Yang Dezhuang

Degradation mechanisms of current gain in NPN transistors

An investigation of ionization and displacement damage in silicon NPN bipolar junction transistors (BJTs) is presented. The transistors were irradiated separately with 90-keV electrons, 3-MeV protons and 40-MeV Br ions. Key parameters were measured in-situ and the change in current gain of the NPN BJTS was obtained at a fixed collector current (Ic = 1 mA). To characterise the radiation damage of NPN BJTs, the ionizing dose Di and displacement dose Dd as functions of chip depth in the NPN BJTs were calculated using the SRIM and Geant4 code for protons, electrons and Br ions, respectively. Based on the discussion of the radiation damage equation for current gain, it is clear that the current gain degradation of the NPN BJTs is sensitive to both ionization and displacement damage. The degradation mechanism of the current gain is related to the ratio of Dd/(Dd + Di) in the sensitive region given by charged particles. The irradiation particles leading to lower Dd/(Dd + Di) within the same chip depth at a given total dose would mainly produce ionization damage to the NPN BJTs. On the other hand, the charged particles causing larger Dd/(Dd + Di) at a given total dose would tend to generate displacement damage to the NPN BJTs. The Messenger–Spratt equation could be used to describe the experimental data for the latter case.

Effect of bias condition on heavy ion radiation in bipolar junction transistors

The characteristic degradations in a silicon NPN bipolar junction transistor (BJT) of 3DG142 type are examined under irradiation with 40-MeV chlorine (Cl) ions under forward, grounded, and reverse bias conditions, respectively. Different electrical parameters are in-situ measured during the exposure under each bias condition. From the experimental data, a larger variation of base current (IB) is observed after irradiation at a given value of base-emitter voltage (VBE), while the collector current is slightly affected by irradiation at a given VBE. The gain degradation is affected mostly by the behaviour of the base current. From the experimental data, the variation of current gain in the case of forward bias is much smaller than that in the other conditions. Moreover, for 3DG142 BJT, the current gain degradation in the case of reverse bias is more severe than that in the grounded case at low fluence, while at high fluence, the gain degradation in the reverse bias case becomes smaller than that in the grounded case.

Effect of Proton Irradiation on Mechanical Properties of Carbon/Epoxy Composites

Irradiation using 120-keV protons was performed on the AG-80 epoxy resin and the unidirectional M40J/AG-80 composite. Changes in the bend strength, bend modulus, interlayer shear strength, and mass loss ratio were examined. Experimental results show that by using proton fluences lower than approximated, the cross-linking density increases with the fluence in the surface layer of the AG-80 epoxy matrix and increases the bend strength and modulus for the composite. Increasing the fluence above 6.3 × 1015 cm−2, the cross-linking density, bend strength, and bend modulus are decreased. The mass loss ratios for both the AG-80 epoxy resin and the M40J/AG-80 composites increase with increasing proton fluence, and then level off.

A study on damage effect of vacuum thermocycling on M40J-epoxy composites

Vacuum thermocycling is performed in unidirectional M40J–AG-80 composites, and changes in the bending strength and modulus, the mass loss ratios, the surface morphology, and the internal structure transitions are examined. Results show that the vacuum thermocycling could cause the debonding in the interfacial layers between the AG-80 epoxy matrix and carbon fibers, as well as the post curing in the epoxy matrix. The changes in the bending strength and modulus, the mass loss ratio, and the surface morphology of the M40J–AG-80 composites can be related to the debonding and the post curing due to vacuum thermocycling.

Wear Behavior of Plasma-Nitrided 2Cr13 Martensitic Stainless Steel under Air and Vacuum

The wear behaviour of the plasma-nitrided 2Cr13 steel disks under air and vacuum have been investigated using a pin-on-disk type tribometer with dry sliding condition. The unnitrided pins of the same material were used for the wear couples. Microhardness measurements, X-ray diffraction analysis, optical microscopy were used to examine the microhardness profile, the surface phases crystal structure and morphology of the specimens. After wear testing, the scanning electron microscopy of the wear tracks on the disk and pin specimens was performed to reveal the wear mechanism. The surface profile of wear tracks of the disk specimens was examined by a profilometer.

Characterization of Stress Distribution and Thermal Expansion Behavior for M40J/AG-80 Composites Experienced Vacuum Thermo-cycling:

The characterization of stress distribution and thermal expansion/contraction distortion is performed for a unidirectional M40J/AG-80 epoxy composite, which experienced vacuum thermo-cycling in a temperature interval of −180 to 140°C under 10-5 Pa. The finite element analysis, using MSC.Marc 2001 software shows that vacuum thermo-cycling leads to stress concentration appearing at the interface layer, providing a stress condition to form debonding. The transverse expansion/contraction distortion changes linearly with temperature for both samples before and after thermo-cycling, while the longitudinal contraction shows a nonlinear behavior after the thermo-cycling. The variation in longitudinal contraction distortion can be attributed to the interface debonding.