**2. Definition of dielectric constant**

Dielectric constant k (also called relative permittivity εr) is the ratio of the permittivity of a substance to that of free space. A material containing polar components, such as polar chemical bonds, which are presented as electric dipoles in Figure 2, has an elevated dielectric constant, in which the electrical dipoles align under an external electric field. This alignment of dipoles adds to the electric field. As a result, a capacitor with a dielectric medium of higher k will hold more electric charge at the same applied voltage or, in other words, its capacitance will be higher. The dipole formation is a result of electronic polarization (displacement of electrons), distortion polarization (displacement of ions), or orientation polarization (displacement of molecules) in an alternating electric field. These phenomena have characteristic dependencies on the frequency of the alternating electric field, giving rise to a change in the real and imaginary part of the dielectric constant between the microwave, ultraviolet, and optical frequency range.

#### Low Dielectric Materials for Microelectronics 61

**Figure 2.** Schematic illustration of a capacitor.

60 Dielectric Material

**Figure 1.** Calculated gate and interconnect dely as a function of technology node according to the National Technology Roadmap for Semiconductores(NTRS) in 1997 (top): █ ▲ gate delay; interconnect delay (Al and SiO2); ● sum of delays (Al and SiO2) and ITRS technology trend targets (bottom)

Dielectric constant k (also called relative permittivity εr) is the ratio of the permittivity of a substance to that of free space. A material containing polar components, such as polar chemical bonds, which are presented as electric dipoles in Figure 2, has an elevated dielectric constant, in which the electrical dipoles align under an external electric field. This alignment of dipoles adds to the electric field. As a result, a capacitor with a dielectric medium of higher k will hold more electric charge at the same applied voltage or, in other words, its capacitance will be higher. The dipole formation is a result of electronic polarization (displacement of electrons), distortion polarization (displacement of ions), or orientation polarization (displacement of molecules) in an alternating electric field. These phenomena have characteristic dependencies on the frequency of the alternating electric field, giving rise to a change in the real and imaginary part of the dielectric constant

**2. Definition of dielectric constant** 

between the microwave, ultraviolet, and optical frequency range.
