Touch Screen

1. Capacitive touch screen

The capacitive touch screen uses the current induction of the human body to work. The capacitive touch screen is a four-layer composite glass screen. The inner surface and the interlayer of the glass screen are each coated with a layer of ITO, and the outermost layer is a thin layer of silica glass protective layer. The interlayer ITO coating is used as the working surface on the four corners. Lead out four electrodes, the inner ITO is a shielding layer to ensure a good working environment. When a finger touches the metal layer, due to the electric field of the human body, a coupling capacitor is formed between the user and the touch screen surface. For high-frequency current, the capacitor is a direct conductor, so the finger draws a small current from the contact point. This current flows from the electrodes on the four corners of the touch screen, and the current flowing through these four electrodes is proportional to the distance from the finger to the four corners. The controller obtains the position of the touch point by accurately calculating the ratio of these four currents. .

Compared with the traditional resistive touch screen, the advantages of the capacitive touch screen mainly include the following aspects, and the operation is novel. The capacitive touch screen supports multi-touch, the operation is more intuitive and interesting. Not easy to touch by mistake. Since the capacitive touch screen needs to sense the current of the human body, only the human body can operate it, and it will not respond when touched with other objects, so the possibility of false touch is basically avoided. High durability. Compared with resistive touch screens, capacitive touch screens have better performance in terms of dustproof, waterproof, and wear resistance.

2. Resistive touch screen

This touch screen uses pressure sensing for control. The main part of the resistive touch screen is a resistive film screen that fits well with the surface of the display. This is a multi-layer composite film. It uses a glass or hard plastic plate as the base layer and is coated with a layer of transparent oxide metal (transparent conductive Resistance) conductive layer, covered with a layer of hardened outer surface, smooth and scratch-resistant plastic layer, and its inner surface is also coated with a layer of coating, there are many small (less than 1/1000 inch) transparent between them The isolation point separates and insulates the two conductive layers. When the finger touches the screen, the two conductive layers are in contact at the touch point, the resistance changes, signals are generated in the X and Y directions, and then sent to the touch screen controller. Commonly used transparent conductive coating materials are: ITO, indium oxide, weak conductor, the characteristic is that when the thickness drops below 1800 angstroms (angstroms = 10-10 meters), it suddenly becomes transparent, and the light transmittance is 80%. The light transmittance decreases when it becomes thinner, and rises to 80% when it reaches a thickness of 300 angstroms. ITO is the main material used in all resistance technology touch screens and capacitive technology touch screens. In fact, the working surface of resistance and capacitance technology touch screens is ITO coating. Unlike nickel-gold coating, the outer conductive layer of the five-wire resistive touch screen uses a nickel-gold coating material with good ductility. Due to frequent touches, the purpose of using nickel-gold material with good ductility is to extend the service life. However, the process cost is relatively high. Although the nickel-gold conductive layer has good ductility, it can only be used as a transparent conductor. It is not suitable for the working surface of the resistive touch screen because of its high conductivity and Moreover, the metal is not easy to be very uniform in thickness, so it is not suitable for the voltage distribution layer and can only be used as the probe layer.