Application Description

Dielectric spectroscopy is a form of impedance spectroscopy where the dielectric properties (dielectric constant and dissipation factor) of a medium or sample are characterized as a function of frequency. A dielectric is an electrical insulator with very low conductivity at DC; because of its polarizability, however, a dielectric can store charges in the low or mid-frequency range. This capacitive effect makes dielectrics useful for charge storage and dissipation. Applications of dielectrics include:

• Low-loss electrical components
• Energy storage devices such as batteries and supercapacitors
• High-k and low-k gates in semiconductor devices
• Piezo- and ferro-electric sensors and transducers

An impedance study of dielectrics is needed to fully understand the material physics as well as to optimize device performance.

Measurement Strategies

Dielectric characterization is carried out on a sample with well-defined geometry contacted with two electrodes. Typically, this is achieved with a parallel-plate fixture (see Figure 1) or an immersion probe with a specific electrode area and spacing. Based on this geometry, R||C or D||C equivalent circuit models can be established, and the dielectric constant (permittivity) is extracted as a result. A fixture such as the one shown in Figure 1 is often combined with a Q meter or an instrument based on an auto-balanced bridge. However, these instruments prohibit measurements at low frequencies and at high impedance.