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Where, C GS and C GD are gate-to-source and gate-to-drain capacitances respectively.
Fig. 7 shows the variation of f T with V GS for V DS =1V. All the capacitances are
extracted from the small-signal ac device simulations at a frequency of 1 MHz. At
lower V GS , till 0.45 V, the f T is almost same for all the devices due to almost same
values of transconductance. The DM-DGS and DMG DGJLT posses almost same
value of f T for V GS > ~ 0.45 V. However, SMG DGJLT presents lower f T compared to
other two devices at higher gate voltage.
The presented I D -V GS characteristics for SMG DGJLT are calibrated with Duarte's
results [16] as shown in Fig. 8 for L = 1 ʼ m, T si = 10 nm, T ox = 7 nm, N ch = 1×10 19 cm -
3
, L S =L D = 10 nm, V DS = 50 mV at room temperature.
10 2
10 1
10 0
10 -1
10 -2
10 -3
Our Simulation for DGJLT
Duarte's Simulation
10 -4
10 -5
10 -6
10 -7
10 -8
10 -9
10 -10
-1.5
-1.0
-0.5
0.0
0.5
1.0
Gate Voltage, V GS (V)
Fig. 8. Calibration of our simulation results for DGJLT with Duarte's simulation. I D -V GS
characteristics at L = 1 ʼm, T si = 10 nm, T ox = 7 nm, N si = 1×10 19 cm -3 , L S /L D = 10 nm, V DS = 50 mV
4
Conclusion
A dual material double-layer gate stack (DM-DGS) structure was incorporated in
symmetric double-gate junctionless transistor (DGJLT), forming DM-DGS DGJLT.
The device characteristics for analog applications were investigated and fair
comparisons with DMG and SMG DGJLT were performed by setting the threshold
voltage same for all the devices. DM-DGS offered superior transconductance, early
voltage and intrinsic gain compared to DMG and SMG DGJLT. However, SMG
DGJLT has higher G m /I D value as compared to the other two devices. Unity gain cut-
off frequency was almost similar for DM-DGS and DMG DGJLT architecture at
higher gate voltage. Using as germanium as substrate material, the conductivity can
further be improved. The ON-state to OFF-state current ratio can be increased by
incorporating high-k spacers on DM-DGS structure.
 
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