Separation of Ionization Traps in NPN Transistors Irradiated by Lower Energy Electrons

Effects of oxide-trapped charge and interface traps induced by ionizing radiation, on the degradation of the electrical properties in NPN bipolar junction transistors (BJTs), are identified in this paper. Ionization traps in 3DG110 NPN BJTs are caused by 110 keV electron irradiations for various fluences, and the key electrical parameters are measured in situ during irradiation. In order to separate the effects of the interface traps and oxide charge on the radiation response in BJTs, the isochronal and isothermal annealing are performed after irradiations. Behavior of the radiation-induced defects is detected by DLTS after the irradiation and the postirradiation annealing. Measurement results indicate that when the change in reciprocal of the gain (Δ(1/ β)) tends to level off, the concentration of oxide-trapped charge increases with increasing irradiation fluence, while that of the interface traps keeps unchangeable. A comparison of DLTS signals with changes in excess base current (ΔI_B) versus base-emitter voltage (V_BE) is conducted to show the role of oxide-trapped charge and interface traps on the excess base current, illustrating that the DLTS analysis is suitable to separate the ionization traps in BJTs.