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Methods of characterising the dielectric properties of thin ferroelectric films

Two methods of characterising thin films have been designed. A 14 GHz Split Post Dielectric Resonator (SPDR) and a Stripline Double Resonator.
The 14 GHz SPDR has been obtained from WUT and fully validated for substrate measurements. The SPDR is a non-destructive technique and has been specially designed to accommodate 10x10x0.5mm substrates, the largest size that films can be deposited onto.

A generic mode matching code has been developed to enable the complex permittivity of the film to be de-embedded from that of the film substrate composite. The code can model arbitrary radial geometries and is therefore suitable for analysing arbitrary circularly symmetrical TE mode DR geometries. (e.g. both DR measurement cells and DR filters). Providing circular symetry is maintained the code can easily deal with very thin films. This code has been validated against black box software from WUT, Microwave Studios (MWS), and in house finite difference code.

A Stripline Double Resonator has been modelled within MWS. Effort was spent on the modelling of the resonator, as this is necessary to de-embed the films complex permitivity from that of the film substrate composite. The difficulty with employing FDTD code is that the ratio of smallest to largest feature size is over 5000. The resonator is capable of measuring the change in complex permittivity of ferroelectric films under tuning. The resonator has been designed to work in the frequency range of the SPDR to allow the two methods to be used in tandem.

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National Physical Laboratory
Hampton Road, Teddington
TW11 0LW Middx.
United Kingdom
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