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).