Characterization of polyester films used in capacitors. II. Effects of heat treatments on transient and steady-state charging currents in polyethylene terephthalate thin films

Abstract

The effects of various heat treatments performed before or after the vacuum deposition of aluminum electrodes on the charging currents flowing through polyethylene terephthalate (PET) thin films (6 and 12 μm) were studied. The amorphous phase of the PET films was characterized by the use of thermally stimulated current/relaxation map analysis spectrometry, allowing precise determination of thermodynamic and thermokinetic parameters. Density measurements were used to calculate the rate of crystallinity achieved after annealing. A correlation was found between the relaxation parameters of the α dipolar relaxation of PET, the rate of crystallinity, and the properties of the charging currents observed from room temperature to 200 °C. Strain-induced crystallization has been put forward to account for the experimental evidences.

Electrical conductivity effects in polyethylene terephthalate films

“…4,6 Figure 3 shows the Arrhenius plot of dc , determined by measuring the currentvoltage characteristic for a linear increasing voltage with a rate of 33 mV/s, in the limited temperature range from 80 to 130°C. The value of the activation energy E determined from this plot, Eϭ2.1 eV, is in agreement with values reported in literature from conductivity measurements: 1.87 and 1.94 eV, 31 1.7 and 2.2 eV, 32 and 1.8 eV.…”

“…The investigation of electrical conductivity effects, such as space-charge formation and electrode polarization, is of particular importance for these and similar applications. [5][6][7][8] The method of thermally stimulated depolarization current ͑TSDC͒ has been widely used to investigate electrical conductivity effects in PET films. [7][8][9][10][11][12] At temperatures higher than that of the glass transition TSDC peak, one or several additional peaks are often observed and attributed to spacecharge effects and charge carrier trapping in the bulk of the sample and/or at the interface between the sample and the electrodes.…”

“…Models have been proposed to account for the observed behavior. 6,12 Transient and steady-state conductivity measurements were employed to separate dipolar from conductivity processes and to investigate the nature of the conduction mechanisms. 5,6,13 So far, less attention has been paid to the use of ac DRS to study effects related to dc conductivity in PET.…”

“…6,12 Transient and steady-state conductivity measurements were employed to separate dipolar from conductivity processes and to investigate the nature of the conduction mechanisms. 5,6,13 So far, less attention has been paid to the use of ac DRS to study effects related to dc conductivity in PET. The ac measurements on biaxially stretched PET films by Miyairi 14 at low frequencies (3ϫ10 Ϫ4 -10 Ϫ1 Hz) and high tempera-tures ͑150-220°C͒ showed a loss peak in tan ␦ attributed to electrode polarization.…”

“…In a previous article 4 we reported the results of DRS measurements on PET films in the frequency range 10 Ϫ2 -10 6 Hz and the temperature range 20-190°C. Both dipolar ␣ and ␤ processes and electrical conductivity effects were studied within the complex permittivity ⑀* formalism.…”