tft lcd principle 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.

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 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.

The transmittance of a pixel of an LCD panel typically does not change linearly with the applied voltage,sRGB standard for computer monitors requires a specific nonlinear dependence of the amount of emitted light as a function of the RGB value.

Less expensive PVA panels often use dithering and FRC, whereas super-PVA (S-PVA) panels all use at least 8 bits per color component and do not use color simulation methods.BRAVIA LCD TVs offer 10-bit and xvYCC color support, for example, the Bravia X4500 series. S-PVA also offers fast response times using modern RTC technologies.

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.

Kawamoto, H. (2012). "The Inventors of TFT Active-Matrix LCD Receive the 2011 IEEE Nishizawa Medal". Journal of Display Technology. 8 (1): 3–4. Bibcode:2012JDisT...8....3K. doi:10.1109/JDT.2011.2177740. ISSN 1551-319X.

K. H. Lee; H. Y. Kim; K. H. Park; S. J. Jang; I. C. Park & J. Y. Lee (June 2006). "A Novel Outdoor Readability of Portable TFT-LCD with AFFS Technology". SID Symposium Digest of Technical Papers. AIP. 37 (1): 1079–82. doi:10.1889/1.2433159. S2CID 129569963.

LCD (Liquid Crystal Display)may be a fresh noun for many users, but the history of this technology may far exceed our imagination. As early as the end of the 19th century, Austrian botanists discovered liquid crystals, that is, a substance has both the fluidity of liquids and certain crystal-like arrangement characteristics.

This phenomenon is called the electro-optic effect. Utilizing the electro-optical effect of liquid crystals, British scientists produced the first liquid crystal display, the LCD display, in the last century.

According to the driving method of the LCD panel, the most common currently is a TFT (Thin Film Transistor) type driver. It achieves independent and precise control of each pixel through the active switch, so it can achieve more fine display effects than the previous passive driver (commonly known as pseudo color). Therefore, most LCD displays,LCD displayTVs and some mobile phones are driven by TFT.

Therefore, as long as we change the voltage value applied to the liquid crystal, we can control the intensity and color of the light that finally appears, so that we can change the color combination with the different hue on theLCD display panel.

In tft-lcd, the TFT functions as a switch tube. The commonly used TFT is a three-terminal device. Use the voltage applied to the gate to control the current between the source and the leakage electrode. For display screens, each pixel is structurally visible as a layer of liquid crystal sandwiched between the pixel electrode and the common electrode. More importantly, from an electrical point of view you can think of it as capacitance.

To charge the pixel P (I, j) in row j and column I, switch T (I, j) on and apply the target voltage to the signal line D (I).When the pixel electrode is fully charged, the charge in the capacitor is preserved even if the switch is disconnected, and the liquid crystal molecules between the electrodes continue to have an electric field. The data (column) driver ACTS to apply the target voltage to the signal line, while the gate (row) driver ACTS to switch on and off. The key to display the image is also the molecular orientation of the liquid crystal under the action of an electric field. In general, the arrangement of LCD molecules can be deformed by the orientation on the inside of the substrate to realize different display modes. Under the action of electric field, the orientation of liquid crystal molecules changes, and the intensity of incident light changes after passing through the liquid crystal layer through the coordination with the polarizer. To achieve image display.

Tft-lcd colorization is generally achieved by adding a layer of color filter on the front panel of the display. It requires a black matrix of red, green, blue and shading on each pixel.

TFT array is formed on TFT substrate; Color filter pattern and ITO conductive layer are formed on the color filter substrate. Using two substrates to form a liquid crystal box; Install the peripheral circuit, assemble the module assembly of backlight, etc.

The function of TFT LCD DRIVER generates various voltages required for liquid crystal display, and processes the instructions sent by the external CPU.

Principle error, LAYOUT error. IM0,IM3 connect wrong, left and right reverse, one of the leads is wrong, the power line is connected wrong, the ground line is not connected, etc.100% of poor.

Initialization code. Partial light, partial not light, common GAMMA code wrong.The GAMMA code shall be provided by the LCD supplier. The initialization code does not change the GAMMA.

Principle: the orientation of polarizer"s suction axis is the same as that on the LCD drawing. Workshop: cut small pieces and draw lines according to the polaroid drawing, and paste them according to the polaroid drawing (top and bottom)

Initialization code. Partial flashing, partial non-flashing, common GAMMA code wrong. The GAMMA code shall be provided by the LCD supplier. The initialization code does not change the GAMMA. The frame rate setting is too small.

TFT-LCD was invented in 1960 and successfully commercialized as a notebook computer panel in 1991 after continuous improvement, thus entering the TFT-LCD generation.

Simply put, the basic structure of the TFT-LCD panel is a layer of liquid crystal sandwiched between two glass substrates. The front TFT display panel is coated with a color filter, and the back TFT display panel is coated with a thin film transistor (TFT). When a voltage is applied to the transistor, the liquid crystal turns and light passes through the liquid crystal to create a pixel on the front panel. The backlight module is responsible for providing the light source after the TFT-Array panel. Color filters give each pigment a specific color. The combination of each different color pixel gives you an image of the front of the panel.

The TFT panel is composed of millions of TFT devices and ITO (In TI Oxide, a transparent conductive metal) regions arranged like a matrix, and the so-called Array refers to the region of millions of TFT devices arranged neatly, which is the panel display area. The figure below shows the structure of a TFT pixel.

No matter how the design of TFT display board changes or how the manufacturing process is simplified, its structure must have a TFT device and control liquid crystal region (if the light source is penetration-type LCD, the control liquid crystal region is ITO; but for reflective LCD, the metal with high reflection rate is used, such as Al).

The TFT device is a switch, whose function is to control the number of electrons flowing into the ITO region. When the number of electrons flowing into the ITO region reaches the desired value, the TFT device is turned off. At this time, the entire electrons are kept in the ITO region.

The figure above shows the time changes specified at each pixel point. G1 is continuously selected to be turned on by the driver IC from T1 to TN so that the source-driven IC charges TFT pixels on G1 in the order of D1, D2, and Dn. When TN +1, gATE-driven IC is selected G2 again, and source-driven IC is selected sequentially from D1.

Many people don’t understand the differences between generations of TFT-LCD plants, but the principle is quite simple. The main difference between generations of plants is in the size of glass substrates, which are products cut from large glass substrates. Newer plants have larger glass substrates that can be cut to increase productivity and reduce costs, or to produce larger panels (such as TFT display LCD TV panels).

The TFT-LCD industry first emerged in Japan in the 1990s, when a process was designed and built in the country. The first-generation glass substrate is about 30 X 40 cm in size, about the size of a full-size magazine, and can be made into a 15-inch panel. By the time Acer Technology (which was later merged with Unioptronics to become AU Optronics) entered the industry in 1996, the technology had advanced to A 3.5 generation plant (G3.5) with glass substrate size of about 60 X 72 cm.Au Optronics has evolved to a sixth-generation factory (G6) process where the G6 glass substrate measures 150 X 185 cm, the size of a double bed. One G6 glass substrate can cut 30 15-inch panels, compared with the G3.5 which can cut 4 panels and G1 which can only cut one 15-inch panel, the production capacity of the sixth generation factory is enlarged, and the relative cost is reduced. In addition, the large size of the G6 glass substrate can be cut into large-sized panels, which can produce eight 32-inch LCD TV panels, increasing the diversity of panel applications. Therefore, the global TFT LCD manufacturers are all invested in the new generation of plant manufacturing technology.

The TRANSISTor-LCD is an acronym for thin-film TFT Display. Simply put, TFT-LCD panels can be seen as two glass substrates sandwiched between a layer of liquid crystal. The upper glass substrate is connected to a Color Filter, while the lower glass has transistors embedded in it. When the electric field changes through the transistor, the liquid crystal molecules deflect, so as to change the polarization of the light, and the polarizing film is used to determine the light and shade state of the Pixel. In addition, the upper glass is fitted to the color filter, so that each Pixel contains three colors of red, blue and green, which make up the image on the panel.

The luminescence principle is tied to the vapor electroplating organic film between the transparent anode and the metal cathode. The electron and electric hole are injected, and the energy is converted into visible light by the composite between the organic film. And can match different organic materials, emit different colors of light, to achieve the requirements of the full-color display.

The organic light display can be divided into Passive Matrix (PMOLED) and Active Matrix (AMOLED) according to the driving mode. The so-called active driven OLED(AMOLED) can be visualized in the Thin Film Transistor (TFT) as a capacitor that stores signals to provide the ability to visualize the light in a grayscale.

Although the production cost and technical barriers of passive OLED are low, it is limited by the driving mode and the resolution cannot be improved. Therefore, the application product size is limited to about 5″, and the product will be limited to the market of low resolution and small size. For high precision and large picture, the active drive is mainly used. The so-called active drive is capacitive to store the signal, so when the scanning line is swept, the pixel can still maintain its original brightness. In the case of passive drive, only the pixels selected by the scan line are lit. Therefore, in an active-drive mode, OLED does not need to be driven to very high brightness, thus achieving better life performance and high resolution.OLED combined with TFT technology can realize active driving OLED, which can meet the current display market for the smoothness of screen playback, as well as higher and higher resolution requirements, fully display the above superior characteristics of OLED.

The technology to grow The TFT on the glass substrate can be amorphous Silicon (A-SI) manufacturing process and Low-Temperature Poly-Silicon (LTPS). The biggest difference between LTPS TFT and A-SI TFT is the difference between its electrical properties and the complicated manufacturing process. LTPS TFT has a higher carrier mobility rate, which means that TFT can provide more current, but its process is complicated.A-si TFT, on the other hand, although a-Si’s carrier movement rate is not as good as LTPS’s, it has a better competitive advantage in cost due to its simple and mature process.Au Optronics is the only company in the world that has successfully combined OLED with LTPS and A-SI TFT at the same time, making it a leader in active OLED technology.

The LTPS membrane is much more complex than a-SI, yet the LTPS TFT is 100 times more mobile than A-SI TFT. And CMOS program can be carried out directly on a glass substrate. Here are some of the features that p-SI has over A-SI:

LCD screens are backlit to project images through color filters before they are reflected in our eye Windows. This mode of carrying backlit LCD screens, known as “penetrating” LCD screens, consumes most of the power through backlit devices. The brighter the backlight, the brighter it will appear in front of the screen, but the more power it will consume.

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 next year, in 1889, the study of thermodynamic equilibrium and the phase transfer German physicist O.L Ehmann, compounds for a more detailed analysis of this. He found that under the polarizing microscope, half of the viscous liquid gonorrhea liquid compounds with different parts peculiar to the crystal birefringence (birefringence) of the optical properties, namely, optical interphase (optically anisotropic). It will be a name to this as the liquid crystal. Since then, scientists will be the nature of this new discovery, known as the fourth state material – LCD (liquid crystal). It at a specific temperature range can have the characteristics of the liquid and solid at the same time.

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.

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.

In accordance with the described above, the lamellar liquid crystal, linear liquid crystal, and LCD screen for cholesterol levels, because of its long liquid crystal molecules like a stick, so point to the direction of the vector and the molecular long axis parallel. To be defined with reference to the refraction coefficient of a single optical axis crystal, it will have two refractive indexes, respectively is perpendicular to the direction of the long axis of the liquid crystal n coming (= ne) and parallel to the long axis of the liquid crystal direction n / / (= no), so when the incident light liquid crystal, will be affected by two refractive indexes, cause in the vertical long axis of the liquid crystal and LCD long axis parallel to the direction of the speed of light will be different.

If with the molecular long axis parallel to the direction of light speed, when less than perpendicular to the speed of the molecular long axis direction, which means that parallel the molecular long axis direction of refractive index is greater than the vertical direction of the refractive index (because the refractive index is inversely proportional to the speed of light), is the one – no > 0. So the birefringence Δ n > 0, we think that it is called optics is a type of LCD, and lamellar liquid crystal and LCD are all belong to the optical is almost linear LCD. If the light of the parallel to the direction of the long axis was faster, On behalf of the flat to the governor of the axis of the refractive index is less than the vertical direction, so the birefringence Δ n < 0. We call it is the optical negative type of LCD. The cholesterol liquid crystal optical negative type of LCD.

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.

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.

We can know from figure 10, when there is no applied voltage between the upper and lower two pieces of glass, the arrangement of LCD will be in accordance with the match to the membrane of the upper and lower two pieces of glass. For TN type of LCD, and match to the film’s point of view of the poor to 90 degrees. (see figure 9) so the liquid crystal molecules are arranged by the up and down automatically rotate 90 degrees when the incident light passes through the upper polarizing film, the polarization of light waves will only order direction. Through the liquid crystal molecules, the liquid crystal molecules rotate for 90 degrees, so when the waves reach the lower polarizing film, the polarization direction of the light just turned 90 degrees. The polarizing film of the lower and upper polarizing film, 90 – degree Angle is just the differences. (see figure 9) so can smoothly through the light, but if we applied voltage between the upper and lower two pieces of glass, because the type TN LCD for the dielectric coefficient of different sex more positive type of LCD (epsilon / / > epsilon coming, represent the parallel direction of the dielectric coefficient is larger than the dielectric coefficient of the vertical direction, so when the liquid crystal molecules are influenced by an electric field, will tend to be parallel to the orientation of the electric field direction.), so we can see from figure 10, At this time, the polarized light wave passing through the upper polarizer will not change the polarization direction when passing through the liquid crystal molecule, so it cannot pass through the lower polarizer.

The so-called NW (Normally white), is to point to when we don’t apply voltage on the LCD screen panel, we can see the panel is pervious to light, also is bright, so-called Normally white. But on the other hand, when we don’t apply voltage on the LCD panel if the panel is not pervious to light, the look is black, it’s called NB (Normally black). We have just mentioned in figure 9 and figure 10 all belongs to the configuration of NW, also we can know from figure 11, For type TN LCD, located in the upper and lower glass is perpendicular to the membrane, and the difference between NB and NW just lies in the relative position of the polarizing film is different. For NB, the fluctuation of the polarizing film polarity is parallel to each other. So when the NB no applied voltage, the light will be because the polarity of the LCD to rotate 90 degrees to be pervious to light. Why there are NW and NB these two kinds of a different configuration of the polarizing film? Mainly for different applications. Commonly used in a desktop computer or notebook computer, most of the NW configuration. That’s because, if you notice, generally the use of computer software environment, you will find that most of the entire screen is a bright spot, that is to say, computer software for the application of white background and black text. Since on the point of the majority, using NW is more convenient, of course. Also because the NW window does not need to add the voltage, the average will compare to save electricity. In turn, said that the application of the NB environment mostly belongs to the screen for the application of black.

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.

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.

Another box in figure 14 glue and spacer structure of two kinds of ingredients. The box adhesive USES is to make the LCD panel in the upper and lower two layers of glass, to be able to stick close and to provide a panel of LCD screen molecules, cut off from the outside world, so the box plastic as its name suggests, is around and around in the panel to the liquid crystal molecules box limited to within a panel. The spacer is mainly provided two-layer glass support, it must be distributed evenly on the glass, or a part but uneven distribution cause spacer gathered together, it will block the light, It is also unable to maintain the appropriate gap between the upper and lower glass, which will lead to uneven distribution of electric field and affect the performance of the crystal 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.

When the light is emitted from the backlight plate, it will pass through the polarizer, glass, LCD screen, color filter, etc. It is assumed that the penetration rate of each part is as follows:

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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.

Scan line: scan line, control TFT switch. The transistors on the control TFT are on/off. When On, data can be transmitted; when off, data can not be transmitted.

Color filter is the key element in the color of liquid crystal display. Through the color filter, the high gray scale liquid crystal display can be fully coloured. So the function of the color filter is to produce RGB Triple Light in the way of filter light, and then mix the three original light with different strong and weak proportions to show all kinds of colors, so that the LCD displays the full color.

The backlight module is mainly used to provide the light source with uniform and high brightness of the liquid crystal panel. Because of the non self luminescence of TFT-LCD, the external light source, such as the light emitting diode and the cold cathode ray tube, must be used.

Therefore, in the design of TFT LCD, to improve the opening rate as much as possible, because only to increase the opening rate, you can increase the brightness, and the brightness of the backlight plate is not so high, can save electricity consumption and cost.

Many people know what the characteristics of TFT LCD screens are, but do you know what are the characteristics of TFT LCD screen material? Today, we will tell you about the knowledge of the characteristics of TFT LCD screen materials.

With the rapid development of TFT array-driven liquid crystal display technology, in recent years, TFT LCD not only occupied the high-end display market such as portable notebook computers but also challenged the desktop display with the improvement of the manufacturing process and cost reduction. Because the TFT array directly drives the liquid crystal molecules, the cross-distortion effect is eliminated, and the display information capacity is large; the use of low-viscosity liquid crystal materials greatly improves the response speed, which can meet the needs of video image display. Therefore, compared with TFT display, TN type, and STN type liquid crystal display have made a qualitative leap and become one of the most promising display technologies in the 21st century.

TFT also adopts the principle of TN type electro-optic effect, but the TFT LCD material is different from the traditional liquid crystal material. In addition to good physical and chemical stability and a wide operating temperature range, TFT LCD materials must also have the following characteristics:

(4) The optical anisotropy (Δn) is matched to the TFT to eliminate the rainbow effect for greater contrast and wide-angle field of view. The range of △n value should be between 0.07~0.11.

At present, among the TFT LCD screen materials, TN type LCD screen has gradually entered a recession period, the market demand is gradually shrinking, the production capacity is excessive, the price competition is fierce, and there is no investment value. STN-type LCD will gradually enter a mature stage, the market demand will grow steadily, and the production technology will be fully mature. The TFT-type LCD is entering a new round of rapid growth, and the market demand will increase sharply, and it is expected to become one of the most promising display materials in the 21st century.

Although liquid crystal materials whose end groups are cyano groups, such as biphenyl and phenylcyclohexane liquid crystals, have been widely used in TN and STN LCDs, their viscosity is higher than that of fluorine-containing liquid crystals with the same molecular structure. These unfavorable factors limit the application of this type of compounds in TFT LCDs. The ester liquid crystal has the characteristics of simple synthesis method, wide variety, and wide phase transition range, but its high viscosity greatly reduces the dosage in TFT formulation. Therefore, the development of new liquid crystal compounds that meet the above requirements has become the focus of liquid crystal chemistry research.

The liquid crystal materials have developed rapidly with the development of liquid crystal devices, from biphenyl nitrile, esters, oxygen-containing heterocyclic benzenes, and pyrimidine ring liquid crystal compounds to cyclohexyl (bi) benzene, diphenylacetylene, ethyl bridge bonds and various fluorine-containing aromatic ring liquid crystal compounds. Japan has synthesized difluoroethylene liquid crystal compounds with stable structure, and its molecular structure is more and more stable, and it continuously meets the performance requirements of STN and TFT LCDs.

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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.

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.

According to real LCD manufacturing conditions, the number of normal LCD panels exceeds greatly the number of defective LCD panels. Therefore, the normal PRs greatly outnumber the defective PRs. As a result, the collected data set for training would be imbalanced if a two-class classification approach is adopted, the SVM by Vapnik [4] for example, the class imbalance problem occurs.

In practice, in addition to the class imbalance problem, the LCD defect detection also suffers from another critical problem resulting from the absence of negative information. To facilitate the following problem description, the normal PR class and the defective PR class are defined as the positive class and negative class, respectively.

The main difference between a normal PR and a defective PR is that their appearances are apparently different, as can be observed from Figure 4. The color (or gray level) of a normal PR is nearly uniform, implying that the variation of the gray-level distribution of normal PRs is very small. On the contrary, the surfaces of defective PR not only contain various kinds of textures, but also vary greatly in color, implying that the variation of the true distribution for negative class in the data space is very large. Collecting a set of positive training data that can represent the true distribution of positive class is easy, because: (1) the variation of positive-class distribution is very small; and (2) most of the LCD panels are normal (the number of normal PRs is considerably large). Therefore, the positive class can be well-sampled during the data collection stage in real practice. However, representative defective PRs are difficult to obtain in practice for several reasons. For example, there are numerous types of defects in array process, more than 10 types at least. However, not all the defects would occur frequently. Some of the defects seldom appear, for example the defect caused by abnormal photo-resist coating (APRC). The defect “APRC” seldom occurs, because equipment/process engineers maintain the coating machines periodically. Even so, the coating machines might still break down occasionally. As a result, the number of available images containing the APRC defects is quite limited. But, the APRC defect has a large variation in color and texture. Unfortunately, limited APRC examples cannot stand for all kinds of APRC defects. Therefore, the collected negative training data are most likely under-sampled. Here, the “under-sampled” means that the collected negative training set cannot represent the true negative-class distribution in the data space, which is the problem of absence of negative information. Due to this problem, numerous false positive (i.e., missing defects) will be produced if a two-class classification approach (e.g., a binary SVM) is applied to the LCD defect detection, which has been evidenced by the results reported in [7]. Compared with two-class classification approach, novelty detection approach is a better choice.

Novelty detection is one-class classification [10,35], which is to solve the conventional two-class classification problems where one of the two classes is under-sampled, or only the data of one single class can be available for training [5,6,9–11,35–40]. As analyzed above, for the LCD defect detection application, the normal PRs can be well-sampled, while the defective PRs are in general undersampled. Therefore, the LCD defect detection can be treated as a typical novelty detection problem. Accordingly, one-class classification is a better solution.

To summarize, it can be seen that the LCD defect detection suffers from two problems simultaneously: one is the class imbalance problem, and the other is the problem of the absence of negative information. For the first problem, there have been many sophisticated solutions, including sampling, cost-sensitive learning, SVM-based, and one-class learning approaches. However, the only solution to the second problem is the novelty detection approach (i.e., one-class classification approach). Therefore, one-class classification would be a more appropriate approach to the LCD defect detection application.

There are several approaches for one-class classification, such as density approach (e.g., Gaussian mixture model [5]), boundary approach (e.g., SVDD [9] and one-class SVM [40]), neural network approach [6,36], and reconstruction-based approach (e.g., the kernel principal component analysis for novelty detection [35]). It has been proven in [9] that when a Gaussian kernel is used, the SVDD proposed by Tax and Duin [9] is identical to the one-class SVM proposed by Schölkopf et al. [40]. This paper focuses on the SVDD since it has been applied to the same application in the works of [7] and [10], and has shown to be effective in detecting defective PRs. However, as discussed in Section 1, generalization performance of SVDD is limited. Therefore, the intent of this paper is on proposing a method to improve generalization performance of SVDD, and applying the improved SVDD to the LCD defect detection treated as a novelty detection problem. The improved SVDD is called quasiconformal kernel SVDD (QK-SVDD). Note that the QK-SVDD and SVDD are not two independent classifiers. To obtain QK-SVDD, one has to train an SVDD first, which will be introduced in Section 2.4. In the following part of the paper, we first introduce the defect detection scheme, and then derive the proposed method in details.