the crossed polarizers, making the display appear bright, it is normally white. When voltage is applied, the molecules align with the electric field and block the light. TN panels are known for their fast response times and low production costs, but they have limited viewing angles and noticeable color changes when viewed from the side ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)). To improve viewing performance, manufacturers often add compensation films. Although newer technologies are now more common, TN panels are still used in affordable monitors and some high-speed gaming displays ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)).
  
  
-#### In-plane switching or fringe-field switching (IPS/FFS)+====  In-plane switching or fringe-field switching (IPS/FFS) ==== 
  
 In-plane switching (IPS) and fringe-field switching (FFS) were developed to improve viewing angles and color accuracy. In these modes, the liquid crystal molecules rotate parallel to the display surface instead of vertically. The electrodes are placed on the same substrate, creating an electric field that keeps image quality more consistent from different viewing angles ((Yang, Deng-Ke, and Shin-Tson Wu. Fundamentals of liquid crystal devices. John Wiley & Sons, 2014.)). FFS is especially popular in high-resolution smartphones and tablets because it provides better light transmission and works well with small pixels. It is also resistant to “push mura,” making it suitable for touch-screen devices. Modern FFS panels can even support refresh rates up to 600 Hz for professional gaming ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)). In-plane switching (IPS) and fringe-field switching (FFS) were developed to improve viewing angles and color accuracy. In these modes, the liquid crystal molecules rotate parallel to the display surface instead of vertically. The electrodes are placed on the same substrate, creating an electric field that keeps image quality more consistent from different viewing angles ((Yang, Deng-Ke, and Shin-Tson Wu. Fundamentals of liquid crystal devices. John Wiley & Sons, 2014.)). FFS is especially popular in high-resolution smartphones and tablets because it provides better light transmission and works well with small pixels. It is also resistant to “push mura,” making it suitable for touch-screen devices. Modern FFS panels can even support refresh rates up to 600 Hz for professional gaming ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)).
  
  
-#### Vertical alignment (VA)+====  Vertical alignment (VA) ==== 
  
 In vertical alignment (VA), liquid crystals have a natural alignment perpendicular to the substrate without the application of any voltage. As a result, the panels can achieve very dark blacks, and hence they have the best contrast ratio, which is always more than 5000:1 among all LCD types ((Yang, Deng-Ke, and Shin-Tson Wu. Fundamentals of liquid crystal devices. John Wiley & Sons, 2014.)). For this reason, VA panels are most preferred in HD TVs. The current VA panels are equipped with multiple domains to tilt molecules in various directions through voltage, which improves the viewing angles. Additionally, the VA panels are suitable for curved displays due to their mechanical stability. Previous versions of VA panels exhibited problems with color washout in extreme viewing angles ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)); however, recent designs have incorporated special pixel structures and light control films to minimize such problems. In vertical alignment (VA), liquid crystals have a natural alignment perpendicular to the substrate without the application of any voltage. As a result, the panels can achieve very dark blacks, and hence they have the best contrast ratio, which is always more than 5000:1 among all LCD types ((Yang, Deng-Ke, and Shin-Tson Wu. Fundamentals of liquid crystal devices. John Wiley & Sons, 2014.)). For this reason, VA panels are most preferred in HD TVs. The current VA panels are equipped with multiple domains to tilt molecules in various directions through voltage, which improves the viewing angles. Additionally, the VA panels are suitable for curved displays due to their mechanical stability. Previous versions of VA panels exhibited problems with color washout in extreme viewing angles ((Jung, Junho, et al. “Recent progress in liquid crystal devices and materials of TFT-LCDs.” Journal of Information Display 25.1 (2024): 121-142.)); however, recent designs have incorporated special pixel structures and light control films to minimize such problems.
-. + 
-### Manufacturers+ 
 +===== Manufacturers ===== 
  
 - LG Display is the primary proponent of IPS and AH-IPS technologies for both desktop monitors and high-end mobile devices - LG Display is the primary proponent of IPS and AH-IPS technologies for both desktop monitors and high-end mobile devices
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 - AU Optronics (AUO) is a versatile producer of both IPS and VA panels, catering to wide-ranging computer and television market needs - AU Optronics (AUO) is a versatile producer of both IPS and VA panels, catering to wide-ranging computer and television market needs
  
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