Instability in vacuum deposited silicon oxide

The instability of vacuum deposited SiO
2
in field-effect transistors is described. Results for an Al-SiO
2
-CdSe system are accounted for by a model in which mobile ions are located predominantly in traps at the SiO
2
interfaces. The asymmetrical drift rate observed was accounted for by a difference in activation energy for release of ions from the two interfaces. The absorption of water vapor caused an increase in both the magnitude of the drift and the transconductance of the transistor during the drift.