Improvement of Retention Property of YMnO 3 /Y 2 O 3 /Si MFIS Capacitor
- PDF / 1,702,957 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 50 Downloads / 210 Views
Improvement of Retention Property of YMnO3/Y2O3/Si MFIS Capacitor Norifumi Fujimura Daisuke Ito, Kousuke Kakuno and Taichiro Ito Dept. of Applied Materials Science, Graduate school of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531, Japan [email protected] ABSTRACT We have been proposing YMnO3 with low remanent polarization and permittivity as a ferroelectric gate transistor, and reported that c-oriented YMnO3 films were obtained on (111)Si with (111) oriented Y2O3 buffer layer. The ferroelectricity was confirmed by pulsed C-V measurement. However, the retention property was not satisfied because of its poor crystallinity. To improve the crystallinity of YMnO3 films, deposition conditions of Pulsed Laser Deposition (PLD) were optimized. The laser power, oxygen pressure and introducing Ozone gas are effective for maintaining the stoichiometry during the deposition. Improvement of the crystallinity of the YMnO3 film makes the retention property better. We also demonstrate the use of epitaxially grown Y2O3 buffer layer to improve the crystallinity of the YMnO3 films. INTRODUCTION Ferroelectric nonvolatile random access memory (FeRAM) has attracted much attention due to its nonvolatile operation and high access speed [1]. We proposed the use of YMnO3 thin films for the ferroelectric gate transistor [2-5]. Because YMnO3 has a relatively low permittivity and remanent polarization and does not include volatile elements such as Pb and Bi, it should have several advantages over Pb(Zr1-xTix)O3 and SrBi2Ta2O9. Highly (0001)-oriented YMnO3 films were obtained on (111)MgO, (0001)ZnO/(0001)sapphire, (111)Pt/(0001)sapphire and (111)Si substrates using a (111) oriented Y2O3 buffer layer, which is an element composed of YMnO3. The Y2O3 has larger dielectric constant compared to SiO2, and higher chemical stability than the other insulator materials [6]. Although we succeeded in obtaining an Y2O3/Si capacitor with excellent dielectric properties [7], the dielectric properties of YMnO3 on the top of the Y2O3 layer still needed to be improved. The retention time of the polarization was about 60 s. To improve the retention property, although the energy band alignment should be carefully designed and quite low leakage current should be achieved, square P-E hysteresis is also required. As only [0001] is the polarization axis in the case of YMnO3, orientation distribution of [0001] is responsible for the retention property. Therefore, we have concentrated to obtain the YMnO3 films with excellent crystallinity. In this paper, the initial stage of YMnO3 growth on a single crystal substrate is carefully studied to optimize the deposition conditions. The results are applied to obtain the good films on Y2O3/Si substrate. The effect of the crystallinity of the epitaxially grown Y2O3 layer on the crystallinity of YMnO3 films is also discussed. EXPERIMENTS To optimize the deposition conditions of the YMnO3 thin film, (111) MgO was used because the composition of the film were able to be evaluated without the
Data Loading...
