Basic structure. The basic structure of capacitive touch screen is: The substrate is a single layer of plexiglass, on the inside and outside of the plexiglass surface evenly forged on a layer of transparent conductive film, respectively, the outer surface of the transparent conductive film on the Four corners of the cone on a narrow electrode. Its working principle is: when the finger touch capacitive touch screen, in the working face to connect high-frequency signal, the finger and touch screen face form a coupling capacitance, this equivalent to the conductor, because there is high-frequency signal on the working surface, finger touch at the touch point suction away a small current, the small current from the touch screen of the electrode four angle outflow,
The current flowing through four electrodes is proportional to the straight line distance from the fingers to the four corners, and the controller calculates the contact point coordinate value by calculating the four current ratio. Capacitive touch screen can be simply seen as a four-layer composite screen composed of the screen body: the outermost layer is the glass layer, then the conductive layer, the third layer is non-conductive glass screen, the fourth layer is also conductive layer.
The most internal conductive layer is the shielding layer, play the role of shielding internal electrical signals, the middle of the conductive layer is the key part of the entire touch screen, Four corners or four edges have a direct lead, responsible for the touch point position detection. The top layer of the coating is tempered glass or polyethylene terephthalate (PET). The advantage of PET is that the touchscreen can be thinner and, on the other hand, cheaper than existing plastic and glass materials. The insulating layer is glass (0.4~1mm), organic film (10~100um), adhesive, air layer. One of the most important layer is indium tin oxide (ITO) layer, the typical thickness of Ito 50~100nm, its block resistance of about 100~300 ohm range.
ITO process Three-dimensional structure of the capacitive touch screen has a great impact, it directly related to the touch screen 2 important capacitance parameters: inductive capacitance (finger and upper ito) and parasitic capacitance (between the upper and lower Ito, the lower Ito and the display screen).
Capacitive touch screen construction is mainly on the glass screen coated with a transparent layer of film, and then a protective glass outside the conductor layer, double glass design can completely protect the conductor layer and sensor, while the higher transmittance, but also better support multi-touch. Capacitive touch screen on the four sides of the touchscreen is plated with a narrow electrode, in the conductive body to form a low-voltage AC electric field. When touching the screen, as a result of the human electric field, the finger and the conductor layer will form a coupling capacitor, the four-sided electrode sends the current will flow to the contact, and the current strength and the distance between the finger to the electrode is inversely proportional to the touch screen controller will calculate the current ratio and strength, accurately calculate the location of the touch point.
Capacitive touch screen double glass can not only protect the conductors and sensors, more effective to prevent external environmental factors on the touch screen, even if the screen stained with dirt, dust or grease, capacitive touch screen can still accurately calculate the touch position. As the capacitance varies with the contact area and dielectric of the dielectric, the stability is poor and the drift phenomenon is often generated. This kind of touch screen is suitable for the debugging stage of system development.