Eisuke Tokumitsu

In situ Raman spectroscopy observation of crystallization process of sol-gel derived Bi4-xLaxTi3O12 films

In situ Raman spectra measurements have been employed to reveal the crystallization process of sol-gel derived Bi4-xLaxTi3O12 (BLT) thin films. The Raman spectra of BLT films with a La composition x of 0.75 were measured with increasing temperature up to 800°C in air and N2 ambient. It is demonstrated that Bi2O2 layered structures form first at 500°C and perovskite structures start to crystallize at 600°C or higher.

Characterization of Hafnium Oxide Thin Films by Source Gas Pulse Introduced Metalorganic Chemical Vapor Deposition Using Amino-Family Hf Precursors

We have characterized hafnium oxide thin films grown on SiO2/p-Si(001) by source gas pulse introduced metalorganic chemical vapor deposition (MOCVD) using tetrakis-diethylamido-hafnium (Hf[N(C2H5)2]4) and tetrakis-dimethylamido-hafnium (Hf[N(CH3)2]4). O2 or H2O is used as oxidant gas. It is demonstrated that the use of H2O can reduce the residual impurity concentrations of hafnium oxide films when the deposition temperature is as low as 280°C. In addition, we have found that the residual impurity concentration of hafnium oxide films grown with Hf[N(C2H5)2]4 is lower than that grown with Hf[N(CH3)2]4. This tendency agrees with the leakage current density. An equivalent SiO2 thickness (EOT) of 1.4 nm with 4.7×10-6 A/cm2 @-1 V have been obtained for the hafnium oxide films grown with Hf[N(C2H5)2]4 at 280°C.

Source Gas Pulse-Introduced MOCVD of HfO2 Thin Films using Hf ( O ­ t ­ C 4 H 9 ) 4

We have characterized HfO 2 thin films grown by source gas pulse introduced metallorganic chemical vapor deposition (MOCVD) technique using Hf(O-t-C 4 H 9 ) 4 as a Hf precursor, and H 2 O or O 2 as an oxidization gas. The Hf precursor and H 2 O (or O 2 ) were alternately introduced with N 2 purge step, which is one growth cycle in this experiment. The residual impurity concentration in HfO 2 thin films can be reduced when the film is grown by pulse-MOCVD using H 2 O. In addition, the leakage current density has been improved for the HfO 2 film grown with H 2 O. This low leakage current density is considered to be due to the lower impurity concentration in the film grown with H 2 O as an oxidization gas.

Preparation and characterization of sol-gel derived (Sr, Ba)Bi2(Ta, Nb)2O9 thin films for ferroelectric-gate FET applications

We have fabricated (Sr,Ba) 0.8 Bi 2.2 (Ta,Nb) 2 O 9 (SBBTN) thin films by the sol-gel technique to obtain a small remanent polarization and a large coercive field for ferroelectric-gate FET applications. Ba and Ta compositions are varied from 0 to 0.2 and from 0 to 0.5, respectively. It is demonstrated that the coercive field becomes large by the partial replacement of Ta with Nb atoms and that the Ba doping results in slight decrease of the remanent polarization. A remanent polarization as small as 5 w C/cm 2 and a coercive field as large as 100 kV/cm can be obtained for Sr 0.6 Ba 0.2 Bi 2.2 Ta 1.5 Nb 0.5 O 9 thin films, which were crystallized at 850°C.

Sm Doping Effects on Electrical Properties of Sol-Gel Derived SrBi 2 Ta 2 O 9 Films

We have characterized (Sr,Sm)Bi 2 Ta 2 O 9 (SSBT) films fabricated by the sol-gel technique on Pt/Ti/SiO 2 /Si substrates. For ferroelectric-gate FET applications, a ferroelectric film which has a small remanent polarization and a relatively large coercive field is required. It is demonstrated that Sm doping in ferroelectric SBT films is effective to reduce the remanent polarization and enhance the coercive field. Sr 0.5 Sm 0.2 Bi 2.2 Ta 2 O 9 films (150nm) crystallized at 850°C exhibits good electrical properties with a remanent polarization of 1.7 μC/cm 2 and a coercive fields of 85 kV/cm. These values are suitable for ferroelectric-gate FET applications.