Impact of Work Function Variation, Line-Edge Roughness, and Ferroelectric Properties Variation on Negative Capacitance FETs

Abstract

In this paper, the impacts of work function variation (WFV), line-edge roughness (LER), and ferroelectric properties variation on the threshold voltage, subthreshold swing (SS), Ion, and Ioff variations are analyzed comprehensively for negative capacitance ultra-thin body SOI MOSFETs (NCSOI) compared with SOI MOSFETs (SOI). For LER induced threshold voltage variation (σVt), NC-SOI MOSFETs exhibit smaller σVt (= 3.8 mV) than the SOI MOSFETs (σVt = 17.6 mV). For analyzing WFV of NC-SOI MOSFETs, two scenarios are considered including (I) same WFV patterns, and (II) different WFV patterns between the external and internal metal gates. Compared with SOI, NC-SOI with scenario (I) exhibits comparable WFV induced σVt (= 16.2 mV), and NC-SOI with scenario (II) exhibits larger WFV induced σVt (= 28.5 mV). In scenario (II), different WFV patterns between the internal and external gates result in VFE (voltage drop across the ferroelectric layer) variations, which increases the WFV induced σVt for NC-SOI. LER dominates energy-delay product variations (σEDP), and NC-SOI MOSFETs show smaller σEDP than SOI MOSFETs. Besides, NC-SOI MOSFETs with thicker ferroelectric layer thickness (TFE), larger coercive electric field (EC), and smaller remnant polarization (P0) show smaller LER induced σVt and σSS. Ferroelectric properties variations show negligible impact on the WFV induced σVt and σSS.

Keywords

• Line-edge roughness
• work function variation
• negative capacitance FET (NCFET)
• ferroelectric properties