Space Charge Behavior in Epoxy‐Based Dielectrics: Progress and Perspective

Abstract

temperature and complex electric field conditions. [1][2][3] Epoxy resin (EP) is a class of polymer oligomers containing two or more epoxide groups based on organic compounds (e.g., aliphatic, alicyclic, and aromatic). As a prepolymer, EP shows excellent performance after its reaction with a curing agent to form an insoluble polymer with a 3D network structure. EP has desirable insulating characteristics, [4][5][6][7] heat resistance, [8] high mechanical strength, [9] low shrinkage, [10] chemical stability, and adhesive properties, which originate from its compact structure and tunable functional groups. The above mentioned outstanding performances, along with characteristics of easy processing and formula design flexibility, enable the extensive use of EP-based materials in power equipment and electronic devices [11] (Figure 1), including bar insulation and impregnating varnish in transformers, main insulation in dry-type bushings and wall bushings, insulator in gas-insulated switchgear (GIS) and gas-insulated transmission line (GIL), epoxy molding compound for integrated circuit (IC) packaging. It is noteworthy that EPs typically possess lower glass transition temperature (T g ) compared to other high-T g dielectric polymer substitutes used in microelectronic systems such as benzocyclobutene, [12] polyimide (PI), [13] and maleimide. [14] Besides high T g , high thermal conductivity and low coefficient of thermal expansion of EPs are always desired for their industrial applications, especially from an electronic packaging perspective. To date, considerable efforts have been made to improve the heat endurance and heat dissipation capabilities of EP-based dielectric materials by inorganic particle doping [15][16][17][18][19][20][21][22][23][24] and chemical modification. [25][26][27] Furthermore, EP is also an indispensable adhesive that is extensively used in power equipment. [28][29][30][31][32] Yet, potential reliability hazards may exist during the operation of power equipment and electronic devices, especially at high temperatures and under high voltage direct current (HVDC) application, one of which is the space charge accumulation in EP-based dielectric materials. [29,30,33,34] The accumulated space charge may cause deterioration/aging and even partial discharge or dielectric breakdown of dielectric materials. [35][36][37][38][39][40] Specifically, the extensive application of EP-based dielectric materials in HVDC transmission projects eagerly calls for relevant studies on the space charge behavior Epoxy-based dielectrics are extensively used in grid-connected energy systems and modern microelectronics as electrical insulation, adhesive, and packaging components. However, space charge accumulation in epoxy-based dielectrics is a foremost factor threatening device stability and lifespan, especially under conditions of high voltage direct current and high temperatures during long-term operation, and thus are investigated systematically. This article reviews the state-of-the-art progress in understanding and r...

Chemical and Mechanical Characterization of Unprecedented Transparent Epoxy–Nanomica Composites—New Model Insights for Mechanical Properties

“…A small influence on the volume resistivity seems related to the amount of mica and possibly due to a different effect on the space charge suppression, the limitation of the motions of molecular chains, and the prevention of the migration of charge carriers. Further experiments will be carried out to explore the dielectric behavior of the mica nanocomposites as a function of compositional parameters, epoxy-based dielectrics having a wide variety of applications in power equipment and electronic devices [ 64 ].…”

Interface Charge Characteristics in Polymer Dielectric Contacts: Analysis of Acoustic Approach and Probe Microscopy

“…Optical methods, such as the Pockels and the Kerr effect, are suitable for testing charges in thin solid samples and liquids, respectively. [11,139] Thermal methods, comprising the thermal pulse method (TPM), thermal step method (TSM), and laser intensity modulation method (LIMM), are also used for measuring charges. [56,140] Acoustic methods, such as the PEA and PWP methods, have been used extensively.…”

“…The recent development of power electronic devices has introduced more complex voltages that are applied to dielectric insulation systems. [11,[193][194][195] (a-c) Reproduced with permission. [54] Copyright 2019, IEEE.…”

“…Currently, acoustic, thermal, and optical methods are widely used for measuring space charges in dielectric structures. [11,56,57] These methods can also measure interface charges for some specific structures. Among them, acoustic methods such as pulsed electro-acoustic (PEA) and pressure wave propagation (PWP), present favorable applications in polymer dielectric systems.…”

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including multi-layered dielectric contact regions in high voltage cables, [6][7][8][9] winding and dielectric contact regions in solid-state transformers, [10] and filler/ matrix contacts in composite materials for electronic device packaging. [11] Under the electric field, the interface charges are formed within various regions, indicating an improvement in electro-acoustic, [12] electro-optic, [13] and electro-thermo [14] conversions in the flexible transducers. Additionally, interface charges accumulate in the narrow regions, resulting in field distortion and device degradation.

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