Detailed C-V Analysis for YbMnO 3 /Y 2 O 3 /Si Structure
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"[email protected] ABSTRACT YbMnO 3 (Yb/Mn = 0.96) thin films were prepared on Y 20 3(11 1)/Si(l 11). Although the sample exhibited ferroelectric type C-V hysteresis, the window width changed depending on the applied bias voltage. Hence, the ferroelectric type hysteresis might include the effect of space charge. To make clear the C-V behavior caused by only ferroelectricity, and to obtain the optimal relationship between ferroelectric and insulator layer thicknesses, the C-V behavior at high frequency was computed for MFIS structure. Relationships between the counter bias voltage applied to the ferroelectric layer and the thickness of dielectric layer were also demonstrated. Compared with the calculated results, experimental C-V characteristics are discussed. INTRODUCTION Recently, Ferroelectric random access memory (FeRAM) has attracted much attention, because of its nonvolatile operation and the high access speed [1,2]. FeRAMs are classified into two types, one is a unit cell of one transistor and one capacitor (ITIC), and the other is a metalferroelectric-semiconductor field effect transistor (MFS-FET). The later has several advantages, namely, non-destructive read out, decreasing memory cell size and lower power requirement. This is because the electrostatic charge induced by the remnant polarization of ferroelectric materials controls the conductivity of the semiconductor [3,4]. However, MIFS-FET has serious problems. One is the formation of an amorphous SiO 2 layer with a low dielectric constant at the film/Si. The other problem is interdiffusion between the film and Si [5]. It deteriorates the properties of FET and the ferroelectric film. To solve these problems, a metal-ferroelectricinsulator-semiconductor field effect transistor (MFIS-FET) structure has also been demonstrated [6] using various insulators such as CeO 2 [7,8] and Bi 2SiO 5 [9]. However, the applied voltage can not be effectively used for polarization due to the existence of the buffer layer with a dielectric constant lower than that of typical ferroelectric films such as Pb(ZrxTiix)0 3 (PZT) and SrBi 2Ta 2O 9 (SBT). We have proposed the use of RMnO3 (Rý rare earth elements) thin films for FeRAM [10]. When R is Y, Er, Ho, Tm, Yb and Lu, RMnO 3 has a hexagonal structure with a unipolarization axis along [0001] [11,12]- Since RMnO 3 has a low permittivity and does not include volatile elements, it is expected to have several advantages over PZT and SBT, especially for the application to MF(I)S-FET. Several reports on thin film growth of YMnO 3 were reported [13,14]. Moreover, we also found that Mn-rich composition and Yb substitution to A-site position improved the dielectric properties of RMnO3 bulk ceramic [15]. YMnO, films deposited on Si substrates crystallized with a (0001) preferred orientation by using an initial layer. The initial layer was deposited without introducing oxygen using YMnO, target; we call the initial layer Y-Mn-O buffer layer. The capacitance-voltage characteristics of Pt/YMnOJ/Y-Mn-O/Si structure showed a hyster
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