Basic Structure Of Capacitive Touch Screen

The basic structure of a capacitive touch screen is: the substrate is a single-layer organic glass, and a layer of transparent conductive film is uniformly forged on the inner and outer surfaces of the organic glass. A narrow electrode is tapered on the four corners of the transparent conductive film on the outer surface. The working principle is that when a finger touches a capacitive touch screen, a high-frequency signal is connected to the working surface. At this time, the finger forms a coupling capacitor with the working surface of the touch screen, which is equivalent to a conductor. Because there is a high-frequency signal on the working surface, the finger absorbs a small current at the touch point when touching. This small current flows out from the electrodes on the four corners of the touch screen, and the current flowing through the four electrodes is proportional to the linear distance between the finger and the four corners, The controller can obtain the coordinate values of the contact points by calculating the four current ratios.
A capacitive touch screen can be simply seen as a screen body composed of four composite screens: the outermost layer is a glass protective layer, followed by a conductive layer, the third layer is a non-conductive glass screen, and the innermost fourth layer is also a conductive layer. The innermost conductive layer is the shielding layer, which plays a role in shielding internal electrical signals. The middle conductive layer is a key part of the entire touch screen, with direct leads on the four corners or edges, responsible for detecting the position of touch points.
The top covering layer is tempered glass or polyethylene terephthalate (PET). The advantage of PET is that the touch screen can be made thinner, and on the other hand, it is cheaper than existing plastic and glass materials. The insulation layer is glass (0.4-1mm), organic film (10-100um), adhesive, and air layer. The most important layer among them is the indium tin oxide (ITO) layer, with a typical thickness of 50-100nm and a block resistance in the range of approximately 100-300 ohms. The three-dimensional structure of ITO technology has a significant impact on capacitive touch screens, which directly affects the two important capacitance parameters of touch screens: induced capacitance (between the fingers and the upper ITO) and parasitic capacitance (between the upper and lower ITOs, and between the lower ITO and the display screen).
The structure of capacitive touch screen is mainly to coat a transparent film layer on the glass screen, and then add a piece of protective glass to the conductor layer. The double glass design can completely protect the conductor layer and the sensor, at the same time, it has higher light transmittance, and can better support multi-touch.
The capacitive touch screen is coated with narrow electrodes on all four sides of the touch screen, forming a low voltage AC electric field within the conductive body. When touching the screen, due to the human electric field, a coupling capacitor is formed between the fingers and the conductive layer. The current emitted by the four electrodes flows to the contacts, and the strength of the current is inversely proportional to the distance between the fingers and the electrode. The controller located behind the touch screen calculates the proportion and strength of the current, accurately calculating the position of the touch point. The dual glass of the capacitive touch screen not only protects the conductor and inductor, but also effectively prevents external environmental factors from affecting the touch screen. Even if the screen is stained with dirt, dust, or oil, the capacitive touch screen can still accurately calculate the touch position.
Due to the variation of capacitance with different contact areas and dielectric properties, its stability is poor and often leads to drift phenomena. This type of touch screen is suitable for the debugging stage of system development.