The working principles of TFT LCD Display

The working principles of TFT LCD Display

The working principles of TFT LCD Display

Aug 16, 2022

LCD display at the most basic level, most (but not all) liquid crystal displays change the polarization state of light passing through the liquid crystal layer. The competition between the boundary conditions and the applied electric field controls the geometry of the layer. Generally, for this type of LCD, nematic liquid crystals are used, and special coatings are applied on the back and front substrates.

The coating is used to create boundary conditions and apply the required electric field. Paste the optical film (including the polarizing film) on the outside of the LCD unit.

They convert light polarization changes into light and dark contrasts. The display structure is assembled in such a way that a zero applied electric field produces an extreme brightness state, and a completely applied electric field causes the other extreme. Midfield produces mid-level brightness.

LCD Display suppliers:
The most common material used to impose boundary conditions is called polyimide.

The polyimide solution (or precursor) is deposited on the substrate and cured. The type of polyimide and the type of liquid crystal define the angle at which the liquid crystal molecules appear at the contact point between the polyimide and the liquid crystal.

If the materials are “similar”, the liquid crystal molecules are flat. If they are different (such as oil and water), the LC molecules stand upright. “Molecular engineering” is used to achieve the ideal application angle, and different types of displays are different. In order to determine the alignment direction, the polyimide surface is subjected to unidirectional rubbing or brushing.

The liquid crystal molecules are aligned parallel to the rubbing direction. If the angle and rubbing direction of the two alignment surfaces do not match, the orientation of the liquid crystal will be elastically deformed. Nematic liquid crystal molecules want to be parallel to each other, but if the rubbing direction on either surface is orthogonal, the liquid crystal molecules will be forced to twist slightly from one molecule to another until the direction of the entire layer is rotated 90°.

There are three possible main deformation modes for nematic liquid crystals. Each has its own spring constant (spring constant). Depending on the molecular structure of the liquid crystal, some deformation may require more or less force. The three main deformations are called unfolding, bending, and twisting. The liquid crystal molecules are forced to twist slightly from one molecule to another until the direction of the entire layer is rotated by 90°.

LCD Display suppliers:
The most common method of applying force to deform the liquid crystal structure is to apply an electric field on or parallel to the liquid crystal layer (a magnetic field can also play a role). In order to apply this field, it is necessary to have a transparent conductor so that the effect of liquid crystal on light can be observed. Indium tin oxide is such a conductor.

LCD manufacturers either buy ITO coated glass or use ITO coating in the manufacturing process. The ITO layer is defined as shape and pattern according to the needs of photolithography. The shape and pattern of the two ITO layers (front and back) define the pixels and icons on the display.

In the application field, the liquid crystal molecules are expected to be aligned with respect to the field with minimal energy.

If the magnetic field is strong enough, the molecular order imposed by the boundary conditions will be overcome, and the magnetic field determines the molecular arrangement.

If the magnetic field is weak, the structure will be deformed by the magnetic field. In either case, when the site is removed, the influence of the boundary conditions takes over, and the liquid crystal orientation is restored to the state before the site application. It is like a spring, deforms when the force is applied, and then returns to its original shape when the force is removed.

In short, this combined structure is like an electrically adjustable shutter, allowing more or less light to pass through.