In the capacitive touch screen, the development of projection-type products is in full swing. As described in Chapter 2, it is different from resistive touch screens. When transparent conductive glass is not used, it is made by bonding multiple transparent conductive films. Therefore, there is no air layer between the capacitive touch screen, which can greatly reduce the reflection of the interface, thereby avoiding the problem of interference fringes and glare, so it has superior optical performance. At this stage, although it is not suitable for text input, it can realize multi-point input operations.
It realizes the touch by detecting the change of the electric quantity of the transparent electrode. The transparent electrode is made by bonding multiple transparent conductive films together through an adhesive layer, which is completed by laminating technology. Therefore, it is particularly important to eliminate the different readability of the ITO film and the part without ITO film through design. Generally speaking, after forming a pattern pattern, it is also important to suppress the reflectance of the ITO film and the part without the ITO film, and the difference in color between transmission and reflection. Achromatization should also be considered for the touch screen. In order to get closer to the color of the glass, the haze needs to be reduced. In addition, since the adhesive layer lamination process is used, it is also important to maintain the consistency of the transparent conductivity and the adhesive layer.
Analog resistive touch screen, can realize text input. The uniformity of the in-plane resistance of the transparent conductive film greatly affects the ability to input characters correctly. The surface resistance used to simulate a resistive touch screen is generally 200~10001V□. Considering the detection accuracy and power consumption of the touch screen, a resistance value of about 500(1/□ is the most ideal.
The production of ITO film is mainly done through the sputtering process in physical vapor deposition. Sputtering film formation is a method in which inert gas is ionized by vacuum discharge in a vacuum device, and ions are accelerated under the action of an electric field to bombard the target, and the target particles that strike out fly to the substrate to form a thin film. The sputtering film has good uniformity and long-term stable quality, which is suitable for long-term mass production. The uniformity of resistance value is particularly important for analog resistive touch screens, so sputtering film formation is most suitable for making this type of transparent conductive film.
The resistance of the ITO line on the thin film substrate is generally 3 x 1CT4? 1 x 10_311 • cm. The advantages of thin film substrates are good flexibility, thinness, resistance to breakage, and low cost. The disadvantage is that the allowable temperature range is small, which limits the ITO film forming process. The allowable temperature of the PET film is more than 100 degrees Celsius. The crystallinity of the deposited ITO film at this temperature is not good, which directly affects the performance of the ITO film. In order to overcome the above-mentioned shortcomings, a low-temperature amorphous ITO film process was developed, and then an annealing process was used to recrystallize to complete the production of high-performance ITO films.
