We have long known that matter exists in three states: solid, liquid, and gas. Although the arrangement of the centroids of liquid molecules does not exhibit any regularity, if these molecules are elongated (or flattened), their orientations may have regularity. Therefore, we can subdivide the liquid state into many types. Liquids without any regularity in molecular orientation are directly referred to as liquids, while liquids with molecular orientation are called "liquid crystals", also known as "LC". Liquid crystal products are actually not unfamiliar to us. Mobile phones and calculators we commonly encounter are all liquid crystal products. Liquid crystals were discovered in 1888 by Reinitzer, an Austrian botanist. They are organic compounds with a regular molecular arrangement that fall between solids and liquids. The most commonly used liquid crystal type is nematic liquid crystal, whose molecular shape is elongated rod-like, with a length and width of about 1nm to 10nm. Under the influence of different electric fields, liquid crystal molecules will undergo a regular 90-degree rotation and alignment, resulting in differences in light transmittance. This produces differences in brightness and darkness when the power is turned on/off. By controlling each pixel based on this principle, the desired image can be formed.

The principle of liquid crystal display (LCD) is that liquid crystals exhibit different optical properties under the influence of different voltages. Physically, liquid crystals are divided into two major categories: passive and active. Passive liquid crystals, also known as passive-type, do not emit light themselves and require an external light source. Depending on the position of the light source, they can be further classified into reflective and transmissive types. Passive LCDs have lower costs, but their brightness and contrast are limited, and their effective viewing angle is relatively small. Color passive LCDs exhibit lower color saturation, resulting in colors that are not vivid enough. The other category is active, primarily TFT (Thin Film Transitor). Each liquid crystal is actually a transistor that can emit light, so strictly speaking, it is not a liquid crystal. An LCD screen is composed of many liquid crystals arranged in an array. In monochrome LCDs, each liquid crystal represents a pixel, while in color LCDs, each pixel is composed of three liquid crystals: red, green, and blue. At the same time, it can be considered that each liquid crystal has an 8-bit register behind it, and the value of the register determines the brightness of each of the three liquid crystal units. However, the value of the register does not directly drive the brightness of the three liquid crystal units; instead, it is accessed through a "color palette". It is not practical to equip each pixel with a physical register. In practice, only one row of registers is provided, which are connected to each row of pixels in turn and loaded with the content of that row. Driving all rows of pixels once displays a complete frame

Liquid crystal appears as a liquid in shape and appearance, yet its crystalline molecular structure exhibits a solid-like morphology. Similar to metals in a magnetic field, when influenced by an external electric field, its molecules undergo precise and orderly alignment; with appropriate control over the molecular arrangement, liquid crystal molecules allow light to penetrate. The path of light through the liquid crystal is determined by the molecular arrangement that constitutes it, which is another characteristic of a solid. Liquid crystal is an organic compound composed of long rod-shaped molecules. In its natural state, the long axes of these rod-shaped molecules are roughly parallel. The first characteristic of a Liquid Crystal Display (LCD) is that it must be filled with liquid crystal between two planes with thin slots, which are perpendicular to each other (intersecting at 90 degrees). That is to say, if the molecules on one plane are arranged in a north-south direction, the molecules on the other plane are arranged in an east-west direction, and the molecules located between the two planes are forced into a 90-degree twisted state. Since light propagates along the direction of the molecular arrangement, the light passing through the liquid crystal is also twisted by 90 degrees. However, when a voltage is applied to the liquid crystal, the molecules will realign vertically, allowing the light to pass straight through without any twisting. The second characteristic of an LCD is its reliance on polarizing filters and the light itself. Natural light is randomly emitted in all directions, and polarizing filters are actually a series of increasingly thinner parallel lines. These lines form a net that blocks all light that is not parallel to these lines. The lines of the polarizing filter are perpendicular to the first one, so it can completely block the polarized light. Only when the lines of the two filters are completely parallel, or when the light itself has been twisted to match the second polarizing filter, can the light penetrate. An LCD is composed of two mutually perpendicular polarizing filters, so under normal circumstances, it should block all attempting light. However, since the space between the two filters is filled with twisted liquid crystal, after the light passes through the first filter, it is twisted by 90 degrees by the liquid crystal molecules and finally passes through the second filter. On the other hand, if a voltage is applied to the liquid crystal, the molecules will realign and become completely parallel, so the light is no longer twisted and is blocked by the second filter. Taking Synaptics TDDI technology as an example, it integrates the touch controller and display driver into a single chip, reducing the number of components and simplifying the design. ClearPad 4291 supports a hybrid multi-touch in-cell design, eliminating the need for a discrete touch sensor by utilizing existing layers in a liquid crystal display (LCD). ClearPad 4191 takes this a step further by utilizing existing electrodes in the LCD, thus achieving a more compact system architecture. Both solutions enable thinner touch screens and brighter displays, contributing to the overall aesthetic improvement of smartphone and tablet designs. For reflective TN (Twisted Nematic) LCDs, the structure consists of the following layers: polarizing filter, glass, two sets of electrodes, one vertical and one horizontal, that are mutually insulated and transparent, liquid crystal, electrodes, glass, polarizing filter, and reflective sheet.