Touch Panel

    A touchscreen is an input device normally layered on the top of an electronic visual display of an information processing system. When touching the image button on the screen, the touch feedback system of the screen will drive a variety of connecting devices based on pre-coding program to replace the mechanical pointing panel, and finally reveal lively video and audio effect via liquid crystal display panel.
    Types
Resistive Touch Screen
    Commonly known as "Soft screen". In electrical engineering, resistive touchscreens are touch-sensitive mobile phone displays composed of two flexible sheets coated with a resistive material and separated by an air gap or microdots. There are two different types of metallic layers. The first type is called Matrix, in which striped electrodes on substrates such as glass or plastic face each other. The second type is called Analogue which consists of transparent electrodes without any patterning facing each other. And Analogue touch screen includes five kinds:
  • Four-Wire Resistive;
  • Five-Wire Resistive
  • Six- Wire Variation
  • Seven-Wire Variation
  • Eight-Wire Variation
Capacitive Touch Screen – Most used
    Commonly known as "Hard screen". As opposed to the resistive touchscreen, the capacitive touchscreen makes use of the electrical properties of the human body. A capacitive screen is usually made of one insulating layer, such as glass, which is coated by a transparent conductive material on the inside. Since the human body is conductive, which means electricity can pass through it, the capacitive screen can use this conductivity as input. When you touch a capacitive touchscreen with your finger, you cause a change in the screen's electrical field. Capacitive touchscreen contains two main categories: Finger touch and Multi-touch.
SAW (Surface Acoustic Wave) Touch Screen
SAW touch screen technology is based upon two transducers and a reflector placed on the glass surface. The waves are dispersed across the screen by bouncing off the reflector arrangement and received by the transducers. The touch is detected when the waves are absorbed. In comparison with the other touch screens; SAW provides superior clarity, resolution and durability, with the ability to interact with a stylus or gloves.
Infrared Touch Screen
Unlike the other types, infrared touch screen technology does not incorporate an overlay. Instead, a frame surrounding the display consists of LEDs on one side and phototransistor detectors on the other. The phototransistors detect an absence of light and relay a signal that determines the coordinates. The touch is identified and located at the point of interruption of the LED beams. Commonly used in outdoor locations, infra red touch screens are durable and can detect any input.
Optical Imaging Touch Screen
Using optical sensors to recognise the touch, this touch screen technology is popular for its versatility and scalability. Optical imaging relies on infrared lights. Two infrared imaging sensors are positioned at the top, which double up as emitters and retro reflective tapes at the three sides. The emitted lights are reflected back to the imaging sensors, which become blocked at the point of touch and create a shadow to locate the touch.
Acoustic Pulse Recognition Touch Screen
An APR touch screen is made up a glass overlay and four transducers attached to the back exterior. When the screen is touched, the friction creates acoustic waves. The transducers detect the acoustic wave, which is then converted into a signal. APR touch screens are water resistant, durable and scalable.
    Materials
For now, the most commonly used material for touch screen is indium tin oxide (ITO), which comes in two forms, film and glass.
  • ITO Film: it includes bright and dull materials, which have many characters: anti-scratch, anti-newton, anti-reflection;
  • ITO Glass: it contains common and reinforced (physical reinforce and chemical reinforce) glass.
    Finger touch/ Multi-touch
  • Finger touch: A type of touch screen ( or other fixed surface ) that is optimized for operation by human finger, as opposed to a stylus. 
  • Multi-touch: The ability for a touch surface to respond to multiple finger touches at the same time, includes: two-touch, five-touch and ten-touch.
Two-Touch
Five-Touch
Ten-Touch
    TOUCH PANEL STRUCTURE
    As the development of touch panel technology, the innovations of mobile phone screen never stop. The technology evolution goes through from common Glass+Glass (G+G) and Glass+Film (G+F), to OGS, On-cell and In-cell, which are the three most advanced mobile phone screens technologies till now. However, the development of touch panel would be toward diversification in the future.
The most common touch panel structures include:
  • G + G: Tempered Glass + Glass
  • G + P: Tempered Glass + PET (plastic cover structure)
  • G + F/G + F+ F: Tempered Glass + Film / Tempered Glass + Film + Film

  • OGS: OGS touch screen is a kind of electronic products protecting screen that made by depositing an Indium tin oxide(ITO, used as electrodes to sense touch) layer on the back of the cover glass and pattern it to create the electrodes. One glass works as protector glass and touch sensor at the same time. OGS screen integrates protector glass with touch panel layer.

  • On-cell/In-cell: On-cell/In-cell technology refers to integrate touch panel and Liquid Crystal Display into a single-layer display. On-cell is to put the Indium tin oxide (ITO) touch panel on the glass layer of display panel; In-cell is to put the ITO touch panel under the glass layer of display panel and integrate with Liquid Crystal Display (LCD).
    The comparison of G+G, G+P, G+F/G+F+F, OGS, On-cell and In-cell
For Short Specification Advantage Shortage
G+G Tempered Glass+Sesor Glass Hard wear-resisting;
Corrosion resistance;
High light transmittance;
Smooth manipulation;
High reliability.
Hard technology;
High cost;
Thick;
Heavy.
G+P Tempered Glass+ PET Low cost;
Simple operation
Poor reliability
Manipulation of the handle viscous
Light transmittance is poor
Resisting abrasion
Not resistant to corrosion
G+F/G+F+F Tempered Glass+Sesor Film
Tempered Glass+2sesor Film
Low cost;
Small quantity production;
Light structure
Low touch sensitivity;
Bad transmittance
OGS One Glass Solution Structure more simple;
Light;
Thin;
Good Transmittance
Need to change tempered glass and touch panel at the same time if broken
On-cell On the LCD panel with touch
sensors
Thin;
Good transmittance
The uneven colors when touch
In-cell Embed the touch panel
function into LCD pixels
Ultra-thin;
High clearly;
Super light
Difficult to ensure that yield and
display performance