Monte Carlo Calculations of Irradiation Test Photon Spectra

Calculations of scattered photon spectra in concrete rooms are made, by means of the Monte Carlo method, for Co-60 sources of the type used in irradiation testing of electronic devices. It is found that the scattered photon spectrum shape is heavily dependent on the location of source and target, and that in devices where dose enhancement can occur, there can be substantial variation in the absorbed dose due to this strong dependence on location. Scattered photon spectra are also obtained for two types of irradiation test cells. Additionally, dose enhancement ratios obtained with a coupled photon-electron Monte Carlo calculation are given for a gold-metallized silicon device.     

Improved Flash X-Ray Simulation Using the Grad-B Interaction

A new concept for improving the simulation capabilities of flash x-ray sources has been analyzed. The method makes use of adiabatic, single-particle drift in externally applied azimuthal magnetic fields in order to focus, reflex, and stagnate a relativistic electron beam at a converter foil. It yields higher extraction efficiencies and softer spectra than those obtained from more conventional schemes. Power deposition in standard dosimetry is enhanced by factors of 2 to 3. Additional enhancement of time-dependent effects may be achieved through bunching.     

Dose and Dose Rate Dependence of 8080a Microprocessor Failures

The occurrence of transient upset and catastrophic failure in 8080A microprocessors was investigated over a dose-rate range of 6 × 10-4 to 3 × 10+10 rads/sec. The transient upset and catastrophic failure levels depended on both dose and dose-rate. For example, the dose at which catastrophic failure occurs is 10 times greater at the highest dose-rates investigated than at the lowest. Irradiation was performed using both low energy (45 kV x-ray tube, 200 kV flash x-ray source) and high energy (Co 60, Linac) sources. The observed transient upset and catastrophic failure levels were significantly higher for low energy irradiation than for high energy irradiation. These results have important implications for models of ionizing radiation effects in MOS devices.     

1988 IEEE Annual Conference on Nuclear and Space Radiation EffectsConference

The following topics are dealt with: basic mechanisms of radiation effects; dosimetry and energy-dependent effects; sensors in and for radiation environments; EMP/SGEMP/IEMP phenomena; radiation effects on isolation technologies; spacecraft charging and space radiation effects; device radiation effects and hardening; hardness assurance and testing techniques; IC radiation effects and hardening; and single-event phenomena. Abstracts of individual papers can be found under the relevant classification codes in this or other issues     

Low Energy Dosimetry With Photon Counting Pixel Detectors Such as Medipix

Hybrid semiconductor photon counting pixel detectors like the Medipix detector have several advantages for an use in X-ray dosimetry. The noiseless photon counting principle allows to monitor low photon energies down to 3.5 keV. Due to the small pixel size (55 mum in case of Medipix2) dosimetry at very high dose rates is possible still processing each photon individually. The large amount of pixels in combination with the possible thickness of the sensor layer enables dosimetry at very low dose rates. A method has been developed to determine personal dose equivalents from the number of counts in energy deposition intervals measured with a semiconductor photon counting pixel detector, despite the strong influence of charge sharing effects among pixels. We tested the method experimentally by reconstructing the air kerma free in air for different qualities of X-radiation in the energy range below 150 keV with an accuracy better than 4%. We show that the response of a dosimeter based on a hybrid photon counting pixel detector can fulfill the IEC type testing requirements. The statistical precision is high due to the thickness and the large area of the sensor layer. We estimate that a dosimeter based on the Medipix detector will be able to cope with dose rates of more than approximately 57 Sv/h for mathdot Hp (0.07) or 19 Sv/h for mathdot Hp(10) . We outline the advantages and perspectives of using this kind of detector in a dosimeter in comparison to standard active personal dosimeters.     

Effects of package geometry, materials, and die design on energydependence of pMOS dosimeters

This paper presents the results of further studies of dose enhancement in dual and single-dielectric pMOSFET dosimeters for various package and die designs. Eight different MOSFET designs and package types were investigated over a photon energy range from 14 to 1250 keV. Seven X-ray effective energies and two radioactive sources of cesium and cobalt provided the radiation. As in a previous study, Rutherford back-scattered electrons were primarily responsible for the dose enhancement factors which achieved values as high as 20. Packages filled with silicon grease, aluminum oxide, or paraffin eliminated the contribution of back-scatter to the enhanced dose. These modifications allowed measurements of the usual dose enhancement at the aluminum or polysilicon gate-silicon nitride (dual dielectric devices), or silicon dioxide interfaces (single dielectric parts), and at the silicon nitride-silicon dioxide interface. In addition to the primary peak in the DEF (dose enhancement factor) curve versus energy at 45.7 keV, there is a second peak at about 215 keV. This peak might be due to enhancements at the interfaces of a MOSFET. These interface effects were small in the single-insulator parts in standard ceramic packages, and significantly larger in the dual-insulator devices. The effects were reduced by filling the packages with the materials as previously described. The geometry of the package, for example, the size of the air gap between the die's surface, and the lid of the package impacts the value of the DEF     

Dose Enhancement at the Emitter Interface of a Bipolar Junction Transistor

This paper constitutes a first step toward solving the genuinely difficult problem of relating electronic circuit performance to the fundamental parameters of the device fabrication process. In particular, this work provides an in-depth analysis of radiation dose enhancement as might be observed, for example, at the emitter contact-bulk emitter interface of a bipolar junction transistor. A closed-form approximate solution to the charge continuity equation demonstrates that (1) the radiation-induced excess carrier density profile is maximized within two diffusion lengths of a dissimilar interface, and (2) impure interfaces, as measured by carrier recombination velocity, can dramatically neutralize the undesired electrical effects of significant dose enhancement.     

Electron Beam Simulation of Pulsed Photon Effects in Electronic Devices at Very High Doses and Dose Rates

Large high-energy flash X-ray simulation facilities are expensive to build and operate. As a result, the radiation effects community has at it's disposal a limited number of X-ray sources with the capability of providing the very high levels of radiation (hundreds of k rad(Si)) required for R and D. Because of the inefficiency of bremsstrahlung production, an accelerator which provides only small doses in the X-ray mode could readily provide the very high total doses and associated dose rates via direct electron irradiation. A prerequisite for electron beam testing is a satisfactory demonstration of the fidelity of the simulation. This paper presents the experimental details and results of such an assessment. It was demonstrated in this work that electron beams do simulate the effects of high-energy bremsstrahlung X-rays when testing semiconductor devices for very high dose and dose rate effects. However, it was also found that the effects of charge deposition from the electron beam can dramatically perturb the nominal irradiation bias conditions. In electronic devices where radiation induced degradation is a function of applied potentials (e.g., MOS devices), this charge capture can totally invalidate the simulation unless the experimenter is aware of and compensates for the effect.     

Development of a radiographic method for measuring the discrete spectrum of the electron beam from a plasma focus device

An indirect method is proposed for measuring the relative energy spectrum of the pulsed electron beam of a plasma focus device. The Bremsstrahlung x-ray, generated by the collision of electrons against the anode surface, was measured behind lead filters with various thicknesses using a radiographic film system. A matrix equation was considered in order to explain the relation between the x-ray dose and the spectral amplitudes of the electron beam. The electron spectrum of the device was measured at 0.6 mbar argon and 22 k V charging voltage, in four discrete energy intervals extending up to 500 ke V. The results of the experiments show that most of the electrons are emitted in the 125–375 ke V energy range and the spectral amplitude becomes negligible beyond 375 ke V.?     

脉冲堆快中子实验装置设计

本文利用蒙特卡罗方法和离散坐标法设计了满足器件辐照效应研究的脉冲堆快中子实验装置.采用SAND-Ⅱ多箔活化法和热释光剂量片法对装置参数进行了测试分析,验证了装置设计参数与实验测量值符合一致.     

Reduction of ?-Particle Sensitivity in Dynamic Semiconductor Memories (16K d-RAMs) by Neutron Irradiation

Trace radioactive impurities found in all semiconductor devices induce soft errors in semiconductor memories by ?-particle emission. Data taken on 16K d-RAMs which have been fast neutron irradiated to fluences from 1013 to 1016 n/cm2 show that soft errors in these devices can be significantly reduced while maintaining acceptable device operation. Reduction in soft error rate by factors as high as 80 are observed following irradiation and thermal annealing. The effect on device parameters is discussed as well as the defects responsible for this beneficial radiation processing. Estimates of the soft error rate improvement to be expected on higher density memory devices (64K and 256K d-RAMs) will also be presented.     

Gamma Total Dose Effects on ALS Bipolar Oxide Sidewall Isolated Devices

Advances in bi-polar technology that increase device performance through the use of oxide sidewall isolation have revived concerns about total dose radiation effects. Extensive Cobalt 60 tests of Texas Instruments ALS devices were conducted and comparative results of "walled" and "nested" emitter devices are included. It was determined that inversion at the Si-SiO2 interface between the isolation oxide and residual EPI material was the source of IIH leakage. Controls were established to improve gamma total dose tolerance.     

Upset Phenomena Induced by Energetic Protons and Electrons

Large scale integrated static Random-Access-Memory devices have been exposed to 18-130 MeV protons and found to exhibit soft errors at rates of about one upset for 109 protons/cm2. These rates are two to three orders of magnitude lower than previously observed for dynamic memory devices exposed under identical conditions. Both sets of data appear to be consistent with model calculations based on the assumption that the errors are the result of secondary particles created in inelastic interactions between the incident protons and the nuclei of atoms comprising the device. The model was found to agree with pulse height spectra obtained with silicon detectors of various thicknesses exposed to 130 MeV protons. Both types of memory devices were also exposed to short bursts (10-150 nsec) of 10 ± 0.5 MeV electrons. A sharp threshold was found in the soft-error response to increasing dose rates. Most devices became more sensitive with increasing duration of the electron pulse in the sense that they required lower dose rates to exhibit soft errors. On the other hand the threshold total dose for failure increased with pulse duration.     

Important Considerations for SEM Total Dose Testing

The kilovolt electron beam utilized in a scanning electron microscope has been of interest as a tool for total dose screening of semiconductor devices for hardness assurance because of its convenience and because devices can be selectively irradiated directly at the wafer level. A number of factors such as the depth-dose distribution of kilovolt electrons, the dose-rate, uniformity of exposure, and device biasing must be considered when applying this technique. This paper is devoted to these and other aspects of SEM total dose testing.     

Radiation dosimetry using three-dimensional optical random access memories

Three-dimensional optical random access memories (3D ORAMs) are a new generation of high-density data storage devices. Binary information is stored and retrieved via a light induced reversible transformation of an ensemble of bistable photochromic molecules embedded in a polymer matrix. This paper describes the application of 3D ORAM materials to radiation dosimetry. It is shown both theoretically and experimentally, that ionizing radiation in the form of heavy charged particles is capable of changing the information originally stored on the ORAM material. The magnitude and spatial distribution of these changes are used as a measure of the absorbed dose, particle type and energy. The effects of exposure on 3D ORAM materials have been investigated for a variety of particle types and energies, including protons, alpha particles and 12C ions. The exposed materials are observed to fluoresce when exposed to laser light. The intensity and the depth of the fluorescence is dependent on the type and energy of the particle to which the materials were exposed. It is shown that these effects can be modeled using Monte Carlo calculations. The model provides a better understanding of the properties of these materials. which should prove useful for developing systems for charged particle and neutron dosimetry/detector applications.     

剂量增强效应简介

本文介绍了剂量增强效应的起因、定义以及器件和电容器的剂量增强效应;提供了一般电子系统中使用的器件在X,γ射线环境中的剂量增强系数参考数据,有较宽的适应范围。     

Cosmic-Ray-Induced Errors in MOS Devices

The results are reported for a comprehensive analytical and experimental study of galactic cosmic-ray-induced errors in MOS devices. An error rate model is described which utilizes exact expressions for a path-length distribution function and a Linear Energy Transfer (LET) spectrum for the cosmic ray environment to calculate the expected cosmic-ray-induced error rate in space for a given parallel-piped-shaped sensitive volume. The model validity is confirmed by comparison of predictions to bit-error data from devices in orbiting satellites, and to cosmic ray simulation measurements on the same device types at a cyclotron. The experimental results and model predictions are described for a wide variety of device types, including NMOS, PMOS, CMOS/bulk, CMOS/SOS, and ANOS.     

Gamma dosimetry using red 4034 Harwell dosimeters in mixed fission neutrons and gamma environments

The radiation tolerance testing of materials or opto-electronic components in a nuclear reactor requires a careful determination of the different components of the mixed gamma-neutron field. While the characterization of the neutron field can be performed using, for example, activation foils and validated by Monte-Carlo computation codes, the experimental measurement of the in-reactor gamma dose rate requires the use of costly ionization chambers. In this paper, we evaluate the possibility of using Red Perspex from Harwell Technologies for routine gamma dosimetry in mixed gamma neutron field. Self-powered gamma detectors and ionization chambers were used as reference dosimeters. We show that the accuracy of the Red 4034 dosimeters is better than 10% in mixed gamma-neutron fields.     

Radiation Effects on MOS Devices: Dosimetry, Annealing, Irradiation Sequence, and Sources

This paper reports on some investigations of dosimetry, annealing, irradiation sequences, and radioactive sources, involved in the determination of radiation effects on MOS devices. Results show that agreement in the experimental and theoretical surface to average doses support the use of thermo-luminescent dosimeters (manganese activated calcium fluoride) in specifying the surface dose delivered to thin gate insulators of MOS devices. Annealing measurements indicate the existence of at least two energy levels, or activation energies, for recovery of soft oxide MOS devices after irradiation by electrons, protons, and gammas. Damage sensitivities of MOS devices were found to be independent of combinations and sequences of radiation type or energies. Comparison of various gamma sources indicated a small dependence of damage sensitivity on the Cobalt facility, but a more significant dependence in the case of the Cesium source. These results were attributed to differences in the spectral content of the several sources.     

Dose intercomparison studies for 60Co gamma-ray and electron beam irradiation in the year 2002

1 Introduction With the rapid development of radiation process- ing by electron beam irradiation in China, it is more Ever since 1962, alanine/EPR dosimetry system and more needed to establish a transfer dosimetryhas been used to measure the absorbed dose.[1] Its ad- system with high accuracy to assure the quality of thevantages over othe…