Polyimide-based field effect transistor structures

Abstract

Because of the electrical insulating properties of polyimide, it is widely used in the packaging of semiconductor chips. However, it has been documented that the electrical resistivity can be decreased by several orders of magnitude to about 0.1--1 O-cm when irradiated with ultraviolet laser light. This unique property of polyimide can be exploited to fabricate devices. In this study, capacitor structures on silicon wafers were created using a laser-modified layer of conducting polyimide as the top plate and a still intact layer unmodified polyimide as the insulator. This work quantifies the properties and quality of these capacitor structures and optimizes the procedure for fabricating them. First, the capacitor-insulator transition of thin film polyimide on silicon wafers were characterized and compared to bulk experiments. Then capacitor structures were fabricated and studied. Finally, an unexpected frequency response was discovered originating from the conductivity of the laser-modified polyimide. This frequency response was successfully modeled in PSPICE.