Synergism between Single Event Effects and Total Ionising Dose by Alexander Christopher Richard Dyer A thesis submitted in fulfillment of the requirement for the degree of Doctor of Philosophy Surrey Space Centre Department of Electronic Engineering Faculty of Engineering & Physical Sciences University of Surrey Guildford, UK July 2015 (cid:13)c <Alexander Christopher Richard Dyer> 2015 Statement of Originality This thesis and the work to which it refers are the results of my own efforts. Any ideas, data, images or text resulting from the work of others (whether published or unpublished) are fully identified as such within the work and attributed to their originator in the text, bibliography or in footnotes. This thesis has not been submitted in whole or in part for any other academic degree or professional qualification. I agree that the University has the right to submit my work to the plagiarism detection service TurnitinUK for originality checks. Whether or not drafts have been so-assessed, the University reserves the right to require an electronic version of the final document (as submitted) for assessment as above. Alexander Christopher Richard Dyer Abstract The space industry is continuing to use commercial off the shelf (COTS) devices in satellites where the ionising radiation environment poses a threat. For device qualification, their single event effects (SEE) and total ionising dose (TID) performances are normally assessed separately. However, it has been shown that there can be a synergistic relationship in static random-access memory (SRAM) between TID and SEEs, where by the single event upset (SEU) cross section increases with dose, with some devices showing a significant increase for doses less than those seen by low earth orbit (LEO) satellites. The mechanism behind this effect in older SRAM technologies is believed to be due to threshold voltage shift imbalances of the nMOS transistors of the cross coupled inverter within the cell. This is due to variations in the build up of trapped charge in the nMOS transistors when they are ON or OFF. This degrades the noise threshold of the cell making it more susceptible to upsets when holding the opposite state to which it was irradiated in. For moremoderndevicesthegateoxideistoothintoholdenoughtrappedchargetocauseasignificant change in threshold voltage. The mechanism for these modern SRAMs is based on the potential betweenthegateoftheONnMOStransistoranditssubstrate,inthissituationfringingfieldsareat their strongest ushering the charge created by ionising radiation towards the boundary of the field oxide and the gate channel. It is at this boundary that a significant amount of trapped charge can create a parasitic leakage current between the transistor’s source and drain. This parasitic leakage current then reduces the voltage seen at its drain and hence degrades the cell’s noise threshold. The main goal of this work is to determine if these mechanisms behind synergy still have a significant affect on the SEU cross section of modern six transistor (6T) SRAMs built on the 180 and 130 nm fabrication processes. Other non-volatile memory devices have also been tested to see if their memory cell or complex CMOS peripheral circuitry suffer any synergistic effects such as an increase in single event functional interrupt (SEFI) or single event latchup (SEL) with increasing dose. To do this test boards containing the devices were irradiated with 60Co γ-rays to 5, 10, 15, 25 krads. These boards, as well as the control group test boards, were then taken to be tested with 23.5, 60.9, 151 and 230 MeV protons to determine the SEE response of the various parts. To help assess these devices a highly adaptable test system was developed consisting of high level control software and a control board. The high level software offers an over-view of key data such as the device under test’s (DUT) current consumption, SEFI and SEL notifications and a preview of the incoming results. The control board is based around Texas Instrument’s microcontroller, the TMS570, and is capable of testing both serial and parallel devices while offering latchup protection via a selectable current limit. From the testing run carried out in this work it was found that the modern SRAM’s tested did not exhibit any significant signs of synergy. However there are concerns over the accuracy of some of the data due to the SRAM’s SEL response dominating behaviour. These results would benefit from further testing at lower proton energies and flux to ensure any synergy effect was not obscured by the SRAM’s SEL response or being close to saturation at 23.5 MeV. The 110 and 65 nm NOR flash memories tested did not show any SEUs in their main memory sectors, while the 110nmSONOSflashfunctionallyfailedatlessthan25krad. Theserialferroelectricrandom-access memory (FeRAM) suffered a few SEFI events at both 10 and 15 krad resulting in the device being non-responsive, while the device suffered a transient error where by two groups of four addresses were reported to contain errors. Lastly an new method for determining if a device is susceptible to synergy has been suggested, in addition to recommendations for improving the test methodology used in this work. i ii Acknowledgements Firstly, I would like to thank my supervisor Prof. Craig Underwood for offering the opportunity to complete a PhD in such an interesting field of research; within the United Kingdom, if not the world, these opportunities are few and far between. Your support throughout the PhD has been greatly appreciated as has your invaluable experience, insight and knowledge in the area. Within Surrey Space Centre there are also a number of other people who have played an important part in this PhD. During my time at SSC, Karen Collar has been its mainstay, always happy to listen to our problems and concerns and has been ever willing to offer support or assistance. I am also thankful for the assistance offered by Dave Fishlock and Andy Walker, especially the technical assistance they provided during the mad rush in the days leading up to my experiments. My time at SSC has also allowed me to make a number of great friends and I hope these friendships continue beyond this PhD. In particular I’d like to thank Claudio for the many heated political and philosophical discussions and his entertaining use of the English language, but above all, his unique view of life which has lead to a great many adventures I would not have otherwise had. I would also like to thank Theo, Ahmed, Salman, Bet, Johnny and Andrea for all the great times we have had over these years. Outside of SSC I would like to thank my childhood friends Mark and Will as well as my Exeter University friends Matt, Will, Berny and Vicky; I am very lucky to have you all as friends and this PhD would not have been possible without you. Lastly, my heart felt gratitude goes to my parents who have always been there offering their eternal love and support, sharing with me all the emotions this PhD has brought. I’m thankful for the opportunity they have provided and the advice they have given throughout my life as well as the trust they have in me. I’m very proud to have them as my parents. I’d also like to thank my sister Alaine for her love, support and with her partner Sulman for bringing into my life an amazing and happy little nephew, Faris. iii iv Table of Contents List of Tables vii List of Figures ix List of Symbols and Acronyms xiii 1 Introduction 1 1.1 Aim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Novel Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4 Thesis Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 Background 7 2.1 Satellite Environment and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.1 Commercial off the Shelf Technology . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.2 Fabrication and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.3 Memory Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.3 Single Event Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.4 Physical Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.4.1 Single Event Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.4.2 Total Ionising Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.5 Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.5.1 Single Event Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.5.2 Total Ionising Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.6 Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.6.1 Fault Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.6.2 Fault Avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.7 Heritage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3 Single Event Effects 45 3.1 SEE Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.1.1 Fabrication Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.1.2 Single Event Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 3.1.3 Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.2 Synergy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.2.1 SRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.2.2 Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 3.2.3 On-obrit Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 v 4 Radiation Effects Board 89 4.1 Aim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 4.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 4.3 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 4.4 Launch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4.5 Commissioning and Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5 Experiment Design 105 5.1 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 5.2 Control Board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.2.1 Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 5.3 Test Boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 5.3.1 Test Board 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 5.3.2 Test Board 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5.3.3 Test Board 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 5.3.4 Test Board 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.3.5 Test Board 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.3.6 Test Board 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 5.4 Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 5.5 Experimental Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 5.5.1 Total Ionising Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 5.5.2 Single Event Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 6 Results 145 6.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 6.2 Fluence Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 6.3 Annealing and Proton Irradiation Dose. . . . . . . . . . . . . . . . . . . . . . . . . . 148 6.4 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 6.4.1 SRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 6.4.2 FeRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 6.4.3 NOR Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 6.4.4 SONOS Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 7 Conclusions and Future Work 175 7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 7.2 SRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 7.3 FeRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 7.4 Flash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 7.5 Technical Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 7.5.1 Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 7.6 Radiation Effects Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 7.7 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Bibliography 181 vi