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ABSTRACT Pt/Bi2SiO1/Si (MIS) and Pt/200nm-Bi 4Ti1 O12/Pt/30nm-Bi 2SiO 5 /Si (MFMIS:Metal/ Ferroelectric/Metal/Insulator/Semiconductor) structures were prepared by MOCVD. Oxygen concentration and the Bi/Ti composition ratio determine Bi4Ti 3O1 2 orientation and Bi4Ti 3 0 1 2 volume in the film, respectively. When the oxygen concentration and the Bi/Ti composition ratio was 33% and 0.65, (001) Bi4Ti30• 2 film with the dielectric constant of 40 was obtained. In addition, the capacitance-vs-voltage (C-V) measurement of the Pt/Bi 2SiOs/Si structure exhibits normal MIS C- V characteristics. The C-V characteristics of Pt1Bi 4Ti3 O12/Pt/ Bi 2SiO 5/Si structure have ferroelectric switching properties with a memory window of about 2.OV Moreover, it is found that the capacitance at zero-bias remains constant for over 24 h. INTRODUCTION Recently, nonvolatile ferroelectric memories (NVFRAM) with nondestructive readout operation have been extensively investigated[l]-[4]. A metal/ferroelectirc/ semiconductor field effect transitor (MFS-FET) is very promising as a non-volatile memory device in the next generation. The most difficult problem of MFS structure is that the ferroelectric thin film must be directly deposited on a Si substrate. When a ferroelectric film is deposited on Si. Si oxidization at ferroelectirc/Si interface and diffusion of ferroelectric components may take place, which causes an increase of operation voltage. We have examined a metal/ferroelectirc/metal/ insulator/semiconductor (MFMIS) structure with a Pt floating gate and an insulating buffer layer to avoid such problems. In the experiments, we first investigated a ferrroelectiric capacitor (MFM) and an MIS diode separately, and then fabricated an MFMIS structure to confirm the electrical properties. The ferroelectic Bi4 Ti3O 12 thin film was obtained by a metal organic chemical vapor deposition (MOCVD) method. MOCVD allows easy composition and crystallinity control, excellent step coverage and a wide deposition area. These are advantages of MOCVD technique for large-scale processing and mass production. Bi 4Ti 3Ol 2 is one of the most interesting ferroelectric materials with Bi layered structure to be studied in recent years[5]-[7]. In this paper, we demonstrate that we can control the orientation and crystallinity of the Bi 4Ti3Ol 2 thin film based on a new process and that we can obtain good diode characteristics for the MFMIS structure when using Bi2 SiO 5 [8] as an insulating buffer layer. EXPERIMENT Bi 4Ti 3O1 2 and BiSiO5 thin films were deposited under growth conditions listed in Table I 123 Mat. Res. Soc. Symp. Proc. Vol. 596 0 2000 Materials Research Society

using a vertical cold-wall type MOCVD system, as shown in Fig. 1. This MOCVD system consists of bubblers for source gases, a constant-temperature box and a reaction chamber. Bi and Ti source gases are transported by Ar carrier gas through the pipes kept at 1609C in the constant-temperature box. The reaction chamber has the nozzle which carries the mixture of the source and 02 gases to a substr