Aging mechanisms in thin film Al-Al2O3-Al capacitors

For substrates with a significant ion current, aging changes are strongly dependent on the applied voltage. On substrates with a very low ionic current (including Corning 7059 glass) a drift of C and tan delta independent of the applied voltage is caused by mechanisms within the capacitance structure; these have been investigated. Capacitor preparation (base electrode 6000 A, a 2000 A layer and a 500 A top layer) is described. The 500 A layer was studied using electron diffraction. No measurable differences were found between samples with a.c. and d.c. voltages and samples without voltage. Plots presented are for aging under temperature stress only (2 hr at 500 C). During anodization interstitial ions and vacancies are created; their recombination can account for a shift in the log I vs E! curves. Changes at the metal/dielectric interfaces are important. Al3+ diffusion from the top electrode to the Al3+ vacancy-rich top region of the oxide is probably involved. 5 ref. --EPAA/AF.