[Tutorial] Explaining the Differences Between Resistive Screens, Capacitive Screens, and Electromagnetic Screens in Different Touch Technologies

Nowadays, there are so many touchscreen phones, and for those who still don't understand, let's let you know the differences between resistive, capacitive, and electromagnetic touch technologies:

1. Resistive Screen
A resistive screen has a conductive film attached to the outside of the glass panel. By pressing, the conductivity of the film changes, allowing it to sense positional information. However, it cannot detect pen pressure, so it cannot form original pen strokes. You can write on a resistive screen with a cheap hard pen or a hard object (like a fingernail), which is convenient to use, and the precision can reach the display pixel accuracy. However, because the display effect is influenced by the transparency of the conductive film, during mobile phone use, the conductive film can get scratched from long-term stylus pressure, leading to progressively worse display quality, and even permanent damage. Because resistive screen technology has such obvious shortcomings, it is gradually being replaced by newer technologies.

2. Capacitive Screen
The surface of a capacitive screen is usually tempered glass, which has high wear resistance, does not easily scratch with frequent use, and does not suffer permanent damage, which is a significant improvement over resistive screens. A capacitive screen forms a capacitance layer on the inside of the glass panel using semiconductor or printing processes on the glass or film. When a finger touches the outside of the glass panel, it causes a change in capacitance, thereby sensing the position.

Capacitive screens are very sensitive to the pads of fingers, so both touch and handwriting can be done with a finger, without the need for additional writing tools. However, capacitive screens are not very responsive to fingernails, so people with long fingernails may find using a capacitive screen inconvenient. Later, specialized capacitive styluses were developed, making writing on a capacitive screen more convenient. But because they mostly simulate the finger pad touch, the tips of capacitive styluses are generally thicker. The so-called capacitive stylus is actually a conductive material with a certain volume and contact area. Interested readers can conduct an experiment: take a small stainless steel spoon, and with the bottom of the spoon touching the capacitive screen, it can trigger the screen, enabling unlocking and other operations. However, if only the tip of the spoon handle touches the screen vertically, it will not trigger. Gradually incline the spoon handle so that more area of the handle contacts the screen, and it will trigger again.This experiment explains why the tips of general capacitive styluses are quite thick. This is because a certain contact area is needed to trigger actions on a capacitive screen. Capacitive styluses on the market are made by wrapping a conductive material with a material that does not easily scratch the screen, shaped like a pen, which makes them very inexpensive.

The figure shows a schematic of capacitive screen touches with a spoon, including the bottom of the spoon, the top of the spoon, and the spoon handle touching horizontally and vertically. Green indicates a successful trigger on the capacitive screen, meaning it has been unlocked.

The theoretical precision of capacitive screens can reach 1–2mm, but since the fingertips or the tips of capacitive styluses are relatively thick, it is difficult to accurately locate within the 1–2mm range. The screen's perception accuracy for fingers and styluses is not high, so it is hard to write smaller fonts on a capacitive screen. Additionally, capacitive screens cannot sense the pressure of a finger, so they cannot replicate original pen strokes.

Increasing the touch sensitivity of capacitive screens and reducing the diameter of the stylus tip are among the future development directions for capacitive touch technology.

3. Electromagnetic Screens

The surface of an electromagnetic screen is the same as a capacitive screen, made of tempered glass. It relies on an electromagnetic induction board located beneath the display or inside the glass cover to detect the position of a specialized electromagnetic pen tip, while also detecting the pressure applied to the tip. The size of the pen tip and the pen can be made similar to a real pen, and using it is not much different from using a real pen.

Electromagnetic screens have high sensitivity and can precisely locate the pen tip. They allow writing characters similar in size to regular handwriting and can sense pen pressure greater than 256 levels. The pressure value is transmitted to the application processor, which synchronously draws strokes and tip effects with varying widths according to the pressure on the display, making the writing effect almost equivalent to writing on paper with a real pen.