MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...

s, reverse short-channel effect (RSCE) is an increase of

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

with decreasing channel length; this is the opposite of the usual

short-channel effect 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 saturati ...

. The difference comes from changes in doping profiles used in modern small device manufacturing. RSCE is a result of non-uniform channel doping (halo doping ) in modern processes. To combat

drain-induced barrier lowering Drain-induced barrier lowering (DIBL) is a short-channel effect in MOSFETs referring originally to a reduction of threshold voltage of the transistor at higher drain voltages. In a classic planar field-effect transistor with a long channel, the bo ...

(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). 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 V_th initially is reduced as channel length increases, but approaches a constant value independent of channel length for large enough lengths.

References

{{DEFAULTSORT:Reverse Short-Channel Effect MOSFETs Transistor modeling

See also

References