Ionizing radiation induced degradation of 30% SiGe HBTs was studied by exposing them to Co60 γ-radiation under bias upto a total dose of 3.2 Mrads. The devices were characterized immediately after each dose using: 1) Gummel measurements 2) Reverse bias E-B and C-B leakage currents and 3) E-B and C-B reverse capacitance measurements. To find out the effect of emitter geometry, devices with different perimeter to area ratios were investigated. The results indicate that the devices are quite rad-hard and the damage is qualitatively similar to that of Si BJTs. The base current IB is observed to increase with dose without any increase in collector current IC, thus causing degradation in gain IC/ IB. Also devices with higher P/A ratio show more degradation compared to the degradation of devices with lower P/A ratio. The reverse C-B and E-B capacitance and E-B and C-B leakage currents do not change due to irradiation. The experimentally observed degradation of SiGe HBTs can be explained considering positive oxide charge generation and interface states generation in the oxide over the E-B junction. This would cause excess recombination in the base region close to the surface and near the E-B junction causing increase of IB. However, no change in the E-B reverse bias leakage current indicates that the generation of interface states is negligible and the degradation is primarily because of the positive charge generation in the oxide.
|Journal||Proceedings of SPIE - the international society for optical engineering|
|Publication status||Published - 1 Jan 2000|
|Event||10th International Workshop on the Physics of Semiconductor Devices 1999 - New Delhi, India|
Duration: 14 Dec 1999 → 18 Dec 1999
Conference number: 10