Reverse short-channel effect

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In MOSFETs, reverse short-channel effect (RSCE) is an increase of threshold voltage with decreasing channel length; this is the opposite of the usual short-channel effect. The difference comes from changes in doping profiles used in modern small device manufacturing.

MOSFET Transistor used for amplifying or switching electronic signals.

The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS transistor, or MOS), is a type of field-effect transistor that is fabricated by the controlled oxidation of a semiconductor, typically silicon. It has an insulated gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. The MOSFET is the basic building block of modern electronics. Since its invention by Mohamed M. Atalla and Dawon Kahng at Bell Labs in November 1959, the MOSFET has become the most widely manufactured device in history, with an estimated total of 13 sextillion (1.3 × 1022) MOS transistors manufactured between 1960 and 2018.

Threshold voltage Minimum source-to-gate voltage for a field effect transistor to be conducting from source to drain

The threshold voltage, commonly abbreviated as Vth, of a field-effect transistor (FET) is the minimum gate-to-source voltage VGS (th) that is needed to create a conducting path between the source and drain terminals. It is an important scaling factor to maintain power efficiency.

In electronics, short-channel effects occur in MOSFETs in which the channel length is comparable to the depletion layer widths of the source and drain junctions. These effects include, in particular, drain-induced barrier lowering, velocity saturation, and hot carrier degradation.

RSCE is a result of non-uniform channel doping (halo doping ) in modern processes. [1] To combat drain-induced barrier lowering (DIBL), MOSFET substrate near source and drain region are heavily doped (p+ in case of NMOS and n+ in case of PMOS) to reduce the width of the depletion region in the vicinity of source/substrate and drain/substrate junctions (called halo doping to describe the limitation of this heavy doping to the immediate vicinity of the junctions). [2] At short channel lengths the halo doping of the source overlaps that of the drain, increasing the substrate doping concentration in the channel area, and thus increasing the threshold voltage. This increased threshold voltage requires a larger gate voltage for channel inversion. However, as channel length is increased, the halo doped regions become separated and the doping mid-channel approaches a lower background level dictated by the body doping. This reduction in average channel doping concentration means Vth initially is reduced as channel length increases, but approaches a constant value independent of channel length for large enough lengths.

See also

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References

  1. http://www.eng.auburn.edu/~niuguof/elec6710dev/html/subthreshold.html#reverse-short-channel-effect-rsce
  2. Kunikiyo, T.; Mitsui, K.; Fujinaga, M.; Uchida, T.; Kotani, N. (1994). "Reverse short-channel effect due to lateral diffusion of point-defect induced by source/drain ion implantation". IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems. IEEE. 13 (4): 507–514. doi:10.1109/43.275360.