Studies Of AZO/Ag/AZO Transparent Heater On PMMA Substrate

Transparent conductive films(TCF)are provided with good transmittance and high electrical conductivity.Thus they are widely used in electric heating windows as transparent heaters for deicing and defrosting.PMMA has partially replaced inorganic tempered glass with its excellent impact strength and low density,widely used in aviation windows at present.However,limited by the low T_g(105°C)of PMMA,most transparent heater materials like ITO cannot obtain excellent optical and electrical properties without annealing.In order to explore more suitable films for PMMA substrate,this paper prepared AZO/Ag/AZO films on the surface of PMMA with magnetron sputtering at low temperature.The optical,electrical,humidity resistance and thermal properties of AZO/Ag/AZO films were studied.(1)The impacts of Ag layer thicknesses and sputtering powers on morphology,interface structure,optical and electrical properties of the AZO/Ag/AZO thin films were studied.The Ag layer grows in discrete circular islands with a thickness below 10 nm.Plasmon resonance absorption leads to low transmittance and grain boundary scattering cause high resistance.A continuous Ag layer is formed above 10 nm which causes transmittance and conductivity properties improved.AZO/Ag/AZO film obtain the best properties with 84.4%transmittance of and 3.4Ω/□sheet resistance at 13 nm Ag layer thickness.The Ag layer has good wettability with 100 W sputtering power both of AZO and Ag,which causes good crystallization.(2)The failure mechanism of the AZO/Ag/AZO film under humid was discussed by characterizing the changes of structure and properties under damp heat test.An encapsulation method was proposed to effectively improve the moisture and heat resistance of the AZO/Ag/AZO film.The results show that a thicker AZO layer leadto better moisture and heat resistance of AZO/Ag/AZO films.The water vapor induced Ag layer agglomeration and lead to film cracks formation which cause the degradation of optical and electrical properties.The laminated AZO/Ag/AZO film effectively prevented the penetration of water vapor with transmittance and haze remained stable in the 30 d damp heat test.(3)The thermal properties of AZO/Ag/AZO transparent heaters on PMMA surface under low voltage was studied.The saturation temperature of AZO/Ag/AZO transparent heaters increases with higher voltage and better conductivity.The surface temperature of PMMA substract can reach up to 99.2°C with 16 nm Ag layer thickness at 5 V voltage.The AZO/Ag/AZO transparent heaters maintained good temperature repeatability during the heating cycle in high-altitude and low-temperature environments.The laminated AZO/Ag/AZO transparent heater has good heating stability at low temperature which are expected to be used in aerospace electrical heating window.(4)The failure model of AZO/Ag/AZO transparent heaters at high temperature were proposed.The failure process is caused by the large current density in the micro-domain.The current gathers at the defect and creates a hot spot which tears the AZO/Ag/AZO film because of the mismatch of the expansion coefficient between the PMMA and the AZO/Ag/AZO.The alternate occurrence of hot spot and crack during heating process leads to the failure of the electrical properties of the AZO/Ag/AZO transparent heaters.