Research On Fully Depleted Silicon On Insulator Negative Capacitance Field Effect Transistor With Variable Ferroelectric Layer

Negative Capacitance Field Effect Transistor（NCFET）is one of the effective solutions for continuing the Moore’s Law in the“post-moore era”due to its high On/Off current ratio,low subthreshold swing and process compatibility.In order to improve the performances of the NCFET,this thesis investigates the Fully Depleted Silicon On Insulator（FDSOI）NCFET with variable ferroelectric layer by using the TCAD tool.The main contents include:（1）The new structures of FDSOI NCFET with Variable Thickness Ferroelectric Layer（VTFL）are proposed.The new structures are the Stepped Thickness Ferroelectric Layer（STFL）FDSOI NCFET and Linear Thickness Ferroelectric Layer（LTFL）FDSOI NCFET respectively.The non-uniform voltage amplification,polarization inversion,channel surface electric field,output characteristics,and transfer characteristics in N-type and P-type STFL/LTFL FDSOI NCFET are studied.Besides,the influences of different kind of ferroelectric materials on the performances are also discussed.Compared with the traditional FDSOI NCFET with a uniform-thickness ferroelectric layer,the non-uniform voltage amplification effect is obtained in the FDSOI NCFET with VTFL,and the voltage is amplified from 1.3 times to 3.3 times.The Ion/Ioff ratio of the NCFET is increased from 1.3×10¹⁰ to 5.2×10¹²,the saturation current of the conventional NCFET is amplified by 6.2 times,and the subthreshold swing is reduced from 62 m V/dec to 42 m V/dec.Which means that the performances of FDSOI NCFET are significantly improved.Meanwhile,the results show that different ferroelectric materials are also essential factors to affect the performance of FDSOI NCFET with VTFL.（2）A new structure of FDSOI NCFET with Variable Material Ferroelectric Layer（VMFL）is proposed.The ferroelectric layer has two regions of different ferroelectric parameters.The non-uniform voltage amplification,polarization inversion,channel surface electric field,output characteristics,and transfer characteristics are studied from the perspectives of ferroelectric parametersαandβ,respectively.Besides,the influences of different thickness VMFL on the performances are also studied.Compared with the traditional FDSOI NCFET,better non-uniform voltage amplification effect and performance of FDSOI NCFET can be obtained with the increasing of ferroelectric parameter|α|,but worse with the increasing of ferroelectric parameterβ.The results for the VMFL FDSOI NCFET show that compared with conventional NCFET,the maximum voltage amplification is increased from 1.27 times to 2.49 times and the minimum is decreased to1.19 times,the maximum Ion/Ioff ratio is increased from 1.2×10¹⁰ to 2.6×10¹¹ and the minimum is decreased to 7.35×10⁹,the maximum saturation current is up to 1.53 times and the minimum is down to 0.87 times,and the minimum subthreshold swing is reduced from 62 m V/dec to 56 m V/dec and the maximum is 62.3 m V/dec.The effect of ferroelectric material parameters on performances is analyzed qualitatively to guide the optimal design of FDSOI NCFET.