Introtofinfets

The scale length of bulk MOSFET is an indication of Lg. Lg>
Dealing with Short Channel Effects in bulk MOSFET
1.Increasing body doping concentration ing halo implant
Short Effects: Subthreshold swing
Biasing a nmos in subthreshold resgion, Vgs < Vth, Vds is large enough.
Id = u Cd W/L (KT/q)^2 (exp(Vgs – Vth)/M))
Short Channel Effects:DIBL
DIBL: drain induced barrier lowering. DIBL = d(Vth)/d(Vds)
Barrier lowering increases as channel length is reduced, even at zero applied drain bias, because the source and drain form pn junction with the body, and so have associated built-in depletion layers associated with them that become significant partners in charge balance at short channel lengths, even with no reverse bias applied to increase depletion width
Conclusion
To reduce short channel effects, we need to reduce Xd(channel depletion layer thickness), Xj( Junction depletion width),Xox (oxide layer thickness under gate).
Cd is capacitance of the depletion layer under gate. M = (1 + Cd/Cox)*KT/q
Id = f(Vgs-Vth) To turn off the transistor, How much reduction of (Vgs-Vth) could lead to a small
enough Id. Subthreshold Swing S = d(Vgs)/d(log(Id)) = 2.3 KT/q( 1+ Cd/Cox) The smaller S is , the better it is. Bad Subthreshold Swing will result in higher off-state current if the Vgs applied
Introduction to FinFet
Haiying Zhao
What does FinFet look like
Gate
Source
Drain
3D view of FinFET
3D view of multi-fin FinFET
What does FinFet look like
Moore’s law and scaling theory
Ideal scaling: Reduce W,L by a factor of a Reduce the threshold voltage and supply voltage by a factor of a Increasing all of the doping levels by a (W,L,tox,VDD,VTH, etc, are scaled down by a factor a) For a ideal square-law device, Id is reduced by a, but gm and intrinsic gain Gm* ro remain the same.
to turn off the transistor is the same.
Short Channel Effects: Velocity Saturation
V = u E ( E is small enough) V = Vsat ( E is strong enough) As Vgs increases , the drain current saturates well before pinch-off occurs.
As scaling into submicron region, Short Channel effects prevent further scaling.
Short Channel Effects:DIBL
DIBL: drain induced barrier lowering. DIBL = d(Vth)/d(Vds)
Barrier lowering increases as channel length is reduced, even at zero applied drain bias, because the source and drain form pn junction with the body, and so have associated built-in depletion layers associated with them that become significant partners in charge balance at short channel lengths, even with no reverse bias applied to increase depletion width