Ionizing Dose Rate Effects in Microprocessors

The total ionizing dose failure levels in microprocessors for various radiation pulse widths appear to be dose-rate dependent. This apparent dose rate effect is demonstrated by comparing the total dose failure levels for 150-ns and 1-?s pulses, and >5-s 60Co irradiation. All irradiations were done while the device was operating under normal bias. Total dose failure level data are presented for five types of microprocessors: RCA 1802, Motorola 6800, Intel 8080 and 8085, and AND 9080. Each type exhibited the same dose-rate effects. This dose-rate dependence is caused by the collapse of the electric field across the gate oxide during irradiation. Resulting failure levels for high dose-rate exposure of MOS devices then approach the total ionizing dose failure levels for unbiased MOS devices which are from 3 to 10 times higher than biased devices. This unbiasing is caused by the large power supply currents which flow during the radiation pulse. These currents are limited by package lead resistances, which in most cases protect the device from burnout.     

系统低剂量率失效和加速模拟试验方法

综述双极器件和双极线性电路在低剂量率辐射环境下的增强损伤,它可引起系统的早期失效。分析了引起低剂量率失效的物理机制,它与MOS器件电离辐射的损伤机制完全不同。为了缩短模拟试验时间和提高效/费比,研究了几种加速模拟试验方法,并对处于低剂量率下系统的加固保证也提出了一些看法。     

A systematic study on MOS type radiation sensors

Radiation sensors based on metal oxide semiconductor (MOS) structure are useful because of their superior sensitivity as well as excellent compatibility with the existing microelectronic technology. In this paper, a systematic study of MOS capacitors built on p- and n-type Si substrates with different SiO₂ thicknesses (10 nm, 50 nm, 100 nm and 240 nm) is presented. MOS device response to gamma radiation up to 256 Gray have been studied from the sensor application point of view. Variation of the radiation induced device response with oxide thickness, substrate type, applied bias and post annealing have been measured and discussed. Radiation induced charge in MOS devices is shown to be a strong function of the oxide thickness as expected. Application of a positive bias to the gate is found to enhance the device sensitivity for both n- and p-type devices. This is explained in terms of the involvement of the interface states in the sensing process. Devices have also been studied after repeated cycles of irradiation and annealing treatment under hydrogen atmosphere. Each cycle consists of gamma irradiation with 60 Gray dose and an anneal at 200 °C for 30 min. The charging-discharging mechanism during these cycles is discussed.     

Dose-Rate Effects in the Permanent Threshold Voltage Shifts of MOS Transistors

Data has been collected that shows the permanent threshold voltage shift occurring in MOS transistors exposed to the same total dose of gamma radiation can be greater in a high dose-rate environment than in a low dose-rate environment. This dose-rate effect is ascribed to a "Photovoltaic" bias generation in the substrate of a device which results in an effective gate bias change (positive for P-channel and negative for N-channel transistors). The bias change ranges from 0 to ±1 volt during the radiation burst. Thus, in a high dose-rate ionizing environment, the permanent gate threshold voltage shift of an MOS device, which is known to be a function of the gate bias during irradiation, will exhibit an indirect dose-rate dependence which is caused by an internal change in instantaneous gate bias.     

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.     

CMOS Shift Register Circuits for Radiation-Tolerant VLSI's

A radiation-tolerant VLSI circuits investigation has been carried out using CMOS/SOS shift registers. Static and dynamic circuit performance degradation is discussed, based on MOS FET parameter shifts due to radiation effects, utilizing ?-ray irradiation and SPICE simulation. Functionality, after radiation doses in excess of 105; rad (Si), is shown for circuits fabricated by radiation-hardened process. Radiation-tolerance superiority of clocked gate CMOS (C2MOS) shift register circuits to transfer gate shift register circuits is discussed, placing emphasis mainly on radiation-bias effects. Based on the above results, the C2MOS is proposed for use in radiation-tolerant SOS VLSI circuits.     

0.18 μm MOS差分对管总剂量失配效应研究

为明确深亚微米MOS差分对管在电离辐射环境下晶体管失配表征方法及损伤机理,本文针对0.18 μm NMOS、PMOS差分对管,进行了⁶⁰Co γ总剂量辐射效应研究。研究结果表明：与PMOS差分对管相比,NMOS差分对管对总剂量辐照更敏感,主要表现在：1) 辐照引起NMOS差分对管转移特征曲线失配增加;2) NMOS差分对管阈值电压失配随辐照总剂量的增加而增大;3) 栅极电流辐照后稍有增加,失配随栅极电压的增加而增大。而PMOS差分对管在整个辐照过程中,无论是曲线还是参数均未出现明显变化,且失配亦未随辐照总剂量的增加而增大。     

线性集成电路的辐照响应和电离辐射损伤评估

利用用于电离辐射效应研究的运算放大器计算机测试系统以及测试分析和数据处理软件对十几种运算放大器进行了~(60)Coγ射线、1.5MeV电子的电离辐射损伤试验及其室温和加温退火特性研究。同时,探讨了运算放大器电离辐射损伤水平的评估方法和损伤机制。     

Equivalence of Radiation Particles for Permanent Damage in Semiconductor Devices

Selected transistors and diodes have been irradiated by various types and energies of dislocating radiation. Irradiation by protons of 10-Mev, neutrons of a reactor spectrum, electrons of 5, 10, and 25-Mev, gamma rays from cobalt-60, and bremsstrahlung from stopping of 5-Mev electrons are discussed. Passive and dynamic monitoring of permanent radiation damage was performed for exposures ranging from "threshold" to failure doses, utilizing various exposure rates. Changes in transistor forward current gain and changes in diode lifetime are presented in terms of integrated "particle" flux. From such analysis, the feasibility of ascribing an equivalence of radiation particles for aermanent damage in transistors and diodes has been successfully shown. Comparative damage curves, correlations of operational degradation with defect densities, and preliminary equivalences are presented.     

Neutron radiation effects on metal oxide semiconductor (MOS) devices

The main purpose of this study is to provide the knowledge and data on Deuterium-Tritium (D-T) fusion neutron induced damage in MOS devices. Silicon metal oxide semiconductor (MOS) devices are currently the cornerstone of the modern microelectronics industry. However, when a MOS device is exposed to a flux of energetic radiation or particles, the resulting effects from this radiation can cause several degradation of the device performance and of its operating life. The part of MOS structure (metal oxide semiconductor) most sensitive to neutron radiation is the oxide insulating layer (SiO₂). When ionizing radiation passes through the oxide, the energy deposited creates electron-hole pairs. These electron-hole pairs have been seriously hazardous to the performance of these electronic components. The degradation of the current gain of the dual n-channel depletion mode MOS caused by neutron displacement defects, was measured using in situ method during neutron irradiation. The average degradation of the gain of the current is about 35 mA, and the change in channel current gain increased proportionally with neutron fluence. The total fusion neutron displacement damage was found to be 4.8 × 10⁻²¹ dpa per n/cm², while the average fraction of damage in the crystal of silicon was found to be 1.24 × 10⁻¹². All the MOS devices tested were found to be controllable after neutron irradiation and no permanent damage was caused by neutron fluence irradiation below 10¹⁰n/cm². The calculation results shows that (n,α) reaction induced soft-error cross-section about 8.7 × 10⁻¹⁴ cm², and for recoil atoms about 2.9 × 10⁻¹⁵ cm², respectively.     

电子束在MOS结构中的能量沉积与辐照效应

根据电子输运“双群理论”计算出电子在Ｓｉ－ＳｉＯ２材料中的能量沉积。用与硅等２效的外推电离室测定了１．０ＭｅＶ和１．５ＭｅＶ的电子束在ＭＯＳ电容芯片中的吸收剂量。用Ｘ光电子谱、俄歇谱、深能级瞬态谱和Ｃ－Ｖ方法测量分析了ＭＯＳ电容Ｓｉ－ＳｉＯ２材料化学结构，界面态密度和Ｃ－Ｖ曲线在辐射前后的变化，根据理论和实验结果，从辐射剂量学的角度分析讨论了电子能量沉积，电离缺陷和辐射效应间的关系，并提出一个关于     

Electron Injection Studies of Radiation Induced Positive Charge in MOS Devices

Avalanche injection and internal photo-emission techniques have been used to study the capture of electrons by positive charges introduced into the oxide layers of MOS capacitors. These two techniques have been used to study the positive charge in Al gate and poly-Si gate capacitors. The electron capture crosssection of this charge has been found to depend on the composition of the interface; positive charge at the Si interface tends to have a coulombic electron capture cross-section (~ 4×10-13cm2), while that at the alumninum interface has a non-coulombic electron capture crosssection (? 10-14cm2). The location of the positive charge induced by radiation under positive or negative bias has been determined in a completely non-destructive manner by photocurrent-voltage experiments. It has been found that under a positive irradiation bias, positive space charge accumulates within ~ 50 A of the Si-SiO2 interface, while under a negative bias, the space charge is within ~ 50 ? of the Al-SiO2 interface. In both cases there is evidence for some charge at the other interface introduced by the irradiation.     

Thin oxide degradation after high-energy ion irradiation

We have investigated the degradation induced by I- and Si-ions on 10- and 3-nm-thick oxide MOS capacitors. Ten-nanometer oxides were biased at low electric field (⩽3.3 MV/cm) during irradiation up to 100 Mrad(Si). DC radiation induced leakage current (RILC) has been observed after irradiation, and the differences of RILC characteristics between 10-nm and thinner oxides are discussed. In 10-nm oxides, RILC is attributed to multitrap assisted tunneling, which is reduced by subsequent Fowler-Nordheim electron injection. The density of the radiation-induced positive charged defect, the positive charge recombination by Fowler-Nordheim electron injection, and the negative charge trapping in radiation-induced neutral electron traps have been also addressed. On the other side, radiation-induced soft breakdown (RSB) is triggered by I-ions in 3-nm oxides at low doses (<1 krad(Si)) for moderate applied electric fields (4.4 MV/cm). Silicon ion irradiation is unable to produce RSB and RILC in 10-nm oxides, but it can generate a peculiar RILC in 3-nm oxides     

不同设计参数MOS器件的射线总剂量效应

采用非加固工艺，通过设计加固手段实现具有辐射容忍性能的器件，可使器件抗辐射加固成本大为降低。本工作研究商用标准0.6μm体硅CMOS工艺下不同设计参数的MOS晶体管的γ射线总剂量辐照特性。通过对MOS器件在不同偏置情况下的总剂量辐照实验，分别对比了不同宽长比（W/L）NMOS管和PMOS管的总剂量辐照特性。研究表明，总剂量辐照引起阈值电压的漂移量对NMOS及PMOS管的W/L均不敏感；总剂量辐照引起亚阈区漏电流的增加随NMOS管W/L的减小而增加。研究结果可为抗辐射CMOS集成电路设计中晶体管参数的选择提供参考。     

Use of Al2O3 layer as a dielectric in MOS based radiation sensors fabricated on a Si substrate

The use of Al₂O₃ dielectric in MOS based radiation sensors has been investigated. Their response has been compared with conventional MOS capacitors with a SiO₂ dielectric. The study includes gamma radiation effects with dose up to 4 Gy. The effect of radiation has been determined from the valance band shift in C-V curves. The amount of charge induced by the radiation has been calculated and compared with the response of MOS capacitors with SiO₂ with the same and different thicknesses. Fading properties have been studied and compared. Results show that MOS capacitors with Al₂O₃ dielectric exhibit sensitivity greater than that obtained from MOS capacitors with SiO₂. This higher sensitivity is attributed to higher trapping efficiency in the Al₂O₃ layer.     

Interface-State Generation in Thick SiO2 Layers

Evidence is presented that interface states are produced by radiation in some MOS structures with thick SiO2 layers (e.g., field oxides) by a mechanism different from the slow two-stage process previously identified in thinner radiation-hardened gate oxides. Production of interface states by the new process occurs promptly after irradiation, is independent of oxide field and polarity, and takes place with nearequal efficiency at room temperature and 77 K.     

Study of Ionizing Radiation Damage in MOS Structures Using Internal Photoemission

The effects of ionizing radiation in large-geometry MOS structures were studied by use of internal photoemission techniques. Barrier heights at both the silicon-silicon dioxide and the silicon dioxide-metal (chromium and aluminum) interfaces were measured before and after irradiation in a Co60 gamma cell. It was determined that the measured barrier energy heights may be considerably reduced by radiation-induced oxide charge. The internal photoemission technique also provided significant information concerning the effects of impurities in the oxide and the related radiation hardness of the oxide layer. Oxide layers doped with chromium ions showed significant electron trapping at two discrete energy levels (3.4 and 3.8 eV). Samples exhibiting the 3.4 eV level showed great radiation hardness, while those with only the 3.8 eV peak were very radiation soft. The information obtained, using the internal photoemission technique, has provided considerable insight into the mechanisms and fabrication processes associated with radiation-hardened MOS devices.     

Radiation and Oxide-Metal Interactions in MOS

Radiation stability of the MOS system is controlled by the oxide-silicon and oxide-metal barriers; oxide-metal interactions and certain dopants appear to affect the radiation sensitivity. It is shown that the OS system behaves differently from the MOS system. The effect of metals have been studied with the use of aluminum, molybdenum and chromium. Chromium appears to be a desirable metal; when this electrode is used other factors also assume importance. The best results obtained with chromium gate p-enhancement transistors are: a shift of only 1.5 V (~1011 charges/cm2) with a Co-60 source depositing 2 x 107 rad(Si) or 1.5 MeV electrons depositing 1014 electrons/cm2. The change in surface mobility is small. Isothermal relaxation experiments show a wide range of activation energies, some of which are characteristic of the metal used. Studies related to the "photocurrent" flowing during irradiation appear to indicate that the prevailing model for radiation "damage" must be altered.     

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.     

Thermally Stimulated Current Measurements on Irradiated MOS Capacitors

Thermally stimulated current and high frequency C-V measurements have been used to study the properties of hole traps near the Si-SiO2 interface in irradiated silicon MOS capacitors. Pre-irradiation bias-temperature (BT) instabilities, both for negative and positive bias, were observed in non-ion-contaminated samples. The activation energy for BT instabilities for both polarities is ~1.0 eV independent of radiation hardness. Distributions of activation energies for trapped holes produced by Co60 irradiation are centered at ~0.85 and ~1.3 eV. The ~0.85 eV distribution occurs only if Na+ was previously present at the Si-SiO2 interface. The ~1.3 eV distribution consists of multiple overlapping distributions. Mechanisms that could lead to these distributions of activation energies are discussed.