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Bipolar junction transistors (BJTs) are generally employed in spacecraft, due to their current drive capability, linearity and excellent matching characteristics. High-energy particles and cosmic rays in space environment remarkably affect electronic devices, especially in BJTs producing total ionizing dose, displacement damage or single event effect. Among them, ionizing irradiation effects on BJTs dominates. For BJTs, ionization damage can induce the oxide trapped charges in SiO2 layer and interface traps in Si/SiO2, resulting in more recombination base current and the degradation of current gain. Consequently, the accumulation of both oxide charges and interface traps causes an increase in the base current.#br#Passivation layer is also an important factor of the irradiation effects of BJTs. Previous works only studied the degradation of electrical properties of the devices with/without passivation layer induced by irradiation, and did not give an influence mechanisms of passivation layer on the irradiation respond of devices. Therefore, the irradiation damage mechanisms of the BJTs with or without nitride passivation layer are not clear so far.#br#In this paper, the impact of Si3N4 passivation layer on ionizing irradiation damage on lateral PNP bipolar transistors (LPNP) was studied by using 60Co gamma irradiation source. The KEITHLEY 4200-SCS semiconductor parameter analyzer was used to measure the relationship between the electrical properties of LPNP transistors and ionization dose, including the Gummel characteristics, the degradation of current gain, etc. The irradiation defects of the LPNP transistors with/without passivation layer structure were analyzed by the deep level transient spectroscopy (DLTS). The experimental results show that the electrical properties of the LPNP transistors with and without passivation layer exhibit similar characteristics. For all samples, the base current increases with increasing the total dose, while the collector current does not almost change. Compared with the LPNP transistors without Si3N4 passivation layer, the degradation of LPNP transistor with Si3N4 passivation layer is severe.#br#Based on the excess base current as a function of base-emitter voltage for the LPNP transistors with/without nitride passivation layer, the degradation of bipolar transistors with nitride passivation layer is severe under the same irradiation conditions. The DLTS analyses show that compared with the bipolar transistors without nitride passivation layer, the signal peak located at about 300 K is shifted to low temperature for the bipolar transistors with nitride passivation layer. The above results show that the LPNP transistors with nitride passivation could produce a large number of interface states with the energy level is closer to the middle of the forbidden band during the irradiation, which is attributed to a large number of hydrogen presence during the processing of fabricated passivation layer.

Polyethylene/carbon nanotube (PE/CNT) composites with high hydrogen content as a kind of structural material for space radiation shielding have extensive potential applications in future aerospace field due to their unusual radiation shielding, lightweight, and easy processing. In the space irradiation environment, the composites are sensitive to radiation damage, which changes their microstructures, directly affecting their mechanical performances and shielding effectiveness. Low energy electrons (200 keV) are important radiation environmental factors. Effects and mechanisms for mechanical damage of PE/CNTs composites induced by low energy electrons are studied, which has important academic value and practical significance. Previous research mainly involves the qualitative evaluations of the changes in the mechanical performance index of polymer nanocomposites. The inner relationship between microstructural change induced by radiation and mechanical behavior of the nanocomposites, especially in the PE/CNTs composites has not been studied in depth so far. In this paper, low-density polyethylene (LDPE)/ multi-walled carbon nanotube (MWCNT) composites are chosen as a research object. Based on 110 keV electron irradiation, tensile deformation mechanism of the LDPE/MWCNT composite is studied. The synchrotron radiation X-ray small angle scattering (SAXS) and wide angle diffraction (WAXD) are used to reveal the real-time microstructure evolutions of the nanocomposites after and before irradiation in the process of stretching. Tensile deformation mechanisms of LDPE/MWCNT composite after and before the 110 keV electron irradiation are revealed. Experimental results show that the tensile deformation behavior for the irradiated LDPE by 110 keV electrons is different from that for unirradiated sample. The electron irradiation increases the tensile strength of the LDPE/MWCNT composite and reduces the elongation at break. Moreover, with increasing the irradiation fluence, the tensile strength and the elongation at break of the LDPE/MWCNT composite significantly increases and decreases, respectively. The electron irradiation could hinder the deformations of the LDPE matrix including crystalline case and amorphous case, constrain the fragmentation of original lamellae, the directional arrangement of the MWCNTs, the formation of new crystal and the rotation of lamellae, especially in higher irradiation fluence. During tensile deformation, the main strengthening mechanism for the irradiated LDPE/MWCNT composites by the 110 keV electrons is crosslinking strengthening effect in LDPE matrix. On the other hand, enhanced interaction (mainly interface strengthening) between MWCNTs and LDPE matrix induced by irradiation is attributed to the main strengthening mechanism for the irradiated LDPE/MWCNT composites. These results could provide a theoretical basis and technical support for the reasonable design and successful application of CNT-based polymer composites as structural material for space radiation shielding.

Electrons are an important constituent part of radiation space of charged particles and could damage microelectronic devices. Therefore, effective radiation protection is very important for the electronic device. So, a radiation protecting material with lightweight, high performance and low cost is urgently needed. Polyethylene (PE) with high hydrogen content/carbon nanotube (CNT) composite as a space shielding material is very promising for spacecraft application in the future. In order to meet the requirement of space applications for PE/CNT composite, it is of important academic value and practical significance to explore melting and crystallization behaviors of LDPE/MWCNT composites. In this paper, melting and crystallization behaviours of the irradiated LDPE/MWCNT composites irradiated by 110 keV electrons are studied by differential scanning calorimetry (DSC), synchrotron radiation X-ray small angle scattering (SAXS) and wide angle diffraction (WAXD). Experimental results show that the irradiation by 110 keV electrons does not affect the thermal characteristics of the LDPE, but can enhance the initial melting temperature and the melting-terminating temperature of LDPE/2% MWCNT composites during melting. Also, the radiation by 110 keV electrons could reduce the initial crystallization temperature and the crystallization-terminating temperature during crystallization. MWCNTs could enhance the initial melting temperature and reduce the melting-terminating temperature of LDPE/2% MWCNT composites during melting. Moreover, MWCNTs could enhance the initial crystallization temperature and crystallinity, and reduce the crystallization-terminating temperature during crystallization. SAXS and WAXD analyses show that with increasing the temperature, long periods of the irradiated/unirradiated LDPE increase during melting. Compared with that of the unirradiated LDPE, at a given temperature, long period of the irradiated LDPE is small. During crystallization, with reducing the temperature, long period of the irradiated/unirradiated LDPE begins to appear and gradually decreases. At the same temperature, long period of the irradiated LDPE is larger than that of the unirradiated one. For LDPE/2% MWCNT composites, long periods of the irradiated/unirradiated samples during melting and crystallization do not exist. The 110 keV electron irradiation mainly influences LDPE matrix of LDPE/2% MWCNT composites during melting and crystallization. The 110 keV electron irradiation can slow down the amorphous region expansion and the initial melting of lamellae of the LDPE matrix during melting. The 110 keV electron irradiation can slow down the amorphous region shrinkage and inhibit crystal from growing up during crystallization. During melting, MWCNTs can hinder the amorphous and crystalline molecular chains of LDPE from moving, which hinders the LDPE matrix from initially melting, but promotes the melting process after the initial melting has begun. During crystallization, MWCNTs could promote the formation of crystal of the LDPE matrix and inhibit the crystal from growing up.

In this paper, compressive behavior of electrodeposited nano-crystalline (nc) Ni at various temperatures and strain rates is studied using a low temperature mechanic test system. Plastic deformation mechanisms of nc Ni caused by compression are characterized by the strain rate sensitivity index, the activation volume, and examined by scanning electron microscopy and high resolution transmission electron microscopic analysis. Results show that at low temperatures, the plastic deformation of nc Ni is mainly dominated by grain boundary accommodated dislocations. In other words, during plastic deformation of nc Ni at low temperatures, the intrinsic dislocation at the grain boundary bends up and expands without obstacles to the opposite grain boundary in the inner grain dislocation-free zone, until the occurrence of similar cutting forest-dislocation behavior appearing at opposite grain boundary. Moreover, the residual dislocations in the grain boundary bending out during plastic deformation could increase the strain compatibility and decrease the stress concentration. At room temperature, the plastic deformation mechanism of nc Ni is controlled by the deformation of grain boundary accommodated dislocations and grain slipping/rotating. Based on the above analyses, differences in compressive behavior of nc Ni at various temperatures and strain rates can be revealed by the correlation of deformation mechanisms of grain boundary accommodated dislocations and residual dislocation movement, temperature and defects in nc Ni.

Due to their unusual electrical conductivity, carbon nanotubes as the ideal candidates for making future electronic components have extensive application potentiality. In order to meet the requirements in space electronic components for carbon nanotubes, effect of 170 keV proton irradiation on structure and electrical conductivity of multi-walled carbon nanotubes (MWCNTs) film is investigated in this paper. Surface morphologies and microstructure of the carbon nanotube films are examined by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy, respectively. Electrical conductivities of the carbon nanotube films before and after 170 keV proton irradiation are measured using four-point probe technique. SEM analysis reveals that when proton irradiation fluence is greater than 51015 p/cm2, the surface of the carbon nanotube film becomes rough and loose, and obvious bending, shrinkage, and entanglement of nanotubes are observed. Moreover, the shrinkage phenomenon of MWCNTs caused by proton irradiation is found the first time so far as we know. Based on Raman and XPS analyses, it is confirmed that 170 keV protons can improve the ordered structure of the MWCNTs, and irradiation fluence plays a key role in reducing the disorder in the MWCNTs. Improvement of the irradiated MWCNTs by 170 keV protons can be attributed to restructuring of defect sites induced by knock-on atom displacements. On the other hand, carbon impurities on surface of the MWCNT film are reduced due to the effect of sputtering by the 170 keV proton irradiation, which is also helpful to the improvement of the structure of carbon nanotubes. EPR spectra show that the electrons delocalized over carbon nanotubes decrease with increasing irradiation fluence, implying that the carbon nanotube film is not sensitive to ionizing radiation induced by the 170 keV protons, and the electrical conductivities of the MWCNTs films may be decreased. Four-point probe technical analysis shows that with increasing irradiation fluence, electrical properties of the carbon nanotubes film deteriorate, which can be attributed to the changes in electronic properties and morphology of the MWCNT films induced by 170 keV protons. Acquired results could be beneficial to tailoring of structure and properties for the carbon nanotubes film irradiated by protons to develop nanoelectronics of radiation-resistant systems.

During serving in orbit, spacecraft will be affected by the radiation environment of the space high-energy charged particles, leading to the performance degradation or even malfunctions of electronic components. The complementary metal oxide semiconductor (CMOS) devices are sensitive to ionization damage. Therefore, it is valuable to research the mechanism of radiation effects on CMOS devices, and is significant to engineering and theory. The CC4013 CMOS integrated circuits are irradiated with 60 MeV Br ions, 5 MeV protons and 1 MeV electrons. Based on the data calculated by Geant4 code, the ionizing absorbed dose induced by 60 MeV Br ions is greatest, and the ionizing absorbed dose induced by 1 MeV electrons is lowest. The degradation of CC4013 device during the irradiation test is in-situ measured with Keithley 4200-SCS semiconductor characteristic system. From the experimental results, the threshold voltage degradation in CC4013 under an exposure of 1 MeV electrons is greatest at the same dose, a little lower under 5 MeV protons, and lowest under 60 MeV Br ions.

Bipolar junction transistors (BJTs), as important electronic components in analog or mixed-signal integrated circuits (ICs) and BiCMOS (Bipolar Complementary Metal Oxide Semiconductor) circuits, are employed in the space environment. Therefore, the research on characteristics and mechanisms of ionization damage in the BJTs is very important. Lower energy electrons are used as irradiation source to study the ionization damage in NPN and PNP transistors. Various bias conditions are imposed on the emitter-base junction to reveal the different bias conditions that contribute to the radiation effect on NPN and PNP transistors during irradiation processing. The semiconductor parameter analyzer, Keithley 4200-SCS, is used to measure the change of electrical parameters of transistors with increasing electron irradiation fluence in situ. Based on the measurement results, we find the degradation of transistors is severe under reverse emitter-base bias, and is lowest under forward emitter-base bias, while it is medium under zero emitter-base bias at a given irradiation fluence.

The high performance nano-crystal Ni material was prepared by the pulse electrodeposition process; the intensity, composition and the microscopic structure of the nano-crystal Ni material were investigated by various measurements. In this paper, the 1 MeV electron was chosen as the irradiation source to investigate the energy loss of high energy electron in the nano-crystal Ni material and conventional bulk Ni material, and the energy deposition process during the electron irradiation was measured by the absorbed dose tablets. The results show that the grain size affects the energy loss process during the 1MeV electron irradiation seriously. The absorbed dose of 1 MeV electron in the nano-crystal Ni material is lower than that in the common Ni material with the same thickness, which indicates that the energy deposition of high energy electron in nano-crystal metal is lower than that in the conventional bulk metal, and the nano-crystal metal has an advantage of radiation resistance.