Analysis of ESD Behavior of Stacked nMOSFET RF Switches in Bulk Technology

The operation of stacked MOSFET circuit for RF switch application under electrostatic discharge (ESD) conditions is studied by transmission line pulse (TLP) and transient interferometric mapping (TIM) techniques combined with circuit simulation. TLP pulses with 100-840 ns durations were applied to the device composed of 16 stacked multifinger MOSFET blocks with gate and drain resistors, fabricated in a bulk technology. ESD discharge paths related to MOSFET channel and to open-base breakdown have been identified to have dominant role in explaining the complex voltage and current waveforms. The overall circuit behavior during TLP pulses is analyzed taking into account calibrated breakdown measurements on test structures. In order to explain the heat dissipation in MOSFET blocks measured by TIM, additional discharge paths related to block-to-block coupling due to parasitic bipolar action have been modeled and discussed. Besides the analysis of the device behavior, we have also investigated peculiar optical TIM signal related to anisotropic reflectivity and phase response due to dense multifinger block structure.