Aluminium Oxide Permittivity in Gigahertz

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Aluminium oxide is an important material in electronics due to its high conductivity (er 10) and low loss at gigahertz. Its excellent electrical properties allow it to be used as a substrate in high frequency devices such as MIM capacitors and antenna windows.

Several studies have shown that the permittivity of Al2O3 is mainly determined by three factors: impurity contents in starting powder, sintered density and average grain size of sintered alumina [8, 9]. In this study, two pure alumina powders (99.9%) with similar dielectric performances (er 10 and quality factor 50,000 GHz) are studied.

The real and imaginary parts of the dielectric constant of aluminium oxide vary slowly with frequency at a few temperatures for sintered and quenched samples. These changes are attributed to space charge polarization and are explained using Jonscher’s power law: sac (o) = s (o) + s1(o) = sdc+Aon; 0 n1, where n is the refraction index of the sample, s is the permittivity, dc is the permeability of free space and Aon is the axial permeability of the sample.

Moreover, the ac conductivity of both sintered and quenched samples varies with temperature in the high-temperature region. This frequency dependence is characterized by a symmetric relaxation of Z’’ with a broad distribution of relaxation times that is attributed to a non-Debye type relaxation mechanism in both materials.

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