Radiation tolerant RF-LDMOS transistors, integrated into a 0.25μm SiGe-BICMOS technology

Mixed signal on-chip solutions for space applications and high energy physics experiments require high voltage RF-LDMOS transistors with sufficient ruggedness against ionizing radiation and single event burnout. We report on a novel hardening by design approach for radiation tolerant integrated RF NLDMOS transistors confirmed by single event burn out (SEB) and total ionizing dose (TID) radiation tests. In order to substantially decrease TID induced leakage currents the shallow trench isolation (STI) of MOS transistors was replaced by narrow junction isolated regions. For a significant increase of the SEB onset voltage a cascode arrangement consisting of an isolated NMOS and NLDMOS was chosen. The floating NMOS-drain/NLDMOS-source node in the cascode arrangement is always reverse biased which efficiently avoids a turn-on of the parasitic npn bipolar transistor. The rad-hard isolated NMOS/NLDMOS cascode features a breakdown voltage BVDS > 50 V, a maximum cut off frequency fT = 5 GHz and a maximum oscillation frequency fMAX = 14 GHz. In comparison with standard NLDMOS transistors the isolated NMOS/NLDMOS cascode device shows an increase of the SEB onset voltage from 14V to 30V at a linear energy transfer LET of 67.7 MeVcm2/mg and a negligible increase of source drain leakage currents up to a TID of 1.5 Mrad after irradiation with a 60Co source.