The Research Of NBTI Effect Mechanism And Modeling In Nanometer MOS Devices

Negative Bias Temperature Instability(NBTI)is mainly caused by the generation of interface defects and hole trapping in gate insulator traps.NBTI effect leads to the shifts in device parameters such as threshold voltage,linear and saturation drain currents,transconductance,subthreshold slope,and thus degrades the performance of analog,digital and memory circuits and shortens the lifetime of devices and circuits as well.NBTI is the critical physical effect for nanometer CMOS devices.Detailed study of NBTI has high academic value and practical value for integrated circuit design.Based on the Reaction-Diffusion theory and classical models,we propose compact analytical models to predict the shift in threshold voltage caused by the NBTI effect for the conditions under DC and low frequency AC stresses.The proposed models have been validated by experimental data.The major content in this thesis consists three parts as follows:1.An improved compact analytical model is proposed and is able to describle longterm NBTI recovery behavior precisely under DC stress.The fast recovery of interface traps as well as the slowing down diffusivity and locking effect of H2 have been seriously involved in modeling work.Considering these three factors,this thesis proposes an improved analytical model,which overcomes the shortage of conventional models and has been validated by 40-nm process experimental data.The achievements are published in Microelectronics Reliability(Vol.75(2017)20-26)which is retrieved by SCI.2.With experimental data in 40-nm process,this thesis provides detailed study of NBTI characteristics and critical parameters.The threshold voltage degradation and the end-of-life of stressed device under different stress voltages and temperatures have been experimentally studied,and then the time exponent,Arrhenius activation energy and field acceleration have been thoroughly investigated.Moreover,the long-term recovery of NBTI effect has been described by the comprehensive models.The achievements are published in Chinese Physics B(Vol.26,No.10(2017)108503)which is retrieved by SCI.3.Focused on low frequency AC NBTI,this thesis proposes analytical iterative and non-iterative models for predicting the time evolution of threshold voltage degradation.With Reaction-Diffusion theory and considering H2 locking effect and electron fast capture/emission in interface traps,we derive iterative expressions,which is the ratio of degradation in real time to that at the end of first AC stress.In long-term degradation,the iterative expression could be simplified as recursion expression and then the non-iterative model is developed.This novel model is able to describe the NBTI degradation behaviors under low frequency AC stress.