LET Values Research Articles

Determination of RBE of 450 MeV/nucleon carbon ions using the micronucleus test and survival of mice after irradiation in different regions of the Bragg curve

Purpose Determination of the value of relative biological effectiveness (RBE) of heavy charged ions in vivo is an important task for their optimal use in particle radiotherapy. The aim of this study was to determine the RBE value of a beam of carbon ions with an energy of 450 MeV/nucleon in different regions of the Bragg curve in irradiation of mice at low, medium, and high doses in comparison with X-ray radiation. Materials and methods SHK mice (n = 330) were irradiated in three regions of the Bragg curve in the dose range of 0–1.5 Gy for cytogenetic damage detection and at a dose of 6.5 Gy for determination of 30-day survival. For irradiation of mice in the Bragg peak, two widths of a spread-out Bragg peak (SOBP) were used: 10 mm (LET ∼100 keV/µm) and 30 mm (LET ∼39 keV/µm). Results The RBE value was 0.8–0.9 before the Bragg peak (LET ∼15 keV/µm) and 0.8 after the peak (LET ∼5 keV/µm), and did not depend on the determination method, despite the differences in LET values. The RBE value determined by the micronucleus test was 1.1–1.7 for the 10-mm-wide SOBP and 1.0–1.3 for the 30-mm-wide SOBP, with the highest RBE value obtained in the low-dose region upon irradiation of mice in the 10-mm-wide Bragg peak. The RBE values in the high-dose region determined by the 30-day survival test lay in the range from 1.4 to 2.6 depending on the width of the Bragg peak and the chosen criterion for calculating the value. The RBE values in the 10-mm-wide Bragg peak (LET ∼100 keV/µm) were higher than those in the 30-mm-wide Bragg peak (LET ∼39 keV/µm) at all used criteria. Conclusions The present findings suggest that there is the complex relationship between LET and organism response to accelerated charged particle radiation, and the contribution of specific factors and mechanisms must be further considered.

Significance of the proton energy loss mechanism to gold nanoparticles in proton therapy: a Geant4 simulation

The biological effectiveness in proton therapy is only slightly greater than of the treatment by X-ray and hence, many researches have suggested the use of gold nanoparticles for increasing the ionization interactions to produce more secondary electrons and elevate the yield of DNA damage. But the ionization interactions also lead to protons energy loss inside the nanoparticles. The present study shows that, the protons slowed-down by High-Z nanoparticles are responsible for dose enhancement rather than the produced secondary electrons. To this purpose, using Geant4 Monte Carlo tool, one million nanoparticles distributed in a proton irradiated volume and variation of the proton’s spectra and the dose related to this variation has been demonstrated. It was found that, the elevation in proton’s LET values when passing through the gold nanoparticles will lead to a more significant dose enhancement than the increased dose due to the extra secondary electrons. Also, it was found that, the mechanism of protons slowing-down by gold nanoparticles has another useful aspect in proton therapy in which, the dose leakage to surrounding healthy tissues will be reduced which must be considered in future investigations more precisely.

Synergistic Effects of Total Ionizing Dose and Single-Event Upset in 130 nm 7T Silicon-on-Insulator Static Random Access Memory

The exposure of spaceborne devices to high-energy charged particles in space results in the occurrence of both a total ionizing dose (TID) and the single-event effect (SEE). These phenomena present significant challenges for the reliable operation of spacecraft and satellites. The rapid advancement of semiconductor fabrication processes and the continuous reduction in device feature size have led to an increase in the significance of the synergistic effects of TID and SEE in static random access memory (SRAM). In order to elucidate the involved physical mechanisms, the synergistic effects of TID and single-event upset (SEU) in a new kind of 130 nm 7T silicon-on-insulator (SOI) SRAM were investigated by means of cobalt-60 gamma-ray and heavy ion irradiation experiments. The findings demonstrate that 7T SOI SRAM is capable of maintaining normal reading and writing functionality when subjected to TID irradiation at a total dose of up to 750 krad(Si). In general, the TID was observed to reduce the SEU cross-section of the 7T SOI SRAM. However, the extent of this reduction was influenced by the heavy ion LET value and the specific writing data pattern employed. Based on the available evidence, it can be proposed that TID preirradiation represents a promising avenue for enhancing the resilience of 7T SOI SRAMs to SEU.

Study on Single Event Effects of Enhanced GaN HEMT Devices under Various Conditions.

GaN HEMT devices are sensitive to the single event effect (SEE) caused by heavy ions, and their reliability affects the safe use of space equipment. In this work, a Ge ion (LET = 37 MeV·cm2/mg) and Bi ion (LET = 98 MeV·cm2/mg) were used to irradiate Cascode GaN power devices by heavy ion accelerator experimental device. The differences of SEE under three conditions: pre-applied electrical stress, different LET values, and gate voltages are studied, and the related damage mechanism is discussed. The experimental results show that the pre-application of electrical stress before radiation leads to an electron de-trapping effect, generating defects within the GaN device. These defects will assist in charge collection so that the drain leakage current of the device will be enhanced. The higher the LET value, the more electron-hole pairs are ionized. Therefore, the charge collected by the drain increases, and the burn-out voltage advances. In the off state, the more negative the gate voltage, the higher the drain voltage of the GaN HEMT device, and the more serious the back-channel effect. This study provides an important theoretical basis for the reliability of GaN power devices in radiation environments.

Dose measurements with radiophotoluminescent glass dosimeters (GD- 352M and GD-302M) in therapeutic proton beams

Radiophotoluminescent glass dosimeters (RPLDs) are increasingly used, especially to measure the doses in therapeutic beams, but the reported data are mainly related to photon and electron beams, while the data for proton beams are limited and not always consistent.In this study, dose measurements were performed with two types of RPLDs: GD-352M and GD-302 M (Asahi Techno Glass Corporation). The dose dependence, long-term fading and response in different Spread out Bragg Peak (SOBP) configurations were evaluated. The dose dependence was measured in the middle of the SOBP for doses ranging from 1 Gy to 120 Gy and a linear dose response was shown for both types of RPLDs. The long-term fading of RPLDs irradiated with proton beams determined under normal ambient conditions over a period of one year is negligible. The GD-352M and GD-302M responses were evaluated in different configurations of the SOPB. The fluence-averaged (LETf) and dose-averaged (LETd) LET values at the positions of the dosimeters were calculated using the PHITS Monte Carlo code. GD-302 M results showed a small under-response compared to the doses provided by treatment planning system (TPS) (within 1.9 %). GD-352M showed an under-response compared to TPS doses for all investigated ranges and modulations with an average under-response of 20 %, indicating the need for correction factors. Both types showed a slight decrease in the response with an increase in the LET.

Novel radiation quality metrics accounting for proton energy spectra for RBE proton models.

For proton therapy, a relative biological effectiveness (RBE) of 1.1 is widely applied clinically. However, due to abundant evidence of variable RBE in vitro, and as suggested in studies of patient outcomes, RBE might increase by the end of the proton tracks, as described by several proposed variable RBE models. Typically, the dose averaged linear energy transfer ( ) has been used as a radiation quality metric (RQM) for these models. However, the optimal choice of RQM has not been fullyexplored. This study aims to propose novel RQMs that effectively weight protons of different energies, and assess their predictive power for variable RBE in proton therapy. The overall objective is to identify an RQM that better describes the contribution of individual particles to the RBE of protonbeams. High-throughput experimental set-ups of in vitro cell survival studies for proton RBE determination are simulated utilizing the SHIELD-HIT12A Monte Carlo particle transport code. For every data point, the proton energy spectra are simulated, allowing the calculation of novel RQMs by applying different power levels to the spectra of LET or effective ( ) values. A phenomenological linear-quadratic-based RBE model is then applied to the in vitro data, using various RQMs as input variables, and the model performance is evaluated by root-mean-square-error (RMSE) for the logarithm of cell surviving fractions of each datapoint. Increasing the power level, that is, putting an even higher weight on higher LET particles when constructing the RQM is generally associated with an increased model performance, with dose averaged (i.e., dose averaged cubed LET, ) resulting in a RMSE value 0.31, compared to 0.45 for a model based on (linearly weighted) , with similar trends also observed for track averaged and -basedRQMs. The results indicate that improved proton variable RBE models can be constructed assuming a non-linear RBE(LET) relationship for individual protons. If similar trends hold also for an in vitro-environment, variable RBE effects are likely better described by or tracked averaged cubed LET ( ), or corresponding -based RQM, rather than linearly weighted or which is conventionally applied today.

The contribution of high-LET track to DNA damage formation and cell death for Monoenergy and SOBP carbon ion irradiation

Carbon ion radiotherapy (CIRT) is a heavy ion charge particle therapy with 29 years of prominent use. Despite advantages like high relative biological effectiveness (RBE), improved quality of life, and reduced treatment time, challenges persist, especially regarding heavy nuclear fragments. Our research addresses these challenges in horizontal irradiation, aiming to comprehend Monoenergetic and Spread-Out Bragg peak (SOBP) carbon ion beam trajectories using cell survival analysis and visualizing biological effects through DNA damage (γ-H2AX). This reveals repair-related protein foci near the Bragg peak. CR-39, a plastic nuclear track detector, was explored to understand high-linear energy transfer (LET) tracks and radiation quality near the Bragg peak. Findings unveil high-LET DNA damage signatures through aligned γ-H2AX foci, correlating with LET values in SOBP. CR-39 visualized high-LET particle exposure, indicating comet-type etch-pits at the Bragg peak and suggesting carbon ion fragmentation. Unexpectedly, dot-type etch-pits in irradiated and post-Bragg peak regions indicated high-LET neutron production. This investigation highlights the intricate interplay of carbon ion beams, stressing the importance of understanding LET variations, DNA damage patterns, and undesired secondary exposure.

Genomic view of heavy-ion-induced deletions associated with distribution of essential genes in Arabidopsis thaliana.

Heavy-ion beam, a type of ionizing radiation, has been applied to plant breeding as a powerful mutagen and is a promising tool to induce large deletions and chromosomal rearrangements. The effectiveness of heavy-ion irradiation can be explained by linear energy transfer (LET; keV µm-1). Heavy-ion beams with different LET values induce different types and sizes of mutations. It has been suggested that deletion size increases with increasing LET value, and complex chromosomal rearrangements are induced in higher LET radiations. In this study, we mapped heavy-ion beam-induced deletions detected in Arabidopsis mutants to its genome. We revealed that deletion sizes were similar between different LETs (100 to 290 keV μm-1), that their upper limit was affected by the distribution of essential genes, and that the detected chromosomal rearrangements avoid disrupting the essential genes. We also focused on tandemly arrayed genes (TAGs), where two or more homologous genes are adjacent to one another in the genome. Our results suggested that 100 keV µm-1 of LET is enough to disrupt TAGs and that the distribution of essential genes strongly affects the heritability of mutations overlapping them. Our results provide a genomic view of large deletion inductions in the Arabidopsis genome.

Three-dimensional numerical simulation of single event upset effect based on 55 nm DICE latch unit

With the development of nanoscale circuit technology, the on-track error rate of digital circuit and the effect of single event upset have become more pronounced. The radiation resistance research on DICE SRAM or DICE flip-flop device has been carried out extensively, including 65 nm, 90 nm, and 130 nm. However, the research on 55 nm DICE latch has not been reported. Using a three-dimensional device model of the 55 nm bulk silicon process established by the simulation tool TCAD, we verify the reinforcement performance of the DICE circuit, and clarify the effects of different incident conditions on DICE circuits. At the same time, we carry out a comparison of anti-SEU performance between NMOS transistor and PMOS transistor in the 55 nm process through comparative simulation experiments and quantitative analysis. The result shows that one of the important factors is the LET value which affects the generation rate of electron-hole pairs. A higher LET value will extend the upset recovery time of device and increase the peak of voltage. In addition, the difference in charge-sharing mechanism between transistors leads to the recovery time of PMOS higher than that of NMOS. As the angle of incidence increases, the charge-sharing mechanism between adjacent devices is enhanced, and electron-hole pairs ionized in sensitive regions increase. Due to the difference in charge mobility, the sensitivity of the angle of incidence of Nhit in DICE is much greater than that of Phit. Therefore, strict tilt angle incident test evaluation is required for DICE device before practical application. Finally, the large distance between adjacent MOS tubes will weaken the charge-sharing mechanism and reduce the charge collection of adjacent MOS tubes. Simulation result shows that the distance between the MOS transistors in the 55 nm process cannot be less than 1.2 μm. The relevant simulation results can provide a theoretical basis and data for supporting the study of the physical mechanism of SEU and reinforcement technology, thereby promoting the application of memory devices to the aerospace field.

Numerical simulation of single-particle transients in low-noise amplifiers based on silicon-germanium heterojunction bipolar transistors and inverse-mode structures

In this work, TCAD simulation modeling is carried out for silicon-germanium heterojunction bipolar transistor (SiGe HBT), and an X-band low noise amplifier (LNA) circuit is built based on the SiGe HBT device model to carry out the hybrid simulation of single-particle transient (SET). The rule of SET pulse varying with LET value and incident angle of ions is studied, and the results show that with the increase of incident LET value, the amplitude of SET pulse at the LNA port increases, and the oscillation time is prolonged; with the increase of incident angle of ions, the amplitude of SET pulse at the LNA port first increases and then decreases, and the oscillation time decreases. With the development of the characterization process, the cutoff frequency (<i>f</i><sub>T</sub>) and the maximum oscillation frequency (<i>f</i><sub>MAX</sub>) of SiGe HBT device with IM structure, are measured considering the use of inverse-mode (IM) common emitter and common-base structures (Cascode) to reduce the sensitivity of the LNAs to single-particle effects. This work calibrates the devices of the TCAD platform as well as the devices of the ADS platform, establishes F-F LNAs as well as I-F LNAs on the ADS, respectively, and verifies the relevant RF performances of the LNA circuits by using the IM-structured SiGe HBTs as the core devices. The SET experiments are performed on the Sentaurus TCAD platform for the F-F LNA circuit and I-F LNA circuit for ions incident on two positions: common base transistor and common emitter transistor, respectively. It is concluded that the LNA with IM structure still shows good RF performance compared with the standard LNA at 130 nm. The transient current duration of the LNA circuit with IM Cascode structure is significantly reduced, and the peak value is reduced by 66% or more, which significantly reduces the sensitivity of the SiGe LNA circuit to SET.

Heavy ion single event effect in double-trench SiC metal–oxide–semiconductor field-effect transistors

In this paper, experiments on 208 MeV Ge ion irradiation with different source-drain bias voltages are carried out for the double-trench SiC metal–oxide–semiconductor field-effect transistors, and the physical mechanism of the single event effect is analyzed. The experimental results show that the drain leakage current of the device increases more obviously with the increase of the initial bias voltage during irradiation. When the bias voltage is 400 V during irradiation, the device has a single event burned at a fluence of 9×10<sup>4</sup> ion/cm<sup>2</sup>, and when the bias voltage is 500 V, the device has a single event burned at a fluence of 3×10<sup>4</sup> ion/cm<sup>2</sup>, so when the LET value is 37.3 MeV·cm<sup>2</sup>/mg, the SEB threshold of DUT does not exceed 400 V, which is lower than 34 % of the rated operational voltage. The post gate-characteristics test results show that the leakage current of the device with a bias voltage of 100 V does not change significantly during irradiation. When the bias voltage is 200 V, the gate leakage and the drain leakage of the device both increase, so do they when the bias voltage is 300 V, which is positively related to bias voltage. In order to further analyze the single particle effect mechanism of device, the simulation is conducted by using TCAD tool. The simulation results show that at low bias voltage, the heavy ion incident device generates electron-hole pairs, the electrons are quickly swept out, and the holes accumulate at the gate oxygen corner under the effect of the electric field, which combines the source-drain bias voltage, leading to the formation of leakage current channels in the gate oxygen layer. The simulation results also show that at high bias voltage, the electrons generated by the incident heavy ion move towards the junction of the N<sup>–</sup> drift layer and the N<sup>+</sup> substrate under the effect of the electric field, which further increases the electric field strength and causes significant impact ionization. The local high current density generated by the impact ionization and the load large electric field causes the lattice temperature to exceed the melting point of silicon carbide, causing single event burnout. This work provides a reference and support for studying the radiation effect mechanism and putting silicon carbide power devices into aerospace applications.

Shoot-through proton FLASH irradiation lowers linear energy transfer in organs at risk for neurological tumors and is robust against density variations

Objective. The goal of the study was to test the hypothesis that shoot-through FLASH proton beams would lead to lower dose-averaged LET (LETD) values in critical organs, while providing at least equal normal tissue sparing as clinical proton therapy plans. Approach. For five neurological tumor patients, pencil beam scanning (PBS) shoot-through plans were made, using the maximum energy of 227 MeV and assuming a hypothetical FLASH protective factor (FPF) of 1.5. The effect of different FPF ranging from 1.2 to 1.8 on the clinical goals were also considered. LETD was calculated for the clinical plan and the shoot-through plan, applying a 2 Gy total dose threshold (RayStation 8 A/9B and 9A-IonRPG). Robust evaluation was performed considering density uncertainty (±3% throughout entire volume). Main results. Clinical plans showed large LETD variations compared to shoot-through plans and the maximum LETD in OAR is 1.2–8 times lower for the latter. Although less conformal, shoot-through plans met the same clinical goals as the clinical plans, for FLASH protection factors above 1.4. The FLASH shoot-through plans were more robust to density uncertainties with a maximum OAR D2% increase of 0.6 Gy versus 5.7 Gy in the clinical plans. Significance. Shoot-through proton FLASH beams avoid uncertainties in LETD distributions and proton range, provide adequate target coverage, meet planning constraints and are robust to density variations.

Simulation of Single-Event Transient Effect for GaN High-Electron-Mobility Transistor.

A GaN high-electron-mobility transistor (HEMT) was simulated using the semiconductor simulation software Silvaco TCAD in this paper. By constructing a two-dimensional structure of GaN HEMT, combined with key models such as carrier mobility, the effects of a different state, different incidence position, different drain voltage, different LET values, and a different incidence angle on the single-event transient effect of GaN HEMT are simulated. LET stands for the linear energy transfer capacity of a particle, which refers to the amount of energy transferred by the particle to the irradiated substance on the unit path. The simulation results show that for GaN HEMTs, the single-event transient effect is more obvious when the device is in off-state than in on-state. The most sensitive location of GaN HEMTs to the single-event effect is in the region near the drain. The peak transient current increases with the increase in the drain bias and incident ion LET values. The drain charge collection time increases with the angle of incidence of heavy ion.

Metal Ions Modify In Vitro DNA Damage Yields with High-LET Radiation.

Cu2+ and Co2+ are metals known to increase DNA damage in the presence of hydrogen peroxide through a Fenton-type reaction. We hypothesized that these metals could increase DNA damage following irradiations of increasing LET values as hydrogen peroxide is a product of the radiolysis of water. The reaction mixtures contain either double- or single-stranded DNA in solution with Cu2+ or Co2+ and were irradiated either with X-ray, carbon-ion or iron-ion beams, or they were treated with hydrogen peroxide or bleomycin at increasing radiation dosages or chemical concentrations. DNA damage was then assessed via gel electrophoresis followed with a band intensity analysis. DNA damage was the greatest when DNA in the solution with either metal was treated with only hydrogen peroxide followed by the DNA damage of DNA in the solution with either metal post irradiation of low-LET (X-Ray) or high-LET (carbon-ion and iron-ion), respectively, and demonstrated the least damage after treatment with bleomycin. Cu2+ portrayed greater DNA damage than Co2+ following all experimental conditions. The metals' effect caused more DNA damage and was observed to be LET-dependent for single-strand break formation but inversely dependent for double-strand break formation. These results suggest that Cu2+ is more efficient than Co2+ at inducing both DNA single-strand and double-strand breaks following all irradiations and chemical treatments.

Investigation of Incident Angle Dependence of Single Event Transient Model in MOSFET

As the manufacturing process level of semiconductor devices continues to improve, the device size gradually decreases, and the devices are affected by the single event effect more and more severely. In this paper, the physical process of single particle incident N-channel Metal-Oxide-Semiconductor Field-Effect Transistor (NMOSFET) is simulated. By changing the particle incidence position, incidence angle, LET value, and temperature, the transient current variation with time is obtained, and the susceptibility of the device to single event effect under the action of four factors is analyzed, which provides the basis for the next research of the device against single event effect and ideas for the radiation hardening of semiconductor devices. In addition, in these experiments, there were bimodal-shaped current pulses that were different from single peak transient current pulses. Therefore, a new model describing the bimodal single event transient (SET) current waveform was proposed, which can be used as a current source model in circuit simulation and help to predict the ability of the circuit to resist the single event effect.

Simulation Studies on Single-Event Effects and the Mechanisms of SiC VDMOS from a Structural Perspective.

The single-event effect reliability issue is one of the most critical concerns in the context of space applications for SiC VDMOS. In this paper, the SEE characteristics and mechanisms of the proposed deep trench gate superjunction (DTSJ), conventional trench gate superjunction (CTSJ), conventional trench gate (CT), and conventional planar gate (CT) SiC VDMOS are comprehensively analyzed and simulated. Extensive simulations demonstrate the maximum SET current peaks of DTSJ-, CTSJ-, CT-, and CP SiC VDMOS, which are 188 mA, 218 mA, 242 mA, and 255 mA, with a bias voltage VDS of 300 V and LET = 120 MeV·cm2/mg, respectively. The total charges of DTSJ-, CTSJ-, CT-, and CP SiC VDMOS collected at the drain are 320 pC, 1100 pC, 885 pC, and 567 pC, respectively. A definition and calculation of the charge enhancement factor (CEF) are proposed. The CEF values of DTSJ-, CTSJ-, CT-, and CP SiC VDMOS are 43, 160, 117, and 55, respectively. Compared with CTSJ-, CT-, and CP SiC VDMOS, the total charge and CEF of the DTSJ SiC VDMOS are reduced by 70.9%, 62.4%, 43.6% and 73.1%, 63.2%, and 21.8%, respectively. The maximum SET lattice temperature of the DTSJ SiC VDMOS is less than 2823 K under the wide operating conditions of a drain bias voltage VDS ranging from 100 V to 1100 V and a LET value ranging from 1 MeV·cm2/mg to 120 MeV·cm2/mg, while the maximum SET lattice temperatures of the other three SiC VDMOS significantly exceed 3100 K. The SEGR LET thresholds of DTSJ-, CTSJ-, CT-, and CP SiC VDMOS are approximately 100 MeV·cm2/mg, 15 MeV·cm2/mg, 15 MeV·cm2/mg, and 60 MeV·cm2/mg, respectively, while the value of VDS = 1100 V.

Research on Temperature Dependence of Single-Event Burnout in Power MOSFETs.

Power MOSFETs are found to be very vulnerable to single-event burnout (SEB) in space irradiation environments, and the military components generally require that devices could operate reliably as the temperature varies from 218 K to 423 K (-55 °C to 150 °C); thus, the temperature dependence of single-event burnout (SEB) in power MOSFETs should be investigated. Our simulation results showed that the Si power MOSFETs are more tolerant to SEB at a higher temperature at the lower LET (10 MeV∙cm2/mg) due to the decrease of the impact ionization rate, which is in good agreement with the previous research. However, the state of the parasitic BJT plays a primary role in the SEB failure mechanism when the LET value is greater than 40 MeV∙cm2/mg, which exhibits a completely different temperature dependence from that of 10 MeV∙cm2/mg. Results indicate that with the temperature increasing, the lower difficulty to turn on the parasitic BJT and the increasing current gain all make it easier to build up the regenerative feedback process responsible for SEB failure. As a result, the SEB susceptibility of power MOSFETs increases as ambient temperature increases when the LET value is greater than 40 MeV∙cm2/mg.

Single proton LET characterization with the Timepix detector and artificial intelligence for advanced proton therapy treatment planning

Objective. Protons have advantageous dose distributions and are increasingly used in cancer therapy. At the depth of the Bragg peak range, protons produce a mixed radiation field consisting of low- and high-linear energy transfer (LET) components, the latter of which is characterized by an increased ionization density on the microscopic scale associated with increased biological effectiveness. Prediction of the yield and LET of primary and secondary charged particles at a certain depth in the patient is performed by Monte Carlo simulations but is difficult to verify experimentally. Approach. Here, the results of measurements performed with Timepix detector in the mixed radiation field produced by a therapeutic proton beam in water are presented and compared to Monte Carlo simulations. The unique capability of the detector to perform high-resolution single particle tracking and identification enhanced by artificial intelligence allowed to resolve the particle type and measure the deposited energy of each particle comprising the mixed radiation field. Based on the collected data, biologically important physics parameters, the LET of single protons and dose-averaged LET, were computed. Main results. An accuracy over 95% was achieved for proton recognition with a developed neural network model. For recognized protons, the measured LET spectra generally agree with the results of Monte Carlo simulations. The mean difference between dose-averaged LET values obtained from measurements and simulations is 17%. We observed a broad spectrum of LET values ranging from a fraction of keV μm−1 to about 10 keV μm−1 for most of the measurements performed in the mixed radiation fields. Significance. It has been demonstrated that the introduced measurement method provides experimental data for validation of LETD or LET spectra in any treatment planning system. The simplicity and accessibility of the presented methodology make it easy to be translated into a clinical routine in any proton therapy facility.

Single-Event Upset Cross-Section Trends for D-FFs at the 5- and 7-nm Bulk FinFET Technology Nodes

At each advanced technology node, it is crucial to characterize and understand the mechanisms affecting performance and reliability. Scaling for all nodes prior to the 5-nm bulk FinFET node had resulted in a decrease in Single-Event Upset (SEU) cross-section at each node. However, this trend unexpectedly reversed for scaling from the 7-nm bulk FinFET node to the 5-nm bulk FinFET node. Experimental results show that the SEU cross-sections for D-FF designs at the 5-nm node are greater than that at the 7-nm for the whole range of particle LET values tested. 3D Technology Computer Aided Design (TCAD) and circuit-level simulations show that the increase in single-event (SE) cross-section with scaling to the 5-nm node is due to interactions between changes in drive current and nodal capacitances. The relative changes in these parameters increased single-event transient (SET) pulse-widths and decreased feedback-loop delays, resulting in an increase in SE cross-sections for the 5-nm node. In addition, the effects of threshold voltage and supply voltage on SEU cross-section for both the 5-nm node and 7-nm node are investigated. The SEU cross-section for the D-FF designs at the 5-nm node shows a stronger dependence on both threshold voltage and supply voltage than that for the 7-nm node. As critical charge decreases with scaling, small differences in critical charge become more significant and manifest as large changes in SEU cross-section, as observed for the 5-nm node. Designers will need to be particularly careful in assessing the overall SE susceptibility of systems developed using the 5-nm bulk FinFET node, particularly when different threshold voltage options and supply voltages are used across the IC.

Efficacy of Transistor Stacking on Flip-Flop SEU Performance at 22-nm FDSOI Node

Fully depleted silicon-on-insulator (FDSOI) technology nodes offer better single-event performance compared with comparable bulk technologies. However, upsets are still possible at nanoscale feature sizes and additional hardening techniques need to be explored. Single-event upset (SEU) performance of multiple flip-flop designs using the stacked-transistor hardening technique at a 22-nm FDSOI technology node is presented in this paper. Irradiation results show significant reductions in SEU cross-sections for stacked-transistor-based hardened designs compared to a conventional design. Alpha particle exposures showed zero upsets for all D-Flip-Flop (DFF) designs tested. When exposed to heavy-ions, the stacked-transistor DFF design showed a 17X improvement over a conventional DFF design at an LET value of 47 MeV-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /mg. The stacked-transistor design with the charge-cancelling technique showed upsets when particle LET exceeded 93.8 MeV-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /mg and at a high angle of incidence. The stacked-transistor design with the interleaving technique showed zero upsets for all test conditions.