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.
Dielectric characterization is carried out on . 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.
Figure 1: Sketch of the MFIA with a third-party dielectric test fixture where a disc sample is inserted between the electrodes. The grey box represents a third-party optional cryostat or furnace chamber that can house the fixture for temperature-dependent tests.
Figure 2: Impedance, phase, dissipation factor and capacitance (from top to bottom) of a dielectric sample are shown as a function of frequency. The data were acquired with the LabOne Sweeper module in dual-plot mode.
Figure 3: Dielectric sample probed at a fixed frequency of 10 Hz with the LabOne Plotter module, using the one-period averaging feature. From top to bottom, the traces with real-time statistics and histogram correspond to absolute impedance, phase, dissipation factor and capacitance.
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.
The Benefits of Choosing Zurich Instruments
Save time by expediting low-frequency measurements thanks to the one-period averaging feature.
Determine real-time equivalent circuit parameters without time-consuming sweeps.