Information Technology Reference
In-Depth Information
Fig. 2.
2-D Schematic diagram of graded doping profile used for simulations
Source/Drain (HDD) and abrupt box shaped Source/Drain extensions have been
defined analytically. Device cross sections along the length and width of the fin are
illustrated schematically in Fig. 1(a) and Fig. 1(b) respectively.
Fig.2 portrays the doping profile selected for graded doping simulations. The channel
is partitioned into 3 regions of equal length. Simulations were carried out by assigning
heavy doping near to source and gradually reducing to drain and vice versa. The results
of these simulations were compared with those of constant channel doping of 1E+16.
Mobility models including doping dependence, high-field saturation (velocity
saturation), and transverse field dependence are specified for all the simulations.
'
BandGapNarrowing (OldSlotboom)
' is the silicon bandgap narrowing model which
is employed for determining the intrinsic carrier concentration [10]. Drift-Diffusion
equations coupled with Continuity and Poisson's equations were solved for the device
structure shown in Fig.1, using Sentaurus Device from the TCAD package.
3
Results and Discussion
3.1
Impact of Fin Width
Width of the fin has been varied from 10nm to 16nm in steps of 2nm, keeping all the
other device parameters constant. For the simulations in this section, undoped channel
is selected. As expected the devices with lower fin widths are exhibiting reduced
SCEs, but reducing the fin width increases the S/D resistance, which as shown in
Fig. 3, leads to the reduction of normalized drain current.
It can be noted from Fig. 4 that the ratio of I
on
to
I
off
is decreasing as we increase
the fin width. When the width of fin is increased from 10nm to 16nm, approximately
two orders of decrease in magnitude for
I
on
/I
off
have been observed and it will affect
the performance of FinFET for analog applications. Threshold voltage was also
decreasing as we increase the fin width. Similar variations for threshold voltage is
demonstrated in [15] for higher fin width devices.
