Stuck Bits Research Articles

Gate breakdown induced stuck bits in sub-20 nm FinFET SRAM

This paper discusses the stuck bits induced by the gate breakdown of PMOS in the sub-20 nm FinFET static random access memory (SRAM) device. After the heavy-ion experiment, several stuck bits are in the FinFET SRAM matrix, which cannot be set or reset. To investigate the factors that caused the stuck bit, we perform the electrical failure analysis (EFA) to measure the electric characteristics of the transistors in the stuck bits and normal cells separately. The measurement results show a clear gate breakdown at the PMOS pull-up (PPU) transistor in all of the measured SRAM cells. Meanwhile, the SPICE simulation based on the EFA results verifies the impact of the damaged PPU. Finally, considering all of the phenomena, the charge deposition from single events is the major mechanism that causes the stuck bits in FinFET SRAM. The experiment results alert a potential gate breakdown risk in the ultra-high-density FinFET SRAM applied in the space environment.

Neutron-induced effects on a self-refresh DRAM

The field of radiation effects in electronics research includes unknowns for every new device, node size, and technical development. In this study, static and dynamic test methods were used to define the response of a self-refresh DRAM under neutron irradiation. The neutron-induced effects were investigated and characterised by event cross sections, soft-error rate, and bitmaps evaluations, leading to an identification of permanent and temporary stuck cells, single-bit upsets, and block errors. Block errors were identified in different patterns with dependency in the addressing order, leading to up to two thousand faulty words per event, representing a real threat from a user perspective, especially in critical applications. An analysis of the damaged cells' retention time was performed, showing a difference in the efficiency of the self-refresh mechanism and a read operation. Also, a correlation of the fault mechanism that generates both single-bit upsets and stuck bits is proposed. Post-irradiation high-temperature annealing procedures were applied, showing a recovery behaviour on the damaged cells.

Electron-Induced Upsets and Stuck Bits in SDRAMs in the Jovian Environment

This study investigates the response of synchronous dynamic random access memories to energetic electrons and especially the possibility of electrons to cause stuck bits in these memories. Three different memories with different node sizes (63, 72, and 110 nm) were tested. Electrons with energies between 6 and 200 MeV were used at RADiation Effects Facility (RADEF) in Jyväskylä, Finland, and at Very energetic Electron facility for Space Planetary Exploration missions in harsh Radiative environments (VESPER) in The European Organization for Nuclear Research (CERN), Switzerland. Photon irradiation was also performed in Jyväskylä. In these irradiation tests, stuck bits originating from electron-induced single-event effects (SEEs) were found, as well as single bit-flips from single electrons. To the best knowledge of the authors, this is the first time that stuck bits from single-electron events have been reported in the literature. It is argued in the article that the single-event bit-flips and stuck bits are caused by the same damage mechanism, which would be large displacement damage clusters, and that the two different fault modes represent different amounts of damage to the memory cell. After a large particle fluence, a rapid increase in the error rate was observed, originating from the accumulation of smaller displacement damage clusters in the memory cells. The 110-nm memory was a candidate component to fly on the European Space Agency (ESA) JUpiter ICy moons Explorer (JUICE) mission, so the SEE cross section as a function of electron energy was compared to the expected electron environment encountered by JUICE to estimate the error rates during the mission.

Radiation-Induced Variable Retention Time in Dynamic Random Access Memories

The effect of gamma-ray and neutron radiations on the variable retention time (VRT) phenomenon occurring in dynamic random access memory (DRAM) is studied. It is shown that both ionizing radiation and nonionizing radiation induce VRT behaviors in DRAM cells. It demonstrates that both Si/SiO2 interface states and silicon bulk defects can be a source of VRT. It is also highlighted that radiation-induced VRT in DRAMs is very similar to the radiation-induced dark current random telegraph signal in image sensors. Both phenomena probably share the same origin, but high-magnitude electric fields seem to play an important role in VRT only. Defect structural fluctuations (without change of charge state) seem to be the root cause of the observed VRT whereas processes involving trapping and emission of charge carriers are unlikely to be a source of VRT. VRT also appears to be the most probable cause of intermittent stuck bits in irradiated DRAMs.

Stuck Bits Study in DDR3 SDRAMs Using 45-MeV Proton Beam

This work shares the observations of stuck bits by proton beam in DDR3 components in 3x-nm technologies. The DDR3 SDRAMs from four major DRAM manufacturers were tested with a 45-MeV proton beam at an operating frequency of 800 MHz. The beam exposure resulted in single bit upset (SBU) and multiple bit upsets (MBUs), as well as single and multiple stuck bits in a word due to micro-dose and displacement damage effects. The number of stuck bits reduced as the refresh interval duration was decreased. Moreover, for the tested samples, the stuck bits were recovered completely and could be run in the normal operation mode after annealing at $150^{\circ}{\rm C}$ . The occurrence of multiple stuck bits in a word was likely due to damages to the control logic and those stuck bits were recovered as well after annealing at $150^{\circ}{\rm C}$ .

Probing the Nature of Intermittently Stuck Bits in Dynamic RAM Cells

A new method is presented and demonstrated to quantify the leakage currents in Intermittently Stuck Bits (ISB's) in SDRAM's, which have been exposed to neutron or proton irradiation. It is argued that these ISB's are caused by Single Particle Displacement Damage Effects (SPDDE's), in the form of displacement damage complexes comprising one or more damage clusters. The leakage current histories of ISB's are compared with a model of the behavior of the displacement damage complexes believed to cause the ISB's.

Those Pig-Men Things

Those Pig-Men Things

The Random Telegraph Signal Behavior of Intermittently Stuck Bits in SDRAMs

This paper reports behavior analogous to the Random Telegraph Signal (RTS) seen in the leakage currents from radiation induced hot pixels in Charge Coupled Devices (CCDs), but in the context of stuck bits in Synchronous Dynamic Random Access Memories (SDRAMs). Our analysis suggests that pseudo-random sticking and unsticking of the SDRAM bits is due to thermally induced fluctuations in leakage current through displacement damage complexes in depletion regions that were created by high-energy neutron and proton interactions. It is shown that the number of observed stuck bits increases exponentially with temperature, due to the general increase in the leakage currents through the damage centers with temperature. Nevertheless, some stuck bits are seen to pseudo-randomly stick and unstick in the context of a continuously rising trend of temperature, thus demonstrating that their damage centers can exist in multiple widely spaced, discrete levels of leakage current, which is highly consistent with RTS. This implies that these intermittently stuck bits (ISBs) are a displacement damage phenomenon and are unrelated to microdose issues, which is confirmed by the observation that they also occur in unbiased irradiation. Finally, we note that observed variations in the periodicity of the sticking and unsticking behavior on several timescales is most readily explained by multiple leakage current pathways through displacement damage complexes spontaneously and independently opening and closing under the influence of thermal vibrations.

Physical Mechanisms of Ion-Induced Stuck Bits in the Hyundai 16M$\,\times\,$4 SDRAM

It was previously thought that stuck bits in the Hyundai 16M times 4 SDRAM were caused by micro-dose. It is argued here that the correct mechanism is micro (i.e., from a single particle hit) displacement damage, which creates a leakage current that drains the storage capacitor.

Ionizing Radiation Effect on Ferroelectric Nonvolatile Memories and Its Dependence on the Irradiation Temperature

We investigate ferroelectric random access memories subjected to X-ray and proton irradiations. We address the radiation damage dependence on irradiation temperature, its stability during annealing and cycling, and the effects of supply voltage and packaging. The radiation damage strongly depends on the irradiation temperature. Immediately after proton or X-ray irradiation, we detect only stuck bits without data corruption, at least at doses up to 9 Mrad(Si) at room temperature. The radiation damage anneals in time as long as several weeks, and the recovery rate is accelerated by either electrical cycling or high temperature annealing. The radiation tolerance is much higher if the device is irradiated unpowered. Finally, we present a degradation model that accounts for the irradiation temperature dependence.

MO‐E‐M100F‐04: Optimizing Low‐Dose Megavoltage Fluoroscopy for 4D Radiotherapy

Purpose: This study explores the feasibility of using megavoltage fluoroscopy (MVF) for on‐line real‐time verification and guidance for gated/4D treatment delivery. Initial experiences in implementing MVF and methods developed to minimize required dose and optimize the signal‐to‐noise ratio will be presented. Methods and Materials: A Siemens LINAC retrofit with a flat panel imager in the beam direction was used to acquire MVF images with 10242 pixel matrix at 7 frames‐per‐second (fps) using 6 MV photons. Image processing software tools were developed to remove artifacts caused by beam pulsing, dead pixels and stuck bits and to average pixels and video frames. The beam delivery rate was adjusted during MVF acquisition in an attempt to minimize the dose per frame. A phantom designed to test the contrast resolution of kilovoltage fluoroscopy systems was used to assess the MVF image quality at different beam delivery rates. Results: Good quality MVF images with sequences longer than a typical respiratory cycle (5 sec) were obtained with an estimated dose as low as 0.6 cGy. Matching the beam pulse frequency to a multiple of the video frame rate minimized striping artifacts. Image sequences acquired at a frame rate of 3.5 fps and beam delivery rate of 12 MU/min had an SNR of 125; the minimum object resolvable during cine display was 0.063 inch in diameter, and the 0.31 inch diameter object was detectable at 2% contrast. Contrast detectability was improved by averaging video frames, reducing spatial resolution and displaying video in high‐speed cine mode. Conclusions: It is feasible to acquire good quality megavoltage fluoroscopy images using a low dose‐rate treatment beam, indicating that MVF can be used to verify or guide gated/4D treatment delivery in real time (e.g. prior or during treatment delivery). Conflict of Interest: This work was supported in part by Siemens OCS.

Ion-induced stuck bits in 1T/1C SDRAM cells

Radiation exposure of certain types of devices tends to stick bits, causing them to not be read out correctly after programming. Evidence of a linear trend in stuck bits in SDRAM memory cells is presented. This trend makes a cross section, as traditionally defined for single-event effects, unambiguous. However, there are considerable part-to-part variations in the cross section.

Simulation of heavy-ion-induced failure modes in nMOS cells of ICs

Simulation results show leakage current induced by the impact of a single heavy ion in an nMOSFET's bird's beak accountable for experimentally observed stuck bits. Parametric extrapolation shows dramatic sensitivity increase for recent local oxidation of silicon technologies.

Hard error dose distributions of gate oxide arrays in the laboratory and space environments

Hard errors or stuck bits observed in a single memory can occur over a broad range of macroscopically measured doses. It is shown here that a major contributing factor to this is the microscopic variation of deposited dose across the large array of gate oxides composing the memory. In addition, processing variations also contribute to the spreading of hard error doses. A statistical model of these factors is presented and compared to Co-60 data. Comparisons are then made between the hard error dose distribution for Co-60 and that expected in the heart of the proton belts. It is shown that even though the average hard error dose in the proton belts is greater, the onset hard error dose can be less. Thus, the relations between the onset dose for hard errors in the two environments should be thoroughly understood before qualifying parts for space applications.

Numerical simulation of hard errors induced by heavy ions in 4T high density SRAM cells

2D numerical simulation of local dose deposition effects in N channel MOS transistors are presented in order to explain experimental observation of stuck bits in 4 T resistor loaded cells of high density SRAMs irradiated by heavy ions. The ion impact location in the channel is shown to strongly modulate the observed threshold voltage shift. This shift variation versus the inverse channel length is super linear, so more important effects are expected for 4T cells as transistor dimensions are reduced. >