Anti-reflective conductive film (AR conductive film)

"AR conductive film" can achieve the functions of defogging and defrosting by applying external voltage to the film stack, and through the design of the film stack, it has an anti-reflection effect, which can be applied to high-end optical products such as automotive lenses.

Spectrum of anti-reflective conductive film (AR conductive film)

Film specifications of anti-reflective conductive film (AR conductive film)

Principle of anti-reflective conductive film (AR conductive film)

For the optical function of the film, when light enters the uncoated glass substrate from the air, each interface will reflect about 4% of the light, which results in only 92% of the light passing through. The anti-reflection coating is coated to make the phase of the light at the upper and lower boundaries of the film. The phase difference is 180°, that is, the reflected light beam destructively interferes, and then achieves the anti-reflection effect (as shown in Figure 1), and at the same time has a good light transmittance [1].

Figure 1. Schematic diagram of anti-reflective film [1]

The conductive function of the film has a wide range of applications. In addition to general conductive effects, it can be used as heating film, antistatic film and even electromagnetic shielding film. However, in optical applications such as displays, smart glass or lenses, the use of metal conductive films will affect optical specifications. Considering price and effect, transparent conductive oxide (TCO) is a better choice over metal conductive films for the optimum optical/conductive coating applications. Metals conduct electricity because the conduction band in the energy band overlaps the valence band [2], so electrons can move freely (as shown in Figure 2), which means that there is no energy gap, that is, no light can be transmitted; TCO has an energy gap of about 2~4.5eV. When energy is applied externally to the transparent conductive film, electrons are easily excited from the valence band to the conduction band. The existence of the energy gap means that the material is likely to transmit light. Therefore, the transparent conductive film is in visible light spectrum range. (VIS) and near-infrared (NIR) bands, so it can transmit light and have a certain degree of conductivity [3].

Figure 2. Energy band structure diagram [2]

TCO is defined as being in the visible light wavelength range (400~700nm), with the light transmittance is above 80%, and the resistivity lower than 1×10-3Ω-cm [3]. The transmittance of TCO is slightly inversely proportional to the conductivity, which means that the higher the transmittance of the film, the worse the conductivity (as shown in Figure 3) [4,5], and TCO is usually a high refractive index material. When TCO is plated on glass, a single interface will reflect about 9.6%. Therefore, it is a big challenge for TCO to be applied to high-end optical products.

Figure 3. Different thickness of the conductive film spectrum and conductivity characteristics (a) 80nm, (b) 150nm, (c) 270nm, (d) 350nm. [5]

Through the simulation and design of optical multilayer film, and the use of different materials for stacking, the reflected light produces destructive interference, so it has anti-reflection effects, but also has the performance of conductive film. The AR conductive film developed by Dah Young has permeability that can reach more than 98%, and with an external voltage of 10 volts can defog within 30 seconds, and the effect of removing 1mm thick frost within 90 seconds.

Figure 4. The heating effect of the AR conductive film coated on different substrates by Dah Young.

Product application of anti-reflective conductive film (AR conductive film)

AR conductive film has excellent optical properties and electrical conductivity. It can be used as a transparent heater to quickly and effectively heat glass and plastic parts (windshields or lampshades) in outdoor surveillance lenses, automobiles, or vehicles. It provides defogging and/or deicing functions in harsh environments, thereby maintaining component performance.

Figure 5. AR conductive film application (A) outdoor surveillance lens [6],

(B) Glasses [7], (C) Car lights [8], (D) Vehicle windshield [9], (E) Cockpit windshield [10].

Reference：

[1]     李正中。薄膜光學與鍍膜技術(第九版)。(2019)。藝軒出版社。

[2]     維基百科。價帶。檢自https://zh.wikipedia.org/wiki/%E5%83%B9%E5%B8%B6。

[3]     大永真空設備股份有限公司。(2013)。透明導電薄膜特性及光電元件應用。檢自https://zh-tw.dahyoung.com/show/show-573518.htm。

[4]     MATERION。Transparent Conductive Oxide Thin Films。檢自https://materion.com/resource-center/technical-papers/thin-films。

[5]     E.M. Mohammed et. al., Brazilian Journal of Physics, vol. 39, no. 4(2009)。檢自https://www.scielo.br/j/bjp/a/n55Q95TBbVhxtRZhYfg6MXm/?lang=en#。

[6]     https://www.grupports.it/costo-installazione-sistemi-videosorveglianza-wireless-bologna-sassuolo/。

[7]     https://spy.com/articles/hacks/cleaning-hacks/best-anti-fog-spray-glasses-1202784370/。

[8]     https://www.dpreview.com/forums/thread/4013959。

[9]     https://www.misterspex.de/brillen-ratgeber/brille-beim-autofahren。

[10]   https://medium.com/faa/crowdsourcing-weather-conditions-129d7231d54。