Improvement of ferroelectric and insulator layers in ferroelectric/insulator/semiconductor stacked gate structure

1.研究表明，通过铁电层的漏电流对金属-铁电-绝缘体-半导体(MFIS)结构的记忆保持性能起主导作用。此外，还特别证实了这一点。SBT膜抑制了泄漏，大大提高了保留性能，然后增加了一个数量级的时间，超过2x10^4s与一些后氧退火处理。我们提出了一个动力学模型，即载流子流过铁电层，注入到铁电和绝缘层之间的界面上，从而使施加在铁电薄膜上的电场逐渐抵消和减小。定性地解释了上述实验结果。提出并制作了一种新的利用电离电势测量的分析仪器，它使我们能够评估有或没有氧后退火的SBT表面，然后考虑MFIS结构的能带图。结果表明，SBT薄膜在退火前主要是空穴导电，退火后空穴势垒高度从1.6 eV增至2.0 eV。这一结果与前面提到的通过退火减少泄漏改善了记忆保持特性的结果是一致的。氧气气氛下的快速热退火工艺大大提高了MFIS二极管的保持时间。在极高的温度和短时间的1000℃和30 S的情况下，保留时间变得超过6x10^5 S(约1周)，并推断为约3x10^7 S(约1年)。为了进一步提高薄膜的保持性，对高压(7atm)氧退火工艺进行了研究，发现退火能有效地降低漏电流，并推测与(BiO_2O_2)和t；2&gt；层不同的是，BixO_y层被加热并抑制了漏电流。

1. It is suggested that leakage current through layer of ferroelectric such as SrBi_2TaO_9 and Sr_2 (Ta_<1-x>, Nb_x)_2O_7 has a dominant effect on memory retention properties of Metal-Ferroelectric-Insulator-Semiconductor (MFIS) structure. Furthermore, it is confirmed especially for the. SBT film that suppression of the leakage improved drastically retention properties, then increased the time by an order of magnitude, more than 2x10^4 s. with some post-oxygen annealing process.2. We proposed a dynamic model where carriers flow though ferroelectric layer and inject into the interface between ferroelectric and insulator layers, thus electric field imposed on the ferroelectric film gradually cancelled and decreased. As a result, experimental results shown above was qualitatively explained.3. A new analysis instrument utilizing ionization potential measurement was proposed and fabricated, which enables us to evaluate the SBT sutface with and without post-oxygen annealing, then to consider the band diagram of MFIS structure. It reveals that, before the annealing, hole conduction dominates the leakage through the SBT film, and that, after the annealing, barrier height against hole increases from 1.6 to 2.0 eV. This result agrees well with the mentioned above, where a reduction of leakage by the annealing improves the memory retention characteristics.4. A Rapid Thermal Annealing process with oxygen atmosphere improved greatly the retention time of MFIS diode. With a very high temperature and short time of 1000℃ and 30 s, the retention time became more than 6x10^5 s (about 1 week), and was extrapolated to about 3x10^7 s (about 1 year).5. A high pressure (7 atm) oxygen annealing was examined in order to improve the retention properties furthermore: It was found that the annealing is effective to reduce the leakage and estimated that Bi_xO_y layer, different from (Bi_2O_2)^<2+> layer, was fermed and suppress the leakage.