Dose Rate Sensitivity Research Articles

The new approach of a simulation low dose rate radiation effects in bipolar integrated circuits

The model is proposed to explain the effects of low dose rate under the radiation influence in bipolar structures, taking into account the effects of subthreshold displacement in high-doped silicon layers. The base current degradation of bipolar transistor is determined of surface and displacement radiation effects in the near-surface base area. The conditions for the enhanced low dose rate sensitivity (ELDRS) in bipolar structures are shown. The presented results of the analysis allow us to explain most of the observed experimental results.

Radiation-tolerant dose sensor based on undoped amorphous silicon

Single-crystal silicon diodes are replacing gas-filled dose-rate meters because they are batch-processable, mechanically robust, compact, and operable at low voltages. However, they are prone to radiation damage in high dose fields. Hydrogenated amorphous silicon (a-Si:H) provides the manufacturing and operational benefits of silicon while adding inherent radiation hardness because of its wider bandgap and disordered microstructure. Previously, sensors with tens of micrometers thick a-Si have been investigated for direct dose sensing in x-ray imaging applications. However, the limited charge carrier lifetimes of the medium can reduce the charge collection efficiency and thereby the sensitivity. If a higher density, higher Z active media is coupled to thin amorphous silicon active layers, then an additional indirect component can be added to this direct signal to exhibit ∼15 μGy/s dose-rate sensitivities at zero and low-bias (<0.5 V) operation. Here we show that thin (150, 300, 450 nm) a-Si:H optical sensors can produce external quantum efficiencies above 40% and internal quantum efficiencies that exceed 70 % over a broad band from 380 nm to 650 nm, resulting in dose-rate sensitivity even at 0 V. When the charge-collecting electrodes abutting the a-Si:H serve the dual purpose as reflective layers in a lossy Fabry-Perot cavity, then internal quantum efficiencies greater than 83 % can be realized in a 30 nm thick layer at 410 nm. Cobalt-60 gamma-ray irradiation to 100 kGy (air) shows no radiation-induced degradation for even the thicker 300 nm sample; rather, a radiation hardening effect is observed as evinced in reduced dark current.

How the Analysis of Archival Data Could Provide Helpful Information About TID Degradation. Case Study: Bipolar Transistors

A critical step of radiation hardness assurance (RHA) for space systems is given by the parts selection in accordance with the observed (or estimated) radiation effects. Although radiation testing is the most decisive way of studying the radiation degradation of electronic components, the increasing use of commercial off-the-shelf (COTS) devices and the challenges posed by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NewSpace</i> are pushing the need of finding new approaches to assess the risk associated with radiation environments. This work tries to evaluate if valuable information might be extracted from archival data to carry out this assessment despite the well-known and dramatic lot-to-lot, or even part-to-part, variability for some technologies and the impact of the different test conditions, such as the bias conditions and the dose rate in enhanced low dose rate sensitivity (ELDRS). These factors are briefly analyzed for some examples. A new radiation database is briefly introduced, and some statistical approaches are cited, apart from the analysis herein followed. To finish, a first analysis on three families of bipolar transistors is presented together with the independent results from three external reports, with a good agreement between the experimental results and the expected ones.

Thermal drift reduction in photodiode dosimeters with switching bias

The effect of temperature on dosimetric measurements is a major limitation of solid-state dosimeters. This is especially true for PIN photodiode dosimeters, where the dark current depends exponentially on temperature. To minimize this effect, a compensation method is presented that relies on the diode structure itself without the need for an external sensor or device. During irradiation, the photodiode is periodically switched from reverse to forward polarization to determine the temperature of the device. This measurement is based on the linear dependence between the temperature and the forward voltage of the diode when it is operated at constant current. An electronic circuit implementing this procedure was developed and used for experimental characterization of the response to radiation of the BPW34S Si PIN photodiode. The proposed procedure reduced the uncertainty due to thermal drift by a factor of 7.5. In addition, an average dose rate sensitivity of 12 ± 2 nC/cGy was measured, with a sensitivity degradation below 2% for the irradiation cycle of 21.4 Gy performed under a 6 MV photon beam. We have shown that a p-n junction can be successfully used to compensate for the temperature effect on the dosimetric measurement.

Influence of temperature and dose rate on radiation-induced attenuation at 1542 nm in fluorine-doped fibers.

Radiation-induced attenuation (RIA) at 1542 nm of fluorine-doped fibers under gamma radiation source has been investigated for different dose rates and temperatures. Both the temperature and dose rate dependencies are unusual. First, the fiber presents an enhanced low dose rate sensitivity that is favored by increasing temperature. Furthermore, in certain conditions, RIA increases with irradiation temperature, which is a very rare phenomenon. We have built a phenomenological model that shows that these behaviors can be explained considering that two color centers previously identified in the literature are responsible for RIA: inherent and strain-assisted self-trapped holes.

Influence of enhanced low dose rate sensitivity on single-event transient degradation in the LM158 bipolar operational amplifier

The synergistic effect of enhanced low dose rate sensitivity and single-event transients (SETs) in the bipolar dual operational amplifier LM158 is studied. The test results show a significant reduction in the SET amplitude and broadening in the SET waveform upon exposure to total ionizing dose radiation. These results are much more prominent for a low dose rate (LDR) irradiation of 0.01 rad(Si)/s than for a high dose rate irradiation of 10 rad(Si)/s. The greater gain degradation in the LM158 with LDR irradiation could be the direct cause of the reduction in the SET amplitude and broadening in the SET waveform, and this is corroborated through HSPICE simulations.

Effects of Bias and Temperature on the Dose-Rate Sensitivity of 65-nm CMOS Transistors

MOS transistors in 65-nm CMOS technology exposed to ultrahigh total ionizing dose (TID) levels show clear evidence of a true dose-rate (DR) dependence. In order to assess the impact of this effect and to understand its origin, an extensive measurement campaign has been carried out at different DRs, different temperatures, and different biases. Both nMOS and pMOS devices with different sizes and geometries were studied. The results obtained clearly show that the DR sensitivity of these devices is due to mechanisms that occur in the spacer insulators. Spacers have only recently been identified as an important element in the radiation response of MOS devices exposed to ultrahigh doses and the mechanisms causing their DR sensitivity appear to be largely compatible with the models developed to explain enhanced low dose-rate sensitivity (ELDRS) in linear bipolar transistors.

Radiation mechanism of gate-controlled lateral PNP bipolar transistors in the hydrogen environment

Hydrogen plays a crucial role in realizing modern silicon devices. Molecular hydrogen may be found in processes of integrated circuit fabrication and packaging, such as wafer cleaning procedure, film depositions, high- and low-temperature anneal and die attachment by forming gas. It has been shown that hydrogen has strong effects on the total dose and dose rate response to bipolar devices. In order to study the relationship between hydrogen and radiation-induced products, we preform two experiments by using gate-lateral PNP transistors. In the first experiment, one set of devices is soaked in 100% hydrogen gas for 60 h and another set is not soaked, they are together irradiated at 5 rad(Si)/s to a total dose of 50 krad(Si). In the second experiment, devices are irradiated at 50 rad(Si)/s to 100 krad(Si), and then one group is annealed in 100% hydrogen gas and the other is annealed in the air for 40 h at the same temperature. The results show that the damage to devices which are soaked in hydrogen before irradiation is stronger than the devices that are not soaked, the anneal characteristics of devices in hydrogen gas are also changed more greatly than in the air. So the hydrogen can enhance the radiation and anneal damage to bipolar transistors. Using the gate-sweep technique, the radiation-induced products are separated and show that the hydrogen that enters into the transistor will cause the interface traps to increase and oxide trapped charge to decrease. The main reason is that the hydrogen can react with the oxide trapped charge to produce protons which can transport to the Si/SiO&lt;sub&gt;2&lt;/sub&gt; interface, and then react with H-passivized bond to create interface trap. Based on the reaction mechanism presented in our work, a numerical model of enhanced low dose rate sensitivity including molecular hydrogen reaction and proton generation mechanism is established. The simulation results for the density of interface traps and oxide trapped charge show a trend consistent with the experimental data, which verifies the correctness of the damage mechanism. This research provides not only the basis of the study of damage mechanism of bipolar devices, but also the powerful support for hydrogen soaking irradiation acceleration method.

Investigation on γ radiation effects of N-channel VDMOSFETs irradiated without electric field stress

The ionizing radiation response of a kind of commercial n-channel VDMOSFETs irradiated without external electric field stress is investigated. The effects of total dose, dose rate and H2 ambient on the radiation response, and the post-irradiation annealing behaviors of the devices have been explored. The devices are degraded obviously after 1200 Gy (Si) γ radiation. No appreciable true dose rate effect (or Enhanced Low Dose Rate Sensitivity, ELDRS) has been observed in the tested devices. The small and irregular variations in performance degradation with dose rate are believed to come from the variability in the radiation response of the devices. In addition, the ambient of 100% H2 accelerates the total dose degradation of the devices. The γ radiation-induced performance degradation contains significantly negative shift of threshold voltage (Vth) and remarkable increase in off-state leakage current (Ileak), which are mainly caused by the increase in radiation-induced oxide-trapped charges. No obvious change in interface states is observed during the whole irradiation experiments and the annealing processes. The bias condition adopted in this work during irradiations is probably the reason for these unexpected phenomena. Furthermore, the annealing results indicate that the radiation-induced oxide-trapped charges seem to possess relatively stable properties, and could not be fully compensated or neutralized at room temperature (RT) or high temperatures, or under positive high electric field stress (PHEFS) of +70 V.

A modified accelerated testing method of ELDRS in extreme-low dose rate irradiation

Low dose rate radiation induced gain degradation in bipolar devices is considered to be the primary threat to the spacecraft reliability and service life. In order to examine the radiation tolerance of bipolar devices, it is recommended to use 10 m rad(Si)/s as the typical dose rate in the standards MIL-STD-883G. There is lack of solid study to prove the dose rate is sufficient enough low. Our latest experiment results showed that the enhanced low dose rate sensitivity (ELDRS) effects was not saturated at 10 m rad(Si)/s. To examine the reliability of bipolar devices in extreme low dose rate environment below 10 m rad(Si)/s in short time, we proposed a modified accelerated testing method of ELDRS effects in extreme-low dose rate irradiation based on elevated temperature irradiation and temperature-switching during irradiation, which is helpful to get quantified results in the whole low dose rate range.

Quantitative proton radiation therapy dosimetry using the storage phosphor europium-doped potassium chloride.

To (a) characterize the fundamental optical and dosimetric properties of the storage phosphor europium-doped potassium chloride for quantitative proton dosimetry, and (b) investigate if its dose radiation response can be described by an analytic radiation transport model. Cylindrical KCl:Eu2+ dosimeters with dimensions of 6mm diameter and 1mm thickness were fabricated in-house. The dosimeters were irradiated using both a Mevion S250 passive scattering proton therapy system and a Varian Clinac iX linear accelerator. Photostimulated luminescence (PSL) emission spectra, excitation spectra, and luminescence lifetimes were measured for both proton and photon irradiations. Dosimetric properties including radiation hardness, dose linearity, signal stabilization, dose rate sensitivity, and energy dependence were studied using a laboratory optical reader after irradiations. The dosimeters were modeled using physical quantities including mass stopping powers in the storage phosphor and water for a given proton beam, and mass energy absorption coefficients and massing stopping powers in detector and water for a given photon beam. KCl:Eu2+ exhibited optical emission and stimulation peaks at 421 and 560nm, respectively, for both proton and photon irradiations, enabling postirradiation readouts using a visible light source while detecting the PSL using a photomultiplier tube. KCl:Eu2+ showed a linear response from 0 to 8Gy absorbed dose-to-water, a large dynamic range up to 60Gy, dose-rate independence measured from 83 to 500MU/min, and a PSL lifetime of <5ms that is sufficiently short for supporting rapid scanning in a two-dimensional geometry. KCl:Eu2+ was highly reusable with only a slight signal decrease of ~3% at accumulated doses over 100Gy, which could be managed by a periodic recalibration. The detected PSL signal strength of the dosimeter in the proton field had been calculated accurately to a maximum discrepancy of 2% using known physical quantities along with its prior signal strength as measured in a photon field at the same dose-to-water. This discrepancy might be attributed to an under-response due to linear energy transfer (LET) effect. However, comparisons of depth-dose measurements in a spread-out Bragg peak (SOBP) field with a parallel-plate ionization chamber showed no clear evidence of LET effects. Furthermore, range measurements agreed with ionization chamber measurements to within 1mm. KCl:Eu2+ showed linear response over a large dynamic range for proton irradiations and reliably reproduced SOBP measurements as measured by ionization chambers. Its relatively low atomic number of 18 and near LET independence make it suited for quantitative proton dosimetry. In addition, its high radiation hardness means that it can be reused numerous times. Any potential measurement artifacts encountered in complex irradiation conditions should be able to be corrected for using known physical quantities.

Enhanced Low-Neutron-Flux Sensitivity Effect in Boron-Doped Silicon.

Space particle irradiation produces ionization damage and displacement damage in semiconductor devices. The enhanced low dose rate sensitivity (ELDRS) effect caused by ionization damage has attracted wide attention. However, the enhanced low-particle-flux sensitivity effect and its induction mechanism by displacement damage are controversial. In this paper, the enhanced low-neutron-flux sensitivity (ELNFS) effect in Boron-doped silicon and the relationship between the ELNFS effect and doping concentration are further explored. Boron-doped silicon is sensitive to neutron flux and ELNFS effect could be greatly reduced by increasing the doping concentration in the flux range of 5 × 109–5 × 1010 n cm−2 s−1. The simulation based on the theory of diffusion-limited reactions indicated that the ELNFS in boron-doped silicon might be caused by the difference in the concentration of remaining vacancy-related defects (Vr) under different neutron fluxes. The ELNFS effect in silicon becomes obvious when the (Vr) is close to the boron doping concentration and decreased with the increase in boron doping concentration due to the remaining vacancy-related defects being covered. These conclusions are confirmed by the p+-n-p Si-based bipolar transistors since the ELNFS effect in the low doping silicon increased the reverse leakage of the bipolar transistors and the common-emitter current gain (β) dominated by highly doped silicon remained unchanged with the decrease in the neutron flux. Our work demonstrates that the ELNFS effect in boron-doped silicon can be well explained by noise diagnostic analysis together with electrical methods and simulation, which thus provide the basis for detecting the enhanced low-particle-flux damage effect in other semiconductor materials.

Microbial radiosensitization using combined treatments of essential oils and irradiation- part B: Comparison between gamma-ray and X-ray at different dose rates

Stored rice and rice products are prone to contamination by pathogenic fungi and bacteria such as Aspergillus niger, Bacillus cereus, and Paenibacillus amylolyticus. Treatment with antimicrobial essential oils (EOs) and irradiation are options to control spoilage organisms. Microbial samples with or without fumigation with an oregano/thyme EO mixture were irradiated at 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5 kGy for calculation of a D10 value. The relative sensitivity was calculated as the ratio of D10 values for the irradiation plus oregano and thyme EO combination and irradiation alone treatments. In all cases, irradiation plus fumigation with the oregano and thyme EO mixture showed increased efficacy compared with irradiation alone. The relative sensitivity of γ-ray irradiation against A. niger was 1.22, 1.33, and 1.24 for radiation dose rates of 10.445, 4.558, and 0.085 kGy/h, respectively, however against B. cereus it was 1.28, 1.45, and 1.49, and against P. amylolyticus it was 1.35, 1.33, and 1.38, for respective γ-ray irradiation dose rates. The relative sensitivity of X-ray irradiation against A. niger, B. cereus, and P. amylolyticus was 1.63, 1.21, and 1.31, respectively, at the X-ray dose rate of 0.76 kGy/h. The results showed that the relative sensitivity of γ-ray irradiation was higher against the two bacteria than the fungus, whereas X-ray showed higher sensitivity against the fungus than the two bacteria. There was no consistent positive or negative relationship between dose rate and relative sensitivity. The results demonstrated the potential of an oregano and thyme EOs mixture as an antimicrobial agent and its efficacy to increase the radiosensitization of A. niger, B. cereus, and P. amylolyticus during γ-ray or X-ray irradiation treatments.

Enhanced low dose rate sensitivity (ELDRS) and reduced low dose rate sensitivity (RLDRS) in bipolar devices

Possible physical mechanism of enhanced low dose rate sensitivity (ELDRS) and reduced low dose rate sensitivity (RLDRS) in bipolar devices is described. Modification of the low dose rate conversion model is presented. The enhanced or reduced sensitivity can be connected with a specific position of the effective Fermi level relatively acceptor and donor radiation-induced interface traps. The qualitative and quantitative analysis of the low dose rate effects is presented. The effect of the oxide trapped charge on the value of the oxide electric field and the yield of the oxide charge were taken into account. It leads to dependence of the accumulation of radiation induced oxide charge and interface traps on the dose rate. In enhancement version the ELDRS and RLDRS conversion model describes the low dose rate effect in as ?true? dose rate effect.

Comparison of holes trapping and protons transport induced by low dose rate gamma radiation in oxide on different SiGe processes

Space-related electronics contain different types of oxide isolations which are the crucial factor resulting in device degradation and failure. Previous studies show that the local oxidation of silicon (LOCOS) isolation Silicon‑germanium heterojunction bipolar transistor (SiGe HBT) experience more significantly low dose rate sensitivity than that of shallow trench (STI) isolation SiGe HBTs and behave a “true” dose rate effect. In our work, the electron-hole pairs (EHPs) generation, holes trapped and protons transport inside oxide are simulated in LOCOS and STI isolation SiGe HBTs to explanation the different response t enhanced low dose rate sensitivity (ELDRS). The simulation results show that LOCOS oxide has a larger generation of EHPs than that of STI oxide leading to more surviving holes and protons release within oxide.

Modulation of radiation resistance by hydrogen soaking and aging treatment in transistors

Modulation mechanisms of hydrogen soaking and aging treatment are investigated for NPN transistors under γ-ray irradiation. Broad impact on low dose rate sensitivity is seen with hydrogen soaking, while enhanced low-dose-rate sensitivity is suppressed after aging treatment. This proves that hydrogen in bipolar transistors has a significant effect on ionization damage in the transistors.

How important is the dose rate sensitivity of 2D and 3D radiation dosimeters?

Several kinds of chemical 3D radiation dosimeters have been fabricated to acquire the dose distribution in clinical radiotherapy. A legitimate concern with every new dosimeter is its dose rate dependent response because, the dose rate in each point of the phantom during a clinical treatment is unknown. Unfortunately, many 3D dosimeters have shown some degree of dose rate dependence. In practice, radiation dosimeters are mostly calibrated using a calibration curve that is obtained by irradiating calibration vials with different doses but using a fixed dose rate. Therefore, when applying a dose calibration to an experimentally obtained dose distribution, a deviation between the measured dose distribution and the actual dose distribution can be expected. In this computational study, the effect of a dose rate dependent dosimeter response on a theoretical dose distribution has been investigated. In order to compare the effect of dose rate, a gamma evaluation is performed between the predefined dose distribution and the dose distribution that is affected by a dose rate dependent radiation response. It is found that a dose rate difference of -10%, results in a gamma pass rate of 100% in the 3D dose distribution.

Mechanism of Degradation Rate on the Irradiated Double-Polysilicon Self-Aligned Bipolar Transistor

The latent enhanced low dose rate sensitivity (ELDRS) effect is observed in the double-polysilicon self-aligned (DPSA) technology PNP bipolar junction transistor (BJT) irradiated with a high and low dose rate gamma ray, which is discussed from the perspective of the three-stage degradation rate of the excess base current. The great degradation rate as a result of the high dose irradiation of the first stage is dominantly ascribed to the positive oxide trap charges accumulated during a short irradiation, and then due to the competition between the recombination of electrons and capture of the hole by the traps. It declined sharply into a degradation rate saturated region of the second stage. However, for the low dose rate, the small increase in the degradation rate in the first stage is caused by the holes escaping from the initial recombination and being transported to the interface to form the interface states. Then, the competition between the steadily increasing interfacial trap charge and the continuously annealed shallow level oxide trap charge leads to the stable increase of degradation under low dose irradiation. Finally, in stage three, the increases of the degradation rates for high and low dose irradiation result from the different amounts of the hydrogen molecules generated by the hole reactive with depassiviated Si suspended bonds, which can interact with the deep level defects and release protons, causing an increase of interfacial trap charges with prolonged irradiation.

Hydrogen soaking irradiation acceleration method: application to and damage mechanism analysis on 3DG111 transistors

Bipolar devices are extremely sensitive to ionization effects, and their low dose rate radiation damage is more serious than their high dose rate radiation damage, which phenomenon is especially named enhanced low dose rate sensitivity. In the actual space radiation environment, the radiation dose rate of the device is extremely low. Currently, the enhanced low dose rate sensitivity effect has become a key factor of evaluating the reliability of spacecraft and its electronic systems, due to the fact that the low dose rate irradiation test needs longer time. The method to speed up the test on the ground is one of the hottest topics in this research area. In recent years, some researches have suggested that the use of hydrogen immersion irradiation for accelerating the test can simulate low dose rate radiation damage to some extent, but the damage mechanism has not been analyzed in detail. In this paper, the mechanisms of electrical properties and deep level defects for the 3DG111 transistor by &lt;sup&gt;60&lt;/sup&gt;Co gamma ray under high and low dose rates in the cases with and without hydrogen are investigated. In order to analyze the damage mechanism of bipolar junction transistor, the excess base current and deep level transient spectrum are measured by using semiconductor parameter analyzer and deep level transient spectroscopy. The experimental results show that the current gain degradation of 3DG111 transistor is more serious under low dose rate radiation than under high dose rate radiation, at the same time, the excess base current of transistor increases significantly. This shows that in the device there appears the enhanced low dose rate sensitivity. Under both high dose rate radiation and low dose rate irradiation, the radiation damage defects are the traps for both oxide positive charge and interface state. Under the low dose rate irradiation, there are two main reasons for the increase in transistor damage. First, the oxide charge concentration increases under low dose rate irradiation, and the oxide charge and interface state energy levels move toward the middle band. Eventually, the space charge region recombination of the transistor is intensified, and thus causing the excessive base current of the transistor to increase and transistor performance to degrade. The comparison shows that the number and type of defects under the high dose rate irradiation are the same as those under the low dose rate irradiation. Based on the analysis, the hydrogen treatment can be used as an effective method of accelerating the assessment of radiation damage enhancement effect at low dose rates.

Total Dose Testing Methodology for Bipolar Circuits Operating in the Jovian Radiation Environment

A total dose testing methodology for qualifying bipolar analog circuits for the Europa Clipper (EC) mission is presented. The method leverages the unique mission dose rate profile to bound device performance and reduces qualification test time from 1 year to 80 days. In addition, a new testing approach that simulates the mission dose profile revealed interesting information about the nature of radiation-induced defects in these “rad-hard” bipolar process lines. Results show that unlike bipolar parts from older generations (very sensitive to enhanced low dose rate sensitivity), these new processes seem to be dominated by oxide traps ( $\text{N}_{\mathrm {ot}}$ ) and not interface traps ( $\text{N}_{\mathrm {it}}$ ). This appears to be consistent with the mitigation used by vendors for reducing hydrogen (H2) contamination in their processing steps.