1. April 30, 2014 1 Cost efficient soft-error protection for ASICs Tuvia Liran; Ramon Chips Ltd. tuvia@ramon-chips.com

2. April 30, 2014 2 What is soft error An error in the functionality of the chip/system due to corruption of data Hard error: An error in the functionality of the chip/system due to permanent damage

3. April 30, 2014 3 Key topics SE basics Sources and mechanisms of SE Single event effects Methodologies for SE mitigation Summary

4. April 30, 2014 4 Terminology SE - Soft Error SER- Soft Error Rate SEE – Single Event Effect – SEU – Single Event Upset – SET – Single Event Transient – SEL – Single Event Latch-up SEFI – Single Event Functional Interrupt LET – Rate of energy loss in Si/SiO 2 [Mev/mg/cm 2 ] SBU- Single bit upset MCU- Multi-cell upset MBU– Multi Bit Upset MTTF – Mean Time to Fail FIT – Failure in Time; =10 -9 /MTTF(h)

5. April 30, 2014 5 Myth Blasting SE is relevant only for space environment SE is affecting memory cells only SE is not a reliability issue DRAM is more sensitive to SE than SRAM Latchup cannot cause SE W R O N G W R O N G W R O N G W R O N G W R O N G

6. April 30, 2014 6 Sources of soft-errors Terrestrial: – Interactions with cosmic particles (Neutrons) – Alpha particles from die/package Space: – Protons (>93%) – Alpha (~6%) – Neutrons – Electrons – Alpha and heavy particles (up to 500Mev)

7. April 30, 2014 7 Interaction of Neutrons Typical flux – 20N/h/cm 2 @ sea level (NYC) Energy of cosmic Neutron – 20-300Mev Strong dependence on altitude Higher concentration in polar areas (Lat >60) Interaction with Boron (20% of B 10 ), mostly in BPSG (@≥0.25 µ ) – most dominant effect Interacts with various nuclei (W, Si, Pb,Au …) Shielding is not practical

8. April 30, 2014 8 Alpha particles Alpha particle == He ++ Energy: 1-6MeV / particle (1.5Mev from N->B 10 ) – ~3.6eV requires to generate e-h pair Penetration range in Si – 15-30 µ Generating ~45fQb / Mev – Critical charge of SRAM cell is ~1fQb – No SEU immune SRAM cell is not practical in VDSM

9. April 30, 2014 9 SEU in SRAM

10. April 30, 2014 10 SBU/MCU in SRAM Single bit upsetMulti cell upset Multi cell upset ≠ Multi bit upset High MUX ratio -> lower MBU

11. April 30, 2014 11 Single Event Transient (SET) Pulses at logic nodes, caused by ionizing particles Typical pulse width is 10÷200pS (@Alpha) Such pulses might cause: – Permanent error if sampled by FF – Permanent error if activates asynchronous signals P(error)=T(pulse)/T(period) =T(pulse)*F

12. April 30, 2014 12 Frequency dependence of SEU/SET Lower effective frequency, such as by clock gating, reduces SET SET can be mitigated by glitch filtering before sampling

13. April 30, 2014 13 Effective glitch filtration Glitch filtering Narrow pulses are filtered by C-element+delay Weak SCAN mux Implementing resistive MUX at the input of the flip-flop will filter narrow glitches 13

14. April 30, 2014 14 Impact of scaling Scaling reduces the “critical charge” Faster devices do not “filter” narrow SET pulses More devices/memory per chip – more sensitive elements Higher frequency increases the probability to SET SE is a major issue in advanced UDSM

15. April 30, 2014 15 SEE mitigation concepts S/W techniques for error correction – Example: 3 processing + voting Mitigation at system level – Example: TMR Mitigation at chip level – Example: EDAC, SE protected FFs Mitigation by circuit – Example: SE protected FFs & SRAM cells Mitigation by Si process – Example: SOI (poor !!!)

16. April 30, 2014 16 SEE sensitivity - application Types of data, sorted by SEE sensitivity: – Configuration (FPGA, CNFREG…) – Control logic (FSM, uCode,…) – Executable data (.exe files, I-Cach,…) – Stored data (databases, D-Cach, …) – Temporary data (Video, Audio, …)

17. April 30, 2014 17 Summary SEE is becoming a significant reliability issue in VDSM technologies SRAMs are typically the most sensitive elements to SEE SE mitigation is possible, mostly by digital techniques and proper methodologies and tools Availability of EDA tools for analyzing SER and mitigating SEE is limited. Optima presents a very interesting tool.