The high frequency conductivity of thin metallic and graphitic nano-films attracts interest due to many potential applications in spin electronics, electromagnetic shielding, flexible antennas, displays, and solar cells. The surface morphology of thin conducting nano-films typically consists of an isolated clustering structure, which can evolve into a conducting percolated network. The high frequency conductance of such materials is not well understood. We present measurements of the microwave conductivity of thin optically transparent films in coplanar waveguide (CPW) configuration. We determine the relation between the experimentally measured scattering parameters S11 and S21, complex impedance (Zs) and propagation constant (gamma ) for the CPW test structure through a signal flow graph method. Once the signal flow is solved for gamma and Zs , then the conductance Gs and the capacitance Cs of the specimen can be determined from conventional transmission line relations. Measurements are carried out on CPWs having a characteristic impedance of 50 Ohms and a propagation length ranging from 450 um to 3,600 um, which are patterned on alumina substrates by lift off lithography. The presented results are general and applicable for characterization of electrical properties of thin nanostructured films at microwave frequencies.
2011 International Conference on Frontiers of Characterization and Metrology for Nanoelectronics
May 23-27, 2011
microwave, coplanar waveguides, conductivity, thin films