Graded-channel fully depleted Silicon-On-Insulator nMOSFET for reducing the parasitic bipolar effects

An extended study of the occurrence of inherent parasitic bipolar effects i n conventional and graded-channel fully depleted silicon-on-insulator nMOSF ETs is carried out. The graded-channel device is a new asymmetric channel M OSFET, fabricated through a simple process variation. Measurements and two- dimensional simulations are used to demonstrate that the graded-channel dev ice efficiently alleviates the parasitic BJT action, improving the breakdow n voltage, by the reduction of impact ionization in the high electric field region. Based on process/device simulation and modeling, multiplication fa ctor and parasitic bipolar gain, which are the responsible parameters for t he parasitic BJT action, are investigated separately providing a physical e xplanation. The abnormal subthreshold slope and hysteresis phenomenon are a lso studied and compared. (C) 2000 Elsevier Science Ltd. All rights reserve d.