NIST researchers develop new microwave characterization tools for thin film circuits.

As the speed of modern electronics increases, thin film dielectric materials are becoming increasingly important circuit elements for integrated electronics, communications, and computing applications. It is important to characterize thin-film dielectric materials over a broad frequency range to ensure adequate performance at the ever-increasing frequencies used by these devices. Also, new thin film materials are being developed that incorporate some functionality in the materials themselves, such as voltage-tunable ferroelectrics.

NIST researchers have developed an experimental method for determining the broadband permittivity of thin-film samples at frequencies up to 40 GHz using coplanar waveguide (CPW) measurements and finite element simulations. This method uses the multiline TRL calibration techniques previously developed at NIST, and is convenient for evaluating thin-film samples with minimal preparation, since metallic conductors can be deposited directly on the film surface in most cases. This technique complements existing thin-film permittivity measurements developed at NIST based on microstrip devices. Consistent values for the permittivity of barium strontium titanate thin films have been successfully extracted for three different cpw geometries incorporated on the same thin-film sample. Measurements of lumped-element devices also on the same sample give consistent permittivity values as well, allowing the frequency range of this technique to be extended to lower frequencies. The simplicity of this technique will allow new materials to be evaluated rapidly for microwave frequency applications.

CONTACT: James Booth, [phone]; [e-mail].