Thickness-Dependent DC Electrical Breakdown of Polyimide Modulated by Charge Transport and Molecular Displacement

Abstract

Polyimide has excellent electrical, thermal, and mechanical properties and is widely used as a dielectric material in electrical equipment and electronic devices. However, the influencing mechanism of sample thickness on electrical breakdown of polyimide has not been very clear until now. The direct current (DC) electrical breakdown properties of polyimide as a function of thickness were investigated by experiments and simulations of space charge modulated electrical breakdown (SCEB) model and charge transport and molecular displacement modulated (CTMD) model. The experimental results show that the electrical breakdown field decreases with an increase in the sample thickness in the form of an inverse power function, and the inverse power index is 0.324. Trap properties and carrier mobility were also measured for the simulations. Both the simulation results obtained by the SCEB model and the CTMD model have the inverse power forms of breakdown field as a function of thickness with the power indexes of 0.030 and 0.339. The outputs of the CTMD model were closer to the experiments. This indicates that the displacement of a molecular chain with occupied deep traps enlarging the free volume might be a main factor causing the DC electrical breakdown field of polyimide varying with sample thickness.

Finite Element Analysis of the Breakdown Prediction for LDPE Stressed by Various Ramp Rates of DC Voltage Based on Molecular Displacement Model

“…The mechanisms of electrical failure of insulators are considerably different between DC and AC power systems [4]. Therefore, the breakdown is hard to predict owing to various factors such as morphology of the insulator [5], the amount of injected charge in the insulator and electrode interface characteristics, local electric field distortion due to accumulated space charge in the insulator, temperature gradient [6][7][8], thickness of the insulator [9][10][11], operating time, and waveform of the applied voltage [12]. These factors are nonlinearly involved in the breakdown phenomenon.…”

Physicochemical Characteristics and Dynamic Charge Mapping in Thermally Aged Two-Layered Polymer Considering Surface States: Experiment and Simulation

“…The injected bipolar charges drifted and diffused through the layered films and then were trapped/detrapped and recombined under the action of electric fields. The time-space dependent equations describing the charge dynamics are as follows [26,27]:…”

“…where j(x, t) is the total convection flux; n(x, t) is the carrier density, representing electrons and holes; D is the diffusion coefficient; ρ is the net charge density, including mobile and trapped electrons and holes; and s i (x, t) is the source term representing the charge trapping/detrapping process and recombination between positive and negative charges [26,27], which can be introduced as follows:…”

Study on Micro Interfacial Charge Motion of Polyethylene Nanocomposite Based on Electrostatic Force Microscope

“…Although the PEA method was used to measure the charge distribution and charge amount of the whole sample, the charge near the surface of the sample occupied most of it [5,8]. Meanwhile, the charge distribution and total amount in the sample corresponded to the charge distribution and amount near the sample surface [22]. Therefore, the change rule of residual charge in the sample by PEA test can provide reference and correspondence for surface charge variation in the EFM test.…”