T. Tabata

Ge MOSFETs performance: Impact of Ge interface passivation

We have systematically investigated Ge interface passivation methods, and the highest electron (1920 cm2/Vs) and hole mobility (725 cm2/Vs) have been demonstrated by dramatic reduction of Dit through the collaboration of self-passivation and valency passivation. In Si passivation, it is found that Si contributes to the upper half (worse) and lower one (better) in the bandgap differently. This study strongly suggests us that high performance Ge CMOS is really feasible.

Corepressive Action of CBP on Androgen Receptor Transactivation in Pericentric Heterochromatin in a Drosophila Experimental Model System

ABSTRACT Ligand-bound nuclear receptors (NR) activate transcription of the target genes. This activation is coupled with histone modifications and chromatin remodeling through the function of various coregulators. However, the nature of the dependence of a NR coregulator action on the presence of the chromatin environment at the target genes is unclear. To address this issue, we have developed a modified position effect variegation experimental model system that includes an androgen-dependent reporter transgene inserted into either a pericentric heterochromatin region or a euchromatic region of Drosophila chromosome. Human androgen receptor (AR) and its constitutively active truncation mutant (AR AF-1) were transcriptionally functional in both chromosomal regions. Predictably, the level of AR-induced transactivation was lower in the pericentric heterochromatin. In genetic screening for AR AF-1 coregulators, Drosophila CREB binding protein (dCBP) was found to corepress AR transactivation at the pericentric region whereas it led to coactivation in the euchromatic area. Mutations of Sir2 acetylation sites or deletion of the CBP acetyltransferase domain abrogated dCBP corepressive action for AR at heterochromatic areas in vivo. Such a CBP corepressor function for AR was observed in the transcriptionally silent promoter of an AR target gene in cultured mammalian cells. Thus, our findings suggest that the action of NR coregulators may depend on the state of chromatin at the target loci.

Oxygen potential engineering of interfacial layer for deep sub-nm EOT high-k gate stacks on Ge

The interfacial layer (IL) control is a key to achieving deep sub-nm EOT gate stacks with maintaining superior interface properties. We propose the thermodynamically robust IL engineering on Ge (Y₂O₃-doped GeO₂ IL). Based on the understanding of Y₂O₃-doped GeO₂ IL, we have demonstrated 0.47-nm-thick EOT on Ge, and the highest electron mobility at high-N_s in Ge n-MOSFETs with sub-nm-thick EOT.

Reconsideration of electron mobility in Ge n-MOSFETs from Ge substrate side — Atomically flat surface formation, layer-by-layer oxidation, and dissolved oxygen extraction

We clarified wafer-related origins for electron mobility degradation in Ge n-MOSFETs. High-Ns electron mobility was dramatically improved thanks to (i) atomically flat Ge surface formation, followed by (ii) layer-by-layer oxidation. (iii) Oxygen-related neutral impurities in Ge substrates could be another origin of the mobility reduction on Ge wafers. By successfully eliminating these scattering sources in Ge n-MOSFETs, we demonstrated intrinsically high electron mobility in a wide range of Ns.

Electron mobility in high-k Ge-MISFETs goes up to higher

This paper will first discuss intrinsic advantages of high-pressure oxidation of Ge and then present further improvement of electron mobility in Ge n-MISFET using high-k gate stacks combined with high-pressure oxidation. The peak mobility is about 1500 cm2/Vsec, which is the highest one to date among unstrained Si and Ge MISFETs. Ge-CMOS is a strong candidate for beyond Si-CMOS.

Layer-by-Layer GeO 2 Formation in the Self-Limited Oxidation Regime of Ge

The Ge oxidation process is discussed from the viewpoints of the O2 pressure dependence of oxidation and Ge/GeO2 interfacial roughness formation in wide ranges of temperature and PO2. The atomic-scale roughness is formed by conventional oxidation, while the low-temperature and high-pressure oxidation (HPO) enable to achieve atomically flat interface.