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

摘要

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 $hbox{p}^{+}$ and $ hbox{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 $muhbox{m}$. Various dc characteristics that directly affect analog circuit performances are evaluated from the fabricated devices: $I$–$V$ characteristics, drain-induced barrier lowering, transconductance $(g_{m})$, drain conductance $(g_{rm ds} = hbox{1}/r_{rm out})$, intrinsic gain $(A_{V} = g_{m}/g_{rm ds})$, and Early voltage $(V_{rm EA} = I_{D}/g_{rm ds})$. From the measurements, the DWFG devices always show improved characteristics over conventional devices ($ hbox{n}^{+}$-doped poly-Si gate). The DWFG device with the shortest $hbox{p}^{+}$ poly-Si gate length $(p = hbox{0.4/0.6})$ shows better $g_{m}$ characteristics than other D- FG devices. The $g_{rm ds}$ characteristics of the fabricated DWFG devices are improved as the length of the $hbox{p}^{+}$ poly-Si increases. The best $A_{V}$ and $V_{rm EA}$ are taken from the device with a p-type-doped poly-Si length of 0.7 $muhbox{m}$ $(p = hbox{0.7/0.3})$.