Investigation Of Synergistic Effects Of Single Event Effect And Total Ionizing Dose On SRAMs And FRAMs

The very large scale integration circuits?VLSI?such as static random access memory?SRAM?and ferroelectric random access memory?FRAM?are widely used in spacecrafts.SRAM has the advantages of high operating speed and low power consumption.FRAM is a type of nonvolatile memory that has a high single event upset resistance owning to the unique properties of ferroelectric materials.With the progress of CMOS technology,the operation voltage,as well as the critical charge of single event effects of SRAMs and FRAMs decreases.Compared with micron-scale devices,there are some new phenomena observed in studies of single event effects and total dose effects of nano-scale SRAMs and FRAMs,which are serious threats to the safety and reliability of spacecrafts.In this paper,90 nm and 65 nm commercial SRAMs and 130 nm commercial FRAMs were irradiated using different types of heavy ions provided by the Heavy Ion Research Facility in Lanzhou?HIRFL?and ⁶⁰Co?rays provided by the Xinjiang Technical Institute of Physics and Chemistry?XTIPC?.With the combination of experiments and TCAD simulations,the degradation of electrical parameters induced by?rays as well as the single event effects induced by different kind of heavy ions on nano-scale SRAMs and FRAMs were investigated.The synergistic effect of total ionizing dose and single event effect on SRAMs and FRAMs were investigated.The main results are as follows:Firstly,the influence of total ionizing dose on electrical parameters of commercial SRAMs and FRAMs was investigated.The standby power supply currents of devices under test were monitored during irradiation,and the mechanism of the increase of standby power supply currents was analyzed.After irradiation,the standby power supply current of all devices increased obviously.Trapped charges induced by?rays in shallow trench isolation led to the increase of off-state current of NMOS transistors,which resulted in the increase of standby power supply current.For SRAMs,the on-state PMOS transistors and the off-state NMOS transistors in memory cells formed the leakage paths.While for FRAMs,the degradation of peripheral CMOS circuits was the main reason of the increase of standby power supply current.Secondly,the single event effects were studied using different kinds of heavy ions with different linear energy transfer?LET?before and after?ray irradiation.Results showed that the single event upset?SEU?cross section of SRAMs increased,but the event cross section of FRAMs decreased after irradiation.No memory pattern dependency was observed.For 90 nm SRAMs,the threshold LET is about 0.5MeV·cm²/mg,and was not influenced by?ray irradiation.The threshold voltage shifts and the increase of off-state leakage current of transistors induced by?ray irradiation led to the alter of single event effect hardness of SRAMs.The saturation cross section increased from 9.0?10^-8 cm²/bit to 1.3?10^-7 cm²/bit,which was an increase of about44%.Besides,there were more multiple-bit upsets?MBUs?after?ray irradiation at the same value of LET.For FRAMs,errors were located in the peripheral CMOS circuits.After?ray irradiation,the threshold voltage shifts of MOS transistors and the decrease of switching voltage of inverters led to about 40%to 70%decrease of the event cross section detected in dynamic mode tests.Finally,TCAD simulations were performed to investigate the influence of heavy ions on 1T/1C cells of FRAMs.Results showed that when a heavy ion struck the NMOS transistor of the 1T/1C cell,the electric potential of the bottom surface of the ferroelectric capacitor decreased.The incident ion generated a difference of electric potential of about 0.7 V,which was about 25%of the operation voltage of this FRAM.With the progress of technology,the operation voltage of FRAMs decreases.The threat of heavy ions on the reliability of FRAM cells should be taken into account.