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Now most of us have touch screen smart phones in the days. They are an important part of our life. We do our various work on it. But have you ever wondered how the screen’s touch pads actually work.
How does touch screen display work?
Three technologies are used for touch screen displays. These techniques are all combined on top of each other. Technologies are actually different layers of touch pads.
- The first layer is a chemically hardened glass. This glass used for smartphones is about 5 times stronger than normal glass. And before the first i-phones were shown in 2007, standard cell-phone screens were made of plastic. And although the plastic does not shatter, it is very easily scratched. If plastic is used in place of glass in smartphone then it will not last even for a week. Because it can easily scratch when placed in pocket due to key or any other item. The glass of the smartphone is so strong because it is an aluminosilicate glass. Soaking it in a bath of molten potassium nitrate hardens it. This causes the sodium atoms in the glass to move outward, and too large potassium atoms to take their place. Since potassium ions are very large in size, they generate substantial compressive forces on the glass surface. Thus atoms are compressed so that it takes more force to break the glass.
- This is followed by another layer which is an approximate capacitive touch screen.. It is placed under chemically hardened glass. This layer senses the presence and location of conductive materials, such as at your fingertips. This touch grid is made up of two transparent patterns. These are diamond grid patterns printed on polyester. It is also an optionally clear insulator in the middle. The diamond grid pattern is printed with a transparent material called indium tin oxide (ITO), which acts as a conductor. This oxide layer consists of capacitors. Now when we move the tip of our finger close to this layer i.e. the capacitor it obstructs the electric field. This changes the number of positive charges on the capacitor. The change in positive charges caused by this disruption is measured and the processor registers it as a touch. The location of the touch is detected by scanning the charges or voltages. Charge or voltage is sent to each row of diamonds in quick succession. It happens that the processor can register multiple touch simultaneously.
- The third layer is one that uses LCD or OLED technology. It is embedded under the second layer. OLED stands for Organic Light Emitting Diode. The high-resolution OLED display produces the high-quality images we see every time we look at our smartphones. Much more complex square grids can be seen whenever we zoom into an image. These are known as pixels. Recent high-end phones can have 3.3 million pixels. This means that there are 10 million microscopes in individually controlled red, green, and blue light in the palm of your hand. OLED displays are made up of red, green, and blue subpixels. The light intensity of each subpixel is controlled by a small thin film transistor that acts as a dimer switch. Each sub-pixel has several layers of structures. Photons are produced by electrons in this subpixel that move from the negative to the positive terminal. When those emitters pass through the middle layer, photons are emitted through the release of energy. The compound used to make the emitting layer determines the color of the emitted light. The intensity of this light depends on how many electrons pass.