Linear Energy Transfer Values Research Articles

In-silico calculations of DNA damage induced by [formula omitted]-particles in the 224Ra DaRT decay chain for a better understanding of the radiobiological effectiveness of this treatment

Diffusing alpha-emitters radiation Therapy (DaRT) is an interstitial brachytherapy technique using 224Ra seeds. For accurate treatment planning a good understanding of the early DNA damage due to α-particles is required. Geant4-DNA was used to calculate the initial DNA damage and radiobiological effectiveness due to α-particles with linear energy transfer (LET) values in the range 57.5–225.9 keV/μm from the 224Ra decay chain. The impact of DNA base pair density on DNA damage has been modelled, as this parameter varies between human cell lines. Results show that the quantity and complexity of DNA damage changes with LET as expected. Indirect damage, due to water radical reactions with the DNA, decreases and becomes less significant at higher LET values as shown in previous studies. As expected, the yield of complex double strand breaks (DSBs), which are harder for a cell to repair, increases approximately linearly with LET. The level of complexity of DSBs and radiobiological effectiveness have been found to increase with LET as expected. The quantity of DNA damage has been shown to increase for increased DNA density in the expected base pair density range of human cells. The change in damage yield as a function of base pair density is largest for higher LET α-particles, an increase of over 50% for individual strand breaks between 62.7 and 127.4 keV/μm. This change in yield shows that the DNA base pair density is an important parameter for modelling DNA damage particularly at higher LET where the DNA damage is greatest and most complex.

Heavy Ion Single Event Effects in CMOS Image Sensors: SET and SEU

High-energy particles in space often induce single event effects in CMOS image sensors, resulting in performance degradation and functional failure. This paper focuses on the formation and morphology of transient bright spots in CMOS image sensors and analyzes the formation process of transient bright spots by conducting heavy ion irradiation experiments to obtain the variation law of transient bright spots with heavy ion linear energy transfer values and background gray values; in addition, we classify the single event upset that occurred in the experiments according to the state of transient bright spots and extract the characteristics of different single event upsets. The failure mechanisms of different single event upsets are analyzed according to their characteristics and are combined with the information given by transient bright spots. This provides an essential reference for rapidly evaluating single event effects and the reinforcement design of CMOS image sensors.

Designing and Reliability Analysis of Radiation Hardened Stacked Gate Junctionless FinFET and CMOS Inverter

Along with radiation sensing, necessity to study and design reliable radiation hardened devices is also increasing now-a-days. These devices are tolerant to high dosage of radiations without causing any physical damage, logic damage or data loss. In the current work, stacked gate Junctionless FinFET (SG JL FinFET) is analyzed as radiation hardened device by studying the impact of radiation of Linear Energy Transfer (LET) values ranging from 2MeV.cm/mg to 10MeV.cm/mg on the device performance. The proposed radiation hardened FinFET is experimentally calibrated with pre and post irradiation data. Single event upset (SEU) study using transient analysis is carried out to study the performance of proposed radiation hardened device at microwave frequency. High-k material-hafnium dioxide is used as gate oxide material to improve radiation hardness of SG JL FinFET. Electrical parameters-drain current, surface potential and SEU generation rate are studied to analyze device characteristics. Optimization of gate oxide, doping concentration, gate metals and temperature is carried out to enhance the reliability of device in terms of radiation hardness. SG JL FinFET is exposed to different types of waves-UV rays, X-ray, and Gamma rays to study the response of device at different frequencies. The comparison of SG JL and SG Inversion Mode (IM) FinFET has been performed. Comparison of SG JL FinFET with previously reported Inverted mode FinFET, L-shaped tunnel FET and Fully Depleted Silicon on Insulator (FD-SOI) MOSFET is carried out to find most suitable device which can provide highest immunity to radiation exposure. Response of JL FinFET based CMOS inverter in presence of radiation is studied and is also compared with other available CMOS inverters.

Data-driven ion-independent relative biological effectiveness modeling using the beam quality Q

Beam quality Q = Z2/E (Z = ion charge, E = energy), an alternative to the conventionally used linear energy transfer (LET), enables ion-independent modeling of the relative biological effectiveness (RBE) of ions. Therefore, the Q concept, i.e. different ions with similar Q have similar RBE values, could help to transfer clinical RBE knowledge from better-studied ion types (e.g. carbon) to other ions. However, the validity of the Q concept has so far only been demonstrated for low LET values. In this work, the Q concept was explored in a broad LET range, including the so-called overkilling region. The particle irradiation data ensemble (PIDE) was used as experimental in vitro dataset. Data-driven models, i.e. neural network (NN) models with low complexity, were built to predict RBE values for H, He, C and Ne ions at different in vitro endpoints taking different combinations of clinically available candidate inputs: LET, Q and linear-quadratic photon parameter α x/β x. Models were compared in terms of prediction power and ion dependence. The optimal model was compared to published model data using the local effect model (LEM IV). The NN models performed best for the prediction of RBE at reference photon doses between 2 and 4 Gy or RBE near 10% cell survival, using only α x/β x and Q instead of LET as input. The Q model was not significantly ion dependent (p > 0.5) and its prediction power was comparable to that of LEM IV. In conclusion, the validity of the Q concept was demonstrated in a clinically relevant LET range including overkilling. A data-driven Q model was proposed and observed to have an RBE prediction power comparable to a mechanistic model regardless of particle type. The Q concept provides the possibility of reducing RBE uncertainty in treatment planning for protons and ions in the future by transferring clinical RBE knowledge between ions.

Biophysical characterization of collimated and uncollimated fields in pencil beam scanning proton therapy

Objective. The lateral dose fall-off in proton pencil beam scanning (PBS) technique remains the preferred choice for sparing adjacent organs at risk as opposed to the distal edge due to the proton range uncertainties and potentially high relative biological effectiveness. However, because of the substantial spot size along with the scattering in the air and in the patient, the lateral penumbra in PBS can be degraded. Combining PBS with an aperture can result in a sharper dose fall-off, particularly for shallow targets. Approach. The aim of this work was to characterize the radiation fields produced by collimated and uncollimated 100 and 140 MeV proton beams, using Monte Carlo simulations and measurements with a MiniPIX-Timepix detector. The dose and the linear energy transfer (LET) were then coupled with published in silico biophysical models to elucidate the potential biological effects of collimated and uncollimated fields. Main results. Combining an aperture with PBS reduced the absorbed dose in the lateral fall-off and out-of-field by 60%. However, the results also showed that the absolute frequency-averaged LET (LETF) values increased by a maximum of 3.5 keV μm−1 in collimated relative to uncollimated fields, while the dose-averaged LET (LETD) increased by a maximum of 7 keV μm−1. Despite the higher LET values produced by collimated fields, the predicted DNA damage yields remained lower, owing to the large dose reduction. Significance. This work demonstrated the dosimetric advantages of combining an aperture with PBS coupled with lower DNA damage induction. A methodology for calculating dose in water derived from measurements with a silicon-based detector was also presented. This work is the first to demonstrate experimentally the increase in LET caused by combining PBS with aperture, and to assess the potential DNA damage which is the initial step in the cascade of events leading to the majority of radiation-induced biological effects.

Dosimetric response of Gafchromic™ EBT-XD film to therapeutic protons.

EBT-XD model of Gafchromic™ films has a broader optimal dynamic dose range, up to 40 Gy, compared to its predecessor models. This characteristic has made EBT-XD films suitable for high-dose applications such as stereotactic body radiotherapy and stereotactic radiosurgery, as well as ultra-high dose rate FLASH radiotherapy. The purpose of the current study was to characterize the dependence of EBT-XD film response on linear energy transfer (LET) and dose rate of therapeutic protons from a synchrotron. A clinical spot-scanning proton beam was used to study LET dependence at three dose-averaged LET (LETd) values of 1.0 keV/µm, 3.6 keV/µm, and 7.6 keV/µm. A research proton beamline was used to study dose rate dependence at 150 Gy/second in the FLASH mode and 0.3 Gy/second in the non-FLASH mode. Film response data from LETd values of 0.9 keV/µm and 9.0 keV/µm of the proton FLASH beam were also compared. Film response data from a clinical 6 MV photon beam were used as a reference. Both gray value method and optical density (OD) method were used in film calibration. Calibration results using a specific OD calculation method and a generic OD calculation method were compared. The four-parameter NIH Rodbard function and three-parameter rational function were compared in fitting the calibration curves. Experimental results showed that the response of EBT-XD film is proton LET dependent but independent of dose rate. Goodness-of-fit analysis showed that using the NIH Rodbard function is superior for both protons and photons. Using the "specific OD + NIH Rodbard function" method for EBT-XD film calibration is recommended.

Effects of Different Factors on Single Event Effects Introduced by Heavy Ions in SiGe Heterojunction Bipolar Transistor: A TCAD Simulation

In this paper, the effects of different factors, including the heavy ions striking location, incident angle, linear energy transfer (LET) value, projected range, ambient temperature and bias state, on the single event transient introduced by heavy ions irradiation in the SiGe heterojunction bipolar transistor (HBT) were investigated by the TCAD simulation. The results show that the current transient peak value, collected charge and carrier type of each terminal are changed by the striking location, incident angle and bias state. The current transient peak value and collected charge increase with the LET value, while they decrease with the ambient temperature. When heavy ions vertically irradiate the collector and substrate, the current transient peak value and collected charge increase with the projected range; therefore, the species of heavy ions should be considered in studying the single event effects of the SiGe HBT induced by heavy ions irradiation. The microphysical mechanism of these factors influencing the single event effects of the SiGe HBT is discussed in this work.

Dosimetric comparison of robust angles in carbon-ion radiation therapy for prostate cancer.

The objective of this study is to compare the plan robustness at various beam angles. Hence, the influence of the beam angles on robustness and linear energy transfer (LET) was evaluated in gantry-based carbon-ion radiation therapy (CIRT) for prostate cancer. 10 patients with prostate cancer were considered, and a total dose of 51.6 Gy (Relative biological effectiveness (RBE) was prescribed for the target volume in 12 fractions. Five beam field plans comprising two opposed fields with different angle pairs were characterized. Further, dose parameters were extracted, and the RBE-weighted dose and LET values for all angle pairs were compared. All plans considering the setup uncertainty satisfied the dose regimen. When a parallel beam pair was used for perturbed scenarios to take into account set-up uncertainty in the anterior direction, the LET clinical treatment volume (CTV) D 95% standard deviation was 1.5 times higher, and the standard deviation of RBE-weighted CTV D 95% was 7.9 times higher compared to an oblique pair. The oblique beam fields were superior in terms of dose sparing for the rectum compared to the dose distribution using two conventional lateral opposed fields for prostate cancer.

Analysis of the relationship between LET, γH2AX foci volume and cell killing effect of carbon ions using high-resolution imaging technology.

The strong cell killing effect of high linear energy transfer (LET) carbon ions is dependent on lethal DNA damage. Our recent studies suggest that induction of clusters of double-strand breaks (DSBs) in close proximity is one of the potential mechanisms. However, the relationship between LET, the degree of DSB clustering and the cell killing effect of carbon ions remains unclear. Here, we used high-resolution imaging technology to analyze the volume of γH2AX foci induced by monoenergetic carbon ions with a clinically-relevant range of LET (13-100keV/μm). We obtained data from 3317 γH2AX foci and used a gaussian function to approximate the probability (p) that 1Gy-carbon ions induce γH2AX foci of a given volume (vth) or greater per nucleus. Cell killing effects were assessed in clonogenic assays. The cell killing effect showed high concordance with p at vth = 0.7μm3 across various LET values; the difference between the two was 4.7% ± 2.2%. This relationship was also true for clinical carbon ion beams harboring a mixed LET profile throughout a spread-out Bragg peak width (30-120mm), with the difference at vth = 0.7μm3 being 1.6% ± 1.2% when a Monte Carlo simulation-derived dose-averaged LET was used to calculate p. These data indicate that the cell killing effect of carbon ions is predictable by the ability of carbon ions to induce γH2AX foci containing clustered DSBs, which is linked to LET, providing the biological basis for LET modulation in the planning of carbon ion radiotherapy.

A compact circuit-level model for single-event burnout in SiC power MOSFET devices

This paper presents a compact circuit-level model for single-event burnout (SEB) in silicon carbide (SiC) metal-oxide field-effect transistors (MOSFETs). Key parameters of the equivalent circuit model of the MOSFET are analyzed and determined in detail, including nonlinear parasitic drain-source capacitance and nonlinear parasitic gate-drain capacitance. The effect of the parasitic bipolar junction transistor is considered and an iteratively optimized double-exponential current source is used to simulate the transient power current generated by incident heavy ions. The equivalent circuit model of the MOSFET is verified by comparing the SPICE simulation curves, TCAD simulation curves, and the curves in the SiC power double trench MOSFET’s datasheet (SCT3080KL). Then, the SEB is caused by heavy ions at various incident positions, linear energy transfer values, drain-source voltage (V ds), and gate-source voltage (V gs) using the TCAD and HSPICE simulations. Simulation results on the SPICE model coincide with the TCAD simulation results. Moreover, this compact model is used to predict the SEB threshold for devices with higher breakdown voltage ratings.

Mechanisms and shielding characteristics of alpha particle-induced soft errors in 28 and 40 nm configuration memories of SRAM-based FPGAs

The Am-241 radioactive source is used to investigate the mechanism of alpha particle-induced soft errors in configuration memories of SRAM-based FPGAs. Aluminum foils with different thicknesses are inserted between the Am-241 source and the devices under test (DUTs) to investigate shielding characteristics. The results show that the per-bit single event upset (SEU) cross section of the 28 nm device is 14.4 % smaller than that of the 40 nm device. The SEU cross section of the devices increases as the operating voltage decreases. After inserting an aluminum foil, a significant drop in the SEU cross section is observed. For an aluminum foil thickness of 18 μm, the SEU cross section of the 28 nm device drops to zero. The particle transport and SEU generation processes are investigated using Monte Carlo simulations. For a 6 μm aluminum foil thickness, the deposited energy (Ed) at the peak of the Ed spectrum is larger than that without the aluminum foil. If the critical charge of the DUT is lower than 1.33 fC, the SEU cross section will decrease, as the thickness of the aluminum foil increases. However, if the critical charge is higher than 1.33 fC, the introduction of the aluminum foil may lead to an increase in the SEU cross section. This is because that, although the aluminum foil slows down the alpha particles and shields part of low-energy alpha particles, the linear energy transfer (LET) value of the alpha particles reaching the sensitive volume increases.

TCAD evaluation of single-event burnout hardening design for SiC Schottky diodes

In this paper, a single-event burnout (SEB) hardening technique for Schottky diodes at a linear energy transfer (LET) value of 0.5 pC/μm (75.5 MeV/mg/cm2) is presented and investigated by 2-D numerical simulations. The simulation results show that, when compared with the conventional junction barrier Schottky (JBS) diode with multiple buffer layers, the proposed structure can significantly reduce the electric field at the metal/SiC interface with the help of the trench, thereby reducing the interface temperature. Moreover, the maximum global temperature of the proposed structure is also reduced. The maximum global temperature of the proposed structure is 1989 K and the temperature at the Schottky contact interface is 439 K for the bias voltage of 1000 V and LET value of 0.5 pC/μm (75.5 MeV/mg/cm2) which shows that the new structure has better SEB performance. In addition, the hardening method proposed in this paper can be applied at different breakdown voltages by adjusting the structural parameters of the device.

Comprehensive study of the radiation effects on the LDMOS transistors

The reliability of power devices is attracting more and more attention, especially in the extreme radiation environment. The laterally diffused metal–oxide–semiconductor (LDMOS) has been widely used in high voltage integrated circuits. In this paper, the radiation effects of LDMOS transistors are extensively investigated through three-dimensional (3D) TCAD simulations, including Total-Ionizing Dose (TID), Single-Event Effect (SEE) and Transient Dose Rate Effect (TDRE). Firstly, the mechanism of TID effect on the LDMOS is revealed in consideration of temperature variations. Secondly, the single-event effect of the LDMOS is studied with different incident positions, linear energy transfer (LET) values, incident lengths, incident angles, bias conditions and temperatures. Besides, the combined effect of total-ionizing dose and single-event burnout is characterized. Finally, transient response of the LDMOS under transient γ radiation is also studied comprehensively. Therefore, it gives an insight into the physical mechanisms and response characteristics of complex radiation effects, which can provide guidance for radiation-hardened by design and application of the LDMOS devices.

A novel method to assess the incident angle and the LET of protons using a compact single-layer Timepix detector

Particle therapy can largely benefit from the detailed and wide-range spectrometric and directional characterization of energetic charged particles provided by compact Timepix detectors. Among several physical quantities that can be derived, the assessment of the linear energy transfer (LET) which is based on the deposited energy and particle's track length remains challenging. Due to the detector's pixel pitch, sensor thickness and charge sharing effect, an accurate estimation of the particle's incident angle and hence the track length, has been limited to particles with incident angles greater than 20⁰ with respect to the normal of the sensor layer. This is critical for clinical beams which are highly directional, and measurements with radiation detectors are generally performed with sensitive volumes orthogonally placed with respect to the beam direction. In this work, we present a novel method in which we exploit the morphological cluster parameters to derive the proton's incident angle, thus enabling a precise directional reconstruction over the full field-of-view 2π (solid angle), and within 2° from the reference angles for Timepix detectors with 300 and 500 μm thick Si sensors. As a consequence, the calculation of the track length was also improved, resulting in a more precise LET estimation. The experimental LET spectra and the frequency-averaged LET (LETF) were compared against Monte Carlo simulations using TOPAS for a wide range of proton energies (12 MeV–200 MeV) and incident angles (0–85⁰). An agreement within 12% was found between measured and simulated LETF. A comparison with LET values based on the PSTAR database also showed an agreement within 10%. We demonstrated the feasibility of a precise LET calculation and directional response with an improved angular resolution down to normal incidence using a single-layer Timepix detector, while avoiding the use of a stacked telescope array.

Effect of overdispersion of lethal lesions on cell survival curves

The linear-quadratic (LQ) model is the most commonly used mechanism to predict radiobiological outcomes. It has been used extensively to describe dose-response in vitro and in vivo. There are, however, some questions about its applicability in terms of its capacity to represent some profound mechanistic behaviour. Specifically, empirical evidence suggests that the LQ model underestimates the survival of cells at low doses while overestimating cell death at higher doses. It is believed to be driven from the usual LQ model assumption that radiogenic lesions are Poisson distributed. In this context, we use a negative binomial (NB) distribution to study the effect of overdispersion on the shapes and the possibility of reducing dose-response curvature at higher doses. We develop an overdispersion model for cell survival using the non-homologous end-joining (NHEJ) pathway double-strand break (DSB) repair mechanism to investigate the effects of the overdispersion on probabilities of repair of DSBs. The error distribution is customised to ensure that the refined overdispersion parameter depends on the mean of the distribution. The predicted cell survival responses for V79, AG and HSG cells exposed to protons, helium and carbon ions are compared with the experimental data in low and high dose regions at various linear energy transfer (LET) values. The results indicate straightening of dose-response and approaching a log-linear behaviour at higher doses. The model predictions with the measured data show that the NB modelled survival curves agree with the data following medium and high doses. Model predictions are not validated at very tiny and very high doses; the approach presented provides an analysis of mechanisms at the microscopic level. This may help improve the understanding of radiobiological responses of survival curves and resolve discrepancies between experimental and theoretical predictions of cell survival models.

A simulation-based evaluation of single-event burnout mechanisms and varied SEB hardening designs in power LDMOS transistors

In this paper, the Single-event burnout (SEB) triggering mechanism for laterally-diffused metal-oxide semiconductor (LDMOS) devices is numerically studied by using the 2D technology computer-aided design device simulator, simultaneously, three hardening designs are proposed for the first time. SEB triggering voltage (VSEB) are extracted and compared between the four structures when the heavy ion with a same linear energy transfer (LET) of 0.2pC/μm strikes the most sensitive point of the devices. The occurrence mechanism of SEB in LDMOS is mainly due to avalanche breakdown caused by high electric field, which further triggers the parasitic BJT and eventually forms regenerative feedback. By comparing the simulation results between conventional LDMOS and proposed hardened LDMOS designs, the VSEB are 197 V of conventional LDMOS, 306 V of NB LDMOS, 291 V of NP LDMOS and 394 V of NP-BP LDMOS, and their breakdown voltage(BV) are 650 V,606 V, 555 V and 553 V respectively. With different LET values, NB LDMOS and NP LDMOS also have better SEB performance than the conventional one.

Characterization of charge sharing induced by high LET heavy ions using inverter chains in a commercial bulk FinFET process

The inverter is one of the most important cell types in any standard cell library at each technology node, and it is also very important for single-event research. The distributions and cross-sections of single-event transients (SETs) and single-event multiple transients (SEMTs) were characterized using 14/16 nm bulk fin field-effect transistor (FinFET) inverters under heavy ion radiation. An inverter with double driving strength (INVX2) was used as an instantiate object to observe the SET and SEMT response. 181Ta with energies of 1891 GeV and 2000.5 MeV were used respectively in the experiments, of which the linear energy transfer (LET) values were 87.4 MeV cm2 mg−1 and 75.4 MeV cm2 mg−1. The test results indicated that: (a) the mean pulse widths of the SET and SEMT were less than 100 ps, and decreased with LET decreasing; (b) there was charge sharing between abutted INVX2 inverters placed horizontally, and the generation probability of SEMT induced by charge sharing was less than 1% even if the LET of heavy ion reached 87.4 MeV cm2 mg−1. The results were beneficial for a better understanding of SET and SEMT tolerance for inverters in FinFET technology.

The influence of hypoxia on LET and RBE relationships with implications for ultra-high dose rates and FLASH modelling

Objective. To investigate relationships between linear energy transfer (LET), fluence rates, changes in radiosensitivity and the oxygen enhancement ratio (OER) in different ion beams and extend these concepts to ultra-high dose rate (UHDR) or FLASH effects. Approach. LET values providing maximum relative biological effect (RBE), designated as LETU, are found for neon, carbon and helium beams. Proton experiments show reduced RBEs with depth in scattered (divergent) beams, but not with scanned beams, suggesting that instantaneous fluence rates (related to track separation distances) can modify RBE, all other RBE-determining factors being equal. Micro-volumetric energy transfer per μm3 (mVET) is defined by LET × fluence. High fluence rates will increase mVET rates, with proportional shifts of LETU to lower values due to more rapid energy transfer. From the relationship between LETU and OER at conventional dose rates, OER reductions in UHDR/FLASH exposures can be estimated and biological effective dose analysis of experimental lung and skin reactions becomes feasible. Main results. The Furusawa et al data show that hypoxic LETU values exceed their oxic counterparts. OER reduces from around 3–1.25 at LETU, although the relative radiosensitivities of the oxic and hypoxic α parameters (the OER(α)) exceed those of the standard OER values. Increased fluence rates are predicted to reduce LETU and OER. Large FLASH single doses will minimise RBE increments due to the β parameter reducing by a factor of 0.5–0.25 consistent with oxygen depletion, causing radioresistance. Similar results will occur for photons. Tissue α/β ratios increase by around 10 in FLASH conditions, agreeing with derived ion-beam dose rate equations. Significance. Increasing dose rates enhance local energy deposition rate per unit volume, probably causing oxygen depletion and radioresistance in pre-existing hypoxic sites during UHDR/FLASH exposures. The modelled equations provide testable hypotheses for further dose rate investigations in photon, proton and ion beams.

Simulation Study of Single-Event Effects for the 4H-SiC VDMOSFET With Ultralow On-Resistance

Silicon carbide (SiC) vertical-diffused metal oxide field transistor (VDMOSFET) is an important power device for aerospace application. However, it is sensitive to heavy particles radiation in space which can cause catastrophic single-event effects (SEEs). In this article, a method of SEE hardening at a high linear energy transfer (LET) value range is studied to the 1.2 kV-rated SiC VDMOSFET by the 2-D numerical simulator SILVACO TCAD. Simulation results illustrate that, compared with the VDMOSFET which only has four buffer (FB-VDMOSFET) layers, the improved MOSFET could increase the abilities of single-event burnout (SEB) and the single-event gate rupture (SEGR) of the device effectively. At the same time, the proposed MOSFET has the lower specific ON-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on, sp}}$ </tex-math></inline-formula> ) at room temperature. As a result, the gate oxide of the FB-VDMOSFET has reached 7.5 MV/cm and the maximum temperature reached 2480 K at a voltage of 600 V and an LET value of 0.5 pC/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> . However, the maximum temperature of the improved VDMOSFET is 2150 K when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\mathrm {DS}}$ </tex-math></inline-formula> = 950 V.

Single-Event Burnout Hardening 4H-SiC UMOSFET Structure

In this paper, we propose 4H-SiC UMOSFET structure with improved single-event burnout (SEB) hardening characteristics, and compare it with the conventional UMOSFET structure by conducting numerical technology computer-aided design (TCAD) simulations. The SEB safe operating areas are extracted when heavy ions with different linear energy transfer (LET) collide with the device. Because integrated heterojunction diode (HJD) in proposed structure features hole collection effect due to the difference of the valence band energy level, the generated hole current can be leaked off efficiently. With a LET value of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.01~{\sim }~0.09$ </tex-math></inline-formula> pC/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu }\text{m}$ </tex-math></inline-formula> , the proposed MOSFET has 25% higher SEB threshold voltage than conventional MOSFET due to the suppressed parasitic BJT operation. Therefore, proposed structure can provide superior SEB viability for space and atmospheric applications.