Layered Al_2O_3-SiO_2 and Al_2O_3-Ta_2O_5 thin-film composites for high dielectric strength, deposited by pulsed direct current and radio frequency magnetron sputtering

摘要

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 Al2O3 with SiO2 or Ta2O5, 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 exceeded the 310 V mu m(-1) achieved for PDC Al2O3. Maximum dielectric strengths were obtained for four layer composites; Al2O3- SiO2-Al2O3-SiO2 (466 V mu m(-1)) andAl(2)O(3)-Ta2O5-Al2O3-Ta2O5(513 V mu m(-1)), each containing two PDC-Al2O3 and two RF-SiO2/Ta2O5 layers. Whilst the average dielectric strength was higher in the Ta2O5 composites, they suffered from higher leakage prior to breakdown with ca. 6.5 nA compared to ca. 0.1 nA for SiO2 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 SiO2. Sputtered composites of Al2O3 and either SiO2 or Ta2O5 had high breakdown strength with reasonable adhesion and could be suitable for insulating copper conductors in the aerospace and automotive industries.