Investigation Of Single Event Effects Induced By Heavy Ions In Micro/Nano SRAM Devices

With the increasing demand of the national space exploration mission,single event effects(SEEs)of aerospace components induced by heavy ions have become the key fac-tor of the reliability of the spacecraft in orbit.In recent years,with the rapid develop-ment of semiconductor technology and the feature size of SRAM devices going into the Micro/Nano scale,the reduction of voltage and capacitance lead to the critical charge de-creased steadily in the storage node.It makes the SEEs of Micro/Nano SRAM devices induced by single heavy ion become more and more sensitive,which seriously threatens the reliability of the spacecraft in orbit.In this paper,devices under test(DUTs)were irradiated by heavy ions provided by the Heavy Ion Research Facility in Lanzhou(HIRFL)cyclotrons.The effects of heavy ion parameters on the SEEs of the Micro/Nano SRAM devices were investigated,which included the effects of heavy ions LET on the single event upset(SEU)sensitivity in the circuit-level hardened SOI/SRAM,the effects of heavy ions energy on the multiple-bit upset(MBU)in the system-level hardened bulk/SRAM and the effects of heavy ions range on the SEU cross-section in the Micro/Nano SRAM devices.The microscopic mechanism of heavy ion parameters affecting the Micro/Nano SRAM devices was revealed.The aim was to provide some basic theoretical guidance and technical support for the radiation hardened and SEEs testing technology of Micro/Nano SRAM devices.Firstly,the effects of heavy ions LET on the SEU susceptibility of unhardened 6T/SRAM and hardened ADE/SRAM with the 0.35 ?m SOI technology was studied.The curve of ?-LET was measured and the critical charge and the saturated cross-section was calculated.The reasons of the difference in the critical charge and the saturated cross-section were analyzed.ADE refered to add a transisitor in the feedback of the conven-tional 6T/SRAM to increase the critical charge.The experimental results indicated that the ADE/SRAM showed the better tolerance of SEU comparing the conventional 6T/SRAM.In detail,it was reflected in,not only increasing the LET threshold from 15.7 MeV·cm2/mg to 28.3 MeV·cm2/mg,but also decreasing the limiting upset cross-section from 4.4 ?m2/bit to 1.6 ?m2/bit.Besides,the resistance of ADE(21 k?)had been gained by measuring the ratio of the limiting upset cross-section of the SEU hardened ADE/SRAM(?ADE)and ?6T of the unhardened 6T/SRAM.Additional,the different sensitivities of 0 ?1 and 1?0 transition had been observed in the ADE/SRAM memory cell.The experimental results showed that it was related to the feedback time(tFB)and recovery time(tREC)of the feed-back loop in the memory cell.When tFB>tREC,an SEU was difficult to occur.However,when tFB<tREC,the storage value was easy to upset.At last,a laser experiment was per-formed to verify the theoretical explanation.In conclusion,it is worth pointing out that the ADE element has a significant effect on improving the device tolerance against SEU.Secondly,the characteristics of heavy ion energy on MBU in the system-level hard-ened bulk/SRAM were studied.The sensitivity of "fake MBU"(FMBU)was investigated in a 65 nm technology SRAM with ECC.The experimental results showed that the radius of the charge tracks produced by the Bi ion covered several sensitive cells,which made the Hamming code failure and reduced the performance of ECC.The reason of inducing the FMBU was analyzed by means of probability theory.The experimental results provided a theoretical guidance and help for the FMBU and MCU data analyzing,which improved and perfected the basic rules extracting MCU from the test data.In addition,the results showed that the performance of hamming encoding was not ideal in Nano scale SRAM.In the future of aerospace applications,it is necessary to consider more advanced algorithms to against SEU.Finally,the threshold ionization range of SOI/SRAMs with four kinds of feature size,namely 0.5 ?m,0.35 ?m,0.18 ?m and 0.13 ?m,was studied using Kr and Bi ions provided by HIRFL.The experimental results showed that the threshold ion range was closely re-lated to the device type and the ion species.It was found that the energy deposition of heavy ions in the sensitive region of the devices was the key factor affecting the SEU cross-section.The threshold ion range of those devices was calculated by the "worst case"formula,and the results of calculation were compared with those of experimental.It was found that the formula could not accurately describe the threshold ion range.Some calcu-lations were greater than the experimental value,while others were less than the experi-mental values.There was a big deviation between the calculated and experimental value.For 0.18 ?m ADE/SRAM,the calculated value was about double compared with that of experimental.These results showed that the threshold ion range was a very important con-sideration to estimate the error rate of devices on orbit.Moreover,there is an urgent need to propose a more accurate model to describe and calculate the threshold ion range.