Self-aligning planarization and passivation for integration applications in III-V semiconductor devices

This work reports an easy planarization and passivation approach for the integration of III-V semiconductor devices. Vertically etched III-V semiconductor devices typically require sidewall passivation to suppress leakage currents and planarization of the passivation material for metal interconnection and device integration. It is, however, challenging to planarize all devices at once. This technique offers wafer-scale passivation and planarization that is automatically leveled to the device top in the 1-3-/spl mu/m vicinity surrounding each device. In this method, a dielectric hard mask is used to define the device area. An undercut structure is intentionally created below the hard mask, which is retained during the subsequent polymer spinning and anisotropic polymer etch back. The spin-on polymer that fills in the undercut seals the sidewalls for all the devices across the wafer. After the polymer etch back, the dielectric mask is removed leaving the polymer surrounding each device level with its device top to atomic scale flatness. This integration method is robust and is insensitive to spin-on polymer thickness, polymer etch nonuniformity, and device height difference. It prevents the polymer under the hard mask from etch-induced damage and creates a polymer-free device surface for metallization upon removal of the dielectric mask. We applied this integration technique in fabricating an InP-based photonic switch that consists of a mesa photodiode and a quantum-well waveguide modulator using benzocyclobutene (BCB) polymer. We demonstrated functional integrated photonic switches with high process yield of >90%, high breakdown voltage of >25 V, and low ohmic contact resistance of /spl sim/10 /spl Omega/. To the best of our knowledge, such an integration of a surface-normal photodiode and a lumped electroabsorption modulator with the use of BCB is the first to be implemented on a single substrate.     

Study of nickel passivation in a borate medium

The adsorption of borate ions at the nickel and/or nickel oxide-electrolyte electrochemical interface was studied at various concentrations and pH values in lithium and borate solutions. First, the passivation range of nickel was estimated using cyclic voltammetry. The nickel passive layer formation kinetics (transfer resistance, capacitance of passive film formed, adsorption capacitance), as well as the semiconducting properties of this oxide layer, were studied using electrochemical impedance spectroscopy (E.I.S.). These electrochemical techniques were used in conjunction with adsorption measurements performed with an electrochemical quartz crystal microbalance (E.Q.C.M.) and with surface analyses (Auger spectroscopy). The nickel oxide showed type p semiconducting properties and was depleted at, corrosion potential. Moreover, very little borate adsorption was observed during the different tests. This may have been the result of the negative surface charge, in the pH and potential conditions applied.     

Exciton photoluminescence in doped quasi-1D structures based on silicon

The dependence of carrier density in silicon quantum wires sheathed with SiO₂ on the wire diameter and the position of impurity atoms in respect to the wire center is analyzed theoretically. It is shown that, as the diameter of wires and nanocrystals decreases, the ionization energy of a dopant increases; therefore, the free carrier density decreases, and the screening of the Coulomb attraction becomes ineffective. As a result, the photoluminescence is defined by the radiative recombination of excitons even in the case of heavily doped Si. These conclusions are supported by the data of experimental study of spectral, excitation-power, and temperature dependences of photoluminescence in porous silicon structures fabricated on lightly and heavily doped Si substrates.     

Simulation of the Forming Behaviour of a Boron Modified P91 Ferritic Steel

The forming behaviour at high temperature of a modified 9%Cr‐1%Mo (P91) ferritic steel containing B and Ti for elevated temperature service was investigated. The microstructure of the as‐received material is mainly martensite at room temperature, but special etching revealed prior austenite grains of about 25 μm in size. Torsion tests were conducted at temperatures in the range 850 to 1250 °C to simulate the hot rolling process under comparable conditions of temperature, strain rate and strain. The deformation data obtained from these tests were correlated with the Garofalo equation with a stress exponent of 4.6 and an activation energy of 315 kJ/mol. This equation was used to predict the formability behaviour for the rolling process and also to determine the maximum forming efficiency and stability of the steel. A temperature of 1200 °C is recommended to conduct the forming process.     

Thermoelastic State of a Conducting Plate under the Action of an Electromagnetic Field in the Form of Damped Sinusoid

We determine the temperature fields and stresses formed in an infinite nonferromagnetic conducting plate of constant thickness under the action of a pulsed electromagnetic field specified by the values of the tangential component of magnetic vector on the surfaces. In the case of electromagnetic action obeying the law of damped sinusoid, we perform the comparative numerical analysis of ponderomotive forces, temperature, and components of the dynamic stress tensor for plates made of stainless steel and copper. It is shown that the influence of electric and thermal conductivity, thermal diffusivity, the coefficient of linear thermal expansion, and Young's modulus on the quantitative and qualitative behavior of the analyzed parameters as functions of time is significant.     

The Influence of the Silicone Carbide Content and Type on the Microstructure and the Flaw Level of Silica Ceramics

Comprehensive studies of the flaw level and some structural characteristics of a composite ceramic material based on Karakeche clay (Kyrgyzstan) are carried out for a range of thermoactivation regimes and impurity contents of silicone carbides of various types.     

Statistical model of an undermoded reverberation chamber

Weibull distribution is adopted to model the electric field component of a Reverberation Chamber (RC). Its first property is to include the asymptotic laws, such as Rayleigh and exponential, and its main advantage lies in the fact that the Weibull shape parameter enables a model of the departure from overmoded to undermoded RC regime. Applications are given, such as an RC modal finite element modeling and a Monte Carlo simulation: they prove that the Weibull two-parameter distribution correctly models the quality factor influence. Moreover, the relevance of the use of this extreme value distribution is illustrated.     

Microfluidic Three-Electrode Cell Array for Low-Current Electrochemical Detection

This paper reports the implementation and calibration of a microscopic three-electrode electrochemical sensor integrated with a polydimethylsiloxane (PDMS) microchannel to form a rapid prototype chip technology that is used to develop sensing modules for biomolecular signals. The microfluidic/microelectronic fabrication process yields identical, highly uniform, and geometrically well-defined microelectrodes embedded in a microchannel network. Each three-microelectrode system consists of a Au working electrode with a nominal surface area of 9 mum², a Cl₂ plasma-treated Ag/AgCl reference electrode, and a Au counter electrode. The patterned electrodes on the glass substrate are aligned and irreversibly bonded with a PDMS microchannel network giving a channel volume of 72 nL. The electrokinetic properties and the diffusion profile of the microchannels are investigated under electrokinetic flow and pressure-driven flow conditions. Cyclic voltammetry of 10 mM K₃ Fe(CN)₆ in 1 M KNO₃ demonstrates that the electrode responses in the cell are characterized by linear diffusion. The voltammograms show that the system is a quasi-reversible redox process, with heterogeneous rate constants ranging from 3.11 to 4.94times10^-3 cm/s for scan rates of 0.1-1 V/s. The current response in the cell is affected by the adsorption of the electroactive species on the electrode surface. In a low-current DNA hybridization detection experiment, the electrode cell is modified with single-stranded thiolated DNA. The electrocatalytic reduction of 27 muM Ru(NH₃)₆ ³⁺ in a solution containing 2 mM Fe(CN)₆ ^3- is measured before and after the exposure of the electrode cell to a 500-nM target DNA sample. The preliminary result showing an increase in the peak current response demonstrates the hybridization-based detection of a complementary target DNA sequence     

Increasing the nominal safety of the no. 5 unit of the Kursk nuclear power plant

The main technical measures for increasing the nominal safety of the No. 5 unit of the Kursk nuclear power plant are presented: optimization of the neutron-physical characteristics of the core, adoption of a comprehensive monitoring, control, and protection system, switching to cluster-type control rods, adoption of a system for limiting radioactive emissions during anticipated accidents with pipeline rupture outside the containment system. __________ Translated from Atomnaya énergiya, Vol. 100, No. 4, pp. 320–327, April, 2006.