Emitter size effect on current gain in fully self-alignedAlGaAs/GaAs HBT's with AlGaAs surface passivation layer

The emitter size effect for fully self-aligned AlGaAs-GaAs heterojunction bipolar transistors (HBTs) with depleted AlGaAs passivation layers, in which the partially thinned AlGaAs emitter is self-aligned by using the dual sidewall process, is investigated. It is demonstrated that drastic improvement in the emitter size effect can be achieved with an AlGaAs passivation layer as small as 0.2 μm in width, due to the surface recombination current reduction by a factor of 1/40 in the extrinsic base region. It has also been found that the base current is dominated by excess leakage current in the proton-implanted isolation region     

Direct Analysis Technique for Long-Finger HBT by Electromagnetic and Device Co-Simulation

This paper presents a direct-analysis technique for transistors with a long-finger structure. The analysis technique is an incorporated simulation between the finite-difference time-domain electromagnetic (EM) and semiconductor device simulations. The co-simulation method can consider various EM couplings and phase shifts on finger electrodes of transistors. The method was applied for InGaP/GaAs HBTs with various finger lengths to investigate gain degradation characteristics as a function of the finger length. As the first step, circuit simulations were done instead of a semiconductor device simulation using SPICE models of the HBT. Both large- and small-signal equivalent-circuit parameters were extracted by measurements to estimate nonlinear and linear characteristics, respectively. Using the extracted small-signal parameters, the gain degradation was estimated. The co-simulation results showed the same tendency as measurement results. Additionally, it was numerically shown that a resistive loss was mainly affected for the gain degradation from a comparison between gold and lossless electrodes.     

Design Considerations on the Minimum Size of Broadband Antennas for UWB Applications

The practical realization of Chu's minimum-sized antenna is investigated using self-complementary antennas. Rigorous bandwidth formulas for broadband antennas are derived for broadband antennas based on Chu's fundamental mode equivalent circuit. By comparing input impedances and radiation patterns, the fabricated self-complementary antenna used for Japan's ultra-wideband higher band (7.25-10.25 GHz) is found approximated by the minimum-sized antenna. Using the rigorous bandwidth formulas above, the fabricated antenna is shown to be smaller than the minimum-sized antenna. This breakthrough is achieved by using a more complicated matching circuit for broadband antennas instead of the single-stage inductor used in bandwidth estimation with the Q factor.     

Roles of lattice fitting in epitaxy

The epitaxial orientations of three series of materials-alkali halides, chalcogenide compounds and face-centered cubic metals-and of indium (face-centred tetragonal structure) and iron (body-centred cubic structure) on a (001) MgO substrate were examined by in situ electron microscopy and diffraction. The lattice parameter ratio ? = a_d/a_s (d, deposit;s, substrate) ranges from 0.95 for LiF to 1.68 for KI, from 1.41 for PbS to 1.53 for PbTe and from 0.84 for nickel to 1.18 for lead. A systematic dependence of the epitaxial orientation on ? is found: alkali halides and chalcogenide compounds with ? around 1 or 1.5 prefer the (001) parallel orientation with (001)_d(001)_s, [100]_d[100]_s, but those with a value of ? around √2 prefer the (001) orientation with (001)_d(001)_s, [110]_d[100]_s. Metals with ? near 1 also prefer the (001) parallel orientation, but copper and nickel with ? around 0.85 prefer the (1$\text{1}$0) orientation with (1$\text{1}$0)_d(001)_s, [11$\text{2}$]_d[100]_s, and gold, indium and lead with values of ? of 0.97, 1.17 (1.09) and 1.18, respectively, favour the (111) orientation with (111)_d(001)_s, [1$\text{1}$0]_d[1$\text{1}$0]_s. The epitaxial relation is discussed in terms of the fit of the lattice spacings of the deposit and substrate crystals.     

Low-frequency noise performance of self-aligned InAlAs/InGaAs heterojunction bipolar transistors

The first measurement of low-frequency noise performance for self-aligned InAlAs/InGaAs HBTs is reported. The 1/f noise obtained was around 20 dB lower than that for AlGaAs/GaAs HBTs at a fixed frequency, which is considered to be caused by the low surface recombination velocity of InGaAs.<>     

Radiologic manifestation of spinal accessory neurinoma: a case report

Spinal accessory nerve neurinoma is very rare; only 12 cases have been reported in the literature. We describe a 54-year-old woman who had a cisterna magna tumor expanding extracranially to the C1 cervical body. The tumor originated from the spinal root of the right accessory nerve. The radiological features including CT, MRI, and angiography are discussed. There have been reports on cranial MRI studies of spinal accessory neurinoma. MRI suggested an extra-axial tumor. The histological diagnosis was mixed Antoni A and B neurinoma. The neuroradiological findings of 12 cases of neurinoma of the accessory nerve reported in the literature are reviewed.     

Involvement of RBP-J in biological functions of mouse Notch1 and its derivatives

Notch is involved in the cell fate determination of many cell lineages. The intracellular region (RAMIC) of Notch1 transactivates genes by interaction with a DNA binding protein RBP-J. We have compared the activities of mouse RAMIC and its derivatives in transactivation and differentiation suppression of myogenic precursor cells. RAMIC comprises two separate domains, IC for transactivation and RAM for RBP-J binding. Although the physical interaction of IC with RBP-J was much weaker than with RAM, transactivation activity of IC was shown to involve RBP-J by using an RBP-J null mutant cell line. IC showed differentiation suppression activity that was generally comparable to its transactivation activity. The RBP-J-VP16 fusion protein, which has strong transactivation activity, also suppressed myogenesis of C2C12. The RAM domain, which has no other activities than binding to RBP-J, synergistically stimulated transactivation activity of IC to the level of RAMIC. The RAM domain was proposed to compete with a putative co-repressor for binding to RBP-J because the RAM domain can also stimulate the activity of RBP-J-VP16. These results taken together, indicate that differentiation suppression of myogenic precursor cells by Notch signalling is due to transactivation of genes carrying RBP-J binding motifs.