The thermal stability in structural and electrical properties of HfO 2 , HfAlO x alloy, and Al 2 O 3 /HfO 2 stack thin films prepared by atomic layer deposition were comparatively investigated. Both HfAlO x and Al 2 O 3 /HfO 2 exhibit improved property against thermal degradation compared to the HfO 2 film. However, the incorporation of Al in alloy form provides characteristics superior to that in stack structure by retaining an amorphous structure up to 1000°C, which suppresses the leakage current and retards the growth of interfacial layer giving rise to lower increment of equivalent-oxide-thickness and interface trap density.

The charging characteristics of metal-oxide-semiconductor ͑p-type͒ structures containing Au nanocrystals in SiO 2 gate oxide were studied. The Au nanocrystals of 2-3 nm in diameter are self-assembled from the agglomeration of an ultrathin Au layer embedded in SiO 2 matrix by annealing at 600°C. A large hysteresis loop is found in the capacitance-voltage ͑C-V͒ relation even at a low operating voltage ͑2 V͒, indicating its significant charge storage effect. Different charging rates for two kinds of trapped carriers ͑electron and hole͒ were found from C-V measurement under various scan rates. The relatively stable retention characteristic for holes trapped in the Au nanocrystals at room temperature was also demonstrated.

The charge storage characteristics of metal-oxide-semiconductor structures containing Au nanocrystals in atomic-layer-deposited high-k gate dielectrics were studied. Cross-sectional high-resolution transmission electron microscopy reveals that the Au nanocrystals are self-assembled in the high-k dielectric matrix after high temperature annealing in N2 ambient. The memory effect was observed from capacitance-voltage (C-V) relations and a satisfactory charge retention characteristic was obtained in the sample using Al2O3 as the gate dielectric than in the one using Hf2AlOx. Moreover, a saturation of electron storage in the metal-oxide-semiconductor capacitors was also observed.

The nonvolatile memory characteristics of metal-oxide-semiconductor (MOS) structures containing Au nanocrystals in the Al 2 O 3 /SiO 2 matrix were studied. In this work, we have demonstrated that the use of Al 2 O 3 as control oxide prepared by atomic-layer-deposition enhances the erase speed of the MOS capacitors. A giant capacitance-voltage hysteresis loop and a very short erase time which is lower than 1 ms can be obtained. Compared with the conventional floating-gate electrically erasable programmable read-only memories, the erase speed was promoted drastically. In addition, very low leakage current and large turnaround voltage resulting from electrons or holes stored in the Au nanocrystals were found in the current-voltage relation of the MOS capacitors.

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