For SNW 2018 in Honolulu, GTS scientists investigated the effectiveness of the performance boost provided through use of ferro-electric materials in negative-capacitance FETs (NC FETs) using a hybrid TCAD/compact modeling approach. They show that, in a practical device, the performance boost is dominated by parasitic capacitances. Studying the impact of the doping profile on NCFET performance shows that tight control of the doping is required to maintain the boost in highly scaled devices.
The left image above shows the polarization curve of a ferro-electric material with remanent polarization of 20μC/cm2 and coercive field of 1MV/cm computed from a third-order Landau-Khalatnikov model; a voltage-driven sweep (blue curve) results in a polarization hysteresis while a charge-driven sweep recovers the negative differential susceptibility region within the hysteresis.
The right image shows the transfer characteristics for a reference DGMOS (without ferro-electric, orange) and NCFET at VDS = 50 mV (linear) and 0.7 V (saturated) respectively; in both cases the doping has an underlap of 2nm and a σ of 1nm; the ferroelectric material in the gate boosts the subthreshold-slope from 64 mV/dec to 57 mV/dec, which is below the thermal limit; the NCFET also shows negative DIBL (the linear and saturated curves cross) and a significantly higher ION.
GTS will take a key role in a joint research project with IuE/TU Wien starting in October 2018. The goals of the project are to develop a prototype of a 3D TCAD model for ferroelectric materials (based on an LGDK approach), as well as an additional set of 3 physically less complex models. The final model will have been validated against experimental results and a database of material parameters for common FE materials developed. Furthermore, it will be harnessed for scientific study of the ultimate scaling limits of FeRAM and NCFET devices.
Short-named TCAD-NCFET, this FFG research grant‘s full title is "Technology Computer Aided Design of Negative Capacitance and Ferro-Electric Transistors".