Charging ahead with Multi-layer Ceramic Capacitor materials

Multi-layered ceramic capacitors (MLCCs) are the foundation of the electronics (passive components) industry. Each layer within a MLCC is made by sintering a powdered, typically a chemically-doped, functional oxide such as Barium Titanate. This processing route generates a complex microstructure that can include grains, grain-boundaries, pores, interface roughness and graded material properties. Many of these microstructural effects are known to influence device performance but the knowledge of their exact mechanism and strength of their effect is limited. At present the favoured approach towards optimising these effects is based on trial and error experimentation; however, this is challenging and time and resource consuming. It would benefit both academics and industry working on MLCC systems to be able to analyse such microstructural phenomena in a resource efficient, controlled and systematic way. This would not only allow a faster route towards optimisation of current materials and devices, but also allow quickly the analysis of rare earth-free sustainable alternatives.
To achieve this, the project will develop new capabilities in modelling functional materials. We shall develop an advanced microstructural package to create realistic three-dimensional microstructures representing the main microstructural features listed above. By combining this with a state-of-the-art finite element modelling package, we shall be able to test what effects these have on device performance and allow us to guide the processing of the underlaying materials. While this proposal will be targeted towards challenges in functional oxide materials for MLCCs, due to the flexibility of the methodologies used, the codes will also be applicable to a much wider range of functional materials and devices. This includes but is not limited to solid oxide fuel cells, thermoelectric generators, piezo-electric sensors & actuators and beyond into magnetic and radiation damaged materials.
The microstructural generation package will be based on two sources. Firstly, systems will be created from the analysis of experimental microstructures supplied by experimental groups and our industrial partner (AvX Ltd). Secondly, artificial systems will be generated using an array of mathematical algorithms, allowing controllable characteristics and a systematic approach in analysis. The first study using this new package will be to better understand how the doping of the ceramic material, that forms the physical 'core-shell' microstructure, can influence the current flow through the microstructure. This will be extended to how inadequate mixing of the dopants into the base material can manifest itself in a poor electrical response and performance of the device. Further analysis will be conducted on the effects of porosity and interfacial ceramic/metal electrode roughness that contribute to advancing degradation in in MLCCs and are ultimately considered to be the limiting factors in device lifetime.

Economy & Society:
Demand for multi-layered ceramic capacitors (MLCCs) from computing, automotive, aerospace and telecommunication industries is for smaller components with stable operation at higher temperatures. This is central to a $10 billion global market with an estimated 2 trillion units sold in 2015, predicted to increase to over 3 trillion by 2020.
It is commonly known that changes in microstructure of functional oxide materials can dramatically affect performance. It is unclear however what microstructural features would be required to increase performance, for example to achieve a suitable temperature stable-high permittivity profile (an important figure of merit known as the Temperature Coefficient of Capacitance, TCC).
While leading companies such as Murata, Kyocera and AVX Ltd possess extensive knowledge in materials development, TCC optimisation is achieved by incremental iterative changes to the processing conditions. This is an experimentally based process and generates a prohibitively high cost in time, resource and money in the R&D requirement, acting as a barrier for commercialising new materials. For the UK to remain competitive with overseas companies, it is essential that necessary fundamental research is made towards enhancing MLCC materials for higher performance applications using a faster, cheaper more robust method.
This proposal addresses this by creating a modelling framework that designs complex polycrystalline microstructures for use in multi-layered systems and solves for their electrical response. This will allow us to identify the desired microstructural features quickly providing, guiding the processing to address key industrial issues. This will save significant time and cost in optimisation but also provide advise on materials where optimisation would be ineffective.
After validating this methodology, we will begin to design materials with improved performance assisted by the experimental groups and our industrial partner AvX Ltd (based in Coleraine, Northern Ireland). Furthermore we will also explore new device concepts for MLCCs allowing the UK to maintain competitiveness in the global market.
People:
A PDRA employed on the project will be trained in generating realistic microstructures and solving for their electrical response. This will provide a valuable extension to their skills. In addition, the individual will have the opportunity to improve their transferable skills (writing, presenting) that will be invaluable in a career inside or outside of academia. The PhD students interacting with the packages will benefit from additional skills in programming, using a high performance cluster but also benefit their work directly. Taught masters and undergraduates within the Materials Science and Engineering department will have the opportunity to work on small research projects associated with this work which will provide useful training for their future careers. Finally this funding will also allow my group to grown and gain new capabilities of our in house finite element modelling package, allowing me to become world leading simulating functional materials and strengthen modelling as a whole in the UK.
Knowledge:
Bringing new modelling methods to experimental research teams in functional materials will be a major impact. The new tools will enable novel approaches in understand how the electrical microstructure and ultimately the response of a given physical microstructure can be controlled. This project will provide a platform to engage the public with more fundamental scientific issues, by using the performance and sustainability of MLCCs as a starting point in developing materials for the future. Therefore, science education of the general public will be a key impact from this project. As the project progresses contact will be made with groups outside academic research and there will be dissemination of the knowledge of these modelling methods into industrial R&D group.