Investigation of enhanced low dose rate sensitivity in SiGe HBTs by 60Co γ irradiation under different biases

This paper evaluates enhanced low dose rate sensitivity (ELDRS) in Silicon-Germanium heterojunction bipolar transistors (SiGe HBTs) which are isolated by LOCOS process. The 60Co gamma irradiations were performed at 80 rad (Si)/s and 0.1 rad (Si)/s respectively in order to investigate dose rate dependence of the SiGe HBT. Devices were set in forward, saturated, cutoff, and all-grounded biases during the irradiation. The degradation mechanism of different dose rate irradiations was analyzed via measurement of forward Gummel mode and inverse Gummel mode both pre- and post- irradiation. The results show that ELDRS exists at forward, saturated, and all-grounded biases irradiations. The dose rate dependences of various irradiated biases are different in the SiGe HBT. The interface-traps both in EB Spacer and LOCOS are the major irradiated damages in the SiGe HBT for the low dose rate irradiation. ELDRS is directly related to the quality, thickness, and shape of oxide layers.