measured three distinguishable components contribute to the measured value, namely the gap resistance and the contact resistances at the inner and outer end of the gap area ( and ). This is expressed in the following formula: As will be derived in the theory section an expression for that allows the extraction of from experimental data as long as is much larger than : Similar to the TLM method and can be obtained with a multiple linear regression analysis utilizing data-pairs of and . Theory TLM In the last section the basic principle of TLM was introduced and now more details about the theoretical background are given. The main purpose here is to find an expression that relates the measurable quantity with the specific contact resistivity which is intended to be determined with TLM. Therefore, in the image to the right a resistor network is illustrated that describes the situation when a voltage is applied between two adjacent metallic pads. The resistor () in the middle takes account for the part that is not covered with metal while the rest describes the situation for the metallic pads. The horizontal resistor elements () represent the resistance due to the semiconductor substrate and the vertical resistor elements () take account for the resistance due to the metal-semiconductor interfacial layer. In this description pairs of horizontal and vertical resistor elements describe the situation within a volume element of length in a metallic pad area. This methodology is also used for the derivation of the telegrapher's equations which are used to describe the behaviour of transmission lines. Because of this analogy, the described measurement technique in this article is often called the transmission line method. By using Kirchhoff's circuit laws the following expressions for the voltage as well as for the current within the above considered length element (read square in the figure in this section) are obtained for a steady state situation where both voltage and current are not a function of time: By taking the limit the following two differential equations are obtained: These two coupled differential equations can be separated by differentiating one with respect to such that the other can plugged in. By doing so finally, two differential equations are obtained which do not depend on each other: Both differential equations have solutions of the form whereat and are constants which need to be determined by using appropriate boundary conditions