Role of ultra thin SiOx layer for epitaxial growth of YSZ/SiOx/(001)Si thin films

The role of an ultra thin SiOx layer for the epitaxial growth of the YSZ (A stabillized ZrO2) thin film on (001) Si substrate through the SiOx layer was investigated by high resolution transmission electron microscope (HRTEM) method, in-situ heating transmission electron microscope method and nano-beam diffraction methods. An ultra thin SiOx layer 1-2 nm in thickness has the effects of inducing crystallization strain relaxation at the YSZ/Si interface; therefore an ultra thin YSZ layer in the very initial stage of the thin film growth could be epitaxially crystallized. The nano-beam (0.4 nm) diffraction analysis, focused on the SiOx layer of the (001) epitaxial YSZ/SiOx/Si thin film, showed a no complete halo pattern, but the diffraction spots convoluted into a halo pattern. The diffraction pattern was not so sharp than YSZ and Si, however there existed an epitaxial relationship the YSZ, SiOx and Si layers. On the other hand, an amorphous-like phase contrast was observed by high coherent HRTEM imaging. This indicates that the ultra thin SiOx layer formed just above the Si surface has a nano-crystalline structure below 1 nm order. Our results indicate that the SiOx layer plays two important roles: (a) it enables strain relaxation in the crystallization process of YSZ layer with increasing the crystallinity of the YSZ layer; (b) it enables the transmission of an epitaxial relationship from the Si (semiconductor) toward the YSZ (oxide) layer.