Semiconductor Devices At Low Dose Rate Radiation Effects And Characterization

Recently, bipolar devices and circuits have been widely used in radioactive fields, like aeronautics and space industry, explosion of nuclear weapons, nuclear reactor and so on. Since Enlow had discovered enhangced low dose rate sensitivity (ELDRS) in bipolar devices in 1991, many researches at home and abroad turned out that ELDRS is showed in lots of other bipolar devices and circuits ELDRS. ELDRS appears to be that being low dose rate irradiated, the current gain of bipolar transistors decreases more obviously, because more oxide trapped charges Nox and interfacial state charges Nit are induced in the passivation layer of SiO2 under low dose rate irradiation. The oxide trapped charges change the surface potential in Si. And the interface trapped charges become recombination centers, which increases the surface recombination-rate So. This results in the pronouced increase of the excess base current with low dose rate, which is more evident in npn transistors than in pnp transistors. With in-depth study in the low frequency noise of electronic devices, people found that the subsurface defects in bipolar transistors caused by irradiation can also result in the change of low frequency noise.This paper has adopted domestic 2N2484(npn),2N2907A(pnp) bipolar transistors and LM117, LM317 three terminal regulators as experimental devices and circuits, according to the requirement of Xidian University Microelectronics College, to carry out irradiation experiments on the 60Coy source of the Westnorthern Cobalt Source Laboratory, with various dosage(10krad,30krad,50krad,70krad, 100krad,150krad) and dosage rate(10rad(Si)/s,0.1rad(Si)/s) of y ray. And it also makes in-depth study in the irradiation results, the damage mechanisms, physical models and characterization methods of the semiconductor devices and circuits. Meanwhile, this paper adds some contents about the low frequency noise irradiation changes and comparison analysis in bipolar devices and circuits. It gives abstract illustrations on the defects of bipolar devices and circuits after being irradiated and the effect that the defects have on electrical parameters and noise parameters. It turns out that with the increase of irradiation dosage and the decrease of irradiation dosage rate, the electrical parameters of bipolar devices and circuits will degenerate continuously, the 1/f noise will increase continuously. Based on the experiment results upon and the study of theory, combined with the available 1/f noise modle, we can introduce radiation mechanism and establish 1/f noise characterization method of bipolar devices and circuits radiation damage.