Dielectric response and polarization mechanism of alkali silicate glasses in gigahertz to terahertz frequency range

Abstract

Oxide glasses are dielectric materials with potential applications in highfrequency communications; hence, their dielectric properties in the gigahertz to terahertz frequency range should be investigated. In this study, the dielectric properties of silica glass and five single alkali silicate glasses were measured at 0.5-10 THz using terahertz time-domain spectroscopy and far-infrared spectroscopic ellipsometry. At 0.5-10 THz, the silica glass exhibited low dielectric dispersion with a low dielectric constant and loss. By contrast, the alkali silicate glasses exhibited high dielectric dispersion, and the dielectric constant and loss were higher than those of the silica glass. The shape of the dielectric dispersion profile depended on the alkali-metal ions; it was broader for lighter ions such as Li ions and sharper for heavier ions such as Cs ions. The peak dielectric loss shifted toward a lower frequency as the weight of the alkali-metal ions in the alkali-silicate glass increased. To understand the dielectric dispersion, the complex permittivity was calculated using molecular dynamics simulations. The theoretical results qualitatively agreed with the experimental data. Ion dynamics analysis revealed that alkali-metal ions vibrate and migrate under an applied electric field, which affects the dielectric constant and loss of alkali-silicate glasses at gigahertz to terahertz frequencies. To fabricate filter devices at low temperatures, alkali metals should be added to silicate glass; therefore, a minimum amount of light alkali metals should be used to minimize the dielectric loss of the glass materials while maintaining productivity.

Analysis of the Dielectric Properties of Alkali-Free Aluminoborosilicate Glasses by Considering the Contributions of Electronic and Ionic Polarizabilities in the GHz Frequency Range

“…In the GDMC-La glasses, the ε GHz increased from 4.66 to 4.93 with increasing the substitution of La 2 O 3 for (Al 2 O 3 + MgO), as shown in Figure 3 B. The ε GHz of the glasses mainly results from the polarizability contribution of their constituents [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Interestingly, with the incorporation of La 2 O 3 up to 0.8 mol%, ε GHz decreased by approximately 1 to 3% compared with that of the reference GDMC-Si59 glass.…”

“…They found that the single- and co-doping of RE species can reduce the dielectric constant of the glasses because of the increase in the polymerization of the glass network structure. Several researchers have studied the dielectric responses and polarization mechanisms of alkali and alkaline earth-modified silicate glasses in the GHz–THz frequency range [ 7 , 9 , 10 , 11 , 12 , 14 ]. It was shown that the alkali-modified silicate glasses exhibit strong dielectric dispersion and show higher dielectric constants than the alkali-free glasses, which is due to the vibrations and migrations of alkali ions that are easily moved in the glass subjected to electromagnetic waves.…”

“…The low dielectric property shortens propagation delay and mitigates signal loss and also leverages larger device geometries that decrease sensitivity to fabrication tolerances. Investigations on the dielectric property are essential for understanding the glass structure as it relates to the polarizability of constituent ions forming the glass [ 9 , 10 , 11 , 12 , 13 ]. Moreover, they can provide insight into the chemical structure of the glass at GHz frequencies, where the electronic and ionic mechanisms contribute to the polarizability.…”

“…In this connection, the characterization of the dielectric properties of glass materials in the GHz frequency range has gained growing interest in designing new glass compositions for use in printed circuit boards (PCBs) as a reinforcing material for high-speed data transmission applications. Since the dielectric constant (ε) is calculated based on the polarizability and density of glasses through the Clausius–Mossotti (CM) equation [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], the investigation of polarizability characteristics such as dielectric polarizability (α D ), oxide ion polarizability (α O2− ), and optical basicity (Λ) is important for understanding the dielectric responses of glasses in the GHz frequency region. The dielectric properties of glasses are also influenced by the low-frequency (GHz–THz) and the high-frequency (optical) modes [ 9 , 10 , 11 , 12 , 14 , 15 , 16 ].…”

“…Since the dielectric constant (ε) is calculated based on the polarizability and density of glasses through the Clausius–Mossotti (CM) equation [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], the investigation of polarizability characteristics such as dielectric polarizability (α D ), oxide ion polarizability (α O2− ), and optical basicity (Λ) is important for understanding the dielectric responses of glasses in the GHz frequency region. The dielectric properties of glasses are also influenced by the low-frequency (GHz–THz) and the high-frequency (optical) modes [ 9 , 10 , 11 , 12 , 14 , 15 , 16 ]. The dielectric constant at a GHz frequency is a result of contributions from the electronic and ionic polarizabilities, whereas the dielectric constant at an optical frequency is a result of contribution from the electronic polarizability [ 7 , 14 , 15 , 16 ].…”