Chaoming Liu

Combined Radiation Effects of Protons and Electrons on NPN Transistors

This paper examines individual radiation effects caused by 110 keV electrons, 70 keV protons and 170 keV protons, and combined radiation effects induced by 110 keV electrons together with 70 keV protons and 110 keV electrons with 170 keV protons on the forward current gain of bipolar junction transistors (3DG112D, NPN). Key parameters were measured in-situ and the change in current gain of the NPN transistors is obtained at a fixed collector current. Experimental results show that the current gain degradation of the NPN transistors is sensitive to both of ionization and displacement damage. The ionization damage is primarily caused by 110 keV electrons, while the displacement damage is mainly induced by 170 keV protons in this study. Under the combined exposure of 170 keV protons and 110 keV electrons, the current gain degradation lies between those given by the individual irradiations. The current gain degradation is mainly caused by the 170 keV protons, and the 110 keV electrons mitigate the degradation to some extent. In the case of combined irradiation of 110 keV electrons and 70 keV protons, no synergistic effect occurs, the current gain degradation is basically controlled by the 110 keV electrons.

Simultaneous and Sequential Radiation Effects on NPN Transistors Induced by Protons and Electrons

This paper examines individual radiation effects caused by 110 keV electrons and 170 keV protons, and combined radiation effects induced by 110 keV electrons together with 170 keV protons on the forward current gain of NPN bipolar junction transistors (3DG130, 3DG112). Key parameters were measured in-situ and the change in current gain of the NPN bipolar junction transistors is obtained at a fixed voltage of base-emitter junction (VBE) during simultaneous and sequential exposures. Experimental results show that the current gain degradation of the NPN bipolar junction transistors is sensitive to both of ionization and displacement damage. The ionization damage is primarily caused by 110 keV electrons, while the displacement damage is mainly induced by 170 keV protons in this investigation. Based on the simultaneous and sequential exposure results, the ionization damage caused by 110 keV electrons can give an enhancing effect to displacement damage induced by 170 keV protons for NPN bipolar junction transistors.

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 (ΔIB) versus base-emitter voltage (VBE) 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.

Synergistic Radiation Effects on PNP Transistors Caused by Protons and Electrons

This paper examines individual radiation effects caused by 110 KeV electrons, 70 KeV electrons and 170 KeV protons, and combined radiation effects induced by 110 KeV electrons together with 170 KeV protons and 70 KeV electrons with 170 KeV protons on the forward current gain of bipolar junction transistors (3CG130, PNP). The combined radiation effects include simultaneous and sequential radiation effects. Key parameters were measured in-situ and the change in current gain of the PNP transistors is obtained at a fixed voltage of emitter-base junction . Experimental results show that the current gain degradation of the PNP transistors is sensitive to both of ionization and displacement damage. The ionization damage is primarily caused by 110 KeV and 70 KeV electrons, while the displacement damage is mainly induced by 170 KeV protons in this investigation. Based on the simultaneous and sequential exposure results, the ionization damage caused by 110 KeV and 70 KeV electrons could give annealing-like and enhancing effects to displacement damage induced by 170 KeV protons for PNP BJTs.

Research on the Combined Effects of Ionization and Displacement Defects in NPN Transistors Based on Deep Level Transient Spectroscopy

The properties of the combined effect between ionization and displacement defects have been researched on the base-collector junctions of 3DG110 silicon NPN bipolar junction transistors (BJTs) irradiated by 6 MeV carbon (C) ions with different fluence. The Gummel curve is used to characterize the degradation of the current gain at a given fluence. Nonlinear relationship, induced by 6 MeV C ions with lower fluence, between irradiation fluence and BJT radiation response can be observed, which is attributed to the combined effect. Evolution of deep level centers is characterized by the deep level transient spectroscopy (DLTS) with various biases. An unusual discovery is that the deep level centers decrease in the amplitude of DLTS peaks with increasing the biases. Based on the results of DLTS measurement, interface traps caused by 6 MeV C ions produce apparent enhanced effect to displacement defects in the base-collector junction of NPN BJT. Meanwhile, two factors, including bias used in DLTS measurement and irradiation fluence, can influence characteristics of DLTS signals caused by oxide-trapped charge. With increasing the bias or the irradiation fluence, both the height and the temperature of the defect peaks induced by the oxide charge in DLTS spectra will increase, illustrating concentration and energy level of the defects are enhanced.

Evolution of Deep Level Centers in NPN Transistors Following 35 MeV Si Ion Irradiations With High Fluence

The properties of deep level centers have been researched on the base-collector junctions of 3DG110 silicon NPN bipolar junction transistors (BJTs) irradiated by 35 MeV silicon (Si) ions with different fluence. The Gummel curve is utilized to characterize the degradation of current gain at a given fluence. 35 MeV Si ions with high fluence can induce high levels of damage on current gain of 3DG110 BJTs, the value of which could be less than 1. Evolution of deep level centers, induced by such high fluence in NPN BJTs, is characterized by the deep level transient spectroscopy (DLTS). SRIM software is employed to estimate the number of vacancies produced by 35 MeV Si ions and to calculate the Si ion end of range in BJTs. Based on the calculations by SRIM and measurements by DLTS, when the irradiation fluence is high enough, 35 MeV Si ions with the end of range deeper than the DLTS-probed depths, can also produce apparent defect clusters, which is similar to those with the end of range in DLTS-probed depths. These irradiation-induced defect clusters can suppress the V2(=/-) DLTS signature. Especially, compared to shallower deep levels, the deeper levels, such as V2(-/0) centers, are the critical defects to degrade the current gain.

Synergistic Effect of Ionization and Displacement Damage in NPN Transistors Caused by Protons With Various Energies

Based on 2N2222 NPN bipolar junction transistors (BJTs), synergistic effect between ionization and displacement defects induced by 3 MeV, 5 MeV and 10 MeV protons were researched. High-energy protons can be incident upon the silicon (Si) BJTs, producing displacement defects in silicon bulk and ionization damage in the oxide layer of BJTs, respectively. Both ionization and displacement damage result in the degradation of current gain of BJTs. At a given displacement dose, 10 MeV protons induce the maximum degradation of current gain of 2N2222 NPN BJTs, while 3 MeV protons cause the minimum degradation. In this case, non-ionizing energy loss (NIEL) methodology is not suitable to normalize the displacement damage induced by 3 MeV, 5 MeV and 10 MeV protons, which is attributed to the synergistic effect of ionization and displacement damage. The displacement defect centers in based-collector junction of 2N2222 transistor induced by 3 MeV, 5 MeV and 10 MeV proton exposures, were discovered and characterized by deep level transient spectroscopy (DLTS). Based on the comparison between the electrical parameters and the DLTS results, it is shown that, interface traps due to ionization damage induced by high-energy protons spread the emitter-base depletion layer, leading to the enhancement effects to displacement damage in the base-collector junction of NPN BJT. Meanwhile, bias voltage used during DLTS measurement influence characteristics of DLTS signals. With the increasing reverse bias, the value of ΔC/C for VO, V2( = / -), E4 and V2(- /0) + E5 centers increases.

Radiation Defects and Annealing Study on PNP Bipolar Junction Transistors Irradiated by 3-MeV Protons

A combined radiation effect is produced by 3-MeV protons, giving by both ionization and displacement damage, on semiconductor devices. In this paper, electrical characteristics and deep level transient spectroscopy (DLTS) are used to measure the radiation defects induced by ionization and displacement damage during the annealing process. A nonlinear relationship between the proton fluence and radiation response is clearly observed in the 3CG110 PNP bipolar junction transistor (BJT). DLTS analysis technique and annealing response of BJTs can provide important information on the nature of the ionization and displacement-induced defects, and measure them quantitatively, especially for the BJT with the combined radiation damage induced by protons. Based on the results of DLTS measurement and current gain annealing, the evolution of the ionization and displacement defects during the irradiation and annealing process is revealed, and the relationship between defects and current gain annealing is studied.

Separation of Interface Traps and Oxide Charge in Ionization Damaged Silicon Bipolar Transistors Based on Experimental Observation

An experimental concept of separating oxide-trapped charge and interface traps in silicon bipolar junction transistors (BJTs) irradiated by Co60 gamma ray is demonstrated. This concept is based on deep-level transient spectroscopy (DLTS) measurements with various filling pulsewidths. The characteristics of oxide-trapped charge and interface traps in bipolar transistors can be obtained by DLTS. The oxide-trapped charge shows positive and negative signals in the collector of NPN and PNP BJTs in DLTS signals, respectively. Unlike the oxide-trapped charge, the interface traps give positive signals in the same region of NPN and PNP BJTs.

Evolution of Activation Energy of Interface Traps in LPNP Transistors Characterized by Deep-Level Transient Spectroscopy

The emission of charge carriers from the interface traps as a function of irradiation dose and bias voltage is investigated in terms of Poole–Frenkel effect (PFE) used by deep-level transient spectroscopy (DLTS). The electrical properties in lateral PNP (LPNP) transistors caused by Co60 gamma-ray radiation are measured in situ during irradiation, showing that the interface traps give the main contribution to the excess base current of LPNP transistors. Based on the DLTS results, with increasing irradiation dose, the density of the charged positive interface traps at a given bias voltage increases. This causes an increase in the electric-field strength in the space-charge region and a decrease in the activation energy of interface traps and an increase in the emission rate of charge carriers from the interface traps, showing a similar feature to the classical PFE. However, the charge sign of the interface traps changes from negative to positive, which is different to the classical PFE, and thus displays a new mode of PFE. In order to confirm this conclusion, various bias conditions are employed during DLTS measurements. With decreasing the reverse bias, the electric-field strength increases, leading to an obvious decrease in activation energy of the interface traps and increase in emission rate of charge carriers. Moreover, the interface traps are shown to be uniformly located at the Si/SiO2 interface, and the uniformly distributed interface traps give the new PFE mode, which is independent of the position in depletion layer.