tft display structure factory

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

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

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

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

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

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

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

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

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

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.

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.

Polysilicon is a silicon-based material about 0.1 to several um in size, composed of many silicon particles. In the semiconductor manufacturing industry, polysilicon should normally be treated by Low-Pressure Chemical Vapor Deposition. If the annealing process is higher than 900C, this method is known as SPC. Solid Phase Deposition. However, this method does not work in the flat display industry because the maximum temperature of the glass is only 650C. Therefore, LTPS technology is specifically applied to the manufacture of flat displays.

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:

2. Vehicle for OLED: High mobility means that the OLED Device can provide a large driving current, so it is more suitable for an active OLED display substrate.

The “reflective” architecture USES an external light source to display the image via a reflector, which saves electricity but is harder to see in the absence of an external light source.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

Brody, T. Peter; Asars, J. A.; Dixon, G. D. (November 1973). "A 6 × 6 inch 20 lines-per-inch liquid-crystal display panel". 20 (11): 995–1001. Bibcode:1973ITED...20..995B. doi:10.1109/T-ED.1973.17780. ISSN 0018-9383.

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.

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

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.

Photolithography is the process of copying Mask graphic structures onto the glass substrate to be etched. There are three main processes: photoresist coating, exposure, and development

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.

Pre-Tilt Angle (Pre-TIlt Angle or TBA: Tilt Bias Angle) characteristic refers to the arrangement of liquid crystal molecules on the mating film is not parallel to the film surface, but one end of the molecule in the friction direction relative to the film surface has a certain warp, the stilt angle is called pre-tilt angle. If there is no pre-tilt angle, under the external electric field, the liquid crystal molecules can stand up randomly from two directions, which will cause poor display.

Assembly is the combination of backlight, screen, control circuit board, and touch screen and other components together to form a complete display module. Assembly is generally done by hand, and skilled workers are very important here.

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

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

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

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

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

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

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

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

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

One feature of the PES pleated filter cartridge is the asymmetrical pore structure and a higher surface area design (0.75 m2/10-inch length), offering a much higher dirt loading capacity and larger effective filtration area than symmetrical membrane pleated cartridge filters.

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

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

TFT LCD screen is mainly composed of three parts: rear panel module, LCD layer and front panel module. A layer of liquid crystal is sandwiched between two glass substrates. A color filter is attached to the front LCD panel, and a thin film transistor (TFT) is made on the back TFT panel. When a voltage is applied to the transistor, the liquid crystal turns, and light passing through the liquid crystal produces pixels on the front panel. As shown in the figure：

The rear plate module refers to the part behind the liquid crystal layer, which is mainly composed of the rear polarizer , the rear glass layer, the pixel unit (pixel electrode, TFT tube), the rear directional film, etc.

The rear glass substrate is divided into many tiny grids, called pixel units (or sub-pixels), by a number of transparent metal film wires arranged horizontally and vertically and insulated from each other. Each cell has a transparent metal film electrode, called the pixel electrode, which is insulated from the surrounding wire. One corner of the pixel electrode is connected with two vertical and horizontal wires through a TFT thin film field effect tube made on glass substrate by printing method to form a matrix structure:

The gate of the TFT field effect tube is connected with the horizontal line, the horizontal line is called the gate scan line or the X electrode, because it plays the role of TFT pass selection, also called the pass selection line; The source pole of the TFT tube is connected with the vertical line, which is called the source line or Y electrode. The drain of the TFT is integrated with the transparent pixel electrode. The function of the TFT tube is a switch tube, using the gate voltage applied to the TFT switch tube, can control the conduction and cut-off of the TFT switch tube.

The LCD screen has a pixel electrode and a thin film transistor (TFT) on the rear glass plate, and a color filter on the front glass plate. The liquid crystal layer is sandwiched between the front and back glass layers.

For TFT LCD screen, each pixel unit can be regarded as a layer of TN liquid crystal sandwiched between the pixel electrode and the common electrode. The liquid crystal layer can be equivalent to a liquid crystal capacitor (CLc), whose size is about 0.1pF. In practice, this capacitor cannot hold the voltage until the next time the picture data is updated, that is, when the TFT tube is fully charged to this capacitor, it cannot hold the voltage until the next time the TFT tube is charged to this point (at the usual 60Hz picture update frequency, it needs to hold the voltage for about 16ms). As a result, if the voltage changes, the gray scale will be incorrect. Therefore, when designing the panel, a storage capacitor Cs (usually formed by the wiring of the pixel electrode and the common electrode) will be added, with a value of about 0.5pF, so that the charged voltage can be maintained until the next image updated.

Red, blue, and green are the so-called three primary colors. That is to say, with these three colors, different colors can be mixed together. The three RGB colors are divided into three independent units, each of which has different gray-scale changes. Then the three adjacent RGB display units are taken as a basic display unit — pixel, and the pixel can have different color changes.

In the figure, the black part between each RGB point, called the black-matrix, is mainly used to cover the part that is not intended to transmit light, such as the pixel electrode wire, TFT tube, etc.

Thin-film transistors play an important role in the digital display industry. You’re probably reading this article on a screen that uses thin-film transistor (TFT) technology. These transistors are the driving force behind flat-panel displays on laptops, desktop computers, tablets, smartphones, and high-definition TVs.

However, TFTs have a range of other commercial applications. Understanding these devices, including their structure, history, and usage, can highlight the value of adopting thin film deposition technology in your lab.

Thin film transistors, also known as TFTs or film transistors, are a type of field-effect transistor most commonly used in liquid crystal displays (LCDs). LCD technology uses one thin-film transistor for every pixel within a flat-panel display, and the transistors essentially act as on/off switches for the individual pixels.

TFTs are produced by depositing a semiconductor and a dielectric layer over a non-conducting substrate, such as glass. In flat-panel displays, thin-film transistors are arranged within a matrix pattern, and these devices are the backbones of active-matrix displays.

In 1957, John Wallmark of the Radio Corporation of America designed a thin-film MOSFET that used germanium monoxide as a gate dielectric. This design allowed Paul K. Weimer, another member of the Radio Corporation of America, to create the first thin-film transistor in 1962. This first thin film transistor (TFT) used a thin layer of cadmium selenide and cadmium sulfide as a semiconductor.

In 1966, Westinghouse Electric employees H. E. Kunig and T.P. Brody created metal-oxide-semiconductor TFTs using indium arsenide as a semiconductor. They developed these transistors in both depletion and enhancement modes, paving the way to utilise TFT technology in on/off modes.

Bernard J. Lechner first conceived the concept of using thin-film transistor devices in liquid-crystal display technology. In 1973, researchers developed a cadmium selenide thin-film transistor (TFT) to use in the first TFT liquid-crystal display. However, the first commercial LCD product using TFT technology was not available until 1984.

In 2012, researchers created the first TFT using indium gallium zinc oxide (IGZO) as a semiconductor [1]. IGZO transistors utilise low power consumption and high refresh rates compared to traditional TFT technology, signifying the next generation of transistor film developments.

Manufacturers produce thin-film transistor (TFT) machinery by layering a semiconductor and dielectric active layer over a substrate. However, manufacturers also include metallic contacts, such as a gate layer, drain metal, and source metal. The above diagram showcases the exact structure of bottom-up (top contact) TFTs.

The primary difference between TFTs and conventional MOSFETs is their semiconductors. TFTs utilise distinct substrates and semiconductors — commonly glass and metal oxides, respectively. However, conventional MOSFETs utilise a semiconductor material that doubles as the substrate. For example, a silicon wafer is commonly used in MOSFET manufacturing.

TFTs and MOSFETS have varying threshold voltages [2], making them each suitable for a different transistor operation. However, TFTs offer some benefits over conventional MOSFETs. For example, the tiny nature of TFTs allows for a smaller electric charge, leading to faster re-drawing within an active matrix display.

Manufacturers can create TFTs using a range of semiconductor materials. But for that, they’ll need thin films, which are made following a deposition process in a vacuum chamber.

Historically, TFTs used thin films of amorphous silicon or polycrystalline silicon as semiconductors, as silicon is abundant in nature and used in many commercial applications. However, researchers have determined that the low mobility of amorphous silicon [3] makes it suboptimal in TFTs, leading to the usage of other semiconductors.

Each semiconductor material above is suitable for TFT production because of its charge carrier mobility. Carrier mobility determines the speed and high-frequency response of the final TFT.

Glass is the most common substrate material within TFTs. This material is necessary for the traditional application of TFTs in LCDs, which we will discuss later. Glass is also suitable because of its non-conductive nature and excellent optical clarity.

However, some manufacturers use flexible plastic substrates within low-temperature TFT manufacturing processes. Researchers have recently developed a method to create incredibly high-performance TFTs on these flexible substrates [4]. Fully printed TFTs can also utilise flexible substrate materials.

The manufacturing of TFTs requires a highly specialised process to deposit the semiconductor onto the substrate. For example, TFTs are extremely sensitive to process temperature. Manufacturing must occur in low-temperature environments, as high temperatures can melt some typical substrates.

Thin-film transistors have numerous device applications. Researchers are still determining the various ways TFTs can assist emerging applications ranging from flexible electronics to integrated circuits.

TFTs have recently become common in a wide range of digital detectors. For example, digital radiography detectors in medical radiography utilise these devices within their image receptors. TFTs also have applications in sensors, such as temperature, gas [5], and biochemical sensors.

Recently, researchers have begun developing optically transparent TFT devices using transparent substrates [6]. With further research, transparent TFTs could operate within head-up displays, which are essential for aircraft and automobile operations. Head-up displays allow users to view information without straying from necessary viewpoints.

Printed TFTs also have applications in flexible and printed electronics. Flexible electronic applications include calculators, cameras, personal entertainment devices, medical devices, and more.

However, the most common usage of thin transistor films is within digital displays. For example, active-matrix organic light-emitting diode (AMOLED) screens have a TFT layer that utilises low-cost, low-temperature manufacturing. Since 2013, all high-resolution electronic visual displays have used TFT active matrix technology [7].

While thin-film transistors have several high-performance applications, these transistors carry advantages and disadvantages within materials science. For example, while TFT displays are fast, sharp, and energy-efficient, they must utilise glass panelling, restricting their usage. A TFT display also necessitates disproportionate viewing angles.

LCD panels use TFT to control their pixels, altering the electric field to change the polarisation, and, thus, the colour output. Each TFT is paired with a pixel within the active matrix and includes a capacitor that allows the pixels to retain their charge, eliminating the need for individual charge carriers and enhancing the screen’s responsiveness.

Using the proper systems ensures that TFTs have the necessary electron mobility, channel width, transfer curves, operational stability, threshold voltage, and electrical performance for their desired applications.

Thin-film transistors play an important role in modern digital displays and materials chemistry as a whole. These devices improve upon conventional MOSFETs by offering faster response times and the ability to retain an electrical charge.

TFTs have a wide range of applications, most commonly in liquid crystal displays. Researchers continue to develop new types of and discover new uses for thin-film transistor devices.

Manufacturing TFTs requires specialised equipment and techniques. Utilising a reliable thin-film deposition system is essential to producing durable, functional thin-film transistors.

[2] Matebesi, Unopa & Mogosetso, Gofaone & Lebekwe, Caspar & Ditshego, Nonofo & Khoo, W. & Mohamed Sultan, Suhana. (2019).“IGZO TFT versus the MOSFET.” BIUST Research and Innovation Symposium 2019.

[5] Frank Liao, Christopher Chen, Vivek Subramanian, “Organic TFTs as gas sensors for electronic nose applications,” Sensors and Actuators B: Chemical, Volume 107, Issue 2, 2005, Pages 849-855, ISSN 0925-4005,https://doi.org/10.1016/j.snb.2004.12.026.

From the MOSFET, the TFT was born. The TFT varies from standard MOSFETs, or bulk MOSFETs, because, as the name implies, it uses thin films. The TFT began a new era of electronics. In 1968, just six years after the first TFT development, Bernard J. Lechner of RCA shared his idea of the TFT Liquid Crystal Display (LCD), something that would boom in popularity in our modern times. The TFT LCD was then first created in 1973 at the Westinghouse Research Laboratories. These LCDs were composed of pixels controlled by transistors. In FETs, substrates were just the semiconductor material, but in manufacturing TFT LCDs, glass substrates were used so that the pixels could be displayed.

But that was not the end of TFT developments. Soon after, in 1974, T. Peter Brody, one of the developers of the TFT LCD, and Fang-Chen Luo created the first active-matrix LCD (AM LCD). An active matrix controls each pixel individually, meaning that each pixel’s respective TFT had its signal actively preserved. This opened doors to better performance and speed as displays became more complex.

Though TFTs can use a variety of materials for their semiconductor layers, silicon has become the most popular, creating the silicon-based TFT, abbreviated as Si TFT. As a semiconductor device, the TFT, as well as all FETs, use solid-state electronics, meaning that electricity flows through the structure of the semiconductor layer rather than vacuum tubes.

Due to the variety in silicon’s possible structures, the Si TFT’s characteristics can vary as well. The most common form is amorphous silicon (A-Si), which is deposited during the first step of the semiconductor fabrication process onto the substrate in low temperatures. It is most usable when hydrogenated into the form A-Si:H. This then significantly alters the properties of A-Si; without the hydrogen, the material struggles with doping (the introduction of impurities to increase mobility of charges); in the form A-Si:H, however, the semiconductor layer becomes much more photoconductive and dopable. The A-Si:H TFT was first developed in 1979 which is stable at room temperature and became the best option for AM LCDs which consequently began rising in popularity after this breakthrough.

A second potential form of silicon is the microcrystalline silicon. Though it retains a similar form to A-Si, this type of silicon also has grains of what is known as crystalline structures. Amorphous structures have a more random, less geometric shape to their network-like structures, but crystalline, on the other hand, is more structured and organized. If grown correctly, microcrystalline silicon has better electron mobility than A-Si:H and greater stability too, as it has less hydrogen within its structure. It is deposited in a similar fashion to A-Si’s deposition.

And lastly, there is polycrystalline silicon, also known as polysilicon and poly-Si. Microcrystalline silicon is the middle between A-Si and poly-Si since poly-Si’s structure is composed of many crystallites. This specific form is made by annealing the silicon material which means adding heat to alter the properties of the structure. With poly-Si, the atoms in the crystal lattice shift and move when heated, and when cooled, the structure recrystallizes.

The biggest difference between these forms, notably A-Si and poly-Si, is that charge carriers are much more mobile and the material is much more stable when it comes to using poly-Si over A-Si. When creating complicated and high-speed TFT-based displays, poly-Si’s characteristics allow for this. Yet, A-Si is still very important due to its low-leakage nature, meaning that leakage current is not lost as heavily when a dielectric insulator is not totally non-conductive.

Several years later, another development was made in 2012 in the form of indium gallium zinc oxide (IGZO) which allowed for a more powerful display in terms of refresh rates and more efficiency in terms of power consumption. This semiconducting material, as stated in the name, uses indium, gallium, zinc, and oxygen. Though it is a form of zinc oxide (ZnO), the addition of indium and gallium allows this material to be deposited in a uniform amorphous phase but also maintaining the oxide’s high carrier mobility.

As TFTs began to increase their presence in display technology, transparent semiconductors and electrodes became more appealing to the manufacturers. Indium tin oxide (ITO) is an example of a popular transparent oxide used for its appearance, good conductivity, and ease of deposition.

Research of the TFT with different materials has led to the application of threshold voltage, or how much voltage is needed to turn on the device. This value is greatly dependent on thickness and choice of the oxide. When it comes to the oxide, this relates back to the idea of leakage current. With thinner layers and certain types of oxide, the leakage current may be greater, but this in turn could lower threshold voltage, as leakage into the device will also increase. In order to tap into the TFT’s potential for low power consumption, the lower the threshold voltage, the better the device’s appeal.

Another branch of development that stemmed from the TFT is that of organic TFTs (OTFT). First created in 1986, OTFTs usually use solution-casting of polymers, or macromolecules. This device made people hesitant, as it tended to have a slow carrier mobility, meaning slow response times. However, researchers have carried out experimentation with the OTFT because it has potential to be applied to displays different from those that traditional TFTs are used for, such as flexible, plastic displays. This research still continues today. With its simpler processing than traditional silicon technology, the OTFT holds much potential for modern day and future technologies.

Steven Van Slyke and Ching Wan Tang pioneered the organic OLED at Eastman Kodak in 1979. The first OLED product was a display for a car stereo, commercialized by Pioneer in 1997. Kodak’s EasyShare LS633 digital camera, introduced in 2003, was the first consumer electronic product incorporating a full-color OLED display. The first television featuring an OLED display, produced by Sony, entered the market in 2008. Today, Samsung uses OLEDs in all of its smartphones, and LG manufactures large OLED screens for premium TVs. Other companies currently incorporating OLED technology include Apple, Google, Facebook, Motorola, Sony, HP, Panasonic, Konica, Lenovo, Huawei, BOE, Philips and Osram. The OLED display market is expected to grow to $57 billion in 2026.

AMOLED (Active Matrix Organic Light Emitting Diode) is a type of OLED display device technology. OLED is a type of display technology in which organic material compounds form the electroluminescent material, and active matrix is the technology behind the addressing of individual pixels.

An AMOLED display consists of an active matrix of OLED pixels generating light (luminescence) upon electrical activation that have been deposited or integrated onto a thin-film transistor (TFT) array, which functions as a series of switches to control the current flowing to each individual pixel.

Typically, this continuous current flow is controlled by at least two TFTs at each pixel (to trigger the luminescence), with one TFT to start and stop the charging of a storage capacitor and the second to provide a voltage source at the level needed to create a constant current to the pixel, thereby eliminating the need for the very high currents required for PMOLED.

TFT backplane technology is crucial in the fabrication of AMOLED displays. In AMOLEDs, the two primary TFT backplane technologies, polycrystalline silicon (poly-Si) and amorphous silicon (a-Si), are currently used offering the potential for directly fabricating the active-matrix backplanes at low temperatures (below 150 °C) onto flexible plastic substrates for producing flexible AMOLED displays. Brightness of AMOLED is determined by the strength of the electron current. The colors are controlled by the red, green and blue light emitting diodes.  It is easier to understand by thinking of each pixel is independently colored, mini-LED.

IPS technology is like an improvement on the traditional TFT LCD display module in the sense that it has the same basic structure, but with more enhanced features and more widespread usability compared with the older generation of TN type TFT screen (normally used for low-cost computer monitors). Actually, it is called super TFT.  IPS LCD display consists of the following high-end features. It has much wider viewing angles, more consistent, better color in all viewing directions, it has higher contrast, faster response time. But IPS screens are not perfect as their higher manufacturing cost compared with TN TFT LCD.

Utilizing an electrical charge that causes the liquid crystal material to change their molecular structure allowing various wavelengths of backlight to “pass-through”. The active matrix of the TFT display is in constant flux and changes or refreshes rapidly depending upon the incoming signal from the control device.