High-field electrical conduction in polyimide films

Abstract

Capacitance transient spectroscopy in metal-insulator-metal systems and its application to the determination of trap parameters in polyimide filmsElectrical conduction current in polyimide films has been measured at high fields ͑Ͼ1.4 MV cm Ϫ1 ͒ using a Au metal ͑M͒-polyimide film ͑P͒-p-silicon ͑S͒-MIS structure. On the basis of the currentvoltage characteristics coupled with the capacitance-voltage characteristics measured under various conditions, it is found that electrical conduction at high fields is mainly due to Fowler-Nordheim type tunneling injection of electrons from the Au gate electrode if it is negatively biased, or from the PI/Si contact if the Au gate electrode is positively biased. The conduction current is strongly dependent on the concentration and the centroid location of the trapped charges. Computer simulation reveals that the trap concentration is of the order of 6ϫ10 17 cm Ϫ3 with its centroid located near the electron injecting contact, and that the trap ledge occurs only when the concentration of the net negatively trapped electron charge is large or the location of its centroid is close to the injecting contact. The decay of the dark charging current after the application of a step-function direct current field is associated mainly with the time-dependent trap-filling process. The photoconduction under an ultraviolet light illumination is due mainly to the photogeneration of free holes. Polyimide is very sensitive to the environmental humidity. Electrical conduction current increases and the breakdown strength decreases rapidly with increasing humidity.

Formation and inhibition of free radicals in electrically stressed and aged insulating polymers

“…Because of the large energy bandgap, the potential barrier height for electrons injected from the electrical contacts to the polymer is usually smaller than that for hole injection, implying that electron injection is dominant in insulating polymers under normal practical conditions. [17][18][19] The nature of the bulk trapping states in polymers has been studied by several investigators. 20,21 Their experimental results have indicated that most bulk traps are acceptor-like electron traps and donor-like hole traps.…”

“…4,[22][23][24] It is most likely that the electrons are injected into the polymer from the metallic cathode mainly by FowlerNordheim tunneling. [17][18][19] These injected electrons will quickly become trapped after one or a few scatterings. According to Kao's model, 5 a transition of an injected electron from an upper energy state (e.g., conduction bands) to a lower one (e.g., traps) due to trapping or recombination involves an energy release.…”

The use of the final thermally stimulated discharge current technique to study the molecular movements around glass transition

“…The data in Figs. [4][5][6][7] show that in the temperature range from 370 to 470 K the β 2 relaxation is entering. For the β relaxation various mechanisms have been proposed involving motions that, while still essentially local in character, encompass larger portions of the repeat unit that respond in a correlated manner.…”

“…Consequently, it has a high potential for microelectronic applications, e.g., as interlayer dielectrics, flexible circuitry substrates, stress buffers, and passivation layers. PI is a hydrophilic polymer and its dielectric properties largely depend upon absorbed water or humidity [4][5][6]. A good deal of work on electrical conduction in PI at low fields [7][8][9][10][11] and high fields [6,12] has been reported.…”

Thermal runaway in polyimide at high electric field probed by infrared thermography

“…1 Due to their excellent thermal, electrical, and mechanical properties, they appear as very interesting for high temperature and high electric field applications. [2][3][4] Although the electrical properties of PI films have been largely investigated since many years, 5-9 their operating limit under high electric field at high temperature still remains unknown up to now. As PI is known to fail via a thermal process, 10,11 resulting from the formation of a spacecharge-limited-current mechanism, 12,13 they have to be used below the temperature runaway when high electric fields are applied to their bulk.…”