Investigation Of Negative Capacitance Field Effect Transistors Based On Ferroelectric Gate Dielectric Layer

Since the world's first germanium transistor and integrated circuit(IC)invented,Microelectronic Technology had laid the material foundation for the information era.ICs`scaling realizes the advantages such as cheaper cost,better performance,and lower power consumption.With feature size scaling down and integration continues to increase,the key to VLSI's further scaling is to solve the power consumption problem.So researchers created many kinds of novel devices to reduce power consumption by means of changing carrier transport mechanism,such as TFET,I-MOS,Spin-MOSFET etc.Those devices have a common problem that is incompatible with traditional silicon-based CMOS process.It is hardly for the Industry to develop a brand new process flow instead the old one because of expensive cost.The other novel devices are to improve gate-to-channel`s control ability,such Fin FET,Nanowire,NCFET etc.The NCFET has the advantages of ultra-low subthreshold swing,better electrical performance,and compatibility with CMOS process,which has made NCFETs a research hotspot in recent years,and it has great application prospects at sub-10 nm process nodes.This paper investigates electrical characteristics of negative capacitance field effect transistors based on ferroelectric gate dielectric layer in terms of simulation and experiment.For the simulation,this paper builds the analytical model of NCFET with DG-MFIS structure,derives the source-drain current I_ds formula of NCFET,and then obtains the simulation results of NCFETs electrical characteristics.The simulation results are as follows:1)Within a certain range,the increase in the thickness of the ferroelectric layer optimizes the capacitance matching,which plays a key role in improving the performance of the NCFET device and reducing the supply voltage of the chip.When the thickness of the ferroelectric layer exceeds a certain degree,an increase in the thickness of the ferroelectric layer will lead to gate capacitance mismatching and cause the problem of unstable device switching.2)The effects of the remanent polarization P_r and the coercive electric field E_c on the electrical characteristics of the NCFETs are negative correlation and positive correlation,respectively.The reason is essentially to affect the capacitance matching by changing the ferroelectric layer capacitance.3)Comparing the electrical characteristics of NCFETs with MFIS structure and NCFETs with MFS structure,it is found that MFS-NCFETs can achieve higher-quality capacitance matching with thinner ferroelectric layers compared to MFIS-NCFETs.However,the process requirements for achieving non-hysteresis MFS-NCFETs will be higher,because MFS-NECFETs are more likely to occur hysteresis.For the experiment,NCFETs based on Hf Zr O_x ferroelectric material gate dielectric layer were prepared by post-gate process.The experiment results are as follows:1)By testing the basic electrical characteristics of NCFETs through experiments,a clear capacitance spike is obtained in the capacitance characteristics,which proves the existence of negative capacitance effect.And it is found that the capacitance spikes decayed with increasing Gate voltage signal frequency.2)Comparing the electrical characteristics of NCFETs and the control devices,it is found that the NCFET annealed at 450?has a 55.2%improvement in I_onof transfer characteristic,and the subthreshold swing of the NCFET is steeper.The smallest SS of NCFET is about 80 m V/decade lower than that of the control device.So in the full voltage V_g test range,the electrical characteristics of the NCFETs are better than the control device.3)The effects of annealing temperature on the transfer characteristic,subthreshold characteristic,and output characteristic of NCFETs are investigated.As a result,it is found that the effects of annealing temperature on the three characteristics are consistent.When the annealing temperature is low,such as 400?,the insufficient crystallization of the ferroelectrics may cause the threshold voltage to drift,which attenuates the electrical characteristics of the NCFETs.As the annealing temperature gradually increases,the degree of ferroelectric crystallization increases,which improved ferroelectricity.So the degree of capacitance matching is gradually enhanced,and the electrical characteristics of NCFETs are optimized.When the annealing temperature is higher than a critical value,such as 550?,the degree of capacitance matching is weakened due to the increase of the P_r,and the electrical characteristics of the NCFETs begin to degrade.