The touch display, as an information input-output device, appeared relatively long ago. Back in the 90s of the last century, it was possible to find PDAs and other portable devices equipped with a touchscreen on sale. As technology advances, touchscreen smartphones have improved and new requirements have been put forward for them, so touchscreens have changed dramatically over the past decade.
The simplest and most affordable sensors for smartphones. They consist of two layers, on which a mesh of transparent conductive material is applied. The lower one is made of glass (mineral or organic), and the upper one is plastic. There is a thin air gap between them. At the moment of touching, the circuit closes between the grids of different layers, and the controller determines the coordinates of the point of pressing.
The advantages of resistive screens are sensitivity to pressure with any object, low cost, simple design and accuracy. The main disadvantage is fragility: the plastic top layer is easy to cut or puncture, after which the contact will be broken and the sensor will not work.
Resistive sensors also have a relatively low transparency (up to 80%), therefore, starting from 2010, they are no longer used on smartphones. Today, such a touchscreen can only be found in cheap Chinese-made phones.
Capacitive smartphone sensors consist of a glass panel covered with a transparent conductive layer and four corner sensors. A weak alternating current is supplied to it, the leakage of which when touched is registered by the sensors, calculating the coordinates of pressing. In addition to the fact that such touchscreens react only to the touch of an object with electrical conduction, they have low accuracy and are not able to simultaneously perceive several clicks.
Capacitive Projection Sensors
The most common type of sensors on modern smartphones. They represent the development of the previous type. Instead of a conductive layer, a grid of electrodes is applied to the panel, which are also energized. At the moment of touching the finger, acting as a capacitor, a leakage current occurs, the location of which is calculated by the controller. This design makes it possible to track several touches (at the moment up to 10, more - it makes no sense) at the same time.
The basic design of such touchscreens is being modified by the manufacturers of mobile devices. On modern OGS displays of smartphones, sensitive electrodes can be mounted directly between crystals (or diodes) of the matrix, and for resistance to damage, the screen is covered with tempered glass.
Previously, it was also practiced to separate the protective glass and the sensor layer: the electrodes were applied to a transparent film, which was covered with glass on top. This approach allowed the sensor to remain operational even in the presence of serious damage (cracks, chips).