Circuit Techniques For Characterization Of Radiation-Induced Soft Errors In Advanced Cmos Processes
2018-05
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Circuit Techniques For Characterization Of Radiation-Induced Soft Errors In Advanced Cmos Processes
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2018-05
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Soft errors induced by particle strikes have been a major concern in reliability critical applications such as defense, space, medicine and finance etc. A number of radiation particles present in the ambient environment can induce errors in circuits which can result in system failure. These can be charged particles such as alpha, electrons, protons or heavy ions or neutral particles like neutrons, laser etc. Radioactive impurities like Uranium and Thorium in chip and packaging materials emit alpha particles that contribute towards errors. Protons, electrons and neutrons are found in space and terrestrial environment that can induce soft errors. When these particles penetrate the silicon, electron hole pairs are generated along the tracks that may be collected by the p-n junctions via drift and diffusion mechanisms. If the collected charge is large enough, the logic state of the junction may change, resulting in what we refer to as a soft error. Continuous process scaling has resulted in shrinking of device features that results in smaller junction area and lower strike probability at or around the junction that can lead to an error induction. The transistors, therefore, have become more and more resilient towards radiation-induced strikes. Advent of FinFET technology has further increased the resilience of devices towards soft errors by employing narrow three dimensional source-drain features that inherently make it difficult for the charge to get collected quickly. However, with process scaling, device density per die has gone up exponentially which means more transistors can be packed in the same die area. This has resulted in a probable rise in overall soft error rate (SER) due to increased number of susceptible nodes. Hence although per device SER has gone down, chip-level SER still remains a critical reliability issue that needs to be dealt with. In order to come up with efficient circuit designs that are immune towards soft errors, it is necessary to accurately and efficiently characterize SER in the given process. In this work, novel circuits have been proposed that capture important circuit parameters impacting SER. First of these is the Back-Sampling Chain (BSC) circuit that employs highly sensitive detection chains with more than 9x sensitivity as compared to conventional circuits. Higher sensitivity is critical in SER characterization since it facilitates higher strike induction resulting in collection of large data in limited beam time. BSC chain is capable of detecting Single Event Transients (SETs), Single Event Upsets (SEUs) and Multi-Bit-Upsets (MBUs), with scalable architecture that can be scaled to millions of stages without compromising on the measurement accuracy. BSC circuit can measure the SET pulse parameters (width and amplitude) while sweeping the sensitivity points that helps in re-construction of individual strike pulses. This, to our knowledge, is the first work to show individual pulse re-construction. Secondly, we show the detailed analysis of neutron-induced soft errors measured from the flip-flop arrays implemented in 14nm FinFET CMOS. Depending on the strike location and circuit topology, the MBU patterns may differ which has been characterized and a qualitative first order analysis has been presented. Seven unique MBU patterns extracted from measured data have been studied and analyzed to find layout dependencies on MBU. Results show strong correlation between the inter-node proximity and MBUs. With lower proximity, MBU induction probability as well as MBU size goes up and vice versa. The multi-cell-cluster (MCU) analysis shows higher SER cross-section for smaller MCU cluster size while the bigger clusters have lower contribution towards overall MBU SER. Thirdly, a 14nm test chip employing a novel NAND/NOR readout chain for characterizing SER in combinational logic gates is proposed. The proposed test structure uses high density standard logic gates as detection circuit for sensing SETs that are then forwarded to a skewed NAND-NOR readout chain which funnels all SET pulses while expanding the pulse width to ensure they reach the final triple modular redundant (TMR) counter. The proposed circuit is compact, has a scalable architecture based on a unit cell layout, and incurs minimal area overhead. Different gate configurations (device size, threshold voltage, fan-out and chain length) were implemented in the 14nm test-chip and irradiated under a neutron beam to collect a massive amount of statistical data. Radiation data captures, for the first time, the impact of various circuit parameters on combinational logic SER in 14nm tri-gate technology.
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University of Minnesota Ph.D. dissertation. May 2018. Major: Electrical Engineering. Advisor: Chris Kim. 1 computer file (PDF); xviii, 108 pages.
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Kumar, Saurabh. (2018). Circuit Techniques For Characterization Of Radiation-Induced Soft Errors In Advanced Cmos Processes. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/215201.
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