Capacitive Touch Panel

 

Touch Panel

Characteristics

Infrared:

  1. Very resistant
  2. Used for bigger displays in the outskirt area (e.g. cash machine)
  3. No abrasion due to use
  4. Can be operated with finger (gloved), as well as with stylus

Resistive:

  1. Very precise
  2. Used for smaller displays
  3. Flat construction (few millimeters)
  4. Cheap production
  5. Can be operated with finger (gloved), stylus etc.

Capacitive:

  1. Less abrasion than resistive touch panels have
  2. Very percise
  3. Flat construction (few millimeters)
  4. Can be operated with bare finger or conductive stylus

Working principle of the different technologies

Infrared:

A frame around the glass sends out infrared rays, which form a grid over the glass surface. When using the panel, the grid is being interrupted and the touch points coordinates are calculated from this interruption. Based on the robust construction, this sort of touch panels are usually used for systems in public places (ticket- or cash machines).

Resistive:

Analog Resistive Touch Panels consist of two transparent layers, the bottom layer is made of glass and the top layer is a flexible synthetic film. When touched, the two layers get in electric contact. The controller calculates the coordinates of the touch point based on voltage change. As resistive touch panels are very precise and can be operated with gloved finger, they are suitable for various devices, such as PDAs, route guidance systems and medical equipment.

Capacitive:

A transparent, conductive coating is added to the glass surface. Voltage is added to the corners, which builds an electric field. When the finger touches the glass, it absorbs some of the voltage. The controller uses the voltage change to calculate the coordinates. This working principle allows operating with bare finger or conductive stylus only. The advantage of capacitive touch panel is that they are more resistant against rough handling than resistive panels are. At the moment they are mainly used for recent mobile phones.

 

Touch Panel
Principle
The principle of a capacitive touch panel is based on sensing the capacitance variation between two conductive layers. That these two conductive layers are arranged parallel and spaced by an isolator layer, so that when electric current is applied, a field of stored electrons, also known as capacitance, is achieved between them. Meanwhile, the human body also has stored electrons and therefore exhibits capacitance. When fingers touch or they are just close in proximity to the panel, the value of capacitance between two conductive layers will be affected and varied. Therefore by sensing this variable, the location of touch can be indicated by the linked controller customized algorithm.

Touch Panel Structure :
1. The driving channels and sensing channels are separated by insulating materials.
2. ITO or Metal material is commonly to be applied in the structure to be bridge, linking two separated TCO electrode. ITO is one of the familiar materials in TCO.

Touch Panel Process :
Mostly the touch panel process is completed by 4-PEP. However, the process for the products with ITO bridge will be 5-PEP.

One Glass Solution(OGS):Cover Lens + Touch Sensor =1 Glass
1. To integrate the touch function and cover lens and keep the characters of the above, the touch sensor and cover lens are simplified to become one glass.
2. The final one glass solution product can be completed by one time sensor process.
3. After the sensor front end process, the mother sheet will be passed to cutting, grinding station, etc.

The advantage of OGS is as listed below:
1. It can provide various colorful solutions and meet customized looks, not only usual black decoration.
2. It is the thinnest and lightest touch sensor solution so far and may in the future.
3. Below figures are sketched for the comparison of touch module structure difference between OGS and other solutions.
*GG2 : The first G is for Cover Glass, G2 means one glass with two-side process and so on.