normally white transmissive lcd panel factory

TFT LCDs have become the norm for small-to-medium size displays in a variety of products within industrial, medical, POS and consumer applications. Compared to passive-addressed monochrome LCDs, TFT … [Read more...]

“Reflective”, “transmissive” and “transflective” are terms often used in connection with liquid crystal display (LCD) technology. They describe the ways in which LCD display modules are illuminated. In contrast to the emissive display technologies, like OLED displays (organic light-emitting diode) and VFDs (vacuum fluorescence displays), LCDs require a light source such as the sun, or artificial room light, or an integrated backlight, which is typically lit by LED (light-emitting diode) semiconductors.

The mode of operation when light from a backlight passes through the LCD glass is called transmissive. The LCD glass or LCD panel functions as an “optical switch” where light from the backlight passes through the LCD cell depending on the orientation of liquid crystal molecules. The orientation can be “switched” on or off by an electrical field. Backlights produce a lot of light, making the display content very bright. The negative side of using backlights is that they require a significant amount of energy within an LCD display module, especially because the backlight is required to be on all the time even if there’s no content showing on the display. In direct sunlight, a transmissive LCD screen can become ‘washed-out’ if the sunlight overpowers the luminance of the backlight. Strong enough backlights to maintain sufficient contrast in direct sunlight – such as in aviation displays – are not compatible with the requirements of portable devices.

Some displays use ambient light rather than a backlight (View our Sun Vision Display brand of outdoor digital signage for an excellent example). This mode of operation is called reflective. In reflective mode, a mirror is installed behind the liquid crystal layer, either inside the LCD cell or on the rear polarizer. Ambient light passes through the LCD cell from the front side and is reflected by the mirror back to the viewer. The advantage is lower power consumption and excellent visibility in direct sunlight, making such displays excellent solutions for outdoor daytime applications. To be visible at night or in dark settings, reflective LCDs require additional lighting.

Transflective LCD displays have both transmissive and reflective characteristics. They contain an integrated backlight unit and a semi-transparent reflector or a reflector with a hole for each pixel. Again, the reflector can be behind the rear polarizer or inside the LCD cell behind the liquid crystal layer. Light from the backlight can pass the semi-transparent reflector and operate the display in the transmissive mode. At the same time, ambient light can be reflected so that the display is visible in direct sunlight as well. Care must be taken to account for the fact that in the transmissive mode of operation the light passes the liquid crystal layer once, while in the reflective mode it passes the liquid crystal layer twice. The appearance of transflective displays is a compromise. It is the most flexible solution as it allows for lower power consumption in bright environments and readability in any lighting condition. This comes at the expense of top performance in the pure illumination modes and sometimes significant additional manufacturing cost.

Important technical improvements of LCD, such as LED backlighting and wide viewing Angle, are directly related to LCD. And account for an LCD display 80% of the cost of the LCD panel, enough to show that the LCD panel is the core part of the entire display, the quality of the LCD panel, can be said to directly determine the quality of an LCD display.

The production of civil LCD displays is just an assembly process. The LCD panel, the main control circuit, shell, and other parts of the main assembly, basically will not have too complex technical problems.

Does this mean that LCDS are low-tech products? In fact, it is not. The production and manufacturing process of the LCD panels is very complicated, requiring at least 300 process processes. The whole process needs to be carried out in a dust-free environment and with precise technology.

The general structure of the LCD panel is not very complex, now the structure of the LCD panel is divided into two parts: the LCD panel and the backlight system.

Due to the LCD does not shine, so you need to use another light source to illuminate, the function of the backlight system is to this, but currently used CCFL lamp or LED backlight, don’t have the characteristics of the surface light source, so you need to guide plate, spreadsheet components, such as linear or point sources of light evenly across the surface, in order to make the entire LCD panel on the differences of luminous intensity is the same, but it is very difficult, to achieve the ideal state can be to try to reduce brightness non-uniformity, the backlight system has a lot to the test of design and workmanship.

In addition, there is a driving IC and printed circuit board beside the LCD panel, which is mainly used to control the rotation of LCD molecules in the LCD panel and the transmission of display signals. The LCD plate is thin and translucent without electricity. It is roughly shaped like a sandwich, with an LCD sandwiched between a layer of TFT glass and a layer of colored filters.

LCD with light refraction properties of solid crystals, with fluid flow characteristics at the same time, under the drive of the electrode, can be arranged in a way that, in accordance with the master want to control the strength of the light through, and then on the color filter, through the red, green, blue three colors of each pixel toning, eventually get the full-screen image.

According to the functional division, the LCD panel can be divided into the LCD panel and the backlight system. However, to produce an LCD panel, it needs to go through three complicated processes, namely, the manufacturing process of the front segment Array,the manufacturing process of the middle segment Cell, and the assembly of the rear segment module. Today we will be here, for you in detail to introduce the production of the LCD panel manufacturing process.

The manufacturing process of the LCD panel Array is mainly composed of four parts: film, yellow light, etch and peel film. If we just look at it in this way, many netizens do not understand the specific meaning of these four steps and why they do so.

First of all, the motion and arrangement of LCD molecules need electrons to drive them. Therefore, on the TFT glass, the carrier of LCD, there must be conductive parts to control the motion of LCD. In this case, we use ITO (Indium Tin Oxide) to do this.ITO is transparent and also acts as a thin-film conductive crystal so that it doesn’t block the backlight.

The different arrangement of LCD molecules and the rapid motion change can ensure that each pixel displays the corresponding color accurately and the image changes accurately and quickly, which requires the precision of LCD molecule control.ITO film needs special treatment, just like printing the circuit on the PCB board, drawing the conductive circuit on the whole LCD board.

This completes the previous Array process. It is not difficult to see from the whole process that ITO film is deposited, photoresist coated, exposed, developed, and etched on TFT glass, and finally, ITO electrode pattern designed in the early stage is formed on TFT glass to control the movement of LCD molecules on the glass. The general steps of the whole production process are not complicated, but the technical details and precautions are very complicated, so we will not introduce them here. Interested friends can consult relevant materials by themselves.

The glass that the LCD board uses makes a craft also very exquisite. (The manufacturing process flow of the LCD display screen)At present, the world’s largest LCD panel glass, mainly by the United States Corning, Japan Asahi glass manufacturers, located in the upstream of the production of LCD panel, these manufacturers have mastered the glass production technology patents. A few months ago, the earthquake caused a corning glass furnace shutdown incident, which has caused a certain impact on the LCD panel industry, you can see its position in the industry.

As mentioned earlier, the LCD panel is structured like a sandwich, with an LCD sandwiched between the lower TFT glass and the upper color filter. The terminal Cell process in LCD panel manufacturing involves the TFT glass being glued to the top and bottom of a colored filter, but this is not a simple bonding process that requires a lot of technical detail.

As you can see from the figure above, the glass is divided into 6 pieces of the same size. In other words, the LCD made from this glass is finally cut into 6 pieces, and the size of each piece is the final size. When the glass is cast, the specifications and sizes of each glass have been designed in advance.

Directional friction:Flannelette material is used to rub the surface of the layer in a specific direction so that the LCD molecules can be arranged along the friction direction of the aligned layer in the future to ensure the consistency of the arrangement of LCD molecules. After the alignment friction, there will be some contaminants such as flannelette thread, which need to be washed away through a special cleaning process.

After the TFT glass substrate is cleaned, a sealant coating is applied to allow the TFT glass substrate to be bonded to the color filter and to prevent LCD outflow.

Finally, the conductive adhesive is applied to the frame in the bonding direction of the glass of the color filter to ensure that external electrons can flow into the LCD layer. Then, according to the bonding mark on the TFT glass substrate and the color filter, two pieces of glass are bonded together, and the bonding material is solidified at high temperatures to make the upper and lower glasses fit statically.

Color filters are very important components of LCD panels. Manufacturers of color filters, like glass substrate manufacturers, are upstream of LCD panel manufacturers. Their oversupply or undersupply can directly affect the production schedule of LCD panels and indirectly affect the end market.

As can be seen from the above figure, each LCD panel is left with two edges after cutting. What is it used for? You can find the answer in the later module process

Finally, a polarizer is placed on both sides of each LCD substrate, with the horizontal polarizer facing outwards and the vertical polarizer facing inwards.

When making LCD panel, must up and down each use one, and presents the alternating direction, when has the electric field and does not have the electric field, causes the light to produce the phase difference and to present the light and dark state, uses in the display subtitle or the pattern.

The rear Module manufacturing process is mainly the integration of the drive IC pressing of the LCD substrate and the printed circuit board. This part can transmit the display signal received from the main control circuit to the drive IC to drive the LCD molecules to rotate and display the image. In addition, the backlight part will be integrated with the LCD substrate at this stage, and the complete LCD panel is completed.

Firstly, the heteroconductive adhesive is pressed on the two edges, which allows external electrons to enter the LCD substrate layer and acts as a bridge for electronic transmission

Next is the drive IC press. The main function of the drive IC is to output the required voltage to each pixel and control the degree of torsion of the LCD molecules. The drive IC is divided into two types. The source drive IC located in the X-axis is responsible for the input of data. It is characterized by high frequency and has an image function. The gate drive IC located in the Y-axis is responsible for the degree and speed of torsion of LCD molecules, which directly affects the response time of the LCD display. However, there are already many LCD panels that only have driving IC in the X-axis direction, perhaps because the Y-axis drive IC function has been integrated and simplified.

The press of the flexible circuit board can transmit data signals and act as the bridge between the external printed circuit and LCD. It can be bent and thus becomes a flexible or flexible circuit board

The manufacturing process of the LCD substrate still has a lot of details and matters needing attention, for example, rinse with clean, dry, dry, dry, ultrasonic cleaning, exposure, development and so on and so on, all have very strict technical details and requirements, so as to produce qualified eyes panel, interested friends can consult relevant technical information by a search engine.

LCD (LC) is a kind of LCD, which has the properties of light transmission and refraction of solid Crystal, as well as the flow property of Liquid. It is because of this property that it will be applied to the display field.

However, LCD does not emit light autonomously, so the display equipment using LCD as the display medium needs to be equipped with another backlight system.

First, a backplate is needed as the carrier of the light source. The common light source for LCD display equipment is CCFL cold cathode backlight, but it has started to switch to an LED backlight, but either one needs a backplate as the carrier.

CCFL backlight has been with LCD for a long time. Compared with LED backlight, CCFL backlight has many defects. However, it has gradually evolved to save 50% of the lamp and enhance the transmittance of the LCD panel, so as to achieve the purpose of energy-saving.

With the rapid development of LED in the field of lighting, the cost has been greatly reduced.LCD panels have also started to use LED as the backlight on a large scale. Currently, in order to control costs, an LED backlight is placed on the side rather than on the backplate, which can reduce the number of LED grains.

At the top of the diffusion plate, there will be 3~4 diffuser pieces, constantly uniform light to the whole surface, improve the uniformity of light, which is directly related to the LCD panel display effect. Professional LCD in order to better control the brightness uniformity of the screen, panel procurement, the later backlight control circuit, will make great efforts to ensure the quality of the panel.

However, it is much simpler to use a side white LED as a backlight. The small circuit board on the far left of the figure above is the backlight of the LED.

Since the LCD substrate and the backlight system are not fixed by bonding, a metal or rubber frame is needed to be added to the outer layer to fix the LCD substrate and the backlight system.

After the period of the Module, the process is completed in LCM (LCDModule) factory, the core of this part of the basic does not involve the use of LCD manufacturing technology, mainly is some assembly work, so some machine panel factories such as chi mei, Korea department such as Samsung panel factory, all set with LCM factories in mainland China, Duan Mo group after the LCD panel assembly, so that we can convenient mainland area each big monitor procurement contract with LCD TV manufacturers, can reduce the human in the whole manufacturing and transportation costs.

However, neither Taiwan nor Korea has any intention to set up factories in mainland China for the LCD panel front and middle manufacturing process involving core technologies. Therefore, there is still a long way to go for China to have its own LCD panel industry.

Newhaven 20x2 character Liquid Crystal Display shows characters with white pixels on a black background when powered on. This transmissive LCD Display requires a backlight for visibility while offering a wide operating temperature range from -20 to 70 degrees Celsius. This NHD-0220DZ-NSW-FBW display has an optimal view of 6:00. This display operates at 5V supply voltage and is RoHS compliant.

Our tft lcd display are widely used on infrared thermometer, coffee machine, treadmill, industrial control, elevator, stereo system, car in-dash board videao door bell etc.

A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directlybacklight or reflector to produce images in color or monochrome.seven-segment displays, as in a digital clock, are all good examples of devices with these displays. They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while other displays have larger elements. LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement. For example, a character positive LCD with a backlight will have black lettering on a background that is the color of the backlight, and a character negative LCD will have a black background with the letters being of the same color as the backlight. Optical filters are added to white on blue LCDs to give them their characteristic appearance.

Glass substrate with ITO electrodes. The shapes of these electrodes will determine the shapes that will appear when the LCD is switched ON. Vertical ridges etched on the surface are smooth.

LCDs are used in a wide range of applications, including LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage. Small LCD screens are common in LCD projectors and portable consumer devices such as digital cameras, watches, digital clocks, calculators, and mobile telephones, including smartphones. LCD screens are also used on consumer electronics products such as DVD players, video game devices and clocks. LCD screens have replaced heavy, bulky cathode-ray tube (CRT) displays in nearly all applications. LCD screens are available in a wider range of screen sizes than CRT and plasma displays, with LCD screens available in sizes ranging from tiny digital watches to very large television receivers. LCDs are slowly being replaced by OLEDs, which can be easily made into different shapes, and have a lower response time, wider color gamut, virtually infinite color contrast and viewing angles, lower weight for a given display size and a slimmer profile (because OLEDs use a single glass or plastic panel whereas LCDs use two glass panels; the thickness of the panels increases with size but the increase is more noticeable on LCDs) and potentially lower power consumption (as the display is only "on" where needed and there is no backlight). OLEDs, however, are more expensive for a given display size due to the very expensive electroluminescent materials or phosphors that they use. Also due to the use of phosphors, OLEDs suffer from screen burn-in and there is currently no way to recycle OLED displays, whereas LCD panels can be recycled, although the technology required to recycle LCDs is not yet widespread. Attempts to maintain the competitiveness of LCDs are quantum dot displays, marketed as SUHD, QLED or Triluminos, which are displays with blue LED backlighting and a Quantum-dot enhancement film (QDEF) that converts part of the blue light into red and green, offering similar performance to an OLED display at a lower price, but the quantum dot layer that gives these displays their characteristics can not yet be recycled.

Since LCD screens do not use phosphors, they rarely suffer image burn-in when a static image is displayed on a screen for a long time, e.g., the table frame for an airline flight schedule on an indoor sign. LCDs are, however, susceptible to image persistence.battery-powered electronic equipment more efficiently than a CRT can be. By 2008, annual sales of televisions with LCD screens exceeded sales of CRT units worldwide, and the CRT became obsolete for most purposes.

9.7″ 1024 x (RGB) x 768 Transmissive Color TFT Display Phoenix Display International PDI097XGBH-01 is a small-size 9.7” color TFT liquid crystal display (LCD) with a module size of 210.20 * 164.20 * 2.8 mm, and active area 196.61 * 147.46 mm. This product is a-Si TFT, Normally White, Transmissive glass with a 1024 * RGB * 768 resolution. Its brightness is 280 nits with a contrast ratio of 500. Using a  TBD driver with a LVDS  interface and a zero insertion force (ZIF) type flex interconnect. This product offers improved contrast , color saturation…

10.1″  1024 x (RGB) x 600 Transmissive Color TFT Display Phoenix Display International PDI101WSBH-11 is a 10.1” color TFT liquid crystal display (LCD) with a module size of 235.00 * 143.00 * 4.5 mm, and active area 222.78 * 125.28 mm. This product is a-Si TFT, Normally White, Transmissive glass with a 1024 * RGB * 600 resolution. Its brightness is 500 nits with a contrast ratio of 600. Using an TBD driver with a LVDS interface and a zero insertion force (ZIF) type flex interconnect. This product offers improved contrast , color saturation and…

10.1″ 1280 * RGB * 800  Transmissive Color TFT Display Phoenix Display International PDI101WXBN-17 is 10.1” color TFT liquid crystal display (LCD) with a module size of 229.70 * 149.15 * 5.0 mm, and active area 216.96 * 135.60 mm. This product is a-Si TFT, Normally White, Transmissive glass with a 1280 * RGB * 800 resolution. Its brightness is 1000 nits with a contrast ratio of 900. Using an HX8861-H11 driver with a LVDS interface and a zero insertion force (ZIF) type flex interconnect. This product offers improved contrast , color saturation and response…

10.1″ 1200 x (RGB) x 1920 Transmissive Color TFT Display Phoenix Display International PDI101WUBN-33 is a 10.1” color TFT liquid crystal display (LCD) with a module size of 143 * 228.6 * 2.5 mm, and active area 135.36 * 216.58 mm. This product is a-Si TFT, Normally White, Transmissive glass with a 1200 * RGB * 1920 resolution. Its brightness is 250 nits with a contrast ratio of 1000. Using a NT51021 driver with a MIPI interface and a zero insertion force (ZIF) type flex interconnect. This product offers improved contrast , color saturation and…

10.1″ 1024 X (RGB) X 600 Transmissive Color TFT Display Phoenix Display International PDI101WSBH-12 is a 10.1” color TFT liquid crystal display (LCD) with a module size of 235.0 * 143.0 * 4.5 mm and active area of 222.72 x 125.28 mm.  This product is a-Si TFT, Normally White, Transmissive glass with a 1024 x 600 resolution. Its brightness is 500 nits with a contrast ratio of 600. Using an HX8282+HX8696 driver with an RGB interface and a zero insertion force (ZIF) type flex interconnect. This product offers improved contrast, color saturation and response time.…

10.1″ 1280 × 800 Transmissive Color TFT Display Phoenix Display International PDI109-28CMI-32A is a small-size 10.1” color TFT liquid crystal display (LCD) with a module size of 229.46mm x 149.1mm x 2.7mm and active area of 229.46mm x 135.6mm.This product is a-Si TFT, Positive, Transmissive glass with a 1280 x 800 resolution. Its brightness is 320 nits with a contrast ratio of 800:1. Using an IC driver with an LVDS interface and a Zero Insertion Force (ZIF) type flex interconnect. This product offers improved contrast, color saturation and response time. Similar product(s): None. All our color displays…

10.1″  1024 x (RGB) x 600 Transmissive Color TFT Display Phoenix Display International PDI101WSBE-13E is a small-size 10.1” color TFT liquid crystal display (LCD) with a module size of 235.00 * 143.0 * 5.0 mm, and active area 222.72 * 125.28 mm. This product is a-Si TFT, Normally White, Transmissive glass with a 1024 * RGB * 600 resolution. Its brightness is 250 nits with a contrast ratio of 500. Using a  TBD driver with a TTL interface and a zero insertion force (ZIF) type flex interconnect. This product offers improved contrast , color saturation…

2.31 inch 320 x 320 TFT IC ILI9342C IPS/TP lcd touch screen display.From 0.96 ~ 10.1 inch professional design, sales, production LCD solution manufacturers.

That shift represents a move away from displays that use shuttered, transmissive light with color filters, such as liquid-crystal displays (LCDs), to emissive displays that produce colors of light via high-intensity emissions of photons, such as organic and inorganic light-emitting diodes (OLEDs and iLEDS), along with enhancements like quantum dots (QDs).

LCDs have been with us for over a quarter-century in consumer televisions and commercial displays, and long before that as simpler, alphanumeric indicators in products like calculators. But R&D on the underlying technology has essentially plateaued: You can now purchase a 70-inch LCD Ultra HDTV with “smart” Internet functionality for less than $600, compared to the $15,000 price tag on a 28-inch VGA LCD TV 20+ years ago.

Prices for finished LCD panels have dropped so low that they are basically consumable and disposable items. The handful of companies that manufacture LCD panels (mostly in China) are cautious about investing substantial sums of money in the technology. And two of the largest players, Samsung Display Company (SDC) and LG Display (LGD), are now winding down LCD panel production in favor of next-generation emissive displays.

Going forward, LGD has placed its bets on large OLED panels(opens in new tab). These panels use underlying IP licensed from Kodak (of all people), based on patents from the mid-1980s. An array of white OLED emitters (made up of blue and yellow compounds) generates bright light that then passes through red, green, and blue color filters. Additional white pixels provide a luminance boost.

The advantages of such a display are many. Emissive displays have much wider viewing angles than transmissive displays. Unlike LCDs, color saturation and contrast is consistent for any viewer at any angle. While OLEDs can’t quite achieve the peak brightness of a full-backlight-array LCD, they can smoothly reproduce very low levels of luminance right down to a deep black. And OLED pixels have faster on-off cycles than LCD pixels, making for sharper rendering of motion images. Plus, they can reproduce over 20 f-stops of light, more than enough for high dynamic range imaging.

The manufacturing process for white OLEDs (WOLEDs—the display industry does love its acronyms) took many years to perfect and reach acceptable manufacturing yields. An equally difficult challenge was to manufacture the tiny indium-gallium-zinc oxide (IGZO) transistors that switch individual OLED pixels on and off. But WOLED is now considered a mature, affordable, and practical display architecture for everything from computer monitors to digital signs. The fact that they can be fabricated onto flexible, bendable, and even transparent substrates makes them attractive for custom installations, with individual screen sizes from 42 inches up to 97 inches available.

We’re also seeing some interesting hybrid emissive display designs, such as Samsung Displays’ new quantum dot OLED hybrid (QD-OLED), which made its debut at CES 2022. SDC was looking for a new product to replace its sunsetting LCD panel fabrication business, and the QD-OLED fits the bill nicely. It combines a blue OLED emitter (manufactured by sister company Samsung Mobile Display) with a layer of red and green quantum dots.

On paper, the QD-OLED could be a real game changer. It has only four layers in its “stack,” compared to five in a WOLED panel and typically 10 in an LCD panel. This design (in theory) should simplify manufacturing complexity and costs, and (again, in theory) get production and manufacturing yields up to usable levels in less time. As of this writing, however, reports from some Asian electronics industry sites cite very low yields on both the QD-OLED layer and the oxide (presumably IGZO) transistor pixel switching layer.

Indicators are that the next generation of direct-view displays will all feature emissive architectures, and for now, it appears they’ll use OLEDs and/or iLEDs to generate light, with or without quantum dots. To be sure, LCD displays aren’t going away any time soon—but their days do appear to be numbered.

To create an LCD, you take two pieces ofpolarized glass. A special polymer that creates microscopic grooves in the surface is rubbed on the side of the glass that does not have the polarizing film on it. The grooves must be in the same direction as the polarizing film. You then add a coating of nematic liquid crystals to one of the filters. The grooves will cause the first layer of molecules to align with the filter"s orientation. Then add the second piece of glass with the polarizing film at a right angle to the first piece. Each successive layer of TN molecules will gradually twist until the uppermost layer is at a 90-degree angle to the bottom, matching the polarized glass filters.

If we apply an electric charge to liquid crystal molecules, they untwist. When they straighten out, they change the angle of the light passing through them so that it no longer matches the angle of the top polarizing filter. Consequently, no light can pass through that area of the LCD, which makes that area darker than the surrounding areas.

Building a simple LCD is easier than you think. Your start with the sandwich of glass and liquid crystals described above and add two transparent electrodes to it. For example, imagine that you want to create the simplest possible LCD with just a single rectangular electrode on it. The layers would look like this:

The LCD needed to do this job is very basic. It has a mirror (A) in back, which makes it reflective. Then, we add a piece of glass (B) with a polarizing film on the bottom side, and a common electrode plane (C) made of indium-tin oxide on top. A common electrode plane covers the entire area of the LCD. Above that is the layer of liquid crystal substance (D). Next comes another piece of glass (E) with an electrode in the shape of the rectangle on the bottom and, on top, another polarizing film (F), at a right angle to the first one.

The electrode is hooked up to a power source like a battery. When there is no current, light entering through the front of the LCD will simply hit the mirror and bounce right back out. But when the battery supplies current to the electrodes, the liquid crystals between the common-plane electrode and the electrode shaped like a rectangle untwist and block the light in that region from passing through. That makes the LCD show the rectangle as a black area.

Let us start with the basics first; refresh the knowledge about TN and LCD displays in general, later we will talk about TFTs (Thin Film Transistors), how they differ from regular monochrome LCD displays. Then we will go on to the ghosting effect, so we will not only discuss the technology behind the construction of the TFT, but also some phenomena, like the ghosting effect, or grayscale inversion, that are important to understand when using an LCD TFT display.

Next, we will look at different technologies of the TFT LCD displays like TN, IPS, VA, and of course about transmissive and transflective LCD displays, because TFT displays also can be transmissive and transflective. In the last part we will talk about backlight.

Let us start with a short review of the most basic liquid crystal cell, which is the TN (twisted nematic) display. On the picture above, we can see that the light can be transmit through the cell or blocked by the liquid crystal cell using voltage. If you want to learn more about monochrome LCD displays and the basics of LCD displays, follow this link.

What is a TFT LCD display and how it is different from a monochrome LCD display? TFT is called an active display. Active, means we have one or more transistors in every cell, in every pixel and in every subpixel. TFT stands for Thin Film Transistor, transistors that are very small and very thin and are built into the pixel, so they are not somewhere outside in a controller, but they are in the pixel itself. For example, in a 55-inch TV set, the TFT display contains millions of transistors in the pixels. We do not see them, because they are very small and hidden, if we zoom in, however, we can see them in every corner of each pixel, like on the picture below.

On the picture above we can see subpixels, that are basic RGB (Red, Green, Blue) colors and a black part, with the transistors and electronic circuits. We just need to know that we have pixels, and subpixels, and each subpixel has transistors. This makes the display active, and thus is called  the TFT display. TFT displays are usually color displays, but there are also monochrome TFT displays, that are active, and have transistors, but have no colors. The colors in the TFT LCD display are typically added by color filters on each subpixel. Usually the filters are RGB, but we also have RGBW (Red, Green, Blue, White) LCD displays with added subpixels without the filter (White) to make the display brighter.

What is interesting, the white part of the RGB and RGBW screen will look exactly the same from a distance, because the lights are mixed and generate white light, but when we come closer to the screen, we will not see white light at all.

Going a little bit deeper, into the TFT cell, there is a part inside well known to us from the monochrome LCD display Riverdi University lecture. We have a cell, liquid crystal, polarizers, an ITO (Indium Tin Oxide) layer for the electrodes, and additionally an electronic circuit. Usually, the electronic circuit consists of one transistor and some capacitors to sustain the pixel state when we switch the pixel OFF and ON. In a TFT LCD display the pixels are much more complicated because apart from building the liquid crystal part, we also need to build an electronic part.

That is why TFT LCD display technologies are very expensive to manufacture. If you are familiar with electronics, you know that the transistor is a kind of switch, and it allows us to switch the pixel ON and OFF. Because it is built into the pixel itself, it can be done very quickly and be very well controlled. We can control the exact state of every pixel not only the ON and OFF states, but also all the states in between. We can switch the light of the cells ON and OFF in several steps. Usually for TFT LCD displays it will be 8-bit steps per color, so we have 256 steps of brightness for every color, and every subpixel. Because we have three subpixels, we have a 24-bit color range, that means over 16 million combinations, we can, at least theoretically, show on our TFT LCD display over 16 million distinct colors using RGB pixels.

Now that we know how the TFT LCD display works, we can now learn some practical things one of which is LCD TFT ghosting. We know how the image is created, but what happens when we have the image on the screen for a prolonged time, and how to prevent it. In LCD displays we have something called LCD ghosting. We do not see it very often, but in some displays this phenomenon still exists.

Another issue present in TFT displays, especially TN LCD displays, is grayscale inversion. This is a phenomenon that changes the colors of the screen according to the viewing angle, and it is only one-sided. When buying a TFT LCD display, first we need to check what kind of technology it is. If it is an IPS display, like the Riverdi IPS display line, then we do not need to worry about the grayscale inversion because all the viewing angles will be the same and all of them will be very high, like 80, 85, or 89 degrees. But if you buy a more common or older display technology type, like the TN (twisted nematic) display, you need to think where it will be used, because one viewing angle will be out. It may be sometimes confusing, and you need to be careful as most factories define viewing direction of the screen and mistake this with the greyscale inversion side.

On the picture above, you can see further explanation of the grayscale inversion from Wikipedia. It says that some early panels and also nowadays TN displays, have grayscale inversion not necessary up-down, but it can be any angle, you need to check in the datasheet. The reason technologies like IPS (In-Plane Switching), used in the latest Riverdi displays, or VA, were developed, was to avoid this phenomenon. Also, we do not want to brag, but the Wikipedia definition references our website.

We know already that TN (twisted nematic) displays, suffer from grayscale inversion, which means the display has one viewing side, where the image color suddenly changes. It is tricky, and you need to be careful. On the picture above there is a part of the LCD TFT specification of a TN (twisted nematic) display, that has grayscale inversion, and if we go to this table, we can see the viewing angles. They are defined at 70, 70, 60 and 70 degrees, that is the maximum viewing angle, at which the user can see the image. Normally we may think that 70 degrees is better, so we will choose left and right side to be 70 degrees, and then up and down, and if we do not know the grayscale inversion phenomena, we may put our user on the bottom side which is also 70 degrees. The viewing direction will be then like a 6 o’clock direction, so we call it a 6 o’clock display. But you need to be careful! Looking at the specification, we can see that this display was defined as a 12 o’clock display, so it is best for it to be seen from a 12 o’clock direction. But we can find that the 12 o’clock has a lower viewing angle – 60 degrees. What does it mean? It means that on this side there will be no grayscale inversion. If we go to 40, 50, 60 degrees and even a little bit more, probably we will still see the image properly. Maybe with lower contrast, but the colors will not change. If we go from the bottom, from a 6 o’clock direction where we have the grayscale inversion, after 70 degrees or lower we will see a sudden color change, and of course this is something we want to avoid.

We will talk now about the other TFT technologies, that allow us to have wider viewing angles and more vivid colors. The most basic technology for monochrome and TFT LCD displays is twisted nematic (TN). As we already know, this kind of displays have a problem with grayscale inversion. On one side we have a higher retardation and will not get a clear image. That is why we have other technologies like VA (Vertical Alignment), where the liquid crystal is differently organized, and another variation of the TFT technology – IPS which is In-Plane Switching. The VA and IPS LCD displays do not have a problem with the viewing angles, you can see a clear image from all sides.

Apart from the different organization of the liquid crystals, we also organize subpixels a little bit differently in a VA and IPS LCD displays. When we look closer at the TN display, we will just see the subpixels with color filters. If we look at the VA or IPS display they will have subpixels of subpixels. The subpixels are divided into smaller parts. In this way we can achieve even wider viewing angles and better colors for the user, but of course, it is more complicated and more expensive to do.

The picture above presents the TN display and grayscale inversion. For IPS or VA technology there is no such effect. The picture will be the same from all the sides we look so these technologies are popular where we need wide viewing angles, and TN is popular where we don’t need that, like in monitors. Other advantages of IPS LCD displays are they give accurate colors, and wide viewing angles. What is also important in practice, in our projects, is that the IPS LCD displays are less susceptible to mechanical force. When we apply mechanical force to the screen, and have an optically bonded touch screen, we push the display as well as squeeze the cells. When we have a TN display, every push on the cell changes the image suddenly, with the IPS LCD displays with in-plane switching, different liquid crystals organization, this effect is lesser. It is not completely removed but it is much less distinct. That is another reason IPS displays are very popular for smartphones, tablets, when we have the touchscreens usually optically bonded.

If we wanted to talk about disadvantages, there is a question mark over it, as some of them may be true, some of them do not rely on real cases, what kind of display, what kind of technology is it. Sometimes the IPS displays can have higher power consumption than others, in many cases however, not. They can be more expensive, but not necessarily. The new IPS panels can cost like TN panels, but IPS panels definitely have a longer response time. Again, it is not a rule, you can make IPS panels that are very fast, faster than TN panels, but if you want the fastest possible display, probably the TN panel will be the fastest. That is why the TN technology is still popular on the gaming market. Of course, you can find a lot of discussions on the internet, which technology is better, but it really depends on what you want to achieve.

Now, let us look at the backlight types. As we see here, on the picture above, we have four distinct types of backlight possible. The most common, 95 or 99 per cent of the TFT LCD displays on the market are the transmissive LCD display type, where we need the backlight from the back. If you remember from our Monochrome LCD Displays lecture, for transmissive LCD displays you need the backlight to be always on. If you switch the backlight off, you will not see anything. The same as for monochrome LCD displays, but less popular for TFT displays, we have the transflective LCD display type. They are not popular because usually for transflective TFT displays, the colors lack in brightness, and the displays are not very practical to use. You can see the screen, but the application is limited. Some transflective LCD displays are used by military, in applications where power consumption is paramount; where you can switch the backlight off and you agree to have lower image quality but still see the image. Power consumption and saving energy is most important in some kind of applications and you can use transflective LCD displays there. The reflective type of LCD displays are almost never used in TFT. There is one technology called Low Power Reflective Displays (LPRD) that is used in TFT but it is not popular. Lastly, we have a variation of reflective displays with frontlight, where we add frontlight to the reflective display and have the image even without external light.

Just a few words about Low Power Reflective Displays (LPRD). This kind of display uses environmental light, ambient light to reflect, and produce some colors. The colors are not perfect, not perfectly clear, but this technology is becoming increasingly popular because it allows to have color displays in battery powered applications. For example, a smartwatch would be a case for that technology, or an electrical bike or scooter, where we can not only have a standard monochrome LCD display but also a TFT LCD color display without the backlight; we can see the image even in

strong sunlight and not need backlight at all. So, this kind of TFL LCD display technology is getting more and more popular when we have outdoor LCD displays and need a low power consumption.

On the picture above, we have some examples of how transmissive and reflective LCD displays work in the sunlight. If we have a simple image, like a black and white pattern, then on a transmissive LCD display, even with 1000 candela brightness, the image probably will be lower quality than for a reflective LCD display; if we have sunlight, we have very strong light reflections on the surface of the screen. We have talked about contrast in more detail in the lecture Sunlight Readable Displays. So, reflective LCD displays are a better solution for outdoor applications than transmissive LCD displays, where you need a really strong backlight, 1000 candela or more, to be really seen outdoors.

To show you how the backlight of LCD displays is built, we took the picture above. You can see the edge backlight there, where we have LEDs here on the small PCB on the edge, and we have a diffuser that distributes the light to the whole surface of LCD screen.

In addition to the backlight, we have something that is called a frontlight. It is similar to backlight, it also uses the LEDs to put the light into it, but the frontlight needs to be transparent as we have the display behind. On the example on the picture above we can see an e-paper display. The e-paper display is also a TFT display variation, but it is not LCD (liquid crystal), it is a different technology, but the back of the display is the same and it is reflective. The example you see is the Kindle 4 eBook reader. It uses an e-paper display and a frontlight as well, so you can read eBooks even during the night.