Thermally stimulated discharge current and fractional polarization studies in polyimide (Kapton-H) samples (original) (raw)
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Space charge analysis in polyimide (kapton–H) samples
Journal of Thermal Analysis and Calorimetry, 2010
The space charge trapping/detrapping in thermally charged polyimide (PI) samples have been studied by means of ''Final Thermally Stimulated Discharge Current'' (FTSDC). We investigate the effects associated with space charge behavior in PI near glass transition region. The FTSDC spectra consist of space charge peak attributed trapping of charges at different trapping levels. The peak positions are found to be very sensitive with poling time, discharging time, and heating rate. The apparent activation energy distributed in the range from 0.51 to 1.12 eV, and the charge released has been found to be varying with poling temperature (T p) and poling time (t c)/discharging time (t d). The decay of space charge (Q) resembled an agreement with interfacial polarization.
Study of trap structure of thermally polarized polyimide
Journal of Applied Polymer Science, 2012
The trap structure of polyimide was studied using open-circuit thermally stimulated discharge current (TSDC). TSDC was observed in 25-lm thin film of polyimide at different condition of polarizing field and temperature. The one-sided vacuum-aluminized samples were used to record the open-circuit thermally stimulated current. The dipolar mechanism of relaxation is a possible mechanism to explain the behavior of TSDC peak at low temperature and field condition; however, hopping transport mechanism is prominent for the sample polarized with higher field and temperature. This is because deeper traps capture the charge carriers at high polarizing field and temperature and their subsequent trapping through hopping process. The influence of surface traps is caused by thermal polarization; it is evident due to lower value of activation energy, since activation energy of TSDC peak is corresponding to surface traps. The morphology of surface traps is verified by measuring the surface roughness using atomic force microscopy. The both type of charges (i.e., heterocharge and homocharge) are responsible for flow of current in presence of air gap. We report the role of surface and deep traps induced due to charging process. V
Improvement of Polyimide Electrical Properties During Short-Term of Thermal Aging
2008 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2008
An atypical enhancement of both the dielectric properties and the static (dc) conductivity in polyimide (PI) films has been observed using isothermal dielectric relaxation spectroscopy at 300°C under air atmosphere during short-term thermal aging (up to 200h). Simultaneously, an increase of the dielectric strength of PI is observed. Despite a close similarity with the typical electrical signature of the crystallization phenomenon occurring in semi-crystalline polymers, DSC measurements have not revealed the presence of an exothermic crystallization peak in PI up to 500°C thus denying this assumption. In this paper, a cross-linking reaction under oxidant atmosphere is therefore proposed for explaining such electrical improvements. Indeed, oxygen diffusion in the polymers' bulk is generally followed by the formation of links between macromolecular chains leading the molecular and charge motions more difficult. This phenomenon, inducing usually an enhancement of the electrical and mechanical properties, is also supported by FTIR chemical changes of PI during aging and theoretical cross-linking mechanisms in presence of oxygen.
Study of relaxation and dielectric response of polyimide films
European Journal of Electrical Engineering
In recent years, polyimides are more and more used as high performance polymers because of their excellent thermal, mechanical and electrical properties. In this work, dielectric properties and relaxation behavior of some Polyimide films were studied on the basis of dielectric constant, dielectric loss and AC conductivity taking into account their variation with frequency and temperature. According to the results, three types of relaxations α, β and γ at decreasing temperature were detected, the origin of these relaxations and the influence of the chemical structure on changes in dielectric and electrical properties were discussed. RÉSUMÉ. Au cours des dernières années, les polyimides sont de plus en plus utilisés comme des polymères à hautes performances en raison de leurs excellentes propriétés thermiques, mécaniques et électriques. Dans ce travail, les propriétés et la relaxation diélectriques de certains films polyimides ont été étudiés sur la base de la constante diélectrique, le facteur de perte diélectrique et la conductivité AC en tenant compte de leur variation avec la fréquence et de la température. D'après les résultats obtenus, trois types de relaxations α, β et γ à température décroissante ont été détectés, l'origine de ces relaxations et l'influence de la structure chimique sur les variations des propriétés diélectriques et électriques ont été discutées.
Field-induced thermally stimulated currents in Kapton-H polyimide films
Physica Status Solidi (a), 1983
Thermally stimulated polarization current (TSPC) is investigated in Kapton-H thin films in the temperature region303 to 523 K under various polarizing fields ranging from 10 to 200 kV cm-l ; and different heating rates. The TSPC spectra reveal the presence of a single peak (P,) around 400 Ii and a steady rise in current at high temperatures where ohmic conduction begins to predominate. During the successive cooling, the current retained its positive polarity, while in the second TSPC cycle a negative current is obtained in low temperature region. This can be accounted for the temperature dependence of saturation polarization. In a few cases the corresponding thermally stimulated depolarization current (TSDC) characteristics are also recorded, which are found to consist of two peaks Pl and P2 located nearly a t 390 and 480 K, respectively. McKeever's analysis implies the association of the maxima P,, P,, respectively, with dipole and space charge origins. The thermal variation in dielectric constant of the material is also deduced from the TSPC curves. The experimental observations are in general agreement with the theoretical predictions. The difference is presumably caused by the fact that the TSPC technique is subject to several limitations like interference of conduction phenomena. Der thermisch stimulierte Polarisationsstrom (TSPC) wird in diinnen Kapton-H-Schichten im Temperaturbereich von 303 bis 523 K bei verschiedenen Polarisationsfeldern von 10 bis 200 kV cm-l und unterschiedlichen Heizgeschwindigkeiten untersucht. Die TSPC-Spektren zeigen ein einzelnes Maximum (P,) bei etwa 400 K und einen stetigen Anstieg des Stromes bei hohen Temperaturen, wo ohmsche Leitfahigkeit zu uberwiegen beginnt. Wahrend der nachfolgenden Abkiihlung behalt der Strom seine positive Polaritat, wahrend im zweiten TSPC-Zyklus ein negativer Strom im Bereich tiefer Temperatur erhalten wird. Dies kann auf eine Temperaturabhiingigkeit der Sattigungspolarisation zuruckgefuhrt werden. In einigen Fallen werden die entsprechenden thermisch stimulierten Depolarisationsstrom(TSDC)-Charakteristiken ebenfalls aufgenommen und gefunden, daI3 sie aus zwei Maxima P1 und Pz bestehen, die bei etwa 390 bzw. 480 K liegen. McKeevers Analyse ergibt eine Verkniipfung der Maxima Pl und Pz mit dem Dipol-bzw. Raumladungsursprung. Die thermische Anderung der Dielektrizitatskonstante des Materials wird ebenfalls aus den TSPC-Kurven abgeleitet. Die experimentellen Beoba,chtungen befinden sich in allgemeiner ubereinstimmung mit theoretischen Vorhersagen. Der Unterschied beruht wahrscheinlich a,uf der Tatsache, dal3 die TSPC-Technik einigen Beschriinkungen, wie Interferenz der Leitungsphanomene, unterworfen ist.
The Scientific World Journal, 2013
The formation mechanism of space charges in polyimide (PI) which was exposed to dielectric barrier discharge (DBD) in SF6medium and the effects of the space charges on interfacial and electrical properties of PI were investigated. The variation of normalized surface charge density on PI sample was calculated and illustrated for different DBD exposure times. The surface potential was measured to determine the effect of the space charges on the sample. Then, the contact angle values were measured to obtain the relation between the surface energy and the surface charge density. The expressions for the total charge and the concentration of trapped electrons were derived by using Poisson and continuity equations at stationary state. The space charges were determined experimentally by using thermally stimulated depolarization current (TSDC) method. Also, SEM image and FTIR spectrum of virgin and treated samples were presented to observe the structural variations. It was seen that the appr...
Electrical conduction processes in polyimide films-I
IEEE Transactions on Dielectrics and Electrical Insulation, 2008
Extensive investigations of the absorption and desorption currents are carried out over the temperature range of 50 to 200 o C and electric fields up to 12 MV/m in 25.5 μm polyimide film base with 12.7 μm coating of Teflon ® FEP on one side. It is believed that this is the first time that studies on this film are reported in the literature.
Electret behaviour of ion irradiated polycarbonate and kapton-H polyimide films
Vacuum, 1997
Vacuum/volume 48/number 12lpages 995 to 99711997 The electret state of a polymer arises from the induced polarization owing to the frozen in phenomenon of electric charges. The study of electret nature using thermally stimulated discharge current (TSDC) technique reveals the nature of various relaxation processes in a polymer. When a polymer is irradiated with high energy ions their dielectric relaxations get affected which can be investigated using above mentioned technique. Reported here are the results of TSD current spectra of films of polycarbonate (PC) (irradiated with 700 MeV Ag+, flux; 7 x IO" and lx IO9 ions/cm') and kapton-H polyimide (irradiated with 700 Mel/O++, flux; 1 x IO5 ions/cm'). The as-received and irradiated samples of PC were polarised at 720°C using a 200 kV/cm electric field while those of kapton-H were polarised at 90°C, field; 733 kV/cm and 18O"C, field; 266 kV/cm. With PC it is observed that the irradiation does not affect the location of TSDCpeak occurring at 144°C (activation energy; 0.6eV); however, the peak magnitude changes with irradiation dose. The peak being associated with dipolar relaxation the ion-irradiation seems to have changed the number of dipoles. The high temperature TSDC spectra is however largely affected by irradiation giving evidence of the presence of new traps. With kapton-H, it is observed that TSD current changes its direction (anomalous TSDC) in irradiated samples in the high temperature region. Such behaviour has not been observed in the thermoelectrets of as-received samples. Only the corona charged electrets were observed to give such anomalous TSDC behaviour. This suggests the creation of new energy traps from irradiation. The bulk nature of this relaxation is confirmed by the TSDC of repoled samples. The irradiation induced shallow energy traps along with dipolar relaxation are also observed from the TSDC spectra in the low temperature region. 0 1998 Elsevier Science. All rights reserved
Effect of metal halides on the electrical properties of polyimides
Polymer, 1988
This article describes the effect of metallic salts, Sn (II), Hg (II), Co (II) chlorides, on the electrical properties of polyimide films derived from 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) and 4,4'diaminodiphenyl ether (E). The effect of temperature/field on the electrical conductivity of the films was studied. An ohmic/sublinear behaviour in undoped film and a non-ohmic behaviour at high field and temperature was observed in doped films. Dielectric characteristics (e and tan 6) as a function of frequency and temperature were also investigated.