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ΔV
T
= S ΔW (1)
S=1 for silicon MOSFET. We define L
M1
and L
M2
as channel lengths for metal M1
and M2 respectively; and L = L
M1
+ L
M2
is the total channel length. The gate length
ratio of the two metal gates and their workfunction difference affect the device
characterises significantly [7]-[9], [11]-[12]. Recently, Lou
et. al.
have reported
that
in a DMG JLT,
out of different combinations of L
M1
and L
M2
; L
M1
/ L =1/2 and work
function difference ʴW= 0.5 gives overall best characteristics of the device [7]. In this
work, L
M1
:L
M2
= 20 nm: 20 nm is considered for both DM-DGS and DMG DGJLT.
For DMG and SMG DGJLT, SiO
2
is used as a gate oxide material having thickness
(T
ox
) of 2 nm. For DM-DGS DGJLT, SiO
2
(oxide thickness = 1 nm) is stacked with
high-k gate dielectric material (HfO
2
) of equivalent oxide thickness (EOT) of 1 nm.
All three devices namely, DM-DGS, DMG and SMG are optimized by adjusting
channel doping concentration (N
ch
) values such that each has a threshold voltage (V
T
)
of 0.31 V. Threshold voltage is defined as the gate voltage corresponding to constant
drain current of 10
-7
A at a drain voltage of 50 mV. The source and drain extensions
(L
S
and L
D
) are taken as 10 nm. The process and device parameters used in this paper
are summarised in Table 1.
Table 1.
Process/Device Parameters
Parameter
SMG
DMG
DM-DGS
L (nm)
40
40
40
L
M1
:L
M2
(nm)
—
20:20
20:20
W
M1
:W
M2
(eV)
5.2 : —
5.2 : 4.7
5.2 : 4.7
N
ch
(cm
-3
)
9.6 E+18
7.85 E+18
8 E+18
T
ox
(nm) (EOT)
2 (SiO
2
)
2 (SiO
2
)
2(SiO
2
:1nm,
HfO
2
:1nm)
T
si
(nm)
8
8
8
Electrical characteristics for the devices are simulated using 2D ATLAS device
simulator [18] with default parameter coefficients. For all simulations, uniform
doping concentration throughout the channel and source/drain regions is assumed.
The simulations are carried out using two carrier scheme, Fermi-Dirac model without
impact ionization, doping concentration-dependent carrier mobility and electric field-
dependent carrier model. Band gap narrowing model is included. Shockley-Read-Hall
(SRH) recombination/ generation are employed in the simulation to account for
leakage currents. The density gradient model is utilized to account for quantum
mechanical effects.
