R&D and TECHNICAL SUPPORT SUPERVISOR
In our previous issue, we talked about TFT display technology. In this issue, we will talk about touch panels, which are the most important components of TFT displays. Touch panels have become an indispensable part of our daily life. With the rise of technologies used in the industrial field, the need for TFT and touch panels is also increasing. There are different touch panel technologies available, including resistive, capacitive, INFRARED and SAW. Resistive touch panels are the first type of touch panels used and are still being used. INFRARED and SAW are usually preferred in large-scale TFTs. Capacitive touch panels are the most widely used technology in small and medium-sized TFTs. In order for the resistive touch panels to be able to detect, pressure must be applied with a finger or other object. That’s why protective glass cannot be applied to it, while there is no such restriction in other technologies. Capacitive touch panels may malfunction in environments where magnetic noise is high, but resistive touch panels are not affected by these noises so much. In addition to not being affected by noise, the resistive touch panels are still being used due to their low costs as well. Standard models of capacitive touch panels cannot detect with gloves, but with the development of capacitive touch technology there are now models that can be used with gloves or even work underwater.
The touch panels are produced separately from the TFT screens, and glued to the TFT screen afterwards. There are two different bonding methods available: tape bonding (also called air bonding) and optical bonding. Tape bonding is a low-cost application method where the touch panel is glued onto the TFT panel only from the edges with a double-sided tape. In the optical bonding method, on the other hand, the touch and TFT panel are glued to cover the entire surface with a transparent adhesive with high light transmittance. The most important difference between these two methods is the transmission of light. In the Tape Bonding method, there is a decrease in the brightness of the screen since there is an air gap in between. Tape bonding is preferred for devices used indoors, while optical bonding is preferred for devices used outdoors. In some applications, the touch panel can also be used without being glued to the TFT screen.
“With the rise of technologies used in the industrial field, the need for TFT and touch panels is also increasing.”
Various filters can be added to the touch panels to increase visibility under the sun. One of the most commonly used methods is AR (Anti Reflective) filter. In this method, the touch panel surface is dulled and the reflections on the screen are eliminated. Capacitive touch panels are divided into two as “surface capacitive touch” and “projected capacitive touch” (PCAP) according to their detection methods. Today, PCAP is used more commonly. The working principle of PCAP touch panels is based on the measurement of capacitance between two conductors. The device detects that this point is “touched”, as the capacitance changes when another conductor, such as a finger, approaches between the two conductors being measured. PCAP touch is available in many different structures, and we will talk about the most commonly used G+G (Glass+Glass) and G+P (Glass+PET) structures. Parallel paths are drawn on the X-axis on one surface of the glass and on the Y-axis on the other surface using ITO material, and this glass is referred to as “ITO glass” (sensor glass). The controller measures the capacitance between these paths, using the scanning method. When the finger gets close to the ITO glass, it detects the “touching” since the capacity here would change. The number of parallel paths on the X and Y axes indicates the resolution of capacitive touch, and the number of sensors must be high to achieve a high-accuracy detection.
“Touch panel prices may vary depending on the technology used.
The choice of tempered glass or PET, the integration of the controller used, and whether the product has a standard or custom design, affects the price.”
The brand and model of the controller integration used also affects the accuracy of the product and therefore its price. A protective layer is added to ITO glass to protect it against external effects. This layer can be a tempered glass or PET. In case of tempered glass, the structure of this layer is expressed as “G+G”, and case of PET it is “G+P”. The structure of G+G is durable and the light transfer is higher, so the price is even higher. Tempered glass (or cover lens) can be in the sizes desired by the user, and the user’s logo can be added to it. The structure of G+P is less durable than the other, and the light transfer is slightly lower. The customer can add his own glass on the product as they desire. A transparent adhesive called “OCA” is used to glue ITO glass to tempered glass or PET. The sensor paths on the ITO glass are taken outside by bonding with an FPC cable. The controller integration is usually on the FPC cable.
“Ozdisan Elektronik has signed a distributorship agreement with Chinese capacitive touch manufacturer FANNAL,
to meet the capacitive touch panel demands from its customers. “
Touch panel prices may vary depending on the technology used. The choice of tempered glass or PET, the integration of the controller used, and whether the product has a standard or custom design, affects the price. The correct product selection should be made according to the specific requirements of the design in hand. Ozdisan Elektronik has signed a distributorship agreement with Chinese capacitive touch manufacturer FANNAL, to meet the capacitive touch panel demands from its customers. FANNAL is one of the top quality manufacturers in China, which produces only capacitive touch panels, specialized in this field, and able to offer solutions for all kinds of needs. The company is able to produce solutions for low-cost projects, as well as address to high-tech applications. They can also produce capacitive touch applications with prices close to resistive touch equivalents. Ozdisan will offer cost-effective and high-quality solutions to its customers by combining its own SATOZ branded TFTs with FANNAL brand capacitive touch panels.
Basic Terms Related to Capacitive Touch Panels;
OCA (Optically Clear Adhesive): A strong adhesive with high light permeability, used to glue the touch layers together.
ITO (Indium Tin Oxide): A transparent material with electrical conductivity. It is commonly used in TFT, LCD and touch panels. Just as copper is used to provide electrical connections on PCBs, ITO chemical is preferred to provide electrical connection on the glasses in these products.
ITO Glass: The glass, drawn on both surfaces of the capacitive touch sensors with ITO material. It can also be referred to as “sensor glass”.
Tempered glass: This can also be referred to as impact-resistant reinforced protective glass, a cover glass or a cover lens.
PET (polyester film): It is a petrochemical material that has a thinner structure than tempered glass.
