Junction Design and Complementary Capacitance Matching for NCFET CMOS Logic
Negative capacitance field effect transistors (NCFETs) are modeled in this study, with an emphasis on junction design, implications of complementary logic, and device Vt menu enablement. Contrary to conventional MOSFET design, increased junction overlap is beneficial to NCFETs, provided the remnant polarization (Pr) is high enough. Combining broad junctions with complementary capacitance matching (CCM) in MFMIS (metal/ferroelectric/metal/insulator/semiconductor) NCFETs, it is shown that super-steep and non-hysteretic switching are not mutually exclusive, and that it is theoretically possible to achieve non-hysteretic sub-5 mV/dec SS over >6 decades. In a CMOS circuit, due to CCM, low-Vt pairs provide steeper subthreshold swing (SS) than high-Vt pairs. Transient power/performance is also modeled, and it is shown that a DC-optimal NCFET design, employing broad junctions, CCM, and a low-Vt NFET/PFET pair, does not translate to improved AC power/performance in unloaded circuits compared to a conventional FET reference. It is also shown that the same non-hysteretic DC design point is hysteretic in AC and may also lead to full polarization switching at higher voltages. Thus, a usable voltage window for AC NCFET operation forces a retreat from the DC-optimal design point.