Dielectric Spectroscopy

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.

Direct I-V measurements using phase-sensitive lock-in detection represent an attractive way to overcome the limitations affecting dielectric characterization. The MFIA Impedance Analyzer can measure impedance accurately up to 1 TOhm while maintaining an excellent phase accuracy of 2 mdeg. Dielectric spectroscopy can be performed straightforwardly with the LabOne^® instrument control software and its Sweeper module (see Figure 2). To study the temporal evolution of the dielectric properties, it is possible to take advantage of the LabOne Plotter (see Figure 3) or Data Acquisition (DAQ) modules to carry out measurements in the time domain. These tools also support temperature-dependent studies, where the MFIA can be integrated with a cryostat or furnace. For low-frequency experiments, test signals from 5 MHz down to 1 mHz can be set in all LabOne modules, including the Sweeper (see Figure 4).

Figure 4: LabOne Sweeper module in dual-trace mode showing the absolute impedance (upper window) and the phase and capacitance (lower window) for an airgap capacitor. The animation is run at a speed x1000.

• You can measure your dielectrics over a wide frequency range down to 1 mHz and over a broad range of impedance values up to 1 TOhm.
• Save time by expediting low-frequency measurements thanks to the one-period averaging feature.
• Determine real-time equivalent circuit parameters without time-consuming sweeps.

• Have high confidence in the obtained results thanks to the excellent phase accuracy of the MFIA and the low baseline of its dissipation factor.
• Integration into existing dielectric testing setups is straightforward thanks to the LabOne APIs.