Introduction and application of Low-E filter
Function and spectrum of Low-E filter
Low-E filter manufacturing process does not require heating to prepare a transparent conductive film function (for example, electromagnetic wave shielding, heating defogging, touch control, transparent antenna, etc.), and can produce a film with high transmittance in the visible light band.
Specification of Low-E filter
※Prepared on PET flexible substrate
Target penetration
Target sheet resistance value
Principle of Low-E filter
Generally speaking, it has acceptable transmittance in the visible light range, and its resistance value is lower than 10-3Ω. cm, with both transparent and conductive properties, it can be called a transparent conductive film (TCF). With the development of science and technology, and the introduction of new electronic products, and many semiconductor materials are constantly being developed and applied in response to the needs of the manufacturing process, especially in the optoelectronic industry. In recent years, the application field and demand continue to expand [1].
TCF can be divided into two categories: thin metal materials and metal transparent conductive oxides:
(1)Thin metal materials such as gold (Au), silver (Ag), aluminum (Al), platinum (Pt) and copper (Cu)... etc. The metal material itself can conduct electricity, and as long as it is thin enough (10nm or less) will also have light transmittance. Because the film layer is thin, the metal film is not continuous, forming island-shaped discontinuous growth on the substrate, which increases the resistance value of the film. In atmosphere oxidation occurs, resulting in drastic changes in resistance and poor stability of the film. To overcome this, the film thickness needs to be increased to obtain sufficient conductivity, which will cause light absorption. Therefore, thin metal transparent conductive films are gradually being replaced with TCF.
(2)Metal transparent conducting oxide (TCO), in order to obtain transparency in the visible light region, the energy gap width of the selected material must be greater than the energy of visible light (about 3.0eV or more). This kind of pure material is insulated at room temperature. In order to increase its conductivity, some impurities are often added to improve its electrical properties. To obtain a good transparent conductive film, it is necessary to control the oxidation state of the film and the quality and amount of impurity ion doping. Among them, indium tin oxide (ITO), which has excellent electrical properties (2~4*10-4Ω-cm) and visible light transmittance (>85%) and other film properties, is the most widely used.
Since ITO contains the expensive and rare element indium, the conductivity and visible light transparency of other TCO films still need to be improved, and due to the inherent brittleness of oxide materials, the flexibility of the film is usually poor, which can no longer meet the current booming development of flexible electronic devices. Therefore, the research on indium-free and flexible TCF with excellent performance has received extensive attention from researchers in recent years [2].
Multilayer film based on TCO/metal/TCO structure is another new type of TCF, which mainly uses a thin intermediate metal layer to obtain good conductivity. The high conductivity of the metal layer allows the metal layer to be thin enough, so it can having good conductivity while also having good light transmittance, and the dielectric layers on both sides can suppress the reflection from the metal layer in the visible light band, thereby providing higher selective transparency. Moreover, the metal layer material has good conductivity and ductility, so that it can still have good conductivity even when the dielectric film is bent and broken. Therefore, compared with the single-layer TCO film, it has better mechanical properties. In addition, this structure does not require heating during the preparation process, and a film with good photoelectric properties can be prepared at room temperature, making it very suitable for continuous deposition using roll-to-roll technology on plastic substrates that are not resistant to high temperatures. , In terms of processing cost, processing speed and thermal budget are unmatched by traditional TCO production.
Product application of Low-E filter
Any transparent conductive film related applications, can also be implemented on flexible plastic substrates.
Transparent heating film: The direct current power source generates heat energy through the impedance circuit, so that the mist will not adhere to the surface. For example, windows, monitors, windshields, mirrors, helmets, goggles, ski goggles, etc.
Transparent LED advertising signs: usually transparent display windows can also be used as LED advertising boards, full color and no film size restrictions.
Touch screen panel: Detect touch action by sensing resistance change. For example, smart phones, tablets, laptops, electronic bulletin boards, etc.
Transparent EMI shielding film: When electronic devices are in operation, they may interfere with each other's systems under the interaction of electromagnetic waves. EMI shielding film can effectively reduce the probability of occurrence. For example, smart phones, tablets, laptops, home appliances, etc.
Reference
[1] National Changhua University of Education. Transparent conductive film materials and manufacturing process. Online date: February 1, 2021, checked from http://blog.ncue.edu.tw/sys/lib/read_attach.php?id=17807.
[2] tradeKorea. (2020). Transparent conductive film. Retrieved December 20, 2020, from https://www.tradekorea.com/product/detail/P772432/Transparent-conductive-film.html