Influence Of Non-uniform Interface Charges On The Threshold Voltage Of PMOS And TFT

With the development of semiconductor technology,devices are increasingly miniaturized,and the Negative Bias Temperature Instability(NBTI)effect of p MOS devices are being aggravated,which is the main factor affecting the life of the device and related circuits,and thus has drawn renewed attention.However,in the actual physical experiments,the hot carrier effect,the NBTI effect and other degradation often occur at the same time,so it is difficult to carry out the independent research of the NBTI effect.Meanwhile,as the size of the device becomes smaller and smaller,the difficulty of experimental measurement increases.Therefore,the traditional experimental method shows shortcomings both in economy and technology,and the use of numerical simulation software in related research is particularly important.In practice,the drain of the device will be biased,and the resulting degradation is also known as the biased DB-NBTI(Drain Bias NBTI)effect.Unlike the traditional NBTI effect,the interface charge generated by its degradation is non-uniformly distributed in the channel direction.The effect of this non-uniformly distributed interface charge on the device has not yet been fully studied.In this paper,the threshold voltage degradation characteristics of non-uniform interface charge p MOS devices and p-channel polysilicon thin film transistor(TFT)were investigated by means of device numerical simulation software and NBTI degradation model.The main contents are summarized as followings:(1)Using the numerical simulation software Genius-Open,the threshold voltage of the device and the charge sharing model are fitted in the case of channel variation.The influence of uniform interface charge on the threshold voltage of p MOS device is studied.The reasonableness of constructing the device model,the selection of the degraded model and the method of extracting threshold voltage are clarified.(2)By dividing the gate and filling the interface charge with different concentrations,the method of introducing the non-uniform interface charge is simulated.The influence of the different position of interface charges on the threshold voltage of p MOS is studied.And the(3)mechanism of the threshold voltage variation is explored by studying the surface potential of the device under different conditions.(4)The interfacial charges distributed in continuous segments are introduced,and the influence of different charge concentration and distribution length on the device threshold voltage is studied.Meanwhile,the interaction between the interfacial charges at different positions is explored.(5)Finally,combined with the polysilicon trap distribution model,this paper studied the p-channel TFT threshold voltage by the numerical simulation of commercial software Medici,including discussion on occasions both considering and not considering the trap model.The position,concentration and continuous distribution length of the interface charge are set respectively,and the influence of them on the TFT threshold voltage is analyzed.Compared with the previous work,the change of the time stress is introduced in this paper,and the degenerate characteristics of the model are considered in the case of the drain model with the bias voltage,which laid a foundation for further theoretical study of NBTI degradation in TFT under actual conditions.