Engineering Novel Functionalities in Ferroelectric Oxide Heterostructures

随着半导体工业正在接近电子元件的进一步几何缩小的基本极限，研究工作越来越多地转向寻找具有新功能的新材料。一类有前途的材料是过渡金属氧化物，具有奇特的现象，如高温超导性，巨磁阻，金属-绝缘体转变，不寻常的磁性和铁电性。其中，铁电氧化物-那些拥有可切换的自发极化-值得特别关注，因为它们在包括铁电随机存取存储器，压电传感器和致动器，热成像和非线性光学在内的广泛技术中具有长期的成功应用记录。然而，当这些材料的尺寸减小到纳米级时，它们的性质会发生显着变化，这为其应用带来了许多挑战，但也为工程新功能提供了新的机会。在这个项目中，我们将使用国家的最先进的人工分层外延超晶格组成的铁电和非铁电氧化物作为一个模型系统来研究的负电容，已被提出作为一种方法，用于提高场效应器件的表面电位和超越传统的CMOS晶体管的功率要求的限制知之甚少的现象。我们将对一系列人工分层材料中的负电容效应进行详细而系统的实验研究，量化该效应，确定其观察的最佳参数，并确定其活跃的温度范围。这项工作将为未来实现利用负电容提高性能的原型场效应器件铺平道路。

As the semiconductor industry is approaching fundamental limits to further geometrical down-scaling of electronic components, research efforts are being increasingly diverted towards the search of new materials with new functionalities. One class of promising materials are the transition metal oxides, featuring exotic phenomena such as high-temperature superconductivity, colossal magnetoresistance, metal-insulator transitions, unusual magnetism and ferroelectricity. Among these, ferroelectric oxides--those possessing a switchable spontaneous polarisation--deserve special attention as they have a long track record of successful application in a wide range of technologies including ferroelectric random access memories, piezoelectric sensors and actuators, thermal imaging and non-linear optics. The properties of these materials, however, change dramatically when their dimensions are reduced to the nanometre scale, posing many challenges for their application but also offering new opportunities for engineering novel functionalities. In this project we will use state-of-the-art artificially layered epitaxial superlattices composed of ultrathin ferroelectric and non-ferroelectric oxides as a model system to study the poorly understood phenomenon of negative capacitance that has been proposed as a method for enhancing the surface potential in field-effect devices and surpassing the power requirement limitations of conventional CMOS transistors. We will conduct a detailed and systematic experimental study of the negative capacitance effect in a range of artificially layered materials, quantifying the effect, determining the optimum parameters for its observation and establishing the temperature range over which it is active. This work will pave the way to future realisation of prototype field-effect devices utilising the negative capacitance for performance enhancement.