Dose Rate Sensitivity Research Articles

Synergistic effect of enhanced low-dose-rate sensitivity and single event transient in bipolar voltage comparator LM139

ABSTRACT The bipolar voltage comparator LM139 were exposed to ionizing radiation with a high-dose-rate of 10 rad(Si)/s and a low-dose-rate of 0.01 rad(Si)/s; then, pulsed laser single-event-transient (SET) testing was performed. The experimental results show that the SET phenomenon of LM139 after low-dose-rate irradiation of 0.01 rad(Si)/s is obviously different from the SET phenomenon of LM139 after high-dose-rate irradiation of 10 rad(Si)/s. After irradiation with the low-dose-rate, the comparator LM139 has Enhanced Low Dose Rate Sensitivity (ELDRS) in terms of the total dose effect, and the SET was further influenced by ELDRS. The greater gain degradation of the internal transistor in LM139 with low-dose-rate irradiation is the direct cause of this phenomenon.

Impact of elevated temperature applied during low dose rate irradiation on the degradation of BiCMOS operational amplifiers

The radiation-induced change in input bias current of bipolar input stage of BiCMOS operational amplifiers susceptible to enhanced low dose rate sensitivity (ELDRS) is studied as a function of the dose rate of gamma-irradiation and of the temperature applied during irradiation. Experimental results and results of the simulation with the conversion model of radiation-induced interface traps formation have shown that degradation enhancement factor KD provided by the temperature applied during irradiation exhibits a nonmonotonic dependence on the dose rate: an elevated temperature provides the maximum increase in the degradation, if the dose rate is chosen from the range 0.1–1 rad(Si)/s, while irradiation with high (≥101 rad(Si)/s) and low dose rate (≤10−2 rad(Si)/s) provides approximately the same values of KD. This range can be recommended for accelerated testing of bipolar and BiCMOS devices, if enhanced degradation in low dose rate conditions of space application is modeled by irradiation at elevated temperature.

Dose-Rate Sensitivity of 65-nm MOSFETs Exposed to Ultrahigh Doses

The radiation response of complementary metal–oxide–semiconductor (CMOS) gate oxides is typically insensitive to true dose-rate effects, but damage in deep-sub-micrometer technologies is dominated by ionization mechanisms in thick isolation oxides surrounding the transistors. Recent results in 65-nm FETs demonstrated that performance degradation in ultrahigh total ionizing dose (TID) experiments is due to defects in the isolation shallow trench isolation oxide or in the materials composing the lightly doped drain spacers. These insulators are thick, deposited, and crossed by a low electric field, characteristics similar to those typical of passivation oxides in linear bipolar technologies for which an enhanced low-dose-rate sensitivity (ELDRS) has been observed and systematically studied. We report in this paper the clear evidence of a dose-rate sensitivity of the TID-induced damage in both 130- and 65-nm CMOS technologies exposed to different radiation sources (X-rays and $\gamma $ -rays from a 60Co source). This sensitivity is attributed to mechanisms similar to those explaining ELDRS in bipolar devices and represents a significant challenge to the definition of a qualification procedure for circuits to be used in extreme radiation environments.

Investigation of enhanced low dose rate sensitivity in SiGe HBTs by 60Co γ irradiation under different biases

This paper evaluates enhanced low dose rate sensitivity (ELDRS) in Silicon–Germanium heterojunction bipolar transistors (SiGe HBTs) which are isolated by LOCOS process. The 60Co gamma irradiations were performed at 80 rad (Si)/s and 0.1 rad (Si)/s respectively in order to investigate dose rate dependence of the SiGe HBT. Devices were set in forward, saturated, cutoff, and all-grounded biases during the irradiation. The degradation mechanism of different dose rate irradiations was analyzed via measurement of forward Gummel mode and inverse Gummel mode both pre- and post- irradiation. The results show that ELDRS exists at forward, saturated, and all-grounded biases irradiations. The dose rate dependences of various irradiated biases are different in the SiGe HBT. The interface-traps both in EB Spacer and LOCOS are the major irradiated damages in the SiGe HBT for the low dose rate irradiation. ELDRS is directly related to the quality, thickness, and shape of oxide layers.

The impact of the oxygen scavenger on the dose-rate dependence and dose sensitivity of MAGIC type polymer gels

Recent developments in radiation therapy aimed at more precise dose delivery along with higher dose gradients (dose painting) and more efficient dose delivery with higher dose rates e.g. flattening filter free (FFF) irradiation.Magnetic-resonance-imaging based polymer gel dosimetry offers 3D information for precise dose delivery techniques. Many of the proposed polymer gels have been reported to exhibit a dose response, measured as relaxation rate ΔR2(D), which is dose rate dependent. A lack of or a reduced dose-rate sensitivity is very important for dosimetric accuracy, especially with regard to the increasing clinical use of FFF irradiation protocols with LINACs at high dose rates. Some commonly used polymer gels are based on Methacrylic-Acid-Gel-Initiated-by-Copper (MAGIC). Here, we report on the dose sensitivity (ΔR2/ΔD) of MAGIC-type gels with different oxygen scavenger concentration for their specific dependence on the applied dose rate in order to improve the dosimetric performance, especially for high dose rates. A preclinical x-ray machine (‘Yxlon’, E = 200 kV) was used for irradiation to cover a range of dose rates from low min = 0.6 Gy min−1 to high max = 18 Gy min−1. The dose response was evaluated using R2-imaging of the gel on a human high-field (7T) MR-scanner. The results indicate that all of the investigated dose rates had an impact on the dose response in polymer gel dosimeters, being strongest in the high dose region and less effective for low dose levels. The absolute dose rate dependence of the dose response in MAGIC-type gel is significantly reduced using higher concentrations of oxygen scavenger at the expense of reduced dose sensitivity. For quantitative dose evaluations the relative dose rate dependence of a polymer gel, normalized to its sensitivity is important. Based on this normalized sensitivity the dose rate sensitivity was reduced distinctly using an increased oxygen scavenger concentration with reference to standard MAGIC-type gel formulation at high dose rate levels. The proposed gel composition with high oxygen scavenger concentration exhibits a larger linear active dose response and might be used especially in FFF-radiation applications and preclinical dosimetry at high dose rates. We propose in general to use high dose rates for calibration and evaluation as the change in relative dose sensitivity is reduced at higher dose rates in all of the investigated gel types.

Estimation of enhanced low dose rate sensitivity mechanisms using temperature switching irradiation on gate-controlled lateral PNP transistor**Project supported by the National Natural Science Foundation of China (Grant Nos. U1532261 and 1630141).

The mechanisms occurring when the switched temperature technique is applied, as an accelerated enhanced low dose rate sensitivity (ELDRS) test technique, are investigated in terms of a specially designed gate-controlled lateral PNP transistor (GLPNP) that used to extract the interface traps (Nit) and oxide trapped charges (Not). Electrical characteristics in GLPNP transistors induced by 60Co gamma irradiation are measured in situ as a function of total dose, showing that generation of Nit in the oxide is the primary cause of base current variations for the GLPNP. Based on the analysis of the variations of Nit and Not, with switching the temperature, the properties of accelerated protons release and suppressed protons loss play critical roles in determining the increased Nit formation leading to the base current degradation with dose accumulation. Simultaneously the hydrogen cracking mechanisms responsible for additional protons release are related to the neutralization of Not extending enhanced Nit buildup. In this study the switched temperature irradiation has been employed to conservatively estimate the ELDRS of GLPNP, which provides us with a new insight into the test technique for ELDRS.

A Multi-Time-Step Finite Element Algorithm for 3-D Simulation of Coupled Drift-Diffusion Reaction Process in Total Ionizing Dose Effect

In order to study the total ionizing dose degradation and enhanced low dose rate sensitivity effect for semiconductor devices in the space environment, we simulate the drift-diffusion-reaction processes in a 3-dimensional SiO2–Si system. Since the time scale of the drift-diffusion processes is much larger than that of the chemical reaction processes, we use a multi-time-step algorithm to calculate the two types of processes, respectively. In this paper, partial differential equations used to describe the electrodiffusion processes are solved by a finite element method, while the chemical reactions taking place independently in every mesh node are solved as ordinary differential equations. We reproduce qualitative properties of total ionizing dose effect and compare our numerical results with experimental data and other simulation results. This paper paves a way for 3-D simulation of total ionizing dose and enhanced low dose rate sensitivity with high efficiency and robustness.

Thin film organic photodetectors for indirect X-ray detection demonstrating low dose rate sensitivity at low voltage operation

Developments in the field of organic semiconductors have generated organic photodetectors with high quantum efficiency, wide spectral sensitivity, low power consumption, and unique form factors that are flexible and conformable to their substrate shape. In this work, organic photodetectors coupled with inorganic CsI(Tl) scintillators are used to showcase the low dose rate sensitivity that is enabled when high performance organic photodetectors and scintillator crystals are integrated. The detection capability of these organic-inorganic coupled systems to high energy radiation highlights their potential as an alternative to traditional photomultiplier tubes for nuclear spectroscopy applications. When exposed to Bremsstrahlung radiation produced from an X-ray generator, SubPc:C60, AlPcCl:C70, and P3HT:PC61BM thin film photodetectors with active layer thicknesses less than 100 nm show detection of incident radiation at low and no applied bias. Remarkably low dose rates, down to at least 0.18 μGy/s, were detectable with a characteristic linear relationship between exposure rate and photodetector current output. These devices also demonstrate sensitivities as high as 5.37 mC Gy−1 cm−2 when coupled to CsI(Tl). Additionally, as the tube voltage across the X-ray generator was varied, these organic-inorganic systems showed their ability to detect a range of continuous radiation spectra spanning several hundred keV.

Excellence is the Real Enemy of Practicality! Relevance to Radiation Countermeasure Development

<p>Radiation countermeasures development was undertaken almost six decade ago at AFRRI, USA with the aim to protect military as well as civilian personals against accidental or deliberate radiation exposure. Later on, with the advancement of radiation technologies and exploration of X-ray or γ-rays for diagnostics and therapeutic purposes, probability of radiation exposure was enhanced multifold. Therefore, importance of radiation countermeasures development was recognised globally. However, despite the concentrated efforts, till date not a single FDA approved radio protective drug is available for emergency uses. Major impediments identified in this are included variability in radio protective efficacy with different experimental models, radiation dose rate, radiation types and differential radio sensitivity of various biological systems. No way to evaluate radio protective efficacy of an agent in human volunteers. It is sufficient to realise that uniform excellence may not be achieved in the area of radiation countermeasure development. However, practical excellence based on the radioprotector’s application scenario can be achieved. Different radiation accidental scenarios and feasible practical parameters of excellence for radiation countermeasure development for particular types of incidental, accidental or deliberated radiation exposure are described.</p>

True dose rate physical mechanism of ELDRS effect in bipolar devices

Physical mechanism of enhanced low dose rate sensitivity effect in bipolar devices is observed. It is shown, that the accumulation of the defects during low dose rate irradiation depends on the irradiation time only, while true dose rate effects contribution to enhanced low dose rate sensitivity effect is related with processes during post-irradiation annealing. The conversion model of low dose rate effect was used for numerical description of the radiation responses of input bias currents of bipolar operational amplifiers in wide range of dose rates.

An Investigation of ELDRS in Different SiGe Processes

Enhanced low dose rate sensitivity (ELDRS) in different process Silicon–Germanium heterojunction bipolar transistors (SiGe HBTs) is investigated. Low and high dose rate irradiations are performed to evaluate the ELDRS of SiGe HBTs manufactured by Tsinghua University (THU). THU SiGe HBTs experience significantly low dose rate sensitivity than that of IBM 8HP SiGe HBTs and behave a “true” dose rate effect. TCAD models were used to explicate the microcosmic structure in THU and IBM 8HP SiGe HBTs. Comparison and discussion show that different SiGe processes may involve different HBT structures and device designs which are the critical influence of ELDRS effect. The different responses of ELDRS should be first attributed to the device structure and design in nature, particularly the geometry of emitter–base junction and the isolation structure.

Impact of Passivation Layers on Irradiation Response of PNP Transistors Under Different Dose Rates

In this paper, the effect of nitride passivation layer on the irradiation response of PNP bipolar junction transistors (BJTs) by Co-60 gamma ray under high and low dose rates is investigated. In order to analyze the damage mechanisms on BJTs with or without nitride passivation layer induced by gamma rays, the excess base current and deep level transient spectroscopy are measured. Experimental results show that there is an enhanced low dose rate sensitivity for PNP transistors with and without nitride passivation layers. In addition, the degradation of PNP BJTs with nitride layer is more serious than that of PNP BJTs without nitride layer under the same irradiation condition. Compared with the PNP BJTS without nitride passivation layer, ionization effect in the PNP BJTs with nitride passivation layer can generate greater density of interface traps with deeper energy level at a given dose rate. Moreover, the irradiated BJTs under the low dose rate produces deeper energy level of interface traps than that under the high dose rate. Based on the analysis, hydrogen is an important factor influencing the dose rate sensitivity and the degradation of the BJT with nitride passivation layers.

ELDRS Susceptibility of Bipolar Transistors and Integrated Circuits During Low Temperature Irradiation

The enhanced low dose rate sensitivity (ELDRS) susceptibility of 2N2222 bipolar transistors and LM111 voltage comparators was investigated during irradiation at low temperature and compared with corresponding room-temperature data. The possible physical mechanism of the ELDRS effect in bipolar transistors and integrated circuits during irradiation at room temperature and low temperature was described. A device that is ELDRS-free at room temperature suffers from this effect during irradiation at low temperature.

Non-equilibrium carrier capture, recombination and annealing in thick insulators and their impact on radiation hardness

This paper describes an approach to prediction of the thick insulators' radiation response based on modeling of the charge yield, which is dependent on irradiation temperature, dose rate, and electric field magnitudes. Temperature behavior of the charge yield and degradation saturation due to the interface precursor depletion has been modeled and simulated. Competition between the time-dependent and true dose rate (ELDRS) effects has been simulated and discussed within a framework of the rate-equation-based mathematical model. It was shown that the precursor trap in the thick insulating oxides can be important at high dose rates. It was also shown that full filling of the shallow hole traps in the insulating oxide bulk can cause suppression of dose-rate sensitivity at relatively high dose rates, especially in thick insulators.

Conversion model of radiation-induced interface-trap buildup and the some examples of its application

It is supposed that the rechargeable radiation-induced positive centers in the oxide must have energy levels within the Si forbidden gap. These assumptions served as the basis for the physical model of the interface-trap build-up and enhanced low dose rate sensitivity (ELDRS) in bipolar devices. As examples of using the proposed conversion model is considered for bipolar devices space application.

Total ionizing dose effects of domestic SiGe HBTs under different dose rates

The total ionizing radiation (TID) response of commercial NPN silicon germanium hetero-junction bipolar transistors (SiGe HBTs) produced domestically are investigated under dose rates of 800 mGy(Si)/s and 1.3 mGy(Si)/s with a Co-60 gamma irradiation source. The changes of transistor parameters such as Gummel characteristics, and excess base current before and after irradiation, are examined. The results of the experiments show that for the KT1151, the radiation damage is slightly different under the different dose rates after prolonged annealing, and shows a time dependent effect (TDE). For the KT9041, however, the degradations of low dose rate irradiation is higher than for the high dose rate, demonstrating that there is a potential enhanced low dose rate sensitivity (ELDRS) effect for the KT9041. The possible underlying physical mechanisms of the different dose rates responses induced by the gamma rays are discussed.

Real-time dosimetry in radiotherapy using tailored optical fibers

Real-time dosimetry plays an important role for accurate patient-dose measurement during radiotherapy. A tiny piece of laboratory fabricated Ge-doped optical fiber has been investigated as a radioluminescence (RL) sensor for real-time dosimetry over the dose range from 1 Gy to 8 Gy under 6 MV photon beam by LINAC. Fiber-coupled software-based RL prototype system was used to assess essential dosimetric characteristics including dose response linearity, dose rate dependency, sensitivity, repeatability and output dependence on field sizes. The consistency level of RL photon counts versus dose rate was also compared with that of standard Al2O3:C chips. Sensitivity of Ge-doped fiber were found to be sufficiently sensitive for practical use and also provided linear dose responses for various dose rates from 100 cGy/min to 600 cGy/min using both 6 MV photon and 6 MeV electron beams. SEM-EDX analysis was performed to identify Ge-dopant concentration level within the optical fiber RL material. Accumulated doses were also estimated using simple integral technique and the error was found to be around less than 1% under dissimilar dose rates or repeat measurements. The evaluation of the Ge-doped optical fiber based RL dosimeter system indicates its potential in medical dosimetry.

Dose-rate sensitivity of deep sub-micro complementary metal oxide semiconductor process

Enhancing low dose rate sensitivity (ELDRS) in bipolar device is a major problem of liner circuit radiation hardness prediction for space application. ELDRS is usually attributed to space-charge effect. A key element is the difference in transport rate between holes and protons in SiO2. Interface-trap formation at high dose rate is reduced due to positive charge buildup in the Si/SiO2 interfacial region (due to the trapping of holes and/or protons) which reduces the flow rates of subsequent holes and protons (relative to the low-dose-rate case) from the bulk of the oxide to the Si/SiO2 interface. Generally speaking, the dose rate of metal oxide semiconductor (MOS) device is time dependent when annealing of radiation-induced charge is taken into account. The degradation of MOS device induced by the low dose rate irradiation is the same as that by high dose rate when annealing of radiation-induced charge is taken into account. However, radiation response of new generation MOS device is dominated by charge buildup in shallow trench isolation (STI) rather than gate oxide as older generation device. Unlike gate oxides, which are routinely grown by thermal oxidation, field oxides are produced using a wide variety of deposition techniques. As a result, they are typically thick (100 nm), soft to ionizing radiation, and electric field is far less than that of gate oxide, which is similar to the passivation layer of bipolar device and may lead to ELDRS. Therefore, dose-rate sensitivities of n-type metal oxide semiconductor field effect transistor (NMOSFET) and static random access memory (SRAM) manufactured by 0.18 m complementary metal oxide semiconductor (CMOS) process are explored experimentally and theoretically in this paper. Radiation-induced leakages in NMOSFET and SRAM are examined each as a function of dose rate. Under the worst-case bias, the degradation of NMOSFET is more severe under the low dose rate irradiation than under the high dose rate irradiation and anneal. Moreover, radiation-induced standby current rising in SRAM is more severe under the low dose rate irradiation than under the high dose rate irradiation even when anneal is not considered. The above experimental results reveal that the dose-rate sensitivity of deep sub-micron CMOS process is not related to time-dependent effects of CMOS devices. Mathematical description of the combination between enhanced low dose-rate sensitivity and timedependent effects as applied to radiation-induced leakage in NMOSFET is developed. It has been numerically found that non time-dependent effect of deep sub-micron CMOS device arises due to the competition between enhanced low dose-rate sensitivity in bottom of STI and time-dependent effect at the top of STI. The high dose rate irradiation is overly conservative for devices used in a low dose rate environment. The test method provides an extended room temperature anneal test to allow leakage-related parameters that exceed postirradiation specifications to return to a specified range.

Characterization of MOSFET dosimeters for low-dose measurements in maxillofacial anthropomorphic phantoms.

The aims of this study were to characterize reinforced metal‐oxide‐semiconductor field‐effect transistor (MOSFET) dosimeters to assess the measurement uncertainty, single exposure low‐dose limit with acceptable accuracy, and the number of exposures required to attain the corresponding limit of the thermoluminescent dosimeters (TLD). The second aim was to characterize MOSFET dosimeter sensitivities for two dental photon energy ranges, dose dependency, dose rate dependency, and accumulated dose dependency. A further aim was to compare the performance of MOSFETs with those of TLDs in an anthropomorphic phantom head using a dentomaxillofacial CBCT device. The uncertainty was assessed by exposing 20 MOSFETs and a Barracuda MPD reference dosimeter. The MOSFET dosimeter sensitivities were evaluated for two photon energy ranges (50–90 kVp) using a constant dose and polymethylmethacrylate backscatter material. MOSFET and TLD comparative point‐dose measurements were performed on an anthropomorphic phantom that was exposed with a clinical CBCT protocol. The MOSFET single exposure low dose limit (25% uncertainty, k=2) was 1.69 mGy. An averaging of eight MOSFET exposures was required to attain the corresponding TLD (0.3 mGy) low‐dose limit. The sensitivity was 3.09±0.13 mV/mGy independently of the photon energy used. The MOSFET dosimeters did not present dose or dose rate sensitivity but, however, presented a 1% decrease of sensitivity per 1000 mV for accumulated threshold voltages between 8300 mV and 17500 mV. The point doses in an anthropomorphic phantom ranged for MOSFETs between 0.24 mGy and 2.29 mGy and for TLDs between 0.25 and 2.09 mGy, respectively. The mean difference was −8%. The MOSFET dosimeters presented statistically insignificant energy dependency. By averaging multiple exposures, the MOSFET dosimeters can achieve a TLD‐comparable low‐dose limit and constitute a feasible method for diagnostic dosimetry using anthropomorphic phantoms. However, for single in vivo measurements (<1.7 mGy) the sensitivity is too low.PACS number: 87.50.wj

엑스선에 의한 반도체 소자의 방사선 손상

Recently, Due to the increased industry using radiation inspection equipment in the semiconductor, this demand of technology research is increasing. Although semiconductor inspection equipment is using low energy X-ray from 40 keV to 120 keV, Studies of radiation damage about the low energy X-ray are lacking circumstance in our country. Therefore, It is study that BJT (bipolar junction transistor) of one type of semiconductor elements are received radiation damage by low energy X-ray. BJT were used to the NXP semiconductor company's BC817-25 (NPN type), and Used the X-ray generator for the irradiation. Radiation damage of BJT was evaluated that confirm to analyse change of collector-emitter voltage of before and after X-ray irradiation when current gain fixed to 10. X-ray generator of tube voltage was setting 40 kVp, 60 kVp, 80 kVp, 100 kVp, 120 kVp and irradiation time was setting 180s, 360s, 540s into 180s intervals. As the result, We confirmed radiation damage in BJT by low energy X-ray under 120 keV energy, and Especially the biggest radiation damage was appeared at the 80 kVp. It is expected that ELDRS (enhanced low dose rate sensitivity) phenomenon occurs on the basis of 80 kVp. This studies expect to contribute effective dose administration of semiconductor inspection equipment using low energy X-ray, Also Research and Development of X-ray filter.