The structural composition of the capacitive touch screen

fundamental structure

The basic structure of the capacitive touch screen is that the substrate is a single-layer plexiglass, a layer of transparent conductive film is evenly forged on the inner and outer surfaces of the plexiglass, and a narrow electrode is placed on the four corner cones of the transparent conductive film on the outer surface. Its working principle is: when the finger touches the capacitive touch screen in the working face on a high frequency signal, fingers and touch screen face form a coupling capacitor, which is equivalent to the conductor. Because the working surface has a high frequency signal, finger touch in the touch point away a small current, and the small current respectively from the four corners of the touch screen electrode flows through the four electrodes. The current is proportional to the straight-line distance between the finger and the four corners. The controller can obtain the coordinate value of the contact point by calculating the proportion of the four currents.
The capacitive touch screen can be simply seen as a screen body composed of four composite screens: the outer layer is a glass protective layer, followed by a conductive layer; the third layer is a nonconductive glass screen; and the fourth layer is also a conductive layer. The innermost conductive layer is the shielding layer, which plays the role of shielding the internal electrical signals. The conductive layer in the middle is the key part of the whole touch screen. There are direct leads on the four corners or four edges, responsible for the detection of the contact position.
The top cover layer is toughened. Glass or polyethylene glycol terephthalate (PET). The advantage of PET is that the touch screen can be thinner, and it is also cheaper than existing plastic and glass materials. The insulation layers are glass (0.4–1 mm), organic film (10–100 mm), adhesive, and an air layer. One of the most important layers is the indium tin oxide (ITO) layer, with a typical thickness of 50 to 100 nm and a block resistance in the range of 100 to 300 ohms. The three-dimensional structure of ITO has a great influence on the capacitive touch screen, which is directly related to the two important aspects of the touch screen capacitance parameters: induction capacitance (finger and upper ITO) and parasitic capacitor (between upper and lower ITO, between lower ITO and display screen).
The structure of the capacitive touch screen is mainly to coat a transparent film layer on the glass screen and then add a piece of protective glass outside the conductor layer. The double glass design can completely protect the conductor layer and the sensor, and at the same time, it has a higher light transmittance and can better support multi-touch.
The capacitive touch screen is plated with long and narrow electrodes on the four sides of the touch screen, forming a low-voltage AC electric field in the conductive body. When touching the screen, the finger and the conductor layer will interact due to the human electric field. A coupled capacitor is formed, and the current generated by the four side electrodes flows to the contact, and the strength of the current is inversely proportional to the distance between the finger and the electrode. The controller behind the touch screen calculates the proportion and strength of the current and accurately calculates the position of the touch point. The double glass of the capacitive touch screen can not only protect the conductor and sensor but also effectively prevent external environmental factors from affecting the touch screen. Even if the screen is stained with dirt, dust, or oil stains, the capacitive touch screen can still accurately calculate the touch location.
Because the capacitance varies with the contact area and the dielectric difference of the medium, its stability is poor and often produces drift phenomena. The touch screen fits for the commissioning stage of system development.