I. Thin Film Transistors
Thin-film transistors are referred to as tft devices, also known as tft switching tubes, which are made based on the principle of field effect tubes, i.e., tft devices are tubes that utilize the electric field effect to control current. Because only one polarity of the carriers involved in the conductive, so, tft device is a unipolar device. tft device also has three electrodes, namely, the source pole s (equivalent to the e pole of the triode), gate g (equivalent to the b pole of the triode) and drain d (equivalent to the c pole of the triode). But the control characteristics of the two are very different, the triode is a current control device, through the control of the base current to control the collector current or emitter current, that is, the need for a signal source to provide a certain current in order to work, therefore, its input resistance is low; tft device is a voltage control device, its output current is determined by the magnitude of the input voltage, basically does not require a signal source to provide current, therefore, its input impedance is very high. Therefore, its input impedance is very high. In addition, tft device also has the advantages of fast switching speed, high frequency characteristics, good thermal stability, low noise, etc. tft device mainly a-si (amorphous silicon) and p-si (polycrystalline silicon) two kinds, of which, p-si (polycrystalline silicon) in the beginning and the development stage, a-si is more widely used. Figure 1-3 shows the internal structure schematic and circuit symbols of a-si amorphous silicon tft device.
When the tft device works like a voltage-controlled bidirectional switch, when no voltage is applied to the gate g, the tft device is in the cutoff state (off state), i.e., the source s and the drain d can not be turned on, and at this time, the resistance between the gate g and the source s (or drain d) is called the turn-off resistance roff. due to the gate g's leakage current is very small or no, so, roff is very high, generally more than 107ω . When a positive voltage greater than its on-state voltage is applied to the gate g, the tft device (a) Structure of tft device (b) Symbol of tft device will be in the on-state, i.e., the source s is turned on to the drain d. At this time, the resistance between the source s and the drain d is called the on-resistance ron, which decreases with the increase of the gate voltage. For tft devices, the source s and drain d have the same characteristics and are functionally interchangeable, and the direction of current between the source s and drain d changes with the direction of the electric field between them. Source and drain are defined in the application circuit, generally the input signal end is called source s, the output signal end is called drain d. In tft LCD, generally the data driver end is connected to the source s of the tft device, and the pixel end is connected to the drain d of the tft device.
II. Liquid Crystal Capacitors and Storage Capacitors
groundTFT liquid crystal displayThe structure can be seen, in the upper and lower two layers of glass asked to sandwich the liquid crystal, liquid crystal is a capacitive material, its equivalent capacitance is generally known as the liquid crystal capacitance clc, its size is about 0.1pf, but in practice, this capacitance can not be able to keep the voltage to the next time to update the screen data, that is to say, when the tft to this capacitor is charged, it can not keep the voltage until the next tft again. When charging this point (with the general 60hz screen update frequency, need to keep about 16ms time), so that the voltage has changed, the gray scale will be displayed incorrectly, therefore, generally in the design of the panel, will be added to a storage capacitor c. (Generally formed by the pixel electrode and the common electrode alignment), its capacity is about 0.5pf, in order to let the charging voltage can be maintained until the next time to update the screen. The next time the screen is updated.
III. Row and column electrodes
From the driving method, tft LCD connects all row electrodes as scanning rows to the gate driver, and all column electrodes as column signal ends to the source driver, thus forming the driving array.
IV. Color Filters
Stripes are often used in oa products, i.e. notebook computers or desktop monitors. Why do we use the bar arrangement for this application? The reason is that most of the software is now a windowed interface, that is, we see the screen content is a large number of varying sizes of the box is composed of, and the strip arrangement can make these box edges look more straight, rather than a straight line looks like a hairy edge or jagged feeling. However, if it is applied to LCD color TV and other products, it is not the same, because most of the TV signal is the character, the character's lines are not straight, most of its outline is an irregular curve, so at the beginning, LCD color TV are using mosaic arrangement (or known as the diagonal arrangement), but Z recent LCD color TV products have been improved to the use of triangular arrangement.
V. Directional Membrane
As we know, TFT liquid crystal display screen before and after (or up and down) two layers of glass is mainly used to clamp the liquid crystal, the rear layer of glass on the thin film transistor (tft), while the front layer of glass is affixed with color filters. But these two pieces of glass in contact with the liquid crystal on the side is not smooth, but there are jagged grooves, set the main purpose of this groove is to make the linear liquid crystal molecules along the grooves, so that the liquid crystal molecules will be neatly arranged. Because if it is a smooth plane, the arrangement of liquid crystal molecules will not be neat, resulting in light scattering, forming the phenomenon of light leakage. In the actual manufacturing process, and can not be made into such a groove distribution of glass, generally in the glass surface coated with a layer of pi (polyimide), and then rubbed with a cloth, so that the surface molecules of the pi is no longer scattered distribution, in accordance with the direction of a fixed and uniform arrangement. And this layer of pi is called directional film, its function is like the groove of the glass, providing liquid crystal molecules are uniformly arranged interface conditions, so that the liquid crystal in accordance with the predetermined order of arrangement.
VI. Frame glue and filler
Frame glue around the LCD screen, its role is to allow the LCD panel in the upper and lower layers of glass can be tightly adhered to the liquid crystal molecules framed within the panel. And filler is mainly to provide support for the upper and lower two layers of glass, it must be evenly distributed in the glass substrate, otherwise, once the distribution is uneven, resulting in part of the filler gathered together, but will hinder the passage of light, but also can not maintain the upper and lower two pieces of glass of the appropriate gap, resulting in the phenomenon of uneven distribution of the electric field, which affects the liquid crystal gray-scale performance.
The above is a brief description of theTFT liquid crystal displayThe main components of the introduction of the description, today I speak here, there are any questions you can directly consult our official website customer service, customer service can help you answer. If you want to know more about the TFT LCD information, you can pay attention to our official website!www.lcdhc.com The editor will keep updating, thank you!