No abstract

Polyimide (PI) is widely used in film form as a passivation material for power semiconductor devices of Si, SiC, GaN, etc. The magnitude of the electric field at the edge termination area of these semiconductor devices is becoming higher and higher due to the increase of operational voltage and /or demand for shrinking the edge termination area to increase device active area. Hence it is concerned that space charge accumulation in the encapsulation and passivation material affects the insulation performance of those devices. In this report, space charge distribution and electric field enhancement associated with the charge accumulation have been investigated for thin PI film with thicknesses of about 20 μm, using Laser Intensity Modulation Method (LIMM). It is shown that the enhancement factor of the internal electric field (the maximum internal electric field divided by the applied field) in PI film is negligibly small (less than 1.1) for applied fields less than 10 kV/mm. However, it can reach much higher like 1.4 at higher applied field like 25 kV/mm. This result implies that electric field at edge termination area should be carefully designed under such an operational electric field as is the case of SiC devices.

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.