Effect of film thickness and electrode material on space charge formation and conductivity in polyimide films

Abstract

Polyimides (PI) are well-known materials used as passivation and insulating layers in microelectronics or power electronics. Though the electric field and temperature withstanding of polyimides have been investigated for long, little information is available on the space charge behavior in relatively thin polyimide films. In this work, the space charge behavior was investigated with the Laser Intensity Modulation Method (LIMM) which is suited for films of several µm in thickness. It is complemented by DC conductivity measurements. The analysis is made on 12 and 18 µm thick PIlayers deposited on Si-substrates with using Al or Au top electrodes. A build-up of negative charges can be observed, irrespective of the polarity of the applied voltage, as the external field is increasing in the range 25-125 kV/mm. With decreasing film thickness, the DC conductivity increases and a diminution of the internal electric field distortion occurs. The native alumina formed between the aluminium electrode and the PI could act as a barrier to electrons injection from the top electrode.

Electric field enhancements due to space charge in thin polyimide film

“…The space charge investigation using the same PI film under extremely higher DC stress, close to breakdown voltages, from 25 to 125 kV/mm has already been reported and discussed with DC conductivity trend in [12] [13]. In the present paper, experimental studies of the space charge dynamics in thin PI films in more moderate electric fields under 25 kV/mm are presented using the LIMM.…”

Behavior of Space Charge in Polyimide and the Influence on Power Semiconductor Device Reliability

“…In [10], the effect of humidity in air and the difference due to electrode material (Al and Au) on space charge formation with time evolution are discussed. Recently, the Laser Intensity Modulation Method (LIMM) [13] has been performed to investigate space charge characteristics in thin PI films with few micrometers in thickness under the DC field up to 125 kV/mm, close to breakdown voltage [14][15][16][17]. In [17], the space charge characteristics were reported under DC voltage of from low field of 2.5 to 125 kV/mm with the correlation with DC conductivity trends.…”