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Capture cross-section data from the literature and recent density-functional theory (DFT) calculations strongly suggest that the 1/f noise of MOS devices is caused by the thermally activated capture and emission of carriers at O vacancy centers near the Si-SiO2 interface. At least two kinds of defects can contribute to the noise of unirradiated and irradiated devices. The first is a "dimer" vacancy associated with the Eδ' center, which is shown by DFT to be a metastable electron trap when the Si-Si spacing is stretched beyond its equilibrium value, as likely can occur in strained SiO2 near the Si-SiO2 interface. The second is a neutral or positively charged Eγ' center, which has two configurations. One is puckered (one of the Si atoms relaxes through its local bonding plane) and forms a dipole after electron capture (E(γ4)'). The other is shown via DFT to be a different kind of puckered configuration, including a fivefold coordinated Si (E(γ5)'); this does not form a dipole. These results strongly suggest a common model of charge exchange with O vacancies can account for much of the oxide-trap charge and 1/f noise in MOS devices. Applying this model to thermally stimulated current (TSC) experiments suggests hole emission in TSC may well be due to the thermal relaxation of a puckered Eγ' into a dimer Eδ'. This can explain literature discrepancies between optical and thermal estimates of trapped-hole energies.