Comparison of neutron irradiation effects on the electrical performances of SiGe HBT and SiBJT

The change of electrical performances of silicon-germanium (SiGe)heterojunction bipolar transistor (HBT) and Si bipolar junction transistor (BJT) was studied as afunction of reactor fast neutron radiation fluence. Alter neutron irradiation, the collector currentI_c and the current gain beta decrease, and the base current I_b increases generally for SiGe HBT.The higher the neutron irradiation fluence is, the larger I_b increases. For conventional Si BJT,I_c and I_b increase as well as beta decreases much larger than SiGe HBT at the same fluence. It isshown that SiGe HBT has a larger anti-radiation threshold and better anti-radiation performance thanSi BJT. The mechanism of performance changes induced by irradiation was preliminarily discussed.

Spillover on a Platinum Electrode Modified by MWNTs

The spillover phenomenon is observed on the platinum (Pt) disk electrode modified bymulti-wall carbon nanotubes (MWNTs). The rate of the spillover of oxygen-containing speciesproduced on Pt surface to and from MWNTs is fast. However for hydrogen-adatoms, thespillover is very weak. The selective spillover on the Pt/MWNTs electrode may provide a novelway to design catalysts.

FORWARD GATED-DIODE METHOD FOR DIRECTLY MEASURING STRESS-INDUCED INTERFACE TRAPS IN NMOSFET/SOI

Forward gated-diode Recombination-Generation(R-G) current method is applied to an NMOSFET/SOI to measure the stress-induced interface traps in this letter. This easy but accurate experimental method can directly give stress-induced average interface traps for characterizing the device's hot carrier characteristics. For the tested device, an expected power law relationship of ANit ～ t0.787 between pure stress-induced interface traps and accumulated stressing time is obtained.

Chemical Sensors Based on Piezoresistive Cantilever Array

U-shaped and rectangle piezoresistive cantilever arrays have been designed with the analysing results of stress,noise and sensitivity of the cantilevers. Based on silicon micromachining technology, the piezoresistive cantilevers were fabricated by using polysilicon as the piezoresistive materials. With the measurement results of noise and sensitivity, the Hooge factor is cMculated to be 3×10^-3, the gauge factor is 27, and the minimum detectable deflection of piezoresistive cantilevers are calculated to be 1.0nm for rectangle cantilever and 0.5 nm for the Ushaped cantilever at a 6 V bias voltage and a 1000 Hz measurement bandwidth. Using polymer-coated cantilevers as individual sensors, their responses to water vapour and ammonia were tested by measuring their output voltage signals. The measured results show that the sensor sensitivity to ammonia can reach a few ppm and the sensor responses are quick.

The Binding Energy, Spin－Excitation Gap, and Charged Gap in the Boson－Fermion Model

In this paper, by applying a simplified version of Lieb's spin-reflection-positivity method, which was recently developed by one of us [G.S. Tian and J.G. Wang, J. Phys. A: Math. Gen. 35 (2002) 941], we investigate some general properties of the boeon-fermion Hamiltonlan, which has been widely used as a phenomenological model to describe the real-space pairing of electrons. On a mathematically rigorous basis, we prove that for either negative or positive couping V, which represents the spontaneous decay and recombination process between boson and fermion in the model, the pairing energy of electrons is nonzero. Furthermore, we also show that the spin-excitation gap of the boson-fermion Hamiltonian is always larger than its charged gap, as predicted by the pre-palred electron theory.

The property of Si/SiGe/Si heterostructure during thermal budget characterized by HRXRD

Si/SiGe/Si heterostructures grown by ultra-high-vacuum chemical vapor deposition (UHVCVD) werecharacterized by Rutherford backscattering/Channeling (RBS/C) together with high resolution X ray diffraction(HRXRD). High quality SiGe base layer was obtained. The Si/SiGe/Si heterostructures were subject to conventionalfurnace annealing and rapid thermal annealing with temperature between 750 ℃ and 910 ℃. Both strain and its re-laxation degree in SiGe layer are calculated by HRXRD combined with elastic theory, which are never reported inother literatures. The rapid thermal annealing at elevated temperature between 880 ℃ and 910 ℃ for very short timehad almost no influence on the strain in Si0.84Ge0. 16 epilayer. However, high temperature (900℃) furnace annealingfor 1h prompted the strain in Si0.84Ge0.16 layer to relax.

A Rigorous Investigation on the Ground State of the Penson—Kolb Model

By using either numerical calculations or analytical methods, such as the bosonization technique, the ground state of the Penson-Kolb model has been previously studied by several groups. Some physicists argued that, as far as the existence of superconductivity in this model is concerned, it is canonically equivalent to the negative-U Hubbard model.However, others did not agree. In the present paper, we shall investigate this model by an independent and rigorous approach. We show that the ground state of the Penson-Kolb model is nondegenerate and has a nonvanishing overlap with the ground state of the negative-U Hubbard model. Furthermore, we also show that the ground states of both the models have the same good quantum numbers and may have superconducting long-range order at the same momentum q ＝ 0. Our results support the equivalence between these models.

Electron irradiation effects on DC electrical performances of SiGe HBT in a comparison with Si BJT

The DC characteristics of SiGe HBT irradiated at different electron dose havebeen studied in a comparison with those of Si B JT. Generally, I_b and I_b - I_(b0) increase, I_c,I_c -I_(c0) and its +/- transition V_(be) as well as DC current gain ft decreases with increasingdose; increase of I_b -I_(b0) with increasing dose for Si BIT is much larger than that for SiGe HBT;beta increases with V_(be) or I_b, but decreases at I_b < 0.25 mA with I_b, and congregates athigher dose; and a damage factor d(beta) is much less at the same dose for SiGe HBT than for Si BJT.SiGe HBT has much better anti-radiation performance than Si BJT. Some anomalous phenomena forincrease of I_c, I_c -I_(c0), I_b -I_(b0) and beta at low dose have been found. Some electron trapshave been measured. The mechanism of changes of characteristics is discussed.

Electrical Performance of Electron Irradiated SiGe HBT and Si BJT

The change of electrical performances of 1 MeV electron irradiated silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) and Si bipolar junction transistor (BJT) was studied. After electron irradiation, both the collector current IC and the base current IB changed a little, and the current gain β decreased a little for SiGe HBT. The higher the electron irradiation fluence was, the lower the IC decreased. For conventional Si BJT, IC and IB increased as well as /? decreased much larger than SiGe HBT under the same fluence. The contribution of IB was more important to the degradation of β for both SiGe HBT and Si BJT. It was shown that SiGe HBT had a larger anti-radiation threshold and better anti-radiation performance than Si BJT. The mechanism of electrical performance changes induced by irradiation was preliminarily discussed.

Interface Reaction of Ta/NiFe and NiFe/Ta and the Dead Layer

The structures of Ta/Ni81Fe19 and Ni81Fe19/Ta are commonly used in magnetoresistance multilayers. It is found that the thickness of dead layer in Ta/Ni81Fe19/Ta was about 1.6±0.2nm. X-ray photoelectron spectroscopy (XPS) was used to study the interfaces of Ta/Ni81Fe19 and Ni81Fe19/Ta. The results show that there is a reaction at the two interfaces: 2Ta+Ni=NiTa2, which caused the thinning of the effective NiFe layer. Furthermore, this reaction could also explain the phenomenon that the dead layer thickness of spin valves multilayers prepared by MBE is thinner than those prepared by magnetron sputtering.

Temperature Characteristics of BJMOSFET

The resolution expression for the temperature dependence of the current and threshold voltage is deduced as well as the analysis of temperature characteristics of BJMOSFET. Equivalent circuit of analysis and simulation has been established for the BJMOSFET temperature characteristics. By using the general circuit simulation software of PSpice9 and computer simulation, characteristic graphs of the BJMOSFET output characteristic, transient characteristic and amplitude-frequency characteristic with temperature variation are obtained. The results accorded very good with theoretical analysis and proved that BJMOSFET has better temperature characteristics than traditional MOSFET.

Development of Silicon Multi-strip Detector

Position sensitive detector is very important for nuclear physics experiment. There several techniques can be used to fabricate position sensitive detector, for example, Si-surface barrier method, diffusion method, ion implantation and planar process etc. Among all the techniques mentioned above planar process is the best one. We have developed batch of position sensitive detector -- silicon multi-strip detector by using planar process.

New type X—ray mask fabricated using inductvely coupled plasma deepetching

The fabrication of X-ray masks is a critical and challenging process in LIGA technique.As inductively coupled plasma(ICP) deepetching appears to be the most suitable source for deep silicon etching,we fabricated a new type X-ray mask using this technique.In comparison with other types of X-ray masks,the mask we fabricated has the advantages of its low cost and its simple fabrication process.Besired microstructures have also been fabricated using this new type X-ray mask in LIGA technique.