Surface impedance of silicon substrates and films

It is shown that at microwave–millimeterwave frequencies and for DC resistivities below ρ+=(2πfτε0εL)−1 silicon should be regarded as a lossy metal characterized by resistivity, skin depth, and surface impedance, while at higher resistivities it may be regarded as a lossy dielectric characterized by a lattice dielectric constant (εL=11.7) and loss tangent. The sheet resistance defined as a ratio of DC resistivity to film thickness is not an adequate parameter to characterize the films at microwave frequencies. The surface impedance of a thin semiconductor film is complex with both real and imaginary parts strongly dependent on frequency, DC resistivity of substrate and film, substrate thickness, and the presence of a ground plane on the backside of the substrat