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

研究了在硅衬底上制作的金属铁电绝缘体半导体结构。研究了由MOCVD制备的PZT F层和在射频溅射的MgO膜、等离子体氧化的Al_2O_3膜和MOCVD制备的TiO_2膜之间的缓冲I层组成的MFIS结构。本研究所获得的重要知识可归纳如下：1.由于PZT的铁电性，以溅射MgO或等离子体氧化Al_2 O_3作为缓冲层的MFIS二极管的电容-电压（C-V）特性呈现滞后曲线，即C-V记忆窗口（宽度小于1V）。在PZT薄膜的结晶性方面，MgO的MFIS比Al_2O_3的MFIS好，而在I/S界面方面，前者的界面态密度（<12>DLTS测量的10 ^ eV^-1cm^-2）是后者的10倍。用MOCVD-TiO_2制作的MFIS二极管的C-V记忆窗口形状好，宽度大于2 V。在三种MFIS二极管中观察到的记忆窗口在形状和宽度上都与不假设漏电流和界面态的理想情况下计算出的记忆窗口有很大的不同，并且还显示出由于载流子注入而导致的宽度减小，这表明当记忆窗口打开时降低I层上的电压成为一个关键问题.用压电响应扫描力显微镜观察了在SrRuO_3（100）衬底上外延生长的PZT薄膜的极化反转过程。研究发现，在开关期间，Pt顶电极的PZT薄膜中有新的形核.用MOCVD方法在Pt/SiO_2/Si衬底上于395 ℃成功地生长了Percent PZT薄膜，其D-电滞回线的拉曼效应足以使MFIS-FET存储器工作。

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.