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EPSRC Reference: GR/S98412/01
Title: A Micromechanical Approach to the Optimal Design of Ferroelectric Thin Film Devices
Principal Investigator: Fleck, Professor N
Other Investigators:
Migliorato, Professor P Chu, Professor D Huber, Dr JE
Researcher Co-Investigators:
Project Partners:
Epson (UK) Ltd
Department: Engineering
Organisation: University of Cambridge
Scheme: Standard Research (Pre-FEC)
Starts: 01 January 2005 Ends: 31 December 2007 Value (£): 242,665
EPSRC Research Topic Classifications:
Electronic Devices & Subsys. Materials Characterisation
EPSRC Industrial Sector Classifications:
Electronics
Related Grants:
Panel History:  
Summary on Grant Application Form
Ferroelectric thin films are growing in significance as non-volatile memory devices. At present, practical device development is ahead of the modelling activity that could allow optimal device design and the development of accurate circuit-level models. The proposed research addresses this imbalance. In particular, the interaction between the stress state of the film and its electrical behaviour has not been addressed. During the last five years, however, models for the non-linear behaviour of ferroelectric materials have advanced significantly. It is now possible to model the coupled switching response in stress and electric field versus strain and electric displacement for complex, multi-axial loading histories. This opens the way to the design and optimisation of ferroelectric devices using micromechanical modelling. A micromechanical model for ferroelectric switching has been developed by two of the investigators. The model is based on incremental domain wall movement, and has the flexibility to represent a variety of microstructures and material compositions, with the same underlying mechanism of switching. At present, this model has been validated against bulk polycrystalline materials, but it has not been extended to the case of thin films, where the microstructural length scale is comparable to the film thickness. Development of a thin film material model is needed and has direct application in the design of thin film devices. This work needs to be backed up with a programme of measurement of thin film properties.Concurrently, techniques for characterising ferroelectric thin films have been developed by two of the investigators, using atomic force microscopy (AFM) to probe the films both electrically and mechanically. This work enables local piezoelectric coefficients and polarisation states to be detected. The work will be extended to validate new models for ferroelectric thin films, and to provide the essential microstuctural inputs for the material model.The proposed work will bring together the recent advances in both modelling and characterisation work and is the logical next step towards optimal device design. A major output will be geometry-performance maps for ferroelectric films which relate design parameters such as film thickness and device spacing to performance measures such as device speed and reliability.
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