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transconductance [9]. Ghosh
et. al.
have shown by analytical modelling that dual
metal gate stack surrounding gate MOSFET shows superior performance than
conventional MOSFET [10]. Kasturi
et. al.
have reported that dual material gate
silicon on Nothing (SON) MOSFET gives higher early voltage and reduced drain
conductance thereby improving analog performance of the device [11]. They have
also showed that the analog performance can be improved by dual material double-
layer gate stack SON architecture [12]. The performance and stability of a transistor
can be further improved using double-stacked active layers with proper material as
gate oxide [13]. Low
et.al
reported that a dual material gate nanowire JLT offers
improved transconductance and unity gain frequency compared to SMG JLT [7].
Combining the advantages of dual material gate along with double-layer gate stack,
we propose a junctionless architecture called DM-DGS DGJLT in this paper. We
have studied the analog circuit performance parameters viz. transconductance (G
m
),
transconductance to drain current ratio (G
m
/I
D
), early voltage (V
EA
), output resistance
(R
O
), intrinsic gain (G
m
R
O
), and cut-off frequency (f
T
) with the help of extensive
device simulations.
2
Device Structure and Simulation
Fig. 1.
Crosssectional view of n-type DM-DGS junctionless symmetric double-gate
transistor (DGJLT)
The device structure for an n-type symmetric DM-DGS DGJLT is shown in Fig. 1.
The operation of DGJLT is explained in [16] and [17]. An n-channel device have an
N
+
- N
+
-N
+
structure and uniform doping in the source, channel and drain region. In
this work, P+ polysilicon gate is used. A dual material gate (DMG) DGJLT has two
metal gates, denoted by M1 and M2, with different workfunction (W), 5.2 eV and 4.7
eV respectively. The first lateral gate is called control gate and the second one, the
screening gate. Due to higher workfunction, the threshold voltage of M1, V
T(M1)
is
greater than V
T(M2)
. Single gate material (SMG) has a workfunction of 5.2 eV. Long
et. al.
reported that the relation between threshold voltage (V
T
) and workfunction of
the two gate materials can be expressed as [9]
