Analysis and Control of Ferroelectric/Semiconductor (Metal) Interface for Their Device-Application

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Metal Ferroelectric Insulator Semiconductor (MFIS) structures made on silicon substrate have been studied. The MFIS structures composed of the PZT F-layer fabricated by MOCVD and the buffer I-layer which is among films of MgO by RF sputter, A1_2O_3 by plasma-oxidation and TiO_2 by MOCVD were examined. The important knowledge derived from this study can be summarized as follows.1. Capacitance-voltage (C-V) characteristics of the MFIS diodes with the buffer I-layer of sputtered MgO or plasma-oxidized A1_2O_3 exhibited hysteresis curves due to the ferroelectricity of PZT, namely, C-V memory-windows (of narrow width less than 1V). In respect of the PZT film's crystallinity, the MFIS with MgO was better than that with A1_2O_3, whereas speaking of the I/S interface the former's interface state-density (lO^<12>eV^-1cm^-2 mesured by DLTS) was ten times as large as the latter's.2. The C-V memory-windows observed in the MFIS diode with the MOCVD-TiO_2 was excellent in shape and of wide width more than 2V.3. All the memory-windows observed in the three kinds of MFIS diodes were remarkably different in shape and width from the ideal one culculated by assuming neither of leakage current and interface state, and also showed the decrease in width due to carrier injection; this suggests that it becomes a critical issue to reduce the voltage across the I-layer when the memory-window opens.4. Polarization switching processes in epitaxial PZT thin films grown on SrRuO_3(100) were observed by means of piezoresponse scanning force microscopy. It was foud that during switching period the new nucleations were induced in the PZT film with Pt top electrode.5. Perovskite PZT films were successfully grown at 395 ℃ on Pt/SiO_2/Si by MOCVD ; they showed D-Ehysteresis of which ramanense is sufficient for the MFIS-FET memory to operate.