Study On Single-event Effect Of 28nm FDSOI Transistor And Cell Circuit

With the scaling down of technology,the gate oxide and buried oxide layer(BOX)of SOI devices become thinner and the influence of Single Event Effect(SEE)becomes critical in SOI device.Fully depleted silicon-on-insulator(FDSOI)devices have attracted much attention in radiation applications because of their extremely thin top silicon film,which can reduce the volume of charge generation.However,when the technology node is scaled down to 28 nm or below,the parasitic bipolar amplification effect in FDSOI devices is further enhanced,and the tolerance to SEE decreases.Single event irradiation poses a great threat to the reliability of device.Therefore,it is necessary to study the influence of single event irradiation on ultra-thin FDSOI devices,and clarify the rules and related physical mechanism of SEE in FDSOI devices.The main contribution of this paper is as follows:Firstly,the Single Event Transient(SET)and charge collection mechanism of 28 nm FDSOI devices are simulated by using Sentaurus TCAD.The SET of 28 nm fdsoi device is studied when the LET value,incident position and incident angle of heavy ion are different.The results indicate that the single event transient current,collected charge and bipolar gain increase with the increase of LET value.When the value of LET is too large,the carrier recombination increases.The bipolar gain and the impact ionization are considerably reduced with the increase of LET.It is found that the most sensitive region in28 nm FDSOI device is the lightly doped drain region near the gate.The larger the incident angle is,the more active regions the particles pass through and the more collected charges are generated.An in-depth analysis shows that the bipolar amplification effect is dominant in the charge collection of 28 nm FDSOI devices,which is the decisive factor for the location of SET sensitive region.On this basis,the effects of gate work function,back-plane layer and the thickness of BOX on SET are further studied.It is found that increasing the Work Function can reduce the SET collected charge.When the incident angle is large and the heavy ion funnels through the drain,the lightly doped drain region,and the body at same time,this theory is no longer valid.The polymeric metal-gate must be chosen carefully for avoiding or minimizing this phenomenon.Comparing the collected charge and bipolar amplification of thick BOX device and thin BOX device with back-plane layer,we found that adding heavily doped ground plane layer under the thin BOX structure can reduce the device sensitivity to SET.Finally,the Single Event Upset effect(SEU)of inverter and SRAM cell based on 28 nm FDSOI is studied by 3D TCAD simulation using Mixed-mode technique,and the performance of SEU hardened circuit is verified.The output of the inverter has a temporary disturbance under single event irradiation,and the amplitude of the disturbance increases with the increase of LET.The SEU hardened inverter is realized by reducing the voltage between the source and drain of the pull-down transistor.When SRAM cell is impacted by heavy ion,the storage level will flip if the collected charge of the node exceeds the critical charge.By comparing the threshold LETs of different incident positions,it is found that the SRAM cell is more susceptible to SEU when heavy ions impact on the lightly doped drain region.Compared with normal incidence,larger incidence angle has more influence on SRAM cell.Finally,it is found that applying reverse bias to the substrate of FDSOI devices can reduce the sensitivity of SRAM cells to single-event irradiation.The reliability of SRAM to SEU can be enhanced by applying reverse substrate bias.