Tunnel injection and irradiation experiments on metal oxide semiconductor (MOS) structures are performed in order to compare the results of both experiments and to check the feasibility of radiation hardness prediction of MOS devices. The comparison is based on the fact that in both hot electron and ionizing irradiation experiments electron-hole pairs are generated in the SiO2. Due to an applied electrical field, these pairs are separated. The fraction of holes, trapped by neutral centers and the number of subsequently captured electrons by these now positively charged traps depend on the amount of available carriers, the magnitude of the respective capture cross sections for electrons and holes, and the number of hole traps. In the case of the tunnel injection experiment the number of the available carriers is a strong function of the field dependent ionization coefficient α. Up to now, its magnitude has not been accurately known. For this reason, a new method is presented which yields additional and reliable figures of α. When comparing the charge accumulation in the SiO2 by means of the flatband voltage shift as a consequence of the tunnel injection and of the irradiation, we determine α for various fields, α=3.3×10−6 exp [78/E(MV/cm)] (cm−1). For this determination we show that it is mandatory to correct for the steady state compensation of positively charged centers by electrons. From the saturation of the flatband voltage shift, caused by these trapped electrons, the field dependent capture cross sections for electrons are deduced. Their values are 2.3×10−14 and 3.5×10−15 cm2 for electrical fields of 7.8 and 8.6 MV/cm, respectively. The feasibility and limitations to predict the radiation hardness of MOS devices are discussed.

This paper presents the change of the midgap voltage ΔVMG and the surface state density Dit caused by bias temperature (BT) stress, ionizing irradiation, and tunnel injection experiments on metal-oxide-semiconductor capacitors. The irradiation tests and the tunnel injection experiments are carried out to find correlations of the degradation mechanisms among the three stress procedures. The BT stress is performed on n- and p-type samples with applied positive and negative fields (1–5 MV/cm). The stress temperatures are 100, 150, and 200 °C; the maximum aging time is 30 h. After BT stress, n- and p-type samples exhibit the same degradations of the midgap voltage VMG and of the interface state density Dit, respectively. The increase of ‖VMG‖ and Dit for negative BT stress is significantly larger than in the case of positive BT stress. An analytical expression which describes the changes of VMG and Dit for negative BT stress is developed. Drastic changes of VMG and Dit are observed after switching the stress voltage from negative values to positive ones or to ground. The ratio of (trapped hole) charges in the oxide and in the interface states is identical in all three experiments.

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budgets, there has been a drastic decrease in the dollar value of the radiation-hardened integrated circuit The radiation hardness of commercial Floating (IC) market, and a concomitant reduction in the Gate 256K E2PROMs from a single diffusion lot number of viable suppliers of radiation-hardened was observed to vary between 5 to 25 krad(Si) when ICs. This trend is expected to continue for the foreirradiated at a low dose rate of 64 mrad(Si)/s. Addi-seeable future. In addition, the capability of radiational variations in E'PROM hardness were found tion-hardened technologies has traditionally lagged to depend on bias condition and failure mode (Le., one to two generations behind commercial technolinability to read or write the memory), as well as the foundry at which the part was manufactured. This variability is related to system requirements, and it is shown that hardness level and variability affect the allowable mode of operation for E2PROMs in space applications. The radiation hardness of commercial 1-Mbit CMOS SRAMs from Micron, Hitachi, and Sony irradiated at 147 rad(Si)/s was approximately 12, 13, and 19 krad(Si), respectively. These failure levels appear to be related to increases in leakage current during irradiation. Hardness of SKAMs from each manufacturer varied by less than 20%, but differences between manufacturers are ogies, leading to reduced system performance. This has prompted a renewed interest in the use of commercial technology -with its enhanced performance and yield, and reduced cost -in military and space systems. But unlike the vendors of hardened technologies, the commercial manufacturer has no interest in identifying and controlling the technology parameters that affect radiation hardness. As such, we expect lower hardness levels for commercial technologies and, perhaps even more importantly, greater variability of commercial technologies in a radiation environment.significant. The Qualified Manufacturer's List approach to radiation hardness assurance is suggested as a way to reduce variability and to improve the hardness level of commercial technologies.In Figure 1 we show the total-dose requirements for pieceparts used on several space-based vehicles, and payloads located on space-based vehicles, as a function of orbit altitude. The vehicle and payload

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