Preferred Orientation in Al2O3 Substrates

The degree of preferred orientation (texture) of doctor-bladed polycrystalline 99.5% Al₂O₃ substrates from 3 sources was evaluated by qualitative optical and quantitative X-ray analyses. The substrates exhibit a fiber texture in which the basal planes lie preferentially in the plane of the substrate. The same texture is weakly evident in the unfired materials. The strength of the texture in fired substrates varies from lot to lot and among suppliers, but its character remains essentially the same. Measurements of dielectric constant, flexural strength, and thermal expansivity are consistent with the observed texture. The possible origins of the texture and its importance in substrate applications are discussed.