Ultra-thin-body PECVD Ge TFT low-voltage flash memory cell with high-k dielectrics for three-dimensional integration

As the scaling of conventional bulk Si flash memory cells approaches its fundamental limits, innovative 3D stacking and new materials must be considered. Ge is one of the promising candidates due to its attractive properties including higher mobility [1], smaller bandgap for supply voltage scaling, and lower processing temperature for compatibility with high-k dielectric [2] and 3D stack technology. Hence, a study the Ge UTB (ultra thin body) structure is pertinent for understanding its prospect as a viable solution [3]. Unlike silicon, however, the lack of a sufficiently stable native oxide hinders the passivation of Ge surfaces. The native germanium oxide is hygroscopic and water-soluble. Several gate dielectric materials with thick EOT on Ge have been reported [4] in early 1990s. Al2O3 has emerged as one of the most promising high-k gate dielectrics for Ge MOSFET and TFT [5] to cope with the issue of the native Ge oxide [6]. In this study, we demonstrate the material and electrical characteristics of stackable Ge TFT flash memory cell with Al2O3 high-k tunnel dielectric, metal NCs and (Ti,Dy)xOy control dielectric. Our proposed planar thin-film process is a simple batch process, and can therefore be used with relatively small cost increase.