| The non-volatile memory can store data for a long time without power supply.It is an important component of the aerospace electronic system.It undertakes the storage task of instructions,codes,state parameters and other data required for the safe operation of spacecraft.Spacecraft will face various complicated space radiation environments when operating in space orbit.A large number of high-energy particles and rays in the space radiation environments can produce space radiation effects on the non-volatile memory in the spacecraft electronic system,seriously affect the normal function of the spacecraft,and even lead to its failure.Among all radiation effects,the single event effect is the most frequent,and its threat to non-volatile memory will increase with the shrink of the feature size of non-volatile memory.Therefore,the study on the single event effect of non-volatile memory is of great significance to improve the application reliability of the aerospace electronic system.At present,the mainstream Flash non-volatile memory has characteristics of mature technology,low price and large storage capacity.Therefore,it dominates the non-volatile memory market and is also the most widely used non-volatile memory in spacecraft.Ferroelectric memory(FRAM)is a type of advanced non-volatile memory with the most successful commercial application by far.Because of its fast reading and writing speed,low power consumption and strong radiation resistance,FRAM has broad application prospects in the aerospace electronic system.Based on the mainstream Flash memory and the advanced FRAM memory,this dissertation performed both the ground irradiation test and simulation on the single event effect of non-volatile memory.The main research contents and relevant conclusions are summarized as follows:(1)The existing test guidelines for single event effect test methods pay attention to the assessment and evaluation of the spatial application and do not fully consider the data processing requirements of mechanism analysis for single event effect.To solve this problem,this dissertation presents a data processing method that uses the multidimensional sequence to represent the dynamic changes of large-scale data in the dynamic test process,by summarizing the common points of different memory test methods.The influence of the single event effect on memory is visualized based on this method.And,it can flexibly extract the data details generated by the single event effect and intuitively obtain the performance law of the single event effect in the memory.It also has the characteristics of feeding back the results of the test rapidly and displaying the data changes in real-time,which provides a basis for the mechanism analysis of the single event effect of non-volatile memory.(2)The ground irradiation test of heavy-ion induced single event effect for four kinds of Flash non-volatile memories that come from domestic and foreign with 90 nm feature size under static test was carried out.Besides,the influence of cumulative total dose effect on the single event effect sensitivity of Flash devices was discussed for the two Flash devices from domestic.The experimental results show that the SEU effects occurred in the cell array of Flash device under irradiation of heavy ion,and the SEU cross-sections of the four devices under heavy ion irradiation with different LET values were obtained.The test results of the total dose effect show that the cumulative dose will worsen the single event effect performance of the Flash cell unit.For example,for the test samples after the accumulation dose of 20 krad(Si)and 40 krad(Si),the SEU cross-section increased by 50% and 100% respectively under heavy ion irradiation with the same LET value.The analysis shows that the single event and total dose effects cause the electron leakage on the floating gate and the transistor threshold voltage drift through ionizing radiation,which leads to the bit flip.After the drift of threshold voltage caused by the total dose effect,the single event effect is easier to cause bit-flips in cell units.(3)The ground irradiation test of heavy-ion single event effect under dynamic test was carried out for the two domestic Flash non-volatile memories with 90 nm feature size.Test results show that SEFI and SEL effects occurred in the dynamic test of the DUT.Besides,under the irradiation of heavy ions with low LET value,the latch-up state propagates from several sectors to the whole device.In the mechanism analysis of SEFI,it is further divided into Bit SEFI,Column SEFI and Sector SEFI according to the behavior of the SEFI in the DUT.The analysis results show that the transient current caused by irradiation is the origin of SEFI,and the SEFI behavior in the DUT is determined by the location where the transient current is generated and collected in the circuit.The analysis results of SEL show that the SEL effect first occurred at circuits in the peripheral circuits under ion irradiation with low LET value,then propagates to more circuits with the accumulation of irradiation,resulting in the latch state in the whole DUT.In addition,a proton irradiation test was also carried out on the test samples.It was observed that the errors occurred in the device,and the analysis results showed that the phenomenon was caused by the TID rather than the SEE effect of the proton.(4)For the commercial FRAM non-volatile memory that comes from foreign with130 nm feature size,the layout scanning irradiation test of the device is carried out to obtain the distribution of the single event effect sensitive area of FRAM memory using the pulsed laser and heavy-ion microbeam.Besides,the reverse engineering analysis of part of the layout is carried out to ascertain the single event effect sensitive element in the DUT.The test results of pulsed laser microbeam and heavy-ion microbeam show that SEU,SEFI and SEL occurred in the FRAM device under irradiation.These SEEs all come from the peripheral circuit of the device,and the cell array of the FRAM device is immune to the SEEs.The results of reverse engineering for the SEE sensitive region show that the N-well resistor is the most sensitive component in the peripheral circuit of the DUT.The single event effect will produce transient current in the N-well resistor,resulting in the failure of write-back operation at the storage unit and the change of storage medium polarization state.(5)Aiming at the single event effect sensitive component of FRAM non-volatile memory(N-well resistor),the single event effect simulation research is carried out based on the TCAD Sentaurus tool,and the single event effect mechanism of N-well resistor and the influence of different element parameters on its single event effect are discussed.The simulation results show that the transient current will appear in the Nwell resistor after the incident of heavy ions.Shortening the length of the N-well resistor and increasing the working voltage can reduce the duration and peak value of transient current.When the output terminal of N-well resistor is connected to the ground,the component is in the worst working condition for singe event effect.The results of mechanism analysis show that the impedance of the N-well resistor comes from the space charge region formed between the N well and the P substrate under reverse bias,and the high concentration carrier produced by the single event effect will neutralize the space charge region,increasing output current of the resistor.The unique aspect ratio design and electric field distribution of the N-well resistor makes the carriers generated by ions in the material need to go through a long drift distance to be collected,resulting in the long duration of the transient current generated in the N-well resistor.(6)Based on the single event effect mechanism of the N-well resistor,a single event effect reinforcement method for the FRAM non-volatile memory that introduces lowdose displacement damage is proposed.Firstly,the influence of this method on the transient current of the N-well resistor is calculated by the TCAD tool,and then the displacement damage is introduced into the FRAM device through a pulse reactor.Finally,the proton and pulse laser microbeam single event effect test is carried out to compare the reinforcement effect of this method.TCAD calculation results show that the duration of transient current generated by the single event effect is significantly shortened after introducing displacement damage.The proton and pulsed laser microbeam test results show that the SEFI and SEU cross-sections of the FRAM device are significantly reduced after a certain dose of neutron pre-radiation,and the hardening of the FRAM device to single event effect is remarkable. |
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