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The electrical characteristics of the tantalum oxide-silicon dioxide double-dielectric structure are described. The MTOS structure (metal-tantalum oxide-silicon dioxide-silicon) is similar to the MNOS double dielectric which is used as a nonvolatile memory element except tantalum oxide (Ta2O5) is used to replace the silicon nitride as the second dielectric. Capacitance voltage measurements show a negative QSSwith magnitudes smaller than those in compatable MNOS devices. Conduction characteristics of both anodic and thermally grown Ta2O5have been studied and both have been found to follow a Poole-Frenkel mechanism. The memory characteristics of the MTOS have been investigated and preliminary data are presented. Where MNOS data are available, the MTOS characteristics have been compared with those of the MNOS structure. It is shown that the threshold voltage of the MTOS device can be shifted using lower gate voltages than are needed for a comparable MNOS device. It thus appears that the MTOS device has some decided potential advantages over the MNOS structure as a nonvolatile memory element.
Angle et al. (1978) studied this question.