Field-Effect Passivation of Lossy Interfaces in High-Resistivity RF Silicon Substrates

In this paper, a novel method for increasing effective resistivity in low-doped silicon substrates is presented. The parasitic surface conduction effect is known to be the dominant cause of RF substrate losses in high-resistivity silicon materials, and the proposed approach passivates the Si/SiO2 interface through the field-effect. The technique is applied below CPW lines in the 45RFSOI node from GLOBALFOUNDRIES on alternate high-resistivity silicon substrates. Small-signal measurement results reveal a strong increase in substrate effective resistivity as a function of the applied bias to the passivation structures, and therefore an appreciable decrease in line loss α. Large-signal measurements performed at 900 MHz further reveal a strong increase in substrate linearity, of approximately 20 dB, achieved through the passivation technique. Finally, a TCAD-based simulation approach enables the investigation into alternate biasing-based passivation structures and the achievable RF substrate figures of merit.