Layered Al2O3-SiO2 and Al2O3-Ta2O5 thin-film composites for high dielectric strength, deposited by pulsed direct current and radio frequency magnetron sputtering

Abstract Multilayer thin films have the potential to act as high dielectric strength insulation for wire and microelectronics. In this study, films consisting of 2, 4 or 8 layers, composed of Al 2 O 3 with SiO 2 or Ta 2 O 5, were prepared via pulsed direct current and radio frequency magnetron sputtering to a thickness of between 152 and 236 nm. The dielectric strengths of all films exceed the 310 Vμm −1 achieved for PDC Al 2 O 3 . Maximum dielectric strengths were obtained for four layer composites; Al 2 O 3 -SiO 2 -Al 2 O 3 -SiO 2 (466 Vμm −1 ) and Al 2 O 3 -Ta 2 O 5 -Al 2 O 3 -Ta 2 O 5 (513 Vμm −1 ), each containing two PDC-Al 2 O 3 and two RF-SiO 2 /Ta 2 O 5 layers. Whilst the average dielectric strength was higher in the Ta 2 O 5 composites, they suffered from higher leakage prior to breakdown with ca. 6.5 nA compared to ca. 0.1 nA for SiO 2 composites. The mechanical properties of the composites were poorer due to increased intrinsic coating stress. Samples exhibited complete interfacial delamination with maximum coating adhesion strengths of 22 and 25 MPa. The variance resulted from larger coefficient of thermal expansion for Ta 2 O 5 compared to SiO 2 . Sputtered composites of Al 2 O 3 and either SiO 2 or Ta 2 O 5 had high breakdown strength with reasonable adhesion and could be suitable for insulating copper conductors in the aerospace and automotive industries.