Jyunji Tanimura

Dielectric properties of (BaxSr1-x)TiO3 thin films prepared by RF sputtering for dynamic random access memory application

Dielectric properties of (Ba0.5Sr0.5)TiO3 and (Ba0.75Sr0.25)TiO3 thin films have been investigated, focusing on the effects of film structure and Ba/Sr compositions on the dielectric properties. Dielectric constant of the films increased with increasing grain size and with improvement in film crystallinity. For the 50-nm-thick films deposited at 660° C, the dielectric constant of 400 for the (Ba0.5Sr0.5)TiO3 film is larger than that of 320 for the (Ba0.75Sr0.25)TiO3 film. This indicated that dielectric constant is affected by the ratio of Ba/Sr composition. Leakage current density of less than 1×10-7 A/cm2 at 1 V and SiO2 equivalent thickness of 0.38 nm are measured at 120° C for 660° C-deposited (Ba0.5Sr0.5)TiO3 film of 30 nm in thickness. The (Ba0.5Sr0.5)TiO3 film has the possibility for application to generations beyond 256 Mbit dynamic random access memories.

SiC homoepitaxy on Al-ion-implanted layers for fabricating power device structures

SiC homoepitaxial layers on 4H-SiC substrates implanted with Al to a dose ≤7.00 x 10 15 cm -2 were investigated. Epilayers of smooth surface morphology were obtained for the Al dose ≤1.84 × 10 15 cm -2 . For the epilayer on the substrate with the Al dose of 1.84 × 10 15 cm -2 , no defect was observed by TEM, and no decrease in electron Hall mobility was measured. Out-diffusion of the implanted Al atoms in the substrate into the epilayers was not observed by SIMS. An accumulation epilayer-chonnel MOSFET was fabricated on the Al-ion-implanted substrate. Field effect mobility as high as 64 cm 2 /Vs was obtained. The results demonstrate that the epilayers are promising for fabricating SiC power device structures.