N-Channel Dual-Workfunction-Gate MOSFET for Analog Circuit Applications

Analog behaviors of n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with dual-workfunction-gate (DWFG) structure are presented. The gate of the n-channel DWFG MOSFET is composed of p
⁺
and n
⁺
poly-Si along the channel carrier flowing direction. To investigate the impact of the proportional length of p- and n-type-doped poly-Si on analog behaviors, they are varied within a total physical gate length of 1.0 μm. Various dc characteristics that directly affect analog circuit performances are evaluated from the fabricated devices:
I
-
V
characteristics, drain-induced barrier lowering, transconductance (
gm
), drain conductance (
g
_ds
= 1/
r
_out
), intrinsic gain (
AV
=
gm
/
g
_ds
), and Early voltage (
V
_EA
=
ID
/
g
_ds
). From the measurements, the DWFG devices always show improved characteristics over conventional devices (n
⁺
-doped poly-Si gate). The DWFG device with the shortest p
⁺
poly-Si gate length (
p
/
n
= 0.4/0.6) shows better
gm
characteristics than other DWFG devices. The
g
_ds
characteristics of the fabricated DWFG devices are improved as the length of the p
⁺
poly-Si increases. The best
AV
and
V
_EA
are taken from the device with a p-type-doped poly-Si length of 0.7 μm (
p
/
n
= 0.7/0.3).