The subthreshold region becomes increasingly important in small geometry circuits as dimensions of MOSFETs continue to shrink in order to reduce cost and to obtain better performance. For short-channel or narrow-channel devices, their potential distribution becomes two-dimensional instead of one-dimensional as for a large device. Thus one dimensional subthreshold model used for large devices is no longer accurate for small geometry devices. Two-dimensional models have to be developed. A two-dimensional analytical subthreshold and punchthrough model for short-channel MOSFETs with nonuniformly doped channel is presented. Analytical expressions for the subthreshold current and gate swing are given. Ion implantation has become a standard MOS process step to adjust threshold voltage and to prevent punchthrough. It has great impact on the subthreshold behaviour of MOSFETs. A detailed examination of how the channel profile affects the subthreshold behaviour has been carried out for large and small geometry devices. The effects of terminal voltages and geometry dependence of the subthreshold behaviour have been studied carefully. A semi-empirical subthreshold model suitable for circuit simulation is proposed based on the experimental observation and theoretical results.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:643285 |
| Date | January 1993 |
| Creators | Cao, Xuezhou |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13306 |
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