Hot-carrier degradation mechanisms in silicon-On-Insulator MOSFETS

The structure, operation principles and basic characteristics of SOI MOSFETs are evoked, before focusing on the degradation aspects. The hot-carrier injection into the front gate oxide and buried oxide is discussed as a function of silicon film thickness, transistor configuration (n- or p-channel, inversion- or accumulation-mode), and stressing bias. The special phenomena involved in ultra-thin, fully-depleted SIMOX MOSFETs are compared to those governing partially-depleted and bulk-equivalent transistors. It is demonstrated that the coupling between back-interface defects and front channel properties is a unique and very challenging degradation feature in SOI. The road map to reach an accurate electrical image of the degraded transistor, by accounting for coupling effects or by avoiding them, is described. Although the aging mechanisms and investigation methods are more sophisticated than in bulk Si, the degradation of SOI MOSFETs does not appear to impede on the development of high performance, low-voltage ULSI SOI circuits.