Engineering Novel Functionalities in Ferroelectric Oxide Heterostructures

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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.