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Liquid crystal displays have become a technology-intensive and capital-intensive high-tech industry, and transparent conductive glass is one of the three main materials for LCDs. The reason why a liquid crystal display can display a specific pattern is to use a transparent conductive electrical film on conductive glass to make electrodes of a specific shape by etching. After the upper and lower conductive glasses are made of liquid crystal cells, apply appropriate voltage signals to these electrodes to make The liquid crystal molecules of the dipole moment are arranged in a specific aspect under the action of the electric field, and only show a pattern corresponding to the electrode wavelength.

In the oxide conductive film, the Sn-doped In2O3 (ITO) film has the highest transmittance and the best conductive performance, and it is easy to etch fine patterns in the acid solution. Its transmittance has reached more than 90%. The transmittance and resistance of ITO are controlled by the ratio of In2O3 and Sn2O3 respectively, usually SnO2: In2O3 = 1: 9.

ITO is an N-type oxide semiconductor-indium tin oxide. ITO thin film is an indium tin oxide semiconductor transparent conductive film. There are usually two main performance indicators: resistivity and light transmittance.

At present, the resistivity of the ITO film layer is generally about 5 * 10-4, preferably up to 5 * 10-5, which is close to the resistivity of the metal. In practical applications, the resistance of the ITO is often characterized by the square resistance. The transmittance can reach more than 90%. The transmittance and resistance of the ITO film are controlled by the ratio of In2O3 and Sn2O3, respectively. Increasing the oxide ratio can increase the transmittance of ITO. Usually Sn2O3: In2O3 = 1: 9, Because the thickness of tin oxide exceeds 200Å, the transparency is usually not good enough-although the conductivity is very good.

For example, when the current flows through the ITO delamination in parallel, where d is the film thickness, I is the current, L1 is the film thickness in the current direction, and L2 is the film length in the direction perpendicular to the current. When flowing through a square conductive film, the layer resistance R = PL1 / dL2 where P is the resistivity of the conductive film. For a given film layer, P and d can be regarded as fixed values, P / d, when L1 = L2, No matter what the size of the square, the resistance of the square film of Anger is the fixed value P / d, which is the definition of the square resistance: R □ = P / d, where the unit of R □ is: Aum / □ (Ω / □), It can be found from this that the sheet resistance is related to the resistivity P of the IOT film layer and the ITO film thickness d and the lower the ITO film resistance value, the greater the film thickness.

At present, ITO glass used in high-end STN liquid crystal display has an R □ of about 10Ω / □ and a film thickness of 100-200um, while the ITO glass of low-end TN products has an R □ of 100-300Ω / □ and a film thickness of 20 -30um.

In the design of LCD traces, the calculation method of ITO resistance shows that the following factors affect the resistance of ITO:

1. Square resistance of ITO glass

To ensure that the wiring resistance is small, the entertainment should make the ITO glass square resistance small, because R □ = P / d, you must choose a material with small P and appropriate d.

2. L1 / L2

L1 / L2 is the ratio of the length of the trace in the parallel current direction and the vertical current direction. When R □ is constant, to ensure that the resistance value of the trace is small, it is necessary to make L1 / L2 small. When L1 is constant, only increase L2 It is also said that when designing, the trace should be as wide as possible; and when L2 is constant, L1 should be small, that is, when the trace width is constant, the thin line should be as short as possible.

3. In the design of LCD display, not only the influence of the wiring cloth on the resistance of ITO, but also the influence of the production process on the resistance of ITO must be considered, so as to select the appropriate ITO glass with a square resistance, so as to control the design to production. To produce high-contrast LCD products, at this time, high duty cycle and COG products are not important, such as the uniformity of ITO film thickness, because the ITO rake material and process are stable, it will cause the same length and width of ITO resistance Change, for example, when the target value is 10Ω, the R □ range is between 8-12Ω, so the conductive glass with uniform ITO film thickness should be used in production to reduce the resistance change, followed by the high temperature resistance of ITO glass, Acidity and alkalinity, because high temperature baking and various acid and alkali liquid immersion are usually used in the LCD production process, and generally in the environment of 300 ° C * 30min, R □ will increase by 2-3 times, and at 10wt % NaOH * 5min and 6wt% HCL * 2min (60 ° C) will also increase to about 1.1 times. It can be seen that high-temperature production and long-term acid and alkali cleaning should not be used in the production process. It should be carried out at a low temperature and the action time should be shortened as much as possible.

4. In the liquid crystal display, the ITO block resistance is equivalent to the voltage divider resistance in the circuit diagram, and its resistance value directly affects the size of the voltage across the circuit, that is, the larger the block resistance, the greater the LCD value voltage. Some data indicate that the square resistance of ITO is reduced from 100Ω / □ to 60Ω / □. (Cell Gap is 6um), the Vth value will decrease by about 0.03V.