Comparison of substrate effects in sapphire, trap-rich and high resistivity silicon substrates for RF-SOI applications

This paper compares insertion loss, harmonics and Q-factor of sapphire, trap-rich silicon and high-resistivity silicon substrates. The concept of substrate characteristic frequency is shown to be useful metric to evaluate substrate behavior. New methods to evaluate substrate properties are introduced using open CPW stubs and parallel plate capacitors. It is demonstrated that sapphire provides the best RF performance, while trap-rich silicon offers limited but adequate performance with a resistivity around a few kΩ-cm. High-resistivity silicon provides the worst RF performance due to unmitigated parasitic conduction.