Study Of Heavy Ion Irradiation Mechanism On SOI FinFET And SEU On SRAM Cell

With the scaling down of conventional planar CMOS devices,the negative impacts of short channel effects,charge sharing and the degenerate of subthreshold character to the electrical behaviors cannot be ignored.As process technology continued to scale down beyond 20 nm,SOI Fin FET structure has become the most promising alternative to replace conventional planar technology.Compared with conventional technology,the low power application,highly integrated,excellent control of the gate and high-performance make SOI Fin FET unmatchable.SOI structures show the advantage of reducing the sensitive volume in the active area of structure,and their hardness against transient effects induced by heavy-ion irradiation is promising.In this work,the major contributions are outlined as follows:Firstly,all the studies in this paper are done by using Sentaurus TCAD.The 3-D structure of 28 nm SOI Fin FET generated from Sentaurus Device Editor has been simulated with different drain biases,ion track lengths,LET values,ion track locations and ion track directions,respectively,to investigate the electrical behavior trends of SOI Fin FET under heavy-ion irradiation.Then,the impact ionization rate,SRH recombination rate,the bipolar amplification and the potential in channel are particularly investigated to explain the transient current and charge collection mechanisms.The results of simulations indicate that the ion strike creates amounts of electron-hole pairs in the device,which induces the significantly charge deposited in channel,resulting in the potential in channel raised and parasitic bipolar transistor turned on.However,when the ion generated carriers density is high enough to collapse the electric field at the channel-to-drain junction and connect the source to the drain,the transistor gain and the impact ionization are considerably reduced or does not exist any longer.Therefore,increasing drain bias,ion track length and LET value,induces consequently the increase of the collected charge and drain current at the drain electrode.And depending on the result of simulation,it is observed that the channel-to-drain junction is the most sensitive volume in SOI Fin FET.As the ion strike track getting close to the channel-to-drain junction region,the drain current and the total collected charge are found to increase,obviously.Besides,the results of simulation also present that the impact of electrical behavior induced by the vertical ion strike is more serious than the horizontal strike.Secondly,this paper analyzed the impact of SOI Fin FET downscaling on the sensitivity to heavy-ion irradiation.It is concluded:the drain current and charge collection are reduced when the Fin thickness and height decreases.This is probably because of the sensitive volume and the charge deposited decreasing,as well as the better control of the gates.These two mechanisms explain the decrease of the collected charge and the bipolar gain when channel thickness and height are reduced.On the contrary,the drain current and charge collection are increased when the gate length decreases.The sensitivity of SOI Fin FET structure to heavy-ion irradiation depends on gate-controlled behavior and the size of sensitive volume.In conclusion,SOI Fin FET configuration with thinner Fin thickness,lower Fin height and longer the gate length appears to be a powerful way to limit their sensitivity to single event effects.Finally,mixed level simulation of single event upset on SOI Fin FET SRAM has been performed with Sentaurus TCAD.We investigated the transient response and the sensitivity to heavy-ion irradiation with different LET values and different ion strike locations,respectively.The results of simulation show that a SEU of SRAM occurs when two parameters over their threshold values.If the collected charges and the peak of transient current at sensitive node induced by ion irradiation exceed their critical values,the radiation will induce soft error at a certain node in SRAM.Therefore,the results also show that the channel-to-drain junction of off-state N type SOI Fin FET is the SEU sensitive region.