tft lcd layers quotation

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.

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.

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.

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.

The thin film transistor liquid crystal display (TFT-LCD) is currently the most widely used liquid crystal display. This article introduces the basic information of TFT-LCD from its structure, principle, manufacturing process, characteristic index, research progress, and application.

TFT-LCD technology is a high technology that combines microelectronics technology and LCD technology. By using microelectronic fine machining technology and Si material processing technology, people have developed the technology of growing Si materials on large-area glass plates and TFT planar array technology. Combined with the increasingly mature LCD manufacturing technology, product quality can be continuously improved, and the automatic large-scale production capacity can be enhanced. In addition, the qualified rate can be improved, the cost can be reduced, and its performance/price ratio can be closer to CRT.

A thin film transistor (TFT) liquid crystal display is an active matrix display formed by integrating a TFT switch into a twisted nematic (TN) liquid crystal display. This way, the shortcomings of passive matrix display, such as cross-interference, less information, and slow writing speed, can be overcome. And the display quality is greatly improved so that it can be applied to the high-resolution panchromatic display of computers and other fields.

The main component of the finished TFT-LCD is an LCD display module (LCM), which is composed of a Panel and a Backlight. As the core part of the whole liquid crystal display, the Panel has the most complicated manufacturing process. What people usually call bright spots are generated during the manufacturing process of the Panel. The quality of the backlight can directly influence the display effect, and it is usually the key factor influencing the life of TFT-LCD.

A TFT array is built on the glass substrate at the lower layer of the panel. The ITO electrode of each pixel is connected to the TFT drain electrode, the grid is connected to the scanning bus, and the original power supply is connected to the signal bus. When the scanning signal voltage is applied, the original source electrode is turned on so that the signal voltage is applied to the storage capacitor and charged. The signal voltage of the storage capacitor is applied to the liquid crystal pixel at the frame rate so that the liquid crystal pixel is in a gated state.

At present, the grayscale has reached 256 levels; that is, 16.7 million colors can be obtained (almost full-color display). Since the industry came into being in the 1990s, the production line of thin film transistor (TFT) liquid crystal display has developed from the first generation to the 11th generation. For each renewal of generation, the area of substrate glass has been greatly increased, the output continuously improved, and the cost continuously reduced.

For the assembly process of the TFT-LCD panel (screen), firstly, the cleaned color film substrate and TFT array substrate are coated with alignment film coating solution and are oriented by friction. Then the array substrate of the TFT is coated with sealing glue, and spacers with a size of 5-10 μ m are scattered on the array substrate as supporting points. Afterward, the array substrate and the color film substrate are assembled and sealed with sealing glue to form an empty box (Cell).

Response time is an important indicator to measure the quality of TFT-LCD, which refers to the response speed of TFT-LCD to input signals, that is, the response time of liquid crystal from dark to bright or from bright to dark. Generally speaking, it is divided into two parts: Tr (Rise Time) and Tf (Fall Time), and the response time is the sum of the two. The smaller the response time, the better. If it exceeds 40 milliseconds, the moving image will be hysteresis. At present, the standard response time of TFT-LCD is about 25 milliseconds, but a few models can reach 16 milliseconds. With 16ms ultra-fast response time, it can display more than 60 frames per second. It means it can completely solve the problems of ghost images and trailing smears existing in traditional LCD screens when playing games or watching DVDs.

Contrast refers to the brightness ratio between the bright area and the dark area of the display screen under the specified lighting conditions and observation conditions. Contrast is a parameter that directly reflects whether the TFT-LCD can present rich color levels. The higher the contrast, the better the layering of the restored picture. Presently, the nominal contrast of TFT-LCD is 250: 1 to 500: 1, and high-end products have a contrast of above 1000: 1. What should be explained here is that contrast must be matched with brightness to produce the best display effect. A high contrast ratio of 400: 1 or 500: 1 will make the display more colorful and softer, and the display effect of playing games or watching movies can be comparable to a CRT display.

The brightness of LCD screen is generally higher than that of traditional CRT display screen, and the brightness of TFT-LCD is generally in cd/m2 (lumens/square meter). The higher the brightness, the stronger the anti-interference ability of the display screen to the surrounding environment, and the brighter the display effect. This parameter should be at least 200cd/m2, preferably above 1000cd/m2 for industrial applications. The higher the brightness of the traditional CRT display screen, the greater its radiation. The luminance of TFT-LCD is obtained by the illumination of the LED (light-emitting diode) backlight, so there is no negative impact on the human body.

TFT-LCD is a backlight display device, and the light emitted by the backlight behind the LCD module inevitably leads to the only best viewing angle-facing up. When you look at TFT-LCD from other angles, color distortion will happen because the backlight can penetrate the next pixels and enter the human eye. The undistorted range is the visual angle of the LCD screen. The viewing angle of TFT-LCD is also divided into horizontal viewing angle and vertical viewing angle, and the horizontal viewing angle is generally larger than the vertical viewing angle. At present, as long as the horizontal viewing angle reaches 120 degrees and the vertical viewing angle reaches 140 degrees, the screen can meet the demands of most users. The latest TFT-LCD panel is produced with wide viewing angle technology, which can reach 140 degrees from top to bottom and 150 degrees from left to right, thus reducing the inconvenience caused by the small viewing angle. Of course, this performance can’t be compared with a CRT display with a viewing angle close to 180 degrees, but it is more than enough for most applications.

The pixel spacing of TFT-LCD refers to the interval between each pixel of the LCD screen. Currently, the standard pixel spacing of mainstream (16:9) 23.6-inch TFT-LCD products is generally 0.276 mm, and the corresponding resolution is 1920 × 1080.

The bandwidth of TFT-LCD is also an indicator to measure the LCD screen. Generally, the bandwidth of TFT-LCD is 80MHz. The large-screen TFT-LCD has the advantages of liquid crystal display and large-screen display, which makes the large-screen LCD products represented by 23.6-inch TFT-LCD favored by consumers. In addition, its visible area is larger than that of 24-inch color TV. Moreover, it has the advantage of no radiation, which can make users watch it at close range.

Since the panel thickness of TFT-LCD is the same, the main factors influencing the thickness of TFT-LCD will be the circuit control panel’s technology, the plastic shell’s design, and the compression of internal space. Of course, with the integration of a few cutting-edge liquid crystal technologies, the latest ultra-thin liquid crystal panels, thinner high-brightness LED technology, coupled with more integrated control IC design and more optimized heat dissipation treatment, the overall size of the product can be significantly reduced.

(5) Large-screen TFT-LCTV has begun to enter large-scale industrial production. The image quality of TFT-LCTV has reached or even exceeded CRT. For example, the resolution of the 86-inch TFT LCTV is 1920 × 1200, and its horizontal and vertical viewing angles are 170 degrees; The 100-inch TFT LC TV has been successfully developed and commercialized.

(6) Large-area low-temperature polysilicon TFT-LCD has been successfully developed and put into industrial production, and amorphous silicon TFT self-scanning LCD has been commercialized;

(7) Reflective TFT-LCD color display is beginning to be commercialized. For example, a 5.8-inch reflective display with a resolution of 400 × 234 and a picture ratio of 16: 9 has a reflectivity of 30%, a response speed of 30ms, and a power consumption of 0.15 watts.

(10) Backlight and inverter. Although reflective LCD is being actively developed, transmissive TFT-LCD with backlight will still be the mainstream product for a long time. The backlight is an essential accessory. Germany has developed a flat fluorescent lamp backlight for liquid crystal modules, with a brightness of 5000-7000cd/m2 and a life of 100,000 hours. Some new self-heating backlights can normally work in the range of-40 ℃ to 85 ℃. OEL backlight and high brightness LED backlight have been successfully developed and started to be used in TFT-LCD, Linfinity. Microelectronics invented a long-life inverter with cold cathode backlight, the modulation range of the light source of which reaches 500: 1.

TFT-LCD is mainly used in computers, video terminals, communication, instrumentation, and other industries. The main application fields are laptops, desktop computer monitors, workstations, industrial monitors, global positioning systems (GPS), personal data processing, game consoles, portable VCDs, DVDs, and other portable devices.

Optical and SEM (scanning electron microscopy) images of fabricated (a, b) CL and (c, d) CLSE pixel structures. The five white line patterns in (d) are the ITO interdigitated pixel and common electrodes. (e) Images from the normal direction and from 50 degrees to the left and right of a 2.3-inch-diagonal display incorporating the IPS TFT-LCD panel. (f) The three-black matrix (BM) patterns (top: BM covering both gate and data lines, middle: BM covering only the data lines, and bottom: without BM) and (g) optical images of pixels without BM (left: LC on and off voltages supplied to every other data line, right: LC off voltage supplied to all data lines).

Figure 3e shows images from the normal direction and from 50 degrees to the left and right of a 2.3-inch-diagonal display incorporating the IPS TFT-LCD panel fabricated in our laboratory, (f) the three black matrix (BM) patterns (top: BM covering both gate and data lines, middle: BM covering only the data lines, and bottom: without BM), and (g) optical images of panel areas without the BM (left: LC on and off voltages supplied to every other data line, right: LC off voltage supplied to all data lines). As can be seen in the image from the normal direction, the brightness and contrast of the display area with the top BM and middle BM patterns are almost the same, but the contrast of the display area without the BM is relatively lower because of the lower darkness level of the LC off pixels indicating “HITACHI”. As shown in Fig. 3g, this is due to light leaking through the aperture between the data line and adjacent common lines. Therefore, in the CL structure, the BM on the drain line is necessary to obtain a high contrast ratio by shielding light leakage. This is the same as in the conventional structure. On the contrary, there is no light leakage along the gate line through the gaps between the gate line and edges of the pixel/common electrodes, as is clearly shown in Fig. 3g. This is a unique advantage of the CL structure because the conventional structure must shield these gaps with the BM to prevent light leakage. The suppression of light leakage along the gate line in the CL structure is due to the driving scheme (see Fig. 2b,a for a comparison with the conventional structure). During the holding period (tOFF) in the conventional structure, regardless of the pixel voltage, Vp (including Vp = 0), nonzero Vgp and Vgc are always applied to keep the TFT off, and these voltages are applied to the LC layer, inducing light leakage as reported in

Figure 4a shows the gate voltage (Vg) dependence of the panel brightness, while the inset shows that of the TFT current (transfer characteristics). The gray curves are for the conventional IPS TFT-LCD with the TFT before enhancement, the common line, and the matrix BM (MBM) shown at the top of Fig. 3f. The blue curves are for the proposed CL structure with the enhanced TFT and the stripe BM (SBM) shown in the middle of Fig. 3f. In this case, enhanced TFT characteristics were obtained by using an MNOS TFT without back-channel oxidation that was enhanced by the BTS process. In both structures, the threshold voltages for panel brightness, defined by extrapolating the straight part of the brightness curves, reflect those of the TFT transfer curves defined as Vg at a drain current of 10−12 A, and they are well matched to be 4 V and 9 V, respectively. The maximum brightness for the CL structure is 137% higher than that for the conventional structure, which is due to the increase in the aperture ratio from 38 to 52% that results from the elimination of the common line and the BM covering the gate line.

(a) Dependence of panel brightness and TFT current on gate voltage for the conventional pixel structure of 38% aperture ratio (AR) with matrix black matrix (MBM) over both drain and gate lines and proposed CL pixel structure of 52% AR with strip black matrix (SBM) over only the drain lines. Transfer characteristics before and after bias temperature stress (BTS) treatment are shown in the inset. (b) Charging and (c) holding characteristics of enhanced TFT of the CL structure with gate as a common line. Vg and Vd in the TFT ON state are 30 V and +/−7 V, respectively.

To estimate the charging and holding characteristics of the MNOS-enhanced TFT in the panel, the gate TFT ON and OFF time dependences of the panel brightness were measured (Fig. 4b,c). The charging characteristics in Fig. 4b are plotted as a function of tON at tOFF = 16.6 ms, Vg = 30 V, and Vd = ± 7 V. The holding characteristics in Fig. 4c are plotted as a function of tOFF at tON = 34 μs. 95.1% charging at tON = 34 μs and 95.3% holding at tOFF = 16.6 ms indicate that the enhanced TFT has sufficient charging and holding performance to drive a standard VGA (640 × 480 pixels) panel (the number of scanning lines is estimated as tOFF/tON = 16.6/0.034 = 488).

To confirm the driving conditions for the CL structure without the BM along the gate line (with the SBM), the tOFF dependence of the contrast ratio (CR) in the CL panel was further investigated as shown in Fig. 5a, where CR is plotted as a function of tOFF for the CL panels with the matrix BM (MBM) and the strip BM (SBM). The inset shows the brightness in the bright (Vd = 7 V) and dark (Vd = 0 V) states of the CL panel with the SBM as a function of tOFF and an optical image of the panel with tOFF = 6.4 ms. The SBM and MBM panels keep CR higher than 240 with tOFF > 16.6 ms, the frame period of a display panel without flicker being noticeable to the human eye. both panels decrease CR when tOFF is less than 16.6 ms; the CR of the SBM panel decreases faster than the CR of the MBM panel. As shown in the inset, the decrease in CR was due to the increase in dark-state brightness with decreasing tOFF as light leakage increases along the gate line. This light leakage is induced by the voltage Vgp = Vgc = VgON = 30 V applied only for 34 μs during the TFT ON (charging) state, which is 1/488th the duration, tOFF = 16.6 ms, of the TFT OFF (holding) state with Vgp = Vgc = VgOFF = 0 V, but the ratio increases with decreasing tOFF and becomes effective enough to switch on LC layer and induce light leakage. However, it should be stressed again that the CL panel with the normal holding (TFT OFF) time of 16.6 ms does not suffer from the light leakage along the gate line, so the aperture ratio can be increased by removing the BM along the gate line.

Figure 6 indicates the effect of bias temperature stress (BTS) on the TFT characteristics. As the stressing time, tS, of the positive gate stress voltage, Vst =  + 77 V, increases from 0 to 3600 s, the transfer (Id-Vg) curve shifts in the positive direction (Fig. 6a). Vth is defined as Vg at which Id = 10−12 A and ΔVth is defined as the Vth shift from the initial value via BTS. As shown in Fig. 6b, ΔVth increases logarithmically with increasing tS: ΔVth = 2.17 + 4.93 × log (tS). The mechanism behind the gate-stress-induced Vth shift is electron tunnel injection from the a-Si:H semiconductor into the SiOx gate insulator. For confirmation, ΔVth of MNOS TFTs with different SiOx thicknesses is plotted as a function of the electric field applied to the SiOx layer in Fig. 6c. Here, the thickness of the SiOx was varied (5, 10, 20, 50 nm), while the SiN thickness was fixed at 200 nm. The electric field applied to SiOx, Eox, was calculated using the following equation,

Effect of bias temperature stress (BTS) on TFT characteristics. (a) The transfer (Id–Vg) curve shifts in the positive direction with positive gate bias stress of Vst =  + 77 V over the duration of 0–3600 s. (b) ΔVth, defined as the Vth shift from the initial value via BTS, increases logarithmically with increasing tS, following ΔVth = 2.17 + 4.93 × log (tS). (c) ΔVth of MNOS TFTs with different SiOx thicknesses from 5 to 50 nm as a function of the electric field applied to the SiOx layer.

Figure 7a shows the effect of back-channel oxidation (BCO) and passivation (PAS) on the Id-Vg characteristics of the MNOS TFT. The Id-Vg curve with Vth = 5.1 V is further enhanced to Vth = 10.9 V after BCO, although there is a slight degradation of the slope of the current increase in the sub-threshold region. The slope recovers after PAS without any change to the enhanced characteristics

(a) Effect of back-channel oxidation (BCO) and passivation (PAS) on Id–Vg characteristics of MNOS TFT. (b) Vth and Vth standard deviation, σVth, after BTS and after BCO without BTS treatments and (c) SiOX thickness as a function of position along gate-line, x.

The advantage of BCO over BTS is the uniformity of the enhanced characteristics; Fig. 7b shows the distribution of the enhanced Vth as a function of position along gate-line, x, for the MNOS TFTs connected with a 90-mm-long gate line in the TFT substrate after BTS and BCO treatments. The average value of Vth and the standard deviation, σVth, for pristine TFTs before BTS or BCO, are 5.1 V and 0.35 V, respectively. After BCO, Vth is uniformly enhanced, with an average Vth = 11 V and σVth = 0.4 V without increasing σVth. On the other hand, after BTS, Vth is nonuniformly enhanced with an average Vth = 9.3 V and σVth of 1.4 V. In particular, Vth increases linearly as a function of position along gate-line, x. As the gate SiOx thickness linearly decreases, from (54 nm) to (47 nm) with increasing x as shown in Fig. 7c, the increase in ΔVth after BTS with x is due to increase in the electric field applied to SiOx as shown in Fig. 6c and Eq. 1.

It has been shown that the Vth of the MNOS TFT is independent of the gate SiOx thickness when the thickness is more than 5 nm8a, Vth of the MNOS TFT with the BCO treatment becomes almost independent of the BCO SiOx thickness. As shown in the inset, the thickness of BCO SiOx composed of oxidized a-Si:H linearly increases with BCO processing time, and the Vth increase almost saturates at a BCO SiOx thickness greater than 5 nm. Therefore, the enhanced MNOS TFT after BCO has a uniformly high Vth that is robust to thickness fluctuations of the gate and BCO SiOx layers. BCO also has an advantage over BTS in terms of the stability of Vth as shown in Fig. 8b, which plots the annealing time dependence of Vth for BCO and BTS. In this experiment, the stoichiometry (x) of the gate SiOx was 1.78 for BTS and 1.78 and 1.9 for BCO. The annealing temperature in the N2 atmosphere was 200 °C. In the case of BTS, Vth decreased to the pristine value after approximately 5 h of annealing, while Vth decreased more slowly in the case of BCO. In particular, the annealing time required for Vth to fall to 7 V was 7.5 times longer than that of BTS. Increasing the stoichiometry (x) of the gate SiOx dramatically improved the BCO-enhanced Vth to as much as 11 V, which was stably maintained after 24 h of annealing at 200 °C.

(a) Dependence of Vth on thickness of back-channel oxidized (BCO) SiOX. The inset shows the SiOx thickness dependence on the BCO process time for RF powers of 200 W and 500 W. (b) Stability of Vth as a function of annealing time for three different TFTs with gate SiOx stoichiometry, x = 1.78 and bias temperature stress (BTS), x = 1.78 and BCO, and x = 1.9 and BCO. The temperature of annealing in the N2 atmosphere was 200 °C. (c) Band diagram of back-channel oxidized MNOS TFT. The red arrows show the electric dipoles at the SiOX/a-Si:H and a-Si:H/BCO SiOX interfaces.

A schematic band model for the MNOS TFT with the BCO treatment and the sectional structure of the interface between the a-Si:H and gate and BCO SiOx are shown in Fig. 8c. The uniformly high Vth that is independent of SiOx thickness is due to the dipoles generated at the channel and back-channel interfaces between a-Si:H and SiOx8 of reference

Thin-Film Transistor Liquid Crystal Displays use thin-film transistors to control the voltage applied to the liquid crystal layer at a sub-pixel level. The structure of TFT LCDs consists of a TFT “sandwich” and a BLU (Backlight Unit). A typical configuration is shown in the schematic diagram below.

Firstly, between the back and front polarizers, TFT LCD cells are made with two glass substrates – one for color filters, the other for a TFT array – and a liquid crystal layer sandwiched in between.

For normally black TFT LCDs, if we follow along a piece of light setting off from its backlight source, it will bea)guided uniformly by LGP;b)reflected and enhanced by BEF and DBEF;c)polarized by the back polarizer;d)polarization changed by twisted LC under the voltage applied by TFT arrays;e)“tinted” red/green/blue by corresponding color filter of the subpixel;f)let through the front polarizer by matched polarization; andg)finally, it will reach the surface and appears in viewer’s eyes.

Normally black LCDs have higher contrast and wider viewing angles without grayscale inversion phenomenon compared to their normally white relatives. And whether TFT LCDs are normally black or white depends on their LC switching mode:

TFT-LCD technology is based on semiconductor IC manufacturing processes, and is unique in that it uses glass substrates rather than traditional silicon wafers. For the TFT manufacturing process, thin film formation, such as CVD and PVD processes, is a very important part. The ODF process has been developed for the assembly of color filters and TFT substrates, and is used in large size LCDs.

First of all, the movement and arrangement of liquid crystal molecules need electrons to drive, so in the carrier of liquid crystal – TFT glass, there must be able to conduct the part to control the movement of liquid crystal, here will use ITO (Indium TIn Oxide, transparent conductive metal) to do this thing. ITO is transparent, also known as thin film conductive crystal so that it will not block the backlight.

The different arrangement of liquid crystal molecules and the rapid movement changes to ensure that each pixel accurately display the corresponding color, and the image changes precisely and quickly, which requires precision control of the liquid crystal molecules. ITO film requires special processing, as if printed circuitry on a PCB board, drawing conductive lines throughout the LCD board.

For array panels with back-channel etched TFT structure.The main process can be divided into 5 steps (5 lightings) according to the sequence of the layers to be made and the interrelationship between the layers.

The process includes: PECVD triple layer continuous film formation, island lithography, island dry lithography and other processes. After these processes, the final amorphous silicon island for TFT is formed on the glass substrate. The graphics obtained after the process is completed are shown in the following figure.

Specific processes include: S/D metal layer sputtering into a film, S/D lithography, S/D wet lithography, channel dry lithography and other processes. After these processes, the source, drain, channel and data lines of the TFT are finally formed on the glass substrate. At this point, the TFT has been produced. The graphics obtained after the process is completed are shown in the following figure.

The process includes PECVD, photolithography, and dry lithography of vias. After these processes, the final TFT channel protective insulation layer and guide through the hole are formed on the glass substrate. The graphics obtained after the process is completed are shown in the following figure.

Color filters can be produced by various methods; photolithography is a typical method. In photolithography, color filters are produced by exposing a glass substrate coated with a photographic color resist through a photomask. The resist is hardened to form the RGB pattern of the LCD.

When making LCD panels it is impossible to produce them one by one, which is too inefficient, so multiple pieces are processed at once and separated by cutting.

A TN or Twisted Nematic TFT LCD is a cost-effective high performance LCD. It offers good brightness performance and fast response times. However, it suffers in one key area and that is its viewing cone. TN LCD’s typically have three good viewing angle directions. In these directions the image is typically clear and colors are consistent up to 80 degrees from the center of the LCD. The remaining viewing direction is usually good through 40-50 degrees from center. Afterwards, the image is likely to invert, almost appearing like an x-ray.

Most off-the-shelf displays are not designed to operate in extreme environments although the use of TFT LCD displays is now common in many outdoor, rugged and/or public access applications. Concerns for high performance viewability, protection against damage and functionality in EMI/RFI sensitive applications can be addressed with combinations of a Display Logic LED Backlight Enhancement and the following solutions.

On most touchscreens there are usually two layers that make up just the digitizer. The glass on top that you touch and the actual digitizer sheet which consists of the touch matrix circuitry. The digitizer sheet is adhered to the glass so it often appears to be one piece. So you where correct to assume glass cover, digitizer and then lcd. The digitizer sheet and glass have a small gap that has an adhesive in it. On both the glass(bottom) and digitizer(top) is a transparent metallic conductive coating which is usually indium tin oxide. The human touch is conductive which allows for the electical sensors in the digitizer and glass sheets to sense the touch at a specific location.

Some of the newest technology such as Super AMOLED is able to get away from the two conductive sheets and has the touch sensors built into only one sheet, so these touchscreens would be an exception. So most forms of touchscreens consist of three or more layers.

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

As light strikes the first filter, it is polarized. The molecules in each layer then guide the light they receive to the next layer. As the light passes through the liquid crystal layers, the molecules also change the light"s plane of vibration to match their own angle. When the light reaches the far side of the liquid crystal substance, it vibrates at the same angle as the final layer of molecules. If the final layer is matched up with the second polarized glass filter, then the light will pass through.

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

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

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

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

A TFT is a type of transistor used in active-matrix LCD screens. TFT LCD screens use a separate transistor to control each pixel in the display. They allow the electrical current that controls each pixel to turn on and off quickly, which decreases response time and makes on-screen motion smoother. TFT LCDs are often used as computer monitors, televisions, mobile phone screens, and other flat-panel color displays.

The name "Thin Film Transistor" is derived from the manufacturing process. The manufacturer first applies thin films of a semiconductor (like amorphous silicon) and dielectric materials to a flat, non-conductive surface (like glass). Unneeded silicon is etched away, leaving only a grid of transistors and the transparent glass surface. These transistor panels are thin enough to fit between a polarized backlight and the layer of liquid crystals. These transistors apply an electrical current to the liquid crystals, altering their arrangement to block light in certain ways. The light then passes through other layers of the screen, including a color filter and polarized light filter, to display the final image.

Not all TFT LCD screens are made the same. There are several types of TFT panels, made by distinct methods, and with different performance characteristics. The two most common types are TN and IPS.

Twisted Nematic (TN) panels contain liquid crystals that twist as an electric current is applied. As the crystals twist, they allow varying amounts of polarized light to pass through. TN panels are the easiest type of TFT LCD to produce and offer the quickest response times. However, TN panels don"t display colors as accurately as other types of panels, particularly when viewed at an angle.

Digimax distribetes a wide range of professional LCD monitors and large format displays for digital signage applications manufactured by Philips: one of the world"s largest manufacturers of TFT monitors, recognized for quality products and cutting-edge solutions.

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.

On the surface level is the other glass substrate. Just beneath this glass substrate is where the actual pixels and sub-pixels reside, forming the RGB color filter. In order to counteract the electrodes of the previously mentioned layer, this surface layer has counter (or common) electrodes on the side closer to the liquid crystals that close off the circuit that travels between the two layers. In both these substrate layers, the electrodes are most frequently made of indium tin oxide (ITO) because they allow for transparency and have good conductive properties.

The outer sides of the glass substrates (closest to the surface or closest to the back) have filter layers called polarizers. These filters allow only certain beams of light to pass through if they are polarized in a specific manner, meaning that the geometric waves of the light are appropriate for the filter. If not polarized correctly, the light does not pass through the polarizer which creates an opaque LCD screen.

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.

The twisted nematic effect is one of the cheapest options for LCD technology, and it also allows for fast pixel response time. There are still some limits, though; color reproduction quality may not be great, and viewing angles, or the direction at which the screen is looked at, are more limited.

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.

Within an LCD, each pixel can be characterized by its three sub-pixels. These three sub-pixels create the RGB colorization of that overall pixel. These sub-pixels act as capacitors, or electrical storage units within a device, each with their own independent structural and functional layers as described earlier. With the three sub-pixels per pixel, colors of almost any kind can be mixed from the light passing through the filters and polarizer at different brightness based on the liquid crystal alignment.