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.
Highlights
Polyimide has excellent thermal stability, outstanding electrical properties, and high mechanical strength and is widely used as a dielectric material in power capacitors for energy storage [1,2,3], the solar array of satellite [4,5], and electronic devices [6], and so on
The simulation results are in good agreement with experiments [15,16]. These results show that the electric field distortion caused by the space charge accumulation under a high field may play an important role in the breakdown characteristics of polyimide
Based on the assumption of no space charge accumulated in the dielectric material, the electrical breakdown strength will not vary with the sample thickness, namely, Fb = V ramp tb /d = Fc
Summary
Polyimide has excellent thermal stability, outstanding electrical properties, and high mechanical strength and is widely used as a dielectric material in power capacitors for energy storage [1,2,3], the solar array of satellite [4,5], and electronic devices [6], and so on. As the voltage level increases and the devices are required to be further miniaturized, dielectric materials with high electrical strength need to be developed. The electrical breakdown mechanism of solid dielectrics is a research focus in the fields of dielectric energy storage and electrical insulation. The electrical breakdown field of dielectric materials depends on sample thickness. The electrical breakdown field of polyimide film under direct current (DC) voltage was measured at various sample thicknesses and various temperatures. The relation between the DC electrical breakdown field and sample thickness obeys an inverse power law with power indexes of 0.16 and 0.25 at 300 ◦ C and 400 ◦ C, respectively
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