Temperature Dependence of Dielectric Breakdown in Polymers

Open Access
Author:
Min, Cheolhong
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 25, 2008
Committee Members:
  • Thomas R Shrout, Thesis Advisor
  • Michael T Lanagan, Thesis Advisor
Keywords:
  • PMMA
  • Polymer Dielectrics
  • P(VDF-TrFE-CTFE) terpolymer
  • Polypropylene
  • Polyimide
  • Electrical Properties
  • Temperature
  • Dielectric Breakdown
Abstract:
Capacitors possess high-power densities and have the ability to deliver energy with short discharge times, which are in the micro-second to nano-second range. Both energy and power density are related to the dielectric materials used in the capacitor. One of the main challenges for capacitors is achieving high energy density as determined by the relative permittivity and dielectric breakdown strength of a material. Polymers are some of the most important dielectric materials for high-power capacitors because polymer films show high breakdown strength. A general trend in polymers is that the breakdown strength increases with decreasing temperature. An understanding of the temperature dependence relationships among electrical properties, polymer chemistry, and crystalline structure may lead to improved energy storage for polymer-based capacitors&#8212;this is the basis of the thesis. Various polymers including polypropylene (PP), polyimide (PI), polymethyl methacrylate (PMMA), poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymer (p(VDF-TrFE-CTFE)) were investigated in this study. Electrical properties of the polymers including low-field (<1X10-3MV/mm) permittivity (¥år), dielectric loss (tan¥ä), high-field (>1MV/cm) permittivity, and dielectric breakdown strength will be discussed. Temperature dependence of low-field permittivity, dielectric loss, and dielectric breakdown in the polymers is also presented. The electrical properties of the polymers have been investigated over a temperature range from -196¡ÆC to 170¡ÆC. Breakdown strength (EBr) of all the polymers was found to decrease with increasing temperature. Maximum energy per unit volume (Evol) of the various polymers at maximum breakdown strength is also introduced using relative permittivity.