how tft display works factory

When compared to the ordinary LCD, TFT LCD gives very sharp and crisp picture/text with shorter response time. TFT LCD displays are used in more and more applications, giving products better visual presentation.

TFT is an abbreviation for "Thin Film Transistor". The colorTFT LCD display has transistors made up of thin films of Amorphous silicon deposited on a glass. It serves as a control valve to provide an appropriate voltage onto liquid crystals for individual sub-pixels. That is why TFT LCD display is also called Active Matrix display.

A TFT LCD has a liquid crystal layer between a glass substrate formed with TFTs and transparent pixel electrodes and another glass substrate with a color filter (RGB) and transparent counter electrodes. Each pixel in an active matrix is paired with a transistor that includes capacitor which gives each sub-pixel the ability to retain its charge, instead of requiring an electrical charge sent each time it needed to be changed. This means that TFT LCD displays are more responsive.

To understand how TFT LCD works, we first need to grasp the concept of field-effect transistor (FET). FET is a type of transistor which uses electric field to control the flow of electrical current. It is a component with three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source.

Using FET, we can build a circuit as below. Data Bus sends signal to FET Source, when SEL SIGNAL applies voltage to the Gate, driving voltage is then created on TFT LCD panel. A sub-pixel will be lit up. A TFT LCD display contains thousand or million of such driving circuits.

Topway started TFT LCD manufacturing more than15 years ago. We produce color TFT LCD display from 1.8 to 15+ inches with different resolutions and interfaces. Here is some more readings about how to choose the right TFT LCD.

The TFT LCD screen display, for the general masses, is no longer a difficult noun. And it is another after semiconductor could create a large number of emerging technology products of the business turnover, more because of its features, thin so it than using the application scope of the cathode ray tube (CRT, cathode ray tube) display made by wider. Today, I’m going to talk about how the TFT LCD Touch Screen Display Works.

As I mentioned earlier, liquid-crystal displays (LCDs) refer to a bunch produced by using the TFT screen LCD display. Now for LCD displays the name is directed mostly used in notebook computers, or desktop computer applications display. Is the thin film transistor TFT LCD display. Abbreviation of TFT LCD. This kind of display form has two main characteristics, one is a thin film transistor, the other is TFT LCD itself. Let’s talk about the TFT screen itself.

This type of TFT LCD screen was first discovered, had been spent more than one hundred years ago. In 1888 AD, the Austrian botanist Friedrich Reinitzer, found in the observation from the plant refined out of benzoic acid cholesterol (cholesteryl benzoate) found that when the melting behavior of the compound heated to 145.5 ℃, Solid can melt, presents a kind of solid phase and liquid phase between the half gonorrhea melt flow of the liquid. This situation will always maintain ℃ temperature rise to 178.5 degrees, to form a clear isotropic liquid (isotropic liquid).

The liquid crystal state, as the name implies, will be a solid lattice and the liquid. When the liquid crystal was found, because of a lot of more phyletic, In 1922, the results observed by g. Friedel with a polarizing microscope divided liquid crystals into Nematic Smectic and Cholesteric categories. However, if they were classified according to the order of molecular arrangement (see figure 3), they could be divided into the following four categories:

Its structure is composed of TFT LCD molecules stick together, forming a layer structure. It’s every layer of the molecular long axis direction parallel to each other. And the long axis direction for each layer plane is vertical or a tilt Angle. Due to its structure is very similar to crystals, so they are called phase. The order parameter S (the order parameter) tend to be 1. Type in layered crystal layer and interlayer bonding can fracture because of temperature, so the layer and interlayer sliding more easily. But each layer within the molecular bonding is stronger, so it is not easy to be interrupted. Therefore in the context of the monolayer, Its arranged orderly and viscosity is bigger. If we use the macroscopic phenomenon to describe the physical properties of liquid crystal, we can make a group of regional average points as the liquid crystal molecules are pointing in the direction of the arrow (director), which is the direction of a group of liquid crystal molecules regional average. And with lamellar liquid crystal, because of its structure, the TFT LCD molecules will cambium-like so can point to a vector of different classification of the different lamellar liquid crystal again. When the long axis of the liquid crystal molecules are vertical stand, Call it “Sematic A phase.” if stand long axis direction of the TFT LCD molecules have some Angle of tilt (tilt), call it “Sematic C phase”. In A, C and other letters to name, which was discovered in accordance with the order to address, and so on, there should be A “Semantic phase B is.” but later found A deformation phase B is C phase, And the liquid crystal molecules in the structure layer by layer, in addition to each layer of TFT LCD molecules have tilt Angle, the tilt Angle between layer by layer will form a helical structure.

Nematic is a Greek word, the word mean in the thread is the same as in English. Mainly because with the naked eye to observe the liquid crystal, it looks like a silk pattern. The LCD screen molecules on the space of the regular arrangement of one dimension, all rod long axis of the liquid crystal molecules will choose a particular direction (that is, pointing vector) as the main shaft and arranged parallel to each other. And don’t like lamellar liquid crystal has a layered structure. Compared with the layer column type liquid crystal alignment is no order, That is to say, its order parameter S is smaller than the lamellar liquid crystal, and its viscosity is smaller, so it is easier to flow (its flow mainly comes from the free movement of molecules in the long axis direction). Linear liquid crystal is the common TFT LCD display screen TN(Twisted nematic) type liquid crystal.

Most of the sources of the name, because are generated by the derivative of the cholesterol. But some without cholesterol structure of LCD screen with this liquid crystal phase. This kind of liquid crystal as shown in figure 5, if it is a layer of a layer to separate, would very much like a linear LCD screen. But look at the Z-axis, may find it pointing in the direction of the arrow will with layers and layers of different distribution, like a spiraling when the pointing vector rotate 360 degrees for molecular layer thickness is called a pitch. Because of its every layer like linear LCD, so also known as Chiral nematic phase. In terms of cholesterol crystal, and pointing in the direction vector of the vertical distribution of LCD screen molecules, due to the different point to vector, will have the different optical or electrical differences, thus has produced different features.

If we are according to the molecular weight of high and low points can be divided into liquid crystal polymer (polymer liquid crystal, the polymer in many of the liquid crystal molecules) and low molecular liquid crystal. This kind of classification of TFT LCD belongs to the application of the low molecular liquid crystal. If the reasons for the formation of liquid crystal state, because it can be divided into type temperature formation of liquid crystal state to a liquid crystal (thermotropic), and because of the concentration and the formation of a liquid crystal state type lyotropic liquid crystal (lyotropic).

The solution so types lyotropic TFT screen molecules in the appropriate solvents reaches a certain critical concentration, the formation of liquid crystal state. Type lyotropic liquid crystal is one of the best examples that is soap. When soap bubbles in the water will not be at once into a liquid, and the bubble in the water for a long time, after the formation of white matter, is its liquid crystal state.

Due to the structure of the liquid crystal molecules for different parties (Anisotropic), so caused by the photoelectric effect will vary because of a different direction, in short, that is, the liquid crystal molecules in the dielectric coefficient and refractive index, and so on photoelectric properties have different sex, so we can use these properties to change the intensity of the incident light, so that the formation of gray-scale, to apply on the display component. We’ll discuss below, is one of the characteristics of liquid crystal belongs to the optical and electrical related, about the following items:

Our dielectric coefficient can be separated into two directions respectively is epsilon / / (and point to parallel component) and epsilon coming (a component perpendicular to the pointing vector). When the epsilon / / > epsilon coming then called the dielectric coefficient of different parts of LCD, can be used in parallel coordination. And epsilon / / < epsilon is called the dielectric coefficient of the different part coming negative type of TFT screen, only can be used in vertical coordination will need the photoelectric effect. When the applied electric field, the liquid crystal molecules will vary with dielectric coefficient is positive or negative, To determine whether the orientation of the liquid crystal molecules is parallel or perpendicular to the electric field, to determine whether the light penetrates. Now on most commonly used type TN LCD TFT LCD that belongs to the dielectric coefficient are type liquid crystal. When the dielectric coefficient of square difference Δ epsilon (= epsilon / / – epsilon) comes, the greater the LCD of the critical voltage (threshold voltage) will be smaller. So the LCD can be in the low voltage operation.

For example, the elastic constant (kappa 11, kappa 22, kappa 33) contains the three most important constants: kappa 11 is the elastic constant at splay, kappa 22 is the elastic constant at the twist. Kappa 33 refers to predominating the elastic constants of bending (bend). The other as the coefficient of viscosity (viscosity coefficients and eta), will affect the rotational speed of the liquid crystal molecules with reaction time (response time), its value as small as possible. But this feature is affected by temperature is the largest. In addition to magnetic susceptibility (magnetic susceptibility), but also because of liquid crystals of different sex, Divided into c / / c coming. And the difference of magnetic susceptibility is defined as Δ c = c / / – c coming. In addition to the conductance coefficient (conductivity), and so on the photoelectric properties. Liquid crystal properties of the most important are the dielectric coefficient and refractive index of liquid crystal. The dielectric coefficient is determined liquid crystal under the influence of the electric field to the characteristics of the liquid crystal molecules, while the refractive index is liquid crystal in the light of its important parameters influencing the light path. The LCD is in using the liquid crystal itself of these features, the appropriate use of voltage, to control the rotation of the TFT LCD molecules, in turn, affect the direction of the light, to form different grayscale, a tool for displaying images. Of course, LCD itself is not alone as the monitor, also need other materials to help, Below, we will introduce the composition of various materials and operating principle of TFT LCD display.

I remember in high school physics class, when to teach the relevant physical properties of light, to do a lot of physical experiments, the purpose is to prove that light is a wave. And the marching direction of light waves, and the electric field and magnetic field perpendicular to each other. Light itself of the electric field and magnetic field component at the same time also is perpendicular to each other. That is to say with the electric field and magnetic field component direction, each other is two parallel to each other. (see figure 7) and the role of the polarizing film is like a fence, usually will be cut off a component perpendicular to the fence, With a fence parallel component only permitted through. So if we picked up a piece of the light polarization slabs, feel like wearing sunglasses, the light became dark. But if the two pieces of polarizing film ideas together, it won’t be the same. When you rotate the two pieces of the relative Angle of the polarizing film, you will find that as the relative Angle is different, the brightness of the light will be more and darker. When two polaroids fence Angle perpendicular to each other, Light was completely failing. (see figure 8) and a liquid crystal display is to use this feature. Use upper and lower two pieces of fences between perpendicular slant plate, filled with liquid crystal, recycle electric field control liquid crystal rotation, to change the direction of light, so that different electric field sizes, can form different gray-scale brightness.

The upper and lower two layers of glass are mainly to grip the LCD with. Below the glass layer with Thin film transistor (thin film transistor, TFT screen), while the layer above the glass with a Color filter (Color filter). If you notice (see figure 3), these two pieces of glass are in contact with the side of the LCD screen, not smooth, but with jagged grooves. The main purpose of the groove with the hope of a long rod, liquid crystal molecules will line up along the grooves. In this way, Liquid crystal molecules are arranged neatly. Because if it is smooth and flat, the arrangement of the liquid crystal molecules will not neat, causing light scattering, forming a light-leaking phenomenon. In fact, this is just a theory that told us to put the glass and LCD interface, complete processing so that the arrangement of liquid crystal has a certain order. But in the actual manufacturing process, and can not be with such a groove, the distribution of glass is made usually in glass coating on the surface layer of the PI (polyimide), and then a cloth to do the action of friction (rubbing), In order to make the surface molecules of PI no longer be scattered and arranged in a fixed and uniform direction, this layer of PI is called the coordination membrane, and its function is just like the grooves in the glass in FIG. 3, which provides the interface conditions for the uniform arrangement of liquid crystal molecules and allows the liquid crystals to be arranged in a predetermined order.

The STN LCD and TN LCD are very similar in structure, the main difference between TN LCD, the arrangement of the liquid crystal molecules, the rotation angle from top to bottom. A total of 90 degrees and type the STN LCD liquid crystal molecules are arranged, the rotation angle will be greater than 180 degrees, usually is 270 degrees. (see figure 12) because of its rotation Angle is different, its characteristics different. We from figure 13 TN type and type the STN LCD voltage of the transmittance curve can know, when the voltage is low, the light penetration rate is very high. With a high voltage, the light of the penetration rate is very low. So they belong to the Normal White polaroids configuration. When the voltage in the middle position, the change of type TN LCD curve is flat, and the change of the STN LCD type curve is steep. So in TN type LCD, when transmittance change from 90% to 10%, corresponding to the voltage difference is larger than the STN LCD. We mentioned before, in the liquid crystal display, The different characteristics of TN and STN will result in TN type LCD, which has more grayscale changes than STN type LCD, so generally TN type LCD has 6~8 bits of changes. It is 64 ~ 256 gray-scale changes. Type the STN LCD for a maximum of 4 bits are only 16 orders of gray-scale changes. In addition, the STN type and TN LCD has a different place is the reaction time (response time) general type the STN LCD it’s response time to type in more than 100 ms and TN LCD its response time is 30 ~ 50 ms as shown in the image change quickly for the STN LCD type ghosting effect phenomenon is easy to happen.

TFT LCD Chinese translation of the name is called a thin film transistor liquid crystal display, from the beginning, we mentioned LCD voltage control is needed to produce gray. And the use of a thin-film transistor to generate the voltage, to control the transition of liquid crystal display, is called a TFT LCD. From the point of the cross-section structure of figure 8, between upper and lower two layers of glass, with LCD, will form a parallel plate capacitor, we call it the CLC (capacitor of liquid crystal). Its size is about 0.1 m3, But on the practical application, the capacitance and unable to keep the voltage to the next time to update the data in the picture.

That is to say, when TFT is good to the capacitor charging power, it is impossible to maintain voltage, until the next TFT this point charge again. (in general of 60 Hz screen update frequency, need time to keep about 16 ms.) as a result, there were changes in voltage, displayed gray scale is not correct. Therefore generally on the design of the panel, we will add a storage capacitor CS (storage capacitor is about 0.5 pF). So charged electric voltage can keep until the next update screen. But the right, long on the glass TFT itself, just use a transistor to make the switch. Its main work is to determine the LCD source voltage on the driver whether to charge to this point. As for this point more charge to high voltage, so as to show how the gray-scale. It is outside of the LCD source driver.

If you have a chance, take a magnifying glass, close to the LCD screen. You will find that as shown in figure 9 shows. We know that red, blue and green, are the so-called primary colors. That is to say, using the three kinds of color, can produce a variety of different colors. In a lot of flat-panel displays, this principle is used to show the color. We put the RGB 3 kinds of color, is divided into independent three points, each has different gray-scale changes, then the three neighboring RGB display point, as the basic unit of a display, Pixel is that this a pixel, and can have different color changes. Then for a need for a 1024 * 768 resolution display screen, we just let the composition of the flat panel display with 1024 * 768 pixels, can show a picture of the right. In figure 9, each point between the Black part of RGB is called the Black matrix. We can find that looking back on it in figure 8Black matrix is mainly used to cover do not intend to previous to light part. Such as some ITOs walk the line, or Cr/Al walk the line or are part of a TFT. This is why we in figure 9, the highlight of each RGB, it seems, is not a rectangle, and also on the top left corner is a piece of black matrix cover part, this part of a black missing Angle is the location of the TFT.

Figure 9 shows the common arrangement of color filters. Stripe is most commonly used in OA products, such as laptops, desktop computers, etc. Why is stripe used in this application? More often than not, the reason is now software is the Windows interface. That is to say, we can see the screen content, is composed of a pile of boxes of various sizes. The strips, just can make the edge of the box, look more straight, and there won’t be a straight line, look have the feeling of burrs or serrated. But if it is applied in the AV products, just not the same. Probably because the TV signal is a character, the character of the line is not straight, the contour is a mostly irregular curve. So in the beginning, the Use Mosaic arrangement used in AV products is (Mosaic, or called arranged diagonally). But the latest AV products, more have been improved to use triangle arrangement (triangle, or known as the delta). In addition to the above arrangement, still have a kind of arrangement, which is called a square arrangement. It is not the same as the first few, it is not three-point to as a pixel, but with four points as a pixel. And just four points are combined to form a square.

The CRT screen, it is using a high-speed electron gun that emits electrons, hits the phosphors on the silver screen, so as to produce the light, to show the picture. LCD itself, however, can only control the brightness of the light through, no glowing function itself. Therefore, a liquid crystal display must be combined with a backplate, to provide high brightness, brightness, and uniform distribution of the light source. We can see in figure 14, of the backplate of the main parts are CCFL (cold cathode tube), reflex plate, guide plate, prism sheet, Diffuser plate, and so on. Tubes are the main light-emitting parts, by a light guide, everywhere. The light distribution and baffle will be limited only to the TFT LCD light direction. Finally, by prism sheet and help diffuser, the light evenly distributed to all areas, provide TFT LCD a bright light. While TFT LCD is borrowed by the rotation of the voltage-controlled liquid crystal, control through the brightness of the light, so as to form different grayscale.

A very important specification of LCD is brightness, and the most important factor to determine the brightness is the opening rate. What is the opening rate? Is simple light can pass through the effective area proportion. 17, let’s look at the picture to the left of figure 17 is an LCD display from directly above or below the past structure. When the light is emitted through the backplate, not all of the light can be through the panel, like for LCD source driver chip and the gate driver chip signal line, and TFT itself, the stored voltage is the use of storage capacity, etc. These places besides incomplete pervious to light, but also because the light through these places is not under voltage control, to display the correct gray-scale, so have to use the black matrix to cover, in order to avoid interference to other correct brightness of the light area. So the effective area of the previous to light, it’s just like figure 17 shows area on the right. This piece of the effective area of the previous to light and the ratio of the total area is called the opening rate.

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A thin-film-transistor liquid-crystal display (TFT LCD) is a variant of a liquid-crystal display that uses thin-film-transistor technologyactive matrix LCD, in contrast to passive matrix LCDs or simple, direct-driven (i.e. with segments directly connected to electronics outside the LCD) LCDs with a few segments.

In February 1957, John Wallmark of RCA filed a patent for a thin film MOSFET. Paul K. Weimer, also of RCA implemented Wallmark"s ideas and developed the thin-film transistor (TFT) in 1962, a type of MOSFET distinct from the standard bulk MOSFET. It was made with thin films of cadmium selenide and cadmium sulfide. The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard Lechner of RCA Laboratories in 1968. In 1971, Lechner, F. J. Marlowe, E. O. Nester and J. Tults demonstrated a 2-by-18 matrix display driven by a hybrid circuit using the dynamic scattering mode of LCDs.T. Peter Brody, J. A. Asars and G. D. Dixon at Westinghouse Research Laboratories developed a CdSe (cadmium selenide) TFT, which they used to demonstrate the first CdSe thin-film-transistor liquid-crystal display (TFT LCD).active-matrix liquid-crystal display (AM LCD) using CdSe TFTs in 1974, and then Brody coined the term "active matrix" in 1975.high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays.

The liquid crystal displays used in calculators and other devices with similarly simple displays have direct-driven image elements, and therefore a voltage can be easily applied across just one segment of these types of displays without interfering with the other segments. This would be impractical for a large display, because it would have a large number of (color) picture elements (pixels), and thus it would require millions of connections, both top and bottom for each one of the three colors (red, green and blue) of every pixel. To avoid this issue, the pixels are addressed in rows and columns, reducing the connection count from millions down to thousands. The column and row wires attach to transistor switches, one for each pixel. The one-way current passing characteristic of the transistor prevents the charge that is being applied to each pixel from being drained between refreshes to a display"s image. Each pixel is a small capacitor with a layer of insulating liquid crystal sandwiched between transparent conductive ITO layers.

The circuit layout process of a TFT-LCD is very similar to that of semiconductor products. However, rather than fabricating the transistors from silicon, that is formed into a crystalline silicon wafer, they are made from a thin film of amorphous silicon that is deposited on a glass panel. The silicon layer for TFT-LCDs is typically deposited using the PECVD process.

Polycrystalline silicon is sometimes used in displays requiring higher TFT performance. Examples include small high-resolution displays such as those found in projectors or viewfinders. Amorphous silicon-based TFTs are by far the most common, due to their lower production cost, whereas polycrystalline silicon TFTs are more costly and much more difficult to produce.

The twisted nematic display is one of the oldest and frequently cheapest kind of LCD display technologies available. TN displays benefit from fast pixel response times and less smearing than other LCD display technology, but suffer from poor color reproduction and limited viewing angles, especially in the vertical direction. Colors will shift, potentially to the point of completely inverting, when viewed at an angle that is not perpendicular to the display. Modern, high end consumer products have developed methods to overcome the technology"s shortcomings, such as RTC (Response Time Compensation / Overdrive) technologies. Modern TN displays can look significantly better than older TN displays from decades earlier, but overall TN has inferior viewing angles and poor color in comparison to other technology.

Most TN panels can represent colors using only six bits per RGB channel, or 18 bit in total, and are unable to display the 16.7 million color shades (24-bit truecolor) that are available using 24-bit color. Instead, these panels display interpolated 24-bit color using a dithering method that combines adjacent pixels to simulate the desired shade. They can also use a form of temporal dithering called Frame Rate Control (FRC), which cycles between different shades with each new frame to simulate an intermediate shade. Such 18 bit panels with dithering are sometimes advertised as having "16.2 million colors". These color simulation methods are noticeable to many people and highly bothersome to some.gamut (often referred to as a percentage of the NTSC 1953 color gamut) are also due to backlighting technology. It is not uncommon for older displays to range from 10% to 26% of the NTSC color gamut, whereas other kind of displays, utilizing more complicated CCFL or LED phosphor formulations or RGB LED backlights, may extend past 100% of the NTSC color gamut, a difference quite perceivable by the human eye.

In 2004, Hydis Technologies Co., Ltd licensed its AFFS patent to Japan"s Hitachi Displays. Hitachi is using AFFS to manufacture high end panels in their product line. In 2006, Hydis also licensed its AFFS to Sanyo Epson Imaging Devices Corporation.

A technology developed by Samsung is Super PLS, which bears similarities to IPS panels, has wider viewing angles, better image quality, increased brightness, and lower production costs. PLS technology debuted in the PC display market with the release of the Samsung S27A850 and S24A850 monitors in September 2011.

TFT dual-transistor pixel or cell technology is a reflective-display technology for use in very-low-power-consumption applications such as electronic shelf labels (ESL), digital watches, or metering. DTP involves adding a secondary transistor gate in the single TFT cell to maintain the display of a pixel during a period of 1s without loss of image or without degrading the TFT transistors over time. By slowing the refresh rate of the standard frequency from 60 Hz to 1 Hz, DTP claims to increase the power efficiency by multiple orders of magnitude.

Due to the very high cost of building TFT factories, there are few major OEM panel vendors for large display panels. The glass panel suppliers are as follows:

External consumer display devices like a TFT LCD feature one or more analog VGA, DVI, HDMI, or DisplayPort interface, with many featuring a selection of these interfaces. Inside external display devices there is a controller board that will convert the video signal using color mapping and image scaling usually employing the discrete cosine transform (DCT) in order to convert any video source like CVBS, VGA, DVI, HDMI, etc. into digital RGB at the native resolution of the display panel. In a laptop the graphics chip will directly produce a signal suitable for connection to the built-in TFT display. A control mechanism for the backlight is usually included on the same controller board.

The low level interface of STN, DSTN, or TFT display panels use either single ended TTL 5 V signal for older displays or TTL 3.3 V for slightly newer displays that transmits the pixel clock, horizontal sync, vertical sync, digital red, digital green, digital blue in parallel. Some models (for example the AT070TN92) also feature input/display enable, horizontal scan direction and vertical scan direction signals.

New and large (>15") TFT displays often use LVDS signaling that transmits the same contents as the parallel interface (Hsync, Vsync, RGB) but will put control and RGB bits into a number of serial transmission lines synchronized to a clock whose rate is equal to the pixel rate. LVDS transmits seven bits per clock per data line, with six bits being data and one bit used to signal if the other six bits need to be inverted in order to maintain DC balance. Low-cost TFT displays often have three data lines and therefore only directly support 18 bits per pixel. Upscale displays have four or five data lines to support 24 bits per pixel (truecolor) or 30 bits per pixel respectively. Panel manufacturers are slowly replacing LVDS with Internal DisplayPort and Embedded DisplayPort, which allow sixfold reduction of the number of differential pairs.

The bare display panel will only accept a digital video signal at the resolution determined by the panel pixel matrix designed at manufacture. Some screen panels will ignore the LSB bits of the color information to present a consistent interface (8 bit -> 6 bit/color x3).

With analogue signals like VGA, the display controller also needs to perform a high speed analog to digital conversion. With digital input signals like DVI or HDMI some simple reordering of the bits is needed before feeding it to the rescaler if the input resolution doesn"t match the display panel resolution.

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Kim, Sae-Bom; Kim, Woong-Ki; Chounlamany, Vanseng; Seo, Jaehwan; Yoo, Jisu; Jo, Hun-Je; Jung, Jinho (15 August 2012). "Identification of multi-level toxicity of liquid crystal display wastewater toward Daphnia magna and Moina macrocopa". Journal of Hazardous Materials. Seoul, Korea; Laos, Lao. 227–228: 327–333. doi:10.1016/j.jhazmat.2012.05.059. PMID 22677053.

In this article, we’ll be covering how TFT displays work, the main differences between TFT and LCD, their typical display specifications and also outline a list of common applications where TFT displays are used.

If you’ve ever purchased a computer monitor or a television, then you’ll likely have heard of the terms TFT and LCD. They stand for thin-film-transistor and liquid-crystal display respectively and are the most common display technologies used in not just monitors and televisions, but also in cameras, GPS devices, tablets, medical equipment and even aircraft computers.

An LCD uses liquid crystals to manipulate light. The molecules that make up the crystals twist depending on their temperature which is altered by using an electrical current. Depending on the rotation of the molecules, they can block the light in various ways to allow different colours to show on the screen or no light at all.

Groups of these molecules form a pixel, a word invented from the term “picture element”. It’s a unit of programmable colour on an LCD display that varies in size depending on a number of conditions, such as the current resolution of the display. Pixels contain red, green and blue colour filters and the molecules are twisted to release a certain amount of each light to create millions of different colour combinations.

Early LCD displays used a matrix of pixels known as passive matrix. This means that each individual pixel is controlled by sending an electrical charge to the row and column that it’s found in. Unfortunately, images on LCD displays were often blurry when the pixels needed to be switched often, such as during high-action scenes, due to the limited number of electrical charges that could be sent in a single second. In addition, the electrical charge would often interfere with adjacent pixels, causing a defect known as crosstalk.

In contrast, LCD displays today use an active matrix of pixels which contains a sheet of thin-film transistors. Each pixel in an active matrix is paired with a transistor that includes capacitors that give each subpixel the ability to retain their charge instead of requiring an electrical charge sent each time it needed to be changed. This means that TFT displays are more responsive than regular LCD monitors. TFT displays are often called TFT-LCD monitors because the two technologies are used together to produce a clear and non-blurry image.

Due to the use of an active matrix of pixels, TFT displays have faster response times which means clearer pictures and less blurring, and also provide more vibrant colours that can be controlled with precision thanks to the thin-film transistors.

TFT displays from GSR Technology come in various different designs and specifications. Here is a list of specifications that are typically listed and their definitions:

Size or format is used to describe the physical distance between opposite corners of a display, usually expressed in inches and often referred to as the physical image size.

Refresh rate is expressed in Hertz and is often included at the end of the resolution specification. Commonly referred to as vertical refresh rate, it is used to measure the number of times a second that the display can update its buffer. Normal displays operate at 60 Hz.

Brightness or luminance is a measurement of luminance and is expressed in nits. Between 200 and 300 nits is where an average display sits, whereas 700 nits offer far greater contrast, resulting in sharper picture quality.

Display resolution will drastically affect the image quality of the display but also require more processing power in order to update the buffer at the optimal refresh rate offered by the panel. Resolution does not necessarily affect the size of the panel itself. However, larger panels with lower resolutions tend to have visible pixels and will create a blurrier image if high-resolution images are displayed. Here are some of the most common display resolutions and their aspect ratios:

Another factor in TFT displays is the range of operating temperatures it can cope with. This is especially important in industrial and automotive uses where equipment surrounding the TFT display can affect the picture quality. Since heat from electrical currents is used to change the orientation of the molecules in each subpixel, outside heat sources can turn the liquid crystals inside a TFT-LCD display into a real liquid due to their sensitivity to temperature changes.

In the major digital products on the news, the screen is often one of the focuses of publicity, with the development of the times, people have become accustomed to high-tech products on the display of splendid luster.

At present, the mainstream display on the market is TFT-LCD, that is, thin film transistor liquid crystal display (Thin Film Transistor-Liquid Crystal Display).

As we mentioned above, people may not think that filtration is so closely connected to the production of TFT-LCD. Below we will explain the importance of filtration in production for flat panel displays.

TFT-LCD combines microelectronics technology with liquid crystal display technology, and its structure is like a “sandwich”. The TFT array is processed on the glass, and the substrate with color filtering film is used to form a liquid crystal box using LCD technology, and then the polarizer is laminated to form a liquid crystal display.

The TFT-LCD array process is similar to that of semiconductors, except that semiconductors use silicon wafers, while thin-film transistors process glass substrates.

In the manufacture of flat panel displays, the glass substrate is first cleaned, and after the film is formed on the surface, the photoresist is evenly coated on the substrate, and after the processes of exposure, development, etching, and stripping, the graphics on the mask plate are transferred to the substrate to form the exact corresponding graphics.

In the TFT-LCD array process, pollutants mainly come from the manufacturing process and the handling, packaging, transportation, and storage of glass substrates, the main pollutants are dust particles, fiber paper dust, mineral oil and grease, and other greases, inorganic particles such as silicon oxide, and residues of the preparation process, water stains, fingerprints, etc.

In flat panel display manufacturing, the residual photoresist needs to be peeled off after the film formation-lithography-etching process, thus bringing the process of this layer of film to an end.

With years of filtration experience and advanced manufacturing technology, Brother Filtration is able to provide helpful membrane-pleated filter cartridges and gas filter housing in every TFT-LCD production process.

The gas filter housing works with the filter cartridge to purge particles from high-purity gas. Different filter cartridges are used to fit inside the housing depending on the various demands.

With the development of digital products, people are longing for more and more high-quality products with better panel displays. Filtration is a crucial part of the production of flat panel displays and helps manufacturers to produce high-quality and more competitive products.

Brother Filtration not only manufactures all kinds of filter products that can be applied in TFT-LCD production but also offers better filtration solutions for panel display manufacturers. If you need more filtration solutions or a better filter cartridge to help your manufacturing, please feel free to contact us directly.

A TFT LCD,  or a thin film transistor liquid crystal display, is one of the fastest growing forms of display technology today. The thin film transistor (TFT) is a type of semiconductor device used in display technology to enhance efficiency, compactness, and cost of the product. In conjunction with its semiconductor properties, the TFT LCD is an active matrix display, controlling pixels individually and actively rather than passively, furthering the benefits of this semiconductor device.

The TFT LCD is built with three key layers. Two sandwiching layers consist of glass substrates, though one includes TFTs while the other has an RGB, or red green blue, color filter. The layer between the glass layers is a liquid crystal layer.

The Architecture of a TFT Pixelbelow) from the other substrate layer of the device and control the amount of voltage applied to their respective sub-pixels. This layer also has pixel electrodes between the substrate and the liquid crystal layer. Electrodes are conductors that channel electricity into or out of something, in this case, pixels.

Between the two substrate layers lie liquid crystals. Together, the liquid crystal molecules may behave as a liquid in terms of movement, but it holds its structure as a crystal. There are a variety of chemical formulas available for use in this layer. Typically, liquid crystals are aligned to position the molecules in a certain way to induce specific behaviors of passing light through the polarization of the light waves. To do this, either a magnetic or electric field must be used; however, with displays, for a magnetic field to be usable, it will be too strong for the display itself, and thus electric fields, using very low power and requiring no current, are used.

Before applying an electric field to the crystals between the electrodes, the alignment of the crystals is in a 90 degree twisted pattern, allowing a properly crystal-polarized light to pass through the surface polarizer in a display’s “normal white” mode. This state is caused by electrodes that are purposely coated in a material that orients the structure with this specific twist.

However, when the electric field is applied, the twist is broken as the crystals straighten out, otherwise known as re-aligning. The passing light can still pass through the back polarizer, but because the crystal layer does not polarize the lights to pass through the surface polarizer, light is not transmitted to the surface, thus an opaque display. If the voltage is lessened, only some crystals re-align, allowing for a partial amount of light to pass and creating different shades of grey (levels of light). This effect is called the twisted nematic effect.

Fig. 3:The top row characterizes the nature of alignment in using IPS as well as the quality of viewing angles. The bottom row displays how the twisted nematic is used to align the crystals and how viewing angles are affected by it.

The light that passes through the device is sourced from the backlight which can shine light from the back or the side of the display. Because the LCD does not produce its own light, it needs to use the backlight in the OLED) have come into use as well. Typically white, this light, if polarized correctly, will pass through the RGB color filter of the surface substrate layer, displaying the color signaled for by the TFT device.

TFT stands for "Thin Film Transistor" and describes the control elements that actively control the individual pixels. For this reason, one speaks of so-called "active matrix TFTs". How are images produced? The basic principle is quite simple: a panel with many pixels is used whereby each pixel can emit any color. To this purpose, a back light is used which is normally comprised of a number of flourescent tubes. In order to light a single pixel, all that needs to be done is for a small "door" or "shutter" to open to let the light pass through. The technology that makes this possible is of course more complicated and involved than the simple explanation above. LCD (Liquid Crystal Display) stands for monitors that are based on liquid crystals. Liquid crystals can change their molecular structure and therefore allow varying levels of light to pass through them (or they can block the light). Two polarizer filters, color filters and two alignment layers determine exactly how much light is allowed to pass and which colors are created. The layers are positioned between the two glass panels. A specific voltage is applied to the alignment layer, creating an electric field - which then aligns the liquid crystals. Each dot on the screen (pixel) therefore requires three components, one for red, green and blue - just as for the tubes within cathode ray tube devices.

If a voltage is applied, i.e. an electric field is created, the liquid crystals are twisted so that they are vertically aligned. The polarized light is then absorbed by the second polarizer. Light can therefore not leave the TFT display at this location.

Figure 4: Pixels of a TFT. The left upper corner of a cell incorporates a T hin F ilm T ransistor. Color filters allow the cells to change their RGB basic colors.

The pixels are decisive and the smaller their spacing, the higher the maximum possible resolution. However, TFTs are also subject to physical limitations due to the maximum display area. With a diagonal of 15 inch (or about 38 cm) and a dot pitch of 0.0117 inch (0.297 mm), it makes little sense to have a resolution of 1280 x 1024. Part 4 of this report covers the relationship between dot pitch and diagonal dimensions in more detail.

Display screen is everywhere nowadays. Do you still remember the TVs or computer monitors 20 years ago? They were quadrate, huge and heavy. Now let’s look at the flat, thin and light screen in front of you, have you ever wondered why is there such a big difference?

Actually, the monitors 20 year ago were CRT (Cathode Ray Tube) displays, which requires a large space to run the inner component. And now the screen here in your presence is the LCD (Liquid Crystal Display) screen.

As mentioned above, LCD is the abbreviation of Liquid Crystal Display. It’s a new display technology making use of the optical-electrical characteristic of liquid crystal.

Liquid crystal is a state of substance that has both the characteristics of liquid and solid crystal. It don’t emit light itself, but it can let the light pass perfectly in specific direction. Meanwhile, liquid crystal molecule will rotate under the influence of a electric field, and then the light goes through it will rotate too. That said, liquid crystal can be a switch of light, which is the key in display technology.

STN LCD: STN is for Super-twisted Nematic. The liquid crystal in STN LCD rotate more angles than that in TN LCD, and have a different electrical feature, allowing STN LCD to display more information. There are many improved version of STN LCD like DSTN LCD (double layer) and CSTN LCD (color). This LCD is used in many early phones, computers and outdoor devices.

TFT LCD: TFT is for Thin Film Transistor. It’s the latest generation of LCD technology and has been applied in all the displaying scenario including electronic devices, motor cars, industrial machines, etc. When you see the word ‘transistor’, you may realize there’s integrated circuits in TFT LCD. That’s correct and the secret that TFT LCD has the advantage of high resolution and full color display.

In a simple way, we can divide TFT LCD into three parts, from bottom to top they are: light system, circuit system and light and color control system.In manufacturing process, we’ll start from inner light and color control system and then stretch out to whole module.

It’s accustomed to divide TFT LCD manufacturing process into three main part: array, cell and module. The former two steps are about the production of light and color control system, which contains TFT, CF (color filter) and LC (liquid crystal), named a cell. And the last step is the assembly of cell, circuit and light system.

Now let’s turn to the production of TFT and CF. Here is a common method called PR (photoresist) method. The whole process of PR method will be demonstrated in TFT production.

Liquid crystal refers to the intermediate status of a substance between solid (crystal) and liquid. When crystals with a high level of order in molecular sequence are melted, they generally turn liquid, which has fluidity but no such order at all. However, thin bar-shaped organic molecules, when they are melted, keep their order in a molecular direction although they lose it in molecular positions. In the state in which molecules are in a uniform direction, they also have refractive indices, dielectric constants and other physical characteristics similar to those of crystals, depending on their direction, even though they are liquid. This is why they are called liquid crystal. The diagram below shows the structure of 5CB (4-pentyl-4’-Cyanobiphenyl) as an example of liquid crystal molecules.

A liquid crystal display (LCD) has liquid crystal material sandwiched between two sheets of glass. Without any voltage applied between transparent electrodes, liquid crystal molecules are aligned in parallel with the glass surface. When voltage is applied, they change their direction and they turn vertical to the glass surface. They vary in optical characteristics, depending on their orientation. Therefore, the quantity of light transmission can be controlled by combining the motion of liquid crystal molecules and the direction of polarization of two polarizing plates attached to the both outer sides of the glass sheets. LCDs utilize these characteristics to display images.

An LCD consists of many pixels. A pixel consists of three sub-pixels (Red/Green/Blue, RGB). In the case of Full-HD resolution, which is widely used for smartphones, there are more than six million (1,080 x 1,920 x 3 = 6,220,800) sub-pixels. To activate these millions of sub-pixels a TFT is required in each sub-pixel. TFT is an abbreviation for "Thin Film Transistor". A TFT is a kind of semiconductor device. It serves as a control valve to provide an appropriate voltage onto liquid crystals for individual sub-pixels. A TFT LCD has a liquid crystal layer between a glass substrate formed with TFTs and transparent pixel electrodes and another glass substrate with a color filter (RGB) and transparent counter electrodes. In addition, polarizers are placed on the outer side of each glass substrate and a backlight source on the back side. A change in voltage applied to liquid crystals changes the transmittance of the panel including the two polarizing plates, and thus changes the quantity of light that passes from the backlight to the front surface of the display. This principle allows the TFT LCD to produce full-color images.

TFT-LCD (thin film transistor liquid crystal display) industries have been grown-up in Taiwan. Many workers are at light-on test workstations in TFT-LCD factories. At the light-on test station, the operator has been exposed to the lower ambient illumination (105.10 lx) for a long time (12hour/1day). There are few researches discussed about health effect of workers of TFT-LCD workers. The aim of this research is to measure the illumination of the light-on test station and to collect the work environmental data for exposure assessment. The work environment information of test workstations has been measured such as ambient illumination and illumination of the five types of test color of LCD (red, green, blue, white, gray), visual angle, and visual distance between worker and LCD test board. The results shows that: 1) the light-on test was a long-term operation of lower ambient illumination (4.00 lx to 105.1 lx) and shorter visual distance (28.04 cm to 34.43cm); 2) the means of illumination of LCD board of different test color are 10.90 lx in red, 41.20 lx in green, 18.00 lx in blue, 67.30lx in white, and 13.80 in gray. Light-on test is a task of low ambient illumination, short visual distance and long-term job in TFT-LCD factories. Some workers complained about visual fatigues. Under this working environment, the more working duration workers have the more visual discomfort they complain. Some administration controls have been suggested such as more time of rest, lubrication of eyes by appropriate solution and job rotation.

TFT displays are also known as an “Active Matrix TFT LCD module” and have an array of thin film transistors fabricated on the glass that makes the LCD. There is one of these transistors for each pixel on the LCD. See our blog post RGB and Color Depth for more on how TFTs show color.

LCDs use voltage applied to a field of microscopic liquid crystals to change the crystal’s orientation. The orientation of the crystals changes the polarization of the liquid crystal creating light or dark pixels on the display.

These pixels are arranged to create characters or graphic images. This type of display may be sunlight-readable and may have a backlight, which allows it to be viewed in dark areas.

Beautiful, complex images: All of our TFT modules are full-color graphic displays. Unlike standard monochrome character displays, you can create complex images for an imaginative user experience.

Thin and light: These are ideal display modules for handheld devices, communications equipment, information displays, and test and measurement equipment.

Single Supply: Most of the TFTs use an integrated controller with built-in voltage generation so only a single 3.3v supply is needed for both the panel power and logic voltage.

Many of the LCD controllers on board our graphic LCD display modules also include a CGROM (character generator ROM) which allows for easy character information as well as full bit-mapped graphic information to be shown.

Some of the graphic LCD displays have the ability to render graphics in grayscale, enabling you to show images and elements of your UI (user interface) with more depth and definition.

Because OLEDs are emissive, these displays can always be used in dark environments. There is usually a software command or hardware setting that will allow OLEDs to be dimmed.

Some OLED displays are bright enough to be sunlight readable–these models will typically take more current and may have a shorter rated lifetime. Additionally, OLEDs have extremely wide viewing angles.

What makes OLEDs useful for display construction is that they can be fabricated in bulk. Using OLED fabrication techniques, all the diodes can be made at the same time, at a much lower cost. OLEDs also come in a wide variety of colors.