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-Vcharacteristics, drain-induced barrier lowering, transconductance (gm), drain conductance (gds= 1/rout), intrinsic gain (AV=gm/gds), and Early voltage (VEA=ID/gds). 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 bettergmcharacteristics than other DWFG devices. Thegdscharacteristics of the fabricated DWFG devices are improved as the length of the p+poly-Si increases. The bestAVandVEAare taken from the device with a p-type-doped poly-Si length of 0.7 μm (p/n= 0.7/0.3).