Investigation Of PI-Based Low-E Film Prepared By Pulse Cathode Arc Discharge

As an effective product of energy conservation, Low-E films can prevent thermal radiation because they have high visible transmittance and high infrared reflectivity. Usually, Low-E films are used at building glasses, car windows, solar collectors and medical devices and so on. At present, the substrate of Low-E films is glass which limits the use of Low-E films. So the research of Low-E films will be transferred to soft substrate-base Low-E films.The system of Low-E films we study in this paper is designed according to Dielectric/Metal/Dielectric structure. Generally, Au/Ag/Cu/Al is often selected as metal layer material. But Au is not usually used because it is too expensive. In contrast, Ag has the properties of high infrared reflection coefficient and low absorption of visible light, which make it to be the most suitable metal material. Dielectric layer of D/M/D structure plays an important part in protecting and connecting, and also can increase the transmittance of visible light. The transmittance is proportional to the difference of refractive index, which means the higher refractive index of dielectric layer, the higher transmittance of Low-E film. TiO2 has the highest refractive index which is between 2.4-2.5, and it almost never absorb visible light. So we select it as dielectric layer material. All Low-E films are deposited by pulsed cathode arc discharge, which has performance of low-substrate temperature. We can change the pulse width and pulse number to control the thickness of films. The anticathode of the device is improved by us to make the distance between substrate and target change easily. The substrate can be fixed by fixer of anticathode. Meantime, we add coil to let the arc reach the substrate straightly because of the magnetic field. This change can improve the efficiency of deposition. The volt-ampere character curves of pulse cathode arc are collected and analyzed and the results satisfy the model of pulsed cathode arc discharge.By controlling the parameters through preparation process, we observe how parameters affect films'preparation. We find that with the raising of discharge voltage, the diameter of sputtering particle increase and the quality of films are improved. But the particle will drop and films become non-uniform if the discharge voltage is too high; meantime, the pressure and distance between PI and target can also affect the films'characters. If the pressure is too low, sputtering rate and the number of particles will decrease. And then film thickness decreases else. With the increase of distance between PI and target, the collision times between particles increase and the particles'energy is lost. So the particle attached to substrate will drop easily and the film thickness decrease.The transmittance of PI, PI/Ag, PI/TiO2 films are analyzed in this paper. The results demonstrate that PI substrate has no effect on transmittance, which can be ignored; single Ag films do not reflect the low transmittance characteristic in infrared region because of oxidation; single TiO2 has high transmittance and can improve the character of PI substrate. Adding a Ti barrier layer can protect Ag film from oxidation when prepare Low-E films. The transmittance of Ag decrease in visible and infrared region with the increase of Ti layer thickness. The experiment tests show that the Ti layer of 1 nm thickness can play an important part in protection. The transmittance of Low-E film can reach to 70%.The wrinkles and cracks are found on surface of films, which are caused by film stress through analysis. The connection between film stress and film defects is introduced in detail. There is shear force between film and PI substrate. PI substrate will deform when metal film deform because of film stress release. By calculation the critical stress is 5.8GPa, and the wavelength of wrinkles is 1.3μm which has a good consistency with experiment result. Film stress is inherent defect of film materials and can lead to distortion, so the analysis of film stress has significance on control of film quality.