Linear Energy Transfer Threshold Research Articles

The dirty and clean dose concept: Towards creating proton therapy treatment plans with a photon-like dose response.

Applying tolerance doses for organs at risk (OAR) from photon therapy introduces uncertainties in proton therapy when assuming a constant relative biological effectiveness (RBE) of 1.1. This work introduces the novel dirty and clean dose concept, which allows for creating treatment plans with a more photon-like dose response for OAR and, thus, less uncertainties when applying photon-based tolerance doses. The concept divides the 1.1-weighted dose distribution into two parts: the clean and the dirty dose. The clean and dirty dose are deposited by protons with a linear energy transfer (LET) below and above a set LET threshold, respectively. For the former, a photon-like dose response is assumed, while for the latter, the RBE might exceed 1.1. To reduce the dirty dose in OAR, a MaxDirtyDose objective was added in treatment plan optimization. It requires setting two parameters: LET threshold and max dirty dose level. A simple geometry consisting of one target volume and one OAR in water was used to study the reduction in dirty dose in the OAR depending on the choice of the two MaxDirtyDose objective parameters during plan optimization. The best performing parameter combinations were used to create multiple dirty dose optimized (DDopt) treatment plans for two cranial patient cases. For each DDopt plan, 1.1-weighted dose, variable RBE-weighted dose using the Wedenberg RBE model and dose-average LETd distributions as well as resulting normal tissue complication probability (NTCP) values were calculated and compared to the reference plan (RefPlan) without MaxDirtyDose objectives. In the water phantom studies, LET thresholds between 1.5 and 2.5keV/µm yielded the best plans and were subsequently used. For the patient cases, nearly all DDopt plans led to a reduced Wedenberg dose in critical OAR. This reduction resulted from an LET reduction and translated into an NTCP reduction of up to 19 percentage points compared to the RefPlan. The 1.1-weighted dose in the OARs was slightly increased (patient 1: 0.45Gy(RBE), patient 2: 0.08Gy(RBE)), but never exceeded clinical tolerance doses. Additionally, slightly increased 1.1-weighted dose in healthy brain tissue was observed (patient 1: 0.81Gy(RBE), patient 2: 0.53Gy(RBE)). The variation of NTCP values due to variation of α/β from 2 to 3Gy was much smaller for DDopt (2 percentage points (pp)) than for RefPlans (5 pp). The novel dirty and clean dose concept allows for creating biologically more robust proton treatment plans with a more photon-like dose response. The reduced uncertainties in RBE can, therefore, mitigate uncertainties introduced by using photon-based tolerance doses for OAR.

Threshold and Characteristic LETs in SRAM SEU Cross Section Curves

Characterizing the sensitivity of a static random access memory (SRAM) to single-event upset (SEU) is an essential task for assuring its soft-error reliability. However, this task often imposes a burden because it usually requires many cycles of accelerator-based irradiation tests. A model recently proposed is a very simple exponential-type equation but has strong potential to reduce the burden because of its capability to predict SEU cross sections in various conditions. The aim of the present study is to revisit the model in terms of threshold parameters called threshold linear energy transfer (LET) and critical charge. Although these threshold parameters are widely used as key parameters that describe whether an SEU occurs or not, they are not seen in the model. This article explores such missing threshold parameters, suggesting that they successfully appear by introducing a factor of five to the original expression.

Technical note: In silico benchmarking of the linear energy transfer-based functionalities for carbon ion beams in a commercial treatment planning system.

The increasing number of studies dealing with linear energy transfer (LET)-based evaluation and optimization in the field of carbon ion radiotherapy (CIRT) indicates the rising demand for LET implementation in commercial treatment planning systems (TPS). Benchmarking studies could play a key role in detecting (and thus preventing) computation errors prior implementing such functionalities in aTPS. This in silico study was conducted to benchmark the following two LET-related functionalities in a commercial TPS against Monte Carlo simulations: (1) dose averaged LET (LETd ) scoring and (2) physical dose filtration based on LET for future LET-based treatment plan evaluation and optimization studies. The LETd scoring and LET-based dose filtering (in which the deposited dose can be separated into the dose below and above the user specified LET threshold) functionalities for carbon ions in the research version RayStation (RS) 9A-IonPG TPS (RaySearch Laboratories, Sweden) were benchmarked against GATE/Geant4 simulations. Pristine Bragg peaks (BPs) and cuboid targets, positioned at different depths in a homogeneous water phantom and a setup with heterogeneity were used for thisstudy. For all setups (homogeneous and heterogeneous), the mean absolute (and relative) LETd difference was less than 1 keV/ m (3.5%) in the plateau and target and less than 2 keV/ m (8.3%) in the fragmentation tail. The maximum local differences were 4 and 6 keV/ m, respectively. The mean absolute (and relative) physical dose differences for both low- and high-LET doses were less than 1 cGy (1.5%) in the plateau, target and tail with a maximum absolute difference of 2cGy. No computation error was found in the tested functionalities except for LETd in lateral direction outside the target, showing the limitation of the implemented monochrome model in the tested TPSversion.

An Analytical Approach to Calculate Soft Error Rate Induced by Atmospheric Neutrons

In the atmosphere, it is generally understood that neutrons are the main contributor to the soft error rate (SER) in electronic devices. These particles are indeed able to trigger nuclear reactions in the sensitive regions of the devices, leading to secondary ions that may ionize the matter sufficiently to upset a memory cell or induce a transient signal, known as soft errors. For reliability purposes, it is crucial to be able to estimate the SER associated with a given technology, which is typically characterized by its sensitive volume and its threshold linear energy transfer (LET). As an alternative to the usual Monte Carlo methods, in this work we present an analytical model for SER prediction, where we separate the radiation–matter interaction from the geometry considerations (sensitive volume). By doing so, we show that the SER can be expressed as the sum of two contributions that can be calculated for any threshold LET and any sensitive volume size. We compare our proposed approach to existing Monte Carlo simulations in the literature, obtaining a very good agreement despite our approximations, thus validating our approach. As an additional result, we can show that, for future down-sized technologies that may be more sensitive to radiation effects, the contribution of neutrons in the 1–10 MeV energy range to the SER is expected to decrease.

Ultra-Strong Comprehensive Radiation Effect Tolerance in Carbon Nanotube Electronics.

Carbon nanotube (CNT) field-effect transistors (FETs) have been considered ideal building blocks for radiation-hard integrated circuits (ICs), the demand for which is exponentially growing, especially in outer space exploration and the nuclear industry. Many studies on the radiation tolerance of CNT-based electronics have focused on the total ionizing dose (TID) effect, while few works have considered the single event effects (SEEs) and displacement damage (DD) effect, which are more difficult to measure but may be more important in practical applications. Measurements of the SEEs and DD effect of CNT FETs and ICs are first executed and then presented a comprehensive radiation effect analysis of CNT electronics. The CNT ICs without special irradiation reinforcement technology exhibit a comprehensive radiation tolerance, including a 1×104 MeVcm2 mg-1 level of the laser-equivalent threshold linear energy transfer (LET) for SEEs, 2.8×1013 MeV g-1 for DD and 2 Mrad (Si) for TID, which are at least four times higher than those in conventional radiation-hardened ICs. The ultrahigh intrinsic comprehensive radiation tolerance will promote the applications of CNT ICs in high-energy solar and cosmic radiation environments.

Single event tolerance of x-ray silicon-on-insulator pixel sensors

We evaluate the single event tolerance of the x-ray silicon-on-insulator (SOI) pixel sensor named XRPIX, developed for the future x-ray astronomical satellite FORCE. In this work, we measure the cross-section of single event upset (SEU) of the shift register on XRPIX by irradiating heavy ion beams with linear energy transfer (LET) ranging from 0.022 to 68 MeV / ( mg/cm2 ) . From the SEU cross-section curve, the saturation cross-section and threshold LET are successfully obtained to be 3.4−0.9+2.9×10−10 cm2/bit and 7.3−3.5+1.9 MeV/(mg/cm2), respectively. Using these values, the SEU rate in orbit is estimated to be ≲ 0.1 event / year primarily due to the secondary particles induced by cosmic-ray protons. This SEU rate of the shift register on XRPIX is negligible in the FORCE orbit.

PS-BBICS: Pulse stretching bulk built-in current sensor for on-chip measurement of single event transients

The bulk built-in current sensor (BBICS) is a cost-effective solution for detection of energetic particle strikes in integrated circuits. With an appropriate number of BBICSs distributed across the chip, the soft error locations can be identified, and the dynamic fault-tolerant mechanisms can be activated locally to correct the soft errors in the affected logic. In this work, we introduce a pulse stretching BBICS (PS-BBICS) constructed by connecting a standard BBICS and a custom-designed pulse stretching cell. The aim of PS-BBICS is to enable the on-chip measurement of the single event transient (SET) pulse width, allowing to detect the linear energy transfer (LET) of incident particles, and thus assess more accurately the radiation conditions. Based on Spectre simulations, we have shown that for the LET from 1 to 100 MeV cm2 mg−1, the SET pulse width detected by PS-BBICS varies by 620–800 ps. The threshold LET of PS-BBICS increases linearly with the number of monitored inverters, and it is around 1.7 MeV cm2 mg−1 for ten monitored inverters. On the other hand, the SET pulse width is independent of the number of monitored inverters for LET > 4 MeV cm2 mg−1. It was shown that supply voltage, temperature and process variations have strong impact on the response of PS-BBICS.

GEANT4 modeling of alpha particles detection efficiency for polycarbonate SSNTD

In this paper, a simple model based on the GEANT4 simulation toolkit is presented to determine the detection efficiency of polycarbonate detectors. Different alpha energies obtained by traveling of 241Am source alpha particles through different air columns are considered. Experimental measurement are also carried out using two different solutions and electrochemical etching conditions. The thicknesses of the bulk and the electrochemical etching layers extracted from the etching process are assumed as the key parameters. When the vertical range of an alpha particle corresponding to a linear energy transfer above the threshold required for forming the tracks lies between the two above thicknesses, the model counts a track. Fitting the modeled and the experimental efficiencies in the energy range 0.2 to 5 MeV shows that the threshold for forming the tracks in polycarbonate is 240 keV μm−1. Finally, the linear energy transfer threshold as well as the model for track formation presented here can be utilized for future investigations on the polycarbonate detector.

Dependence of Temperature and Back-Gate Bias on Single-Event Upset Induced by Heavy Ion in 0.2-μm DSOI CMOS Technology

The dependence of temperature and back-gate bias on single-event upset (SEU) sensitivity is investigated based on a 0.2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> double silicon-on-insulator (DSOI) technology. At room temperature, an obvious decrease in SEU cross section with the negative back-gate bias is experimentally observed for a DSOI static random access memory (SRAM). The physical mechanism of single-event effect (SEE) is explained through technology computer-aided design (TCAD) simulations. TCAD simulations were also performed to explain the impact of back-gate bias on charge collection and full width at half maximum (FWHM) of the pulsewidth at various temperatures. Both charge collection and FWHM of the pulsewidth increase significantly with temperature rising from 240 to 400 K. It is demonstrated that the SEU threshold linear energy transfer (LET) for a DSOI 6T SRAM cell decreases with an increase in temperature. Compared with a fully depleted SOI (FDSOI) technology, the unique independent back-gate bias scheme for a DSOI SRAM cell exhibits higher tolerance to SEU. At 400 K, it is found that the SEU threshold LET (LET_th) for a DSOI 6T SRAM cell increases by 12.5&#x0025; with back-gate bias of nMOS reduced from 0 to &#x2212;15 V.

Radiation effects in a SPACIROC2 ASIC and long-term reliability

The study presented in this paper outlines the measurements done to evaluate the performance of the second version of the SPACIROC ASIC in ionizing radiation environments using different types of particle beams: ions, protons and X-rays. From ion beam tests, the threshold linear energy transfer (LET) for SEU production was restricted between (4.4 ± 0.4) MeV·cm2/mg and (8.6 ± 0.8) MeV·cm2/mg. The corresponding cross-section value for the latter is (1.6-1.4 +4.18)· 10-6 cm2/device — with asymmetric errors corresponding to 95% confidence level (CL) — and (0.5-0.34 +0.6)· 10-5 cm2/device (CL 95%) for a LET of 11.2 ± 1.1 MeV·cm2/mg. A cross-section for high energy hadrons (HEH) above 20 MeV till about 1 GeV was measured and we place the actual value in 0.32 · 10-12 cm2/device–6 · 10-12 cm2/device interval with a high CL of about 95%. A room-temperature annealing process was observed and precisely measured over time, which efficiently mitigates within few days all residual TID effects that were induced at a very high dose rate of order of 100s rad/s. The obtained results are extrapolated to a few accelerator and space-based applications and we predict no major operational impediments within the lifetime of these experiments.

IDeF-X HD: A CMOS ASIC for the Readout of Cd(Zn)Te Detectors for Space-Borne Applications

IDeF-X HD is a 32-channel analog front-end with self-triggering capability optimized for the readout of [Formula: see text] pixels CdTe or CdZnTe pixelated detectors to build a low power micro-gamma camera. IDeF-X HD has been designed in the standard AMS CMOS 0.35[Formula: see text][Formula: see text]m process technology. Its power consumption is 800[Formula: see text][Formula: see text]W per channel. The energy range of the ASIC can be extended to 1.1[Formula: see text]MeV thanks to the in-channel adjustable gain stage. When no detector is connected to the chip and without input current, a 33 electrons rms ENC level is achieved after shaping with 10.7[Formula: see text][Formula: see text]s peaking time. Spectroscopy measurements have been performed with CdTe Schottky detectors. We measured an energy resolution of 4.2[Formula: see text]keV FWHM at 667[Formula: see text]keV ([Formula: see text]Cs) on a single-pixel configuration. Meanwhile, we also measured 562[Formula: see text]eV and 666[Formula: see text]eV FWHM at 14[Formula: see text]keV and 60[Formula: see text]keV, respectively ([Formula: see text]Am) with a 256 small pixel array and a low detection threshold of 1.2[Formula: see text]keV. Since IDeF-X HD is intended for space-borne applications in astrophysics, we evaluated its radiation tolerance and its sensitivity to single event effects. We demonstrated that the ASIC remained fully functional without significant degradation of its performances after 200 krad and that no single event latch-up was detected putting the linear energy transfer threshold above 110[Formula: see text]MeV/(mg/cm2). Good noise performance and radiation tolerance make the chip well suited for X-rays energy discrimination and high energy resolution. The chip is space qualified and flies on board of the solar orbiter ESA mission launched in 2020.

The Influence of Ion Track Characteristics on Single-Event Upsets and Multiple-Cell Upsets in Nanometer SRAM

The influence of ion track characteristics on single-event upsets (SEU) and multiple-cell upsets (MCUs) is investigated in 65-nm static randon access memory (SRAM) above the heavy-ion linear energy transfer (LET) threshold. The experimental results show that for the incident heavy ions with the same or similar LET but different energies, SEU cross section of low-energy ions is higher than high-energy ions when the LET values are located below the knee point of low-energy SEU event cross section curves. With the LET values increasing above the knee point, SEU cross section of high-energy ions is higher than low-energy ions. When the effective LETs of different-energy ions within the sensitive region are the same, MCU mean, MCU ratio, and MCU event cross sections of high-energy ions are greater than those of low-energy ions due to larger track radius. During the test evaluation of heavy-ion single-event effect (SEE) in nanometer devices, it may be advisable that the SEU LET threshold be obtained with low-energy ions and the SEU saturation cross section be obtained with high-energy ions.

Influences of supply voltage on single event upsets and multiple-cell upsets in nanometer SRAM across a wide linear energy transfer range* *Project supported by the Major Program of the National Natural Science Foundation of China (Grant Nos. 11690043 and 11690040).

The influences of reducing the supply voltage on single event upset (SEU) and multiple-cell upset (MCU) in two kinds of 65-nm static random access memories (SRAMs) are characterized across a wide linear energy transfer (LET) range. The results show that the influence of the voltage variation on SEU cross section clearly depends on the LET value which is above heavy ion LET threshold no matter whether the SRAM is non-hardened 6T SRAM or radiation-hardened double dual interlocked cells (DICE) SRAM. When the LET value is lower than the LET threshold of MCU, the SEU only manifests single cell upset, the SEU cross section increases with the decrease of voltage. The lower the LET value, the higher the SEU sensitivity to the voltage variation is. Lowering the voltage has no evident influence on SEU cross section while the LET value is above the LET threshold of MCU. Moreover, the reduction of the voltage can result in a decrease in the highest-order MCU event cross section due to the decrease of charge collection efficiency of the outer sub-sensitive volume within a certain voltage range. With further scaling the feature size of devices down, it is suggested that the dependence of SEU on voltage variation should be paid special attention to for heavy ions with very low LET or the other particles with very low energy for nanometer commercial off-the-shelf (COTS) SRAM.

Soft error study on junctionless silicon nanotube FET based 6T SRAM cell

In this work, the response of Junctionless Silicon Nanotube FET (JL SiNT FET) to the heavy ion irradiation and the soft error performance of JL SiNT FET based SRAM circuit are investigated using 3D numerical simulations. The impact of single event transient (SET) is studied at different locations of junctionless SiNT with different incident angles to identify the sensitive location of the device. After SET analysis, JL SiNT FET based 6T SRAM cell is studied for single event upset (SEU). Heavy ion study of JL SiNT FET is compared with junction based SiNT FET. The simulation result shows that the threshold linear energy transfer (LETth) of JL SiNT FET based SRAM is approximately three times lesser than the junction based SiNT FET SRAM.

Exploiting Transistor Folding Layout as RHBD Technique Against Single-Event Transients

Radiation-hardening techniques can be extensively used in the design level to improve the robustness of very large-scale integration (VLSI) circuits used in space applications. Accordingly, this work analyzes the efficiency of transistor folding layout in improving the single-event transient (SET) robustness of digital circuits. Additionally, diffusion splitting is proposed to reduce the area overhead of multiple-finger designs. Besides increasing threshold linear energy transfer, results show that both techniques can also reduce the overall cross section and the in-orbit SET rate for protons and heavy ions in low-earth orbit (LEO) and international space station (ISS) orbits.

Influence of fin width on single event-upset characteristics of FinFET SRAM

In this paper, the influence of fin width on single event-upset (SEU) characteristics of 14 nm bulk and SOI FinFET 6 T SRAM is investigated by 3D TCAD mixed-mode simulation. Simulation results show that the threshold linear energy transfer (LETth) of SOI FinFET SRAM is larger than bulk FinFET SRAM. Moreover, the LETth of bulk and SOI FinFET SRAM increases with fin width scaling, and LETth of SOI FinFET SRAM increases more rapidly than bulk FinFET counterpart. The results indicate that bulk and SOI FinFET SRAM would be more immune to SEU response as fin width scales down, especially for SOI FinFET SRAM. Furthermore, the effect of fin width on critical charge and collected charge are explored to explain the fin width dependence of LETth in FinFET SRAM. Both critical charge and collected charge decrease with fin width reducing. However, the collected charge decreases much faster, which becomes the dominant factor for single event sensitivity of FinFET SRAM with fin width scaling.

ОЦЕНКА СООТВЕТСТВИЯ ИНТЕГРАЛЬНЫХ СХЕМ ТРЕБОВАНИЯМ ПО СТОЙКОСТИ К ВОЗДЕЙСТВИЮ ТЯЖЕЛЫХ ЗАРЯЖЕННЫХ ЧАСТИЦ

The goal of qualification or monitoring of electronic device radiation testings is to ensure that devices meet the set of requirements. In some cases, this can be achieved without full characterization of radiation behavior, which leads to significant cost reduction of radiation testing. In this paper, we propose an approach to determining the test standards for evaluating the compliance of integrated circuits with the requirements for radiation hardness under heavy charged particle fluxes in outer space, set as restrictions on the frequency of single radiation effects (SER). The SER calculation is based on the known cosmic rays spectrum and effect’s cross-section dependence on linear energy transfer (LET) obtained during radiation testing. The SEE qualification based on test results for just one LET value is performed using additional conservative limits on saturated cross-section and threshold LET values. Analysis of compendium of experimental data has shown that for main SEE types these limiting values can be set as 3 MeVcm 2 /mg for threshold LET and 30% of chip surface area for saturated cross-section. Those assumptions allows us to calculate fluence and ion LET value required for part qualification for the required SER values. The proposed approach can be used to justify test requirements for SEE testing of integrated circuits.

ТРЕБОВАНИЯ И НОРМЫ ИСПЫТАНИЙ ПО РАДИАЦИОННОЙ СТОЙКОСТИ ИНТЕГРАЛЬНЫХ СХЕМ К ЭФФЕКТАМ ВОЗДЕЙСТВИЯ ТЯЖЕЛЫХ ЗАРЯЖЕННЫХ ЧАСТИЦ

The paper presents an analysis of existing approaches to estimation of single event rate (SER) in integrated circuits under effects of charged particles of space radiation environment. These issues are of significant importance in the light of the expansion of the scope of practical application of cyber-physical control systems for space objects, since it is mainly due to the SER that information is lost in the register elements and in the memory cells of the electronic blocks of spacecraft. It is shown that existing models based on energy deposition in fixed sensitive volume are not applicable for SER estimations in case of high threshold linear energy transfer (LET) values. An alternative approach is proposed. It is based on diffusion charge collection model, which can be used to estimate the SER cross-sections in isotropic particle field. A universal dependence for SER estimation in integral circuits (ICs) at geostationary orbit is proposed and used as a basis for establishing classification of devices based on hardness assurance levels. The obtained results provide the grounds for setting test requirements that has to be met during single event effects testing of ICs.

Prediction of proton single event upset sensitivity based on heavy ion test data in nanometer hardened static random access memory

In order to evaluate the radiation tolerance to proton single event effect(SEE) in nanometer dual interlocked cell (DICE) hardening device accurately, single event upset (SEU) linear energy transfer (LET) threshold at heavy ion normal and tilt incidence, and the worst case SEU orientational angle are acquired based on the analysis of heavy ion SEU testing data in 65 nm dual DICE static random access memory (SRAM). It is proved that dual DICE design is effective for improving the LET threshold against SEU. Howerer, heavy ion tilt incidence at the worst orientational angle will significantly reduce the SEU threshold and increase the SEU cross section. The worst orientational angle for SEU in DICE SRAM is the large tilting angle along the well. The maximum LET value and the emission angle distribution of secondary particle induced by the nuclear reaction between protons with different energy and layers with different multiple metallization are obtained by using Monte-Carlo simulation. The maximum LET value of secondary particle from proton-copper spallation reaction is higher than 15 MeV·cm&lt;sup&gt;2&lt;/sup&gt;/mg for 100 MeV and 200 MeV protons. Secondary particles with the maximum energy and longest range are emitted preferentially in the forward direction. Proton SEU sensitivity is further predicted through combining heavy ion test data with Monte-Carlo simulation. Proton SEU test data verify the effectiveness of the prediction method and the accuracy of the prediction results. The research results indicate that the tolerance of nanometer DICE hardening technique against proton SEU will be overestimated if SEE evaluation test is carried out with only 100 MeV proton accelerator or normal incidence. Proton single event upset in nanometer dual DICE SRAM has an evident dependence on tilt angle and orientational angle. By adopting the above prediction method, whether proton SEE test needs performing or not in nanometer radiation-hardening device can be judged and screened. The requirements for the maximum energy of proton accelerator can be ascertained. In order to ensure that the devices are applied to space with high reliability, SEE test should be carried out including tilt incidence at the worst orientational angle in nanometer DICE hardening device in the process of heavy ion and proton SEE test evaluation.

Single event transient sensitivity analysis of different 32 nm CMOS majority voters designs

As a consequence of the technology scaling, the reduced amount of energy needed to store information impacts the Linear Energy Transfer Threshold (LETth), implying in circuits more sensitive to radiation faults. Hardware redundancy techniques such as the Triple Modular Redundancy are constantly used to mitigate this problem. However, the weakness of the redundancy technique is the voter circuit, and for this reason, alternative designs have been proposed in the literature to improve the robustness of this block. This work investigates the robustness of different majority voter topologies in the presence of Single Event Transient (SET). A layout-level analysis using stick diagrams is fulfilled to analyze the impact a SET causes in diffusion areas shared by transistors, and a fault masking ratio is used to measure the voter robustness. Then an electrical-level analysis was done based on the information provided from the previous study to investigate the threshold LET. The results obtained in this study shown that the topologies can endure a LET up to 1.86 MeV·cm−2/mg considering the 32 nm CMOS technology.