Abstract
In this study, the effects of postannealing on ZnO and Al~2~O~3~ films grown for a thinโfilm transistor (TFT) by the atomic layer deposition (ALD) method were examined using transmission electron microscopy (TEM) and energyโdispersion spectroscopy. Samples were subjected to rapid thermal annealing for 30โs at 610, 615, 620, and 800โยฐC in a N~2~ atmosphere. At these temperatures, the polycrystalline ZnO layer in a TFT channel rapidly degraded to amorphous, and in the Al~2~O~3~ layer of a gate oxide layer of the TFT, a ZnAl~2~O~4~ spinel structure was formed because of Al and Zn diffusion. This spinel structure was observed to be independently nucleated, and there were no specific postgrowth crystallographic orientation relations. Additionally, in electrical properties of ZnOโTFTs with ZnO/Al~2~O~3~ layers, typical TFT characteristics was shown until the annealing temperature increased to 600โยฐC, and the V~th~ gradually decreased from 4.2, 3 to 1.8โV. However, in the 700โยฐC annealed case, the TFT devices are always opened, and the ZnAl~2~O~4~ generation and the ZnO layer degradation was related to the drastic changes of these ZnOโTFTs characteristics. During postannealing, rapid degradation of the ZnO channel layer and phase transformation by means of diffusion should be carefully considered.