A hot filament activated plasma-assisted chemical vapour deposition (PACVD) technique was developed to deposit BN films under a wide range of conditions. Using this technique, mixed-phase boron nitride (BN) films, containing crystallites of the cubic phase embedded in a hexagonal matrix, were deposited from a non-toxic source material, borane-ammonia (BH3-NH3) at a substrate temperature of up to 350 degrees C. These films showed good thermal and chemical stability, with smooth surface topography. It was found that the increased ion bombardment at higher r.f. power contributed to increasing the volume fraction of the cubic phase in the film. The film properties, e.g. refractive index and stress, are directly correlated with the increasing cBN content of the film produced by higher activation energy. Hardness of the film measured by ultra-low load indentation showed an improvement over the silicon substrate. The electronic properties of these films were measured, and exhibited high resistivity and breakdown field strength, and a low level interface state density.