Alumina dielectric permittivity

The growth of an anodic alumina film, at a constant current, is characterized by a virtually linear increase of the electrode potential with time, exemplified by Fig. 10, with a more or less notable curvature (or an intercept of the extrapolated straight line) at the beginning of anodization.73 This reflects the constant rate of increase of the film thickness. Indeed, a linear relationship was found experimentally between the potential and the inverse capacitance78 (the latter reflecting the thickness in a model of a parallel-plate capacitor under the assumption of a constant dielectric permittivity). This is foreseen by applying Eq. (38) to Eq. (35). It is a consequence of the need for a constant electric field on the film in order to transport constant ionic current, as required by Eqs. (39)-(43). 

As is evident from the data in Table 7.4, alumina is not the most suitable material to fidfill the requirements for an ideal electronic substrate. In particular, its thermal conductivity is among the lowest Hsted, the rather high dielectric permittivity may lead to inductive crosstalk and noise generation as well as signal delay in the... 

The effects of temperature and frequency on the permittivity and dissipation factor of a high-purity alumina ceramic are shown in Fig. 5.24. The discrepancies between the permittivity levels in Fig. 5.24 and values given elsewhere are probably due to differences in microstructure and measurement technique. Reliable room temperature values for er for single-crystal sapphire at 3.4GHz are 9.39 perpendicular to the c axis and 11.584 parallel to it, which are close to the values measured optically. The average er to be expected for a fully dense ceramic form is therefore 10.12, and values close to this have been determined. Nothwithstanding the uncertainties there is no doubt that the general behavioural pattern indicated by Fig. 5.24 is correct and typical of ceramic dielectrics. 

The progress in the oxidation of LDPE modified with maleic anhydride and alumina proceeds somewhat similar at various doses, because oxygen diffusion is hindered by filler nanoparticles [102]. The noticeable difference between pristine and modified LDPE consists of the presence of maleic anhydride, which interacts with molecular chains due to the electronegativity of oxygen atoms. The same radiation dose affects differently the dielectric behavior of the nanocomposites depending on the filler content. The dose of 50 kGy applied on LDPE-g-AM filled with 5 wt% nano-Al203 leads to a relative permittivity smaller than unfilled LDPE. y-Radiation can lead to a decrease in the dielectric losses of LDPE AI2O3 nanocomposites for properly chosen combination dose-fiUer content. 

Using standard alumina, the substrate itself can be used as the capacitor dielectrics. However, because of the considerable thickness of substrates (250 pm or more) and the relatively low permittivity of about 10, the capacitance density is very low (e.g., 0.34 pF/mm d = 250 pm). 

Therefore, it is desirable to design in low dielectric constant media, such as the silicates. For instance, silica with a relative permittivity of abont 4 wonld yield a transmission delay about twice that of pure vacuum (e =1), whereas alumina with a relative permittivity of about 10 would yield about 3 times the delay. The lowest dielectric constant ceramic packaging is silica based, snch as qnartz or Northrop Grnmman s low- TLTCC. Higher dielectric constants also contribnte to the losses of the material. Power absorption P is related to both the dielectric loss and dielectric constant of the material by... 

---