Sodium migration through electron-gun evaporated Al 2O 3 and double layer Al 2O 3SiO 2 structures

Abstract

Sodium migration through electron-gun evaporated Al 2O 3 and through double-layer Al 2 O 3SiO 2 structures has been investigated. Electron-gun evaporated Al 2O 3 does not require high-temperature processing and is, consequently, compatible with low-temperature and thin-film techniques. For evaluation, the Al 2O 3 films were deposited on silicon or on thermal SiO 2 grown on silicon. Annealing at 320°C removed the radiation damage in the thermally grown SiO 2. Sodium-contaminated devices have been investigated by means of standard bias-temperature tests, in which the parallel shift of C- V curves is observed. It was found that sodium is more soluble in this Al 2O 3 than in thermal SiO 2 and drifts through the Al 2O 3 only slightly slower than it drifts through thermal SiO 2. The drift behavior is similar in the two cases: An asymmetrical response is observed in the forward and reverse directions, and the time constants decrease exponentially with applied field. The double-oxide Al 2O 3SiO 2 structure may be used to advantage since the field in the Al 2O 3 will be lower than the average field in the oxide combination, resulting in slower sodium drift. Furthermore, the sodium will drift readily only to the Al 2O 3-SiO 2 interface and must overcome a substantial barrier before penetrating into the underlying SiO 2.