Microstructures And Ignition Characteristics Of Aluminum-Based Multilayer Energetic Thin Films

Metal film bridge initiating explosive devices have many advagtages such as small ignition power, high reliability, large area integration comparing to traditional metal wire bridges. However, in practical applications, the output energy of metal film bridges is still low, small gap between the bridge and powder may lead to unsuccessful ignition. To further improve the ignition reliability of the metal film bridges, different modulation period of Al/NiO multilayer energetic thin films were prepared by DC magnetron sputtering. We studied the preparation and properties of the multilayer thin films. Through a mask process, the Al/NiO multilayer thin films were integrated on the Cr bridge to make（Al/NiO）_n/Cr composite igniters, the ignition performances were studied. Details are as follows:Monolayers of Al films and NiO films with different thickness were prepared on Al₂O₃ ceramic substrates by DC magnetron sputtering. Residual O₂ of the vacuum chamber and O₂ in the air caused the partial oxidation of Al films. NiO films were polycrystalline, the resistivity of NiO films was 8.5 Ωcm, the ratio of N i and O atoms was about 1:1. There are some holes on the surface of Al and NiO films, which is caused by the film growth mechanisms and surface defects of the substrates.Al/NiO multilayer energetic thin films were prepared by alternatively depositing Al films and NiO films, the total thickness of multilayer thin films was 3 μm, period thicknesses was 250 nm, 500 nm, 750 nm, 1000 nm, 1500 nm respectively. Al/NiO multilayer films with different periods have well-defined, heterogeneous structure. Al films on the surface become rough due to oxidation in the air, and there are some agglomeration between Al particles. The Ni atoms were detected in the as-deposited Al/NiO multilayer films with period thicknesses was 250 nm, this means that a small number of N i atoms were not oxidized and diffuse into top Al monolayer. After annealing at different temperatures, more oxygen atoms diffuse into Al monolayer significantly, the thickness of Al₂O₃ layer increases and much larger amount of N i atoms accumulates at the surface indicating that redox reaction has happened and more metal Al is oxidized. The thermal conductivity of Al/NiO multilayer films decreases with increasing the interface number. Exothermic reactions of Al/NiO multilayer films had two steps include a solid-solid process and a solid- liquid process, the energy density of Al/NiO multilayer films was about 2440 J/g, which was 71.8% of the theoretical value.Cr film bridges were prepared by DC magnetron sputtering and a wet etching process, the resistance of the bridge is 2 Ω. Different modulation period of Al/NiO multilayer energetic thin films were integrated on Cr film bridge to make（Al/NiO）_n/Cr igniters. Firing circuit test system（47 μF, 40 V） is adopted to apply the currents across the energetic igniters. All igniters can be ignited successfully. When the period thicknesses of the multilayer films was 1000 nm, the ignition time was shorter, the sparks’ distance was longer. The Al/NiO multilayer energetic thin films integrated onto the Cr film bridge can significantly improve the Cr film bridges’ ignition performance.