Charge trap spectroscopy in polymer dielectrics: a critical review

Abstract

Trapping phenomena are essential features controlling the transport properties of insulating materials. Depending on the energy depth, traps can either assist transport or lead to long-lasting storage of charges. The consequences of charge trapping are non-linear phenomena and electric field distribution distortion in the dielectric bulk. The important characteristics about traps are the nature of the levels, their depth in energy, and their density. In this review, we discuss the different techniques available to probe the energetics of traps, particularly in insulating polymers. The methods implemented for approaching the characteristics of traps range from atomistic simulation based on known physical/chemical defects, identification by spectroscopic techniques, and coupled opticalelectrical or thermal-electrical techniques. The review is focused on methods involving thermal or optical excitation coupled to detection using electrical or luminescence response with questioning about the physical hypotheses behind the analysis and the difference in response obtained through the various approaches. The technical implementation of these methods is described, along with examples of application. The differences in trap depth estimation from optical and thermal methods is discussed as well as the impact of having distributed trap depths. The input of luminescence techniques, which provide a fingerprint of chemical groups involved in charge recombination, is put forward.

Charge Trap Spectroscopies in Polymer Dielectrics: Application to BOPP

“…The analysis of TSDC peak poses the problem of solving the case of distributed processes. Different results showed that in presence of a distribution of trap depths, an underestimate of the activation energy is obtained [1]. However, in general, energies found in TSDC tend to match those found in isothermal decay.…”

“…Different methods have been implemented over the years to get insight into fundamental properties of traps that are the physical-chemical nature, the energy depth, and the amount. Methods can be with or without stimulation of charge detrapping and are based on either pure electrical response such as surface potential decay, coupled thermal-electrical effects as with thermally stimulated discharge current (TSDC) or couple electrical-optical effects as in photostimulated discharge (PSD) for example, as reviewed recently [1].…”

Biaxially oriented silica–polypropylene nanocomposites for HVDC film capacitors: morphology-dielectric property relationships, and critical evaluation of the current progress and limitations

“…The fact that polymers exhibit complex TSDC spectra comprising of several overlapping of (quasi-) continuous trap bands-along with the TSDC polarity reversal effect observed in the deep trap region in Figure 9a-complicate the analysis and evaluation of trapping parameters (trap depth and density of occupied states) as discussed in detail elsewhere 86,88 . Due to these reasons we do not attempt e.g.…”

“…Due to these reasons we do not attempt e.g. peak-fitting 86 , deconvolution 89,90 or numerical methods 91,92 to derive trap parameters here, as the results would be largely inconclusive 88 . Nevertheless, the TSDC results presented herein clearly indicate a modification of trap density of states (DOS) and a more homogeneous distribution of charge in the silica-containing samples, and the results are consistent with the PEA space charge depolarization behavior measured from the nonoriented cast films (Figure 4), thereby confirming the modification of charge trapping properties also in silica-BOPP thin films.…”

Evidence for Local Spots of Viscous Electron Flow in Graphene at Moderate Mobility

“…Since all residues result from resists and, hence, are insulating, they affect the work-function of graphene by the formation of interface dipoles [24][25][26][27] or by trapped charges. 28 Dipoles from residues on top or below graphene are known to locally dope graphene. 29 This has been evidenced, e.g., via intentionally preparing self-assembled polymer films on the substrate prior to graphene deposition.…”