Electrical and interfacial properties of metal-polyimide-silicon structures

The electrical and interfacial properties of gold-polyimide-silicon structures were studied experimentally by measuring the capacitance-voltage (C-V) characteristics. Two different polyimides of PMDA-ODA (synthesized from pyromellitic dianhydride and oxydianiline) and BTDA-ODA (from benzophenone tetracarboxylic dianhydride and oxydianiline), respectively, were employed. Polyimide coatings on n-type silicon (with a doping level N=5×10 14 cm-3) were prepared by spin coating followed by thermal cure to range from 0.4 to 2.1 μm in thickness. The resulting high frequency C-V plots of these structures were well defined and could be described by the basic theory on metal-insulator-semiconductor (MIS) devices. Distinct differences in the C-V characteristics were observed, depending upon the polyimides. PMDA-ODA dielectrics resulted in C-V hysteresis, believed to be caused by charge injection. On the other hand, BTDA-ODA showed much smaller hysteresis, but some stretch-out in the C-V curve. These differences are attributed to the different interfacial properties of these polyimides in contact with silicon substrates.