Designing geometry for the circular transmission line model to determine sheet resistance under contacts

The Circular Transmission Line Model (CTLM) can be used as a convenient tool for determining the sheet resistance under an ohmic contact. However the model assumes that electrodes are at an equipotential and in order to examine this assumption, an investigation has been undertaken to show the minimum requirements for attaining reliable measurements. Using test structures of nickel deposited on germanium it has been shown that the geometry of the structure has a significant impact on results obtained. In addition to this, care should be taken when testing samples to ensure that suitable probe positions and a sufficient number of probes are used.