The Impact of Guard Rings on Proton Radiation Effects in SiGe HBTs

The effects of proton radiation on SiGe HBTs with guard rings are investigated in this work. DC measurements on pre- and post-radiated devices show that different effects on the forward-mode and on the inverse-mode Gummel characteristics are observed due to the implementation of guard rings for SiGe HBTs. The inverse-mode Gummel plot shows a distinctive increase of emitter current after proton radiation, which has not been observed in any previous studies. SPICE Gummel-Poon models were extracted for both pre- and post-radiated devices. By analyzing the measured and simulated results, the parasitic substrate-collector junction diode associated with SiGe HBTs has been identified to be the source of the new phenomenon. It is believed that the radiation damages in the substrate-collector junction near the deep trench edges cause the increase of the emitter current observed in the inverse-mode Gummel plot