Semi-insulating silicon for microwave integrated circuits

Within the last few years, silicon devices have been introduced that operate well above 100 GHz. When attempting to use these high speed silicon devices in microwave applications however, signal propagation problems arise due to the conductive and therefore lossy silicon substrate. But in silicon, many of the transition metals have states near the center of the gap and so could be used to form semi-insulating (SI) wafers. In this paper, the calculated and measured resistivities for gold doped n-type and silver doped p-type silicon are shown. Due to the smaller bandgap, the maximum resistivity of SI silicon is about 10⁵ Ω-cm. It is shown that uniform, high resistivity wafers can be obtained by extended annealing above 1000°C.